The structure and the chemical state of the metal oxide support have significant effect on the activity of noble metal nanoparticles for the catalytic oxidation of organic pollutants. In this work, we report the synthesis of porous tricobalt tetraoxide-supported palladium (Pd/Co3O4) catalysts derived from direct pyrolysis of metal-organic framework (MOF) for the complete oxidation of benzene. The porosity and nanoparticle size of the catalyst could be controlled by adjusting the calcination temperature. The X-ray photoelectron spectroscopy (XPS) analyses reveal that the surface adsorbed oxygen, which is associated with the PdOx species, is crucial for catalytic performance. H2-temperature programmed reduction (H2-TPR) results indicate that the reducibility of the catalyst has significant effect on the catalytic activity for the oxidation of benzene. In general, Pd nanoparticles supported on the porous polyhedron Co3O4 support calcined at 350 °C (Co3O4-PP-350), which possess abundant porous structures and the most active surface adsorbed oxygen, exhibit the highest activity for the complete catalytic conversion of benzene compared with those supported on the porous polyhedron Co3O4 support calcined at 250 °C (Co3O4-PP-250), 550 °C (Co3O4-PP-550), and the Co3O4 nanoparticle support calcined at 350 °C (Co3O4-NP-350).

The hydrothermal growth of ZnO nanorods on graphene draws a specific interest for the advantages of low-temperature processability over a large area and low cost, but challenges still remain in directly growing uniform ZnO seed layers on pristine graphene without impairing its beneficial properties. In this work, the direct growth of ZnO seed layers on graphene via H2O-based atomic layer deposition (ALD) has been investigated. It is found that uniform ZnO thin films can be deposited on graphene via ALD using a combination of single-layer graphene/Cu stacks as substrates and a facile pre-H2O treatment process. After growing ZnO nanorods on graphene, its photovoltaic application in a Cu2ZnSn(SxSe1−x)4 (CZTSSe) solar cell is demonstrated. The performance of graphene-based cells approaches that of ITO-based cells with similar architectures, highlighting that graphene is a potential replacement for ITO in optoelectronic devices. The method reported herein for fabricating ZnO nanorods on graphene using ALD–ZnO as seed layers preserves its properties, and is thus applicable to a wide variety of graphene-based nanoelectronic devices.

The role of MoS2 as an effective interfacial layer in graphene/silicon solar cells is systematically investigated by varying MoS2 film annealing temperature and thickness. It is found that the power conversion efficiency (PCE) is increased by ∼100% from ∼2.3% to ∼4.4% with 80 °C annealed MoS2 film whereas it drops significantly to ∼0.6% with 200 °C annealed MoS2 film. The results are well explained based on the device energy band diagram. That is, the incorporation of MoS2(80) films leads to the formation of type II structure, facilitating hole transport; while valence band mismatch is formed with MoS2(200) films due to the increase in the work function of MoS2. Besides, the PCE increases gradually with decreasing MoS2 film thickness, and “saturates” at about 2 nm. The PCE can be further enhanced to ∼6.6% with the aid of silicon surface passivation. Our work demonstrates that MoS2 is an excellent interfacial layer to improve the PCE with low-temperature annealing (80 °C in air), which may be helpful in developing efficient and low-cost G/Si solar cells.

We show that interface tailoring is an effective approach towards high performance G/Si Schottky-barrier solar cells. Inserting a thin graphene oxide (GO) interfacial layer can improve the efficiency of graphene/silicon solar cells by >100%. The role of the GO interfacial layer is systematically investigated by varying the annealing temperature and thickness of the GO film. It is found that GO cannot be treated as the common thought, i.e., an insulator. In other words, the G/GO/Si solar cell is not suitable to be treated as a “MIS” cell. In contrast, it should be regarded as a p-doped thin layer. The effects of GO film thickness on device response are also studied and there exists an optimal thickness for device performance. A record 12.3% (device size: 3 × 3 mm2) power conversion efficiency is achieved by further performance optimization (chemical doping graphene and antireflection coating).

