Research Information System
Chemistry of Materials, vol.35, no.24, pp.10446-10456, 2023 (SCI-Expanded)
Chalcogenide-based aerogels are emerging porous semiconducting nanomaterials that appeal to applications in clean energy and the environment. Here, we report a novel gel, potassium-tin-molybdenum-sulfides (KTMS), that integrates the electrostatically bound K+ ions in the covalent network of Sn-Mo-S. Its gelation requires a concurrent reduction of Mo6+ → Mo4+/5+ and the oxidation of S2- → Sn- (n ≈ 1) and Sn2+ → Sn4+. KTMS is an amorphous semiconductor showing quantum confinement effects on band gap energies, 2.1 → 1.4 → 0.9 eV for its wet- → aero- → xerogels. Synchrotron X-ray pair distribution function (PDF) and extended X-ray absorption fine structure (EXAFS) revealed a complex local structure of KTMS consisting of molecular Mo2(S2)6 and Mo3S(S2)6 clusters. In addition, the Sn-S coordination is related to crystalline Na4Sn3S8 and SnS2. KTMS also demonstrated the removal of the radionuclides of Cs+, Sr2+, and UO22+ from ppm to ppb levels with distribution constants (Kd) up to ≥104 mL/g. Notably, despite the lack of atomic periodicity in the amorphous KTMS, the K+ ion is ion-exchangeable with chemically diverse Sr2+, Cs+, and UO22+ in aqueous solutions; especially the ion-exchange properties of Sr2+ and UO22+≡(O═U═O)2+ is not known to any chalcogels known to date. The sequestration of Cs+ and Sr2+ was achieved by the exchange of K+ in the amorphous KTMS, and the removal of [O═U6+═O]2+ synergistically involves surface sorption via ─S····U6+═O22+ covalent interactions and ion-exchange via the hard-soft Lewis acid-base paradigm. Overall, cooperative roles played by the diverse bonding motifs, surface-exposed Lewis basic frameworks, and polarizability of the (poly)sulfides make it an exceptional adsorbent for chemically diverse radioactive species. This finding will guide the design of superior sorbents for chemically distinct metal ion separation.