Inversely Vulcanized Porous Copolymer Monolith for Efficient Removal of Metal Ions from Water

Heavy metal pollution poses a significant threat to the environment and human health. Developing efficient adsorbent materials for removing these contaminants from water is crucial. Sulfur-based polymers derived from inverse vulcanization were found to be promising candidates for the adsorption of several heavy metals from water. In this work, polysulfides bearing β-diketone functional groups are synthesized for the first time through the inverse vulcanization between acetoacetoxyethyl methacrylate (AAEMA) and sulfur. Successful copolymerization and the incorporation of the acetoacetate moiety into the polymer chain are confirmed by NMR, FT-IR, Raman, XPS, XRD, DSC, and TGA analyses. A porous variant of the adsorbent is made using a facile template-assisted method exploring NaCl as a porogen. The porous polymer is analyzed using X-ray micro-CT and SEM to get insights into the internal porous architecture as well as the surface porosity of the adsorbent. Energy-dispersive X-ray (EDAX) and CHNS(O) analyses of the adsorbent reveal a sulfur-rich surface with uniformly distributed oxygen and carbon. Heavy metal adsorption studies of the synthesized polymer are conducted in a multielement solution containing different types of metal ions. The porous adsorbent exhibited remarkable heavy metal chelation properties, with a removal efficiency of 100% for Hg²⁺ and 72-96% removal for Cr³⁺, Pb²⁺, Co²⁺, Fe³⁺, Ni²⁺, Ag⁺, and Cu²⁺. The synergistic interplay between the thiol functional groups, polysulfide loops, and the strong binding affinity of the β-diketone moiety and hydroxyl group coupled with the polymer's well-defined porous structure collectively enhances its adsorption capacity toward heavy metal ions. A prototype of an identical porous adsorbent in monolithic form has been constructed. The porous monolith retains all the benefits of porous adsorbent in particulate form while allowing the separation of the adsorbent from the treated water by simply lifting it as a single unit, eliminating the necessity for filtration as is necessary with particulate adsorbents.