Sustainable approach for the sequestration of lead from water involving the synergistic influence of PET waste and l-cysteine encapsulated in sodium alginate beads

Abstract

The toxicity of heavy metals, particularly lead, in water is a significant environmental and health concern. Carbonaceous adsorbent materials derived from waste sources exhibit promising potential for sequestering toxic metals from water. Herein, we developed a sustainable approach using valorised waste polyethene terephthalate (PET) obtained from plastic bottles as a carbonaceous adsorbent material via microwave assistance and functionalized it with L-cysteine to incorporate surface functionalities for effective coordination with lead ions. The adsorbent was further encapsulated using a sodium alginate matrix to form a hydrogel, which increased the adsorption capacity and enabled scaling up. Analytical surface characterisations, including FE-SEM, EDS, BET, TGA, XPS, XRF, FT-IR spectroscopy, and PXRD, were performed to study the adsorbent. The maximum adsorption capacity under optimised conditions was found to be 370.84 mg g⁻¹. Kinetic studies revealed that the system follows a pseudo-second-order model, and thermodynamic analysis showed that adsorption is spontaneous and exothermic in nature. The interaction of lead ions with the surface of the adsorbent was further corroborated using molecular dynamics (MD) simulations. The prepared adsorbent was tested in tap water and drinking water, and the adsorbent material exhibited 86.04% and 90.00% removal of lead, respectively. Lead was successfully desorbed using 0.1 M NaOH. In addition to supporting sustainable waste management, this work presents a relatively low-cost, eco-friendly adsorbent system that can serve practical utility in real-world applications for the remediation of lead-contaminated water.