Redox‐Active SnMoS _x Chalcogels for Multi‐Electron Reductive Separation of Chromate and Pertechnetate

ABSTRACT

High‐valent oxyanions, such as chromate (Cr ^VI O ₄ ²⁻ ) and pertechnetate ( ⁹⁹ Tc ^VII O ₄ ⁻ ), are highly soluble, weakly coordinating, and exceptionally stable, making their removal from water and nuclear waste extremely challenging. Here, we report a redox‐coupled metathesis strategy to synthesize a sulfide‐rich SnMoS _x nanoparticle‐aggregated chalcogel and demonstrate its redox‐mediated, high‐capacity removal of both Cr(VI) and ⁹⁹ Tc(VII) from aqueous solutions, including Hanford low‐activity nuclear waste condensate streams. Synchrotron X‐ray pair distribution function and X‐ray absorption spectroscopy reveal Mo─S motifs resembling Mo ₂ (S ₂ ) ₆ and Mo ₃ S(S ₂ ) ₆ clusters, while Sn─S coordination approximates Sn ₂ S ₇ ‐like units, generating a framework enriched in reactive polysulfides. This unique coordination and redox landscape enables a concurrent near‐quantitative removal of Cr(VI) (>99%) and efficient capture of Tc(VII) (>73%) from representative nuclear waste simulants. Moreover, SnMoS _x exhibits a Cr ⁶⁺ removal capacity of 672 mg g ^{− 1} from aqueous solutions. Mechanistic analysis shows that Cr(VI) undergoes multi‐electron reduction to insoluble Cr(III) via electron transfer from Mo ⁵⁺ /Mo ⁴⁺ and S _x ²⁻ centers, with a similar pathway proposed for Tc(VII). These results establish SnMoS _x chalcogels as a distinct class of porous, redox‐active materials capable of transforming and immobilizing recalcitrant high‐valent oxyanions, offering a general strategy for the separation of highly stable inorganic oxoanions from chemically complex solutions.