An ion-imprinted amino-functionalized silica gel sorbent prepared by hydrothermal assisted surface imprinting technique for selective removal of cadmium (II) from aqueous solution

A new ion-imprinted amino-functionalized silica gel sorbent was synthesized by the hydrothermal-assisted surface imprinting technique using Cd²⁺ as the template, 3-2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AAAPTS) as the functional monomer, and epichlorohydrin as the cross-linking agent (IIP-AAAPTS/SiO₂) for the selective removal of Cd²⁺ from aqueous solution, and was characterized by FTIR, SEM, nitrogen adsorption and the static adsorption-desorption experiment method. The specific surface area of the IIP-AAAPTS/SiO₂ sorbents was found to be 149 m² g⁻¹. The results showed that the maximum static adsorption capacities of IIP-AAAPTS/SiO₂ sorbents by hydrothermal heating method and by the conventional heating method were 57.4 and 31.6 mg g⁻¹, respectively. The IIP-AAAPTS/SiO₂ sorbents offered a fast kinetics for the adsorption and desorption of Cd(II). The relative selectivity coefficients of IIP-AAAPTS/SiO₂ sorbents for Cd²⁺/Co²⁺, Cd²⁺/Ni²⁺, Cd²⁺/Zn²⁺, Cd²⁺/Pb²⁺ and Cd²⁺/Cu²⁺ were 30.68, 14.02, 3.00, 3.12 and 6.17, respectively. IIP-AAAPTS/SiO₂ sorbents had a substantial binding capacity in the range of pH 4-8 and could be used repeatedly. Equilibrium data fitted perfectly with Langmuir isotherm model compared to Freundlich isotherm model. Kinetic studies indicated that adsorption followed a pseudo-second-order model. Negative values of ΔG° indicated spontaneous adsorption and the degree of spontaneity of the reaction increased with increasing temperature. ΔH° of 26.13 kJ mol⁻¹ due to the adsorption of Cd²⁺ on the IIP-AAAPTS/SiO₂ sorbents indicated that the adsorption was endothermic in the experimental temperature range.