Functional Design And Performance Study Of Catalyst-silica Composite Nanostructure

In recent years,the application of mesoporous silica to immobilize catalysts has draw significant interesting on research.Nanocatalysts are easy to aggregate and difficult to recover,which makes them need to be immobilized in proper carriers.The performance of the catalyst is extremely influenced by the interaction between carriers and catalysts,thus,the design of the carrier morphologies is crucial for improving the perfoamence of catalyst.For immobilizing of catalysts,it’s very challenging to achieve high loading rate,catalytic activity and stability at the same time.In order to solve the above problems and promote further application of nanocatalysts such as medicine and other fields,it is necessary to design specific pore structures or new composite methods for different catalysts.Mesoporous silica is one of the excellent supports due to its adjustable pore size,large specific surface area and biocompatibility.In order to improve the catalytic activity,different morphological silica structures were designed and novel composite approaches were applied to obtain immobilized nanocatalysts.The thesis has investigated the morphology,structure and catalytic properties of various novel nanostructures.（1）Synthesis and performance studies of silica nanostructures with wide pore size distribution for immobilization of large molecule size enzymes.In this work,we prepared porous silica nanosheets with mesopore in the size range from several to dozens of nanometers,which may solve the low loading rate of large molecule size enzymes.Without any surface modification,the porous silica nanosheets show excellent immobilization capability（27 wt%）of alcohol dehydrogenase（ADH,>10 nm）.In addition,this ADH-silica nanosheets system showed effective catalytic performance not only with pure ethanol,but also alcohol drinks with complicated gradients or after relative harsh treatments.The substrate conversion rate increases about 30%.（2）Synthesis and catalytic application of silica nanosheets with morphology self-adjusting properties for efficient gold nanocatalysts immobilization.A network structure of silica nanosheets with self-adjusting morphology was prepared,which may accomplish the immobilization of gold nanoparticles with high loadings and activities without surface modification.When loading gold nanoparticles,due to the incomplete silica framework（4 nm pores）,the network structure has changed significantly,which strengthens the fixation of gold nanoparticles inside the nanosheets.In addition,the resulting gold nanoparticle-loaded silica nanosheets show high performance for the catalytic reduction of nitrophenols.The substrate conversion rate reaches 99%.（3）Bowl-like nanoreactor composed of packed gold nanoparticles and its enhanced photothermal effect for enzymatic reaction.In order to address the problem that some temperature-sensitive enzymes require high temperature for efficient catalysis,we prepared a novel bowl-like plasma nanoreactor made of dense gold nanoparticles connected with thin silica nanosheets.The open-ends bowl-like spheres have the advantages of facile mass transfer,large binding surface and high photothermal conversion at the same time.An extremely high photo-induced heating conversion efficiency can be achieved for the bowl-like spheres,which can reach 185℃at the maximum under 532 nm laser irradiation with low power（90 m V）.When used for the enzymatic reaction（COX enzyme）,the system showed much improved enzymatic catalysis performance due to the activation of COX by the light-induced thermal effect.The substrate conversion rate improves about 36%.（4）Synthesis of gold-silica multifunctional catalyst and its dual-enzyme activity.The surface-modified gold nanoparticles can only display one type of enzyme activities due to the coverage of stable groups,which limits the application of gold nanastructures with multiple types of enzyme activities.In order to solve the problem,chloroauric acid ions was adsorbed by electrostatic on the surface of silica nanospheres,then a hollow sphere structure composed of silica nanosheets embedded with gold nanoparticles was obtained in the subsequent hydrothermal process.The gold nanoparticles in this structure are evenly dispersed and very stable,and they show both peroxidase-like activity and glucose oxidase-like activity because they have not been wrapped by surfactant.（5）One-pot synthesis of gold/platinum alloy-silica composite catalyst for simple glucose detection cascade reaction.The monometallic gold-silica multifunctional catalyst demonstrated in the previous work shows low activity and is difficult to use for practical testing.To address this problem,this paper introduces gold-platinum alloys to modify the structure of gold to enhance its catalytic activity.Specifically,a silica nanosheet structure embedded with gold/platinum alloy nanoparticles was prepared using a one-pot method.The composite structure exploits the synergistic inter-metal interaction greatly enhancing its enzyme-like activity,which has a detection limit of 10μM as a peroxidase-like enzyme to detect H₂O₂.The composite structure can simulate both glucose oxidase-like and peroxidase-like activites in glucose detection,so that the detection can be conveniently completed without adjusting the p H of the environment,and the detection range is 0.2-0.5 m M.