An asymmetric zinc porphyrin (ZnPy) derivative bearing one benzoic acid and three 3-pyridines as meso-position substituents (zinc-5-(4-carboxyphenyl)-10,15,20-tri(3-pridyl)porphyrin, ZnMT3PyP) was used to sensitize graphitic carbon nitride (g-C3N4) for visible-light-driven photocatalytic H2 production. It was found that ZnMT3PyP exhibits more excellent photosensitization and stability on g-C3N4 than its counterpart bearing one benzoic acid and three phenyls (zinc-5-(4-carboxyphenyl)-10,15,20-triphenylporphrin, ZnMTPP) under visible light (λ > 420 nm) irradiation even though they have very similar physicochemical properties such as optical absorption capacities and energy band structures. Especially, ZnMT3PyP-Pt/g-C3N4 gives an apparent quantum yield (AQY) up to 25.1% at λ = 420 nm light illumination, greater than that (11.6%) of ZnMTPP-Pt/g-C3N4. The differences in photosensitization and stability between ZnMT3PyP and ZnMTPP are mainly due to the substitution of 3-pyridine for the phenyls in ZnMTPP, which leads to the electron transfers between ZnMT3PyP and g-C3N4 faster than that between ZnMTPP and g-C3N4. The present results provide a new insight applying porphyrin derivatives to the photocatalytic H2 production and open up a new path for further improving the conversion efficiency of solar energy to hydrogen energy through molecular designing.Keywords: Graphitic carbon nitride; Photocatalytic hydrogen production; Pyridine substituent; Zinc porphyrin derivative;

Although AgIn5S8 as one kind of ternary chalcogenides has been extensively investigated due to its band-edge positions meeting the thermodynamic requirement for water photosplitting, very little attention has been focused on the crystallinity and facet effects of AgIn5S8 on its photocatalytic activity. Herein, a facile hydrothermal route was developed to fabricate regular single-crystalline AgIn5S8 octahedrons with only {111} facets exposed. Also, the effects of the hydrothermal reaction conditions on the composition, crystal phase, crystallinity, and morphology of the obtained AgxInyS(x+3y/2) products (hereafter denoted as AIS-x, where x represents the pH value of the reaction solution) were investigated, and it was found that the accurately released S2– ions from the thermal decomposition of thioacetamide (TAA) is the central factor for the nucleation and growth of the AgIn5S8 octahedrons. The experimental results indicate that the resultant regular AgIn5S8 octahedrons (AIS-10.6) exhibit the best photocatalytic activity for H2 production among those AgxInyS(x+3y/2) products, and the higher crystallinity and fewer defects of the AgIn5S8 octahedrons compared to the other AgxInyS(x+3y/2) products can retard the photogenerated charge recombination, while those indium atoms with higher density in the exposed {111} facets might be beneficial for the photocatalytic H2 production reaction by acting as active sites to promote the charge separation and transfer processes. The results presented here provide new insights into the significance of crystallinity and exposed facets in the visible-light-responsive activity of AgIn5S8, thus paving new ways into the design and synthesis of high-performance, cost-effective AgIn5S8 photocatalysts for H2 production.Keywords: AgIn5S8 octahedron; exposed facet; hydrogen production; photocatalytic activity; visible-light response;

•g-C3N4 nanodots (CNDs) decorated brookite TiO2 quasi nanocube (BTN) is prepared.•BTN-CNDs has enhanced CO2-reduction activity as compared to g-C3N4 and BTN alone.•Highly dispersed CNDs on BTN surface cause better adsorption capacity of reactants.•The CH4 generation selectivity is due to the synergistic effect of CNDs and BTN.•Photosensitization is proposed to explain the BTN-CNDs’ CO2-reduction activity.A new kind of brookite TiO2/g-C3N4 nanocomposite, in which g-C3N4 nanodots (CNDs) with a mean size of ∼2.8 nm are decorated on brookite TiO2 quasi nanocube (BTN) surfaces (hereafter referred as BTN-CNDs heterojunction), is prepared via a facile calcination process of the mixture of urea and the home-made BTN powders, and then used as visible-light-responsive photocatalyst for CO2 reduction. Electron microscopy, X-ray powder diffraction (XRD), ultraviolet-visible light (UV-vis) diffuse reflectance absorption spectra (DRS), X-ray photoelectron spectra (XPS) and its valance band (VB) spectra are adopted to investigate the microstructure, composition, energy band structure, and the possible photogenerated electron transfer processes between BTN and CNDs. After optimizing the photocatalytic condition, enhanced visible-light-driven CO2-reduction activity and selectivity for CH4 generation as compared to g-C3N4 and BTN alone are observed, and a photosensitization mechanism is proposed to explain the differences in the photocatalytic performance among g-C3N4, BTN, and BTN-CNDs. The pronounced CH4 generation activity and selectivity over BTN-CNDs heterojunction demonstrate a new strategy for improving the interfacial charge transfer and the photocatalytic CO2 reduction performance though tailoring the microstructures of the semiconductor-based nanocomposites.Pronounced CO2-reduction activity and selectivity for CH4 generation are achieved from g-C3N4 nanodots decorated brookite TiO2.Download high-res image (114KB)Download full-size image

•CuPc(tBu)4 as additive is first introduced into the perovskite precursor solution.•The effects of CuPc(tBu)4 additive on the devices' photovoltaic performance are investigated.•CuPc(tBu)4 additive can improve the quality of perovskite layer.•Power conversion efficiency of the planar perovskite solar cell is enhanced from 15.3% to 17.3%.Solution processable planar heterojunction perovskite solar cell has drawn much attention as a promising low-cost photovoltaic device, and much effort has been made to improve its power conversion efficiency by choosing appropriate additives for the perovskite precursor solution. Different to those additives reported, a soluble and thermal stable tert-butyl substituted copper phthalocyanine (CuPc(tBu)4) as additive is first introduced into the perovskite precursor solution of a planar perovskite solar cell that is fabricated via the one-step solution process. It is found that the pristine device without CuPc(tBu)4 additive exhibits a power conversion efficiency of 15.3%, while an extremely low concentration (4.4 × 10−3 mM) of CuPc(tBu)4 in the precursor solution leads to the corresponding device achieving an enhanced power conversion efficiency of 17.3%. CuPc(tBu)4 as an additive can improve the quality of perovskite layer with higher crystallinity and surface coverage, then resulting in enhanced light absorption and reduced charge recombination, and thus the better power conversion efficiency. The finding presented here provides a new choice for improving the quality of perovskite layer and the photovoltaic performance of the planar heterojunction perovskite solar cells.Download high-res image (231KB)Download full-size image

•xLi2MnO3·(1−x)LiMnO2 nanorods are prepared by a pyrolysis reduction of m-Li2MnO3.•m-LiMnO2 content in the nanorods is adjustable by changing the stearic acid amount.•Those nanorods has initial charge/discharge profile similar to Li-rich material.•Improved cyclic and rate performance with higher reversible capacity is obtained.Layered-layered type xLi2MnO3·(1−x)LiMnO2 (x = 0.91, 0.78, 0.67, 0.54, 0.42, and 0.32) nanorods with a diameter of 100–200 nm and length of 400–1000 nm are prepared through a pyrolysis reduction process of monoclinic Li2MnO3 (m-Li2MnO3) nanorods. All the synthesized xLi2MnO3·(1−x)LiMnO2 nanorods exhibit the main characteristic diffraction peaks of m-Li2MnO3 in addition to some weak peaks attributable to m-LiMnO2 especially for those composites with x < 0.67. When used as cathode material of Li-ion battery, those xLi2MnO3·(1−x)LiMnO2 nanorods show an initial charge/discharge profile similar to the Li-rich solid solution in the voltage window of 2.0–4.8 V. The m-LiMnO2 portion in those synthesized composites can significantly enhance the reversible capacity but lower the cyclic stability, while the m-Li2MnO3 portion can improve the cyclic stability due to its retardation effect of the layered-to-spinel transformation during the charge/discharge processes, and thus xLi2MnO3·(1−x)LiMnO2 nanorods with x = 0.54 exhibits the best cyclic and rate performance since it contains appropriate m-Li2MnO3/m-LiMnO2 contents to balance the reversible capacity and Jahn-Teller effect. The present findings demonstrate an effective strategy for the development of low-cost pure Mn-based Li-rich layered cathode materials with adjustable reversible capacity, cyclic and rate performance by tailoring the composition.Download high-res image (382KB)Download full-size image

•Synthesis of ruthenium(II) complexes bearing rigid N′NN′-typed pincer ligands.•Catalytic dehydrogenation of primary alcohols to carboxylic acids and H2.•Higher yields and higher selectivity obtained in the homogeneous alcohol-CsOH system.•Quantitative yield of benzoic acid and TON∼10000 achieved in 24 h.Mono-cationic Ru(II)-complexes [Ru(L)X(CH3CN)2]⋅X 1∼4 (1, L = 2,6-bis(benzimidazol-2-yl) pyridine (L1), X = Cl; 2, L = L1, X = OTf; 3, L = 2-(N-benzyl-benzimidazole-2-yl)-6-(benzimidazole-2-yl)pyridine (L2), X = Cl; 4, L = 2,6-bis(N-benzyl-benzimidazole-2-yl)pyridine (L3), X = Cl) were prepared and fully characterized. The two acetonitrile ligands of each complex are coordinated to the metal center cis to each other. Complex 2 was also structurally characterized by X-ray crystallography. It was found that complexes 1∼4 can catalyze the acceptorless dehydrogenation of primary alcohols to corresponding carboxylic acids and H2 in the basic aqueous solution, and the reactivity follows the order 1 = 2 > 4 > 3. Furthermore, complexes 1 or 2 can efficiently catalyze the conversion of various primary alcohols to carboxylic acid in good yields (72%–98%) and high selectivity in an alcohol/CsOH system (1/1, mol/mol). Using an excess amount of alcohol to CsOH results in the formation of the carboxylic acid in higher yield (up to 100%, based on CsOH) and higher turnover numbers (TON ∼ 10000) accompanied by the H2 evolution. Complexes 1 and 2 can act as a new class of phosphine- and N-heterocycle carbene free Ru(II) complexes for efficient conversion of primary alcohols to carboxylic acids and H2 in a homogeneous system.Download high-res image (146KB)Download full-size image

•Ti foil-based TiO2 composite film containing rutile and anatase phases is prepared.•Rutile TiO2 sea urchin-like microspheres is covered by anatase nanotubes layer.•Anatase nanotubes layer on rutile microstructures can enhance the electron lifetime.•Composite film-based cell shows better efficiency than the rutile film-based one.Ti foil-based TiO2 films containing rutile sea urchin-like hierarchical microspheres covered with self-organized anatase nanotubes layer were fabricated through two-step hydrothermal processes. The first-step hydrothermal treatment of TiCl4 solution caused a thick rutile film on Ti foil, in which the sea urchin-like rutile microspheres (RMS) with mean size of 5–6 μm are composed of nanorods with ∼200 nm diameter and 1–2 μm length. After the second-step hydrothermal treatment, a thin self-organized layer of anatase nanotubes (ANT) with ∼10 nm diameter formed on those RMS to form Ti foil-based RMS/ANT composite film. The corresponding dye-sensitized solar cell using the Ti foil-based RMS/ANT film as photoanode achieved an efficiency of 5.42%, much better than that (0.73%) of the single RMS film-based one. The thin ANT layer on the RMS film can not only enhance the dye-loading, but also retard the charge recombination. All these lead to higher photocurrent and better photovoltaic conversion efficiency than the single RMS film-based solar cell. The above results present an efficient approach to improve the photovoltaic performance of the rutile-based solar cells by designing photoanode materials with hierarchical structures to counterbalance rutile’s inherent shortages such as low dye-loading and poor conductivity as compared with anatase.Download high-res image (279KB)Download full-size image

[RuCl(L1)(MeCN)2]Cl (1) and [RuCl(L2)(MeCN)2]Cl (2) complexes were prepared through the reaction of [RuCl2(p-cymene)]2 with 2,6-bis(benzimidazole-2-yl)-4-hydroxy-pyridine (L1) or 2,6-bis(benzimidazole-2-yl) pyridine (L2) in acetonitrile, respectively. The treatment of [Ru(OTf)(L2)(MeCN)2]OTf (3) with 1 equivalent of PPh3 in ethanol resulted in the formation of [Ru(L2−1)(MeCN)(PPh3)2]OTf (4), in which one of the N–H moieties of L2 is deprotonated to give an anionic ligand (L2−1). It was found that complex 1 can catalyze the hydrogenation of CO2 to formate salts, producing sodium formate in 34.0% yield with a turnover number (TON) of 407 under the optimized conditions. Further investigations revealed that complexes 1–4 can efficiently catalyze the hydrogenation of sodium bicarbonate to sodium formate, and the catalytic activity follows the order 4 > 1 > 2 ≈ 3. In particular, sodium formate was obtained in good yield (77%) with a high TON (1530) when complex 4 was used as the catalyst. The present results illustrate a new example of Ru(II) complexes bearing a rigid N′NN′ framework for the efficient hydrogenation of CO2 to formate salts in a homogeneous system.

Acceptorless dehydrogenation of alcohols to carboxylic acid derivatives catalyzed by a transition metal complex is an important reaction in modern organic synthesis and catalysis, for which nickel complexes have rarely been developed. Herein we report three Ni(II) complexes bearing pyridine-based N′NN′ type pincer ligands, which catalyze the acceptorless dehydrogenation of primary alcohols to carboxylic acids under anhyrous conditions. The complex [NiCl2(L3)] 3 (L3 = 2,6-bis(diethylaminomethyl)pyridine) displays the best catalytic reactivity, catalyzing the primary alcohols to carboxylic acids and H2 in good yields (40–90%). Further investigation reveals that an unexpected alcohol etherification occurs, which gives the second oxygen atom for the formation of the carboxylic acid. Our results give a thread for the design of new nickel complexes without phosphine and N-heterocycle carbene ligands for the acceptorless oxidation of alcohols.

A sea urchin-like rutile TiO2 microsphere (RMS) film was fabricated on Ti foil via a hydrothermal process. The resulting rutile TiO2 hierarchical microspheres with a diameter of 5–6 μm are composed of nanorods with a diameter of ∼200 nm and a length of 1–2 μm. The sea urchin-like hierarchical structure leads to the Ti foil-based RMS film possessing much better light-scattering capability in the visible region than the bare Ti foil. By using it as an underlayer of a nanosized anatase TiO2 film (bTPP3) derived from a commercially available paste (TPP3), the corresponding bilayer Ti foil-based quasi-solid-state dye-sensitized solar cell (DSSC) only gives a conversion efficiency of 4.05%, much lower than the single bTPP3 film-based one on Ti foil (5.97%). By spin-coating a diluted TPP3 paste (sTPP3) on the RMS film prior to scraping the bTPP3 film, the resulting RMS/sTPP3/bTPP3 film-based DSSC achieves a significantly enhanced efficiency (7.27%). The electrochemical impedance spectra (EIS) show that the RMS/sTPP3/bTPP3 film possesses better electron transport capability and longer electron lifetime than the bTPP3 film. This work not only provides the first example of directly growing rutile TiO2 hierarchically structured microsphere film on Ti foil suitable for replacing the rigid, heavy and expensive transparent conductive oxide (TCO) glass substrate to serve as a light-scattering underlayer of Ti foil-based quasi-solid-state DSSCs, but also paves a new route to develop Ti foil-based flexible DSSCs with high efficiency, low cost and a wide application field through optimizing the composition and structure of the photoanode.

As a promising approach to achieving two objectives with one strategy, photocatalytic CO2 conversion for C1/C2 “solar fuels” production can provide a package solution to the current global warming and growing energy demand by using inexhaustible solar energy and increasing atmospheric CO2. Although numerous efforts have been made to enhance the CO2 conversion efficiency through developing photocatalysts and CO2 reduction systems in recent years, some challenges still remain in improving the activity and selectivity of the CO2 photoreduction reactions. This review gives an overview of fundamental aspects and recent research advances of heterogeneous photocatalytic CO2 conversion systems in the last 3 years, and the catalysts are categorized as one-step excitation semiconductor systems, one-step excitation photosensitized semiconductor systems, and two-step excitation hybrid systems such as semiconductor heterojunction and Z-scheme systems. Also, some suggestions are given for further confirming that the carbon-containing “solar fuels” are derived from CO2 rather than from the possible carbonaceous impurities in the photocatalytic system, because most of the papers cited in this review have not demonstrated that CO2 is the actual carbon source for photoreduction through 13CO2 labeling or other techniques. Lastly, a short perspective on the challenges and new directions in this field is proposed, which would be of great interest for the further improvements of activity and selectivity of the CO2 reduction reactions.Keywords: photoactivity; photocatalyst; photocatalytic CO2 conversion; selectivity; solar fuel production

Photocatalytic water splitting by solar light has received tremendous attention for the production of clean and renewable hydrogen energy from water. Some challenges still remain in improving the solar-to-hydrogen energy conversion efficiency, such as utilizing longer-wavelength photons and enhancing the photocatalytic activity and stability of H2 production over semiconducting materials. Dye sensitization, as a successful strategy for extending the spectral responsive region (even to near-IR light) of wide bandgap semiconductors for H2 production, was developed more than 30 years ago, but it still lacks the corresponding specialized review. This review emphasizes especially the fundamental aspects and the research advances in heterogeneous dye-sensitized semiconductor suspension systems for visible (and even near-IR) light responsive photocatalytic H2 production, and the commonly used dyes, semiconductors, co-catalysts and electron donors are systematically discussed. Also, a short perspective on the challenges and new directions in this field is proposed, which would be of great interest in the field of solar fuel conversion.

