Mechanism of Cd (II) sorption on silica synthesized by sol–gel method

The present work deals with the Cd2+ sorption studies on silica synthesized by sol–gel method. The surface structure of silica is investigated by X-ray diffraction (XRD), surface area analysis (SAA), particle size distribution, thermal analysis (TG–DTA–DTG), scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) analysis. The adsorption of Cd2+ ions is found to increase with increasing concentration and temperature of electrolyte solution. The Langmuir model is used to interpret sorption of cadmium ions on the solid surface. The sorption of Cd2+ ion is found to increase with the increase in surface area of the solid. The values of both the adsorption enthalpy ΔH and entropy ΔS are found to be positive, which explains the sorption process to be endothermic and spontaneous in nature. The silica dissolved from the solid is also noted. Further, the mechanism of the sorption reaction is well explored.