Synthesis And Photocatalytic Properties Of Silver Vanadate Microplates And Its Heterojunction

With the increasingly serious environmental pollution, human survival and development arethreatened. It is more urgent to discovery new and efficient materials to control theenvironmental pollution. Photocatalytic degradation of pollutant using semiconductor material isan efficient and environmentally friendly, much to be concerned in recent years. Titaniumdioxide (TiO2) is the oldest and still the most widely used photocatalyst because of its low cost,nontoxicity, relatively high chemical stability and large availability. However, its relatively wideband gap (3.2eV) significantly limits its photocatalytic applications because only~4%of theavailable sunlight energy can be utilized. So it is very necessary to develop new, efficient andvisible light response photocatalytic materials. Recently, Ye have reported the new use of aAg3PO4semiconductor in photocatalytic applications, which exhibits extremely highphotooxidative capabilities for organic dyes decomposition under visible light irradiation. Sincethen, the studies of silver-based photocatalysts have been usually reported.In the present work，we around the new silver-based photocatalysts, prepared silvervanadate(Ag4V2O7) microplates via hydrothermal method with surfactant polyvinylpyrrolidone(PVP). Furthermore, Ag4V2O7/AgBr heterojunction was successfully synthesized. The structure,morphology, chemical composition, optical properties and photocatalytic activity werecharacterized by a variety of methods. The main content of this paper is summarised as follows:(1) Ag4V2O7microplates were synthesized via a simple hydrothermal route with theassistance of urea which would decompose into the alkali (NH3) slowly. Urea played a role tocontrol the nucleation and crystal-growth rate through neutralization the excess nitric acid. Inaddition, the suitable amount of added polyvinylpyrrolidone played a key role in the formation ofAg4V2O7microplates, which may selectively stabilize the Ag4V2O7{001} facets. Ag4V2O7microplates exhibited high activity toward the degradation of methyl blue (MB). The degradationrate of methyl blue (10mg/L) was up to96.4%after illuminating for125min under250W metalhalide lamp (λ﹥420nm) (2) Ag4V2O7/AgBr heterojunction was successfully synthesized via an in situanion-exchange reaction between KBr and Ag4V2O7microplates which were served as astemplates and silver sources. As a result, AgBr nanoplates of approximately200-300nm wereclosely attached to the surface of Ag4V2O7microplates. We found that the photocatalytic activityof Ag4V2O7/AgBr heterojunction was far greater than pure Ag4V2O7through photocatalyticdegradation of methylene blue, rhodamine B and methyl orange solution. Photodegradationexperiment showed the descending order of photocatalytic degradation rate of the three tdyes:MB﹥RhB﹥MO. The as-prepared Ag4V2O7/AgBr heterojunction exhibited greatly enhancedphotocatalytic properties for the degradation of dyes, which may be primarily ascribed to theheterojunction which is beneficial for charge transfer and suppressing recombination ofphotogenerated electron hole pairs effectively and the relatively higher surface energy of AgBr{111} facets. At the same time, we concluded the·O2-radicals and photogenetated holes werekey factors in photooxidation process of MB, and corresponding·OH radicals were insignificant.