•High-quality brookite nanocubes and rice-like particles are hydrothermally prepared.•Brookite film of nanocube underlayer and rice-like particle overlayer is fabricated.•Bilayer pure brookite-based DSSCs fabricated has higher VOC than the P25-based one.•Bilayer cell’s efficiency is improved by 41% compared to the nanocube-based one.•Efficiency is close to the record one in the area of pure brookite-based solar cell.A novel bilayer brookite TiO2 film photoanode consisting of quasi nanocube film as underlayer and rice-like submicrometer particle film as overlayer are fabricated for improving the photovoltaic properties of the pure brookite-based dye-sensitized solar cells (DSSCs). The brookite TiO2 nanocubes have a mean size of ∼50 nm, and the brookite TiO2 rice-like particles have diameter of ∼600 nm and length of ∼1100 nm. An optimal photovoltaic conversion efficiency of 5.51% is obtained from the bilayer brookite-based solar cell, with ∼41% improvement in the efficiency as compared to the single brookite nanocube film-based one (3.91%) under AM 1.5G one sun irradiation. The bilayer brookite-based solar cell shows not only reduced charge recombination and dark current, but also prolonged electron lifetime compared to the single brookite nanocube film-based one. All these lead to a higher photocurrent and voltage, and then to the improved efficiency of the brookite-based solar cell. The present results demonstrate a clear advance towards efficient improvement of the photovoltaic performance of pure brookite-based solar cells.

•Novel iodine-free ionic liquid gel electrolyte for Ti-foil-based DSSCs is prepared.•An optimal PEO/PEG weight ratio of 1/3 is used as gelator of DMPII and KI.•Reduced charge recombination is obtained by adding PEG into PEO-based electrolyte.•The DSSC has higher efficiency than that with single PEG- or PEO-based electrolyte.A novel iodine-free ionic liquid (IL) gel electrolyte is prepared by using polyethylene oxide (PEO)-polyethylene glycol (PEG) as gelator of 1,2-dimethyl-3-propylimidazolium iodide (DMPII) and potassium iodide (KI), which act as charge transfer intermediate and auxiliary in the electrolyte, respectively. By changing the PEG/PEO weight ratio, the obtained iodine-free IL gel electrolytes for a Ti-foil-based dye-sensitized solar cells (DSSCs) show different visible light absorption and rheological characteristics, and an optimal photovoltaic conversion efficiency of 6.44% can be obtained from the solar cell fabricated with iodine-free IL gel electrolyte containing a PEG/PEO weight ratio of 1/3, while the corresponding value of the solar cell fabricated with the IL gel electrolyte using single PEG and PEO as gelator is 5.79% and 5.43%, respectively. The present iodine-free IL gel electrolytes could not only overcome the visible light absorption and the leakage problems of the conventional I3−/I− liquid electrolyte, but also reduce the charge recombination and the dark current of the solar cell, and demonstrating a feasible approach for improving the photovoltaic performance of the Ti-foil-based DSSCs that need a back-side illumination in the practical application.

Zinc phthalocyanine (ZnPc) derivatives containing bulky 2,6-diphenylphenoxy peripheral substituents with different structures and symmetries are used as sensitizers of graphitic carbon nitride (g-C3N4) for photocatalytic H2 production. It is found that an A2BC type asymmetrical ZnPc derivative (Zn-di-PcNcTh-1) containing four 2,6-diphenylphenoxy substituents, a thiophene unit and a fused benzene ring bearing one carboxylic group shows an obvious red-shift in the Q-band absorption with a broader absorption spectrum as compared to its symmetrical analogue (Zn-tetrad-Pc-1) containing eight 2,6-diphenylphenoxy substituents. The asymmetrical Zn-di-PcNcTh-1 with an additional carboxyl group exhibits a higher dye-loaded amount and stable grafting on g-C3N4 than the symmetrical Zn-tetrad-Pc-1, and thus causing more efficient interfacial electron transfer in Zn-di-PcNcTh-1/g-C3N4. Especially, an impressively high apparent quantum yield (3.05%) can be obtained under 730 nm monochromatic light irradiation, higher than that (1.14%) of Zn-tetrad-Pc-1 without a carboxyl group. The present results not only provide a significant advance in the molecular engineering aspect of ZnPc derivatives for effectively utilizing the red/near-IR light of sunlight, but also exhibits a promising strategy for improving the solar-to-hydrogen conversion efficiency.

•Four V-shaped organic dyes with triphenylamine core have been synthesized.•Four different polycyclic donors are employed for structure optimization.•The photovoltaic performances of the dyes are characterized.•A highest power efficiency of 4.04% without coadsorbent has been achieved.A new series V-shaped organic dyes featured with triphenylamine as core/π-linker has been synthesized for the application of dye-sensitized solar cells. Four different polycyclic aromatic subunits have been introduced as donor group in this series of dyes (named DH-6 to DH-9). These dyes have been systematically characterized and employed in DSSC devices. Among the fabricated devices, DH-6-based cell exhibits the highest power conversion efficiency of 4.04% with a short-circuit current density of 8.02 mA cm−2, an open-circuit photo voltage of 0.73 V and a fill factor of 0.69 under AM 1.5 illumination without coadsorbent that reaches 83% of the reference dye N719-based cell. This result indicates that other than electron-donor, triphenylamine could also be a promising π-linker to construct high-performance metal-free organic sensitizer.

•Novel asymmetric ZnPc derivative was prepared as dye of DSSCs.•Zn-tri-PcNc-9 with six diphenylthiophenol groups has broad Q-band absorption.•CDCA as coadsorbent can retard ZnPc molecule aggregates and charge recombination.•Zn-tri-PcNc-9-sensitized cell containing CDCA yields 3.61% efficiency.•S atoms in ZnPc’s substituents expand the solar cell’s red/near-IR responsive range.Asymmetric zinc phthalocyanine derivative (Zn-tri-PcNc-9) bearing one carboxylic and six bulky diphenylthiophenol groups was synthesized as a sensitizer for dye-sensitized solar cells. The obtained Zn-tri-PcNc-9 exhibits strong and expanded Q-band absorption peak (at ∼741 nm) in the red/near-IR light (600–800 nm) range, and its photovoltaic performance in sensitizing TiO2-based solar cell can be significantly improved by using chenodeoxycholic acid (CDCA) as co-adsorbent due to the retarded charge recombination. Under an optimal sensitization condition, the corresponding solar cell exhibits an efficiency of 3.61%, which is improved by 144% as compared to the solar cell without CDCA. Moreover, Zn-tri-PcNc-9-sensitized solar cell shows a maximum incident photo-to-current conversion efficiency of 31.6% at ∼730 nm, red-shifted by ∼20 nm as compared to that (∼710 nm) of its O-substituted analog (Zn-tri-PcNc-8) bearing six diphenylphenoxy groups, suggesting an effective solution to expand the red/near-IR responsive range of the ZnPc-sensitized solar cell, and also demonstrating a possibility for future panchromatic sensitizing agents in dye-sensitized solar cells.

A new route is carried out to achieve broad spectral responsive photocatalytic H2 production over g-C3N4 co-sensitized by an indole-based D-π-A organic dye (LI-4) and an asymmetric zinc phthalocyanine derivative (Zn-tri-PcNc) with complementary absorption spectra. Experimental results indicate that both LI-4 and Zn-tri-PcNc are efficient photosensitizers of g-C3N4 for H2 production, and their co-sensitized g-C3N4 (LI-4/g-C3N4/Zn-tri-PcNc) exhibits an extremely high H2 production activity (371.4 μmol h–1) under visible/near-infrared (NIR) light (λ ≥ 420 nm) irradiation, which approximates the summation of the H2 production activity of LI-4/g-C3N4 (233.8 μmol h–1) and Zn-tri-PcNc/g-C3N4 (132.3 μmol h–1), although LI-4 and Zn-tri-PcNc can just absorb the light in the range of 400–600 and 600–750 nm, respectively. Moreover, the co-sensitized catalyst shows a broad visible/NIR light responsive range (400–800 nm) with impressively high apparent quantum yields (AQY) of 16.3, 7.7, and 1.75% at 420, 500, and 700 nm monochromatic light irradiation, respectively. The present work gives a new advance toward panchromatic light responsive photocatalytic application by combining the photosensitization of two different dyes with complementary absorption spectra on one kind of semiconductor.Keywords: asymmetric zinc phthalocyanine; broad spectral responsive range; co-sensitization; metal-free organic dye; photocatalytic H2 production

Brookite TiO2 quasi nanocubes with high phase purity and thermal stability were synthesized through a hydrothermal process. The obtained brookite TiO2 quasi nanocubes have a mean size of ∼50 nm with a specific surface area of ∼34.2 m2 g−1. When used as a photoanode material, the single brookite TiO2 nanocubes film-based dye-sensitized solar cell (DSSCs) shows higher open-circuit voltage but lower conversion efficiency than the single nanosized anatase TiO2 film-based one with a similar film thickness; while using the brookite TiO2 nanocubes as an overlayer of the nanosized anatase TiO2 film, the fabricated bilayer solar cells exhibit significant enhancement in both the open-circuit voltage and short-circuit current. In addition, the corresponding bilayer solar cell with an optimized overlayer thickness gives a conversion efficiency up to 8.83% with a 23.8% improvement when compared to the single anatase cell (7.13%). The brookite nanocubes used as an overlayer not only reduce the charge recombination and dark current, but also prolong the electron lifetime, which leads to an enhanced voltage and photocurrent, and therefore the improved photovoltaic performance of the bilayer solar cell. These results demonstrate the simple fabrication method used to prepare brookite TiO2 nanocubes and their application as an overlayer are promising and offer a strategy for the development of low-cost and high efficiency DSSCs through tuning the photoanode's components and structure.

Photocatalytic CO2 reduction into renewable hydrocarbon solar fuels is considered as a promising strategy to simultaneously address the global energy and environmental issues. In this study, a binary g-C3N4/ZnO photocatalytic system was constructed via a one-step facile calcination method and further used as a photocatalyst for CO2 reduction. It was shown that the as-prepared g-C3N4/ZnO photocatalytic system exhibited enhanced photocatalytic activity for CO2 reduction by a factor of 2.3 compared with pure g-C3N4, while maintaining the original selectivity of pure g-C3N4 to convert CO2 directly into CH3OH. For the first time, the coupling effect of ZnO responsible for the improved photoactivity of g-C3N4 was fully illustrated and a direct Z-scheme mechanism rather than the conventional heterojunction-type mechanism was proposed to explain the better performances of the g-C3N4/ZnO binary composite photocatalytic system. The enhancement of photocatalytic CO2 reduction activity is attributed to the highly efficient ZnO-to-g-C3N4 electron transfer occurring at the intimate contact interface between the g-C3N4 phase and ZnO phase. This work will provide new deep insights into the rational construction of a g-C3N4-based photocatalytic system and the design of a direct Z-scheme system without an electron mediator for photocatalytic CO2 reduction reactions.

Asymmetric zinc porphyrin (ZnPy) was synthesized and used to sensitize nanosized TiO2. The visible-light-driven activity of CO2 photoreduction to generate CO/CH4 in the gas phase was observed from the ZnPy-sensitized TiO2 without loading noble metal, and the mechanism was discussed.

A robust polymer/polymer surface heterojunction (SHJ) catalyst for wide visible-light-driven H2 production is fabricated by a facile rotary evaporation of poly(3-hexylthiophene) (P3HT) solution containing graphitic carbon nitride (g-C3N4). The photocatalytic H2 production activity of the obtained SHJ catalyst (P3HT/g-C3N4) is significantly affected by the types of sacrificial reagents, and ascorbic acid (AA) shows the best photoactivity among the commonly used sacrificial reagents. The SHJ catalyst containing 3 wt % P3HT gives a H2 evolution activity up to 3045 μmol/h in a saturated AA solution, which is ∼491 times higher than that (6.2 μmol/h) of P3HT/g-C3N4 without AA solution under λ ≥ 500 nm light irradiation. Especially, the SHJ catalyst containing 3 wt % P3HT shows a record apparent quantum yield (AQY) of 77.4% at 420 nm light irradiation in the field of g-C3N4-based catalyst, and wide visible/NIR-light-responsive ability with AQY of 59.4%, 20.2%, 3.2% and 0.68% at 500, 600, 700 and 800 nm monochromatic light irradiation, respectively. The extremely high photoactivity is caused by the wide visible-light absorption, efficient charge transfer at the interface of P3HT/g-C3N4 and suitable oxidation half-reaction caused by the added AA as a sacrificial reagent. This study not only demonstrates a new direction for the solar fuel conversion over the large family of polymer-based semiconductors but also emphasizes the importance of oxidation half-reaction caused by the sacrificial reagent, which can significantly affect the photoactivity for H2 production.Keywords: Hydrogen production; Polymer/polymer heterojunction catalyst; Robust photoactivity; Sacrificial reagent; Wide visible-light response;

•Layered xLi2MnO3·(1 − x)LiMnO2 nanoplates are firstly prepared by pyrolysis reduction.•Transition metal layer of the nanoplate is parallel to the plate’s radial direction.•Nanoplate can retard the phase transformation and improve the cyclic stability.•Electrochemical property is improved by tailoring the morphology and composition.•Improved cyclic performance with reversible capacity up to 270 mAh g−1 is obtained.Layered xLi2MnO3·(1 − x)LiMnO2 (x = 0.57, 0.48, and 0.44) nanoplates are firstly prepared by pyrolysis reducing the electrochemically inactive monoclinic Li2MnO3 nanoplates, which is synthesized via a solid-state reaction by using home-made MnO2 nanoplates as self-template. The obtained xLi2MnO3·(1 − x)LiMnO2 nanoplates have a diameter of ∼200 nm and thickness of ∼60 nm with high crystallinity and the transition metal layers parallel to the plate’s radial direction. Although these xLi2MnO3·(1 − x)LiMnO2 nanoplates cause a longer Li+ diffusion distance, and then a lower reversible capacity as compared to the nanoparticle-like counterpart, the nanoplate-like morphology of these xLi2MnO3·(1 − x)LiMnO2 (especially with x < 0.5) are beneficial for retarding the layer-to-spinel phase transformation during the charge/discharge processes, and resulting in significant improvement of the cyclic stability. Moreover, the reduced reversible capacity caused by the longer Li+ diffusion distance of the nanoplate-like morphology can be offset by decreasing the x value, and the xLi2MnO3·(1 − x)LiMnO2 nanoplates with x = 0.44 performs a maximum reversible capacity as high as 270 mAh g−1 with a well cyclic performance. The present findings indicate that the cyclic performance and reversible capacity of xLi2MnO3·(1 − x)LiMnO2 can be improved by tailoring the particle’s morphology and composition, and demonstrate a simple and effective strategy for the development of the Co/Ni-free Mn-based layered Li-rich cathode materials with good cyclic and high reversible capacity.

•Novel asymmetric ZnPc derivatives were prepared as dye of DSSCs.•Zn-tri-PcNc-5 with six diphenylthiophenol groups shows more Q-band redshift than Zn-tri-PcNc-4.•Zn-tri-PcNc-4 with six diphenylphenoxy groups yielded 3.22% efficiency.•Zn-tri-PcNc-4-sensitized cell has higher efficiency than Zn-tri-PcNc-5-sensitized one.Asymmetric ZnPc derivatives with two carboxyl and six diphenylphenoxy or diphenylthiophenol groups were synthesized as dye of DSSCs. Those ZnPcs exhibit strong red/near-IR light absorption, and Zn-tri-PcNc-5 with six diphenylthiophenol groups shows obvious redshift in the Q-band and enhanced absorbance compared to Zn-tri-PcNc-4 with six diphenylphenoxy groups, while Zn-tri-PcNc-4 yielded a 3.22% efficiency in sensitizing TiO2-based solar cell, much higher than that (1.30%) of the S-substituted analog (Zn-tri-PcNc-5). The decreased efficiency of Zn-tri-PcNc-5 is due to the molecular orbital shift to negative direction, stemmed from S atoms instead of O atoms in the six substituents of Zn-tri-PcNc-4, which leads to insufficient driving force for the electron injection. The present results demonstrate that the optimization of molecular orbital levels of ZnPcs via changing the substituents’ “push–pull” effect is an effective approach to improve the ZnPc-sensitized cell performance.

A series of carbon-coated Ni (Ni@C)–Cd0.8Zn0.2S nanocomposites were fabricated via a facile hydrothermal process using pre-prepared Ni@C as a starting material. The obtained products were characterized by X-ray diffraction, UV-Vis diffuse reflectance absorption spectroscopy, X-ray photoelectron spectroscopy and electron microscopy. It was found that the introduction of Ni@C nanoparticles can improve both the visible light-induced photocatalytic H2 production activity and stability of the Cd0.8Zn0.2S solid solution, and the Ni nanoparticles encapsulated by several graphite-like carbon layers show high chemical and thermal stability. Among those products with various Ni@C contents, the 5 wt% Ni@C–Cd0.8Zn0.2S nanocomposite exhibits the maximum photoactivity (969.5 μmol h−1) for H2 production, which is ∼3.10 times higher than that (312.6 μmol h−1) of pristine Cd0.8Zn0.2S. This significant enhancement in the photoactivity by loading Ni@C nanoparticles can be attributed to the metallic Ni in the Ni@C acting as a co-catalyst, while the graphite-like carbon shells acting as the Cd0.8Zn0.2S nanoparticles' support and electron acceptor, which causes an effective photogenerated carrier separation in space and an improvement in the photoactivity and stability for H2 production. The present findings demonstrate a cost reduction strategy by using a non-noble metal co-catalyst for efficient and stable light-to-hydrogen energy conversion.

A novel composite electrode containing brookite TiO2 quasi nanocubes and anatase TiO2 sea urchin-like microspheres is fabricated for improving the dye-sensitized solar cell's performance. The brookite nanocubes have a mean size of ∼50 nm, and the anatase microspheres with ∼3 μm diameter display hierarchical structures composed of secondary TiO2 nanoribbons and nanoparticles. An optimal efficiency of 7.09% is obtained from the solar cell fabricated with a composite TiO2 electrode containing 30 wt% nanocubes and 70 wt% microspheres, with 81% or 30% improvement in the efficiency as compared to the single nanocube or microsphere film-based cell. Those brookite nanocubes in the microsphere film can fill the interspaces of the hierarchical microspheres, which can not only enhance the dye-loading, but also reduce the charge recombination. All these lead to a higher voltage and current, leading to the improved performance of the anatase TiO2 film-based solar cell.

