Self-propelled thiol functionalized SiO₂@MnO₂ microstructure for dynamic extraction of pollutants from the aquatic...

The global freshwater crisis is intensifying day by day which is driven by both the insufficiency of freshwater supplies to meet anthropogenic and ecological demands and also the widespread lack of access to safe, affordable drinking water. In particular critical aspect of this crisis is the contamination of water resources with toxic heavy metals, notably lead (Pb) and cadmium (Cd). This poses significant threats to human health due to their long-term neurotoxic effects and environmental persistence. In this study, we report the development and application of a novel self-propelled Janus microstructure for the efficient removal of Pb²⁺ and Cd²⁺ ions from various aquatic environments, which includes seawater, groundwater, and lake water. The self-propelled microstructure comprises of thiol-functionalized silica-coated manganese dioxide (SiO₂@MnO₂@SH), synthesized to exploit self-diffusiophoretic motion in the presence of hydrogen peroxide, thereby enhancing adsorption dynamics. The synthesized material was extensively characterized in terms of crystallinity, morphology, and surface chemistry using XRD, SEM, and ATR-FTIR, respectively. In the FTIR spectra, the characteristic peak of thiol functional group around 2550 cm^- 1 is observed in the synthesized SiO₂@MnO₂@SH microstructure. Pores are observed in the SEM image of H₂O₂ treated SiO₂@MnO₂@SH microstructure. The SiO₂@MnO₂@SH microstructure demonstrated remarkable adsorption capacities, achieving over 99% removal efficiency for Pb at a pH range of 2-4 and more than 96% for Cd at pH 2-3. Adsorption data were fitted to Langmuir isotherm, Freundlich isotherm, and Sips isotherm models, indicating favorable sorption behavior. Kinetic studies were performed at 277 K and 301 K to evaluate the influence of thermal conditions on adsorption rates. A density functional theory investigation was also conducted to elucidate the fundamental mechanistic pathways governing the interfacial interactions. From the DFT cluster analysis, the calculated binding energies are - 175.95 kcal mol^- 1 for Cd²⁺ and - 179.91 kcal mol^- 1 for Pb²⁺. The findings confirm that the SiO₂@MnO₂@SH microstructure, when activated by H₂O₂, serves as an effective and dynamic adsorbent system for the decontamination of Pb and Cd from polluted water systems, offering a promising approach for advanced water purification technologies.