Pt in/on silica nanoparticles were synthesized by flame spray pyrolysis (FSP) followed by H2 reduction at different temperature and tested in benzene complete oxidation reaction. The Pt clusters diffusion from the interior to the exterior of the SiO2 matrix followed by aggregation in/on the SiO2 matrix was observed with elevated temperature (300–1100 °C) and time (0–5 h). The aggregation of the Pt clusters on the surface of the SiO2 matrix was also evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM), and CO-pulse chemisorption. The effect of heat treatment temperature and time on the Pt/SiO2 structure was discussed. In combination with the experimental study, a further physical model describing the structural transformation was developed to complementarily depict the diffusion and aggregation process. The developed physical model correlated well with the experimental data. The catalytic activities increased with the elevated temperature until Pt3Si species was present at 1100 °C. The improved catalytic activities were attributed to the structural transformation induced by the elevated temperature. The rate of the Pt clusters diffusion to the surface and aggregation on the surface determined the Pt dispersion, which is the key mechanism in determining the catalytic activity.

A series of highly active Pt–TiO2 catalysts have been prepared by impregnation methods via different reduction processes and used for catalytic decomposition of benzene. The oxidized and reduced Pt–TiO2 catalysts exhibit apparent differences in physical/chemical features (e.g. particle size, chemical state, and electronic property of Pt nanoparticles, and surface oxygen) and catalytic activities for benzene oxidation. Nearly 100 % benzene conversion is achieved on Pt–TiO2 catalysts obtained by the sodium citrate (C6H5Na3O7·2H2O, Na3Ct) reduction at approximate 160 °C. Metallic Pt nanoparticles have strong capacity for oxygen activation, and the negative charges and rich chemisorbed oxygen on the surface of metallic Pt nanoparticles are probably responsible for their high catalytic activities for benzene oxidation.

•Optimized deposition parameters of a seedless flame-base nanowire film fabrication method, leading to nanofibrous film with densified nanowire distribution and sub-wavelength scale gaps.•Discussed the change of nanowire growth trend caused by precursor diffusion condition fluctuation.•Good versatility possessing enhanced anti-fogging and anti-reflective properties.Here we report a multifunctional SiO2 nanofibrous film fabricated on plain glass by the seedless flame spray pyrolysis method. The SiO2 nanowires show different morphologies as growth time increase due to the alteration of gas precursor diffusion conditions. The growth route of nanowires has been divided into several stages due to the different dominant growth type. The densification and overlapping caused by radial and axial growth in competitive relation endow the as-made SiO2 films with increased surface area and sub-wavelength scale structure. Combining the hydrophilicity of flame-made SiO2 and the special fibrous structure, the nanofibrous SiO2 film exhibits considerable anti-fogging and anti-reflective properties.

Spherical boehmite particles with hollow interiors were synthesized in the hydrothermal condition using aluminum nitrate as Al3+ source, urea as precipitator and citric acid as structure directing agent, which was further transformed to hollow γ-Al2O3 products after simply heating post-treatment under 700 °C for 4 h. The crystal phase, morphologies and microstructure of the sample were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. It is suggested that the as-synthesized boehmite powder possesses hollow interior with ca.1 μm in diameter and shells with 100 nm in thickness, and the calcinated sample have γ crystal phase without morphological changes after heat post-treatment. The interesting hollow structure evolution was further investigated by comparative experiments and a reasonable evolution mechanism was proposed, in which the chelation of citric acid with Al3+ species and the dissolution of boehmite play the critical role in forming the hollow structure of boehmite.

Nanostructured ZnO materials including Zn@ZnO core–shell structure (CS), ZnO hollow sphere (HS), and hierarchically structured ZnO hollow microsphere with nanorods (HSNR) grown on the outer surface were prepared by a simple and versatile chemical vapor deposition process. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and room temperature photoluminescence spectroscopy were used to characterize the morphology and crystalline structure of the samples. It was found that the gas-sensing property of the three structured ZnO had different responses in resistive mode using formaldehyde gas as the probe. In contrast with CS and HS samples, the HSNR exhibits better sensing property because it has more oxygen vacancies and more surface sites, which produce a higher resistance. However, the higher work function of Zn core than that of the ZnO sheath forms the ohmic contact, producing negative charge accumulating layers within ZnO side of Zn–ZnO junction, thus contributing a lower sensing response of CS model when exposed to the targeted formaldehyde gas.