•ZnPcs with six diphenylphenoxy and one/two carboxyl groups are used as dyes for DSSCs.•Effect of carboxyl group number on the ZnPc-sensitized cell property are scrutinized.•Grafting two carboxyl groups on ZnPc leads to the enhanced photocurrent and efficiency.•ZnPc with one COOH has a higher open-circuit voltage than its analog with two COOH.Asymmetric zinc phthalocyanines containing tribenzonaphtho-condensed porphyrazine with six bulky diphenylphenoxy and one or two carboxyl groups are used as sensitizers for dye-sensitized solar cells (DSSCs). It is found that Zn-tri-PcNc-4 having two carboxyl groups shows a slight redshift in the Q-band absorption but a significantly decreased absorbance as compared with Zn-tri-PcNc-8 having one carboxyl group, and Zn-tri-PcNc-4 can be more stably and perpendicularly grafted onto the TiO2 surface than Zn-tri-PcNc-8, which further leads to the differences in the interfacial charge transfer dynamics and dye-loaded amount. Zn-tri-PcNc-4 with two carboxyl groups grafted onto the TiO2 electrode surface of DSSC results in a photovoltaic conversion efficiency of 3.22%, higher than that (3.01%) of the analog with one carboxyl group (Zn-tri-PcNc-8), which exhibits a lower short-circuit current but much higher open-circuit voltage. The additional carboxyl group in Zn-tri-PcNc-4 leads to the enhanced dye-loaded amount and the molecular orbital energy level shift toward positive direction, causing more efficient electron injection and higher short-circuit current than Zn-tri-PcNc-8; while the two carboxyl groups of Zn-tri-PcNc-4 would cause more protonation of TiO2 surface, which possibly leads to the downward shift of TiO2 conduction band edge, and then to the decreased open-circuit voltage. The present results demonstrate the molecular engineering aspect of ZnPc dyes in which the fine tuning of the energy levels and molecular structures is crucial for high conversion efficiency of DSSCs.

•Anatase TiO2 microspheres with hierarchical nanoribbon structure are prepared.•Bilayer solar cell using the microspheres as overlayer of nano-TiO2 film is reported.•Bilayer cell exhibits better performance than the single nano-TiO2 film-based one.•TiO2 microspheres overlayer can enhance both light harvesting and dye-loading.•Bilayer cell exhibits decreased charge recombination and an improved voltage.Sea urchin-like TiO2 microspheres are synthesized through a facile one-step solvothermal process by using titanium tetrabutoxide (TBOT) as titanium source. The obtained TiO2 microspheres with ∼3 μm diameter display anatase phase and hierarchical structures composed of TiO2 nanoribbons containing secondary nanoparticles with an average particle size of ∼15 nm. By using as photoanode material, the anatase TiO2 microspheres film-based dye-sensitized solar cells (DSSCs) show higher short-circuit current but slightly lower conversion efficiency than the TiO2 nanoparticles (P25) film-based one; while the bilayer film-based solar cell by using the TiO2 microspheres as overlayer of the P25 film exhibits significantly improved photovoltaic performance with an efficiency up to 7.14%, improved by 26.6% as compared to the P25 film-based one (5.64%). The anatase TiO2 microspheres as overlayer can not only enhance the light harvesting capability due to their scattering effect of the sea urchin-like hierarchical structures, but also contribute to the larger dye-loading amount, which lead to a decrease in the charge transfer resistance, charge recombination and dark current, and then resulting in the improved photovoltage and photovoltaic performance. The simple fabrication method of the bilayer solar cell, which contains a photoanode composed of P25 film as underlayer and sea urchin-like TiO2 hierarchical microspheres as overlayer, demonstrates a strategy for the development of the low cost and high efficiency solar cells through tuning the photoanode's component and structure.

Highly asymmetric zinc phthalocyanine derivative (Zn-tri-PcNc) with intense near-IR light (650–800 nm) absorption is utilized as a sensitizer to extend the spectral response region of graphitic carbon nitride (g-C3N4) from ∼450 nm to more than 800 nm. Ultraviolet–visible light (UV-vis) diffuse reflectance absorption spectra (DRS), photoluminescence (PL) spectra, time-resolved photoluminescence spectra (TRPS), and energy band structure analyses are adopted to investigate the photogenerated electron transfer process between Zn-tri-PcNc and g-C3N4 on both thermodynamics and dynamics aspects. After optimizing the photocatalytic condition and adding chenodeoxycholic acid (CDCA) as coadsorbent, Zn-tri-PcNc sensitized g-C3N4 photocatalyst shows a H2 production efficiency of 125.2 μmol h–1 under visible/near-IR-light (λ ≥ 500 nm) irradiation, corresponding to a turnover number (TON) of 5008 h–1 with an extremely high apparent quantum yield (AQY) of 1.85% at 700 nm monochromatic light irradiation. The present work should be the rarely fundamental investigation on the utilization of near-IR light of solar radiation for the photocatalytic H2 production from water splitting over a dye-sensitized semiconductor.Keywords: graphitic carbon nitride; hydrogen production; near-IR light utilization; photocatalysis; zinc phthalocyanine derivative

Size controllable and thermally stable rice-like brookite TiO2 particles with high phase purity were synthesized through a hydrothermal process. By varying the reaction conditions, the average diameter (brachyaxis) of the rice-like brookite TiO2 particles can be tuned over a wide range from ca. 200 nm to 1200 nm. Moreover, the brookite phase can be maintained, even with calcination at a temperature up to 800 °C, and a brookite-to-anatase phase transition and then to rutile can be observed upon further enhancing the calcination temperature from 850 °C to 1000 °C. The obtained brookite TiO2 submicrometer particles were used as a light scattering overlayer on a nano-sized TiO2 (P25) film-based photoanode to fabricate bilayer TiO2 film-based dye-sensitized solar cells (DSSCs). It is found that the brookite TiO2 scattering layers can improve the performances of the P25 film-based solar cells to different extents by enhancing the light-harvesting capability, and the optimal diameter of the rice-like brookite TiO2 particles as a scattering layer material is determined to be ∼600 nm, its corresponding solar cell gives an overall conversion efficiency up to 7.57%, with a ∼33% improvement in the efficiency as compared to that (5.70%) of the individual P25 film-based one under standard AM 1.5G 1 sun irradiation. The above results on the brookite TiO2 particles represent a clear advance towards efficient light scattering materials for the nanosized TiO2 film-based solar cells.

Extremely efficient photocatalytic H2 production with a turnover number (TON) of 25002 for 20 h over graphitic carbon nitride (g-C3N4) sensitized by zinc phthalocyanines (ZnPcs) with asymmetric and electronic directional structures is successfully carried out under λ ≥ 500 nm light irradiation, and an impressive apparent quantum yield (AQY) higher than 1.0% is obtained under 700 nm monochromatic light irradiation. Based on the photoactivity, photofluorescence (PL), time-resolved fluorescence spectroscopy (TRFS), photocurrent, and electrochemical impedance spectroscopy (EIS) results, it is found that the asymmetry and electronic directionality of ZnPcs can significantly influence the photogenerated electron transfer between ZnPcs and g-C3N4 and further influence the photocatalytic H2 production activity of the phthalocyanine-sensitized g-C3N4 system. The present work exhibits the promising application of phthalocyanine materials in extending red/near-IR light utilization and gives some suggestions and routes for the design and synthesis of phthalocyanine derivatives for solar energy conversion applications.

Co-sensitization by using two or more dyes with complementary absorption spectra as sensitizers of a semiconductor to expand the spectral response range of dye-sensitized solar cells (DSSCs) is an effective approach to enhance device performance. To improve the light-harvesting capability in the near-infrared (IR) region, zinc phthalocyanine (Zn-tri-PcNc-1) was applied to combine with a D-π-A triarylamine–bithiophene–cyanoacrylate-based organic dye (DH-44) for fabrication of a co-sensitized solar cell. The resulting co-sensitized device shows an efficient panchromatic spectral response feature in the range of 320–750 nm and gives an overall conversion efficiency of 6.61%, which is superior to that of the individual dye-sensitized solar cells under standard AM 1.5G one sun irradiation. The above results represent a clear advance toward efficient and low-cost co-sensitized solar cells with a panchromatic spectral response.Keywords: Co-sensitization; dye; Dye-sensitized solar cell; Spectral responseD;

In-doped TiO2 thin film was introduced at the interface of fluorine-doped tin oxide (FTO) substrate and mesoporous TiO2 film by spin-coating method, and its application as a new compact layer material for dye-sensitized solar cells (DSSCs) was investigated. The scanning electron microscopy (SEM), UV-visible spectroscopy, current-voltage characteristics, Mott-Schottky analysis, electrochemical impedance spectroscopy (EIS) analysis and open-circuit voltage decay (OCVD) technique are used to characterize the morphology, optical transmittance and flat-band potentials (Vfb) of In-doped titania compact film and its effect to the photoelectron conversion process. It was found that In-doping increased the transmittance of TiO2 compact layer, the interfacial resistance between FTO substrate and porous TiO2 film and the flat-band potential of TiO2 film. The In-doped TiO2 compact layer effectively suppressed the charge recombination from FTO to the electrolyte, increased the optical absorption of dye and then increased the short-circuit photocurrent density (Jsc). Furthermore, In-doped TiO2 compact layer acted as a weak energy barrier, which increased the electron density in the mesoporous TiO2 film, thus improved open-circuit photovoltage (Voc). As a result, the overall energy conversion efficiency of the DSSC with In-doped TiO2 compact layer was enhanced by 11.9% and 6.9% compared to the DSSC without compact layer and with pure TiO2 compact layer, respectively. It indicated that In-doped TiO2 is a promising compact layer material for dye-sensitized solar cells.

We firstly demonstrate the opposite photocatalytic activity orders of low-index facets of anatase TiO2 in the liquid phase for rhodamine B (RhB) photocatalytic degradation and in the gaseous phase for the photoreduction of CO2 to CH4. The photocatalytic activity order in the liquid phase for RhB photocatalytic degradation is revealed as {001} > {101} > {010}, whereas the photocatalytic activity order {010} > {101} > {001} is found in the gaseous phase for the photoreduction of CO2 to CH4. The atomic arrangement of the different facets, UV-vis diffuse reflectance spectra, photoluminescence spectra and attenuated total reflectance Fourier transform infrared spectroscopy analysis show that the photoactivity order in the gas phase for the photoreduction of CO2 to CH4 mainly depends on the CO2 molecule adsorption properties on the different exposed facets, and the separation efficiency of the photo-generated carriers determines the photoactivity order for the dye degradation reaction in the liquid phase. These findings also provide a new direction to design efficient photocatalysts and the tuning of their photoreactivity for environmental and energy applications.

Zinc phthalocyanine (ZnPc) derivatives with asymmetric (Zn-tri-PcNc-2) or symmetric (Zn-tetrad-Nc) structure, which possess wide spectral response in the visible/near-IR light region, are synthesized and utilized as a sensitizer of graphitic carbon nitride (g-C3N4) with 0.5 wt% Pt-loading for photocatalytic H2 production. The experimental results indicate that Zn-tri-PcNc-2 exhibits much better photosensitization on g-C3N4 than Zn-tetrad-Nc under visible/near-IR light although Zn-tetrad-Nc possesses wider and stronger optical absorption property than Zn-tri-PcNc-2. Zn-tri-PcNc-2-Pt/g-C3N4 exhibits an average H2 production rate of 132 μmol h−1, which is much better than that (26.1 μmol h−1) of Zn-tetrad-Nc-Pt/g-C3N4 under visible-light (λ ≥ 500 nm) irradiation. Moreover, Zn-tri-PcNc-2-Pt/g-C3N4 also shows much higher apparent quantum yield (AQY) than Zn-tetrad-Nc-Pt/g-C3N4 under red/near-IR light irradiation. Especially, Zn-tri-PcNc-2-Pt/g-C3N4 exhibits impressively higher AQY (1.07%) than that (0.22%) of the Zn-tetrad-Nc-Pt/g-C3N4 under 700 nm monochromatic light irradiation. The much better photoactivity of Zn-tri-PcNc-2-Pt/g-C3N4 than Zn-tetrad-Nc-Pt/g-C3N4 is caused by the asymmetric structure of Zn-tri-PcNc-2, which can result in the electronic orbital directionality of its excited state, much faster photogenerated electron transfer to g-C3N4, and higher red/near-IR light utilization efficiency as compared to Zn-tetrad-Nc-Pt/g-C3N4. The present results provide an important insight into the effects of molecular structure and optical absorption property of phthalocyanine derivatives on the photoactivity of the dye-sensitized semiconductor, and also guide us to further improve the solar energy conversion efficiency by optimizing the molecular structure and effectively utilizing the visible/near-IR light of sunlight.

Novel highly asymmetric zinc tetraazaporphyrin (TAP) derivatives (Zn-tri-TAPNc and Zn-tri-PcNc) with one carboxyl and three tert-butyl peripheral substituent groups were synthesized. A highly asymmetric zinc phthalocyanine (ZnPc) derivative (Zn-tri-PcNc) has a benzo-annelated ring which contains tribenzonaphtho-condensed tetraazaporphyrin with the same peripheral substituents as Zn-tri-TAPNc. As a sensitizer for the TiO2-based dye-sensitized solar cell, Zn-tri-PcNc derived from the benzo-annelation of the TAP macrocycle showed improved light harvesting and electron injection efficiency, which can retard the charge recombination, resulting in a great improvement in the incident photon-to-current conversion efficiency (IPCE). The Zn-tri-PcNc-sensitized solar cell exhibited a higher conversion efficiency (2.89%) than the Zn-tri-TAPNc-sensitized one (1.20%) under AM 1.5G solar irradiation. The present results on the TAP macrocycle's benzo-annelation demonstrate that optimization of molecular structure via changing the peripheral substituent group's “push–pull” effect and enlarging the conjugated π-system is an effective approach to improve the performance of the tetraazaporphyrin-based dye-sensitized solar cell.

•Three D–π–A organic dyes containing a π-linker of 2,2′-bithiophene unit linked with three electron-donors have been designed.•The photovoltaic performances of the dyes are characterized and they exhibit relatively high open voltage.•The structure–performance relationship is primarily studied with the aid of theoretical calculation.A series of new organic dyes containing 2,2′-bithiophene unit as a π-linker to connect three electron-donors (including carbazole, DH-45; phenothiazine, DH-46; triphenylamine, DH-47) at 3,4′,5′-positions have been designed and synthesized for dye-sensitized solar cells. The experimental results and theoretic calculations indicated that the large steric hindrance among three electron-donors and 2,2′-bithiophene ring partially destroys the whole molecular coplanarity and weakens intramolecular charge transfer (ICT), which results in the narrow, blue-shift of absorption band and decrease of short-circuit current (Jsc). However, the twisted conjugation skeleton for the dyes is favorable for the spatial charge separation that enhances the open-circuit voltage (Voc). Among them, the dye containing carbazole donating group (DH-45) shows best optimized structure for intramolecular charge transfer (ICT) and exhibits better photovoltaic performances than that of the other two dyes (DH-46 and DH-47).Three new D–π–A conjugated organic sensitizers based on 3,4′,5′-trisubstituted 2,2′-bithiophene were conveniently synthesized. And the photovoltaic performances as well as the structure–property relationship were studied.

AgIn5S8/TiO2 nanocomposite is prepared through a one-pot hydrothermal method, which is used for photocatalytic H2 production under visible-light irradiation. The effects of AgIn5S8/TiO2 molar ratio in the nanocomposites on the crystal phase, microstructure, optical absorption properties, and photocatalytic H2 evolution activity are investigated comparatively. The pristine AgIn5S8 shows a sharp absorption edge at ∼705 nm, corresponding to a bandgap of ∼1.76 eV, and its visible-light-driven photoactivity for H2 production can be remarkably enhanced by coupling with TiO2. The AgIn5S8/TiO2 nanocomposite with molar ratio of 1:10 has the maximum photoactivity for H2 production, improved by 7.7 times as compared with the pristine AgIn5S8. The enhanced photoactivity can be ascribed to some AgIn5S8 nanoparticles closely contacting the TiO2 nanoparticles to form heterojunction structure. This configuration of the composite photocatalyst results in an efficient charge separation at the interface, followed by fast diffusion of photoelectrons generated in AgIn5S8 toward TiO2, which is beneficial for separating the photogenerated carriers in space and improving the photoactivity.Keywords: AgIn5S8; heterojunction; hydrogen production; nanocomposite; photocatalyst

Anatase TiO2 nanocrystals with {101}, {001} or {010} single facets of 90% level exposure were controllably synthesized from potassium titanate (PT) without fluorine and organic capping surfactants, and characterized by X-ray diffraction patterns (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and fast Fourier transformation (FFT). The liquid-phase photocatalytic reduction (O2˙− generation) and oxidation (˙OH generation) activity orders of anatase TiO2 facets are {001} > {101} > {010} upon removing facet synergetic effect and surface fluorine effect. UV-vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra showed that absorbance edge order, and separation efficiency order of photoexcited holes and electrons are {001} > {101} > {010}, which explains the photocatalytic activity order well together with the atomic arrangement of different facets.

A new class of metal-free organic dyes (DH-41–DH-44) containing triphenylamine group as an electron donor, cyanoacrylic acid group as an electron acceptor and a π-linker of 2,2′-bithiophene unit with two hexyl groups at different β-substituted positions have been designed and synthesized. Their photovoltaic performances are characterized experimentally and the structure–performance relationship is explored with the aid of theoretical calculation. Although all the DH dyes show the same structural backbone, changing β-substituted positions of hexyl group at 2,2′-bithiophene unit can alter the molecular coplanarity of conjugated skeleton and the intramolecular charge transfer (ICT) that finally affects the UV–Vis absorption and the photovoltaic performances of the DH dyes. By comparison, the dyes with two hexyl groups at nonortho β-positions of 2,2′-bithiophene unit shows less steric hindrance and better molecular coplanarity that is favorable for improving photovoltaic performances. Among them, DH-44 has the best optimized structure for ICT, so it shows broadened and red-shifted absorption with high molar extinction coefficient, and exhibits excellent photovoltaic performances with high power conversion efficiency of 5.86%, which reaches over 95% of the reference dye N719-based cell fabricated and measured under the same conditions.Graphical abstractNew class of D-π-A structural organic dyes containing a π-linker of 2,2′-bithiophene unit with two hexyl groups at different β-substituted positions have been designed and synthesized. Their photovoltaic performances are characterized experimentally and the structure–performance relationship is explored with the aid of theoretical calculation.Highlights► New D-π-A organic dyes containing a π-linker of 2,2′-bithiophene unit have been obtained. ► The dye with good coplanar structure exhibits excellent photovoltaic performances. ► The structure–performance relationship is explored with the aid of theoretical calculation.

