Preparation, characterization of thiol-functionalized silica and application for sorption of Pb2+ and Cd2+

Ordered thiol-functionalized microporous silica with BET surface area 1136.64 m2/g and high thiol group density was prepared by co-condensation of 3-mercaptopropyltrimethoxysilane and tetramethoxysilane in the hydroalcoholic medium with cetyltrimethylammonium bromide. These samples were characterized through BET analysis, XRD, TEM, IR and Raman spectroscopy, 29Si NMR and elemental analysis. The sorption behaviors and mechanisms of Pb2+ and Cd2+ on the samples were studied. The maximum sorption amounts of Pb2+ and Cd2+ were 130 and 39 mg/g, respectively. Freundlich isotherm was proved to describe the sorption data better than Langmuir isotherm and pseudo second order kinetic model could fit the sorption kinetic processes well. The pH and electrolyte NaNO3 influenced the sorption of Pb2+ and Cd2+ on the samples significantly. According to hard and soft acids and bases theory and the information analyzed from XPS, the sorption mechanisms could be explained as primary chemical adsorption and secondary physical adsorption.