Preparation Of Monolithic Macroporous-Mmesoporous SiO₂ And Their Application In Lipase Immobilization

The immobilized enzyme not only retains the activity and selectivity of the free enzyme,but also overcomes the shortcomings of low stability,susceptibility to degeneration and inactivation due to environmental influences,difficulty in recovery,and inability to recycle of free enzyme.Therefore it has a wider application space.At present,the use of various nanomaterials for immobilizing enzymes is a research hotspot in this field,however nanomaterials are easy to agglomerate or difficult to recycle and reuse,which limits their practical application.The hierarchical porous monolithic material not only has a large specific surface area,and diverse and adjustable channel structures,but also is easy to recycle due to its macro-size,which can significantly improve the immobilization efficiency,catalytic activity and reusability of enzyme molecules.The enzymes immobilized on this material havs good application prospects.This thesis is devoted to the preparation of monolithic hierarchical porous silica materials,and to study their application in lipase immobilization.Monolithic macroporous-mesoporous SiO₂ materials were prepared by using an epoxy resin macroporous polymer as template,they have high porosities,high specific surface areas and multi-level channel structures,and were used as carriers for lipase immobilization.The prepared immobilized enzymes were used for the chiral resolutionof（R,S）-1-phenylethanol.1.A monolithic macroporous-mesoporous SiO₂ was prepared by using an epoxy resin macroporous polymer with columnar structure as template.Under solvothermal conditions,the macroporous mesoporous SiO₂ material was epoxy modified with silane coupling agent（KH560）.The epoxy-functionalized macroporous-mesoporous silica（EMMS）was used as support for immobilization of lipase.The results show that the epoxy-functionalized material has the same three-dimensional continuous channel structure as that of the SiO₂ material,and has a high specific surface area.The activity of the immobilized lipase（PFL@EMMS）reached a maximum of 3750.2 U/g under the optimal conditions.And the enzyme activity recovery rate was as high as 218%.Compared with the free enzyme,the immobilized lipase showed good stability,and the relative enzyme activity remained 42.3%after 9 times of reaction.2.A monolithic titanium-silicon material（MNCMM-TiSi）constructed of microporous-mesoporous ultra-thin nano-film was prepared by using the pillared epoxy resin macroporous polymer as monolithic macroporous template and cetyltrimethylammonium bromide（CTAB）as mesoporous porogen through the titanosilicate species assembled with CTAB micelles growing into nanofilm on the surface of the polymer skeleton by hydrogen bonding and electrostatic interaction.The activity of immobilized lipase（PFL@MNCMM-TiSi）reached 3990.3 U/g under optimal conditions and the enzyme activity recovery rate reached 246%.The stability of the immobilized lipase were significantly improved.The initial enzyme activity retained 68.3%after 60 days of storage.3.The chiral resolution of（R,S）-1-phenylethanol was performed using the PFL immobilized on EMMS（PFL@EMMS）as a chiral catalyst.Effects of solvent,water activity,reaction time,catalyst dosage and the molar ratio of（R,S）-1-phenylethanol to acyl donor on the resolution were investigated.It was found that when n-hexane was used as solvent,0.15 g of immobilized enzyme was added（10mL of reaction solution）,the molar ratio of 1-phenylethanol to vinyl acetate was of 1:3,and the hydrated salt pair of Cu SO₄·5/3 was used to adjust the water activity of the system,after 48 h reaction at 50℃,the conversion rate reached 51.2%and the enantioselectivity E>200.4.The chiral resolution of（R,S）-1-phenylethanol was also carried out by using the PFL immobilized on MNCMM-TiSi（PFL@MNCMM-TiSi）.The results showed that when cyclohexane was used as solvent,0.20 g of immobilized enzyme was added（10mL of reaction solution）,the molar ratio of（R,S）-1-phenylethanol to acyl donor was 1:4,and the hydrated salt pair of CuSO₄·5/3was added to regulate the water activity,after 48 h of reaction time,the ee_p value of（R,S）-1-phenylethanol transesterification resolution reaction catalyzed by the immobilized PFL reached98.5%,conversion rate C was 49.8%,and E value was more than 200.