Radiation grafting mediated tailoring of a mercury (Hg(II)) selective adsorbent “RAdMer”: Mechanistic insights, uptake performance and reusability evaluation in artificially contaminated groundwater

Abstract

The presence of mercury (Hg(II)) in water bodies poses a pressing threat not only to aquatic life forms but also human health. This work proposes the fabrication of a novel thiol (-SH), amine (–NH–) and carboxylic (-COOH) group containing trifunctional adsorbent based on a radiolytically surface engineered biodegradable platform for selective sequestration of Hg(II) from aqueous media. Polyacrylonitrile (PAN) was gamma radiolytically incorporated onto cotton fabric via Radiation Induced Graft Polymerization (RIGP) process, followed by chemical conversion of the nitrile groups using dl-Cysteine as the trifunctional agent. The developed adsorbent RAdMer was characterized by FTIR, TGA, SEM-EDX, EDXRF, XRD, CHNS, 13C NMR and XPS techniques, and tested for Hg(II) removal in batch and continuous flow adsorption modes. Adsorption kinetics and equilibrium characteristics were validated using various theoretical models as well column adsorption models. Density Functional Theory (DFT) calculations performed to determine the complexation mechanism revealed the binding to be occurring predominantly in a 1:2 metal to ligand ratio with calculated binding affinity of −19.63 kcal.mol−1. RAdMer demonstrated fast uptake kinetics with over 60 % of total Hg(II) adsorption occurring within the first 30 min, while peak adsorption capacity was calculated at 174.3 mg.g−1. Moreover, RAdMer could be reused for >5 iterative cycles using an optimized HCl-Thiourea eluent system. Acting upon the UNOs SDG6 principle of providing “clean water and sanitation for all”, RAdMer efficiency was demonstrated with Hg(II) spiked ground water samples to successfully achieve the WHO permissible limit of <1.0 μg.L−1, and can therefore be potentially upscaled as an efficient methodology for remediation of Hg(II) ions in contaminated water.