Surface functionalization of mesoporous silica MCM-41 with 3-aminopropyltrimethoxysilane for dye removal: kinetic, equilibrium, and thermodynamic studies

Abstract

Mesoporous silica MCM-41 was synthesized and functionalized with a silane coupling agent (3-aminopropyltrimethoxysilane, APTMS) for the removal of Acid Blue 25 (AB25, anionic dye) and Methylene Blue (MB, cationic dye) from aqueous solutions as adsorbents. The synthesized (MCM-41) and functionalized (f-MCM-41) materials were characterized using field emission scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, particle size analysis, nitrogen gas adsorption-desorption analysis, X-ray diffraction spectrometry, and Fourier transform infrared spectrometry. The results indicate that the surface modification of MCM-41 with APTMS was successfully carried out. Batch experiments were performed to examine AB25 and MB removal by MCM-41 and f-MCM-41 under various experimental conditions. The results show that f-MCM-41 was a good adsorbent for anionic AB25, but not for cationic MB. This could be attributed to the presence of amine groups on the surfaces of f-MCM-41 from the APTMS modification. Conversely, MCM-41 was good for MB removal, but not for AB25 removal. AB25 removal in f-MCM-41 was sensitive to solution pH, with decreasing adsorption capacity as pH increased from 4.1 to 9.4. MB removal in MCM-41 was sensitive to solution pH in the opposite manner, with increasing adsorption capacity as pH increased from 4.1 to 10.3. Thermodynamic analysis showed that the adsorption of AB25 to f-MCM-41 and of MB to MCM-41 decreased with increasing temperature from 15 to 45°C, indicating the exothermic nature of the sorption process. This study demonstrated that surface functionalization with silane coupling agents can help to make MCM-41 useful for the removal of various types of dyes.

Keywords:

• Dye removal
• MCM-41
• Mesoporous silica
• Silane coupling agent
• Surface functionalization

Acknowledgments

This work was supported by the National Research Foundation of Korea, funded by the Ministry of Education, Republic of Korea (grant number 2014–027899).