ZnO-coated SiO2 nanocatalyst preparation and its photocatalytic activity over nitric oxides as an alternative material to pure ZnO

Core-shell nanospheres, CSNp, consisting of silica as a core and zinc oxide as a shell were prepared via a simple and environmentally friendly procedure. Silica cores with a mean diameter of 300 nm were prepared through the hydrolysis-condensation reactions in the presence of hyperbranched poly(ethylene)imine (HBPEI) followed by calcination and chemical surface modification with the use of HBPEI. To fabricate the core-shell structure, various amounts of zinc nitrate hexahydrate were precipitated using the carboxymethyl poly(ethylene)imine polymer (Trilon P) as a precipitator. To this suspension, the as synthesized modified silica powder was added with the aim to develop electrostatic bonds between the carboxyl groups of TRILON P and the amino groups of the cationic HBPEI polymer. The optimization of processing parameters led to the development of homogeneous core-shell structures bearing a well-developed nanocrystalline zinc oxide shell over each silica core. The material with the optimum shell showed excellent photocatalytic activity over nitric oxides as the photocatalytic yield reached 72.9%.