Difa Xu

Photocatalytic activity of Ag2MO4 (M = Cr, Mo, W) photocatalysts

Ag-containing semiconductors have attracted significant attention because of their unique photosensitivity that provides these materials with visible-light photocatalytic activity. This study systematically investigates the correlation among the photophysicochemical performance, crystal structure, electronic structure, and photocatalytic activity and stability of three Ag-containing photocatalysts Ag2MO4 (M = Cr, Mo, W) prepared by microemulsion based on experimental and theoretical results. The results showed that the photocatalytic activity and stability of the three photocatalysts strongly depend on the light absorption performance of these photocatalysts. Ag2CrO4 had the best light absorption performance, exhibiting the highest photocatalytic activity for methylene blue degradation under visible-light irradiation that is 3.5 and 1.5 times that of Ag2MoO4 and Ag2WO4, respectively. Meanwhile, the photocatalytic stability followed the same light absorption performance order. The theoretical calculation showed that a stronger crystal field and a smaller Ag–O distance lower the conduction band bottom of Ag2CrO4 and Ag2WO4, respectively. This reduction in the conduction band caused the band gap, light-absorption, and subsequent photocatalytic activity and stability of these photocatalysts to differ. The present work contributes to deeply understand and feasibly construct Ag-containing photocatalysts with high photocatalytic activity.

Hybrid carbon@TiO2 hollow spheres with enhanced photocatalytic CO2 reduction activity

Photocatalytic conversion of carbon dioxide (CO2) into solar fuels is an attractive strategy for solving the increasing energy crisis and greenhouse effect. This work reports the synthesis of hybrid carbon@TiO2 hollow spheres by a facile and green method using a carbon nanosphere template. The carbon content of the carbon@TiO2 composites was adjusted by changing the duration of the final calcination step, and was shown to significantly affect the physicochemical properties and photocatalytic activity of the composites. The optimized carbon@TiO2 composites exhibited enhanced photocatalytic activity for CO2 reduction compared with commercial TiO2 (P25): the photocatalytic CH4 production rate (4.2 μmol g−1 h−1) was twice that of TiO2; moreover, a large amount of CH3OH was produced (at a rate of 9.1 μmol g−1 h−1). The significantly improved photocatalytic activity was not only due to the increased specific surface area (110 m2 g−1) and CO2 uptake (0.64 mmol g−1), but also due to a local photothermal effect around the photocatalyst caused by the carbon. More importantly, UV-vis diffuse reflectance spectra (DRS) showed a remarkable enhancement of light absorption owing to the incorporation of the visible-light-active carbon core with the UV light-responsive TiO2 shell for increased solar energy utilization. Furthermore, electrochemical impedance spectra (EIS) revealed that the carbon content can influence the charge transfer efficiency of the carbon@TiO2 composites. This study can bring new insights into designing carbon@semiconductor nanostructures for applications such as solar energy conversion and storage.

Effects of the preparation method on the structure and the visible-light photocatalytic activity of Ag2CrO4

Summary Silver chromate (Ag2CrO4) photocatalysts are prepared by microemulsion, precipitation, and hydrothermal methods, in order to investigate the effect of preparation methods on the structure and the visible-light photocatalytic activity. It is found that the photocatalytic activity of the prepared Ag2CrO4was highly dependent on the preparation methods. The sample prepared by microemulsion method exhibits the highest photocatalytic efficiency on the degradation of methylene blue (MB) under visible-light irradiation. The enhanced photocatalytic activity could be ascribed to the smaller particle size, higher surface area, relatively stronger light absorption, and blue-shift absorption edge, which result in the adsorption of more MB molecules, a shorter diffusion process of more photogenerated excitons, and a stronger oxidation ability of the photogenerated holes. Considering the universalities of microemulsion, precipitation, and hydrothermal methods, this work may also provide a prototype for the comparative study of semiconductor based photocatalysis for water purification and environmental remediation.

Review on nanoscale Bi-based photocatalysts

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

Facile Hydrothermal Synthesis of ZnWO4 for Enhanced Photocatalytic Performance

ZnWO4 with controllable morphology was successfully synthesized via a facile hydrothermal method. The relationships between the structure, morphology, and catalytic activity were systemically studied by varying both the hydrothermal time and pH value. The optimal synthesis conditions for ZnWO4 with superior catalytic activity were a hydrothermal time of 12 h and a pH value of 10. Impressively, the highest photocatalytic activity for the degradation of RhB was 91% for 60 min under ultraviolet light. The increased photodegradation performance was mainly ascribed to the high crystallinity and enlarged surface area of the optimal ZnWO4.

Fabrication of metal/semiconductor hybrid Ag/AgInO2 nanocomposites with enhanced visible-light-driven photocatalytic properties

Recently, exploration of the potential application of heterogeneous photocatalysis has attracted significant interest in the fields of environmental remediation and energy conversion. The metal–semiconductor hybrid nanostructures play very important roles in solar-to-chemical energy conversion due to their unique optical characteristics and catalytic properties. In this study, a novel photocatalyst constructed using Ag and AgInO2 was developed to improve the visible-light-driven properties. The photocatalytic efficiency of Ag/AgInO2 for the degradation of methylene blue (MB) reached 97.8%, which was much higher than that of pure AgInO2. Characterization results show that the as-prepared nanocomposites can not only broaden the visible-light absorption range but also promote the separation of the photogenerated electron–hole pairs. Trapping experiments confirmed that superoxide radicals (˙O2−) and holes (h+) were the predominant contributors in the degradation of the organic dye MB. These encouraging results provide an alternative approach for the development of metal–semiconductor hybrid nanostructures towards improving the efficiency of solar-energy utilization in the near future.

Indium-Containing Visible-Light-Driven (VLD) Photocatalysts for Solar Energy Conversion and Environment Remediation

Indium-containing visible-light-driven (VLD) photocatalysts including indiumcontaining oxides, indium-containing sulfides, indium-containing hydroxides, and other categories have attracted more attention due to their high catalytic activities for oxidation and reduction ability under visible light irradiation. This chapter will therefore concentrate on indium-containing nano-structured materials that demon‐ strate useful activity under solar excitation in fields concerned with the elimination of pollutants, partial oxidation and the vaporization of chemical compounds, water splitting, and CO2 reduction processes. The indium-containing photocatalysts can extend the light absorption range and improve the photocatalytic activity by doping, heterogeneous structures, load promoter, and morphology regulation. A number of synthetic and modification techniques for adjusting the band structure to harvest visible light and improve the charge separation in photocatalysis are discussed. In this chapter, preparation, properties, and potential applications of indium-contain‐ ing nano-structured materials used as photocatalysis will be systematically summar‐ ized, which is beneficial for understanding the mechanism and developing the potential applications.