Redox-Active SnMoSx Chalcogels for Multi-Electron Reductive Separation of Chromate and Pertechnetate.

High-valent oxyanions, such as chromate (CrVIO4 2-) and pertechnetate (99TcVIIO4 -), 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 SnMoSx nanoparticle-aggregated chalcogel and demonstrate its redox-mediated, high-capacity removal of both Cr(VI) and 99Tc(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 Mo2(S2)6 and Mo3S(S2)6 clusters, while Sn─S coordination approximates Sn2S7-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, SnMoSx exhibits a Cr6+ 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 Mo5+/Mo4+ and Sx 2- centers, with a similar pathway proposed for Tc(VII). These results establish SnMoSx 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.