Effects of porogen and cross-linking agents on improved properties of silica-supported macroporous chitosan membranes for enzyme immobilization.

A series of silica-supported macroporous chitosan membranes (CM15, CM20, and CM25) was prepared by varying the ratio of 70-230-μm-sized silica particles. These synthesized membranes were further cross-linked using different cross-linking agents for covalent immobilization of biological macromolecules especially enzymes and in this study, Bovine serum albumin and laccase. Effects of silica particle and cross-linking agents on their flow rates, surface properties, and chemical and biological properties were explored. Pore size of as-synthesized membranes was 0.1192, 0.1268, and 0.1623 μm, respectively, for CM15, CM20, and CM25. The effect of various parameters such as temperature and pH on the relative activity of both free and immobilized enzymes was studied in details. The relative enzyme activity upon immobilization was greatly enhanced several folds of its original activity. The stability of enzymes over a range of temperature and pH was significantly improved by immobilization. The optimum temperature and pH were determined to be 50 °C and pH 3, respectively, for both the free and the immobilized enzymes. The immobilized enzyme possessed good operational stability and reusability properties that support its potentiality for practical applications. Among three membranes, CM25 is confirmed to be efficient candidate due to its improved characteristics.