In this paper, a simple way is developed for the synthesis of the ZnO micro-windbreak film (ZMW) based on layered basic zinc salt precursor. The ZnO products maintain the original morphologies of precursors without deformation. Scanning electron microscopy, transmission electron microscopy, infrared spectrum and X-ray diffraction are used to characterize the detailed structures of the as-prepared products. Because of better gas diffusion in single layer ordered flower arrays (highly exposed surfaces) and thin belt-like branches (high diffusion coefficient) than other hierarchical structures, ZMW exhibits the highest responses to benzene gas. High responses allow ZMW to be used for the detection of benzene at ppb-level. By simply sputtering the platinum on both faces of ZMW to enhance the surface reaction, the optimal operating temperature for benzene detection could be reduced to 350 °C and the responses are significantly improved.

•Ce–Mn oxides for catalytic oxidation of benzene were synthesized by flame spray pyrolysis (FSP).•Ce–Mn oxides of size <40 nm and specific surface areas of 20–50 m2/g were formed with different Ce–Mn ratios.•Relative lower benzene conversion temperature (T95 ≈ 260 °C) was achieved by 12.5%-Ce–Mn oxides.•Better activity was attracted to the synergetic effect of Ce and Mn and small particle sizes as well.Flame spray pyrolysis (FSP) was utilized to synthesize Ce–Mn oxides in one step for catalytic oxidation of benzene. Cerium acetate and manganese acetate were used as precursors. The materials synthesized were characterized using X-ray diffraction (XRD), N2 adsorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and H2-temperature programmed reduction (H2-TPR) and their benzene catalytic oxidation behavior was evaluated. Mn ions were evidenced in multiple chemical states. Crystalline Ce–Mn oxides consist of particles with size <40 nm and specific surface areas (SSA) of 20–50 m2/g. Raman spectrums and H2-TPR results indicated the interaction between cerium and manganese oxides. Flame-made 12.5%-Ce–Mn oxide exhibited excellent catalytic activity at relatively low temperatures (T95 about 260 °C) compared to other Ce–Mn oxides with different cerium-to-manganese ratios. Redox mechanism and strong interaction conform to structure analysis that Ce–Mn strong interaction formed during the high temperature flame process and the results were used to explain catalytic oxidation of benzene.

Silica hollow spheres treated by 3-aminopropyltriethoxysilane (KH550) and hydrochloric acid showed good compatibility with polyurethane due to the improved functional group matching and charge matching between them. The resultant composite thin film exhibited excellent thermal insulation (0.05 W m−1 K−1) and light transmission (above 80%), which were quantitatively evaluated by thermo-resistance superposition method and UV–vis spectra, respectively. Moreover, finite element simulation was used to calculate thermal conductivity of the composite thin film. The simulated value was close to the experimental one, which confirmed the effectiveness of the modifications.Graphical abstractHighlights► Silica hollow spheres are selected as the thermal insulation additives. ► KH550 and HCl together enhance the compatibility between the filler and substrate.► Finite element simulation is used to confirm the effectiveness of modification method. ► The composite behaves excellent insulation coupling with light transmission.

CeO2 hollow nanospheres were synthesized by a low-cost and environmentally benign one-pot hydrothermal route. Templates, surfactants, or other auxiliaries were not used in the route. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and nitrogen adsorption–desorption measurements were used to characterize the products. The average diameter of hollow spheres, with shells of approximately 30 nm, was about 300 nm. The formation of these hollow spheres involved a transformation from Ce(OH)CO3 solid spheres to CeO2 hollow nanospheres. The CeO2 hollow nanospheres exhibited a higher catalytic activity on CO oxidation than CeO2 nano-octahedrons.

Different morphologies of β-FeOOH were prepared by hydrothermal synthesis using NaH2PO4 as structural modifier. The rod-shaped, straw-like and flower-like products could be controllably obtained. The as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Ultraviolet-visible (UV-Vis) absorption spectroscopy. The experimental results show that the morphology manipulation could be achieved by adding different amounts of NaH2PO4. XRD pattern indicates that the asprepared sample is the pure tetragonal phase of β-FeOOH. UV-Vis absorption spectra of the products are affected by their morphologies, which shows that both the rod-shaped and straw-like β-FeOOH have outstanding absorption ability on the whole UV area (200–400 nm), which will have vast application prospects in UV protection.

