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.