The development of a facile, low-cost, and eco-friendly approach to the synthesis of aromatic amines remains a great scientific challenge. TiO2, as a low-cost and earth abundant metal oxide, is usually not active for thermo-catalyzed nitro reduction. Herein, we report a composite nanosheet catalyst, composed of nitrogen-doped TiO2 and carbon (N-TiO2@C), which exhibits highly efficient, thermo-catalytic performance for selective nitroaromatic reduction at room temperature. The N-TiO2@C nanosheet catalyst is synthesized via a facile approach where C3N4 nanosheets are utilized not only as a structure-directing agent to control the shape, size, and crystal phase of TiO2 but also as a source of nitrogen for doping into both TiO2 and carbon nanosheets. Furthermore, the origin of the superior performance of the N-TiO2@C nanosheet composite catalyst, along with a possible nitroaromatic reduction mechanism, has also been explored.Keywords: nanosheets; nitro reduction; nitrogen doping; noble metal free; TiO2;

The controlled synthesis of strontium carbonate (SrCO3) micro-/nanostructures with various morphologies, such as sphere, pompon, arborization, spindle, and hexagonal prism, are successfully achieved through rather facile hydrothermal processes. The morphology of SrCO3 can be elegantly adjusted by employing different CO32− sources and controlling the viscidity of the organic solvents. The underlying mechanism of morphology evolution is discussed. Moreover, the SrCO3-loaded TiO2 (SrCO3/TiO2) nanocomposites are shown to improve the activity for oxidizing hydrocarbon gases under simulated solar light irradiation. The 5.0 wt% SrCO3 (nanosphere)/TiO2 exhibited the highest performance toward the oxidation of the hydrocarbons gases, and its activity on methane oxidation is more than double that of P25 TiO2. These results are valuable for both carbonate synthesis and their use in the oxidation of hydrocarbons gases.

•In2O3-Ag-Ag3PO4 composites with Z-scheme configuration are fabricated.•The photocatalysts show efficient activities toward ethylene degradation under visible light irradiation.•The stability of Ag3PO4 was obviously improved.•The reaction process of ethylene photodegradation was investigated by in-situ IR.Photocatalytic degradation of ethylene under visible light remains a challenge at the frontiers of chemistry. In this study, In2O3-Ag-Ag3PO4 composite semiconductors with Z-scheme configuration were fabricated for the first time by in-situ synthesis of Ag3PO4 on In2O3 and subsequent photoreduction of Ag3PO4 to generate nano silver. Their performances on photocatalytic degradation of ethylene under visible light illumination were investigated. Results demonstrated that both the activity of ethylene photocatalytic degradation and Ag3PO4 photostabilization are considerably improved by making such a Z-scheme composite. According to the material design perspective and the application in the field of environmental pollutant remediation, the present research will provide potential value for further study on the removal of HC (Hydrocarbons) from the atmosphere and the stability concern of Ag3PO4 and other materials with photocorrosion.Download high-res image (122KB)Download full-size image

Efficient separation and extraction of photo-induced carriers are crucial aspects of efficient semiconductor photocatalytic systems employed for photocatalytic oxidation (PCO) technology. In this study, a Pt-loaded KSr2Nb5O15 composite, as a novel photocatalyst, is reported for gaseous ethylene photo-oxidation, performing excellent PCO activity. Tungsten bronze-type KSr2Nb5O15 (KSNO) with surface oxygen vacancies is prepared by a facile and low-cost molten salt synthesis method at 1200 °C for 6 h and a possible morphology evolution process was proposed. Pt was loaded on KSNO through a facile photodeposition method. The strong metal–support interaction (SMSI) between the Pt nanoparticles and the oxygen-deficient KSNO support is beneficial for superior photocatalytic efficiency and stability toward ethylene photo-oxidation. What's more, the structure and charge transfer path in the synthesized photocatalysts were investigated by X-ray photoelectron spectroscopy (XPS), high-resolution electron microscopy, and electron paramagnetic resonance (EPR).

Organic–inorganic hybrid materials crystallized in noncentrosymmetric (NCS) structures have been receiving considerable attention due to their fascinating physical properties and promising applications. Herein, bulk single crystals of an NCS organometallic compound, MnHg(SCN)4 (MMTC), are grown via a temperature lowering method. The grown crystals present negative uniaxial characteristics with large birefringence, good optical homogeneity and high thermal conductivities. In addition, their Raman scattering properties are measured using spontaneous Raman spectroscopy, which show that the MMTC crystal exhibits a large Raman shift (2148.1 cm−1), narrow line-width (4.468 cm−1) and high Raman gain coefficient (1.753 times higher than that of crystalline YVO4). Moreover, the direct current conductivity, dielectric, and piezoelectric constants of MMTC are also measured, which display that the crystal also possesses a strong piezoelectric response of d15 = 22.7 pC N−1. Furthermore, structure property relationships are discussed on the basis of the structure of the crystal. As a multi-functional crystal, MMTC is a particularly promising candidate for stimulated Raman scattering in the visible and near-infrared regions and piezoelectric applications at room temperature.

