Glycometallate surfactants. Part 1: non-aqueous synthesis of mesoporous silica

Abstract

A novel two step procedure for the synthesis of hexagonal mesoporous silica has been developed. The first non-aqueous step involves the use of ethylene glycol both as solvent and chelating alkoxide. In this step a cetyltrimethylammonium glycosilicate(IV), CTA₂[Si₂(OCH₂CH₂)₅], building-block is synthesized under non-aqueous conditions by solubilizing SiO₂ with NaOH in ethylene glycol in the presence of CTACl. Alternatively, CTA₂[Si₂(OCH₂CH₂)₅] can be formed by reacting sodium glycosilicate(IV), Na₂[Si₂(OCH₂CH₂)₅], with CTACl under non-aqueous conditions in ethylene glycol. The glycosilicate(IV) is a structurally well defined dimeric anion based on trigonal-bipyramidal silicon(IV) containing two bidentate and one bridging monodentate glycolate ligand. In ethylene glycol the glycosilicate(IV) surfactant CTA₂[Si₂(OCH₂CH₂)₅] self-assembles into a lamellar mesophase containing bilayers of cationic CTA⁺ that are charge-balanced by [Si₂(OCH₂CH₂)₅]^2– counter-anions. In the second step of the preparation, controlled hydrolysis of the lamellar glycosilicate(IV) phase with water leads to a well ordered hexagonal mesoporous silica in which the extent of condensation-polymerization of the silica is insufficient to sustain the integrity of the structure when the CTA⁺ cation is removed from the channels. Structure re-enforcement can however be achieved by various post-treatments of the vacuum dehydrated mesoporous silica that enable the creation of stable silica-based mesoporous materials with a wide range of elemental compositions. In this paper a post-treatment with Si₂H₆ at 100 °C was employed to produce extensively polymerized hexagonal mesoporous silica that is stable to removal of the surfactant. The method described in this paper is a novel approach to the synthesis of stable and structurally well defined mesoporous silica-based materials with a wide range of elemental compositions.

References

1. C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 1992, 359, 710.
2. J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. T. Schmitt, C. T.-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc., 1992, 114, 10834.
3. A. S. Kertes and H. Gutmann, in Surface and Colloid Science, ed. E. Matijevic, Interscience, New York, 1975.
4. E. Ruckenstein and R. Nagarajan, J. Phys. Chem., 1980, 84, 1349.
5. R. Nagarajan and C.-C. Wang, J. Colloid Interface Sci., 1996, 178, 471 and references therein.
6. M. Sjoberg, U. Henriksson and T. Wärnheim, Langmuir, 1990, 6, 1205.
7. R. Palepu, H. Gharibi, D. M. Bloor and E. Wynn-Jones, Langmuir, 1993, 9, 110.
8. T. Wärnheim and A. Jönsson, J. Colloid Interface Sci., 1988, 125, 627.
9. R. K. Iler, The Chemistry of Silica, Wiley & Sons, New York, 1979.
10. R. M. Laine, K. U. Blohowiak, T. R. Robinson, M. L. Hope, P. Nardi, J. Kampf and J. Uhm, Nature, 1991, 353, 642.
11. K. Y. Blohowiak, D. R. Treadwell, B. L. Mueller, M. L. Hoppe, S. Jouppi, P. Kansal, K. W. Chew, C. L. S. Scotto, F. Babonneau, J. Kampf and R. M. Laine, Chem. Mater., 1994, 6, 2177.
12. P. Kansal and R. M. Laine, J. Am. Ceram. Soc., 1994, 77, 875.
13. P. Kansal and R. M. Laine, J. Am. Ceram. Soc., 1995, 78, 529.
14. K. W. Chew, B. Dunn, T. Faltens, M. L. Hoppe, R. M. Laine, L. Nazar and H. K. Wu, Am. Chem. Soc. Polym. Prepr., 1993, 34, 254.
15. B. Herreros, S. W. Carr and J. Klinowski, Science, 1994, 263, 1585.
16. B. Herreros, T. L. Barr, P. J. Barrie and J. Klinowski, J. Phys. Chem., 1994, 98, 4570.
17. S. Inagaki, Y. Fukushima and K. Kuroda, J. Chem. Soc., Chem. Commun., 1993, 680.
18. N. H. Ray and R. J. Plaisted, J. Chem. Soc., Dalton Trans., 1983, 475.
19. J. Nathan and E. Oldfield, J. Am. Chem. Soc., 1985, 107, 6769.
20. R. K. Harris and C. T. G. Knight, J. Mol. Struct., 1982, 78, 273.
21. E. Lippmaa, M. Mägi, A. Samoson, G. Engelhardt and A.-R. Grimmer, J. Am. Chem. Soc., 1980, 102, 4889.
22. D. Graf, S. Bauer-Mayer and A. Schnegg, J. Appl. Phys., 1993, 74, 1679.
23. L. Ling, S. Kuwabara, T. Abe and F. Shimura, J. Appl. Phys., 1993, 73, 3018.
24. E. Chomski, Ö. Dag, A. Kuperman, N. Coombs and G. A. Ozin, Chem. Vap. Deposit., 1996, 2, 8.
25. Ö. Dag, A. Kuperman, P. M. Macdonald and G. A. Ozin, Stud. Surf. Sci. Catal., 1994, 84, 1107.
26. W. K. Chang, N. Y. Liao and K. K. Gleason, J. Phys. Chem., 1996, 100, 19653.