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 (S₂/SiO₂) had been synthesized by a simple co-condensation of bis[3-(triethoxysilyl)propyl]disulfide and tetraethoxysilane via sol–gel transformation. The S₂/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 S₂/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 ΔH ^o suggested endothermic nature of Cd²⁺, Pb²⁺ and Cu²⁺ adsorption on S₂/SiO₂ sorbent. Increase in entropy of adsorption reaction was shown by the positive values of ΔS ^o and the negative values of ΔG ^o indicating that the adsorption was spontaneous in nature.