Tuned bimetallic MOFs with balanced adsorption and non-radical oxidizing activities for efficient removal of arsenite

The removal of arsenic from contaminated water is important for environmental protection and drinking water safety worldwide. In this study, bimetallic metal–organic frameworks (MOFs) with catalytic and adsorptive effects were synthesized and combined with peroxymonosulfate (PMS) for efficient As(III) oxidation and As(III)/As(V) removal. The molar ratio of Fe and Mn precursor was adjusted to balance the adsorption and catalytic processes of As(III) in the system. The results showed that among the Fe/Mn-MOFs and MIL-88(Fe) tested, the Fe/Mn-MOFs with an Fe/Mn molar ratio of 1:1 (Fe0.3Mn0.3-MOFs) could achieve the best catalytic and adsorption performance with 98% removal of As(III). The performance of Fe0.3Mn0.3-MOFs in natural contaminated water was also verified. Electron spin resonance detection and quenching experiments have revealed that trivalent arsenic oxidation is facilitated primarily by a non-radical process through singlet oxygen. Density-functional theory, XPS and FTIR analyses reveal the structures, corresponding binding energies and binding sites for the adsorption of As(III)/As(V) by Fe0.3Mn0.3-MOFs. The coupling of Fe0.3Mn0.3-MOFs to the PMS system was still able to achieve 78% arsenic removal after five cycles, showing good reliability and effectiveness in arsenic removal. This study provides a new insight into the catalytic and adsorption mechanisms in MOFs/PMS systems and provides a theoretical basis for the application of MOFs in the remediation of arsenic contaminated water.