Synthesis,Modification And Photocatalytic Performance Of Silver-based Photocatalysts

Compared with the conventional TiO₂ photocatalyst,silver-based materials have attracted a great deal of attentions due to their excellent photocatalytic performance.However,the rapid recombination of photogenerated charges and the poor photostability cause an obvious decrease of their photocatalytic performance.In addition,there is also a lack of deep research on the photocatalytic properties of silver-based materials.In view of the above issues,the present investigations are focused on the photocatalytic activity,the stability of structure and performance,and the unique photocatalytic selectivity of silver-based photocatalyst.The main results could be summarized as follows:?1?To improve the photocatalytic performance of silver-based photocatalysts,the amorphous Ti???as a hole cocatalyst was first successfully loaded on the surface of various silver-based photocatalysts?AgCl,AgBr,AgI,Ag₂O,Ag₂CO₃,and Ag₃PO₄?.The results show that Ti???cocatalyst can be used as a general hole cocatalyst to effectively enhance the photocatalytic performance of silver-based photocatalysts via improving the separation of photogenerated carriers.However,owing to the rapid transfer of photogenerated holes by Ti???cocatalyst,more photogenerated electrons would reduce the surface lattice Ag⁺ions of silver-based photocatalyst to metal Ag,causing an obvious destruction of structure on their surface and decreased photocatalytic performance.To further improve the stability of silver-based photocatalysts?taking AgBr as an example?,the amorphous Fe???electron-cocatalyst was further loaded on the surface of Ti???/AgBr.It was found that the dual cocatalysts modified Fe???-Ti???/AgBr photocatalyst showed an obviously higher photocatalytic activity and photoinduced stability than the single-cocatalyst modified photocatalysts?such as Ti???/AgBr and Fe???/AgBr?owing to the synergistic effect of amorphous Ti???and Fe???cocatalysts.?2?In the process of photocatalytic decomposition of mixed organic pollutants,it is quite important to selectively remove the targeted organic dyes.In this study,a series of silver-based compounds such as AgCl,AgBr,Ag₂O,Ag₂CO₃,and Ag₃PO₄were first prepared via a simple precipitation method,and then the metal Ag was loaded on the surface of silver-based materials via a photoreduction method.In the photocatalytic degradation of methyl orange?MO?and methylene blue?MB?mixed dyes,MB and reactive brilliant red X-3B mixed dyes,MB and rhodamine B?RhB?mixed dyes,silver-based materials showed preferential adsorption but non-preferential decomposition towards sulfur-containing dyes?MB?.As a consequence,a possible photocatalytic selectivity mechanism was proposed to account for the photocatalytic selectivity,namely,the metallic Ag on the surface of silver-based materials displays a preferential adsorption towards MB due to the strong affinity between silver and surful compounds.Since the metallic Ag is closer to the conduction band of photocatalysts,and most of the MB is adsorbed on the surface of metallic Ag,the other dyes?MO,brilliant red X-3B or RhB?which are near to valance band are first decomposed by the photogenerated holes,resulting in their excellent selective decomposition.