Microstructure Regulation Of Ag Cocatalysts And Their Effect On Photocatalytic H₂-Production Performance Of Titanium Dioxide

TiO₂ plays an important role in the field of photocatalytic H₂ production due to its chemical stability,non-toxicity and harmlessness.However,the low separation efficiency of photogenerated electrons and holes for pure TiO₂ greatly limits its further commercial application.Research indicates that cocatalysts modification is one of the effective ways to improve the photocatalytic H₂-evolution performance of TiO₂.Metallic Ag is widely used as an excellent electron cocatalyst for rapidly capturing and transferring photogenerated electrons owing to its outstanding electrical conductivity,which can enhance the separation efficiency of photogenerated carriers.Nevertheless,metallic Ag shows a low rate of interfacial H₂-evolution reaction for photocatalytic H₂-evolution system.To further boost the H₂-evolution rate of metallic Ag,this study mainly focuses on the structure modulation of metallic Ag by in situ sulfidation of Ag nanoparticles and one-step photoinduced synthesis of Ag-Ni nanoparticles,and explores their effect on the photocatalytic H₂-production performance of traditional TiO₂ photocatalyst.The main results can be summarized and shown as follows:First,metallic Ag was loaded on the surface of TiO₂ nanoparticles by photoinduced reduction method,and then Ag₂S was modified on the Ag surface by in situ sulfidation using Na₂S solution as sulfur source to obtain high-efficiency TiO₂/Ag-Ag₂S photocatalyst.It was found that the Ag₂S amount on the Ag surface could be easily controlled by the Na₂S solution,and the resulting TiO2/Ag-Ag2S?40uL?photocatalysts clearly exhibited a significantly higher photocatalytic H₂-evolution activity(119.11?mol h^-1)than that of pure TiO₂,TiO₂/Ag and TiO2/Ag2S photocatalysts by a factor of 51.8,3.9 and 3.6 times,respectively.Based on the present results,a synergistic effect of dual electron-cocatalyst?metallic Ag and Ag2S?is proposed for the improved photocatalytic H2-evolution activity,namely,the Ag nanoparticle functions as an effective electron-transfer mediator for the steady capture and rapid transportation of photogenerated electrons from TiO₂surface,while the Ag₂S serves as the interfacial active site to effectively adsorb H⁺ions from solution and promote the rapid H₂-evolution reaction.Hence,it is clear that the excellent synergistic effect between Ag and Ag₂S accounts for the greatly improved photocatalytic H₂-evolution performance of TiO₂/Ag-Ag₂S photocatalyst.Second,Ag-Ni core-shell nanoparticles were deposited on the TiO₂ surface by a one-step photoinduced reduction method to obtain the highly efficient TiO₂/Ag-Ni photocatalyst by using ethanol as a sacrificial agent.Moreover,the sacrificial agent of ethanol also served as the raw material for following H₂-production reaction.The photocatalytic result showed that the TiO₂/Ag-Ni photocatalyst exhibited more efficient photocatalytic H₂-evolution activity compared with the bare TiO₂,TiO₂/Ag and TiO2/Ni photocatalysts.In particular,the TiO2/Ag-Ni?1.5:1.5?photocatalyst clearly exhibited the highest photocatalytic H₂-evolution activity(146.70?mol h^-1),which is higher than that of TiO₂(1.86?mol h^-1),TiO₂/Ag(27.07?mol h^-1)and TiO₂/Ni(87.69?mol h^-1)photocatalysts by a factor of 78.9,5.4 and 1.7 times,respectively.In addition,the photocatalytic cycle tests exhibited that the TiO₂/Ag-Ni photocatalyst could maintain a stable photocatalytic H₂-production rate in pure ethanol sacrificial agent,indicating the excellent stability of TiO₂/Ag-Ni photocatalysts.According to the experimental results,the Ag-Ni core-shell cocatalyst not only can rapidly transfer photogenerated electrons,but also provide more active sites in ethanol,thus significantly improving the photocatalytic H₂-production rate of TiO₂.