Manganese dioxide-loaded mesoporous SBA-15 silica composites for effective removal of strontium from aqueous solution

Manganese dioxide-loaded mesoporous SBA-15 silica (MnO2/SBA-15) composites with short pore length were aprepared for the first time by simply immersing SBA-15 into a KMnO4 and MnCl2 mixed solution. Adsorption of Sr2+ from aqueous solution by using the MnO2/SBA-15 was investigated by varying the pH, contact time, initial Sr2+ concentration, MnO2 content and temperature. The adsorption process was rapid during the first 40 min and reached equilibrium in 120 min. The Sr2+ adsorption capacity increased with increasing pH, MnO2 content and temperature, and the adsorption capacity of SBA-15 was significantly improved by the loading of MnO2. Moreover, the experimental adsorption data were analyzed using different equilibrium isotherm, kinetic and thermodynamic models. The results showed that the isotherm data were well-described by the Langmuir model. The maximum Sr2+ adsorption capacity was determined to be 75.1 mg g−1 at 283 K based on the Langmuir model. The analyzed kinetic data indicated that the Sr2+ adsorption process was well fitted by the pseudo-second order model. Furthermore, the thermodynamic parameters of adsorption were also determined from the equilibrium constant values obtained at different temperatures. The results suggested that the adsorption process was spontaneous and endothermic, and the overall mechanism of Sr2+ adsorption was a combination of physical and chemical processes.