A dual template ion-imprinted polymer based on acrylamide monomer/modified graphene oxide for simultaneous adsorption of Ni(ii) and Cd(ii)

The use of ion-imprinted polymers (IIPs) to target hazardous heavy metal ions is an effective solution for addressing water pollution by recognizing and adsorbing specific metal cations. Although dual-template IIPs can offer enhanced efficiency as opposed to single-template IIPs due to their ability for simultaneous adsorption of ions, they have been rarely investigated. This work aimed to develop a new dual-template IIP-based adsorbent for the uptaking of Cd(II) and Ni(II) from aqueous solutions, simultaneously. Surface imprinting technology was employed to synthesize this IIP using modified graphene oxide (GO) as a substrate matrix, acrylamide (AAm) as a monomer, and ethylene glycol dimethylacrylate (EGDMA) as a cross-linker. The prepared GO-IIP was characterized using FT-IR spectroscopy, SEM, EDX, and TGA, and the results were compared with those of the non-ion imprinted polymer (GO-NIP) as the control sample to enhance the understanding of functional groups, morphological changes, elemental composition, and thermal behavior, respectively. By carrying out batch experiments to examine the key parameters affecting the adsorption process, it was found that adsorption took place rapidly within the first 15 min. The maximum adsorption of Cd(II) and Ni(II) occurred at an initial concentration of 300 mg L⁻¹, a temperature of 25 °C, a pH of 6, and an equilibrium contact time of 3 h. The equilibrium experiments demonstrated a strong fitting with the Langmuir isotherm model, revealing maximum monolayer adsorption capacities of 188.67 mg g⁻¹ for Cd(II) and 153.13 mg g⁻¹ for Ni(II). A comparison of the maximum adsorption capacities between GO-IIP and GO-NIP exhibited significant differences [78.12 mg g⁻¹ for Cd(II) and 61.35 mg g⁻¹ for Ni(II)], highlighting the superior performance of the imprinted adsorbent for ion removal. Moreover, the adsorption was spontaneous, exothermic, and physio-chemical in nature based on the calculated thermodynamic parameters.