Synthesis, Modification And Enzyme Immobilization Of Periodic Mesoporous Organosilicas

Periodic mesoporous organosilicas (PMOs) with optimum mesostructure, morphology and surface nature may be a promising candidate for enzyme immobilization owing to its high surface area, tunable pore size, large pore volume and other properties associated with the bridged organic groups. It is of considerable significance to immobilize enzymes on special supports due to the advantage of immobilized enzyme such as increased mechanical or thermal stability, ease to separating and recycling. In this thesis, PMOs with various mesostructures and morphologies was synthesized by a so-called low temperature route. Various organic groups such as amino, carboxylic and epoxy were used to terminally functionalize PMOs by the co-hydrolysis and condensation method. A Co3O4/PMOs core-shell nanosphere was also synthesized. Some of these materials were used as supports for enzyme immobilization and the stability, catalytic property of the immobilized enzyme were detected. Finally, the adsorption behavior of enzymes on the supports was investigated. More detail is discussed chapter by chapter as follows:PMOs with various mesostructures and morphologies was synthesized using tetraethyl orthosilicate (TEOS) and 1,2bis(triethoxysilyl)ethane (BTESE) as co-precursors, triblock copolymer F127 as a template and 1,3,5-trimethylbenzene (TMB) as a swelling agent at low temperatures. At a TEOS/BTESE molar ratio of 1.65, a mesophase transformation from 2D hexagonal structure via 3D cellular foam structure to 3D cubic structure can be realized by varying the synthesis temperatures from 20℃to 8℃. The effect of the hydrophobic property of silicate precursors and synthesis temperatures on the hydrophilic-hydrophobic property of F127 is responsible for the mesostructure transformation. Organosilicas materials with various morphologies can be synthesized by varying the molar ratio of TEOS /BTESE at 20℃. Hollow nanospheres with a size of about 20nm are obtained at the TEOS /BTESE molar ratio of 0 and 0.55. As the molar ratio increases to 1.65, a formation of irregularly shaped particles composed of very small spherical aggregates is observed. With the molar ratio further increasing to 4.95, PMOs with regular hexagonal shape corresponding to a highly ordered mesostructure are prepared. Such morphology is quite rare for PMOs synthesized by using nonionic surfactants as structure directing agent. The variation of material morphology may be due to the competition between the Gibbs free energy and the surface tension.Bifunctional PMOs with ethane bridging groups within the network and terminal functional groups (amino, carboxylic and epoxy) in the pore channels were synthesized by the co-condensation of BTESE and aminopropyltrimethoxysilane (APTMS), 2-cyanopropyltriethoxysilane (CTES), 3-glycidoxypropyltrimethoxylsilane (GPTMS), respectively, in the presence of triblock copolymer P123 surfactants under acidic conditions. The solid-state nuclear magnetic resonance (NMR) spectra show that the functional groups are expectably attached covalently to the pore surface of PMOs. Small angle X-ray diffraction (XRD) and Tranmission electron microscopy (TEM) analysis reveal that the bifunctional PMOs retain a desirable mesoscopic ordering and pore structure, and the mesostructure of the bifunctional PMOs is influenced by the types of organosilanes and the degree of functionalization. The functionalized PMOs are used as supports for laccase immobilization. The results show that the pore size of bifunctional PMOs and the interactions between laccase and the functional groups have an important influence on the stability of immobilized laccase.A monodisperse nanosize Co3O4 core-mesoporous ogranosilica shell nanosphere was synthesized by corporative self-assembly of organosilica precursor and cetyltrimethylammonium bromide (CTAB) molecules on the Co3O4 nanoparticle surface. The obtained Co3O4/PMOs core-shell nanosphere is highly propitious to the immobilization of Microperoxidase-11 (MP-11) and possesses mimetic peroxidase activity similar to that found in natural peroxidase as demonstrated by the following facts: (1) Co3O4/PMOs core-shell nanosphere can catalyse different peroxidase substrates such as 2,2′-azinobis(3-ethylbenzthiazolin-6-sulfonate) (ABTS) and TMB in the presence of H2O2; (2) The catalysis by Co3O4/PMOs core-shell nanosphere conforms to typical Michaelis-Menten kinetics. This property of Co3O4/PMOs core-shell nanosphere could enhance the catalytic activity of immobilized MP-11.Adsorption behavior of enzyme on PMOs with various mesostructures and surface properties as well as core-shell structure was investigated. The results show that (1) PMOs with 3D cubic structure is much more qualified for papain adsorption than that with 2D hexagonal structure. The adsorption for both PMOs can be described by the Langmiur isotherm, pseudo-second-order kinetic and intraparticle diffusion models. (2) The adsorption of laccase on bifunctional PMOs can be described by the Freundlich isotherm. The experimental kinetic data can be fitted by pseudo-second-order kinetic and intraparticle diffusion models. The pore size of bifunctional PMOs and the interaction between the enzyme and the terminal functionl groups have an influence on the kinetic rate constants. (3) The adsorption of MP-11 on Co3O4/PMOs core-shell nanosphere can be described by the Langmiur isotherm, the pseudo-second-order kinetic and intraparticle diffusion models.