Sea urchin-like anatase TiO2 microspheres with hierarchical structure were prepared by a solvothermal method, and were applied for fabricating quasi-solid-state flexible dye-sensitized solar cells through a simple method of mixing it with ethanol and HCl. The flexible solar cells were investigated by the methods of electrochemical impedance spectra, open-circuit voltage decay and photocurrent–voltage curves. It is found that the hierarchical TiO2 microsphere-based solar cell shows encouraging performance (shot-circuit current density of 11.49 mA cm−2, open-circuit voltage of 0.67 V, fill factor of 0.56, and conversion efficiency of 4.32%), which is much better than that of commercial TiO2 nanoparticles (P25)-based one, due to its excellent particle interconnections, low electron recombination and high specific surface area.Highlights► Sea urchin-like TiO2 spheres were used to prepare flexible electrode. ► Quasi-solid state dye-sensitized solar cell was fabricated by the electrode. ► TiO2 spheres can supply sufficient surface area for dye adsorption. ► Sea urchin-like structures ensure good particle interconnection. ► TiO2 sphere-based flexible cell shows higher efficiency than the P25-based one

A novel binary ionic liquid electrolyte containing lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and binary ionic liquids, which is composed of 1-butyl-3-methylimidazolium iodide (BMII) and 1-butyl-3-methylimidazolium thiocyanate (BMISCN), is developed for dye-sensitized solar cells (DSSCs). It is found that incorporation of LiTFSI as charge transfer promoter with BMII has positive effect on the interfacial charge transfer of the dye/TiO2 film, further addition of BMISCN into the above composite electrolyte can take advantage of its low viscosity to enhance the ionic conductivity and reduce the interfacial charge transfer resistance, and a photovoltaic conversion efficiency of 5.55% is obtained from the solar cell fabricated with the optimized binary ionic liquid electrolyte without iodine participation under AM 1.5 illumination at 100 mW cm−2, with a 108.6% improvement in the efficiency with lower resistance and higher ionic conductivity as compared to the solar cell fabricated with single BMII ionic liquid-based electrolyte. The above results should be attributed to the reduced charge recombination and the effective interfacial charge transfer in the solar cell.

An efficient plastic crystal-based electrolyte is prepared by employing succinonitrile as solid solvent and binary ionic liquids as charge transfer mediators for dye-sensitized solar cells (DSSCs). It was found that combining succinonitrile with ionic liquids could improve the mechanical property of electrolyte and avoid the fluidity of ionic liquid, and the fabricated solid-state solar cell shows an overall conversion efficiency of 2.14%, which can be further improved to 5.50% after optimizing the addition amount of lithium perchlorate (LiClO4) as charge transfer promoter into the plastic crystal electrolyte, and the role of LiClO4 in the plastic crystal ionic liquid electrolyte is evaluated through electrochemical and photoelectrochemical measurements. The knowledge obtained from this plastic crystal-based electrolyte exhibits new eyeshot to find solid-state electrolyte for DSSCs with high performance.Graphical abstractLiClO4 was incorporated into the iodine-free plastic crystal electrolyte to inhibit the crystallization of succinonitrile, and increase the charge transfer through enhancing charge exchange reaction between I−/I3−, therefore improve the conversion efficiency of DSSC.Highlights► Succinonitrile plastic crystal ionic liquid electrolyte was developed for solar cell. ► Succinonitrile can improve the mechanical property of ionic liquid electrolyte. ► Wiping out of I2 can avoid its light absorption and volatility. ► LiClO4 can promote the charge transfer of the plastic crystal-based electrolyte. ► Li+ ions can enhance the charge exchange between I−/I3− in the electrolyte.

This perspective gives an overview of recent developments in heterogeneous photocatalytic CO2 reduction for C1/C2 fuels production over semiconductors, which has been known for several decades as a potential feasible means to store intermittent solar energy and to recycle CO2. In recent years, significant efforts have been made in order to further improve the photoactivity and the selectivity through developing novel photocatalysts and its CO2 photoreduction reaction systems, which would be of great interest in the field of solar conversion and CO2 resource utilization.

Two kinds of graphitic carbon nitride (g-C3N4) were synthesized through a pyrolysis process of urea or melamine. It is found that the obtained g-C3N4, as photocatalysts, can reduce CO2 to organic fuels under visible light, and exhibit different photoactivity and selectivity on the formation of CH3OH and C2H5OH. The product derived from the urea (denoted as u-g-C3N4) shows a mesoporous flake-like structure with a larger surface area and higher photoactivity for the CO2 reduction than the non-porous flaky product obtained from melamine (denoted as m-g-C3N4). Moreover, using u-g-C3N4 as a photocatalyst can result in the formation of a mixture containing CH3OH and C2H5OH, while m-g-C3N4 only leads to the selective formation of C2H5OH. The present interesting findings could shed light on the design of efficient, eco-friendly and convenient photocatalysts and the tuning of their photoreactivity in the field of sustainable light-to-energy conversion.

•Li2MnO3 is chemically activated by the pyrolysis of in situ formed lithium stearate.•Layered structure is maintained with Mn valence state reducing and 23% Li losing.•An initial charge/discharge profile similar to the Li-rich solid solutions.•An improved rate performance with reversible capacity of 255 mAh g−1 is obtained.Li2MnO3 is chemically activated by the pyrolysis process of an in situ formed lithium stearate derived from the chemically adsorbed stearic acid on the Li2MnO3 particle surfaces. It is found that different Mn-containing compounds are formed depending on the pyrolysis temperature under N2 atmosphere. When the pyrolysis reaction temperature is 340 °C, the layered structure of Li2MnO3 can be maintained and the average valence of Mn is reduced from +4.00 to +3.48 associated with 23% Li ions losing; while the pyrolysis reactions at 400–600 °C lead to the formation of orthorhombic LiMnO2 and/or cubic MnO. As cathode material for Li-ion battery, the activated Li2MnO3 derived from the pyrolysis process at 340 °C exhibits an initial charge/discharge profile similar to the Li-rich solid solution materials but with a much larger reversible discharge capacity (255 mAh g−1) and a dramatically improved rate performance as compared to the pristine Li2MnO3. The present findings indicate that the pyrolysis of in situ formed lithium stearate is a simple and effective way to chemically activate Li2MnO3 so as to improve the cyclic capacity and rate performance.

•Highly asymmetric zinc phthalocyanine derivative is used as dye of the solar cell.•Chenodeoxycholic acid (CDCA) as coadsorbent hinders the phthalocyanine aggregation.•Dye-adsorption temperature significantly impacts the solar cell's performance.•An optimal dye adsorption condition leads to efficient electron injection.•Efficiency of solar cell is improved by 47% as compared to the cell without CDCA.Highly asymmetric zinc phthalocyanine derivative (Zn-tri-PcNc) containing tribenzonaphtho-condensed porphyrazine with one carboxyl and three tert-butyl (t-Bu) substituent groups is used as a sensitizer to fabricate dye-sensitized solar cells (DSSCs), and the effects of chenodeoxycholic acid (CDCA) as a coadsorbent and the dye adsorption temperature on the solar cell's performance are investigated. It is found that CDCA coadsorption can hinder the dye aggregation, which is beneficial for improving the electron injection efficiency and retarding the charge recombination, and thus resulting in the enhancement of the short-circuit current density and open-circuit photovoltage. Moreover, the dye adsorption temperature on electrode also shows a significant impact on the photovoltaic performance of the solar cell, and an optimal dye adsorption condition of the TiO2 electrode is found to be 5 × 10−5 M Zn-tri-PcNc ethanol solution containing 7.5 mM CDCA at 5 °C, which can contribute to the maximum conversion efficiency of 2.89% with short-circuit current density of 9.42 mA cm−2 and open-circuit photovoltage of 0.48 V, improved by 47% as compared to the solar cell fabricated with TiO2 electrode sensitized by the zinc phthalcoyanine in absence of CDCA.

A novel nanostructured carbon/TiO2 nanocomposite photocatalyst is firstly fabricated via a facile hydrothermal process by using fullerene (C60) decorated single-walled carbon nanotubes (SWCNTs) as carbon source, which is denoted as C60-d-CNTs. The obtained nanostructured carbon/TiO2 nanocomposites are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectra (DRS), Raman spectra, X-ray photoelectron spectroscopy (XPS) and photoluminescence spectra (PL), and then are used as catalysts for photocatalytic hydrogen production. It is found that the kinds and contents of various carbon nanostructured materials (such as SWCNTs, C60 and C60-d-CNTs) coupled with TiO2 can significantly enhance the photoactivity for hydrogen production, and the 5 wt% C60-d-CNTs/TiO2 nanocomposite exhibits the best performance. Experimental results suggest that the C60-d-CNTs as a novel carbon nanostructured material could be more beneficial for the photogenerated carrier separation than SWCNTs and C60 when these carbon nanostructured materials are coupled with TiO2.

Although dye-sensitized semiconductors for photocatalytic H2 production have been reported for more than 20 years, the spectral response is still focused on the region of 400–600 nm and it is almost never extended to >600 nm. The present work successfully uses zinc phthalocyanine (Zn-tri-PcNc) and naphthalocyanine (Zn-tetra-Nc) to sensitize TiO2 for photocatalytic H2 production, which expands the spectral response of dye-sensitized semiconductors by harvesting light from 600 to 800 nm. Zn-tri-PcNc/TiO2 has a H2 production amount of 567.4 μmol with a turnover number (TON) of ∼7565, which is much higher than that of Zn-tetra-Nc/TiO2 (236.5 μmol H2 with a TON of ∼3153). In particular, Zn-tri-PcNc-sensitized TiO2 shows an apparent quantum yield (AQY) of up to 0.2% under 700 nm monochromatic light irradiation and ∼0.1% under monochromatic light irradiation between 500 and 800 nm, indicating its efficient visible/near-IR-light-driven photocatalytic H2 production. Future work on the panchromatic responsive dye-sensitized semiconductor system can be carried out using phthalocyanines co-sensitized with other dyes to utilize the whole visible/near-IR light of sunlight.

Single-crystal β-MnO2 hollow bipyramids (HB-β-MnO2) were synthesized via a template-free hydrothermal method. The as-synthesized hollow bipyramids with 100–300 nm pores along the axis direction of the β-MnO2 bipyramids are formed through self-assembly and phase transformation processes from α-MnO2 nanowires to β-MnO2 bipyramids followed by chemical etching of their metastable crystal faces. Compared to the commercial bulk β-MnO2 (c-β-MnO2), the as-synthesized HB-β-MnO2 exhibits a better electrochemical performance with an initial discharge capacity of 269 mA h g−1, which equates to up to 0.87 Li+ intercalation per β-MnO2 unit, while only 0.2 Li+ intercalation per β-MnO2 unit is observed for the commercial c-β-MnO2. The excellent electrochemical activity of the as-synthesized HB-β-MnO2 can be attributed to its hollow structure and single crystal nature. The former can provide higher contact area with the electrolyte and is able to act as a buffer against volume change during the charge/discharge processes, while the latter contributes to good electronic conductivity and stable structural integrity. Moreover, the initial HB-β-MnO2 bipyramids undergo an irreversible phase transformation to orthorhombic LixMnO2 after the first discharging process, which shows good structural stability and capacity (up to 150 mA h g−1) after 50 charge/discharge cycles.

Stannite-type multicomponent sulfide (Ag2ZnSnS4) nanoparticles with particle diameters of 100–200 nm were synthesized through a solvothermal treatment combined with a post-annealing process under N2 atmosphere. The obtained Ag2ZnSnS4 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities for hydrogen production of Ag2ZnSnS4 were evaluated under visible light (λ ≥ 420 nm) irradiation. It was found that the 1.0 wt% Pt-loaded Ag2ZnSnS4 displayed a photocatalytic hydrogen evolution activity of 580 μmol h−1 with a fairly good apparent quantum efficiency of 15.2% at 420 nm incident light irradiation.

•AgIn5S8/TiO2 heterojunction composite is prepared by a low-temperature process.•Efficient visible-light-driven photocatalytic H2 production with better durability.•Its photoactivity is better than the counterpoint derived from hydrothermal method.•Heterojunction results in fast carrier separation and the improved photoactivity.•Beneficial for developing efficient photocatalyst and tuning the spectral response.AgIn5S8 and AgIn5S8/TiO2 heterojunction nanocomposite with efficient photoactivity for H2 production were prepared by a low-temperature water bath deposition process. The resultant AgIn5S8 shows an absorption edge at ∼720 nm, corresponding to a bandgap of ∼1.72 eV, and its visible-light-driven photoactivity (100.1 μmol h−1) for H2 evolution is 9 times higher than that (11 μmol h−1) of the product derived from a hydrothermal process, while the obtained AgIn5S8/TiO2 heterojunction nanocomposites prepared by using commercially available TiO2 nanoparticles (P25) as TiO2 source exhibit remarkably improved photoactivity as compared to the pristine AgIn5S8, and the AgIn5S8/TiO2 nanocomposite with molar ratio of 1:10 shows a maximum photocatalytic H2 evolution rate (371.1 μmol h−1), which is 4.3 times higher than that (85 μmol h−1) of the corresponding AgIn5S8/TiO2 nanocomposite derived from a hydrothermal method. This significant enhancement in the photocatativity of the present AgIn5S8/TiO2 nanocomposite can be ascribed to the better dispersion of the AgIn5S8 formed on TiO2 nanoparticle surfaces and the more intimate AgIn5S8/TiO2 heterojunction structure during the water bath deposition process under continuously stirring as compared to the corresponding nanocomposite derived from a hydrothermal method. This configuration of nanocomposite results in fast diffusion of the photogenerated carriers in AgIn5S8 towards TiO2, which is beneficial for separating spatially the photogenerated carriers and improving the photoactivity. The present findings shed light on the tuning strategy of spectral responsive region and photoactivity of photocatalysts for efficient light-to-energy conversion.

Carbon coated LiFePO4 (LiFePO4/C) nanocomposite is successfully synthesized at a comparatively low temperature (400 °C) via a pyrolysis process of in situ formed lithium stearate. The obtained products are characterized by X-ray diffraction, electron microscopy, thermogravimetry, infrared and X-ray photoelectron spectroscopy. Experimental results indicate that the in situ formed lithium stearate can decompose at ∼290 °C, which is beneficial for the formation of carbon coating and reduction of Fe3+ species, and then the crystallized LiFePO4/C nanocomposite can be formed at 400 °C without other intermediate products. As cathode material of Li-ion battery, the obtained LiFePO4/C nanocomposite exhibits a good rate and cycling performance with a high discharge capacity of ∼160 mAh g−1 (>94% theoretical capacity of LiFePO4) at a current density of 1 C (170 mA g−1), and ∼96% of its initial capacity can be retained after 200 charging/discharging cycles. Even at a high current density (10 C), the LiFePO4/C nanocomposite still presents a discharge capacity as high as ∼100 mAh g−1. The excellent electrochemical performances of the present LiFePO4/C nanocomposite mainly originate from the good crystallinity, small particles and enhanced electronic conductivity of the materials coated and linked by carbon layers.Highlights► In situ forming lithium stearate in the precursor. ► Carbon coated polycrystal LiFePO4 is prepared by lithium stearate pyrolysis. ► Samples with good cyclic and rate performance can be prepared at 400 °C. ► Crystallized directly after Fe3+ reduction. ► Low temperature, short time and no involved intermediate compounds.

•Single-crystalline LiMn2O4 nanorods were synthesized via template-engaged reaction.•Phase transformation from tetragonal β-MnO2 to cubic LiMn2O4 was explored.•LiMn2O4 nanorods deliver 125 mAh g-1 at 1C and 75% capacity retention at 3C.•Recycled LiMn2O4 nanorods still keep spinel structure and single-crystal nature.Single-crystalline LiMn2O4 nanorods with a diameter of ~ 100 nm were synthesized via a template-engaged reaction by using tetragonal β-MnO2 nanorods as starting material. The investigations on the structures and morphologies of both the precursor and the final product reveal that a minimal structure reconstruction can be responsible for the chemical transformation from tetragonal β-MnO2 nanorods to cubic LiMn2O4 nanorods. The obtained LiMn2O4 nanorods as cathode material for Li-ion battery exhibit superior high-rate capability and good cycling stability in a potential range of 3.5–4.3 V vs. Li+/Li, which can deliver an initial discharge capacity of 125 mAh g− 1 (> 84% of the theoretical capacity of LiMn2O4) at a current rate of 0.5 C, and about 75% of its initial capacity can be remained after 500 charge–discharge cycles at a current rate of 3 C. Importantly, the rod-like nanostructure and single-crystalline nature are also well preserved after prolonging the charge/discharge cycling time at a relatively high current rate, indicating good structural stability of the single-crystalline nanorods during the lithium intercalation/deintercalation processes, and such high-rate capacity and cycling performance can be ascribed to the favorable morphology and the high crystallinity of the obtained LiMn2O4 nanorods.

Well-crystallized FeSbO4 nanorods with rutile-like structure are synthesized through a solid-state reaction and used as cathode material of Li-ion battery for the first time. The obtained nanorods can react with ∼11 Li-ions per FeSbO4 unit with a specific discharge capacity of 1 100 mAh·g− between 0.1 and 2.0 V. Three discharge plateaus can be observed during the fully discharging process, but the reversible reaction with ∼1 Li occurs between 1.5 V and 4.5 V vs. Li+/Li, and the reversible capacity is only 50–80 1 mAh·g−. FeSbO4 nanorods have a stable cyclic performance between 1.5 V and 4.5 V and it can be used as cathode material for rechargeable Li-ion battery.

