Preparation Of Supported Catalysts Containing Nickel,Cobalt And Silver Nanoparticles And Their Catalytic Performance For The Reduction Of P-Nitrophenol

With the rapid development of the chemical industry,the discharge of industrial wastewater has increased sharply.Among them,p-nitrophenol（4-NP）is one of the common toxic pollutants in wastewater.The organic pollutant 4-NP has high stability and toxicity,which exist in water for a long time will cause great harm to the ecological environment and human health.Therefore,how to develop a stable,efficient,and green catalyst to treat 4-NP in wastewater is crucial.Metal nanoparticles have been the focus of current research in multidisciplinary fields such as chemistry,environment,and materials due to their easy availability and preparation.However,pure metal nanoparticles are not easy to recover in practical catalysis research,and the particle dispersibility is not good,which may cause secondary pollution of water bodies.In this paper,modified silicon wafers,multi-walled carbon nanotubes（MWCNTs）,and carboxylated SiO₂ were selected as the active carriers to prepare three catalysts of MWCNTs-ZIF-67,SiO₂-COOH@Ag,and MWCNTs-ZIF-67 by hydrothermal method,co-precipitation method,etc.Na BH₄ is used as a reducing agent,and the performance of the three catalysts for the reduction of 4-NP was investigated.The kinetics and the mechanism of the catalytic reduction reaction were also studied.The main research contents are as follows:（1）A modified silicon-based material was prepared by a simple method,and then a modified silicon-based nickel-cobalt alloy composite（NiCo/Si）was prepared by a hydrothermal method.The composite material was characterized by FT-IR,SEM,TEM,and XPS.In the presence of Na BH₄,the reduction of 4-NP by the composite material were investigated.The results showed that the NiCo/Si catalyst has good catalytic performance compared with the present of no catalyst,or only silicon-based materials,or nickel-cobalt alloys.Further research showed that when the ratio of nickel and cobalt is 2:1,the catalytic rate is the fastest,which with the catalytic rate of0.8425 min^-1.The catalyst also showed high reusability,and the catalytic conversion still reached 90%in the fifth cycle.（2）Magnetic MWCNTs-ZIF-67 composite was prepared at room temperature by a simple co-precipitation method using MWCNTs and ZIF-67 as the raw materials.In the presence of Na BH₄,the catalytic activity of MWCNTs-ZIF-67 for the reduction of4-NP was detected.The results show that MWCNTs-ZIF-67 has superior catalytic reduction performance for 4-NP with the reaction rate constant of 0.4973 min^-1 and the reduction efficiency of 4-NP reaches more than 99%within 6 min.After 5 times of recycling,the catalytic activity of the composite is still high.（3）Using the sol-gel method,the SiO₂ nano-microspheres was synthesized,which were carboxylated then to prepare SiO₂-COOH.Finally,SiO₂-COOH@Ag nanomaterials were obtained by depositing metallic silver on the surface of SiO₂-COOH microspheres by dipping method.In the present of Na BH₄,the catalytic performance of SiO₂-COOH@Ag nanomaterials and the influencing factors of the catalytic system on the degradation rate of 4-NP were investigated.When the catalyst dosage was 10 mg,the Ag₂SO₄ solution concentration was 0.5 mol/L,and the reaction temperature was 30°C,the catalytic degradation efficiency of 4-NP could reach 99.96%.