An insight on the design of mercapto functionalized swelling brittle micas

Thiol-functionalized montmorillonite prepared by one-step mechanochemical grafting and its adsorption performance for mercury and methylmercury

The preparation of low-cost and highly efficient functional materials for the cleanup of mercury-contaminated water by adsorption in an environmentally friendly way is of great significance. In this study, thiol-functionalized montmorillonite (BSH-MMT) was prepared by a novel one-step mechanochemical grafting method and applied to aqueous Hg²⁺ and CH₃Hg⁺ adsorption. Characterization results showed that thiol groups were successfully grafted by chemical bonding with Si-OH or broken SiO bonds. The maximum adsorption capacities of BSH-MMT for Hg²⁺ and CH₃Hg⁺ were 104.79 mg g^-1 and 39.27 mg g^-1, which were approximately seven- and nine-fold that of pristine MMT, respectively. Adsorption kinetics and isotherm fitting indicated that Hg²⁺ adsorbs heterogeneously, while CH₃Hg⁺ proceeds through monolayer adsorption, both with chemical adsorption as the rate-limiting step. BSH-MMT maintained high adsorption performance over a wide pH range and in the presence of humic acid because of the high affinity of thiol groups toward mercury. The primary adsorption mechanism of thiol-ligand complexation was confirmed by the results of X-ray photoelectron spectroscopy and X-ray absorption spectra, in which a complex structure of bis-coordinated S-Hg-S (2.30 Å distance) was observed. These results demonstrated that mechanochemical grafting is a promising one-step method to prepare thiol-functionalized montmorillonite for effective cleanup of Hg²⁺/CH₃Hg⁺ contamination in water.

Pb2+, Cd2+ and Hg2+ removal by designed functionalized swelling high-charged micas

The increasing accumulation of toxic heavy metals in the environment has generated the need of efficient removal systems, being the adsorption method the most popular one applied in aqueous solutions. Of particular concern is the case of Pb²⁺, Cd²⁺ and Hg²⁺ due to their high potential hazard. In this paper, we describe the feasibility of a new family of nanomaterials, swelling high charge micas, in the removal of these cations from aqueous solutions. Batch adsorption experiments were carried out in the as-made micas, NaMn, and after functionalization with ethylammonium, EA-Mn, and mercaptoethylammonium, MEA-Mn. The results have demonstrated that all of them are efficient heavy metal adsorbents, being Na-M2 the best adsorbent for Pb²⁺ and Cd²⁺_, and, MEA-M2 for Hg²⁺.