5124
Chem. Mater. 2002, 14, 5124-5133
Templated Growth of Alumina-Based Fibers through the Use of Anthracenic Organogelators M. Llusar,†,‡ L. Pidol,† C. Roux,† Jean L. Pozzo,§ and C. Sanchez*,† Laboratoire de Chimie de la Matie` re Condense´ e, UMR CNRS 7475, Universite´ Pierre et Marie Curie, F-75252 Paris Cedex 05, France, Departament de Quı´mica Inorga` nica i Orga` nica, Universitat jaume I, 12071 Castello´ , Spain, and Photochimie Organique, UMR 5802, Universite´ de Bordeaux I, F-33405, France Received June 28, 2002. Revised Manuscript Received September 20, 2002
DDOA (2,3-bis(n-decyloxy)anthracene) has been successfully employed as a template to direct the growth of high-surface alumina-based fibers exhibiting bimodal porosity. Hybrid gels were obtained after thermal aging (at 40 °C) of an aqueous ethanol solution of AlCl3 entrapped by a previously formed DDOA organogel. SEM characterization showed that the hybrids were constituted by submicronic fibers (200-500 nm) aggregated into fibrous bundles (1-2 µm thick), and evidenced an important effect of pH conditions on fibers thickness and on fibers aggregation (intertwined or highly co-aligned). By calcining at 350 °C, the organic imprint was satisfactorily removed (confirmed by FTIR, EDAX, and chemical analyses) without disruption of the fibrous assemblies, leading to high surface (150-300 m2/g) aluminabased fibrous materials with an anisotropic porosity at the meso- (around 3-10 nm) and macroscales (confirmed by nitrogen sorption measurements and by TEM characterization). Very interestingly, the fibrous morphology was highly preserved after calcination at 800 °C and crystallization of transition aluminas and R-Al2O3.
1. Introduction Apart from the high-temperature stable oxide R-Al2O3 (corundum) and from aluminum hydroxides Al(OH)3 and oxyhydroxides AlO(OH), aluminas also exist as a large variety of metastable variants known as transition aluminas.1-3 Among these transition aluminas, partially amorphous or crystalline γ-Al2O3 (the first member of the series resulting from dehydration of boehmite: AlO(OH) f γ-Al2O3 f δ-Al2O3 f θ-Al2O3 f R-Al2O3)4-6 is an extremely important technological material, owing to its widespread use as sorbent7 or as high surfacearea support material for automotive catalytic converters8 and for other types of catalysts, such as those * To whom correspondence should be addressed. Phone: 33 1 44275534. Fax: 33 1 44274769. E-mail:
[email protected]. † Laboratoire de Chimie de la Matie ` re Condense´e. ‡ Departament de Quı´mica Inorga ` nica i Orga`nica. § Photochimie Organique. (1) (a) Euzen, P.; Krokidis, X.; Raybaud, P.; Toulhoat, H.; Le Loarer, J. L.; Jolivet, J. P.; Froidefond, C. In Alumina, Handbook of Porous Materials; Schueth, F., Sing, K., Weitkamp, J. Eds.; