Synthesis And Properties Of Highly Efficient Photocatalysts Of Silver Salt And Its Composites

It is an urgent task to explore effective methods for resolving the issues about lacking of energy and deterioration of environment in order to meet the increasing need of human. Compared with other conventional methods, photocatalysis is one of the most advanced technologies for dealing with the two critical problems both in scientific and technological fields, because of its convenient and practical properties. Thanks to excited electron-hole pairs trigger redox; consequently, the contaminants are degraded under irradiation. Semiconductors play a fundamental role in photocatalysis. Water splitting, another application of photocatalysis, converts solar energy to chemical energy and electrical energy.An exceptionally efficient photocatalyst, silver orthophosphate (Ag3PO4), can harness visible-light then efficiently oxidize water to release oxygen as well as degrade organic contaminants such as rhodamine B, and orange II. It has a suitable band gap of2.45eV and could achieve90%quantum efficiency, which is a value significantly higher than that of other reported semiconductors. The investments about such effective semiconductor photocatalysts that split water easily to hydrogen and oxygen degradation under visible-light irradiation still are the tough tasks. In several decades, the study of those materials mainly focused on effective and stable materials in practical applications. Although Ag3PO4is effective, the stability is considerably low.Firstly, the relationship between photocatalytic activity and Ag3PO4particle size is an important issue in developing the effect over the catalytic activity and stability. Till now, systemic report about the relationship is rarely. This study aimed at systemic investigating the relationship between Ag3PO4particle size and catalytic performance under visible-light irradiation (λ>420nm) in the degradation of bisphenol A2,2-bis (4-hydroxyphenyl) propane(BPA). According to the results of characterization, it could be concluded that the Ag3PO4activities were decreased because agglomeration of Ag3PO4itself and generated Ag nanoparticles covered the surface of Ag3PO4in applications. The catalysts SP and SP-50, with the relatively lower catalytic stability, exhibited more serious agglomeration effect and generated more Ag nanoparticles. However, the SP-400catalyst which possessed appropriate particle size, exhibited better catalytic stability. Therefore, the decrease of photocatalytic activity of Ag3PO4catalyst would be mainly attributed to the formation of Ag over the Ag3PO4surface and the catalyst agglomeration.About morphology aspect, concave trisoctahedral Ag3PO4and flower-like Ag3PO4were synthesized easily by ions-exchange method by adjusting pH with NaOH/KOH solutions. Compared with spherical Ag3PO4, the two exhibited higher photocatalysis activity owing to the concave trisoctahedral Ag3PO4formed by higher energy facet{221} and{332}; flower-like Ag3PO4with more complex facets.Unfortunately, the disadvantage of Ag3PO4is intrinsic. In order to improve the stability of Ag3PO4, Ag3PO4/WO3composites were prepared through a deposition-precipitation method. These photocatalysts were evaluated in the degradation of rhodamine B (RhB), methyl orange (MO) and salicylic acid under visible-light irradiation (λ>420um). The synergistic effect between Ag3PO4and WO3was confirmed by notably higher photocatalytic activity compared to pure Ag3PO4and WO3catalysts. The effect of Ag3PO4:WO3ratio on the catalytic activity was systemically studied. Especially the catalyst AW6/4exhibited the highest catalytic activity. The degradation rates of RhB, MO and salicylic acid could reach up to97%under visible-light irradiation for6min,35min and105min, respectively. Moreover, the AW6/4photocatalyst showed higher recyclability than pure Ag3PO4catalyst. Further More, AW6/4photocatalyst could be recycled for five runs in the degradation of RhB, and three runs in the degradation of MO. The characterization of used catalysts proved that Ag3PO4was effectively protected in Ag3PO4/WO3composites and much less metallic Ag was formed over the surface of Ag3PO4/WO3catalysts. The improvement of photocatalytic activity and stability is mainly attributed to the highly effective separation of photogenerated electron-hole pairs caused by special transfer pathway of electrons and holes in Ag3PO4/WO3compositesLastly, epitaxial assembly of Cu2O@Ag and Ag cage were highly yielded respectively through introducing [Ag(NH3)2]+complexant to the dispersed Cu2O suspension under visible-light irradiation, without any other chemical. The [Ag(NH3)2]+complexant played a critical role in the Ag-shell growth and kept the morphologies of Cu2O template. In the paper, a versatile synthesis route was described to synthesize metal Ag over Cu2O semiconductor in assistant of ammonia solution. Cu2O@Ag yolk-shell and Ag cage were prepared by using the weakly reductive Cu2O and [Ag(NH3)2]+complexant as precursors. It is a novel synthesis method and general rule for epitaxial growth of heterostructure. Then the applications of photocatalysis of RhB, CO oxidation and SERS were performed. The properties of Cu20@Ag yolk-shell are better than pure Cu2O and Ag cage for formed metal/semicaonductor composites.