Efficient As(III) removal from water by ZrO₂ modified covalent organic framework under visible light irradiation

Adsorption-oxidation is a promising technique to decontaminate As(III) polluted water. In present study, ZrO₂-modified covalent organic framework (ZrO₂-COF) was fabricated and used to remove arsenic from water under visible light irradiation. The results showed that ZrO₂-COF (0.2 g/L) could efficiently capture As(III) (5 mg/L) from water and then oxidize the adsorbed As(III) into less toxic As(V) under visible light irradiation (60 min), achieving the complete decontamination of As(III) polluted water. Based on characterization results and theoretical calculations, we found that in ZrO₂-COF composite, ZrO₂ served as sites for adsorption of As(III)/the latter transformed As(V), while COF worked as photocatalytic center for As(III) oxidation. Effective As(III) removal could also be achieved by ZrO₂-COF under visible light irradiation in complex water chemistry conditions including wide solution pH range (3-11), broad solution ion strength range (1-100 mM), the copresence of natural organic matter (0.1-1 mg/L humic acid) and various coexisting ions in solutions, as well as in real water samples. In addition, we found that ZrO₂-COF had excellent reuse performance in 4 consecutive cycles. Our results showed that under visible light irradiation, ZrO₂-COF composites could be a promising technique for efficient As(III) removal from water.