Preparation And Photocatalytic Activity Research Of Silver Orthophosphate Series Compound Semiconductor Materials

Silver orthophosphate can not only absorb solar energy with a wavelengthshorter than530nm and achieve quantum efficiencies of up to90%but alsoshow strong photooxidative ability, so it has great potential in water splitting anddegradation of pollutants. However, as Ag3PO4is a light-sensitive reagent andslightly soluble in aqueous solution, it will dramatically reduce the structuralstability in the photocatalytic process. Moreover, Ag3PO4will be photo-corrodedand decompose to weakly active Ag in the absence of sacrificial reagent, andaccordingly, the photocatalytic activity gradually deteriorates, which is the mainhindrance for the practical application of Ag3PO4. Therefore, it will be the focusof future research to develop a facile and efficient way to modify the stability ofAg3PO4photocatalyst and enhance its photocalytic activity without usingsacrificial reagents.In this paper, cubic silver orthophosphate photocatalyst with goodphotocatalytic activity was fabricated through a silver-ammine assisted methodby using AgNO3, Na2HPO4and NH3·H2O. Heterostructured Ag3PO4/TiO2composite photocatalyst was prepared via a coprecipitation method by depositingAg3PO4nanoparticles onto the surface of TiO2microspheres. Ag3PO4/Bi2WO6composite photocatalyst with good visible-light catalytic activity was preparedvia an in situ precipitation method by loading Ag3PO4nanoparticles onto thesurface of flower-like Bi2WO6microspheres. Ag/Bi2WO6composite with goodvisible-light catalytic activity was synthesized by a photoreduction process.X-ray diffraction, scanning electron microscopy, energy dispersive X-rayanalysis, UV-Vis diffuse reflectance spectrometer and photoluminescenceemission spectrometer were employed to investigate the phase composition,micro-structure and optical absorption properties of as-prepared samples. The photocatalytic activity of as-prepared samples was tested by the photocatalyticdegradation of Rhodamine B aqueous solution under light irradiation. The effectsof the structure, morphology and loading content on the photocatalytic activitywere discussed. What’s more, the reasons and mechanism of enhancedphotocatalytic activity were also explored.The results were shown as followings:(1) the as-prepared cubic Ag3PO4crystals are bounded entirely by six of {100} facets and exhibit much betterphotocatalytic activity than spheres. This is due to the higher absorptionefficiency of the visible light photons，effectively separation of electrons andholes and catalytically active sites on their surfaces of cubic silverorthophosphate photocatalyst which is dominated by the highly active {100}facets.(2) The as-prepared Ag3PO4/TiO2composite semiconductors exhibitsignificantly enhanced optical absorption properties in the visible light region.The formation of heterojunction promotes the separation of photoinducedelectrons and holes and thus enhances the photocalytic activity of Ag3PO4/TiO2composites. Moreover，when the molar ratio of Ag3PO4to TiO2is10at%,Ag3PO4/TiO2composite exhibits the best photocalytic activity.(3) Theas-prepared Ag3PO4/Bi2WO6composite semiconductors exhibit stronger opticalabsorption ability in the wavelength range of430-530nm. The photocatalyticactivity of Ag3PO4/Bi2WO6composites is much higher than that of singleAg3PO4and Bi2WO6due to the formation of heterostructured Ag3PO4/Bi2WO6.The heterojunction can inhibit the combination of photogeneratedelectrons-holes and extend the life of the charge carriers to improve theefficiency of the quantum.(4) The as-prepared Ag/Bi2WO6compositesemiconductors have a significantly enhanced optical absorption and display anobvious red shift due to the surface plasmon resonance (SPR) of Agnanoparticles on the surface of pure Bi2WO6. The SPR of Ag can enhance thelight-harvesting ability of Ag/Bi2WO6composites. In addition, the loading ofappropriate content of Ag will contribute to improve the photocatalytic activity.The enhanced photocatalytic activity could be attributed to the synergistic effectof the strong SPR effect and the effective separation of photogenerated electronsand holes caused by Ag nanoparticles.