Ceramics of the Bi(Ni3/4W1/4)O3–PbTiO3 (BNW–PT) ferroelectric system were synthesized using a conventional solid-state sintering process. A morphotropic phase boundary (MPB) region separating tetragonal and rhombohedral phases has been determined based on X-ray diffraction (XRD) analysis. The composition-dependent phase transition behavior, thermal expansion, di/ferro/piezoelectric properties have been systemically investigated. The volume TECs (thermal expansion coefficients) for 0.1BNW–0.9PT and 0.2BNW–0.8PT are −1.01 × 10−5 per °C and −0.94 × 10−5 per °C, respectively, indicating the negative thermal expansion of some compositions for the binary system. The BNW–PT ceramics have Curie temperatures, TC, ranging from 460 °C to ∼152 °C with the variation of BNW constituent. The tetragonal-rich composition 0.20BNW–0.80PT is found to have the largest remnant polarization, Pr ∼ 23.4 μC cm−2. The highest piezoelectric coefficient d33 ∼ 145 pC N−1 is achieved at MPB composition 0.32BNW–0.68PT. The maximum strain value ∼0.194% is also obtained in the 0.32BNW–0.68PT ceramic.

Ferroelectric perovskites have attracted extensive attention recently, because of their fascinating physical properties and novel characteristics owing to the coupling of electric polarization with other functional properties. Herein, single crystals of a bismuth layered-perovskite ferroelectric oxide Bi2WO6 (BWO) were grown by a flux growth method. The grown crystals exhibit platelet morphology with a dominant (001) orientation face. The linear and nonlinear optical properties of BWO crystals were studied in detail. The optical transmittance spectrum shows that BWO is a direct transition semiconductor with a band gap of 2.75 eV and a wide transmission window up to 5 μm. Second harmonic generation (SHG) measurements indicate that the crystal is also a phase matchable nonlinear optical material with a large SHG response of approximately 2.1 times that of KH2PO4. The dielectric and ferroelectric properties measured perpendicular to the ab plane exhibit an oxygen vacancy associated dielectric loss peak and a non-ferroelectric P–E loop. Moreover, we found that the BWO crystal possesses a significant photoresponse in the broadband wavelength of visible light, showing fast response (<0.1 s), high ON/OFF current ratio (>103), excellent flexibility and robustness. The origin of physical properties was interpreted on the basis of the crystal structure combined with density functional theory (DFT) calculations. The BWO single crystals with large SHG response, rich electrical behavior and broad spectral photoresponse are promising materials for nonlinear optical, electrical and optoelectronic applications.

We report herein a C3N4 templating method for successfully synthesizing defective, porous TiO2 nanosheets with Pt decoration as an efficient photocatalyst for C2H4 oxidation. During the synthetic procedure, C3N4 not only acts as a 2D template to direct synthesize porous TiO2 nanosheets (TiO2-NS) but also facilitates oxygen vacancy formation on TiO2. The resultant TiO2-NS shows enhanced UV and visible-light photoactivities toward C2H4 oxidation as compared to blank TiO2 (TiO2-B) prepared without C3N4 template. Subsquently, Pt nanoparticles are homogeneously decorated onto the surface of TiO2-NS. The as-obtained Pt-TiO2-NS exhibits efficient photocatalytic activity and stability toward ethylene oxidation.Keywords: C3N4; ethylene oxidation; oxygen vacancy; photocatalysis; TiO2

Highly active Pt/TiO2 catalysts were prepared by a simple photo-reduction method and used for catalytic oxidation of alkanes (C2H6 and C3H8) and alkenes (C2H4 and C3H6). It was found that significantly improved photo-activity can be reached even by loading a very small amount of Pt (0.2–0.5 wt%). Moreover, the Pt loading resulted in unexpected visible light activity for the oxidation of small molecule hydrocarbons. Further investigation using photoluminescence spectra indicate that the Pt loading helps reduce the charge carrier recombination within the TiO2 nanoparticles. Electron Paramagnetic Resonance (EPR) spectra reveal both oxygen molecules and lattice oxygen participate in the hydrocarbons' photooxidation. The transfer and reaction mechanisms of charge carriers during the photo-oxidation process are discussed in detail.

