Fabrication Of High Silica ZSM-5 Zeolite And Gold Nanoparticles Nanocomposite And Its Catalytic Reduction Mechanism Of P-nitrophenol

In recent years,the environmental pollution problem has been getting more and more serious due to the fast development of industry.The noble metal nanoparticles have been applied to deal with the environmental pollutants widely for their unique and excellent physiochemical properties.Gold nanoparticles(Au NPs)heterogeneous catalysis is one of high active and stable method so that attracted by scientists.In this paper,Au NPs have been anchored on the surface of defect-free high silica ZSM-5zeolite to prepare Au/ZSM-5 zeolite nanocomposites.The loading efficiency of Au NPs could be improved by changing the fabrication conditions,and the prepared Au/ZSM-5 nanocomposites was utilized for the catalytic reduction of 4-nitrophenol(4-NP).The main content is as follows:(1)In this paper,we have fabricated the defect-free high silica ZSM-5 zeolite by hydrothermal method.It was found that the ZSM-5 zeolite has fluffy structure on its surface after the addition of certain amounts of MWCNTs in synthesis gel through aging time for one day.The Au/ZSM-5 composites were fabricated by decorating Au NPs on ZSM-5 zeolite surface through the enhanced sol-gel immobilization method.The ICP-MS results show that the loading efficiency of Au NPs on the surface of ZSM-5 zeolite with fluffy structure was up to 82%,while the loading efficiency of Au NPs on the surface of conventional ZSM-5 zeolite was only 10.7%.Additionally,it was found that the more MWCNTs was added,the higher loading efficiency of Au NPs was achieved.More types of hydroxyl groups were found in zeolite with fluffy structure according to the NMR characterization results,these hydroxyl groups might be related to the improvement of Au NPs.(2)The prepared Au/ZSM-5 composites were utilized for the reduction of 4-NP with the NaBH₄as the reducing agent.The experiment results demonstrate that the composites which fabricated by Au NPs and ZSM-5 zeolite with fluffy structure(Au/M_2.5-ZSM-5(2d))possess higher reduction activity.2 mg of Au/M_2.5-ZSM-5(2d)was utilized to investigate the affecting factors in the reduction of 4-NP reaction,it was found that the optimal initial 4-NP concentration was 0.2 m M and the optimal solution p H was 5 in the reduction reaction.Additionally,the Au/M_2.5-ZSM-5(2d)composites has exhibited good universality by using tap water,peach lake water and Xiangjiang river water as water sources to simulate the degradation of 4-NP in real water samples.In the recycling experiment,Au/M_2.5-ZSM-5(2d)still had a catalytic efficiency of 86.2%after fifteen cycles.The ESR characterization of 4-NP and NaBH₄revealed the presence of H free radicals(·H)in the solution system,indicating that·H may be the key species to achieve reduction in the experiment of conversion from4-NP to 4-AP.