This study elucidates the structural changes of sulfidized zerovalent iron (S-nZVI) in anoxic groundwater, presents a compelling evidence on the structural robustness of the material and explains how S-nZVI long-term reactivity is achieved.

GR SO4 is among the best performing Febearing minerals for As removal.• Both pH and the presence of competing aqueous ions affect As removal efficiency. • Long term experiments showed that GR SO4 with As adsorbed onto its surface is stable for up to 90 days. • High-resolution electron microscopy revealed that As is preferentially adsorbed at the GR particle edges.Editor: José Virgílio Cruz Arsenic (As) contamination in groundwater is a significant health and environmental concern worldwide because of its wide distribution and toxicity. The fate and mobility of As is greatly influenced by its interaction with redox-active mineral phases, among which green rust (GR), an Fe II -Fe III layered double hydroxide mineral, plays a crucial role. However, the controlling parameters of As uptake by GR are not yet fully understood. To fill this gap, we determined the interfacial reactions between GR sulfate (GR SO4 ) and aqueous inorganic As(III) and As(V) through batch adsorption experiments, under environmentally-relevant groundwater conditions. Our data showed that, under anoxic conditions, GR SO4 is a stable and effective mineral adsorbent for the removal of As(III) and As(V). At an initial concentration of 10 mg L −1 , As(III) removal was higher at alkaline pH conditions (~95% removal at pH 9) while As(V) was more efficiently removed at near-neutral conditions (N99% at pH 7). The calculated maximum As adsorption capacities on GR SO4 were 160 mg g −1 (pH 8-9) for As(III) and 105 mg g −1 (pH 7) for As(V). The presence of other common groundwater ions such as Mg 2+ and PO 4 3− reduces the efficiency of As removal, especially at high ionic strengths. Long-term batch adsorption experiments (up to 90 days) revealed that As-interacted GR SO4 remained stable, with no mineral transformation or release of adsorbed As species. Overall, our work shows that GR SO4 is one of the most effective As adsorbents among iron (oxyhydr)oxide phases.

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The dithiol functionalized UiO-66-(SH) is developed as an efficient adsorbent for the removal of mercury in aqueous media. Important parameters for the application of MOFs in real-life circumstances include: stability and recyclability of the adsorbents, selectivity for the targeted Hg species in the presence of much higher concentrations of interfering species, and ability to purify wastewater below international environmental limits within a short time. We show that UiO-66-(SH) meets all these criteria.