Removal of bisphenol A by integrated adsorption and biodegradation using immobilized laccase onto defective PCN-224

Abstract

Environmentally widespread endocrine-disrupting chemicals, such as bisphenol A (BPA), have posed a risk to living things. Laccase, a kind of oxidoreductase, can effectively catalyze the degradation of phenolic compounds like BPA. Herein, a defective metal-organic framework (dPCN-224) with BPA adsorption capability was synthesized and used for laccase immobilization. The material was extensively characterized and successful immobilization of laccase via hydrophobic interaction was confirmed. The immobilization reached an enzyme loading density of 80 mg/g onto dPCN-224 and the laccase@dPCN-224 showed high activity recovery (90.0% vs. free laccase) and increased thermostability, pH tolerance, and organic co-solvent resistance over the free enzyme. Moreover, at various concentrations (0.5–20 mg/L), the BPA removal efficiencies of laccase@dPCN-224 were 3.3–5.0 times higher than those of free laccase due to the cooperative effect of adsorption and enzymatic degradation. The BPA bound on laccase@dPCN-224 could be almost completely biodegraded by adding 0.5 mM of electro-mediator (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)). In addition, after five consecutive batch cycles, the BPA removal efficiency of laccase@dPCN-224 kept as high as 98.1% at 5 mg/L BPA. Taken together, the results proved the potential of laccase@dPCN-224 for applications in addressing environmental BPA pollutions.