One dimensional structures of TiO2 (nanowires and nanotubes) are promising for dye-sensitized solar cells due to reduced electron recombination; however, the small surface area is the main hurdle in the application of one dimensional anatase structures to dye-sensitized solar cells because of insufficient dye adsorption. Here, we address this problem with the preparation of a TiO2 nanotube film with a high specific surface area. This film was self-assembled by ultra-fine TiO2 nanotubes with diameter <10 nm via a simple hydrothermal method, and was applied to dye-sensitized solar cells on flexible Ti metal using a transplanting technique. Due to the higher surface area and one-dimensional structure, 6.23% efficiency was obtained with this ultra-fine TiO2 nanotube film, which was superior to that of conventional TiO2 nanoparticles.

A highly conductive Ni-coated commercial paper substrate (square resistance <1 Ω) was prepared by chemical deposition, and used as the substrate for a flexible TiO2 film electrode derived from a binder-free TiO2 paste, and heat treated at 250 °C. A low-cost, quasi-solid-state and TCO-free highly bendable paper-based dye-sensitized solar cell with conversion efficiency up to 2.90% is fabricated successfully by applying an iodine-free electrolyte. This encouraging result indicates that commercial paper is a promising material for use in dye-sensitized solar cells because of its flexibility, low cost and relatively high resistance to temperature. Compared with the rigid transparent conducting oxide (TCO) coated glass and flexible conductive plastic substrates, the potential of using mature paper making and coating technologies will greatly reduce the cost of the current photovoltaic devices.

Walnut-like In2S3 microspheres were synthesized through an ionic liquid-assisted solvothermal method for the first time. The crystal structure and morphology of the as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS) and nitrogen adsorption–desorption measurement. It was found that the additional amount of ionic liquid, solvothermal temperature and time played crucial roles in controlling the structure and morphology of the In2S3 microspheres. A possible formation mechanism of the walnut-like In2S3 microsphere was proposed on the basis of the experimental results.

Multiwalled carbon nanotubes (MWCNTs) and ZnIn2S4 composites were prepared by a facile hydrothermal method, which was used for hydrogen production under visible-light (λ ≥ 420 nm) irradiation. The obtained MWCNTs/ZnIn2S4 composites were characterized by X-ray diffraction (XRD), thermogravimetric and differential scanning calorimetry analyses (TG-DSC), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption spectra (DRS), Fourier transform IR spectroscopy (FTIR) and Photoluminescence spectra (PL). It was found that the MWCNTs were embedded into the interior of floriated ZnIn2S4 microspheres. The effects of the composite ratio in the MWCNTs/ZnIn2S4 on the photocatalytic activity for hydrogen production were investigated. The results show that the 3 wt% MWCNTs/ZnIn2S4 composite reaches its maximum photocatalytic hydrogen production efficiency with an apparent quantum efficiency as high as 23.3% under 420 nm light irradiation. The significantly enhanced photoactivity for the present composite originates from the synergetic effect of its component intrinsic properties. A possible mechanism of the MWCNTs/ZnIn2S4 composite as a photocatalyst for H2 evolution was proposed.

Porous graphitic carbon nitride (g-C3N4) was prepared by a simple pyrolysis of urea, and then a g-C3N4–Pt-TiO2 nanocomposite was fabricated via a facile chemical adsorption followed by a calcination process. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance absorption spectra, and electron microscopy. It is found that the visible-light-induced photocatalytic hydrogen evolution rate can be remarkably enhanced by coupling TiO2 with the above g-C3N4, and the g-C3N4–Pt-TiO2 composite with a mass ratio of 70:30 has the maximum photoactivity and excellent photostability for hydrogen production under visible-light irradiation, and the stable photocurrent of g-C3N4–TiO2 is about 1.5 times higher than that of the bare g-C3N4. The above experimental results show that the photogenerated electrons of g-C3N4 can directionally migrate to Pt-TiO2 due to the close interfacial connections and the synergistic effect existing between Pt-TiO2 and g-C3N4 where photogenerated electrons and holes are efficiently separated in space, which is beneficial for retarding the charge recombination and improving the photoactivity.

Three new organic dyes with one, two and three branched D–π–A structures derived from an electron donating triphenylamine core and connected by 1,2,3-triazole group to an electron deficient cyanoacrylate system have been conveniently synthesized via a ‘Click’ reaction. It was found that all three dyes show UV–vis absorptions in the 300–500 nm range with high molar extinction coefficients. A red-shift of UV–vis absorption band was observed in the solid thin film compared with the dioxane solution. Dye-sensitized solar cell devices based on the dyes were fabricated and tested. The one branched triphenylamine-based dye exhibits the highest energy conversion efficiency. Increase of the branched D–π–A structure around the triphenylamine core results in the decrease of energy conversion efficiency of the dyes, which can be attributed to less attachment of the dyes onto TiO2 photoanode with the enlarged molecular size of the corresponding multibranched structure.New organic dyes based on triphenylamine core have been synthesized via a ‘Click’ reaction. The introduction of 1,2,3-triazole bridge enhances the Voc and fill factor of the DSSCs, and the increment of branched D–π–A structure results in the decrease of energy conversion efficiency.Highlights► Three new triphenylamine-based organic dyes were conveniently synthesized via a “Click” reaction. ► The bridging 1,2,3-triazole group has been introduced into dyes for DSSCs for the first time. ► The photovoltaic performance was discussed using results from the experimental study and DFT calculations.

Two new organic dyes with tert-butyl-capped N-arylcarbazole as a donor, cyanoacrylic acid as an acceptor and a bithiophene unit as a π-linker (DH-11 and DH-12) have been synthesized and characterized for dye-sensitized solar cells (DSSCs). It is found that the introduction of tert-butyl-capped N-arylcarbazole as an electron donor can efficiently suppress the intermolecular aggregation and improve the photovoltaic performances. The DSSC devices based on the dyes show relatively high power conversion efficiency of 3.67 and 3.75% for DH-11 and DH-12, respectively, which reaches over 65% of the reference dye N719-based cell fabricated and measured under the same conditions. This infers that the tert-butyl-capped N-arylcarbazole unit is a promising electron-donor that can be employed to design metal-free sensitizers with a new structural skeleton.

Multiwalled carbon nanotubes (MWCNTs)/Cd0.8Zn0.2S nanocomposites were synthesized via the simple co-precipitation of pretreated MWCNTs, acetates and sodium sulfide. The photocatalytic activities for hydrogen production of the produced MWCNTs/Cd0.8Zn0.2S with different amount of MWCNTs were systematically investigated under visible-light (λ ≥ 420 nm) irradiation. Enhanced photoactivity of the nanocomposite was observed and can be attributed to the synergetic effect of its components’ intrinsic properties, such as excellent light absorption and charge separation on the interfaces between the modified MWCNTs and Cd0.8Zn0.2S. It is also found that the nanocomposite with 15 wt% MWCNTs shows a higher photocatalytic hydrogen production efficiency and photostability than the pristine CdS and Cd0.8Zn0.2S nanoparticles. The MWCNTs/Cd0.8Zn0.2S nanocomposite holds promise for hydrogen production by improving the visible-light-driven photoactivity and photostability of Cd0.8Zn0.2S.Highlights► MWCNTs/Cd0.8Zn0.2S nanocomposites are prepared for the first time. ► Efficient chemically bonding between the modified MWCNTs and Cd0.8Zn0.2S nanoparticles. ► Enhanced visible-light absorption and charge separation efficiency. ► Enhanced visible-light-driven photocatalytic H2 production efficiency with better durability. ► Beneficial for developing broad spectral responsive photocatalysts for H2 production.

WO3 with various morphologies and crystal phases were prepared via a hydrothermal process in the presence of different Na2SO4 concentrations. Experimental results indicated that the preferred growth face ((200) crystal plane) of hexagonal WO3 could adsorb abundant Na+, which induced the WO3 growing along [001] crystal direction to form nanorods, and hexagonal phase WO3 nanorods with diameter of 30–150 nm and length of 0.5–5 μm were obtained in the presence of 0.25 M Na2SO4, while excessive Na2SO4 led to a mixed crystal consisting of cubic H2W2O7 and hexagonal WO3. The photoactivities for O2 evolution for various products were investigated by using Fe(NO3)3 as a sacrificial reagent under visible-light irradiation, and the hexagonal phase WO3 nanorods show a better photoactivity than the other products with different morphologies and crystal phases due to its fast three-dimensional photogenerated carrier transfer along its special rod-shaped structure.Graphical abstractAs a preferred growth plane, (200) plane of h-WO3 can adsorb abundant of Na+, which induces the WO3 growing along [001] direction to form nanorods with high length–diameter ratio.Highlights► WO3 with various morphologies were hydrothermally prepared. ► Hexagonal WO3 nanorods with diameter of 30–150 nm can be obtained from 0.25 M Na2SO4 solution. ► Hexagonal WO3 nanorods show a better photoactivity than the other products. ► The good photoactivity can be due to its fast carrier transfer along its rod-shaped structure.

A series of graphene oxide (GO)–cadmium sulfide (CdS) nanocomposites were fabricated via a facile precipitation process by using Cd(Ac)2, Na2S, and prefabricated GO as raw materials. The obtained GO–CdS nanocomposites are composed of CdS nanoparticles with an average diameter of ca.10 nm, which are well dispersed and immobilized on GO sheets. By using Na2S/Na2SO3 as sacrificial reagent, the GO–CdS nanocomposites exhibit higher photoactivity for hydrogen production than the bare CdS under visible-light irradiation. Among various composite photocatalysts prepared, 5 wt % GO–CdS shows maximum hydrogen production efficiency. Our findings demonstrate that the coupled GO can serve as CdS supporting matrix, cocatalyst, and electron acceptor for effective charge separation, and therefore provide an inexpensive means to achieve high-performance visible-light-driven photocatalysts for hydrogen production without noble metal-loading.

Submicrometer-sized monodispersed TiO2 spheres were synthesized by a controlled hydrolysis of titanium tetraisopropoxide (TTIP) and subsequent solvothermal treatment. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–visible spectroscopy analyses revealed that aqueous ammonia concentration and calcining temperature significantly influence the morphology, crystallization, dye loading, and light scattering capacity of TiO2 microspheres. And it was found that the TiO2 microspheres prepared by this method showed a good thermal stability of phase. Bilayered dye-sensitized solar cells (DSSCs) composed of TiO2 microspheres as the scattering cover layers and TiO2 nanocrystallines as the underlayer exhibited a remarkable improvement in the power conversion efficiency (8.25%) compared with the nanocrystalline TiO2 DSSC (6.38%), owing to high light scattering efficiency and the dye-loading capacity of the microsphere cover layer. In addition, electrochemical impedance spectra (EIS) and open-circuit photovoltage decay curves (OCVD) testing indicated that the microsphere cover layer passivated the surface states, increased the density of bulk traps, enlarged the lifetime of electrons, and promoted more efficient charge-transfer, which was also an important reason for the improved power conversion efficiency of double-layered DSSCs.

TiO2 nanoparticles with diameter <10 nm were synthesized by a facile, non-hydrothermal method at low temperature. A porous TiO2 film electrode consisting of the obtained small TiO2 nanoparticles and commercial TiO2 nanoparticles without any organic binder was prepared at low temperature. The photovoltaic performance of the solar cell based on the TiO2 electrode was investigated by the current–voltage and electrochemical impedance spectra. All the experimental results indicate that the addition amount of the small TiO2 nanoparticles in the binder-free paste affects the photovoltaic performance of the photoelectrode greatly. The overall energy conversion efficiency of the optimized binder-free photoelectrode achieves 3.53% without high-temperature sintering. Additionally, the performance of the small particles derived from this facile method can be comparable with that of small ones obtained from traditionally hydrothermal method, indicating the small particles in our study can be applied to flexible dye-sensitized solar cells. And the present low-temperature preparation of photoelectrode containing small TiO2 nanoparticles shows an encouraging performance on both conductive glass and plastic substrates and could be suited in the industrial and large-scale application due to its low energy cost and relatively high conversion efficiency.

A novel iodine-free quasi solid-state electrolyte employing an ionic liquid (1, 2-dimethyl-3-propylimidazolium iodide, DMPII) as charge transfer intermediate was developed for dye-sensitized solar cells (DSSCs). Simultaneously, potassium iodide (KI) was incorporated into the electrolyte as charge transfer auxiliary agent. The dependences of photovoltaic performances and ionic conductivities on the iodine-free quasi solid-state electrolyte containing different KI concentrations were investigated. The strong interactions between the potassium cations and polyethylene oxide (PEO, MW = 100,000) can prevent the crystallization of the electrolyte and enhance its ionic conductivity. An optimal photoelectric conversion efficiency (η) of 5.87% can be obtained for the DSSC fabricated with the iodine-free electrolyte containing 5 wt% KI, and the corresponding value without KI is 4.05%, indicating the remarkable progress made by addition of KI into electrolyte.

The In2S3/(Pt-TiO2) nanocomposite photocatalyst consisting of floriated In2S3 decorated with TiO2 nanoparticles was synthesized by a multi-step method, which was used for the hydrogen production under visible-light (λ ≥ 420 nm) irradiation. The obtained In2S3/(Pt-TiO2) nanocomposite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption spectra (DRS), and photoluminescence spectra (PL). It is found that the Pt-TiO2nanoparticles embedded in the interstices of the floriated In2S3 formed intimate contacts between the In2S3 and Pt-TiO2, which is a benefit to significantly enhance the charge separation and then the photocatalytic activity. The effects of the mass ratio in the In2S3/(Pt-TiO2) nanocomposites and Pt-loaded amount on the photoactivity for the hydrogen production were investigated comparatively. The results show that the In2S3/(Pt-TiO2) nanocomposite with a mass ratio of 3:2 has the maximum photocatalytic hydrogen production rate of 135 μmol h−1 under visible-light irradiation, and the possible mechanism of the obtained In2S3/(Pt-TiO2) nanocomposite as a photocatalyst for hydrogen production was proposed.

The flexible DSSCs based on conducting plastic substrates are fabricated using electrodes made of tetrabutoxytitanium (TBOT) mixed with P25 TiO2 nanoparticles at low temperature. To investigate the effects of TBOT on the flexible dye-sensitized solar cells, electrochemical impedance spectroscopy (EIS) is performed in the dark and under illumination conditions. Resistances for electron transport through TiO2, charge-transfer resistance related to the TiO2/redox electrolytes interface recombination, electron transport time and electron lifetime are quantified under different weight ratios of TBOT/P25. Additionally, the photovoltaic characteristics I–V curves and incident photon to current conversion efficiencies (IPCE) of flexible anodes made of different weight ratios of TBOT/P25 are obtained as well. It is found that the electrode under weight ratio 0.17 has the smallest inherent resistance, longest electron transport time and electron lifetime, lowest recombination rate and best performance with conversion efficiency 3.94%. These results indicate that after the weight ratios of TBOT/P25 is optimized, TBOT could enhance the interconnection between the TiO2 particles, improve the conductivity of the electrode and decrease the charge recombination. Above results demonstrate that adding TBOT to TiO2 is an easy and efficient method to improve the performance of the flexible DSSC fabricated at low temperature.Research highlights▶ Tetrabutoxytitanium (TBOT) enhances the interconnection between P25 and decreases the inherent impedance of the flexible cell. ▶ TBOT prolongs the electron transport time and electron lifetime of the flexible cell. ▶ TBOT improves the performance of the flexible cell.

A novel CuI-based iodine-free gel electrolyte using polyethylene oxide (PEO, MW = 100,000) as plasticizer and lithium perchlorate (LiClO4) as salt additive was developed for dye-sensitized solar cells (DSSCs). Such CuI-based gel electrolyte can avoid the problems caused by liquid iodine electrolyte and has relative high conductivity and stability. The effects of PEO and LiClO4 concentrations on the viscosity and ionic conductivity of the mentioned iodine-free electrolyte, as well as the performance of the corresponding quasi solid-state DSSCs were investigated comparatively. Experimental results indicate that the performance of DSSCs can be dramatically improved by adding LiClO4 and PEO, and there are interactions (Li+–O coordination) between LiClO4 and PEO, these Li+–O coordination interactions have important influence on the structure, morphology and ionic conductivity of the present CuI-based electrolyte. Addition of PEO into the electrolyte can inhibit the rapid crystal growth of CuI, and enhance the ion and hole transportation property owing to its long helix chain structure. The optimal efficiency (2.81%) was obtained for the quasi solid-state DSSC fabricated with CuI-based electrolyte containing 3 wt% LiClO4 and 20 wt% PEO under AM 1.5 G (1 sun) light illumination, with a 116.2% improvement in the efficiency compared with the cell without addition of LiClO4, indicating the promising application in solar cells of the present CuI-based iodine-free electrolyte.Highlights► A novel CuI-based iodine-free gel electrolyte for DSSC is firstly prepared. ► Such CuI-based electrolyte has relative high conductivity and stability. ► Addition amount of LiClO4 and PEO in the electrolyte is optimized. ► Cell performance is improved by 116.2% compared with the cell without LiClO4.

Reduced graphene oxide (RGO)–cadmium sulfide (CdS) nanocomposites were successfully prepared by a one-pot solvothermal process without pretreatment of graphene oxide (GO) and a precipitation process, in which GO needs to be pre-reduced by hydrazine. The as-obtained RGO–CdS nanocomposites were used as photocatalysts for hydrogen production under visible light irradiation, and it was found that the product derived from the one-pot solvothermal process showed much better photoactivity than that from the precipitation method.

Lead molybdate (PbMoO4) microcrystals with preferentially exposed (001) facets have been synthesized by a facile surfactant-assisted hydrothermal process in the presence of cetyltrimethylammonium bromide (CTAB). The effects of the CTAB addition amount, hydrothermal temperature on the morphologies and the crystal facets of PbMoO4 were investigated in detail. Experimental results indicate that the diffraction peak intensity ratio of (112) to (001) crystal facets for the product can be delicately controlled by simply adjusting the addition amount of CTAB and hydrothermal temperature. And the products derived from hydrothermal treatment at 180 °C for 24 h in the presence of 0.05 M CTAB exhibit obvious exposed (001) facets with a minimum peak intensity ratio (I112/I004 = 0.08) of the (112) and (004) crystal facets. Moreover, the obtained PbMoO4 with preferentially exposed (001) facets exhibits greatly enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) under UV light irradiation in comparison with the PbMoO4 obtained in the absence of CTAB and the commercial phototcatalyst (P25).

