Research On The Performance Of Ag-based Nanomaterials For Catalytic Reduction Of 4-nitrophenol

4-Nitrophenol?4-NP?reduction into 4-aminophenol?4-AP?induced by sodium borohydride?NaBH₄?catalyzed by Ag nanoparticles is a new method to treat 4-NP in wastewater with great potential applications.The agglomeration of nanoparticles will be improved and their sizes will be controlled effectively after being inmobilized on the surface of inorganic nanometal oxides with low price and abundant special morphologies to increase the stabilities and catalytic abilities of active components.In this text,three different nanometal oxides such as zinc oxide?ZnO?nanorods,titanium oxide?TiO₂?nanospheres and?-alumina??-Al₂O₃?hollow nanospheres are selected as the supports to immobilize Ag nanoparticles.The catalytic abilities,kinetics,thermodynamics and mechanism of these catalysts toward 4-NP reduction were investigated.Main contents are as follows:?1?Ag/ZnO nanorods composites are prepared with high purity where the ZnO nanorods are chosen as the support to immobilize Ag nanoparticles.The Ag nanoparticles were dispersed well on the surface of ZnO nanorods.There are strong metal-interface interactions between Ag nanoparticles and ZnO nanorods.Ag/ZnO nanorods showed enhanced catalytic abilities,stabilities and good regeneration performances toward 4-NP reduction.The apparent rate constant(k_app)was 2 times than that of uninmobilized Ag nanoparticles.?2?Ag/TiO₂ nanospheres composites are prepared with high purity and high activity where the TiO₂ nanospheres are chosen as the support to immobilize Ag nanoparticles.The dispersibility of Ag nanoparticles was improved due to the inmobilizing of uniformly TiO₂ nanospheres,which enhanced the size effect of Ag nanoparticles.Further the catalytic ability of Ag/TiO₂-0.50 toward 4-NP reduction was increased,where 4-NP reduction finished in 5 min and the k_app was 5 times than that of uninmobilized Ag nanoparticles.The catalytic abilities,stabilities and regeneration performances were raised greatly.Moreover,the catalytic process was nonspontaneous,endothermic and the disorder chaos increased at the solid-liquid interface.?3?Ag/?-Al₂O₃ hollow nanospheres composites are prepared with high activity and high stability where the?-Al₂O₃ hollow nanospheres are chosen as the support to immobilize Ag nanoparticles.?-Al₂O₃ three-quarter nanospheres have rough,porous and hollow surfaces with high specific surface areas,which played a good role of dispersing and protecting Ag nanoparticles and contolled their size.The 4-NP reduction catalyzed by Ag/?-Al₂O₃-0.50 finished in 3.5 min;Its k_app was 8 times than that of uninmobilized Ag nanoparticles,indicating that Ag/?-Al₂O₃-0.50 had a excellent catalytic abilities,stabilities and regeneration performances toward4-NP reduction.In addition,the catalytic process was nonspontaneous,endothermic and the disorder chaos increased at the solid-liquid interface.The catalytic abilities of above-mentioned catalysts were better than that of reported Ag-based catalysts.The kinetics datas indicated that the catalytic process was fitted well by Langmuir-Hinshelwood?L-H?,where the step of intermediate 4-hydroxyaminophenol?4-Hx?converted into 4-AP was the rate controlled step.