Sol-gel derived organic-inorganic hybrid sorbent for removal of Pb2+, Cd2+ and Cu2+ from aqueous solution

This manuscript reported sol-gel derived organic-inorganic hybrid sorbent for the removal of Cd2+, Pb2+ and Cu2+ ions from aqueous solutions. The hybrid sorbent (S-2/SiO2) had been synthesized by a simple co-condensation of bis[3-(triethoxysilyl)propyl]disulfide and tetraethoxysilane via sol-gel transformation. The S-2/SiO2 was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, elemental analysis and thermogravimetric analysis. The influences of different adsorption parameters, such as pH value of solution, contact time and initial concentrations of metal ions on the adsorption amount of Cd2+, Pb2+ and Cu2+ were examined. The optimum pH for adsorption was found to be in the range of 3.7-8.5. The adsorption rates of Cd2+, Pb2+ and Cu2+ by S-2/SiO2 were rapid. Ho's pseudo-second-order model best described the kinetics of the adsorption reaction. The adsorption process of metals followed Langmuir isotherm model, and the experimental values of maximum adsorption capacities for Cd2+, Pb2+ and Cu2+ were 26.8, 56.7 and 13.3 mg g(-1), respectively. The positive values of Delta H (o) suggested endothermic nature of Cd2+, Pb2+ and Cu2+ adsorption on S-2/SiO2 sorbent. Increase in entropy of adsorption reaction was shown by the positive values of Delta S (o) and the negative values of Delta G (o) indicating that the adsorption was spontaneous in nature.