Laccase immobilization on hierarchical micro/nano porous chitin/graphene oxide beads prepared via Pickering emulsion template for dye decolorization

Abstract

Nowadays, the removal of dye molecules from water sources is a major environmental concern and challenge. Enzymatic degradation (biological) and adsorptive (physical) dye removal are considered to be the most effective dye removal techniques. Laccase catalysis is a reliable method to remove synthetic dyes from water to reduce environmental pollution, but free laccase has the disadvantages of low stability and non-reusability. In this study, stable Pickering emulsions were prepared using chitin (Ch) and graphene oxide (GO) composite solutions. Ch/GO composite aerogel beads with hierarchical porous structure were obtained by emulsion template method combined with freeze-drying, and then used for laccase immobilization and dye decolorization experiments. The results showed that the immobilized laccase had better thermal stability compared to the free enzyme, and it was found that the optimum pH of the immobilized laccase was 3.4 and the optimum temperature was 55 °C. In the cyclic decolorization experiments of acid Big Red GR, the decolorization rate of CH/GO-30 was maintained at 100% after 5 cycles of ABTS (2,2-biazo-bis(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt) by enzyme catalysis and carrier adsorption synergistically. The preparation of Ch/GO composite aerogel beads by the Pickering emulsion template method is simple and green, without the use of surfactants, avoiding secondary pollution to the environment, and has potential industrial applications in the decolorization and biodegradation of dye wastewater.