Polynary Semiconductor Photocatalysts Zn₃（OH）₂V₂O₇·2H₂O And Zn₃V₂O₈: Synthesis And O₂Evolution Performance From Photocatalytic Water Splitting

Artificial photosynthesis is a highly-promising strategy to convertsolar energy into hydrogen energy for the relief of the global energy crisis.Water oxidation is the bottleneck for its kinetic and energetic complexitycompared to water reduction in the further enhancement of the overallefficiency of the artificial photosystem. Besides, semiconductorphotocatalysts have recently been the research focus due to their stabilityand simplicity. Therefore, developing efficient and cost-effectivesemiconductor photocatalysts for water oxidation is significant. In thisarticle, O2evolution performance from photocatalytic water splitting of thepolynary semiconductor photocatalyst Zn3V2O8and its precursorZn3(OH)2V2O7·2H2O was investigated. The contents and results are listedas follows:1. Zn3(OH)2V2O7·2H2O was synthesized via a hydrothermal method.The pH value during the hydrothermal process was changed to study itseffect on the crystal size, the exposed facet and the local structure, thus theinfluence on the photocatalytic O2evolution performance. The precursorprepared at the lower pH value had the effective exposed crystal facet andthe local structure with larger distortion which facilitated the photocatalyticO2evolution. Then Zn3(OH)2V2O7·2H2O was calcined in air underdifferent temperatures to get different products. The effect of thecalcination temperature on the phase, the crystal size distribution and the morphology was investigated to discuss their influence on thephotocatalytic activity. Zn3V2O8calcined at400℃had the more uniformmorphology beneficial to photocatalysis.2. First-principles calculations were employed to study the H2Oadsorption energy on different facets, the density of states and charges ofthe facets and the optimal adsorption position. These calculation resultswere used to discuss the influence of the electronic structure on thephotocatalytic activity and they confirmed the former discussions about therelationship between the local structure and the photoactivity.3. Graphene was used to modify Zn3V2O8to get the compositestructure Zn3V2O8/RGO. The relationship between the graphene contentand the photocatalytic O2evolution activity as well as the photocatalyticperformance of the composite structure under two different light irradiationwere investigated. The charge transfer mechanisms based on the bandcoupling under different light irradiation were proposed.