•The photocurrent and IPCE of YxBi1-xVO4 thin film electrode are investigated for the first time.•YxBi1-xVO4 thin films exhibit photoinduced hydrophilicity.•Photoelectrocatalytic activity of Y0.05Bi0.95VO4 thin film electrode is investigated.Y3+ doped BiVO4 powder has been shown the potential to be an efficient photocatalyst for water splitting and hydrocarbon gas degradation. However, the photoelectric property of YxBi1-xVO4 has not been investigated. What’s more, in some special fields, it is vital to apply thin film and it is electrode instead of powder due to some kind of necessity, such as thin film solar cell and photoelectrocatalysis. Also, there is less report on the photoelectric and photocatalytic properties of Y3+ doped BiVO4 thin film. Here, relatively dense and flat YxBi1-xVO4 thin film was in-situ fabricated on FTO substrate by using a solution polymeric method. It was found that by increasing Y3+ content, the crystalline phase of the YxBi1-xVO4 thin film changed from monoclinic and tetragonal mixture phase to tetragonal solid solution phase, and the conduction band of YxBi1-xVO4 film showed more negatively shift. For the first time, we extensively investigated the photocurrent, incident photon to current efficiency (IPCE) and photoinduced hydrophilicity properties of YxBi1-xVO4 thin film electrode. Their corresponding electrochemical impedance spectroscopy, which revealed charge transfer characteristics were studied simultaneously. Due to the excellent photoelectric performance, the Y0.05Bi0.95VO4 (composite of monoclinic BiVO4 and tetragonal YVO4) thin film electrode exhibited the best photocatalytic activity to degrade Rhodamine B in water than other thin film electrodes.The Y0.05Bi0.95VO4 thin film electrode exhibited highest photocurrent density and photoelectrocatalytic activities on the decomposition of RhB.

Photocatalytic oxidation of ethylene continues to be a challenge at the frontier of chemistry. Previous investigations have shown that BiVO4 possesses strong photo-oxidative properties which can efficiently oxidize water and decompose organics in aqueous solutions; however, its conduction band minimum is too low to utilize the photo-generated electrons. Herein we report for the first time its effects on gaseous C2H4 photo-oxidation by fabricating YxBi1−xVO4 (x = 0.00–1.00) semiconductors with a polymeric method. Phase analysis identified that there are both a region of monoclinic and tetragonal phase coexistence (0.05 ≤ x ≤ 0.45) and a solid solution region (0.5 ≤ x ≤ 1.0). UV-visible diffusive reflectance spectra and Mott–Schottky analysis revealed that the incorporation of Y3+ widened the band gap by shifting upward the conduction band minimum as well as shifting downward the valance band maximum. Remarkable C2H4 photodegradation was obtained upon the Y0.85Bi0.15VO4 photocatalyst and its superior performance is ascribed to the synergistic effect of C2H4 adsorption, active oxygen species ˙O2− utilization, and relatively large surface area. The present study will be valuable for further investigation on both BiVO4 and hydrocarbons (HC) degradation.

A facile, one-step hydrothermal method has been developed to fabricate tin oxide–reduced graphene oxide (Sn–RGO) nanocomposites with tunable composition, morphology, and energy band structure by utilizing graphene oxide (GO) as a multifunctional two-dimensional scaffold. By adjusting the GO concentration during synthesis, a variety of tin oxide nanomaterials with diverse composition and morphology are obtained. Simultaneously, the varying of GO concentration can also narrow the bandgap and tune the band edge positions of the Sn–RGO nanocomposites. As a result, the Sn–RGO nanocomposites with controllable composition, morphology, and energy band structure are obtained, which exhibit efficient photoactivities toward methyl orange (MO) degradation under visible-light irradiation. It is expected that our work would point to the new possibility of using GO for directing synthesis of semiconductor nanomaterials with tailored structure and physicochemical properties.Keywords: composition modulation; graphene oxide; morphology control; tin oxide; visible-light photocatalysis

Nano Cu2O/TiO2 heterojunctions with different weight percentage of Cu2O were fabricated by a facile impregnating method for propane oxidation at room temperature. The results indicate that the as-formed Cu2O/TiO2 heterojunctions can remarkably improve the propane photooxidation activity. Especially, for the 0.1 wt% Cu2O decorated TiO2 junctions, the activity was triple of that of the commercial P25. Moreover, the stability of Cu2O was significantly improved during the HC photooxidation. A direct Z scheme electrons and holes transfer mode was suggested to account for the improved activity as well as stability of the junctions. This study may provide a new way to improve photocatalytic activities by utilizing cheap and less stable materials.

