An innovative approach towards the selective recovery of Pb(ii) and Cd(ii): thiol-functionalized TiO2-based magnetic core–shell nanoparticle-loaded hydrogel†

Abstract

Selective elimination of contaminants from the aquatic medium is essential to harmonize the rapid growth of developmental accomplishments with the necessity for fresh water to ensure sustainability. Lead and cadmium are pollutants that originate primarily from industrial activities, and numerous materials have previously been reported for their selective removal. However, a challenge remains in creating effective field deployable materials. Herein, we report the synthesis and capabilities of a tactically designed, thiol-functionalized TiO₂-based magnetic core–shell nanoparticle-loaded hydrogel as a benchmark sorbent for lead and cadmium. The developed synthesis approach involved the creation of a magnetic Fe₃O₄ core and the fabrication of a TiO₂ shell over it, involving hydrolysis and condensation reactions, followed by thiol functionalisation of the TiO₂ shell. The obtained core–shell Fe₃O₄@TiO₂-SH magnetic nanoparticles were impregnated (27%) and cross-linked into an alginate polymer to form hydrogel (Fe₃O₄@TiO₂-SH-Ca-Alg) beads. After characterisation, the beads were applied to efficiently eliminate lead and cadmium from diverse aquatic media without impacting water quality limits. Investigation of the driving forces behind the remarkable lead and cadmium affinity was carried out with the support of experimental outcomes and theoretical calculations. Detailed density functional theory calculations were performed to determine the preferred binding site of Cd²⁺/Pb²⁺, structural changes due to their adsorption, and selectivity of the metal ion. Optimisation of key parameters and assessment of isotherm, kinetic, and diffusion models were carried out. Sorption capacities of Pb(II) and Cd(II) were recorded as 37.1 and 31.6 mg g⁻¹, respectively. Largely, outstanding stability, no impact on water quality, and efficacy for the removal of Pb(II) and Cd(II) from natural water selectively mark beads as an impeccable paradigm for sustainable water treatment applications.