Preparation Of Silver / Bismuth - Based Semiconductor Nanocomposites And Its Photocatalytic Activity

Recent studies have indicated the silver-containing and bismuth-containing semiconductors with relatively narrow band-gap and special crystal structures exhibit great potential applications in degradation of organic pollutions by visible light. For homogenous material, however, the photocorrosion unavoidably of silver-containing photocatalysts and low separation efficiency of carriers in bismuth-containing photocatalysts become important problems which the two kind of photocatalysts urgently await to be solved in practical application.In this work, we start with the two main challenges facing silver-containing and bismuth-containing photocatalysts. Firstly, the inhibition of photocorrosion for Ag₂CO₃ in the solution was studied. Subsequently, we constructed the type-II Ag₂CO₃/Bi₂WO₆ heteroj unction and Z-scheme AgI/Ag/Bi₂MoO₆ photocatalytic system, and that explored their photocatalytic activity and photostability in detail. The content of the thesisis divided into five chapters:In chapterl, we described the research background and the basic theory of semiconductor photocatalysis. We introduced the application of semiconductor photocataiysts in the water splitting, degradation of pollutants and CO2 conversion. We introduced the effective ways to improve photocatalytic properties and analyzed the advantages of type-II heteroj unction and Z-scheme photocatalytic system in the separation of photoinduced electron-hole pairs. At last, we described the research progress and confronting problems of silver/bismuth-containing composite photocatalysts.In Chapter 2, the porous Ag₂CO₃ nanorods were controllable synthesized via a one-pot aqueous solution reaction using PVP as the dispersing agent. The possible growth process and procedure mechanism were studied. Photocatalytic results show that the porous Ag₂CO₃ nanorods exhibit excellent photodegradation of rhodamine B （RhB） under visible-light irradiation, particularly the photoactivity performance and stability can be further improved in the presence of NaHCO₃. It is indicated that NaHCO₃ can prevent effectively the photocorrosion and promote the probability of electron-hole separation.In Chapter 3, the novel Ag₂CO₃/Bi₂WO₆ heterojunction were prepared via a facile microwave-assisted solution-phase reaction and deposition process. The photocatalytic evaluation demonstrates that the photocatalytic performance is greatly influenced by the content of deposited Ag₂CO₃ and the 30 wt% Ag₂CO₃-loaded Bi₂WO₆ sample exhibited the highest photocatalytic activity for the degradation of RhB and MO. Meanwhile, it also possesses excellent cycling stability under visible light irradiation. The dramatically enhanced photocatalytic activity and stability can be mainly ascribed to well-matched energy bands and heterojunctions between Ag₂CO₃ and Bi₂WO₆, which can effectively improve the separation of photo-induced electron-hole pairs at the heterojunction interfaces.In Chapter 4, hierarchically structured AgI/Ag/Bi₂MoO₆ hollow microspheres were successfully synthesized via an in situ deposition and photochemical reduction process. Under visible light, the AgI/Ag/Bi₂MoO₆ hollow microspheres exhibit enhanced photocatalytic activity compared with pure Bi₂MoO₆ for the decomposition of RhB. The excellent photocatalytic activities of ternary AgI/Ag/Bi₂MoO₆ composite can be mainly ascribed to the efficient separation of photo-induced charge carriers through a Z-scheme system consists of Bi₂MoO₆, Ag and AgI.