Preparation And Application Of Materials Based On Ordered Meso/Macro Porous SiO₂ Based Materials

Mesoporous/macroporous materials have been extensively studied due to their highly ordered and easily controlled pore structure, large surface area and narrow pore size distribution. These features are of great interest for various potential applications such as catalysis, adsorption, separations, and biomedical systems. More and more specialists and scholars have dedicated to explore their synthesis and relative performance. Based on special characters that combining high diffusion of macroporous with high surface area and high pore volume ratio of mesoporous silica, hierarchical mesoporous/macroporous silica materials have high accessibility and storage capacity. In recent years, various kinds of templating approaches have been proposed to synthesize hierarchically porous silica materials. For example, colloidal particles, polymers, emulsion droplets were employed to create macroporous structures while surfactants were employed to create mesoporous structures. However, there still exist many problems such as the adjustment of both well-ordered mesostructure and well-defined morphology, control of interaction of different templates and the improvement of synthesis process. In this thesis, we use the dual-templating method in order to synthesize hierarchical mesoporous/macroporous silica materials with high-density macropores and well-ordered and adjustable mesopores. Subsequently, we use the obtained materials as support to explore its catalytic performance in the direct hydroxylation of benzene to phenol. The main contents are as follows:1. In the fabrication process, using polystyrene(PS) and P123 as templates, tetraethoxysilane(TEOS) as the source of silicon, hierarchical macro-mesoporous silica material with 3-D interconnected macroporous structures, well-ordered mesostructure and controlled pore size based polystyrene microspheres has been synthesized. In addition, we research into the factors which influence the pore structure and morphology of the silicas.2. Iron doped mesoporous/macroporous silica materials(Fe/Si O2) are prepared via impregnation of mesoporous/macroporous silica materials into iron nitrate nonahydrate(Fe(NO3)3·9H2O) solution, evaporation, and subsequent simple thermal condensation. This experiment uses Fe/Si O2 as catalyst to evaluate the direct hydroxylation of benzene to phenol. It is found that the optimal reaction temperature was 60 °C, reaction time 2 h, the mole ratio of benzene and hydrogen peroxide 1:1.3. The obtained graphitic carbon nitride materials are used to be support of catalyst. Iron doped graphic carbon nitride(Fe/g-C3N4) is prepared as mentioned above. The catalytic efficiency of Fe/g-C3N4 is tested by tracking the reaction of hydroxylation of benzene to phenol. It is found that the Fe/g-C3N4 hybrid materials show good catalytic performance for the phenol production from benzene.4. Fe/g-C3N4 and mesoporous/macroporous silica(Fe/g-C3N4/Si O2) hybrid materials were fabricated by a facial thermal polymerization approach using melamine, iron nitrate nonahydrate(Fe(NO3)3·9H2O) as precursors and mesoporous/macroporous silica as a support. The as-synthesized Fe/g-C3N4/Si O2 composites could be used as heterogeneous catalysts for the oxidation of benzene to phenol using H2O2 as benign oxidant under ambient conditions. It is found that the Fe/g-C3N4/Si O2 hybrid materials show a catalytic performance for the phenol production from benzene to sole Fe/Si O2 and Fe/g-C3N4 catalysts. Under the optimal conditions, up to 13.4% phenol yield is achieved over the hybrid materials, with 53.2% phenol selectivity.