Synthesis Of Monolayer Aggregate Nanometer Gold Carrier Catalyst And Its Catalytic Performance Regulation

Au nanoparticles (AuNPs) have important applications in a variety of catalytic reaction system due to their higher surface area, catalytic activity and chemical stability. The AuNPs size, dispersion, shape, surface composition and structure are the main factors that influence its catalytic properties. In order to improve AuNPs catalytic activity, researchers usually load AuNPs on the surface or into the skeleton structure of the carrier materials through in situ fabrication method. It can not only control the AuNPs size, shape and dispersion, but also can effectively prevent from aggregation and decreasing of specific surface area.Infact, catalytic activity and selectivity of supported gold catalyst depends on the higher dispersion and stability of AuNPs, the interaction between carrier materials and AuNPs as well as its surface structure.The various functional molecules can regulate AuNPs properties and surface structure. Among them, organic mercaptan and thiol compounds can greatly improve AuNPs functionality, biocompatibility and targeting specific properties by self-assembly method. The self-assembly single molecular layer of alkanethiols on AuNPs surface can form good steric effect to stabilize AuNPs leading to easily dispersed in a solvent. Moreover, it is accessible to obtain controllable single molecular layer structure.Based upon our group’s previous research work, in this thesis, we proposed a novel method to synthesize AuNPs on the shell layer of composite microspheres with inorganic-organic hybrid network structure as carrier material. Its restricted structure space can control the size and shape of AuNPs. In addition, the surface covering layer density of AuNPs cab be regulated by desorption of alkanethiol molecules in an excess of sodium borohydride solution. Comparing to those of gold nanoclusters modified by alkanethiol without supported material reported in the literature, the structure of the synthesized carrier is more accessible to control the stability and surface activity of AuNPs. Moreover, the surface structure of AuNPs assembled the alkanethiol monolayer can regulate the catalytic activity.This thesis involves three parts:(1) The copolymer of N-isopropylacrylamide (NIPAM) and methacryloxy propyl trimethoxyl silane (MPTMS) with the organic-inorganic hybrid network structure were synthesized using Polystyrene/silica (PS/SiO2) composite microspheres as the core component. After the surface modification by (3-mercapto propyl) trimethoxysilane (MPS), loading AuNPs PS/SiO2/P(NIPAM-co-MPTMS)-Au supported catalysts were fabricated through in-situ reduction using sodium borohydride as the reducing agent and sodium citrate as stabilizer and reducing agent The alkanethiols self-assembled monolayers were formed onto the AuNPs surface of PS/SiO2/P(NIPAM-co-MPTMS)-Au(SR) supported catalyst.(2) The catalytic reduction of4-nitrophenol (4-NP) to4-aminophenol (4-AP) was chosen as a model reaction, using sodium borohydride as reductant. In the same reaction conditions, we conduct the catalytic activity between PS/SiO2/P(NIPAM-co-MPTMS)-Au and PS/SiO2/P(NIPAM-co-MPTMS)-Au(SR) two type of the supported catalysts. The results showed that the catalytic activity of PS/SiO2/P(NIPAM-co-MPTMS)-Au(SR) significantly decreased. This is due to the thiol molecules were occupied on the surface of AuNPs, leading to reduce the surface active sites, which can inhibit the reaction substrate and catalyst contact.(3) In an excess of sodium borohydride solution, the catalytic reduction of4-nitrophenol (4-NP) to4-aminophenol (4-AP) was chosen as a model reaction to evaluate the catalytic performance of PS/SiO2/P(NIPAM-co-MPTMS)-Au and PS/SiO2/P(NIPAM-co-MPTMS)-Au(SR) supported catalysts in the same conditions. The results showed that the surface covering alkanethiol chains onto AuNPs cab be regulated by desorption effect of excess sodium borohydride to Au-S bond. The surface structure of AuNPs was significantly influenced by the chain length and dosage of alkanethiol, and sodium borohydride dosage. The catalytic activity of PS/SiO2/P(NIPAM-co-MPTMS)-Au(SR) supported catalysts can be adjusted by changing the surface structure of AuNPs. According to the results, we proposed the possible mechanism for the regulated catalytic activity based on the changing of the surface micro-environment of AuNPs.