Synthesis And Photocatalytic Activity Of Silver (I)-based Semiconductor Composites

Photocatalysis is an environmental control technique, because it can make use ofsolar energy and decompose organic pollutants thoroughly without secondarypollution. Currently, inadequate visible light utilization and low quantum efficiencyhave become the main factors restricting the development of photocatalytic technique.Thus, it is very imperative to enlarge the optical response range of photocatalyst andimprove the quantum efficiency of catalyst. Silver (I)-based semiconductor possesseshigh photocatalytic activity, but it is easily influenced by photocorrosion, whichleading to its weak stability. In this thesis, we focused on preparing silver (I)-basedcomposites by combination silver (I)-based semiconductors with other supportmaterials (graphene oxide, nitrogen-doped graphene, and graphitic carbon nitride) orsemiconductors and enhancing adsorption capacity, narrowing band gap width, andimproving efficient separation of photogenerated electron hole pairs. Thus, iteventually improves their photocatalytic activity for the degradation of organic dyesunder visible light irradiation. The main contents and major results are given asfollows:1. Graphene oxide-Ag2CO3(GO-Ag2CO3) composites have been prepared by asimple and effective precipitation method between GO-Ag(NH3)2+and NaHCO3,which exhibited a higher photocatalytic activity toward degradation of organic dyes,including rhodamine B (RhB), methylene blue (MB) and methyl orange (MO), inaqueous solution, than pure Ag2CO3crystal under visible light. The Ag2CO3crystalwith0.9wt%GO content exhibited the highest photodegradation efficiency fororganic dyes, which was2times of pure Ag2CO3crystal. The improved photocatalyticactivity of GO-Ag2CO3composites was attributed to the corporative effects ofhigh-surface-area of GO sheets, enhanced absorption of organic dyes, small band gap,more efficient separation of photogenerated electron hole pairs, and good electronacceptor of GO. The photocorrosion of Ag2CO3crystal can be efficiently inhibited byGO, since the transfer of photogenerated electrons from the surface of Ag2CO3crystalto GO sheets can reduces the possibility of decomposing Ag+to Ag0, which resulted in an improved stability and recyclability of GO-Ag2CO3composite in thephotocatalytic reaction. The degradation of RhB by GO-Ag2CO3composite couldmainly be attributed to holes and superoxide radicals, while the hydroxyl radicals onlyplayed a relatively minor role in the whole process. At last, we proposed a possiblemechanism. This facile and straightforward method has promising applications in thefabrication of different graphene oxide-based heterostructure photocatalysts.2. Nitrogen-doped graphene modified AgX@Ag (NG-AgX@Ag, X=Br, Cl)composites were prepared by a simple co-precipitation method under ambientcondition. The composites possessed higher photocatalytic activity thancorresponding bare AgX@Ag towards degradation of RhB aqueous solution undervisible light irradiation, which can be ascribed to the corporative effects of more lightharvest, enhanced adsorption capacity and more efficient separation ofphotogenerated electron-hole pairs after integrated with nitrogen-doped graphene. TheNG-AgX@Ag (X=Br, Cl) composites exhibited efficiencies of86%and89%forphotodegradation of RhB, which were about2times and1.8times of correspondingbare AgX@Ag (X=Br, Cl), respectively. The composites also had a relatively highstability. This investigation should open up new possibilities for the development ofnew highly efficient and stable NG-based plasmonic photocatalysts that utilize visiblelight as an energy source.3. A series of graphitic carbon nitride/silver carbonate (g-C3N4/Ag2CO3)submicrorod hybrids with different weight addition ratios of g-C3N4have beenprepared for the first time by a facile precipitation method. It is found thatg-C3N4/Ag2CO3submicrorod hybrids with a proper addition amount of g-C3N4exhibithigher photocatalytic activity than Ag2CO3submicrorod toward degradation of dyeunder visible light irradiation. The Ag2CO3crystal with3.5wt%g-C3N4contentexhibit the highest photodegradation rate constants for RhB and MB in aqueoussolution, which are ca.2times and1.7times of pure Ag2CO3crystal, respectively.This work might provide a simple and high-efficient approach for removal of organicpollutants by using solar energy.4. A facile hydrothermal (solvothermal) method was adopted to prepare ZnOnano-materials with three kinds of morphology, including nanorods, nanoparticles and short nanorods. Then we successfully obtained three kinds of Ag3PO4-ZnOcomposites with different molar ratios of Ag3PO4to ZnO by in situ precipitation route.The effects of different molar ratios of Ag3PO4to ZnO on the photocatalyticperformance of RhB degradation under visible light irradiation were studied. It wasfound that Ag3PO4-ZnO nanorod, Ag3PO4-ZnO nanoparticle and Ag3PO4-ZnO shortnanorod composites with the molar ratios of Ag3PO4to ZnO are1:40,1:40and1:120,respectively, exhibited higher photocatalytic activity than corresponding pure ZnO. Atthe same time, their stability and recyclability is better than pure Ag3PO4nanoparticles.Finally, we examined the effects of different scavengers on the degradation efficiency,which indicated that the degradation of RhB over Ag3PO4-ZnO compositephotocatalysts was mainly attributed to hydroxyl radicals or direct oxidization byholes.5. The Ag3PO4-Bi2O2CO3composite photocatalyst was successfully synthesized viathe reported hydrothermal technique and then in situ precipitation method. Theas-prepared composites exhibited higher visible light photocatalytic activity for RhBdegradation than pure Bi2O2CO3. The improved photocatalytic activity ofAg3PO4-Bi2O2CO3composite was attributed to the enhanced light harvest and moreefficient separation of photogenerated electron hole pairs. The photocatalyticdegradation reaction follows a pseudo-first-order dynamics. The study of the reactionkinetics indicated that the initial concentration of the dye solution is much lower, thedegradation efficiency is much higher. At last, controlled experiment proved that thedegradation of RhB was mainly attributed to holes and superoxide radicals, while thehydroxyl radicals and electrons only played a relatively minor role in the wholeprocess.6. Pure Ag2SO3sub-microparticles were prepared by a simple precipitationmethod between aqueous AgNO3and Na2SO3solutions. Universal organic dyes (RhB,MB and MO) degradation ability, recycling performance, reaction dynamics andeffects of different scavengers on the degradation efficiency were studiedsystematically. The results showed that Ag2SO3sub-microparticles exhibited highervisible light photocatalytic activity than commercial TiO2(P25), and thepseudo-first-order rate constant is1.7times of P25. The photocorrosion of Ag2SO3 sub-microparticles can be efficiently inhibited by adding Na2SO3in the repeatedphotocatalytic degradation reaction system of organic dyes. The degradation of RhBwas mainly attributed to holes and superoxide radicals, while the hydroxyl radicalsonly played a relatively minor role. To improve the photocatalytic activity andstability, GO-Ag2SO3, Ag2SO3/Ag2SO4and Ag2SO3@SiO2composites were alsoprepared.