Cd(II)-imprinted polymer sorbents prepared by combination of surface imprinting technique with hydrothermal assisted sol–gel process for selective removal of cadmium(II) from aqueous solution

A new ion-imprinted thiocyanato-functionalized silica gel sorbents was synthesized by the combination of a surface imprinting technique with a hydrothermal-assisted sol–gel process with Cd(II) as the template, 3-thiocyanatopropyltriethoxysilane (TCPTS) as the functional monomer, and epichlorohydrin as the cross-linking agent (IIP-TCPTS/SiO2) for the selective removal of Cd(II) from aqueous solution. The Cd(II)-imprinted thiocyanato-functionalized silica sorbents was characterized by FTIR, SEM, nitrogen adsorption and the static adsorption–desorption experiment method. The results showed that the maximum static adsorption capacity of IIP-TCPTS/SiO2 sorbents prepared by hydrothermal heating method was 2.3 times as much as the conventional heating method. The IIP-TCPTS/SiO2 sorbents offered a fast kinetics for the adsorption and desorption of Cd(II). The static uptake capacity and selectivity coefficient of IIP-TCPTS/SiO2 sorbents were higher than those of the non-imprinted sorbents. IIP-TCPTS/SiO2 sorbents had a substantial binding capacity in the range of pH 4.2–8.6 and could be used repeatedly. The Langmuir adsorption model was more favorable than the Freundlich adsorption model. Kinetic studies indicated that the adsorption followed a pseudo-second-order model. Various thermodynamic parameters such as ΔG°, ΔH° and ΔS° were evaluated with results indicating that this system was a spontaneous and endothermic process. The results showed that IIP-TCPTS/SiO2 sorbents could be employed as an effective material for the selective removal of Cd(II) from aqueous solutions.