Rusheng Yuan

A Templated Method to Bi2WO6 Hollow Microspheres and Their Conversion to Double-Shell Bi2O3/Bi2WO6 Hollow Microspheres with Improved Photocatalytic Performance

Bi(2)WO(6) hollow microspheres with dimension of ca. 1.5 μm were synthesized via a hydrothermal method using polystyrene particles as the template. The as-prepared Bi(2)WO(6) hollow microspheres can be further transformed to double-shell Bi(2)O(3)/Bi(2)WO(6) hollow microspheres. The samples were fully characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, N(2)-sorption Brunauer-Emmett-Teller surface area, UV-vis diffuse-reflectance spectroscopy, and X-ray photoelectron spectroscopy. The as-formed double-shell Bi(2)O(3)/Bi(2)WO(6) hollow microspheres exhibit enhanced photocatalytic activity due to the hollow nature and formation of the p-n junction between p-type Bi(2)O(3) and n-type Bi(2)WO(6). The study provides a general and effective method in the fabrication of composition and dimension-tunable composite hollow microspheres with sound heterojunctions that may show a variety of applications.

Facile One-Pot Solvothermal Method to Synthesize Sheet-on-Sheet Reduced Graphene Oxide (RGO)/ZnIn2S4 Nanocomposites with Superior Photocatalytic Performance

Highly reductive RGO (reduced graphene oxide)/ZnIn2S4 nanocomposites with a sheet-on-sheet morphology have been prepared via a facile one-pot solvothermal method in a mixture of N,N-dimethylformamide (DMF) and ethylene glycol (EG) as solvent. A reduction of GO (graphene oxide) to RGO and the formation of ZnIn2S4 nanosheets on highly reductive RGO has been simultaneously achieved. The effect of the solvents on the morphology of final products has been investigated and the formation mechanism was proposed. The as-prepared RGO/ZnIn2S4 nanoscomposites were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), N2-adsorption BET surface area, UV-vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM). The photocatalytic activity for hydrogen evolution under visible light irradiations over the as-prepared RGO/ZnIn2S4 nanocomposites has been investigated. The as-prepared RGO/ZnIn2S4 nanocomposites show enhanced photocatalytic activity for hydrogen evolution under visible light irradiations and an optimum photocatalytic activity is observed over 1.0 wt % RGO incorporated ZnIn2S4 nanocomposite. The superior photocatalytic performance observed over RGO/ZnIn2S4 nanocomposites can be ascribed to the existence of highly reductive RGO which has strong interactions with ZnIn2S4 nanosheets. The existence of the strong interaction between ZnIn2S4 nanosheets and RGO in the nancomposites facilitates the electron transfer from ZnIn2S4 to RGO, with the latter serving as a good electron acceptor, mediator as well as the co-catalyst for hydrogen evolution. This study can provide some guidance for us in the developing of RGO-incorporated nanocomposite photocatalysts.

Reduction degree of reduced graphene oxide (RGO) dependence of photocatalytic hydrogen evolution performance over RGO/ZnIn2S4 nanocomposites

Reduced graphene oxide (RGO)/ZnIn2S4 nanocomposites with RGO in different reduction degrees have been prepared and their photocatalytic performance for H2 evolution under visible light irradiation has been evaluated. The reduction degree of RGO in the RGO/ZnIn2S4 nanocomposite synthesized via a direct hydrothermal process was low and the resultant RGO/ZnIn2S4-hydrothermal exhibited lower photocatalytic performance for H2 evolution even when compared to pure ZnIn2S4. The reduction degree of RGO in the RGO/ZnIn2S4 nanocomposite can be increased by a further photoreduction or hydrazine reduction. These highly reductive RGO/ZnIn2S4 nanocomposites showed significantly enhanced photocatalytic activity for H2 production under visible light irradiation. Highly reduced RGO in the RGO/ZnIn2S4 nanocomposites serves as a good electron acceptor/mediator as well as the H2 evolution site to promote the photocatalytic water splitting over ZnIn2S4. A correlation between the photocatalytic performance for H2 evolution and the RGO reduction degree over RGO/ZnIn2S4 nanocomposites was shown for the first time. This study provides new insights in the developments of RGO-based nanocomposite materials for photocatalytic applications.

A simple and highly efficient route for the preparation of p-phenylenediamine by reducing 4-nitroaniline over commercial CdS visible light-driven photocatalyst in water

Highly efficient photocatalytic reduction of 4-nitroaniline to p-phenylenediamine over a commercial CdS photocatalyst was observed under visible light irradiation (λ ≥ 420 nm) in water. The conversion of 4-nitroaniline and the selectivity of p-phenylenediamine were ∼100% and ∼98% after 9 min of visible light irradiation, respectively. The photoreduction efficiency of 4-nitroaniline over the CdS photocatalyst remained above 95% in the 5th cycle of testing. Its photocatalytic activity was much higher than those of nitrogen-doped TiO2 and commercial TiO2 photocatalysts. Further experimental results revealed that the ammonium formate and N2 atmosphere were indispensable for the photocatalytic reduction of 4-nitroaniline over the CdS photocatalyst. On the basis of the results of electron spin resonance, photoexcited electrons and ·CO2− radicals were detected in the present system. These species had strong reductive powers, and were therefore able to efficiently reduce 4-nitroaniline to p-phenylenediamine.

