Laccase immobilization on titania nanoparticles and titania-functionalized membranes

Abstract

Bio-catalytic degradation of recalcitrant micropollutants with enzymes such as laccase provides an environmentally attractive alternative to the conventional filtration and adsorption processes. However, enzyme loss and denaturation remain key challenges for their potential use in water treatment applications. In this work, laccase immobilization on TiO2 nanoparticles and TiO2 blended polyethersulfone (PES) membranes were investigated due to TiO2's chemical stability, ease of functionalization, and architecture. Different surface modification and functionalization strategies on support materials were compared based on enzyme loading, apparent activity, activity recovery, and stability. When coupling agent 3-aminopropyltriethoxysilane (APTES) and cross-linker glutaraldehyde (GLU) were applied sequentially, effective coupling of laccase was achieved based on 2,2′-azino-bis-(3-ethyl benzothiazoline-6-sulfonic acid) (ABTS) assays. TiO2 functionalized PES membrane showed better enzyme immobilization efficiency than the non-functionalized membrane. Optimal performance was observed for PES membrane containing 4wt% TiO2, where TiO2 not only provided the enzyme coupling sites but also affected the membrane surface morphology and hydrophilicity to favor the enzyme immobilization. These bio-catalytic membranes also displayed good enzyme stability, tolerance to wider pH range and vigorous filtration conditions required for water treatment applications. Kinetic study also indicated that the enzyme affinity to assay substrate was maintained after immobilization when compared with packed bed and batch reactors.