Metal–Organic Framework with a Redox-Active Bridge Enables Electrochemically Highly Selective Removal of Arsenic from Water

Selective removal of trace, highly toxic arsenic from water is vital to ensure an adequate and safe drinking water supply for over 230 million people around the globe affected by arsenic contamination. Here, we developed an Fe-based metal-organic framework (MOF) with a ferrocene (Fc) redox-active bridge (termed Fe-MIL-88B-Fc) for the highly selective removal of As(III) from water. At a cell voltage of 1.2 V, Fe-MIL-88B-Fc can selectively separate and oxidize As(III) into the less harmful As(V) state in the presence of a 100- to 1250-fold excess of competing electrolyte, with an uptake capacity of >110 mg-As g^-1 adsorbent. The high affinity between the uncharged As(III) and the μ₃-O trimer (-36.55 kcal mol^-1) in Fe-MIL-88B-Fc and the electron transfer between As(III) and redox-active Fc⁺ synergistically govern the selective capture and conversion of arsenic. The Fe-based MOF demonstrates high selectivity and capacity to remediate arsenic-contaminated natural water at a low energy cost (0.025 kWh m^-3). This study provides valuable guidance for the tailoring of effective and robust electrodes, which can lead to a wider application of electrochemical separation technologies.