How to promote separation of photo-generated carriers is one of the key issues determining the photocatalytic activity of a semiconductor. In this paper, we report a new strategy that utilizing an internal electric field of polar semiconductors to improve photocatalytic activity and, proving it by liquid-phase photodegradation (photocatalytic RhB degradation) as well as gas-phase photodegradation (photocatalytic oxidation of CH4) experiments upon the self-assembled NaNbO3 oriented nanocuboids that were fabricated by a facial hydrothermal route. The formation conditions and mechanisms of the ordered nanostructures were also discussed.

Various potassium niobate (KNbO3) nanostructures, including nanowires, nanotowers, nanocubes and nanorods, were successfully fabricated through rather facile hydrothermal processes. By adjusting the concentration of potassium hydroxide, reaction temperature and reaction time, the product morphologies can be easily controlled. High crystallinity as well as the active (001) crystal plane exposed on KNbO3 nanocrystals offer enhanced photocatalytic activity for rhodamine B decomposition in aqueous solutions under UV-visible light irradiation. The level of photocatalytic activity depends strongly on the microstructure of KNbO3 and the photoreactivity towards RhB degradation follows the order of KNbO3 nanocubes > nanowires > nanorods > nanotowers. The KNbO3 nanocubes prepared at 200 °C for 7 days in the presence of 6.5 M KOH exhibited the enhanced photocatalytic performance for the degradation of RhB to 89% after 240 min of irradiation under a sunlight simulator.

•High performance BCTS ceramics were fabricated by an improved method and systematically characterized.•The electric field and temperature dependences of electrical properties for BCTS ceramics were carried out.•BCTS multilayer actuators with various layers were, for the first time, fabricated.In this study, an improved method was developed for the preparation of lead-free (Ba1−xCax)(Ti0.91Sn0.09)O3 (BCTS) (0.02 ≤ x ≤ 0.07) ceramics by combining the conventional solid-state reaction with a gel precursor mixing method. The effects of Ca content on the microstructural, dielectric, impedance, piezoelectric and ferroelectric properties of the ceramics were systematically investigated. Dense ceramics with a uniform distribution of grain size and sharp grain boundaries were developed. Extremely high electrical properties of d33 ∼620 pC/N, kp ∼46% and ε ∼14500 were obtained at x = 0.03. A dielectric loss peak was observed, correlating to the oxygen vacancy relaxation at elevated temperature. Moreover, the dielectric properties vs. DC bias electric field and the temperature dependences of electrical properties were studied as well. Lastly, BCTS-based monolithic multilayer piezoelectric actuators were successfully fabricated showing large displacements under low driven voltages. These results would be valuable for understanding the electric properties of BCTS ceramics that would in turn extend their applications in multilayer piezoelectric devices.

Because of the high C–H bond energy as well as the non-polar feature of CH4 molecules, oxidation of methane under mild conditions remains a challenging task for both C1 utilization and atmospheric environmental cleansing. Here we report that by using a sol–gel method SrCO3 decorated SrTiO3 nanocatalysts (SrTiO3-S) with an average particle size of ∼25 nm can be readily prepared, which surprisingly show efficient performance for photocatalytic oxidation of methane with the activity close to fourfold of P25, a benchmark photocatalyst. Further investigation revealed a synergistic effect between SrCO3 and SrTiO3 when combined together into a composite material as both of which are totally inactive for methane oxidation if used alone. Gas adsorption characterization disclosed that the SrCO3 can adsorb methane and cannot adsorb carbon dioxide, whereas the SrTiO3 will preferentially adsorb CO2 instead of CH4. Photocurrent and photoluminescence measurements indicate that SrCO3 exhibits a negligible photocurrent response relative to the SrTiO3 semiconductor under simulated solar light illumination but the formation of the SrCO3/SrTiO3 junction structure (SrTiO3-S) helps reduce surface recombination of the photogenerated electrons and holes. All these results refer to the synergistic mechanism in which the SrCO3 acts as a trapping agent to adsorb methane and weaken its C–H bond while the SrTiO3 acts as a photocatalyst to activate and oxidize methane under light illumination. The underlying photooxidation mechanism is further investigated with the aid of in situ electron paramagnetic resonance and infrared spectroscopy.

