Preparation, characterization, and use of trimethoxy[3-(methylamino)propyl]silane functionalized SBA-15 for Congo Red adsorption

Mesoporous materials have a broad range of applications in industry, and one of which is their potential use in adsorptive separations. This research investigates the use of a secondary amine-functionalized SBA-15 for the separation of a diazo dye, Congo Red (CR), from aqueous solutions. The synthesized SBA-15 was modified with trimethoxy[3-(methylamino)propyl] silane by a post-grafting method. The produced material was characterized using X-ray diffraction, N2 physisorption, scanning electron microscopy, and transmission electron microscopy. The hexagonal mesostructure was preserved after functionalization; however, the specific surface area, pore diameter, and total pore volume of SBA-15 silica decreased. The adsorption of the diazo dye reached equilibrium by 50 minutes, and the data followed pseudo-second-order kinetics. While the yield increased with rising dosage and temperature, it decreased with CR concentration. The maximum adsorption capacity of functionalized SBA-15 (F-SBA-15) for CR uptake was found to be 211.07 mg/g. Thermodynamic data and parameters indicated the potential combination of physical and chemical interactions occurring during the adsorption process. The separation was endothermic and non-spontaneous; the equilibrium data fitted to the Freundlich adsorption isotherm at all tested temperatures. This study demonstrates that the secondary amine-functionalized SBA-15 can be used for the elimination of a toxic anionic diazo dye from aqueous solutions.