Efficient upcycling of polyvinyl chloride into N,S-codoped porous carbon for enhanced Pb(ii) ion adsorption

Abstract

A green and sustainable strategy was proposed to efficiently convert polyvinyl chloride (PVC) waste into high-value porous carbon adsorbents for simultaneous waste plastic resourcing and heavy metal pollution control. The synthesis integrates solvothermal pretreatment with dimethylformamide (DMF), followed by KOH activation and heteroatom doping using thiourea as the N/S source. Solvothermal pretreatment increases carbon yield to 40 wt%. NS-PVC has a hierarchical pore structure with a high specific surface area of 1096.53 m² g⁻¹, moderate pore size distribution, and rich oxygen-containing, sulfur-containing, and nitrogen-containing functional groups, and comparative experiments confirmed that the doped N and S heteroatoms had a synergistic effect and promoted the adsorption performance, demonstrating exceptional removal efficiency (96%) for the high-concentration Pb(II) solution (1500 mg L⁻¹), with a maximum adsorption capacity of 149.2 mg g⁻¹. Through adsorption kinetics and isotherm studies, it was confirmed that the adsorption process of Pb(II) on NS-PVC was endothermic and consistent with the pseudo-second-order kinetic model and Langmuir models. By comparing the physicochemical properties of NS-PVC before and after the adsorption of Pb(II), it was confirmed that the adsorption of Pb(II) on NS-PVC was controlled by a combination of chemisorption and physisorption, including ion exchange, surface complexation, pore filling and electrostatic attraction.