Amine functionalization of iron-based metal-organic frameworks MIL-101 for removal of arsenic species: Enhanced adsorption and mechanisms

Abstract

Chronic exposure to inorganic arsenic (As)-contaminated water seriously threatens human health. Although iron-based metal-organic frameworks (MOFs) for arsenic removal have been developed, their practical application has been challenging due to their lack of binding sites and low stability. In this study, we attempted to improve the arsenic adsorption capacity of MIL-101(Fe) in water by amine functionalization. NH2-MIL-101(Fe) was synthesized using a facile solvothermal method. It adsorbed > 70 % arsenate (As (V)) throughout a wide pH range of 4–9, exhibited high anti-interference ability and reusability, and effectively eliminated arsenic from contaminated river samples, demonstrating its great potential in As-polluted water treatment. Best adsorption effectiveness at pH 7 indicated that the electrostatic attraction between -NH2 and As (V) was not its primary adsorption mechanism. Instead, FTIR and XPS analyses revealed that the complexation between Fe and As was the key mechanism. NH2-MIL-101(Fe) had substantially better As (V) and arsenite (As (III)) adsorption capacities (147.7 mg/g and 153.4 mg/g, respectively) than MIL-101(Fe) (82.8 mg/g and 131.2 mg/g, respectively). This is because amine modification increased the Fe content and Fe3+/Fe2+ ratio, as well as the specific surface area and pore volume. This research elucidates how amine modification affects the ability of Fe-MOFs to adsorb arsenic.