One of the challenges in realizing metal oxide semiconductor gas sensors is to enhance the sensitivity of active materials in order to respond to the low concentration of detecting gases effectively and efficiently. In this report, transition metals such as Mn, Ni, Cu, and Co are used as dopants for the synthesis of highly formaldehyde-sensitive ZnO nanorods prepared by plasma enhanced chemical vapor deposition (PECVD) method. All the doped ZnO nanorods show improved formaldehyde-sensitivity as compared to undoped ZnO nanorods, and a gas sensitivity maximum of ∼25/ppm was obtained by using 10 mol% CdO activated 1.0 mol% Mn doped ZnO nanorods. Moreover, the ZnO nanorods have a higher sensitivity as compared to ZnO nanomaterials prepared by other methods such as precipitation and hydrothermal, which can be attributed to the abundant crystal defects induced by the dopants in a short crystallization process in this PECVD method.

CeO2 nano-octahedrons were synthesized with a facile hydrothermal synthesis process where Ce(NO3)3·6H2O and urea were used as a cerium resource and mineralizer respectively and no surfactant or template was applied. The effects of synthesis parameters such as reaction temperature, reaction time, as well as the dosages of Ce (NO3)3·6H2O and urea were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis were conducted to characterize the crystalline and morphology of the obtained CeO2 powders. The optimal reaction condition to prepare the CeO2 of the desired fluorite structure was established. The possible mechanism of synthesis of CeO2 with a nano-octahedron morphology was illustrated.

The thermophysical property of hollow silica spheres was studied by the experimental test 3ω method, theoretical calculation and finite element simulation. The experimental values of the thermal conductivity, less than 0.02 W m−1 K−1, indicated that the powder silica hollow spheres are indeed the high efficient heat-insulating materials. The influences of the particle size and packing density on the thermal conductivity were observed. Then the formula interpreting aerogels were used to calculate the thermal conductivity of hollow silica spheres. The calculated values were larger than the experimental ones. Moreover, ANSYS software was applied to develop a heat conduction model for this type materials based on their hollow structure features. The geometry of the materials was discrete and finite element analysis was performed. The simulated values were close to that of air and a little higher than the experimental and calculated ones. And the possible reasons causing such differences were proposed.Graphical abstractHighlights► Sub-micrometer silica hollow spheres was selected as the research object. ► Research methods included experimental, calculation and simulation. ► The differences caused by the three different methods were explained reasonably.

SiO2 nanospheres with tailorable interiors were synthesized by a facile one-spot microemulsion process using TEOS as silica source, wherein cyclohexane including triton X-100 and n-octanol as oil phase and Zn2+ or NH3·H2O aqueous solution as dispersive phase, respectively. The products were characterized by Scanning Electron Microscopy, Transmission Electron Microscopy and X-ray Powder Diffraction. It was suggested that the as-synthesized silica nanospheres possessed grape-stone-like porous or single hollow interior, and also found that the ammonia dosage and aging time played key roles in controlling the size and structure of silica nanospheres. Furthermore, the comparative results confirmed that in-situ zinc species [ZnO/Zn(OH)2] acted as the temporary templates to construct grape-stone-like interior, and a simultaneously competing etching process occurred owing to the soluble Zn(NH3)42+ complex formation while the additional excessive ammonia was introduced. With the aging time being extended, the in-situ nanocrystals tended to grow into bigger ones by Ostwald Ripening, producing single hollow interior.Graphical AbstractFormation process of SiO2 nanospheres with porous and single hollow interior.Highlights► ZnO/Zn(OH)2 nanocrystals as the temporary templates shape the interior structures of SiO2 nanospheres. ► Fabrication of porous and single hollow interiors needs no additional processes such as roasting or dissolving. ► Tailorable interiors can be easily obtained through adjusting the aging time of temporary templates.

