Significantly improving the Cu2+ removal performance of conducting polymer-based adsorbent from aqueous solution through cross-linking modification

Through cross-linking modification of poly(o-phenylenediamine) (PoPD) to increase the adsorption active sites, the Cu²⁺ adsorption capacity of PoPD was improved significantly. According to FT-IR, XRD, SEM and BET results, both PoPD and the cross-linked PoPD had porous or surface-adhesive porous morphology with a typical mesoporous character, the specific surface area of the latter was increased obviously from the former. Both of them showed excellent Cu²⁺ adsorption capabilities with the maximum adsorption q^exp_max of 76.51 and 85.49 mg·g⁻¹, and the corresponding removal ratios of 60.21% and 68.39%, respectively. The adsorption capacity was increased to its 1.54 times with pentaerythritol tris[3-(1-aziridinyl)propionate] (cross-linking agent-III) as cross-linking agent at pH = 5 and 25°C. Because temperature could affect the adsorption behavior of materials and the adsorption process is endothermic with ΔG < 0, the process should be accompanied by spontaneous chemical changes. The XRD, SEM–EDX mapping and XPS results showed that Cu²⁺ was successfully removed from the aqueous solution. Additionally, the adsorption was mainly based on the cation-π interaction and the formation of Cu-N bonds.