Multiwalled carbon nanotubes (MWCNTs)/CdS nanocomposites containing different MWCNT contents were synthesized hydrothermally via direct growth of CdS nanoparticles on the functionalized MWCNT surface. The effects of the hydrothermal temperature and MWCNT content in the nanocomposites on the photoactivity for hydrogen production were investigated comparatively under visible light (λ ≥ 420 nm) irradiation. It was found that 10 wt % MWCNTs/CdS showed much higher photocatalytic hydrogen production efficiency and photostability than the pure CdS nanoparticles. The significantly enhanced photoactivity of the nanocomposite was attributed to the synergetic effect of the intrinsic properties of its components, such as excellent charge transfer and separation on the interfaces between the modified MWCNTs and CdS nanoparticles, resulting from the direct growth of CdS nanoparticles on the MWCNT surface during the hydrothermal process. The present MWCNTs/CdS nanocomposite reveals obvious predominance, such as enhanced visible-light-driven photoactivity and photostability of CdS for hydrogen production.

Anatase TiO2 fusiform nanorods with diameters 20–80 nm and lengths 200–400 nm are synthesized by a two-step hydrothermal method, and the effects of the obtained TiO2 nanorod content in a P25-based electrode on the performances of dye-sensitized solar cell were investigated by using photocurrent–voltage, open-circuit voltage decay and electrochemical impedance spectroscopy measurements. The results show that those fusiform TiO2 nanorods in the P25-based electrode not only provide a straight path for the electron transport but also function as scattering particles to increase light harvesting efficiency of the solar cell, and the optimal conversion efficiency of 4.68% is obtained from a solar cell fabricated with a P25-based electrode containing 10 wt % nanorods, with a 66.5% improvement in the efficiency with lower resistance and longer electron lifetimes as compared to the bare P25-based solar cell. This should be attributed to the reduced charge recombination and the sufficient scattering effect of the nanorods in the film electrode.

A series of ZnIn2S4 floriated microspheres consisting of flakes were synthesized by a facile template-free hydrothermal method. The obtained ZnIn2S4 products were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, UV−vis diffuse reflectance absorption spectroscopy, and nitrogen adsorption measurement. The effects of hydrothermal temperature and pH value on the crystal structures, morphologies, and optical properties of ZnIn2S4 microspheres were investigated. The photocatalytic activities for hydrogen production of the as-prepared samples were evaluated under visible-light (λ ≥ 420 nm) irradiation. It was found that the 1.0 wt % Pt-loaded ZnIn2S4 prepared hydrothermally at 160 °C with pH = 1.00 showed a higher and steady photoactivity for H2 evolution from aqueous solutions containing sacrificial reagents SO32− and S2− than the products prepared at other hydrothermal temperatures. Moreover, an apparent quantum efficiency of up to 34.3% was achieved under incident monochromatic light of 420 nm, significantly higher than previously reported values.

Floriated ZnFe2O4 with porous nanorod structures were successfully synthesized via mild hydrothermal and calcination processes by using cetyltrimethylammonium bromide (CTABr) as a template-directing reagent. The resulting ZnFe2O4 was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS) and nitrogen adsorption measurement. It was found that the floriated ZnFe2O4 nanostructures were composed of porous nanorods with an average length of 122 nm and diameter of 29 nm. The obtained ZnFe2O4 with a bandgap of ∼1.94 eV was firstly used as a visible-light-driven photocatalyst for hydrogen production, and exhibits remarkable photostability in an aqueous suspension by using CH3OH as a sacrificial reagent. Moreover, the possible photo-reaction mechanism for the hydrogen production from CH3OH aqueous solution was proposed for better understanding the photocatalytic behavior of ZnFe2O4 without Pt-loading.

The dye-sensitized solar cells (DSSCs) using Ti foil supporting substrate for fabricating nanocrystalline TiO2 flexible film electrodes were developed, intending to improve the photoelectrochemical properties of flexible substrate-based DSSCs. The obtained cells were characterized by electrochemical impedance spectra (EIS), open circuit voltage decay (OCVD) measurement and Tafel plots. The experimental results indicate that the most important advantage of a Ti foil-based TiO2 flexible electrode over a FTO glass-based electrode lies in its reduced sheet resistance, electron traps, and the retarded back reaction of electrons with tri-iodine ions in DSSCs. All above characteristics for the Ti substrate TiO2 films are beneficial for decreasing the charge recombination in the TiO2 electrode and prolonging the electron lifetimes for the DSSCs, as well as improvement of the overall solar conversion efficiency. The photocurrent of the cell fabricated with the Ti foil-based flexible electrode increased significantly, leading to a much higher overall solar conversion efficiency of 5.45% at 100 mW/cm2 than the cell made with FTO glass-based TiO2 electrodes. Above results demonstrate that Ti foil is a potential alternative to the conventional FTO glass substrate for the DSSCs.

Dye-sensitized solar cells (DSSCs) were fabricated by using porous ZnO electrodes derived from home-made ZnO nanoparticles. Electrochemical impedance spectra and open-circuit photovoltage decay curves measurements were performed to investigate the photoelectrochemical characteristics of ZnO films annealed at different temperatures. The experimental results indicate that the effects of the bulk traps and the surface states within the ZnO films on the recombination processes of the photoinjected electrons in DSSCs depend on the annealing temperature. The DSSC based on the ZnO electrode annealed at 400 °C exhibits an optimal energy conversion efficiency of 3.92% under the illumination of one sun simulated sunlight because the farthest decrease in the effects of both bulk traps and surface states at this film can maintain a lower charge recombination probability. This result indicates that the ZnO film electrode has promising application in the field of DSSCs, and the optimization of porous film fabrication condition is efficient for the improvement of ZnO-based DSSC’s performances.

Alumina particles with mesostructures were synthesized through a chemical precipitation method by using different inorganic aluminum salts followed by a heterogeneous azeotropic distillation and calcination process. The obtained mesoporous γ-alumina particles were systematically characterized by the X-ray diffraction, transmission electron microscopy and nitrogen adsorption–desorption measurement. Effects of the aluminum salt counter anion, pH value and the azeotropic distillation process on the structural or textural evolution of alumina particles were investigated. It is found that Cl− in the reaction solution can restrain the textural evolution of the resultant precipitates into two-dimensional crystallized pseudoboehmite lamellae during the heterogeneous azeotropic distillation, and then transformed into γ-Al2O3 particles with mesostructures after further calcination at 1173 K, whereas coexisting SO42− can promote above morphology evolution and then transformed into γ-Al2O3 nanofibers after calcination at 1173 K. Moreover nearly all materials retain relatively high specific surface areas larger than 100 m2 g−1 even after calcinations at 1173 K.Co-existing Cl− is beneficial for the formation of γ-alumina nanoparticles with mesostructures during the precipitation process. Interparticle and intraparticle mesopores can be derived from acidic solution and near neutral solution, respectively.

Mesoporous TiO2 (m-TiO2) nanoparticles were used to prepare the porous electrodes for dye-sensitized solar cells (DSSCs). Experimental results indicate that the MgO covered on TiO2 electrode can act as barrier layer for the interfacial charge recombination processes, whereas some MgO immingled among TiO2 networks due to the part reconstruction of the electrode during the second annealing process can retard the electron transport within electrode. The optimal conversion efficiency is obtained from solar cell fabricated with TiO2 electrode modified with 0.2 M Mg2+ solution, with a 39% improvement in the efficiency as compared to the unmodified one. The suppression of interfacial charge recombination and the enhanced dye adsorption capacity contribute to the improved photovoltaic performance for the Mg2+-modified electrode, and the retardation of electron transport and injection by excessive Mg2+ modification is responsible for the efficiency losses of the corresponding TiO2-based solar cell. This indicates that controlling the extrinsic parameters such as the electron transport and recombination is very important to improve the photovoltaic performance of TiO2-based solar cell.

Photocatalytic degradation of commercial phoxim emulsion in aqueous suspension was investigated by using La-doped mesoporous TiO2 nanoparticles (m-TiO2) as the photocatalyst under UV irradiation. Effects of La-doping level, calcination temperature, and additional amount of the photocatalyst on the photocatalytic degradation efficiency were investigated in detail. Experimental results indicate that 20 mg L−1 phoxim in 0.5 g L−1 La/m-TiO2 suspension (the initial pH 4.43) can be decomposed as prolonging the irradiation time. Almost 100% phoxim was decomposed after 4 h irradiation according to the spectrophotometric analyses, whereas the mineralization rate of phoxim just reached ca. 80% as checked by ion chromatography (IC) analyses. The elimination of the organic solvent in the phoxim emulsion as well as the formation and decomposition of some degradation intermediates were observed by high-performance liquid chromatography−mass spectroscopy (HPLC-MS). On the basis of the analysis results on the photocatalytic degradation intermediates, two possible photocatalytic degradation pathways are proposed under the present experimental conditions, which reveal that both the hydrolysis and adsorption of phoxim under UV light irradiation play important roles during the photocatalytic degradation of phoxim.

Microspheric and lamellar BiVO4 powders were selectively prepared through a hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as a template-directing reagent. The as-prepared BiVO4 powders were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption−desorption experimentation, Fourier transform infrared spectrometry, and UV−vis diffuse reflectance spectroscopy. Experimental results indicate that microspheric BiVO4 with particle sizes in the range of 7∼12 μm can be derived from a relatively low hydrothermal temperature (≤160 °C) and possess a mixed crystal consisting of tetragonal and monoclinic phases, whereas lamellar BiVO4 with a pure monoclinic phase can be obtained at a higher hydrothermal temperature (200 °C). Their photocatalytic activities for O2 evolution were investigated by using Fe(NO3)3 as a sacrificial reagent under visible-light irradiation, and the lamellar BiVO4 shows a better photoactivity than the microspheric product due to its pure monoclinic crystal phase. Moreover, the effects of CTAB content on the morphologies and crystal phases of the obtained products were also discussed. It was found that the addition of CTAB can adjust the morphologies of BiVO4 and obstruct the crystal phase transformation from the mixed crystal to pure monoclinic BiVO4 during the hydrothermal process.

A meso-macroporous TiO2 film electrode was fabricated by using mesoporous TiO2 (m-TiO2) nanoparticles through a screen-printing technique in order to efficiently control the main fabrication step of dye-sensitized solar cells (DSSCs). The qualities of the screen-printed m-TiO2 films were characterized by means of spectroscopy, electron microscopy, nitrogen adsorption–desorption and photoelectrochemical measurements. Under the optimal paste composition and printing conditions, the DSSC based on the meso-macroporous m-TiO2 film electrode exhibits an energy conversion efficiency of 4.14%, which is improved by 1.70% in comparison with DSSC made with commercially available nonporous TiO2 nanoparticles (P25, Degussa) electrode printed with a similar paste composition. The meso-macroporous structure within the m-TiO2 film is of great benefit to the dye adsorption, light absorption and the electrolyte transportation, and then to the improvement of the overall energy conversion efficiency of DSSC.

The photocatalytic activities of CdS nanoparticles immobilized in porous regenerated cellulose (RC) films with different pore sizes were investigated. The resulting CdS/RC nanocomposite films were characterized by using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, thermal gravimetric analysis, and UV−vis diffuse reflectance spectroscopy. The mean pore sizes of the porous RC films can be modulated from about 20 to 57 nm by adjusting the concentration of the cellulose solution, and the porous structures within RC film act as reacting sites to lead to the embedment of CdS nanoparticles with a mean particle diameter of about 8 nm. The photocatalytic H2 evolution efficiencies over the obtained CdS/RC nanocomposite films were investigated by using Na2S−Na2SO3 mixed solution as a sacrificial reagent under visible-light (λ ≥ 420 nm) irradiation. Experimental results indicate that the present nanocomposite films revealed obvious predominance, such as high visible-light photoactivity for H2 production, enduring photostability, and convenient regeneration in comparison with CdS nanoparticles suspension system. This new pathway for the fabrication of portable visible-light-driven photocatalyst is important for the H2 production via “green” processes.

The photocatalytic degradation of a commercial methamidophos (MAP) emulsion in aqueous suspension containing mesoporous titania (m-TiO2) nanoparticles under UV irradiation was investigated. The mineralization rate of MAP went up steadily as prolonging the irradiation time and reached ca. 95% after 4 h irradiation based on determination of the end-products (NO3−, PO43−, and SO42−) of MAP through IC analysis. Moreover, the degradation kinetics of MAP followed the first-order reaction and has been monitored through GC-PFPD analysis, which also showed that MAP and the organic solvent as well as additive in the pesticide emulsion can be degraded readily and simultaneously. Photodegradation intermediates derived from two different concentrations of MAP were detected by GC-MS technique. The experimental facts indicated that the photodegradation mechanism of MAP mainly involves electron transfer process and hydroxylation process, and the dominant mechanism for MAP degradation in the initial steps can be attributed to the electron transfer process, which resulted in the formation of all intermediates containing P species detected in the initial photodegradation stage.

The photocatalytic hydrogen production over TiO2TiO2 nanoparticles with mesostructures has been studied using CH3OHCH3OH as a sacrificial reagent. The effects of the calcination temperature, Pt-loading, amount of TiO2TiO2 and methanol as well as irradiation time on the H2H2 evolution rate were investigated in detail. The results indicated that the as-synthesized TiO2TiO2 nanoparticles without calcination, having a large specific surface area (438m2/g) and small crystallite size (2.3 nm) dispersed among the amorphous mesoporous domains, exhibited the best photocatalytic activity for H2H2 production compared with the samples calcined at different temperatures and the commercial photocatalyst P25 (Degussa, Germany) under the same photoreaction conditions. The presence of mesostructured TiO2TiO2 nanoparticles with a uniform dispersion of the co-catalyst (Pt) has resulted in an effective, faster charge separation, which, in turn, leads to a higher photocatalytic activity for H2H2 production.

Gd3+-doped mesoporous TiO2 (m-TiO2) nanoparticles were synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as surfactant-directing agent and pore-forming agent. The resulting products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), diffuse reflection spectra (DRS), and linear sweep voltammetry (LSV) etc. Experimental results indicate that different Gd3+-doping levels make great impact on the photocatalytic activity of the obtained m-TiO2 nanoparticles and the 3.5 at.% Gd3+-doped m-TiO2 nanoparticles calcined at 300 °C exhibit the optimal photoactivity on the degradation of Rhodamine B (RB), which is as nearly two times as that of the commercial photocatalyst P25. The mesoporosity, anatase wall as well as the cooperativity of ‘lattice Gd3+’ and ‘free Gd3+’ in the m-TiO2 nanoparticles can be used to explain the observed high photoactivity of the doped m-TiO2 nanoparticles.

A novel photocatalyst WO3/TiO2 nanocomposite was prepared through a hydrothermal method by using cetyltrimethylammonium bromide (CTAB) as surfactant. The obtained WO3/TiO2 was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and diffused reflectance spectroscopy (DRS). Photocatalytic experiments indicate that the nanocomposites show much higher photoactivity than that of pure TiO2 in the photodegradation reaction of Rhodamine B (RhB). The increased photoactivity of WO3/TO2 may be attributed to the improvement of the light absorption properties and the slow down of the recombination between the photoexcited electrons and holes during the photoreaction.

Mesoporous TiO2 (m-TiO2) nanoparticles were used to prepare the porous film electrodes for the dye-sensitized solar cells (DSSCs). The obtained m-TiO2 porous electrodes were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electrochemical impedance spectra (EIS), and open-circuit photovoltage decay curves (OCVD). Experimental results indicate that the effect of bulk traps and the surface states within the m-TiO2 porous films on the recombination processes of the photoinjected electrons in DSSCs depends on the annealing temperature. Moreover, the homemade m-TiO2 nanoparticles show much higher photoelectric conversion efficiency than the nonporous TiO2 nanoparticles (P25). The mesostructures within the m-TiO2 nanoparticles, which can be maintained even after annealing at 500 °C, are of great benefit to the dye adsorption, and then to the improvement of the photoelectrochemical properties of DSSCs.

Nd3+-doped titania nanoparticles with mesostructures were synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as directing and pore-forming agent. The obtained materials were characterized by XRD, nitrogen adsorption–desorption, TEM and DRS. The existence of neodymium ion affect significantly the phase transition of the amorphous to anatase, and the band-gap energy was reduced because of the defect energy level induced by the 4f atomic orbital of Nd3+ with the optimal content of 1.5 at.% Nd. Density functional theory calculations can explain the band-gap narrowing. The maximum photocatalytic activity corresponds to the 0.5 at.% Nd3+-doped anatase nanopowders with mesostructures, which is higher than that of undoped samples.

A series of Dy-doped tungsten trioxide (WO3) nanopowders were synthesized via dipping the WO3 into Dy(NO3)3 solution. The WO3 nanoparticles were freshly synthesized through precipitation process from Na2WO4 and hexadecyltrimethylammonium bromide (CTAB). The obtained samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), diffuse reflectance absorption spectroscopy (DRS) and liquid nitrogen adsorption–desorption. Its photoactivity was evaluated through the photodegradation of Rhodamine B (RB) in aqueous solution. The effects of photoreaction conditions on the photoactivity of the obtained samples were investigated in detail. The experimental results indicated that Dy-doping not only improved the light absorption of WO3, but also enhanced the photoactivity and photostability of WO3.

CdS/Rectorite nanocomposites were prepared through hydrothermal method by using Cd[NH2CSNH2]2Ac2 complex as precursor of CdS which was derived from cadmium acetate and thiourea. The obtained nanocomposites were characterized by X-ray diffraction (XRD), Fourier transfer infrared spectra (FTIR), diffusion reflection spectra (DRS), transmission electron microscopy (TEM) and the selected area electron diffraction (SAED) patterns. Experimental results indicate that CdS exist in at least three forms: CdS adsorbed at surface, CdS pillared in montmorillonite-like layers of Rectorite and CdS pillared in the new layered structure formed during the hydrothermal process. Those CdS crystals are hexagonal symmetry. The photoactivity and photostability of the obtained CdS/Rectorite nanocomposites are improved significantly compared to that of the reference Rectorite and pure CdS.CdS/Rectorite nanocomposites were synthesized by hydrothermal method. Its absorptive property and photoactivity for Rhodamine B were enhanced significantly compared with that of the Rectorite. The nanocomposites are expected to be useful in various applications, for instance, adsorption and photodegradation of various organic contaminants.

