Molybdenum-Oxysulfide-Functionalized MgAl-Layered Double Hydroxides─A Sorbent for Selenium Oxoanions.

Effective removal of chemically toxic selenium oxoanions at high-capacity and trace levels from contaminated water remains a challenge in current scientific pursuits. Here, we report the functionalization of the MgAl layered double hydroxide with molybdenum-oxysulfide (MoO2S2) anion, referred to as LDH-MoO2S2, and its potential to sequester SeVIO42- and SeIVO32- from aqueous solution. LDH-MoO2S2 nanosheets were synthesized by an ion exchange method in solution. Synchrotron X-ray pair distribution function (PDF) and extended X-ray absorption fine structure (EXAFS) revealed an unexpected transformation of the MoO2S22- to Mo2O2S62- like species during the intercalation process. LDH-MoO2S2 is remarkably efficient in removing SeO42- and SeO32- ions from the ppm to trace level (≤10 ppb), with distribution constant (Kd) ranging from 104 to 105 mL/g. This material showed exceptionally high sorption capacities of 237 and 358 mg/g for SeO42- and SeO32-, respectively. Furthermore, LDH-MoO2S2 demonstrates substantial affinity and efficiency to remove SeO32-/SeO42- even in the presence of competitive ions from contaminated water. Hence, the removal of selenium (VI/IV) oxoanions collectively occurs through reductive precipitation and ion exchange mechanisms. This work provides significant insights into the chemical structure of the MoO2S2 anion into LDH and emphasizes its exceptional potential for high-capacity selenium removal and positioning it as a premier sorbent for selenium oxoanions.

Metal-sulfide/polysulfide functionalized layered double hydroxides - recent progress in the removal of heavy metal ions and oxoanionic species from aqueous solutions.

Water constitutes an indispensable resource for global life but remains susceptible to pollution from diverse human activities. To mitigate this issue, researchers are committed to purifying water using a variety of materials to remove harmful chemicals, such as heavy metals. Layered double hydroxides (LDHs), with their intriguing, layered structure and chemical behavior, have attained substantial attention for their effectiveness in removing heavy metal cations and various inorganic oxoanions from water. To enhance the efficiency, considerable endeavors have focused on functionalizing LDHs with different chemical species. Intercalation with metal sulfides has proven to be particularly effective, facilitating heavy metal absorption through multiple mechanisms, including ion-exchange, reductive precipitation, and surface sorption. This review concentrates on the synthesis and performance of polysulfide (Sx, x = 2-5), Mo-S, and Sn-S anion intercalated LDHs for heavy metal cations and inorganic oxoanion sorption, along with their mechanisms. Furthermore, the discussion includes prospects for expanding the chemistry of metal sulfide intercalated LDHs, with existing challenges and future outlooks.

Amorphous K-Co-Mo-Sx Chalcogel: A Synergy of Surface Sorption and Ion-Exchange.

Chalcogel represents a unique class of meso- to macroporous nanomaterials that offer applications in energy and environmental pursuits. Here, the synthesis of an ion-exchangeable amorphous chalcogel using a nominal composition of K2CoMo2S10 (KCMS) at room temperature is reported. Synchrotron X-ray pair distribution function (PDF), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) reveal a plausible local structure of KCMS gel consisting of Mo5+ 2 and Mo4+ 3 clusters in the vicinity of di/polysulfides which are covalently linked by Co2+ ions. The ionically bound K+ ions remain in the percolating pores of the Co-Mo-S covalent network. XANES of Co K-edge shows multiple electronic transitions, including quadrupole (1s→3d), shakedown (1s→4p + MLCT), and dipole allowed 1s→4p transitions. Remarkably, despite a lack of regular channels as in some crystalline solids, the amorphous KCMS gel shows ion-exchange properties with UO2 2+ ions. Additionally, it also presents surface sorption via [S∙∙∙∙UO2 2+] covalent interactions. Overall, this study underscores the synthesis of quaternary chalcogels incorporating alkali metals and their potential to advance separation science for cations and oxo-cationic species by integrating a synergy of surface sorption and ion-exchange.