Kinetic and Isotherm Studies of Ni²⁺Adsorption on Poly(methacrylic acid) Synthesized through a Hierarchical Double-Imprinting Method Using a Ni²⁺ Ion and Cationic Surfactant as Templates

A novel poly­(methacrylic acid) material (IIP/CTAB) was prepared by a hierarchical double-imprinting process with Ni²⁺ ion and cationic surfactantcetyltrimethylammonium bromide (CTAB) as templates, and it was employed to adsorb Ni²⁺ ions from aqueous medium. Other poly­(methacrylic acid) materials single-imprinted (IIP/no CTAB) and nonimprinted (NIP/no CTAB) were investigated in adsorption studies. All the synthesized polymers were characterized by FTIR, SEM, and nitrogen adsorption–desorption isotherm. The maximum Ni²⁺ adsorption capacities of IIP/CTAB and NIP/no CTAB were found to be 33.31 and 18.64 mg g^–1, respectively, at pH 7.25. The relative selectivity coefficient (k′) values for Ni²⁺/Cu²⁺, Ni²⁺/Mn⁺, Ni²⁺/Co²⁺ and Ni²⁺/Pb²⁺ systems were higher than 1, thus confirming the significant improvement in the selectivity of the polymer. The kinetic data were described very well by the pseudo-second-order model, thereby confirming the chemical nature of the Ni²⁺ adsorption (chemisorption), whereas the dual-site Langmuir–Freundlich equation provided the best fit to the isotherm data, suggesting the existence of two kinds of adsorption sites (with low and high binding energies) on the polymer surface. The high chemical stability of IIP/CTAB was verified with 300 Ni²⁺ adsorption–desorption cycles using 1.0 mol L^–1 HNO₃ as stripping agent.