Studies On Preparation And Application Of Mesoporous Silicas Assembles By Metallic Tin

Metal incorporated mesoporous materials have a large number of potential applications in catalysis, sensing, adsorption, photonics and electroluminescence. In the present thesis, tin was incorporated into mesoporous silica(MPS) and periodic mesoporous organosilica(PMOs) via an impregnation and direct hydrothermal systhesis method using SnCl₂·2H₂O as tin source, respectively, and the structure of the final materials denoted as SnO₂/MPS or Sn-PMOs and their catalysis in the hydroxylation of phenol were also investigated by mesns of XRD, TEM, N2 adsorption-desorption, UV-Vis, XPS and FT-IR measurements.The results of XRD, EDS and FT-IR show that SnO₂ has been successfully confined in the pore channels of MPS by the impregnation method. The mesoscopic ordering of SnO₂/MPS depends on the solvent used during the systhesis: samples synthesized in ethanol retain an intact hexagonal symmetry while water as solvent leads to an amorphous structure. The presence of SnO₂ within MPS causes a drecease of pore volume, pore size and surface area due to the occupation of the pore space by SnO₂ species.For the samples SnO₂/MPS synthesized by the hydrothermal-calcined process, the molar ratio of silica to tin species(nSi/nSn) has a considerable effect on the distribution status of tin species within MPS and the pore structure of silica hosts. At a low concentration of tin species (nSi/nSn=100), a majority of tin is highly dispersed within the framework by replacing a fraction of silicon atoms. As the content of tin species increases to nSi/nSn=50, a fraction of tin transfers into crystalline SnO₂ confined into the pore channels of MPS, and the tin-incorporated silica still preserves a highly ordered mesoscopic structure and a desirable pore structure. More SnO₂ nanoparticles are confined into the pore channels when the tin concentration further increases to nSi/nSn=10, but at the cost of the mesoscopic ordering and the pore structure of silica hosts.The bridged orgnic groups–CH₂-CH₂- within the framework of the samples Sn-PMOs synthesized by hydrothermal-solvent extracted method remain intact and do not cleave under the systhesis conditions. At a low tin concentration in the mixture (nSi/nSn=100 and 50), tin species are demonstrated to enter the framework as the substitutes of a fraction of silicon atoms. When the tin concentration further increases to nSi/nSn=20, additional crystalline SnO₂ nanoparticles are observed in the pore channels, leading to a significant loss of mesoscopic ordering and a decrease of pore volume, pore size and surface area.The catalysis of Sn-incoporated silica mesoporous materials in the hydroxylation of phenol is closely related to the amount and distribution status of tin species within the silica hosts.The samples Sn-PMOs-50 show the best catalytic activity, with a phenol conversion up to 39.2% and a CAT and HQ selectivity of 46.3% and 24.8%, respectively.