Sn-, Ni-, Fe- and Al-doped ZnO and pure ZnO are prepared by coprecipitation method, and characterized by scanning electron microscope (SEM), energy diffraction spectra (EDS) and X-ray diffraction (XRD). Their formaldehyde gas sensing properties are evaluated and the results show that 2.2 mol% Sn dopant can increase the response of ZnO by more than 2 folds, while other dopants increase little response or even decrease response. Further, CdO is used to activate ZnO based formaldehyde sensing material. It is demonstrated that 10 mol% CdO activated 2.2 mol% Sn-doped ZnO has the highest formaldehyde gas response, with a linear sensitivity of ∼10/ppm at lowered work temperature of 200 °C than 400 °C of pure ZnO, and high selectivity over toluene, CO and NH3, as well as good stability tested in 1 month.

ZnO thin films prepared by using quantitative filter paper as a template and Zn(CH3CO2)2·2H2O ethanol precursor solution were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of sample calcination temperature, precursor concentration and filter paper types were studied, and the growth process was investigated by infra-red (IR) spectroscopy and thermogravimetric analysis/differential thermal analysis (TGA/DTA). The results show that samples soaked in a 1.5 mol/L Zn(CH3CO2)2·2H2O ethanol solution and calcined at 600 °C yield ZnO films of uniform particle size, approximately 30, 40 and 50 nm, for fast-, medium- and slow-speed filter papers, respectively. The formaldehyde gas sensing properties of the ZnO nanoparticles were tested, showing that the material prepared from fast-speed filter paper has a higher response to 120–205 ppm formaldehyde at 400 °C than that prepared from medium- or slow-speed paper, which depends on the particle size.ZnO thin films were prepared by using quantitative filter paper as a template and 1.5 mol/L Zn(CH3CO2)2·2H2O ethanol solution and calcined at 600 °C. The ZnO nanoparticles prepared from fast-speed filter paper has a higher response to 120–205 ppm formaldehyde at 400 °C than those prepared from medium- or slow-speed paper.

Gas sensing property of ZnO nanorods prepared by plasma-enhanced chemical vapor deposition (CVD) method is studied using formaldehyde as the probe gas, and the intrinsic defects are investigated by photoluminescence (PL). The results show that high ratio of visible to ultra-violet luminescence cannot account for high gas response. The PL spectra are Gaussian decomposed to subpeaks according to their origination, which are separated into donor- (DL) and acceptor-related (AL) ones. A conclusion is derived that where the content of DL is high and that of AL is low, the gas response is high. This conclusion is further confirmed by tuning the PL spectra and gas sensing property through annealing in different atmospheres.

Zinc oxide nanoparticles are prepared by calcining zinc hydrocarbonate precursors at 300–700 °C (ZnO300–700), and corresponding gas sensing property are tested at 300 °C by using formaldehyde as the probe. Although the nanoparticle sizes are found to gradually increase with calcination temperature, the sensor measurements reveal the size-independent behavior that ZnO500 and ZnO300 have the highest and lowest responses, respectively. Spectroscopic characterization further reveals nonstoichiometric compositions of ZnO nanoparticles: ZnO300 has the largest excess oxygen (oxygen interstitial, Oi), whereas ZnO500 has the largest excess zinc (oxygen vacancy, VO and/or zinc interstitial, Zni). Accordingly, a new sensing mechanism is proposed for ZnO nanoparticle sensors. Excess zinc favors chemisorption of oxygen onto the nanoparticle surface, leading to reacting with more formaldehyde molecules to get a high signal. On the contrary, excess oxygen inhibits free oxygen to be chemisorbed onto the nanoparticle surface, and thus decreases the gas response. Finally, this new sensing mechanism is verified by testing gas response of ZnO500 nanoparticles annealed at different atmospheres.

