Jun Dai

Visible-light-induced photocatalytic reduction of Cr(VI) with coupled Bi2O3/TiO2 photocatalyst and the synergistic bisphenol A oxidation.

Coupled Bi2O3/TiO2 photocatalysts were fabricated by sol–gel and hydrothermal methods and characterized using various spectroscopy techniques. Photocatalytic reduction of Cr(VI) in aqueous solution, together with the synergistic effect of photodegradation of bisphenol A (BPA), was investigated using these coupled Bi2O3/TiO2 under visible-light irradiation. Coupling of Bi2O3 inhibited the phase transformation from anatase to rutile and extended absorption region to visible light. Bi ions did not enter TiO2 lattice and were more likely to bond with oxygen atoms to form Bi2O3 on the surface of TiO2. Photovoltage signals in visible range revealed the effective interfacial charge transfer between Bi2O3 and TiO2. Two percent Bi2O3/TiO2 exhibited the highest photocatalytic activity of visible-light-induced reduction of Cr(VI). The addition of BPA effectively increased the photocatalytic reduction of Cr(VI). Simultaneously, the presence of Cr(VI) promoted the degradation of BPA, which was demonstrated by the investigation of TOC removal yield and generated intermediates. A possible mechanism of photocatalytic reduction of Cr(VI) and degradation of BPA in Bi2O3/TiO2 system was proposed. The synergistic effect, observed between reduction of Cr(VI) and degradation of BPA, provides beneficial method for environmental remediation and purification of the complex wastewater.

Enhanced photocatalytic activities of visible-light driven green synthesis in water and environmental remediation on Au/Bi2WO6 hybrid nanostructures

A series of Au/Bi2WO6 nanocomposites with different weight ratios of Au were fabricated via a hydrothermal combined with a rapid reduction–deposition method. Au/Bi2WO6 nanocomposites are proven to serve as selective visible light photocatalysts toward aerobic oxidation of benzylic alcohols and reduction of heavy ions Cr(VI), instead of being nonselective in water. Loading Au NPs greatly enhances the photocatalytic activity of Bi2WO6 for the selective oxidation of alcohols and reduction of heavy metal ions. The enhancing effect is dependent on the weight ratios of Au to Bi2WO6 in the hybrid nanostructures. The optimal catalysts for alcohol oxidation and Cr(VI) reduction are 2.0 wt% and 1.0 wt% Au/Bi2WO6, respectively. Furthermore, we find that loading Au results in an obvious increase in photo-induced generation of charge carriers and active radicals determined by electron spin resonance spectroscopy (ESR). ESR signals denoting photogenerated holes and catalytic activity of alcohol oxidation have a similar dependence on the amounts of Au loading. Besides, the generation and transfer of photogenerated electrons induced by Au loading, as well as the relationship with the photocatalytic activity of Cr(VI) reduction, have been examined using photoelectrochemical characterization. The possible roles of Au deposition in improving the photocatalytic redox activity of Bi2WO6 are also discussed.

Bismuth Tungstate-Reduced Graphene Oxide Self-Assembled Nanocomposites for the Selective Photocatalytic Oxidation of Alcohols in Water

The selective conversion of alcohol into aldehyde in water was achieved over Bi2WO6‐reduced graphene oxide (RGO) photocatalysts. The Bi2WO6‐RGO‐H catalysts were synthesized by an electrostatic self‐assembly method followed by hydrothermal reduction. It was found the valence band and conduction band edges of Bi2WO6‐RGO‐H underwent a continuous increase in energy with the increasing weight ratio of graphene oxide, which resulted in a high selectivity to aldehydes. Furthermore, Bi2WO6‐RGO samples with different degrees of reduction of RGO were prepared, and the conversion of alcohol was influenced greatly by the RGO reduction degree. Based on the results of photo‐electrochemistry and photoluminescence spectroscopy, the clear enhancement in alcohol conversion can be ascribed to the efficient separation of photogenerated charge carriers, which results from the fast migration of photoelectrons between excited Bi2WO6 and highly reduced RGO. Additionally, based on the results of radical‐trapping and ESR spectroscopy, the primary reactive species and a plausible pathway for alcohol oxidation over Bi2WO6‐RGO were proposed.

In-Situ Synthesis of Hydrogen Titanate Nanotube/Graphene Composites with a Chemically Bonded Interface and Enhanced Visible Photocatalytic Activity

Hydrogen titanate nanotube (HTT)/graphene nanocomposites are synthesized by hydrothermal reduction of graphene oxide (GO) and simultaneous preparation of nanotubular HTT via an alkaline hydrothermal process. By using this facile in-situ compositing strategy, HTT are densely supported upon the surface of graphene sheets with close interface contacts. The as-prepared HTT/graphene nanocomposites possess significantly enhanced visible light catalytic activity for the partial oxidation of benzylic alcohols. The amount of graphene has significant influence on catalytic activity and the optimal content of graphene is 1.0 wt %, giving a normalized rate constant k of 1.71 × 10−3 g/m2·h, which exceeds that of pure HTT and HTT/graphene-1.0% mixed by a factor of 7.1 or 5.2. Other than the general role of graphene as a high-performance electron acceptor or transporter, the observed enhancement in photocatalytic activity over HTT/graphene can be ascribed to the improved interfacial charge migration from enhanced chemical bonding (Ti–C bonds) during the in-situ compositing process. The formation of Ti–C bonds is confirmed by XPS analysis and the resulting enhanced separation of photoinduced charge carriers is demonstrated by electrochemical impedance spectra and transient photocurrent response.

