Rapid arsenic mitigation in naturally contaminated groundwater using defect-enriched UiO-66-NH2: Selectivity, mineral preservation and mechanistic insights

Arsenic contamination of groundwater represents a severe global health hazard, requiring point-of-use technologies that achieve ultra-low residual concentrations while maintaining overall water quality. Here, we evaluate a defect-enriched UiO-66-NH 2 , synthesized via a modulator-assisted solvothermal method , for rapid arsenic mitigation directly in naturally contaminated groundwaters from the Pannonian Basin (Vojvodina, Serbia). At a low dose (0.5 g·L −1 ), UiO-66-NH 2 decreased total dissolved arsenic from ∼227 µg·L −1 to <10 µg·L −1 within 15 min at natural pH (7.80), while simultaneously suppressing phosphate below the limit of detection (LOD, ∼2.9 μg·L −1 P), one of the most competitive oxyanions, demonstrating robustness in complex hydrochemical matrices. Full water-chemistry analysis revealed pronounced selectivity toward arsenic. Changes in other constituents were minimal: Na + and K + (≤ 5% removal), while boron and lithium concentrations remained unchanged. Only moderate reductions in Ca 2+ and Mg 2+ occurred, indicative of a beneficial water-softening side effect. Rapid arsenic uptake occurred within the first minutes of contact, consistent with fast surface adsorption on defect-exposed UiO-66-NH 2 sites. Uptake remained effective across pH 4–9, avoiding the need for pH adjustment. DFT calculations combined with FT-IR spectroscopy support a multi-step adsorption mechanism in which arsenic immobilization is most plausibly governed by inner-sphere coordination at Zr-based adsorption environments, assisted by electrostatic and hydrogen-bonding interactions enabled by the -NH 2 functionality. Unlike laboratory studies using synthetic water, these results demonstrate direct risk mitigation under real exposure conditions, establishing UiO-66-NH 2 as a practical point-of-use adsorbent for arsenic hazard mitigation in real groundwater at environmentally relevant concentrations.