| Magnetic mesoporous silica as a new type of network composite materials,is combined with magnetic nanoparticles and mesoporous materials.This new type of magnetic mesoporous materials as carriers has become the current focus in some study such as enzyme immobilization,heavy metal adsorption,drug delivery and so on.Due to the iron source magnetic layer is easy to dissolve under acidic conditions,it is rare to study for the preparation of magnetic mesoporous materials under acidic conditions using iron as a magnetic layer and silica as a mesoporous layer.Therefore,the preparation of magnetic mesoporous materials is very innovative under acidic conditions.In this paper,the preparation of mesoporous SiO2/dense SiO2/Fe3O4hollow microspheres under acidic conditions was studied.The effect of the dense SiO2 layer on the magnetic layer,and the effect of the amount of co-surfactant CTAB and hydrochloric acid concentration on microstructure of obtained materials were investigated in detail.Furthermore,the papain and laccase immobilization property of the mesoporous Si O2/dense SiO2/Fe3O4 multiply coated hollow microspheres was discussed.More detail is discussed chapter by chapter as follows:Firstly,the monodisperse SiO2 microspheres were prepared by a seeding technique.The?-FeOOH hollow microspheres were prepared by a core-shell structure method.Then,the dense SiO2 layer was coated on the?-FeOOH nanorods.The average thicknesses of the dense SiO2 layer were 2.7 nm,4.2 nm and 7.1 nm with the addition amount of TEOS increasing.After that,the dense SiO2/?-FeOOH hollow microspheres are soaked in 2 M hydrochloric acid for 24 hours.It was found that when the thickness of the dense SiO2 layer is around 2.7 nm,the composite microspheres have collapsed.Then,it can be seen from the N2 adsorption-desorption isotherms and the corresponding pore size distributions that when the thickness of the dense SiO2 layer is around 7.1 nm,the too thick dense SiO2 layer jams the pore formed by the interconnections of the magnetic nanorods.Therefore,the ideal thickness of the dense SiO2 layer is 4.20 nm.The mesoporous Si O2/dense SiO2/Fe3O4 hollow microspheres were successfully prepared under acidic conditions.Firstly,the effects of hydrochloric acid concentration on the preparation of mesoporous SiO2/dense SiO2/Fe3O4 hollow composite microspheres were discussed detailedly.It is obvious from the TEM photographs and pore size analysis that when the concentration of hydrochloric acid is2 M,the morphology and pore size are the best.Secondly,the effects of CTAB on the morphology and pore size of mesoporous SiO2/dense SiO2/Fe3O4 hollow composite microspheres were studied.When the CTAB is 0.05 g,the microstructure is the most regular and the spherical shape is the best.The immobilization of papain and laccase was studied by mesoporous SiO2/dense SiO2/Fe3O4 hollow composite microspheres.When the peak pore size of mesoporous SiO2/dense Si O2/Fe3O4 hollow composite microspheres was 3.74 nm,the immobilized amount of papain reached the maximum?222 mg/g?.And,the pH stabilities and temperature stabilities of the immobilized papain activity were much higher than that of free papain activity.Then,when the peak pore size of the mesoporous SiO2/dense SiO2/Fe3O4 hollow composite microspheres is 4.30nm,the immobilized amount of laccase reached the maximum?234 mg/g?.The pH stabilities and temperature stabilities of the immobilized laccase activity were much higher than that of free laccase activity.And the removal of 2,4-dichlorophenol by immobilized laccase can reach about 80%. |
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