Polydopamine-Cross-Linked Enzyme Aggregates: Overcoming Activity Inhibition by Heavy Metals and Their Recovery and Reuse

Abstract

Chemical industry wastewater contains toxic organic and inorganic species. To remove these pollutants, enzyme-based methods have attracted wide attention because of their merits such as mild operating conditions, low energy consumption, reduced byproducts, and low toxicity. However, the inhibition of enzymatic activity by heavy metals due to the metal–enzyme interactions limits their applications in wastewater treatment. To tackle this challenge, here we have developed polydopamine (PDA)-cross-linked enzyme aggregates (PCLEAs), in which enzyme aggregates were in situ cross-linked through the formation of imine bonds or/and Michael addition reactions. PDA exhibited a higher affinity for heavy metals compared to enzymes, resulting in improved enzyme activity and recovery and reuse of heavy metals to afford PCLEA containing heavy metals (PCLEA-HMs). Several PCLEA-HMs were synthesized through combinations of enzymes, including lipase and glucose oxidase (GOx), and heavy metals, including Pd, Pt, Au, Ag, Mn, and Zn salts. Their structures and catalytic properties were systematically studied to obtain a better understanding of structure–activity relationships. Additionally, the photothermal effect of polydopamine could promote catalytic performance, contributing to enhanced activity under irradiation. The PCLEA-HMs could be utilized for the cascade degradation of 4-nitrophenyl acetate and the detection of phenol. This strategy advances the development of PCLEA-HMs for practical chemical wastewater treatment.