Removal of cadmium from aqueous solution by organic-inorganic hybrid sorbent combining sol-gel processing and imprinting technique

An organic-inorganic hybrid sorbent with high adsorption capacity was prepared by surface imprinting technique combined with sol-gel processing with 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane as a functional precursor and silica as the support for the removal of Cd(II) ion from aqueous solution, and was characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, nitrogen gas sorption and thermogravimetric analysis. The influences of different adsorption parameters, such as pH value of solution, contact time and the initial concentrations of Cd(II) ions on the adsorption amount of Cd(II), were examined. The optimum pH for adsorption was found to be in the range of 4–8. The adsorption rate of Cd(II) on the imprinted hybrid sorbent was rapid. The relative selectivity coefficients of the imprinted hybrid sorbent were higher than those of the non-imprinted sorbent. Ho’s pseudosecond-order model best described the kinetics of the adsorption reaction. The adsorption process of metals followed Redlich-Peterson and Langmuir isotherms models, and the experimental value of maximum adsorption capacity for Cd(II) was 77.2mg·g−1. The positive values of ΔH ○ suggested endothermic nature of Cd(II) adsorption on the imprinted hybrid sorbent. Increase in entropy of adsorption reaction was shown by the positive values of ΔS ○ and the negative values of ΔG ○ indicating that the adsorption was spontaneous.