Polymer Coated Modification And Application Research Of Magnetic Mesoporous Silica

Magnetic mesoporous silica materials having exceptionally high surface area, periodicity in pores of nanoscale dimensions, biocompatibility and biodegradable are one kind of new nanocomposites and have been widely used in targeted drug delivery, catalysis, enzyme, and sewage treatment. Chitosan (CS) is a type of natural polyaminosaccharide, synthesized from the deacetylation of chitin which is the second most abundant polymer in nature. Chitosan is widely used in wastewater treatment and biological medicine because of its special characteristics such as cheapness, biocompatibility, biodegradability, non-toxicity, adsorption properties. In order to get one kind of composite material with the characteristics of both chitosan and magnetic mesoporous silica, chitosan coated magnetic mesoporous silica (Fe3O4/mSiO2/CS) composites were prepared in this paper. Chitosan-polymethacrylic acid (PMAA) co-coated magnetic mesoporous silica (Fe3O4/mSiO2/CS-PMAA) nanoparticles were also synthesized to improve the composites’properties. The main contents and conclusions of this paper are as followes:1. Fe3O4 nanoparticles were prepared by hydrothermal method and chemical precipitation method. Fe3O4/mSiO2 nanoparticles were synthesized through sol-gel method with Fe3O4 nanoparticles as core and mesoporous silica as shell and the surfactants were removed from the mesopores by ion exchange with NH3NO3/ethanol solutions. Because Fe3O4/mSiO2 nanoparticles with Fe3O4 nanoparticles prepared by hydrothermal method as core were seriously agglomerative, Fe3O4 nanoparticles prepared by chemical precipitation method were used as core. The products were characterized by fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results showed that the Fe3O4/mSiO2nanoparticles were quite uniform in size with an average diameter of 100nm. The specific surface areas and total pore volumes of Fe3O4mSiO2 nanoparticles were calculated to be 665.48m2/g and 1.00cm3/g, respectively. The pore-size distribution of the Fe3O4/mSiO2 nanoparticles exhibited a single peak and implied the formation of uniform mesoporous with sizes of 2.9nm.2. Fe3O4/mSiO2/CS nanoparticles were prepared through "two-step"method and "one-step" method with Fe3O4/mSiO2 nanoparticles as core. About two-step method: Firstly, Fe3O4/mSiO2 nanoparticles were modified with succinic anhydride to get carboxylic acid-grafted magnetic mesoporous. Then chitosan was modified to the magnetic mesoporous silica nanoparticles through the interaction between the carboxyl on magnetic mesoporous silica nanoparticles and the amino of chitosan (CS) to get chitosan coated magnetic mesoporous silica nanoparticles with CS thickness 10nm. The behavior of drug release from Fe3O4/mSiO2/CS nanoparticles in different pH was tested and results showed that the nanocomposites had pH response. The operations of "two-step" method were complex and toluene, N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) which were organic solvents difficult to remove were used in the experimental process, therefore "one-step" method was used to synthesize Fe3O4/mSiO2/CS nanoparticles. About "one-step"method: nanoparticles were prepared by directly coating CS on the surface of nanoparticles with λ-(2,3-epoxypropoxy)proppytrimethoxysilane (KH560) serving as a linker to bridge the Fe3O4/mSiO2 nanoparticles and CS. Fe3O4/mSiO2/CS nanoparticles exhibited uniform sphere and the thickness of CS was about 5nm. The nanocomposites were used as absorbents to remove methylene blue (MB) in water. Results showed that the nanocomposites had a well adsorption for MB and the adsorption capacity was about 43mg/g. The MB adsorption kinetic and adsorption isotherm analysis were also studied. Results showed that the pseudo-second order equation was the most suitable one to describe the adsorption kinetics of MB for the nanocomposites, and the adsorption isotherm model of MB onto the nanocomposites belonged to Freundlich isotherm model. The nanocomposites with MB could be easily separated and collected under magnetic field.3. In order to improve the adsorption capacity of methylene blue, CS and PMAA co-coated magnetic mesoporous silica nanoparticles (Fe3O4/mSiO2/CS-PMAA) were synthesized through in-situ polymerization. The products were characterized by TEM, RT-IR, Thermal gravity analysis(TGA), Zeta potential. Results exhibited that the content of CS and PMAA was about 23%. The Zeta potential removed toward negative position after coating polymers and magnetic saturation became lower from 21.9eum/g to 6.1eum/g. Magnetic measurements revealed that the nanocomposites still possess superparamagnetic properties. The effects of initial MB concentration and contact time on the adsorption process were examined. The adsorption capacity of Fe3O4/mSiO2/CS-PMAA nanocomposites reached 101mg/g. The pseudo-second order equation was the most suitable one to describe the adsorption kinetics of MB for the nanocomposites and the adsorption isotherm was better explained by the Freundlich.