Multiscale investigation of oxidative aging on thiol–functionalized montmorillonite: Correlating structural and chemical degradation to the reduced affinity for Hg(Ⅱ) and MeHg

Thiol–functionalized montmorillonite, characterized by its high–density adsorption sites, has demonstrated excellent application performance in Hg pollution control. However, the influence of aging on its structure and adsorption properties remains unclear. To comprehensively explore the structural characteristics and Hg adsorption capacity of thiol–functionalized montmorillonite after aging conditions, this study employed 1%–5% H₂O₂ chemical oxidation to simulate natural aging processes. Characterization results indicated that H₂O₂ treatment led to reductions in both the specific surface area and the interlayer spacing. Moreover, partial oxidation of –SH groups to –SO₃H was observed, along with an increase in acidic functional groups such as –COOH. Two–dimensional correlation spectroscopy (2D–COS) identified the functional groups aging sequence as follows: –OH (H₂O) > Si/Al–OH > Si–O–Si > –SH > –CH₂ – > –SO₃H. Adsorption capacities for Hg(II) and MeHg decreased from 103.03 to 44.87   mg/g, and from 39.50 to 16.87   mg/g, respectively. In parallel, the desorption rate increased from 11.25% to 39.12%. Density functional theory (DFT) calculations further confirmed an increase in the adsorption energy of the aging materials and verified that –SH groups possess the strongest binding ability toward Hg species.