Preparation Of Metal Nanoparticles Functionalized Silica Hollow Nanospheres For Heterogeneous Catalysis

Hollow structured nanospheres have wide applications in the field of optical, electronic,biomedical and catalysis due to its unique nanostructures. Compared to the traditionally supported catalysts, the hollow nanoreactors showed unique properties as supporter for catalysis. In this thesis, the hollow nanospheres with small particle sizes were successfully fabricated, the structure and components of the porous materials can be modified and adjusted.Their potential applications in heterogeneous catalysis were investigated. The main results are summarized as follows:1) Ultra-small Au nanoparticles(< 2 nm) supported on hollow silica nanospheres were successfully fabricated with the aid of chemical modification(-SH groups) or through simple immersion method, leading to supported catalysts Au/SH-HNS and Au/HNS. The resulting solid catalysts showed good thermal stability and the small particle sizes could be remained even at high temperature of 350 o C. Such catalysts were catalytically active in the oxidation of styrene using O2 as oxidant under 1 atm pressure. The catalytic results showed that the activity strongly depends on the Au loading amount, and the loading of 4-5 wt% led to the highest activity. Significant rate enhancement was observed with gold nanoparticles supported on pure silica in comparison with thiol modified silica nanospheres, suggesting the negative effects of thiol groups. The solid catalyst could be reused at least 8 reaction cycles without significant decrease in activity and selectivity. This study not only supplies an active,recoverable catalyst for the green transformation of styrene, but also demonstrates that the hollow silica nanosphere material has a superior ability in stabilizing metal nanoparticles against growth.2) Ultra-small silica hollow nanospheres(particle size of 18±2 nm) with finely engineered inner and outer hydrophilic/hydrophobic surface properties were fabricated by using phenyltrimethoxysilane(PTMS) and tetramethoxysilane(TMOS) as precursors and F127(EO106PO70EO106) as single micelle template. The surface of hollow nanospheres could be transfered from hydrophilic to super hydrophobic through tuning the content of phenyl groups. Notably, the location of phenyl groups could be controlled. At PTMS/TMOS mass ratio less than 1/3, the selective integration of phenyl group in the inner surface was observed due to the diffusion and condensation of hydrophobic PTMS into the hydrophobic core of F127 single micelle. The condensation of TMOS around hydrophilic EO region of F127 results in the formation of hydrophilic outer surface. At high PTMS/TMOS mass ratio, phenyl group could be incorporated homogeneously in both the inner and outer surface. The location of phenyl group has been further confirmed by measuring the acid concentration for the sulfonated samples and the influence of the inner/outer surface properties on the catalytic performance of silica hollow nanospheres was investigated in hydrogenation of 4-nitrophenol and selective oxidation of benzyl alcohol reactions in water medium after loading with Pdnanoparticles.