Laccase-immobilized bacterial cellulose/TiO2 functionalized composite membranes: Evaluation for photo- and bio-catalytic dye degradation

Abstract

Bacterial cellulose (BC) was prepared by the fermentation of Komagataeibacter xylinus. Subsequently, through site-directed surface oxidation chemistry, the hydroxyl groups of BC were successfully oxidized into aldehyde groups that served as anchors for covalent immobilization of laccase (Lac) to the newly developed oxidized BC (OBC) membrane. TiO2 was additionally co-immobilized to OBC to produce a novel material in which dye degradation was carried out under specific conditions. Atomic Force Microscopy (AFM) and Scanning Electron Microscope (SEM) confirmed the installation of both TiO2 and laccase on the surface of OBC nanofiber membrane. The optimum pH, temperature, thermal stability, operational stability of the OBC/Lac and OBC/TiO2-Lac membrane were also studied in detail. In addition, the effect of the temperature and pH on dye degradation was also investigated. The results showed that the oxidation process successfully introduced aldehyde groups onto the BC (FT-IR), and also improved the stability of the immobilized laccase. Compared with free laccase, the optimum pH of immobilized laccase shifted to lower pH, while the optimum temperature decreased from 55°C to 50°C. The dye degradation experiments showed that the optimum pH for dye degradation was 5.0–6.0, while the optimum temperature was ~40°C. Under UV illumination, the dye degradation efficiency was significantly improved. Therefore, functionalized composite bacterial cellulose nanofiber membranes with a combined bio- and photo- catalytic property are a potentially valid approach for industrial textile dye degradation.