AbstractThrough 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 qexpmax 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.