Designed Synthesis, Morphology Control And Catalytic Application Of Functional PMO Materials

Periodic mesoporous organosilicas (PMOs) are synthesized from the hydrolysis-condensation of organo-bridged precursors (R'O)3Si-R-Si(OR')3 in the presence of surfactant. Due to the ordered mesoporous structure, high content and uniform distribution of organic groups, vacant channel pore, tunable physical and chemical properties, PMO materials have opened new opportunities for designing and synthesizing, at molecular level, the hybrid porous materials with different functionality and interesting properties. PMO materials are of potential importance for applications in adsorption, separation, catalysis, optical, electrical and host-guest chemistry. Moreover, some special applications of PMO depend on the macroscopic morphology of these materials. Accordingly, the research work described in this PhD thesis focuses on:1) designed synthesis of new types of organo-bridged PMO materials; 2) morphology-controlled synthesis of functional PMO materials with certain morphology; 3) applications of functional PMO materials with special morphology in heterogeneous organocatalysis.In Chapter I, we reviewed the recent progress in PMO materials, mainly focusing on:1) the functional design, synthesis and applications of molecularly-ordered PMO, chiral PMO and optical PMO materials; 2) morphology-controlled synthesis and applications of PMO materials with micro/nano spheres, polyhedron, films, helical rods and hollow structures, with the emphasis on the preparation of hollow-structured PMO spheres.In Chapter III, polyethynylbenzene-bridged PMO materials have been successfully synthesized under acidic conditions from the single-source precursors of bis- or tris(triethoxysilylethynyl)benzene in the presence of Brij 76 as a structure-directing agent. The 1,4- and 1,3-diethynylbenzene-bridged PMO materials have ordered mesotructure and high surface area; while the 1,3,5-triethynylbenzene-bridged hybrid material shows an amorphous structure due to the severe cleavage of Si-C bonds.In Chapter IV, molecularly-ordered phenylene-bridged PMO nanosphere (denoted as MO-PhPMO) has been successfully synthesized using CTAB as a structure-directing agent and NaOH as the base in an extremely diluted solution of BTEB. The formation of molecular-scale periodicity of PMO is influenced by the concentrations of CTAB, NaOH and BTEB in the initial gels, as well as the temperature applied in the synthetic procedure. Based on this method, the hollow-structured phenylene PMO (denoted as MO-H-PhPMO) with a crystal-like wall was synthesized for the first time by using hematite nanoparticles as the hard template. The particle size of H-PhPMO is mostly in the range of 150-300 nm with a hollow core diameter of ca.90 nm.In Chapter V, the hollow-structured phenylene PMO was facilely functionalized with MacMillan catalyst (denoted as H-PhPMO-Mac) via a co-condensation process and "click chemistry" post-modification. The catalytic test in the asymmetric Diels-Alder reaction indicate that these hollow-structured MacMillan-catalyst-functionalized PhPMO spheres, i.e., the H-PhPMO-Mac catalyst, exhibits higher catalytic activity than solid (non-hollow) PhPMO-Mac catalyst and can well be applied as a water-tolerant and highly efficient catalyst. The H-PhPMO-Mac catalyst can be reused at least for seven runs without significant loss of catalytic activity. Moreover, the catalysts prepared via the co-condensation process and "click chemistry" post-modification exhibit higher catalytic efficiency than those prepared via the grafting method.