Mesoporous Organic Silica Magnetic Microspheres: Controllable Synthesis And Laccase Immobilization

Enzyme has been applied very widely in many fields since it is effective, quitespecific when used in catalytic converters. However, enzyme is sensitive to thereaction environment, especially temperature and pH, so it is easy to be destroyed toloose catalytic activity. Enzyme can’t be reclaimed in reaction system. All thequestions limited greatly the application of the enzyme. The technology of enzymeimmobilized gives a good solution to the problems. The immobilized enzyme havebetter pH stability and thermal stability than free enzyme. The immobilized enzymehas a great potential for application in many areas such as biomedicine andenvironment defense. Mesoporous material possesses uniform pore size distributionand high surface area, which is very beneficial to enzyme immobilization. Magneticmesoporous material as a kind of enzyme carrier has attracted much attention becauseit possesses both mesoporous and magnetic properties. In this thesis, adjustable poresize and function modification of the magnetic mesoporous silica was investigatedbased on the synthesis of the hollow magnetic mesoporous silica microspheres. Thestability of the laccase immobilized on the mesoporous composite microspheres wasalso be studied. More detail is discussed chapter by chapter as follows:In the acidic condition, cationic surfactant （CTAB）, silicon source （TEOS） andexpanding agent （TMB） react with each other with hydrolysis-polycondensationmethod, then the products were roasted to remove the surfactant and reduced toprepare a series of magnetic mesoporous microspheres with different pore size. Thepore size can be adjusted from2.9nm⁵.1nm by changing the doses of expandingagent. The mesoporous composite spheres which added expanding agent show anobvious increase in surface area and pore size, from504m²·g^-1to719m²·g^-1, from2.9nm to5.1nm, separately. With the increase of expanding agent dose, both thesurface area and pore size of mesoporous composite spheres reveal a trend of increaseat first and then decrease. When n（TMB）:n（CTAB） is1.5:1, the sample has the largestsurface area (719m²·g^-1), and when n（TMB）:n（CTAB） is2:1, the sample has thebiggest pore size （5.1nm）.Mesoporous composite microspheres with different pore size were used toimmobilize laccase. The samples added expanding agent have a higher laccaseimmobilization, M3samples has the biggest one (250mg·g^-1). The temperature stability of the immobilized laccase is improved a little. The immobilized laccase canstill keep50%activity under60℃, but when the expanding agent was added more,the temperature stability of immobilized laccase decreases. The pH stability ofimmobilized laccase was also improved, it can keep60%activity when pH is6.0.Adding expanding agent can improve the immobilized laccase stability becausethicker pores strengthen the protection to laccase.Amino-group was successfully introduced to the mesoporous SiO₂/Fe₃O₄composite microspheres by chemical modification with post-synthesis. The surfacearea and pore volume of amino-functional mesoporous spheres decrease largely, from686m²·g^-1to170m²·g^-1， from0.87cm3·g^-1to0.30cm3·g^-1, respectively.Epoxy-functional mesoporous composite spheres were also been prepared by theco-condensation of tetraethyl orthosilicate （TEOS） and3-glycidoxypropyltrimethoxylsilane （GPTMS）. The surface area and pore volume of epoxy-functional mesoporousspheres have a modest decline, from686m²·g^-1to539m²·g^-1, from0.87cm3·g^-1to0.70cm3·g^-1, respectively. The epoxy-functional mesoporous spheres were also used toimmobilize laccase. The researches show that10%-epoxy-functional mesoporousspheres have a largest laccase immobilization (283.6mg·g^-1). The stability of theimmobilized laccase is also improved. The immobilized laccase can keep60%under60℃, and keep70%when pH is7.0.