Constructing a stable photocatalytic functional layer through cross-linking of chitosan and l-mannose for efficient removal of doxycycline hydrochloride in single-pass flow mode

Abstract

The development of technologies for effectively eliminating antibiotic pollutants from aquatic environments is crucial for preserving environmental quality. In this study, the 0D/3D Ag/AgI/MOF-808 photocatalysts were immobilized on the surface of polyethersulfone membrane using the Schiff-base reaction between chitosan and l-mannose to form a photocatalytic membrane (PES-CSLM-1) with a unique “sandwich” structure, which consists of a cross-linked layer, a functional layer, and a supporting layer. Under 240 min of visible light irradiation, the removal rate of doxycycline hydrochloride (DOX) (10 mg/L) by PES-CSLM-1 membrane was more than 90 %, which was 26.2 % higher than that of PES-CS membrane. The flux recovery rate of the membrane after photocatalytic self-cleaning reached 92.2 %, notably surpassing that achieved through physical cleaning (73.75 %), indicating that the photocatalysis effectively converted irreversible pollutants into reversible pollutants. After four cycles, the DOX removal efficiency of PES-CSLM-1 remained near 80 %, and the membrane structure and crystal structure did not change significantly. ·OH and ·O2− play important roles in the degradation process of DOX, and three potential degradation pathways for DOX were proposed. Toxicity analysis revealed that the environmental risk was significantly reduced during the DOX degradation process.