Flaky monoclinic La2Ti2O7 was prepared via a hydrothermal method based on the reaction of Ti(SO4)2 and La(NO3)3. Relative to the solid-state reaction sample, the flaky La2Ti2O7 showed higher surface areas, much smaller crystal size and more efficient light absorption. All these factors led to the higher photoactivity to produce H2 from water splitting under UV irradiation.

Titania was synthesized from laurylamine hydrochloride (LAHC) and Ti(SO4)2 under different acidic conditions. The effect of acidity on the structural and textural evolution of titania has been investigated by X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron micrographs (TEM), FTIR spectroscopy and thermogravimetric analysis (TGA). With increasing the pH value in the initial mixture, the obtained samples transformed from nanoparticles with intra-particle mesostructures (pH 0.6 and 2.0) to nanoparticles with nonporous structure (pH 3.7), and finally to worm-like porous materials with inter-particle mesostructures (pH 4.2) resulted from the aggregates of nanoparticles. The obtained mesoporous nanoparticles (pH 0.6 and 2.0) have mean diameter of ca. 25 nm, and the pore size distributions are bimodal with fine intra-particle pores and larger inter-particle pores. The intra-particle mesostructure not only retard the growth of nanocrystallites, but also prevent phase transition of anatase to rutile at high temperature. The BET surface area of the TiO2 calcined at 300 °C decreased from 212 to 74 m2/g with pH increasing from 0.6 to 4.2.

Mesoporous titania nanoparticles with high specific surface area and thermal stable anatase wall was synthesized from surfactant laurylamine hydrochloride (LAHC) and inorganic precursor Ti(SO4)2. The as-synthesized and calcined materials were characterized by X-ray diffraction, nitrogen adsorption–desorption, transmission electron micrographs, Fourier transform infrared spectroscopy and thermogravimetric analysis. The obtained mesoporous TiO2 nanoparticles have mean diameter of 25.5 nm. The specific surface area of the mesoporous nanosized TiO2 calcined at 400 °C exceeded 189 m2 g−1, and that of the samples after calcinations at 500 °C still have 151 m2 g−1. The obtained anatase mesoporous TiO2 nanoparticles show relative high thermal stability.

Cerium-doped mesoporous TiO2 nanoparticles with high surface area and thermal stable anatase wall were synthesized via hydrothermal process in a cetyltrimethylammonium bromide (CTAB)/Ti(SO4)2/Ce(NO3)4/H2O system. The obtained materials were characterized by XRD, FESEM, HRTEM, FTIR spectroscopy, nitrogen adsorption and DRS spectra. Experimental results indicated that the doping of cerium not only increased the surface area of mesoporous TiO2 nanoparticles, but also inhibited the mesopores collapse and the anatase-to-rutile phase transformation. Moreover, the undoped, doped anatase mesoporous nanoparticles exhibit higher photocatalytic activity than commercial photocatalyst (Degussa, P25), but the maximum photodegradation rate corresponds to the undoped mesoporous TiO2 nanoparticles. The lower photocatalytic activities of cerium-doped samples compared with undoped one may be ascribed to that the doped cerium partially blocks titania's surface sites available for the photodegradation and absorption of Rhodamine B (RB).Cerium-doped mesoporous TiO2 nanoparticles with high surface area and thermal stable anatase wall were synthesized via hydrothermal process. Experimental results indicated that the doping of cerium not only increased the surface area of mesoporous TiO2 nanoparticles, but also inhibited the mesopores collapse and the anatase-to-rutile phase transformation. Moreover, the undoped, doped anatase mesoporous nanoparticles exhibit higher photocatalytic activity than P25, but the maximum photodegradation rate corresponds to the undoped mesoporous TiO2 nanoparticles. The lower photocatalytic activities of cerium-doped samples compared with undoped one may be ascribed to that the doped cerium partially blocks titania's surface sites available for the photodegradation and absorption of Rhodamine B.

Lanthana-doped mesoporous TiO2 nanoparticles with high specific surface area and thermal stable anatase wall was synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as surfactant-directing agent and pore-forming agent. The resulting materials were characterized by XRD, FESEM, TEM, FT-IR spectroscopy, and nitrogen adsorption. The as-synthesized mesoporous doped TiO2 nanoparticles have mean diameter of 20 nm with mean pore size of 2.2 nm. The specific surface area of the as-synthesized mesoporous nanosized doped TiO2 exceeded 460 m2/g, and that of the samples after calcination at 500 °C still have 243 m2/g. Compared with undoped sample and P25, the lanthana-doped mesoporous TiO2 nanoparticles show better activities on the oxidation of rhodamine B (RB). The large surface area and more active sites for combining with RB due to the present of lanthanum ion can explain the high photocatalytic activity of lanthana-doped mesoporous TiO2 nanoparticles.Lanthana-doped mesoporous TiO2 nanoparticles with high specific surface area and anatase wall was synthesized via hydrothermal process. The obtained doped TiO2 nanoparticles have mean diameter of 20 nm with mean pore size of 2.2 nm. The specific surface area of the samples after calcination at 500 °C still have 243 m2/g. The doped TiO2 nanoparticles show better activities than P25 on the oxidation of rhodamine B.

Eu2+,Dy3+ co-doped strontium aluminate (SrAl2O4) phosphor nanoparticles with high brightness and long afterglow were prepared by glycine–nitrate solution combustion synthesis at 500 °C, followed by heating the resultant combustion ash at 1100 °C in a weak reductive atmosphere of active carbon. The average particle size of the SrAl2O4:Eu,Dy phosphor nanoparticles ranges from 15 to 45 nm as indicated by transmission electron microscopy (TEM). The broad-band UV-excited luminescence of the SrAl2O4:Eu,Dy phosphor nanoparticles was observed at λmax=513 nm due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion. The results indicated that the main peaks in the emission and excitation spectrum of phosphor nanoparticles shifted to the short wavelength compared with the phosphor obtained by the solid-state reaction synthesis method. The decay speed of the afterglow for phosphor nanoparticles was faster than that obtained by the solid-state reaction method.

Eu2+, Dy3+ co-doped strontium aluminate (SrAl2O4) phosphor nanometer powders with high brightness and long afterglow were prepared by heating the precursor gel (resulted from sol–gel method) at 900 °C and a reductive atmosphere of active carbon. The average particle size of the SrAl2O4:Eu, Dy phosphor powders was 59±7 nm and its optical properties have been studied systematically. The broad band UV excited luminescence of the SrAl2O4:Eu, Dy was observed at λmax=506 nm due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion. The results indicated that the main peaks in the emission and excitation spectrum shifted to the short wavelength compared with phosphor obtained by the solid-state reaction synthesis method. The decay speed of the afterglow for nanometer phosphors was faster than that obtained by the solid-state reaction method.

Nickel oxide (NiO) nanotubules were fabricated by a dodecylsulfate-mediated templating method in a homogeneous precipitation process. The nanotubules obtained have diameters of 20–160 nm and wall thickness of 8–50 nm with lengths up to several micrometers. The crystallinity, morphology and structure features of the NiO nanotubules were investigated by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), infrared (IR) spectrum, etc.

Slurry sampling in combination with fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) was employed for the direct determination of trace impurities in silicon carbide ceramic powders. The vaporization behaviors of silicon and five trace elements (Al, Cr, Cu, Fe and V) were studied in the presence and absence of polytetrafluoroethylene (PTFE) as fluorinating reagent. It was found that, during a 60 s ashing step at 800 °C, about 97% of 100 μg of SiC can be decomposed and evaporated without considerable losses of the trace elements investigated. Calibration was performed using the standard addition method and the calibration curve method, applying spiked slurries and aqueous standard solutions, respectively. The accuracy was checked by comparison of the results with those obtained by solution fluorination assisted ETV-ICP-AES and pneumatic nebulization (PN)-ICP-AES involving wet chemical decomposition of the sample. Detection limits between 0.3 μg g−1 (Al) and 0.08 μg g−1 (Cu) were achieved. The precision, expressed as the relative standard deviation (RSD), was between 6.0% (for 18.2 μg g−1 of Cr) and 2.8% (for 177 μg g−1 of Fe).

•Brookite TiO2 (BTN) is used as photocatalyst for H2 production for the first time.•Cu nanoclusters (CuNCs) with size of 1–2 nm on BTN act as an efficient co-catalyst.•H2 production activity of 1.0% Cu/BTN is 5.2 times higher than that of BTN alone.•CuNCs with high surface area and dispersion cause an effective charge separation.•CuNCs provide an inexpensive and efficient mean of enhancing photoactivity of TiO2.Brookite TiO2 quasi nanocubes (BTN) decorated with various Cu nanoclusters (CuNCs) contents (hereafter referred to as Cu/BTN composite) were synthesized via a facile chemical reduction process by NaBH4. The obtained products and its Cu's existential state were characterized by X-ray diffraction, UV–Vis diffuse reflectance absorption spectroscopy, electron microscopy, X-ray photoelectron spectroscopy and X-ray fluorescence spectroscopy. It was found that the introduction of CuNCs with small size of ∼1–2 nm on BTN surfaces can improve the photocatalytic H2 production activity, and the maximum photoactivity (225 μmol h−1) for H2 production over 1.0 mol% Cu/BTN composite is similar to that (220 μmol h−1) of the benchmark photocatalyst (P25) under the optimum photoreaction conditions, which is 5.2 times higher than that (42.5 μmol h−1) of the BTN alone. This significant enhancement in the photoactivity of BTN is deemed to result from the metallic CuNCs with high surface area and dispersion, which favour the co-catalyst functions to cause an effective photogenerated carrier separation in space and an improvement in the photocatalytic activity and stability for H2 production. The present results not only demonstrate the brookite TiO2 would be a potential effective photocatalyst for H2 production, but also provide an inexpensive, efficient and stable means of enhancing light-to-hydrogen energy conversion by using metallic Cu nanoclusters alternative to the commonly used noble metal co-catalyst.Cu nanoclusters are shown to be a promising alternative to noble metal co-catalyst to provide an inexpensive and efficient means of enhancing H2 production activity of brookite TiO2.Download high-res image (330KB)Download full-size image

Dye-sensitized solar cells (DSSCs) were fabricated by using porous ZnO electrodes derived from home-made ZnO nanoparticles. Electrochemical impedance spectra and open-circuit photovoltage decay curves measurements were performed to investigate the photoelectrochemical characteristics of ZnO films annealed at different temperatures. The experimental results indicate that the effects of the bulk traps and the surface states within the ZnO films on the recombination processes of the photoinjected electrons in DSSCs depend on the annealing temperature. The DSSC based on the ZnO electrode annealed at 400 °C exhibits an optimal energy conversion efficiency of 3.92% under the illumination of one sun simulated sunlight because the farthest decrease in the effects of both bulk traps and surface states at this film can maintain a lower charge recombination probability. This result indicates that the ZnO film electrode has promising application in the field of DSSCs, and the optimization of porous film fabrication condition is efficient for the improvement of ZnO-based DSSC’s performances.

•A novel visible-light-driven Ni@C/CdS nanocomposite is first prepared.•Enhanced visible-light-driven photocatalytic H2-production efficiency with better durability.•Beneficial for developing efficient and low-cost photocatalysts.Carbon encapsulation strategy of Ni co-catalyst is applied to the fabrication of novel carbon-coated Ni (Ni@C)/CdS nanocomposite photocatalyst with high efficiency and good stability via a facile solvothermal process by using a pre-prepared Ni@C as a starting material. It is found that the metallic Ni nanoparticles encapsulated in the graphite-like carbon shells show a high chemical and thermal stability, and the resultant Ni@C/CdS nanocomposite shows an average photocatalytic H2-production activity of 622.7 μmol h−1 during 5-h visible-light irradiation and an apparent quantum yield up to ca. 20.5% under 420 nm monochromatic light irradiation. The metallic Ni in Ni@C acted as co-catalyst while the graphite-like carbon as CdS nanoparticles’ support and electron acceptor, which resulting in the efficient charge separation, and then the enhanced photoactivity and stability for H2 production as compared to the pristine CdS nanoparticles. The present novel carbon encapsulation strategy of Ni co-catalyst can shed light on the fabrication of new cheap photocatalyst with excellent photoactivity and stability for H2 production.Graphical abstractCarbon encapsulation of Ni co-catalyst is applied to the fabrication of Ni@C/CdS with an apparent quantum yield up to ca. 20.5% under 420 nm light irradiation. Ni in Ni@C acted as co-catalyst while the graphite-like carbon as CdS support and electron acceptor, resulting in the enhanced photoactivity and stability for H2 production.Download high-res image (248KB)Download full-size image

•N-, C- and S-doped ZnO investigated by DFT calculation.•Stronger visible light absorption induced by both N and C doping.•N-, C- and S-doped ZnO with lighter electrons and heavier holes.•N, C and S doping facilitating separation of photogenerated charge carriers.In general, N-, C- and S-doped ZnO exhibit much higher phototcatalytic activity than the pure ZnO. However, the essential factors and underlying mechanism regarding the enhancement of photocatalytic activity are still unclear. In this work, the electronic structures, optical properties and effective masses of charge carriers are investigated by first-principle density functional theory calculation. Due to the nature of p-type doping, N and C doping can generate vacant states above the Fermi level and shift the conduction band into lower energy region, resulting in narrowing of band gap. Thus, N- and C-doped ZnO demonstrate much stronger light absorption in both visible and ultraviolet region. In contrast, because of the absence of vacant states, only limited enhancement of light absorption is observed for S-doped ZnO whose improved photocatalytic performance can only be attributed to the direct reduction of band gap. The calculation of the effective masses show that ZnO typically possess light electrons and heavy holes, confirming its intrinsic character of n-type semiconductor, while N, C and S doping can generally render electrons lighter and holes heavier, resulting in slower recombination rate of photogenerated electron–hole pairs. Noticeably, C doping can discourage such recombination to the greatest extent and separate electron–hole pairs most efficiently compared with N and S doping, serving as a potentially promising pathway to increase the quantum efficiency of ZnO-based photocatalysts. This work will provide some new insights into the understanding of doping effect over the enhancement of photocatalytic activity of N-, C- and S-doped ZnO.Download high-res image (119KB)Download full-size image

Acceptorless dehydrogenation of alcohols to carboxylic acid derivatives catalyzed by a transition metal complex is an important reaction in modern organic synthesis and catalysis, for which nickel complexes have rarely been developed. Herein we report three Ni(II) complexes bearing pyridine-based N′NN′ type pincer ligands, which catalyze the acceptorless dehydrogenation of primary alcohols to carboxylic acids under anhyrous conditions. The complex [NiCl2(L3)] 3 (L3 = 2,6-bis(diethylaminomethyl)pyridine) displays the best catalytic reactivity, catalyzing the primary alcohols to carboxylic acids and H2 in good yields (40–90%). Further investigation reveals that an unexpected alcohol etherification occurs, which gives the second oxygen atom for the formation of the carboxylic acid. Our results give a thread for the design of new nickel complexes without phosphine and N-heterocycle carbene ligands for the acceptorless oxidation of alcohols.

Extremely efficient photocatalytic H2 production with a turnover number (TON) of 25002 for 20 h over graphitic carbon nitride (g-C3N4) sensitized by zinc phthalocyanines (ZnPcs) with asymmetric and electronic directional structures is successfully carried out under λ ≥ 500 nm light irradiation, and an impressive apparent quantum yield (AQY) higher than 1.0% is obtained under 700 nm monochromatic light irradiation. Based on the photoactivity, photofluorescence (PL), time-resolved fluorescence spectroscopy (TRFS), photocurrent, and electrochemical impedance spectroscopy (EIS) results, it is found that the asymmetry and electronic directionality of ZnPcs can significantly influence the photogenerated electron transfer between ZnPcs and g-C3N4 and further influence the photocatalytic H2 production activity of the phthalocyanine-sensitized g-C3N4 system. The present work exhibits the promising application of phthalocyanine materials in extending red/near-IR light utilization and gives some suggestions and routes for the design and synthesis of phthalocyanine derivatives for solar energy conversion applications.

This perspective gives an overview of recent developments in heterogeneous photocatalytic CO2 reduction for C1/C2 fuels production over semiconductors, which has been known for several decades as a potential feasible means to store intermittent solar energy and to recycle CO2. In recent years, significant efforts have been made in order to further improve the photoactivity and the selectivity through developing novel photocatalysts and its CO2 photoreduction reaction systems, which would be of great interest in the field of solar conversion and CO2 resource utilization.

Asymmetric zinc porphyrin (ZnPy) was synthesized and used to sensitize nanosized TiO2. The visible-light-driven activity of CO2 photoreduction to generate CO/CH4 in the gas phase was observed from the ZnPy-sensitized TiO2 without loading noble metal, and the mechanism was discussed.

Novel highly asymmetric zinc tetraazaporphyrin (TAP) derivatives (Zn-tri-TAPNc and Zn-tri-PcNc) with one carboxyl and three tert-butyl peripheral substituent groups were synthesized. A highly asymmetric zinc phthalocyanine (ZnPc) derivative (Zn-tri-PcNc) has a benzo-annelated ring which contains tribenzonaphtho-condensed tetraazaporphyrin with the same peripheral substituents as Zn-tri-TAPNc. As a sensitizer for the TiO2-based dye-sensitized solar cell, Zn-tri-PcNc derived from the benzo-annelation of the TAP macrocycle showed improved light harvesting and electron injection efficiency, which can retard the charge recombination, resulting in a great improvement in the incident photon-to-current conversion efficiency (IPCE). The Zn-tri-PcNc-sensitized solar cell exhibited a higher conversion efficiency (2.89%) than the Zn-tri-TAPNc-sensitized one (1.20%) under AM 1.5G solar irradiation. The present results on the TAP macrocycle's benzo-annelation demonstrate that optimization of molecular structure via changing the peripheral substituent group's “push–pull” effect and enlarging the conjugated π-system is an effective approach to improve the performance of the tetraazaporphyrin-based dye-sensitized solar cell.

