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

Abstract

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 (MoO 2 S 2 ) anion, referred to as LDH-MoO 2 S 2 , and its potential to sequester Se VI O 4 2− and Se IV O 3 2− from aqueous solution. LDH-MoO 2 S 2 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 MoO 2 S 2 2− to Mo 2 O 2 S 6 2− like species during the intercalation process. LDH-MoO 2 S 2 is remarkably efficient in removing SeO 4 2− and SeO 3 2− ions from the ppm to trace level (≤10 ppb), with distribution constant (K d ) ranging from 10 4 to 10 5 mL/g. This material showed exceptionally high sorption capacities of 237 and 358 mg/g for SeO 42− and SeO 3 2−, respectively. Furthermore, LDH-MoO 2 S 2 demonstrates substantial affinity and efficiency to remove SeO 3 2− /SeO 4 2− 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 MoO 2 S 2 anion into LDH and emphasizes its exceptional potential for high-capacity selenium removal and positioning it as a premier sorbent for selenium oxoanions.