Fast oxidation and deep removal of As(III) by integrating metal-organic framework ZIF-67 and sulfite: Performance and mechanism

Elimination of As(III) from water has gotten more attention in comparison with As(V) due to its higher mobility and toxicity. In this work, we provide an effective method by integrating a cobalt-based metal-organic framework ZIF-67 and sulfite (S(IV)) to purify As(III)-laden water. The coupled oxidation with adsorption process (i.e., As(III) removal by ZIF-67/S(IV)) surpasses a divided preoxidation-adsorption process (i.e., As(V) removal by ZIF67) for arsenic removal from the multi-component water containing various coexisting anions. Herein, the mechanism investigation corroborated that the S(IV) plays dual roles as a complexing ligand and a precursor of oxysulfur radicals. The enhanced As(III) removal is attributed to the S(IV) activation on the ZIF-67 surface via various reactions (e.g., surface complexation and intramolecular electron transfer), which not only generates SO4 center dot- radicals for rapid oxidation of As(III) to As(V), but also provides more adsorption sites for the immobilization of the oxidized product (As(V)). Furthermore, the combined process can rapidly treat arsenic in the realistic contaminated water from 242 to 7 mu g L-1 within 15 min, directly meeting the provisional maximum contaminant level (<10 mu g L-1). Overall, the proposed work may aid the rational design of S(IV) mediated oxidation-adsorption process to remove arsenic from a variety of contaminated waters.