Synthesis Of Bismuth-based Z-scheme Composite Photocatalyst And ItsPhotocatalytic Purification Performance OfToluene

Volatile organic compounds (VOCs) emitted from cooking, painting, and furnishings represent the majority of indoor air pollutants. Photocatalytic oxidation (PCO) is one of the promising methods for eliminating VOCs due to its advantages of being a simple and mild reaction. As one of important visible-light-driven photocatalysts, Bismuth-based photocatalysts attract lots of attentions. However, single-phase Bismuth-based photocatalysts suffer from high recombination rate of photoelectron-hole pairs, resulting in low photocatalytic activities. Thereby the development of PCO in environmental governance, such as air purification and organic pollutants degradation, may be restricted. In this paper, photocatalysts with narrow bandgap (BiV04, Bi2O3, and g-C3N4) were selected as basic photocatalysts. Two different types of visible-light-driven Z-scheme composite photocatalysts were synthesized. Due to the efficient seperation rate of photoelectron-hole pair, the photocatalytic purification performance of VOCs was enhanced. The physical, optical, and photoelectrochemical performance of the composite photocatalyst were analyzed by a series of characterizations. The main research works were as follows:Reduced graphene oxide (RGO) was chosen as electron mediator. BiVO4 and Bi2O3, acting as important visible-light-driven photocatalysts, were chosen as basic photocatalysts. A Z-scheme photocatalytic system:BiVO4/RGO/Bi2O3 composite photocatalyst with enhanced visible-light-driven photocatalytic purification of toluene was synthesized by photoreduction and evaporation-induced self-assembly process. With the irradiation of visible light for 7 h, BiVO4/RGO/Bi2O3 had a large mineralization rate, which reached up to 95.6%. The production rate of CO2 (k2) for BiVO4/RGO/Bi2O3 is 6.7,2.1, and 1.5 times higher than that of Bi2O3, BiVO4, and 3, respectively. The improved photocatalytic performance can be attributed to the characteristics of RGO:(i) the improved adsorption of visible light, (ii) the larger specific surface areas and profuse interfacial active sites, and (iii) the accumulation of charge transport by shuttling them from the BiVO4 to Bi2O3 resulting in the more efficient separation of photoexcited electron-hole pairs.BiVO4/g-C3N4 with different amounts of BiVO4 were synthesized through calcination treatment. From the process of visible-light-driven photocatalytic purification of toluene, it can be seen that 3 wt% BiVO4/g-C3N4 diaplayed the highest photocatalytic activity, the toluene degradation rate of which was larger than that of pure BiVO4 and g-C3N4 by a factor of 5.9 and 3.6, respectively, and production rate of CO2 (k) of which was larger than that of pure BiVO4 and g-C3N4 by a factor of 6.4 and 3.2, respectively. The remarkably improved photocatalytic performance should be attributed to the following reasons:(i) the increased specific surface area and pore volume not only improved the adsorption capacity, but also increased the interfacial active sites; (ii) the red-shift absorption edge accelerated the absorption of visible light; (iii) the fabrication of a direct Z-scheme system of BiVO4/g-C3N4 promote the efficient separation rate of photoinduced charge carriers.