Synthesis of structurally stable MCM-48 using mixed surfactants as co-template and adsorption of vitamin B12 on the mesoporous MCM-48

Structurally stable MCM-48 mesoporous silica has been facilely synthesized by a new method using mixtures of cationic surfactant cetyltrimethylammonium bromide (CTAB) and nonionic poly(ethylene oxide)-poly( propylene oxide)-poly(ethylene oxide) triblock copolymer surfactant (Pluronic P123) as co-template. For comparison purpose, the cubic MCM-48 material was also prepared via only CTAB as the structure-directing agent under the same synthesis conditions. The products obtained by different templating methods were thoroughly characterized by XRD, N-2 sorption, TEM and FT-IR spectroscopy. The results showed that the synergism effects of the binary system of cationic and nonionic surfactants favored the formation of cubic MCM-48 with extremely low molar ratio of CTAB to SiO2 (0.125:1). From the FT-IR spectra, the stronger intensity of Si-O-Si peaks and the reduction in the absorbance of the Si-OH stretch band of the product obtained via mixed surfactants, and combination of XRD, N-2 sorption, TEM, all measurement results clearly proved its structural stability. The improvement of the stability is attributed to the introduction of P123 resulting in pore wall thickened and a Si-OH group reduction on the pore surface. The adsorption of vitamin B12 on the mesoporous MCM-48 obtained by different templating methods were studied. The MCM-48 obtained via mixed surfactants showed higher adsorption capacity compared with the one obtained via the single cationic CTAB templating route, which is associated with proper amount of Si-OH group on the pore surface and slit-shape pore structure. (C) 2010 Elsevier B.V. All rights reserved.