| In addition to greater surface area, size controllable properties and excellent surface effect of the nonmaterial’s basic characteristics, nano-TiO2 also has excellent biocompatibility and chemical stability. It will be good at adsorbing enzyme. However, protein adsorption with hydrophobic amino acids was limited because a lot of hydroxyl groups was on its surface. Therefore, the hydrophobic modification of nano TiO2 in order to improve its adsorption of hydrophobic protein attracted people in recent years.The current common methods about hydrophobic modification of nano TiO2 contained coupling agent method, the esterification method and surface active agent method. KH-570 as a hydrophobic chain with long silane coupling agent, KH-570 with a long hydrophobic chain silane coupling agent was widely applied to the hydrophobic modification of the materials. This paper used the hydrophobic nano-TiO2 with in-situ preparation of KH-570 to immobilize lipase as a carrier, the performance and catalytic properties of immobilized enzyme was studied, and the immobilized interface features were analysised.Hydrophobic nano-TiO2 was in-situ prepared by sol-gel method using y-mehhacryloxy propyl trimethoxyl silane as modifying agent. Effects of the adding amount of KH-570, hydrochloric acid and the reaction time on the lipophilic degree of hydrophobic nano-TiO2 was studied. The prepared samples were characterized by FT-IR, TG, XRD and the contact angle. Results indicated that:the lipophilic degree was 61.05% using 0.4mL KH-570,6.0mL hydrochloric acid at the reaction time of 4h; A stable chemical bond was formed between KH-570 and the hydroxyl of nano-TiO2, the contact angle was 119.3°showing high hydrophobicity.The adsorption of lipase onto TiO2 was investigated by using hydrophobic nano-TiO2 as the carriers. The effects of lipase concentration, pH and time on immobilization capacity were studied. The results showed when the lipase concentration was 1.0mg·mL-1, the adsorption capacity reached saturation, when the pH was 8.0, the immobilization capacity reached the highest point, the immobilization capacity of lipase on hydrophobic nano-TiO2 reached equilibrium at 240 min. The Langmuir model and Freundlich model is adopted to fit the isotherm adsorption data of hydrophobic nano TiO2 imbobilized lipase,results indicated that the adsorption model provide a better correlation of the Freundlich model, close to the multilayer adsorption theory, adsorption behavior is initiative. The optimum temperature of the immobilized enzyme catalysis, the optimum pH stability, thermal stability and operation were studied, and the enzymatic reaction kinetics were analysised. The experimental results showed that compared with the free enzyme immobilized enzyme, the optimum temperature and the optimum pH increased, thermal stability and operating stability increased. Immobilized enzyme of the maximum reaction rate decreased, but its affinity with the substrate incresed. The reaction activation energy of immobilized enzyme reduced, showing thermal stability incresed.The lipase was immobilized by hydrophobic nano-TiO2 with in-situ modification of KH-570. The prepared samples were characterized by SEM, XRD, FT-IR, TG-DTA and N2 adsorption-desorption. Results indicated that:compared to the original particles, the morphology and size of hydrophobic nano-TiO2 after immobilizing lipase had no obvious changes and the lipase immobilization made XRD peak intensity relatively weakened with small effect on the crystalline structure, the specific surface area,pore volume and pore radius of hydrophobic nano-TiO2 after immobilizing lipase was smaller than that before; FT-IR showed that lipase space conformation was changed after immobilization; TG-DTA concluded that the lipase was immobilized via physical adsorption. |
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