Facile one-pot preparation of α-SnWO4/reduced graphene oxide (RGO) nanocomposite with improved visible light photocatalytic activity and anode performance for Li-ion batteries

α-SnWO4/reduced graphene oxide (RGO) nanocomposite was prepared via a facile one-pot hydrothermal reaction between GO, SnCl2·2H2O and (NH4)5H5[H2(WO4)6]·H2O. A simultaneous reduction of GO to RGO and the formation of nanocrystalline α-SnWO4 on RGO was achieved without using any extra reducing agent. The as-prepared α-SnWO4/RGO nanocomposite was fully characterized by X-ray diffraction (XRD), fourier transformation infrared spectroscopy (FT-IR), Raman, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and N2-sorption BET surface area. The photocatalytic performance of the sample was investigated by the decomposition of Methyl Orange (MO) under visible light irradiation. The electrochemical properties of α-SnWO4/RGO and α-SnWO4 as anode materials were revealed for the first time. α-SnWO4/RGO nanocomposite showed improved photocatalytic activity and enhanced anode performance for Li-ion batteries as compared to pure α-SnWO4.

Enhanced photocatalytic performances of TiO2-graphene hybrids on nitro-aromatics reduction to amino-aromatics

Graphene sheets have been considered as acceptors and transporters of photoinduced electrons generated from illuminated photocatalysts. Herein, we utilize these electrons with the help of graphene sheets in photocatalytic selective reduction. First, graphene-modified TiO2 hybrids are prepared by electrostatic assembly and in situ photocatalytic reduction processes using P25 and graphene oxide as precursors and then the photocatalytic reduction of nitro-aromatics to the corresponding amino-aromatics with these hybrids is examined under UV light irradiation. Results indicate that the addition of graphene sheets can effectively minimize the recombination of photogenerated charge carriers derived from the irradiated TiO2 and better encourage these separated electrons to participate in the reactions, which effectively improves the reduction ability of these TiO2-graphene hybrids in the presence of oxalic acid as hole scavengers. Besides the enhanced conversion rate, higher yields of amino-aromatics are achieved when using the graphene-modified TiO2 as a photocatalyst compared with those for pure TiO2.

Controlled preparation of In2O3, InOOH and In(OH)3via a one-pot aqueous solvothermal route

Pure cubic In2O3, orthorhombic InOOH and cubic In(OH)3 nanocrystals were separately synthesized via a one-pot aqueous solvothermal route at low temperature by simply regulating the amount of water in the ternary system H2O–DMF–In(NO3)3·4.5H2O.

Assembly of evenly distributed Au nanoparticles on thiolated reduced graphene oxide as an active and robust catalyst for hydrogenation of 4-nitroarenes

Thiol-functionalized reduced graphene oxide (SRG) was prepared by coupling the carboxyl groups on the pre-carboxyl-functionalized graphene oxide (GO) with cysteamines through amide bonds. The as-prepared SRG can function both as a support and reducing agent for the formation of Au/SRG nanohybrids with evenly distributed Au nanoparticles on RGO. The thiol linkage on the RGO can act as anchor for Au nanoparticles and due to the existence of the strong interaction between them, the agglomeration of Au nanoparticles can be significantly impeded. The step-by-step assembly process of the Au/SRG nanohybrid was monitored and the products obtained were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), atomic force microscopy (AFM), powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The as-prepared Au/SRG nanohybrid showed superior catalytic performance for the hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). It is expected that the method for the preparation of the Au/SRG nanohybrids can also be applied to the preparations of other RGO-based nanohybrid materials which may find a variety of interesting applications.

Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO2 Using DRS, PL, and EPR

The electronic structure and photoactivation process in N-doped TiO(2) is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat- and photoinduced N-doped TiO(2) catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti(3+) states are formed to enhance the optical absorption in the visible-light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N-doped TiO(2), the DRS absorption and PL emission in the visible spectral region of 450-700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N(s)·, oxygen vacancies with one electron (V(o)·), and Ti(3+) ions are produced with light irradiation and the intensity of N(s)· species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO(2) corresponding to the main absorption band at 410 nm of N-doped TiO(2), but oxygen vacancies and Ti(3+) states as defects contribute to the visible-light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N-doped TiO(2) is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen-vacancy-related defects leads to quenching of paramagnetic N(s)· species but they stabilize the active nitrogen species N(s)(-).

Modulating Crystallinity of Graphitic Carbon Nitride for Photocatalytic Oxidation of Alcohols

Exploiting efficient photocatalysts with strengthened structure for solar-driven alcohol oxidation is of great significance. The photocatalytic performance of graphitic carbon nitrides can be considerably promoted by modulating its crystallinity. Results confirmed that a high crystallinity accelerates the separation and transfer of photogenerated charge carriers, thus providing more free charges for photoredox reactions. More importantly, the high crystallinity facilitated the adsorption of benzyl alcohol and desorption of benzaldehyde and simultaneously lowered the energy barrier for O2 activation. As a result, the crystalline carbon nitride exhibited a roughly twelvefold promotion with respect to the normal carbon nitride. The remarkable enhancement of activity can be attributed to the synergistic effects of increased electron-hole separation and increased surface reaction kinetics. These findings will open up new opportunities to modulate the structure of polymers for a wide variety of organic reactions.