Efficient photocatalytic oxidation of methane over β-Ga2O3/activated carbon composites

Efficient oxidation of methane over heterogeneous catalysts under ambient conditions is still a challengeable study toward C1 utilization and atmospheric cleansing. In this study, by using a hydrolysis method combined with an impregnation process, β-Ga2O3 nanoparticles supported uniformly on activated carbon (AC) can be obtained readily. The as-prepared Ga2O3/AC composites show efficient performance for photocatalytic oxidation of CH4 under ultraviolet irradiation. The experimental results indicate that photocatalytic activity toward CH4 oxidation is strongly dependent on the weight ratio of Ga2O3 to AC. 15%-Ga2O3/AC exhibits the highest catalytic activity, which is more than sixfold of P25, a benchmark photocatalyst. The photoluminescence spectra show the decreased recombination centers and the diminished recombination of photo-generated electrons (e−) and holes (h+) when Ga2O3 nanoparticles were deposited on AC. Further investigation reveals that the excellent photo-oxidation activity for CH4 over Ga2O3/AC can be ascribed to a synergistic effect involving strong adsorption capacity and improved separation of photo-generated e−/h+ pairs. Moreover, the photocatalytic oxidation of CH4 obeys pseudo-first-order kinetics and the cycling experiment indicates that Ga2O3/AC composites possess stable photocatalytic performance for CH4 oxidation. The underlying photo-oxidation mechanism is also investigated using electron paramagnetic resonance (ESR) and radical scavenging experiments. This study demonstrates that photocatalysis with Ga2O3/AC is a highly efficient method toward the oxidation of low concentrations of CH4, which provides valuable information for atmospheric environmental cleansing.

Bis(benzoato-κO,O')(1,10-phenanthroline-κN,N')lead(II) benzoic acid mono-solvate.

The reaction of lead acetate, benzoic acid and 1,10-phenanthroline (phen) in aqueous solution yielded the title complex, [Pb(C7H5O2)2(C12H8N2)]·C7H6O2. In the crystal, the PbII ion is hexacoordinated by two N atoms from one 1,10-phenanthroline ligand and four O atoms from two chelate benzoate anions. If the second benzoate ligand is treated as one coordination site, the overall coordination may be represented as a distorted pseudo-square pyramid. An intermolecular O—H⋯O hydrogen bond links the solvent benzoic acid molecule with a metal-coordinated benzoate ligand. The shortest Pb⋯Pb distance is 3.864u2005(4)u2005Å, indicating a weak metal–metal interaction. Two complex molecules related by an inversion centre form dimeric units via Pb⋯O interactions of 3.206u2005(4)u2005Å.

Facile Synthesis of Novel CaIn2S4/ZnIn2S4 Composites with Efficient Performance for Photocatalytic Reduction of Cr(VI) under Simulated Sunlight Irradiation

A series of novel and efficient heterostructured composites CaIn2S4/ZnIn2S4 have been synthesized using a facile hydrothermal method. XRD patterns indicate the as-prepared catalysts are two-phase composites of cubic phase CaIn2S4 and hexagonal phase ZnIn2S4. FESEM (field emission scanning electron microscope) images display that the synthesized composites are composed of flower-like microspheres with wide diameter distribution. UV–Vis diffuse reflectance spectra (DRS) show that the optical absorption edges of the CaIn2S4/ZnIn2S4 composites shift toward longer wavelengths with the increase of the CaIn2S4 component. The photocatalytic activities of the as-synthesized composites are investigated by using the aqueous-phase Cr(VI) reduction under simulated sunlight irradiation. This is the first report on the application of the CaIn2S4/ZnIn2S4 composites as stable and efficient photocatalysts for the Cr(VI) reduction. The fabricated CaIn2S4/ZnIn2S4 composites possess higher photocatalytic performance in comparison with pristine CaIn2S4 or ZnIn2S4. The CaIn2S4/ZnIn2S4 composite with a CaIn2S4 molar content of 30% exhibits the optimum photocatalytic activity. The primary reason for the significantly enhanced photoreduction activity is proved to be the substantially improved separation efficiency of photogenerated electrons/holes caused by forming the CaIn2S4/ZnIn2S4 heterostructured composites. The efficient charge separation can be evidenced by steady-state photoluminescence spectra (PLs) and transient photocurrent response. Based on the charge transfer between CaIn2S4 and ZnIn2S4, an enhancement mechanism of photocatalytic activity and stability for the Cr(VI) reduction is proposed.