Organic–inorganic hybrid materials crystallized in noncentrosymmetric (NCS) structures have been receiving considerable attention due to their fascinating physical properties and promising applications. Herein, bulk single crystals of an NCS organometallic compound, MnHg(SCN)4 (MMTC), are grown via a temperature lowering method. The grown crystals present negative uniaxial characteristics with large birefringence, good optical homogeneity and high thermal conductivities. In addition, their Raman scattering properties are measured using spontaneous Raman spectroscopy, which show that the MMTC crystal exhibits a large Raman shift (2148.1 cm−1), narrow line-width (4.468 cm−1) and high Raman gain coefficient (1.753 times higher than that of crystalline YVO4). Moreover, the direct current conductivity, dielectric, and piezoelectric constants of MMTC are also measured, which display that the crystal also possesses a strong piezoelectric response of d15 = 22.7 pC N−1. Furthermore, structure property relationships are discussed on the basis of the structure of the crystal. As a multi-functional crystal, MMTC is a particularly promising candidate for stimulated Raman scattering in the visible and near-infrared regions and piezoelectric applications at room temperature.

Iron-nickel oxide porous nanosheets were synthesized via a controlled transformation from LDH precursors, which exhibit advanced OER performance with a low overpotential of 213 mV at 10 mA cm−2, small Tafel slope (32 mV dec−1) and long-term stability, due to their high specific surface area, abundant active sites, small charge transfer resistance, and suitable adsorption energy for intermediates.

Photocatalytic oxidation of ethylene continues to be a challenge at the frontier of chemistry. Previous investigations have shown that BiVO4 possesses strong photo-oxidative properties which can efficiently oxidize water and decompose organics in aqueous solutions; however, its conduction band minimum is too low to utilize the photo-generated electrons. Herein we report for the first time its effects on gaseous C2H4 photo-oxidation by fabricating YxBi1−xVO4 (x = 0.00–1.00) semiconductors with a polymeric method. Phase analysis identified that there are both a region of monoclinic and tetragonal phase coexistence (0.05 ≤ x ≤ 0.45) and a solid solution region (0.5 ≤ x ≤ 1.0). UV-visible diffusive reflectance spectra and Mott–Schottky analysis revealed that the incorporation of Y3+ widened the band gap by shifting upward the conduction band minimum as well as shifting downward the valance band maximum. Remarkable C2H4 photodegradation was obtained upon the Y0.85Bi0.15VO4 photocatalyst and its superior performance is ascribed to the synergistic effect of C2H4 adsorption, active oxygen species ˙O2− utilization, and relatively large surface area. The present study will be valuable for further investigation on both BiVO4 and hydrocarbons (HC) degradation.

Various potassium niobate (KNbO3) nanostructures, including nanowires, nanotowers, nanocubes and nanorods, were successfully fabricated through rather facile hydrothermal processes. By adjusting the concentration of potassium hydroxide, reaction temperature and reaction time, the product morphologies can be easily controlled. High crystallinity as well as the active (001) crystal plane exposed on KNbO3 nanocrystals offer enhanced photocatalytic activity for rhodamine B decomposition in aqueous solutions under UV-visible light irradiation. The level of photocatalytic activity depends strongly on the microstructure of KNbO3 and the photoreactivity towards RhB degradation follows the order of KNbO3 nanocubes > nanowires > nanorods > nanotowers. The KNbO3 nanocubes prepared at 200 °C for 7 days in the presence of 6.5 M KOH exhibited the enhanced photocatalytic performance for the degradation of RhB to 89% after 240 min of irradiation under a sunlight simulator.

Ferroelectric perovskites have attracted extensive attention recently, because of their fascinating physical properties and novel characteristics owing to the coupling of electric polarization with other functional properties. Herein, single crystals of a bismuth layered-perovskite ferroelectric oxide Bi2WO6 (BWO) were grown by a flux growth method. The grown crystals exhibit platelet morphology with a dominant (001) orientation face. The linear and nonlinear optical properties of BWO crystals were studied in detail. The optical transmittance spectrum shows that BWO is a direct transition semiconductor with a band gap of 2.75 eV and a wide transmission window up to 5 μm. Second harmonic generation (SHG) measurements indicate that the crystal is also a phase matchable nonlinear optical material with a large SHG response of approximately 2.1 times that of KH2PO4. The dielectric and ferroelectric properties measured perpendicular to the ab plane exhibit an oxygen vacancy associated dielectric loss peak and a non-ferroelectric P–E loop. Moreover, we found that the BWO crystal possesses a significant photoresponse in the broadband wavelength of visible light, showing fast response (<0.1 s), high ON/OFF current ratio (>103), excellent flexibility and robustness. The origin of physical properties was interpreted on the basis of the crystal structure combined with density functional theory (DFT) calculations. The BWO single crystals with large SHG response, rich electrical behavior and broad spectral photoresponse are promising materials for nonlinear optical, electrical and optoelectronic applications.