Preparation Of Janus Magnetic-Mesoporous Silica Microsphere And Study Of Its Supported Au Catalyst

In recent years,Janus nanocomposite particles(NCPs)have received widespread attention from researchers,due to their asymmetry characteristics in morphologies,compositions and properties,which make them have broad application prospects in the fields of solid surfactants,catalysis,self-driven motors,biomedicine,et al.However,because of the preparation process of Janus nanoparticles involves thermodynamics and dynamics factors,its structure is difficult to be precisely regulated.Meanwhile,the synthesis of functionable Janus NCPs is still under exploration.Therefore,how to controllably design and synthesize Janus NCPs and deeply understand its formation mechanism to expand its functionality and realize its efficient controllable preparation and practical application,is a common concerned topic in this field.In this thesis,an organosilane with a reactive group is selected.By regulating the wettability between the seed particles and the organosilane to control the initial heterogeneous nucleation numbers and simultaneous controlling the reaction kinetic of hydrolysis and condensation of organosilane from the sol-gel reaction conditions to control the growth model,we controllably synthesized the mesoporous organosilca Janus NCPs,and deeply studied its formation mechanism.The surface of the Janus NCPs had been modified,and the hydrophilicity and hydrophobicity of the Janus NCPs were investigated.We further synthesized Janus NCPs with significant difference in aspect ratio,and assembled them with gold nanoparticles to form Janus structural catalysts.The catalytic properties of the Janus structural catalysts with different aspect ratios on the nitroaromatic compounds were investigated.The main research content and results are summarized as follows:(1)Kinetics-Controlled Preparation and modification of Janus Fe3O4-mesoporous Silica NCPsThe sodium citrate stabilized Fe3O4 nanoparticles(Fe3O4 NPs)were used as seeds and dispersed in a surfactant cetyltrimethylammonium bromide(CTAB)aqueous solution,and then an organosilane 1,2-bis(triethoxysilyl)ethylene(BTTE)with active C=C bonds was added dropwise.Under the catalysis of ammonia,BTTE was heterogeneously nucleated on the surface of Fe3O4 NPs,and thus the Janus Fe3O4-mesoporous silica(Fe3O4-oSiO2)NCPs were obtained.The effect of the reaction parameters,such as BTTE content,CTAB content,and the reaction temperature on the morphologies of the Janus Fe3O4-oSiO2 were investigated.The growth mechanism of these Janus Fe3O4-oSiO2 NPs was proposed,and extended to design and synthesis of other types of seed particles and silane coupling agents.The surface of oSiO2 nanorods of Janus Fe3O4-oSiO2 NPs can be modified through thiol-ene click reactions to gain.Janus NCPs with different wettabilities.(2)Preparation of Janus Fe3O4-SiO2-NH2-Au NCPs and its catalytic reduction propertiesBased on the controllable preparation of Janus NCPs,BTTE and tetraethoxysilicate(TEOS)were used as mixed precursor.By changing the overall amount of BTTE/TEOS,SiO2 nanorods of significant difference in aspect ratio with length from 81±15 nm,388±66,to 10000±151 nm were obtained.After adsorbing Au NPs,different Janus structural Fe3O4-SiO2-NH2-Au catalysts were obtained.The catalytic reduction performances of 4-nitrophenol(4-NP)and 2-nitroaniline(2-NA)in the presence of NaBH4 reducing agent were studied.The catalytic rate constants(k)of the three catalysts for 4-NP and 2-NA were 0.69,1.73,7.96 min-1 and 1.66,2.11,11.0 min-1,respectively.As the aspect ratio increases,their catalytic activity increases significantly,which is higher than the counterpart Au-loaded magnetic mesoporous silica catalysts reported in current literatures.The catalysts can be easily recycled under a magnetic field and show high stability and catalytic activity even after 7 times repeated use.