Anodic aluminum oxide (AAO)/Al composite structure was prepared and used to fabricate metal oxide gas sensing film through electrophoretic deposition (EPD) process, and Ga-doped ZnO (GZO) and GZO post-treated in H2 (GZO-H) were used as high resistance and low resistance metal oxide models. The results showed that, in EPD process, Al (residual Al after anodic oxidation) plays as the electrode with the electric field penetrating the pores of AAO. And dispersant such as alcohols were preferred as H2 would be produced on the AAO/Al electrode in aqueous dispersion, which destroyed both the AAO layer and the GZO (or GZO-H) film. While in the gas sensing process, AAO (AAO layer) plays as the insulative layer between GZO (or GZO-H) film and Al substrate. The thickness of AAO layer should be properly tailored (i.e. >80 μm) as to make its resistance far larger than that of the GZO film, which prevents the current leakage from the GZO film to the Al substrate. While the thickness can be 10 μm when GZO-H film was used as its resistance is smaller. The AAO/Al composite structure made the EPD process feasible for gas sensing film fabrication, without any further treatment, which showed prospect in fabrication of metal oxide semiconductor gas sensors.

Fe-, Ti-, Sn-doped (1.8, 7.4 and 3.4 mol% respectively) and pure ZnO are prepared by hydrothermal method using 10 mol% precursors, whose gas sensing property is studied using formaldehyde as the probe. The results show that the maximum response of pure ZnO to 205 ppm formaldehyde is ∼43 (at relative humidity 70 ± 10%) at 400 °C. But the gas response maxima shift to 300 °C for Fe–ZnO (∼52–205 ppm) and Sn–ZnO (∼140–205 ppm), and to 200 °C for Ti–ZnO (∼26–205 ppm). Beyond the maxima, the response of Fe–ZnO is lower than that of pure ZnO, while that of Sn–ZnO is always higher. The morphology, crystal structure, vibration modes, bandgap and crystal defects are studied to investigate the different doping effects on gas sensing property of ZnO. The results show that the secondary phase identified by X-ray diffraction and Raman spectra, and the crystal defects detected by photoluminescence might account for the different sensing behaviors.

The activated carbon with high surface area was prepared by KOH activation. It was further modified by H2SO4 and HNO3 to introduce more surface functional groups. The pore structure of the activated carbons before and after modification was analyzed based on the nitrogen adsorption isotherms. The morphology of those activated carbons was characterized using scanning electronic microscopy (SEM). The surface functional groups were determined by Fourier transform infrared spectroscopy (FTIR). The quantity of those groups was measured by the Boehm titration method. Cr(VI) removal by the activated carbons from aqueous solution was investigated at different pH values. The results show that compared with H2SO4, HNO3 destructs the original pore of the activated carbon more seriously and induces more acidic surface functional groups on the activated carbon. The pH value of the solution plays a key role in the Cr(VI) removal. The ability of reducing Cr(VI) to Cr(III) by the activated carbons is relative to the acidic surface functional groups. At higher pH values, the Cr(VI) removal ratio is improved by increasing the acidic surface functional groups of the activated carbons. At lower pH values, however, the acidic surface functional groups almost have no effect on the Cr(VI) removal by the activated carbon from aqueous solution.

A two-sensor array was fabricated to improve gas selectivity, an intrinsic disadvantage of mono-metal oxide semiconductor gas sensor. The sensors comprising the array were made of Ga-doped ZnO (GZO) annealed at different temperatures, and the selectivity over relative humidity (RH 0–70 ± 10%) was greatly improved in formaldehyde gas sensing. The physical and mathematical principle for high selectivity is based on the different responses of the two sensors to analyte (formaldehyde) and to interferent (RH), that is, one sensor has larger response to formaldehyde than the other but the same response to RH. But under the same fabrication process for ZnO without Ga dopant, one sensor was insensitive either to formaldehyde or to RH due to the reaction of ZnO with the SiO2 substrate. Consequently, such a sensor array cannot be fabricated using ZnO sensors without Ga dopant. Possible mechanism concerning interactions between GZO and the two gases (formaldehyde and water vapor) was discussed.

Catalyst and reaction conditions are the main affecting factors for the yield and quality of carbon nanotubes (CNTs) produced by the chemical vapor deposition (CVD) method. In this paper a ternary component catalyst based on Fe–Ni–Mo/MgO was explored using methane as precursor. The influences of temperature and methane concentration were investigated, and the as-produced CNTs were characterized by SEM, HRTEM, XRD and TGA. The diameter of the CNTs is in the range of 20–30 nm and the maximum carbon yield can reach up to 80 times of the catalyst under the selected condition. The purity of the as-prepared CNTs is over 93%. Our results indicated that this novel tercomponent catalyst presented a good catalytic activity for manufacturing high quality and quantity of CNTs.

