Research On The Self-catalytic Synthesis Of Metal Oxides/Silica Nanocomposite

Metal oxide nanoparticles?mNPs?have become a research hotspot in many fileds such as physics,chemistry,materials and life sciences in recent years due to their quantum size effect,high specific surface area and high atomic ratio of surface atoms.However,m NPs have very high surface energy,which makes them easy to agglomeration during practical applications,resulting in reducing reaction activity,therefore,composites materials are always constructed to protect the m NPs.Silica,as one of carrier materials,has becoming an ideal carrier materia l for many m NPs due to its good ultraviolet transmittance,high chemical stability and easy acquisition.In this thesis,we designed a new and simple self-catalytic synthetic route to obtain organic-inorganic hybrid metal salt/silica materials under near-neutral reaction environment using the protonated amine groups as catalytic site without any additional acid or basic catalyst to obtain metal oxide nanoparticles/silica nanocomposite?mNPs@SiO₂?in-situ.Firstly,copper arginine salt was prepared by using arginine and copper nitrate as reactant.The protonated amine group in this obtained molecular was used as a catalytically active site to realize the self-catalytic hydrolysis and condensation of tetraethylorthosilicate?TEOS?in the mixture of water and ethanol to form Si-O-Si networks.Copper arginine was encapsulated in Si-O-Si networks in the same time,obtaining organic-inorganic hybrid copper arginine/silica nanocomposite.Finally CuO@SiO₂ nanocomposite was obtained by further calcination.The effects of the ratio of water and ethanol on the structure and morphology of the product were investigated.With the increase of the amount of ethanol,the morphology tend to be more prilling,and the content of CuO NPs was increased.The material construction mechanism based on "supramolecular assembly-coating" was proposed.The prepared material was applied to the degradation of organic dyes,with the catalytic activity coefficients to be K'=28.4 s^-1·g^-1.Secondly,targeting the disadvantages of low m NPs content and poor dispersion due to the uncontrollability of the coating process,we took the prepared bromoacetate metal salt?MBA?as the metal oxide precursor,3-aminopropyltriethoxysilane?APTES?and TEOS as dual silicon source,the protonated amine group was taken as the catalytically active site to induce the self-catalytic hydrolysis and condensation of APTES and TEOS to form Si-O-Si networks.Meanwhile,MBA was introduced into the Si-O-Si network by covalent introduction,which can ensure a molecular-level dispersion of metal ions,favoring the in-situ generation of m NPs with an average particle size below 5 nm with highly dispersed characteristics.The obtained materials have spherical morpholopgy.The ratio of water and ethanol has significant effect on the morphology of the product while the ratio of two silicon sources has impact on the size of the as-obtained nanocomposite.An “aggregation-growth” mechanism can explain the formation of nanocomposite.CuO@SiO₂,Co₃O₄@SiO₂ and Ag-Co₃O₄@SiO₂ nanocomposite were obtained by this route,which has excellent catalytic activity,superparamagnetism performance.Finally,in order to obtain materials with nanoscale size and realize controlled synthesis of nanocomposite,the feasibility,universality and controllable synthesis method of self-catalytic preparation of m NPs@SiO₂ by APTES as a single silicon source were discussed.The mechanism of nucleation-aggregation with "water clusters" as template was proposed.The effects of different molecular weights of PVP,dosage of APTES,temperature and solvents on the morphology of the materials were investigated.By precisely adjusting the ratio of water to ethanol,both of the nanocomposite size and m NPs size can be controlled simultaneously.The controllable synthesis of materials can be explained by reaction kinetics and thermodynamics as well as intramolecular interactions.CuO@SiO₂ material with excellent catalytic performance,ZnO@SiO₂ nanocomposite with tunable fluorescence properties and CdO@SiO₂ nanocomposite was prepared.