Surface Functionalization Of Magnetite Nanoparticles And Its Application In Heterogeneous Reaction

Thanks to the fast respond to an external magnetic field,superparamagnetic magnetite nanoparticles are widely applied in various fields,such as catalysis,biotechnology,magnetic resonance imaging(MRI)and data storage.However,the bare magnetite nanoparticles can be easily corrupted or destroyed in acidic media,which extremely restrict their applications and stabilities.In this paper,we adopted the strategy of coating the magnetite nanoparticles with silica and studied the formation and structure of the coated magnetic nanoparticles by changing the synthetic methods and controlling the thickness of silica,then performed their stability in acidic media.On this basis,the surface wettability of nanoparticles was tuned via the "grafting from" strategy with different monomer ratio,the nanoparticles were applied in the typical liquid/liquid heterogeneous oxidation reaction.In the first part,the core-shell magnetite@silica was synthesized in a one-pot process using reverse micelles as nanoreactors.The core diameter of the magnetite nanoparticles can be controlled by adjusting the mole ratio of polar solvent and surfactant(w=polar solvent/surfactant).When the w value changed from 14.4 to 11.6,the diameter of the nanoparticles changed from about 7 nm to 5 nm.The thickness of silica shell can be adjusted with different amount of adding TEOS,it can be varied from about 5nm to 2nm when the adding amount changed from 12mL to 4mL.The results showed that the magnetite was coated with silica successfully,the size of as-synthesized silica coated magnetic nanoparticles was controllable.After the coating,the saturated magnetization decreased from 53.89emu/g(bare magnetite)to 35.53emu/g(with about 2nm silica shell)and 16.66emu/g(with about 5nm silica shell),however,the coercivity was about 0,which showed the strong superparamagnetism of the coated nanoparticles.In the second part,the surface of the coated magnetite nanoparticles with silica was modified via surface initiated atom transfer radical polymerization(ATRP).The a-bromoisobutyryl bromide was grafted onto the surface of the nanoparticles as ATRP initiator,which subsequently initiated random copolymerization of hydrophobic styrene(St)and hydrophilic hydroxyethyl methacrylate(HEMA).The surface wettability of nanoparticles can be adjusted by changing the volume ratio of monomers.The surface functionalized nanoparticles were applied into the benzyl alcohol oxidation in Aneilli system,the results showed that when the monomer ratio is 4/1 in volume,the nanoparticles promotion to the oxidation was the most efficient.