Needle-like zinc oxide with high electrical conductivity has been successfully prepared in large-scale from calcining the need-like precursor synthesized by a simple co-precipitation approach with ZnCl2 as Zinc source, GaCl3 as Gallium source and NH4HCO3 as precipitant under an optimized conditions (45 °C and pH = 7.4–7.5). The as-fabricated products were characterized by means of TEM, SEM, XRD, EDS and XPS. Their electrical conductivities were also studied, showing that the volume resistivity of the needle-like zinc oxide with 2.2 mol% Ga3+ dopant was lower than 20 Ω·cm.

CrOx/CeO2 catalysts supported on porous silica sphere have been prepared and characterized by N2-BET, XRD, XPS, H2-TPR and NH3-TPD methods. The effects of the molar ratio between CrOx and CeO2 in the catalysts for NOx selective catalytic reduction with ammonia were studied. It was indicated by the results that high NOx conversion (98%) could be obtained by the catalyst with proper Cr/Ce molar ratio (25/75) at 150 °C (W/F = 0.25 g s/cm3). The result might be contributed to the redox property and NH3-chelate ability of the CrOx–CeO2 binary oxide in the catalysts.

The role of MoS2 as an effective interfacial layer in graphene/silicon solar cells is systematically investigated by varying MoS2 film annealing temperature and thickness. It is found that the power conversion efficiency (PCE) is increased by ∼100% from ∼2.3% to ∼4.4% with 80 °C annealed MoS2 film whereas it drops significantly to ∼0.6% with 200 °C annealed MoS2 film. The results are well explained based on the device energy band diagram. That is, the incorporation of MoS2(80) films leads to the formation of type II structure, facilitating hole transport; while valence band mismatch is formed with MoS2(200) films due to the increase in the work function of MoS2. Besides, the PCE increases gradually with decreasing MoS2 film thickness, and “saturates” at about 2 nm. The PCE can be further enhanced to ∼6.6% with the aid of silicon surface passivation. Our work demonstrates that MoS2 is an excellent interfacial layer to improve the PCE with low-temperature annealing (80 °C in air), which may be helpful in developing efficient and low-cost G/Si solar cells.

The hydrothermal growth of ZnO nanorods on graphene draws a specific interest for the advantages of low-temperature processability over a large area and low cost, but challenges still remain in directly growing uniform ZnO seed layers on pristine graphene without impairing its beneficial properties. In this work, the direct growth of ZnO seed layers on graphene via H2O-based atomic layer deposition (ALD) has been investigated. It is found that uniform ZnO thin films can be deposited on graphene via ALD using a combination of single-layer graphene/Cu stacks as substrates and a facile pre-H2O treatment process. After growing ZnO nanorods on graphene, its photovoltaic application in a Cu2ZnSn(SxSe1−x)4 (CZTSSe) solar cell is demonstrated. The performance of graphene-based cells approaches that of ITO-based cells with similar architectures, highlighting that graphene is a potential replacement for ITO in optoelectronic devices. The method reported herein for fabricating ZnO nanorods on graphene using ALD–ZnO as seed layers preserves its properties, and is thus applicable to a wide variety of graphene-based nanoelectronic devices.

We show that interface tailoring is an effective approach towards high performance G/Si Schottky-barrier solar cells. Inserting a thin graphene oxide (GO) interfacial layer can improve the efficiency of graphene/silicon solar cells by >100%. The role of the GO interfacial layer is systematically investigated by varying the annealing temperature and thickness of the GO film. It is found that GO cannot be treated as the common thought, i.e., an insulator. In other words, the G/GO/Si solar cell is not suitable to be treated as a “MIS” cell. In contrast, it should be regarded as a p-doped thin layer. The effects of GO film thickness on device response are also studied and there exists an optimal thickness for device performance. A record 12.3% (device size: 3 × 3 mm2) power conversion efficiency is achieved by further performance optimization (chemical doping graphene and antireflection coating).