Preparation Of MIL-88B(Fe) Supported Au NPs Composite And Its Reduction Behavior And Mechanism On P-nitrophenol

Owning to the rapid economic development and the wanton discharge of industrial sewage,people’s living environment is seriously threatened,and at the same time,it effects a negative impact on the ecosystem.The increasingly serious water pollution problem needs to be solved urgently.To develop efficient,green and safe catalysts for efficient remediation of refractory organic pollutants in wastewater is an important issue facing the field of environmental pollution control and remediation.The catalytic reduction technology of precious metal nanomaterials has become the current preferred material for transforming and degrading pollutants in water on account of high efficiency,environmental protection and other advantages.Compared with many metal nanomaterials,gold nanoparticles（Au NPs）are favored by many scholars due to their large specific surface area,good optical properties,mild reaction conditions,and high catalytic efficiency.Among them,the research of heterogeneous catalysis technology in which Au NPs are dispersed on solid supports has been attracting much attention.In this paper,Au/MIL-88B（Fe）composite materials were prepared by a green and facile one-step synthesis method,and having the 4-NP（4-nitrophenol）catalytic hydrogenation with the reduction of Na BH₄ to test the catalytic activity of Au/MIL-88B（Fe）,while changing the test conditions to explore the practical environmental applicability and stability of Au@MIL-88B（Fe）.The main research contents are as follows:（1）Preparing Au/MIL-88B（Fe）by a hydrothermal strategy:having N,N-dimethylformamide（DMF）as a stabilizer for Au NPs,then mixing tiny Au MNPs into the internal and external surface of MIL-88B（Fe）.The results show that the optimal amount of chloroauric acid is 2m L（10mg/m L）and the concentration of Na BH₄ is 30m M,the formed Au loading and loading rate are the best.The catalytic active sites increase with the high loading efficiency.Moreover,the Au NPs existing outside of MIL-88B（Fe）pores shows preeminent dispersibility with the bridging effect of DMF.（2）The catalytic reaction efficiency of the Au/MIL-88B（Fe）complex was tested using the4-NP hydrogenation reduction reaction as a model.The research results show that the Au/MIL-88B（Fe）complex has high catalytic activity in the 4-NP（0.5 m M,50 m L）hydrogenation catalytic reaction（the reaction is completed within 6 minutes and 30s）,and the reaction rate constant is 0.659 min^-1.Through tests under different experimental conditions,it was determined that the optimal dosage of the complex was 5 mg,the optimal p H of 4-NP was 5,and the optimal concentration of Na BH₄ in the reduction system was 50 m M.The compound also shows good versatility in reducing other nitrophenol pollutants（2-NP,3-NP and 2,4-DNP）and azo dyes（MO,CR and EBT）.Au/MIL-88B（Fe）has rapid catalytic efficiency in the presence of various environmental water samples and common inorganic salts,showing satisfactory application potential.After 10 cycles of use,the conversion rate of 4-NP is still as high as 90.8%,indicating that the compound has good reusability and stability.Catalytic reduction of 4-NP follows the Langmuir-Hinshelwood model,and the active product of the reaction is verified by ESR analysis as Au-H.It shows that in the experiment of converting 4-NP to 4-AP,H radical（·H）may be the key species to achieve reduction.The development of this work and the conclusions obtained provide new ideas for the preparation of Au NPs-based catalysts.The high efficiency and stability shown in the hydrogenation reaction of nitrophenol shows Au NPs-based catalysts owing great application potential in the actual purification field.