MCM-41

MCM-41 (Mobil Crystalline Materials) is an amorphous silica comprising of an array of unidirectional, 2-D hexagonal mesopore structure with an extremely high surface area of ˃ 1000 m2/g-1. This mesoporous molecular sieve (M41S) was discovered by scientists of Mobil Oil Research and Development 1992. Since that, it has attracted extensive attention of researchers in academia and industry because of its large pore, large surface area, thernal stability and mild acidy property, and it has been implemented in order to increase the acidity, ion exchange capacity and specific catalytic activity of mesoporous silica molecular sieves (Hui K. S., 2006).

There are three different mesophases in MCM that have been identified, Lamellar (MCM-50), cubic (MCM-48), and hexagonal (MCM-41) phases. MCM-41 possesses highly regular arrays of uniform-sized channels whose diameters are in the range of 15-100 Å depending on the templates used, the addition of auxiliary organic compounds, and the reaction parameters (Xiu S. Zhao, 1996).

Cubic

Hexagonal

Lamellar

MCM-41 can be synthesized by mixing organic amine (surfactants), silica, and/or silica-alumina source to form a supersaturated solution while maintaining the mixture at a temperature between 70 and 150 °C for selected periods of time. The figure (below) shows the mechanism of liquid crystal templating via two possible pathways (Beck et al., 1992a).

The randomly ordered rodlike micelles interact with silicate species by Cou-lombic interactions in the optimal reaction mixture to produce approximately two or three monolayers of silicate encapsulation around the external surfaces of the micelles. These randomly ordered composite species spontaneously pack into a highly ordered mesoporous phase with an energetically favorable hexagonal arrangement, accompanied by silicate condensation. With the increase in heating time, he inorganic wall continues to condense (Xiu S. Zhao, 1996).

Reference : K.S. Hui, C.Y.H. Chao 2006 J. Haz. Mater. B137 1135-1148

                 Xiu S. Zhao, G.Q. (Max) Lu, and Graeme J. Millar Ind. Eng. Chem. Res. 1996, 35, 2075-2090

             George L. Athens, Ramzy M. Shayib, Bradley F. Chmelka J. Cur. Opi. Int. Sc. 14 (2009) 281-292

             Beck, J.S; Vertuli, C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C.T-W.;  

                              Olson, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. A New 

                               Family of Mesoporous Molecular Sieves Prepared with Liquid Crystal Templates. J. 

                              Am. Chem. Soc. 1992a, 114, 10834-10843.