Amino-modified microporous hyper-crosslinked resins for heavy metal ions adsorption

In this work, a high surface area micro/mesoporous hyper-crosslinked resin based on vinylbenzyl chloride and divinylbenzene is synthesized through a solvent-free polymerization followed by Friedel-Crafts alkylation. The hyper-crosslinked resin is then functionalized with amino moieties and the effect of the functionalization on the adsorption of metal ions is evaluated. After a chemical-physical characterization of the hyper-crosslinked resins, equilibrium adsorption tests of Pb(II) and Cu(II) in water are performed. The plain and amino-modified hyper-crosslinked resins (HCLR and HCLR-NH2) exhibit specific surface area (SSA) of about 1800 m2/g and 800 m2/g, respectively. They both exhibit micro/mesoporous structure, and their pore size distribution is modified upon functionalization. The amino-functionalization, while reducing prevalently the mesoporosity of the resin, does not significantly affect the micropores. HCLR-NH2 displays higher efficiency in removing both metal ions from aqueous solution compared to the unmodified resin. HCLR-NH2 is able to capture up to about 70 % of Pb(II) and up to about 48 % of Cu(II) dissolved in water at 5 mg/L concentration while in the same tests, HCLR captures about 25 % of Pb(II) and 17 % of Cu(II). The resins adsorption mechanisms follow the Langmuir model, suggesting a specific and functional groups-related adsorption mechanism. Therefore, the major adsorption capacity of HCLR-NH2 is to be primary attributed to the grafted amino moieties, which establish chelating interactions with the metal cations. Overall, results assess the relevance of the micropores and the amino functionalization to capture Pb and Cu ions via adsorption.