Synthesis, characterization, and use of an amine-functionalized mesoporous silica SBA-15 for the removal of Congo Red from aqueous media

In this study, SBA-15 was synthesized and functionalized with [3-( N , N -dimethylamino)-propyl] trimethoxysilane (AF-SBA-15) using a post-grafting method and evaluated for use in the removal of an anionic synthetic dye (Congo Red, CR) from aqueous media. The synthesized mesoporous materials were characterized by small-angle XRD, N 2 adsorption–desorption, FT-IR, and SEM techniques. The ordered hexagonal structure of pure SBA-15 and amine-functionalized SBA-15 (AF-SBA-15) was confirmed by small-angle XRD analysis; surface area, pore size, and pore diameter were determined by nitrogen adsorption–desorption analysis. Kinetics showed that the process reached equilibrium after 90 min; adsorption followed pseudo-second-order kinetic model. Maximum efficiency was obtained at the unadjusted pH (8.8) of the aqueous media, and the efficiency was negatively affected by CR concentration, but increased with dose and temperature. While pure SBA-15 could not adsorb CR, the highest adsorption capacity and efficiency obtained with AF-SBA-15 were calculated to be 186.41 mg/g and 95.3%, respectively. The data were successfully fitted to Langmuir adsorption isotherm ( R 2 > 0.99), and consistently, thermodynamics signified possible physico-chemical interactions between CR and AF-SBA-15. The process was shown to be endothermic and non-spontaneous. The results show that amine-functionalized SBA-15 can be used to efficiently remove toxic anionic colorants from aqueous media. Graphical abstract The proposed mechanisms for the adsorption of CR onto AF-SBA-15 under acidic and neutral conditions of media.