Preparation and catalytic degradation of phenol achieved by utilizing pH and Upper Critical Solution Temperature dual responsive intelligent enzyme catalysts

Abstract

Phenolic compounds are toxic substances that exert harmful effects on all living organisms. Irrigation farmland with phenolic wastewater can result in reduced crop yields or even crop failure, while consuming phenolic wastewater has a strong carcinogenic effect. Horseradish peroxidase (HRP), a heme-containing peroxidase, is capable of catalyzing the oxidative conversion and coupling reaction of phenols in sewage to form polymerization products in the presence of hydrogen peroxide (H2O2). However, free HRP can only function within a relatively narrow range of temperature and pH conditions, and its excellent water solubility makes it difficult to recover, thereby significantly increasing the cost of enzyme utilization. The immobilized enzyme was prepared by incorporating HRP and self-synthesized UCST (Upper Critical Solution Temperature) and pH dual responsive polymer P(NAGA-b-AA-b-VBA). The loading capacity of HRP reached 295 mg/g while maintaining the UCST performance. Compared to the free enzyme, the immobilized enzyme exhibited enhanced pH stability, thermal stability and storage stability. In laboratory experiments as well as actual water samples, the immobilized enzyme achieved phenol degradation rates of 90.4% and 88.4% respectively, within 1 h. After five cycles, the immobilized enzyme retained 80.1% catalytic activity with a recovery rate of 84.5%. Furthermore, it was demonstrated that the biological toxicity of the reaction product was significantly lower than that of simulated pollutant phenol.