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

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.