Controlled Synthesis And Properties Of Mesoporous Silicate Composite Nanoparticles

In recent years, core-shell nanocomposite materials are widely applied in manyfields, because their many properties are better than the single component material.Nanocomposite materials have widely applied in many fields including packing, optics,catalysts, biomedicine, drug delivery, multifunctional coating materials. Herein, asimple method was employed to the preparation of mesoporous Ni3Si2O5(OH)4andMnSiO3core-shell microspheres. And mesoporous Ni/SiO2microspheres have beensuccessfully synthesized by reduction of Ni3Si2O5(OH)4. The as-obtained productswere characterized by scanning electron microscopy (SEM), transmission electronmicroscopy(TEM), X-ray powder diffraction (XRD) and Brunauer-Emmett-Teller(BET). The effects of catalysts structure, reaction temperature, reaction pressure on thesilica supported nickel catalyst were also investigated in the liquid-phasehydrogenation of m-dinitrobenzene to m-phenylenediamine. The main points can besummarized as follows:1. The mesoporous nickel-silica composite hollow microspheres have beensuccessfully prepared. we reported a process for synthesizing mesoporous Ni/SiO2hollow microspheres by reduction of Ni3Si2O5(OH)4, which were synthesized by theabove self-template approach. N2adsorption-desorption isotherm and pore diameterdistribution were measured on an ASAP2020apparatus. The surface areas werecalculated by the Brunauer-Emmett-Teller (BET) method. The BET surface areas ofthe Ni3Si2O5(OH)4microspheres and the Ni/SiO2microspheres are about214.21m2/gand222.81m2/g, respectively. The pore volume of the Ni3Si2O5(OH)4microspheres and the Ni/SiO2microspheres are about0.42cm3/g and0.49cm3/g, respectively. Amajority of the pores for the Ni3Si2O5(OH)4microspheres and the Ni/SiO2microspheres are about7.76nm and8.85nm, respectively. Hence, the morphology andsize of the Ni3Si2O5(OH)4before and after reduction changed slightly. The Ni/SiO2microspheres which were synthesized by reduction of Ni3Si2O5(OH)4have relativelylarger surface areas.2. The catalytic activity of Ni/SiO2catalysts were also evaluated by them-dinitrobenzene hydrogenation reaction. These mesoporous Ni/SiO2microsphereswith large BET surface areas, exhibit good catalytic activity in m-dinitrobenzene andhigh selectivity of m-phenylenediamine in the end. By studying the influence ofcatalysts structure, reaction temperature and reaction pressure to the m-dinitrobenzeneliquid hydrogenation process, determined the appropriate reaction conditions of them-dinitrobenzene liquid hydrogenation process. Under the appropriate condition, theselectivity rate of the m-phenylenediamine was reached to94%and the conversion rateof the m-dinitrobenzene was reached to100%.3. The SiO2/MnSiO3core-shell microspheres and MnSiO3hollow microsphereswere prepared by a hydrothermal method at180°C. The morphology of products maybe affected by changing the molar ratio of Si/Mn. The chamber and shell thickness ofthe manganese silicate microspheres can be controlled by adjusting the syntheticparameters of MnSiO3, such as the reaction time. Temperature is also an importantfactor. With the increasing of reaction temperature, the disappearance of the silica coreis accelerated, which may shorten the formation time of the MnSiO3hollowmicrospheres. N2adsorption-desorption isotherm and pore diameter distribution weremeasured on an ASAP2020apparatus. The BET surface areas of the mesoporousSiO2/MnSiO3core-shell microspheres and MnSiO3hollow microspheres correspondingto reaction time of6h and24h are about424.12m2/g and493.98m2/g, respectively.The pore volume of the mesoporous SiO2/MnSiO3core-shell microspheres andMnSiO3hollow microspheres are about0.33cm3/g and0.44cm3/g, respectively. Amajority of the pores for the mesoporous SiO2/MnSiO3core-shell microspheres andMnSiO3hollow microspheres are about3.03nm and3.44nm, respectively. Hence, theSiO2/MnSiO3core-shell microspheres and MnSiO3hollow microspheres which weresynthesized by a hydrothermal method have relatively larger surface areas. Using H2asreducing agent, manganese oxides were obtained by reduction of MnSiO3hollow microspheres. With the process of drying, the products could be oxidized by oxygen inthe air after the reduction.