A novel nanostructured carbon/TiO2 nanocomposite photocatalyst is firstly fabricated via a facile hydrothermal process by using fullerene (C60) decorated single-walled carbon nanotubes (SWCNTs) as carbon source, which is denoted as C60-d-CNTs. The obtained nanostructured carbon/TiO2 nanocomposites are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectra (DRS), Raman spectra, X-ray photoelectron spectroscopy (XPS) and photoluminescence spectra (PL), and then are used as catalysts for photocatalytic hydrogen production. It is found that the kinds and contents of various carbon nanostructured materials (such as SWCNTs, C60 and C60-d-CNTs) coupled with TiO2 can significantly enhance the photoactivity for hydrogen production, and the 5 wt% C60-d-CNTs/TiO2 nanocomposite exhibits the best performance. Experimental results suggest that the C60-d-CNTs as a novel carbon nanostructured material could be more beneficial for the photogenerated carrier separation than SWCNTs and C60 when these carbon nanostructured materials are coupled with TiO2.

Photocatalytic water splitting by solar light has received tremendous attention for the production of clean and renewable hydrogen energy from water. Some challenges still remain in improving the solar-to-hydrogen energy conversion efficiency, such as utilizing longer-wavelength photons and enhancing the photocatalytic activity and stability of H2 production over semiconducting materials. Dye sensitization, as a successful strategy for extending the spectral responsive region (even to near-IR light) of wide bandgap semiconductors for H2 production, was developed more than 30 years ago, but it still lacks the corresponding specialized review. This review emphasizes especially the fundamental aspects and the research advances in heterogeneous dye-sensitized semiconductor suspension systems for visible (and even near-IR) light responsive photocatalytic H2 production, and the commonly used dyes, semiconductors, co-catalysts and electron donors are systematically discussed. Also, a short perspective on the challenges and new directions in this field is proposed, which would be of great interest in the field of solar fuel conversion.

Brookite TiO2 quasi nanocubes with high phase purity and thermal stability were synthesized through a hydrothermal process. The obtained brookite TiO2 quasi nanocubes have a mean size of ∼50 nm with a specific surface area of ∼34.2 m2 g−1. When used as a photoanode material, the single brookite TiO2 nanocubes film-based dye-sensitized solar cell (DSSCs) shows higher open-circuit voltage but lower conversion efficiency than the single nanosized anatase TiO2 film-based one with a similar film thickness; while using the brookite TiO2 nanocubes as an overlayer of the nanosized anatase TiO2 film, the fabricated bilayer solar cells exhibit significant enhancement in both the open-circuit voltage and short-circuit current. In addition, the corresponding bilayer solar cell with an optimized overlayer thickness gives a conversion efficiency up to 8.83% with a 23.8% improvement when compared to the single anatase cell (7.13%). The brookite nanocubes used as an overlayer not only reduce the charge recombination and dark current, but also prolong the electron lifetime, which leads to an enhanced voltage and photocurrent, and therefore the improved photovoltaic performance of the bilayer solar cell. These results demonstrate the simple fabrication method used to prepare brookite TiO2 nanocubes and their application as an overlayer are promising and offer a strategy for the development of low-cost and high efficiency DSSCs through tuning the photoanode's components and structure.

Photocatalytic CO2 reduction into renewable hydrocarbon solar fuels is considered as a promising strategy to simultaneously address the global energy and environmental issues. In this study, a binary g-C3N4/ZnO photocatalytic system was constructed via a one-step facile calcination method and further used as a photocatalyst for CO2 reduction. It was shown that the as-prepared g-C3N4/ZnO photocatalytic system exhibited enhanced photocatalytic activity for CO2 reduction by a factor of 2.3 compared with pure g-C3N4, while maintaining the original selectivity of pure g-C3N4 to convert CO2 directly into CH3OH. For the first time, the coupling effect of ZnO responsible for the improved photoactivity of g-C3N4 was fully illustrated and a direct Z-scheme mechanism rather than the conventional heterojunction-type mechanism was proposed to explain the better performances of the g-C3N4/ZnO binary composite photocatalytic system. The enhancement of photocatalytic CO2 reduction activity is attributed to the highly efficient ZnO-to-g-C3N4 electron transfer occurring at the intimate contact interface between the g-C3N4 phase and ZnO phase. This work will provide new deep insights into the rational construction of a g-C3N4-based photocatalytic system and the design of a direct Z-scheme system without an electron mediator for photocatalytic CO2 reduction reactions.

Anatase TiO2 nanocrystals with {101}, {001} or {010} single facets of 90% level exposure were controllably synthesized from potassium titanate (PT) without fluorine and organic capping surfactants, and characterized by X-ray diffraction patterns (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and fast Fourier transformation (FFT). The liquid-phase photocatalytic reduction (O2˙− generation) and oxidation (˙OH generation) activity orders of anatase TiO2 facets are {001} > {101} > {010} upon removing facet synergetic effect and surface fluorine effect. UV-vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra showed that absorbance edge order, and separation efficiency order of photoexcited holes and electrons are {001} > {101} > {010}, which explains the photocatalytic activity order well together with the atomic arrangement of different facets.

One dimensional structures of TiO2 (nanowires and nanotubes) are promising for dye-sensitized solar cells due to reduced electron recombination; however, the small surface area is the main hurdle in the application of one dimensional anatase structures to dye-sensitized solar cells because of insufficient dye adsorption. Here, we address this problem with the preparation of a TiO2 nanotube film with a high specific surface area. This film was self-assembled by ultra-fine TiO2 nanotubes with diameter <10 nm via a simple hydrothermal method, and was applied to dye-sensitized solar cells on flexible Ti metal using a transplanting technique. Due to the higher surface area and one-dimensional structure, 6.23% efficiency was obtained with this ultra-fine TiO2 nanotube film, which was superior to that of conventional TiO2 nanoparticles.

A highly conductive Ni-coated commercial paper substrate (square resistance <1 Ω) was prepared by chemical deposition, and used as the substrate for a flexible TiO2 film electrode derived from a binder-free TiO2 paste, and heat treated at 250 °C. A low-cost, quasi-solid-state and TCO-free highly bendable paper-based dye-sensitized solar cell with conversion efficiency up to 2.90% is fabricated successfully by applying an iodine-free electrolyte. This encouraging result indicates that commercial paper is a promising material for use in dye-sensitized solar cells because of its flexibility, low cost and relatively high resistance to temperature. Compared with the rigid transparent conducting oxide (TCO) coated glass and flexible conductive plastic substrates, the potential of using mature paper making and coating technologies will greatly reduce the cost of the current photovoltaic devices.

The In2S3/(Pt-TiO2) nanocomposite photocatalyst consisting of floriated In2S3 decorated with TiO2 nanoparticles was synthesized by a multi-step method, which was used for the hydrogen production under visible-light (λ ≥ 420 nm) irradiation. The obtained In2S3/(Pt-TiO2) nanocomposite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption spectra (DRS), and photoluminescence spectra (PL). It is found that the Pt-TiO2nanoparticles embedded in the interstices of the floriated In2S3 formed intimate contacts between the In2S3 and Pt-TiO2, which is a benefit to significantly enhance the charge separation and then the photocatalytic activity. The effects of the mass ratio in the In2S3/(Pt-TiO2) nanocomposites and Pt-loaded amount on the photoactivity for the hydrogen production were investigated comparatively. The results show that the In2S3/(Pt-TiO2) nanocomposite with a mass ratio of 3:2 has the maximum photocatalytic hydrogen production rate of 135 μmol h−1 under visible-light irradiation, and the possible mechanism of the obtained In2S3/(Pt-TiO2) nanocomposite as a photocatalyst for hydrogen production was proposed.

A series of carbon-coated Ni (Ni@C)–Cd0.8Zn0.2S nanocomposites were fabricated via a facile hydrothermal process using pre-prepared Ni@C as a starting material. The obtained products were characterized by X-ray diffraction, UV-Vis diffuse reflectance absorption spectroscopy, X-ray photoelectron spectroscopy and electron microscopy. It was found that the introduction of Ni@C nanoparticles can improve both the visible light-induced photocatalytic H2 production activity and stability of the Cd0.8Zn0.2S solid solution, and the Ni nanoparticles encapsulated by several graphite-like carbon layers show high chemical and thermal stability. Among those products with various Ni@C contents, the 5 wt% Ni@C–Cd0.8Zn0.2S nanocomposite exhibits the maximum photoactivity (969.5 μmol h−1) for H2 production, which is ∼3.10 times higher than that (312.6 μmol h−1) of pristine Cd0.8Zn0.2S. This significant enhancement in the photoactivity by loading Ni@C nanoparticles can be attributed to the metallic Ni in the Ni@C acting as a co-catalyst, while the graphite-like carbon shells acting as the Cd0.8Zn0.2S nanoparticles' support and electron acceptor, which causes an effective photogenerated carrier separation in space and an improvement in the photoactivity and stability for H2 production. The present findings demonstrate a cost reduction strategy by using a non-noble metal co-catalyst for efficient and stable light-to-hydrogen energy conversion.

Zinc phthalocyanine (ZnPc) derivatives with asymmetric (Zn-tri-PcNc-2) or symmetric (Zn-tetrad-Nc) structure, which possess wide spectral response in the visible/near-IR light region, are synthesized and utilized as a sensitizer of graphitic carbon nitride (g-C3N4) with 0.5 wt% Pt-loading for photocatalytic H2 production. The experimental results indicate that Zn-tri-PcNc-2 exhibits much better photosensitization on g-C3N4 than Zn-tetrad-Nc under visible/near-IR light although Zn-tetrad-Nc possesses wider and stronger optical absorption property than Zn-tri-PcNc-2. Zn-tri-PcNc-2-Pt/g-C3N4 exhibits an average H2 production rate of 132 μmol h−1, which is much better than that (26.1 μmol h−1) of Zn-tetrad-Nc-Pt/g-C3N4 under visible-light (λ ≥ 500 nm) irradiation. Moreover, Zn-tri-PcNc-2-Pt/g-C3N4 also shows much higher apparent quantum yield (AQY) than Zn-tetrad-Nc-Pt/g-C3N4 under red/near-IR light irradiation. Especially, Zn-tri-PcNc-2-Pt/g-C3N4 exhibits impressively higher AQY (1.07%) than that (0.22%) of the Zn-tetrad-Nc-Pt/g-C3N4 under 700 nm monochromatic light irradiation. The much better photoactivity of Zn-tri-PcNc-2-Pt/g-C3N4 than Zn-tetrad-Nc-Pt/g-C3N4 is caused by the asymmetric structure of Zn-tri-PcNc-2, which can result in the electronic orbital directionality of its excited state, much faster photogenerated electron transfer to g-C3N4, and higher red/near-IR light utilization efficiency as compared to Zn-tetrad-Nc-Pt/g-C3N4. The present results provide an important insight into the effects of molecular structure and optical absorption property of phthalocyanine derivatives on the photoactivity of the dye-sensitized semiconductor, and also guide us to further improve the solar energy conversion efficiency by optimizing the molecular structure and effectively utilizing the visible/near-IR light of sunlight.

We firstly demonstrate the opposite photocatalytic activity orders of low-index facets of anatase TiO2 in the liquid phase for rhodamine B (RhB) photocatalytic degradation and in the gaseous phase for the photoreduction of CO2 to CH4. The photocatalytic activity order in the liquid phase for RhB photocatalytic degradation is revealed as {001} > {101} > {010}, whereas the photocatalytic activity order {010} > {101} > {001} is found in the gaseous phase for the photoreduction of CO2 to CH4. The atomic arrangement of the different facets, UV-vis diffuse reflectance spectra, photoluminescence spectra and attenuated total reflectance Fourier transform infrared spectroscopy analysis show that the photoactivity order in the gas phase for the photoreduction of CO2 to CH4 mainly depends on the CO2 molecule adsorption properties on the different exposed facets, and the separation efficiency of the photo-generated carriers determines the photoactivity order for the dye degradation reaction in the liquid phase. These findings also provide a new direction to design efficient photocatalysts and the tuning of their photoreactivity for environmental and energy applications.

Reduced graphene oxide (RGO)–cadmium sulfide (CdS) nanocomposites were successfully prepared by a one-pot solvothermal process without pretreatment of graphene oxide (GO) and a precipitation process, in which GO needs to be pre-reduced by hydrazine. The as-obtained RGO–CdS nanocomposites were used as photocatalysts for hydrogen production under visible light irradiation, and it was found that the product derived from the one-pot solvothermal process showed much better photoactivity than that from the precipitation method.

Size controllable and thermally stable rice-like brookite TiO2 particles with high phase purity were synthesized through a hydrothermal process. By varying the reaction conditions, the average diameter (brachyaxis) of the rice-like brookite TiO2 particles can be tuned over a wide range from ca. 200 nm to 1200 nm. Moreover, the brookite phase can be maintained, even with calcination at a temperature up to 800 °C, and a brookite-to-anatase phase transition and then to rutile can be observed upon further enhancing the calcination temperature from 850 °C to 1000 °C. The obtained brookite TiO2 submicrometer particles were used as a light scattering overlayer on a nano-sized TiO2 (P25) film-based photoanode to fabricate bilayer TiO2 film-based dye-sensitized solar cells (DSSCs). It is found that the brookite TiO2 scattering layers can improve the performances of the P25 film-based solar cells to different extents by enhancing the light-harvesting capability, and the optimal diameter of the rice-like brookite TiO2 particles as a scattering layer material is determined to be ∼600 nm, its corresponding solar cell gives an overall conversion efficiency up to 7.57%, with a ∼33% improvement in the efficiency as compared to that (5.70%) of the individual P25 film-based one under standard AM 1.5G 1 sun irradiation. The above results on the brookite TiO2 particles represent a clear advance towards efficient light scattering materials for the nanosized TiO2 film-based solar cells.

Multiwalled carbon nanotubes (MWCNTs) and ZnIn2S4 composites were prepared by a facile hydrothermal method, which was used for hydrogen production under visible-light (λ ≥ 420 nm) irradiation. The obtained MWCNTs/ZnIn2S4 composites were characterized by X-ray diffraction (XRD), thermogravimetric and differential scanning calorimetry analyses (TG-DSC), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption spectra (DRS), Fourier transform IR spectroscopy (FTIR) and Photoluminescence spectra (PL). It was found that the MWCNTs were embedded into the interior of floriated ZnIn2S4 microspheres. The effects of the composite ratio in the MWCNTs/ZnIn2S4 on the photocatalytic activity for hydrogen production were investigated. The results show that the 3 wt% MWCNTs/ZnIn2S4 composite reaches its maximum photocatalytic hydrogen production efficiency with an apparent quantum efficiency as high as 23.3% under 420 nm light irradiation. The significantly enhanced photoactivity for the present composite originates from the synergetic effect of its component intrinsic properties. A possible mechanism of the MWCNTs/ZnIn2S4 composite as a photocatalyst for H2 evolution was proposed.

Two kinds of graphitic carbon nitride (g-C3N4) were synthesized through a pyrolysis process of urea or melamine. It is found that the obtained g-C3N4, as photocatalysts, can reduce CO2 to organic fuels under visible light, and exhibit different photoactivity and selectivity on the formation of CH3OH and C2H5OH. The product derived from the urea (denoted as u-g-C3N4) shows a mesoporous flake-like structure with a larger surface area and higher photoactivity for the CO2 reduction than the non-porous flaky product obtained from melamine (denoted as m-g-C3N4). Moreover, using u-g-C3N4 as a photocatalyst can result in the formation of a mixture containing CH3OH and C2H5OH, while m-g-C3N4 only leads to the selective formation of C2H5OH. The present interesting findings could shed light on the design of efficient, eco-friendly and convenient photocatalysts and the tuning of their photoreactivity in the field of sustainable light-to-energy conversion.

Porous graphitic carbon nitride (g-C3N4) was prepared by a simple pyrolysis of urea, and then a g-C3N4–Pt-TiO2 nanocomposite was fabricated via a facile chemical adsorption followed by a calcination process. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance absorption spectra, and electron microscopy. It is found that the visible-light-induced photocatalytic hydrogen evolution rate can be remarkably enhanced by coupling TiO2 with the above g-C3N4, and the g-C3N4–Pt-TiO2 composite with a mass ratio of 70:30 has the maximum photoactivity and excellent photostability for hydrogen production under visible-light irradiation, and the stable photocurrent of g-C3N4–TiO2 is about 1.5 times higher than that of the bare g-C3N4. The above experimental results show that the photogenerated electrons of g-C3N4 can directionally migrate to Pt-TiO2 due to the close interfacial connections and the synergistic effect existing between Pt-TiO2 and g-C3N4 where photogenerated electrons and holes are efficiently separated in space, which is beneficial for retarding the charge recombination and improving the photoactivity.

Floriated ZnFe2O4 with porous nanorod structures were successfully synthesized via mild hydrothermal and calcination processes by using cetyltrimethylammonium bromide (CTABr) as a template-directing reagent. The resulting ZnFe2O4 was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS) and nitrogen adsorption measurement. It was found that the floriated ZnFe2O4 nanostructures were composed of porous nanorods with an average length of 122 nm and diameter of 29 nm. The obtained ZnFe2O4 with a bandgap of ∼1.94 eV was firstly used as a visible-light-driven photocatalyst for hydrogen production, and exhibits remarkable photostability in an aqueous suspension by using CH3OH as a sacrificial reagent. Moreover, the possible photo-reaction mechanism for the hydrogen production from CH3OH aqueous solution was proposed for better understanding the photocatalytic behavior of ZnFe2O4 without Pt-loading.

A novel iodine-free quasi solid-state electrolyte employing an ionic liquid (1, 2-dimethyl-3-propylimidazolium iodide, DMPII) as charge transfer intermediate was developed for dye-sensitized solar cells (DSSCs). Simultaneously, potassium iodide (KI) was incorporated into the electrolyte as charge transfer auxiliary agent. The dependences of photovoltaic performances and ionic conductivities on the iodine-free quasi solid-state electrolyte containing different KI concentrations were investigated. The strong interactions between the potassium cations and polyethylene oxide (PEO, MW = 100,000) can prevent the crystallization of the electrolyte and enhance its ionic conductivity. An optimal photoelectric conversion efficiency (η) of 5.87% can be obtained for the DSSC fabricated with the iodine-free electrolyte containing 5 wt% KI, and the corresponding value without KI is 4.05%, indicating the remarkable progress made by addition of KI into electrolyte.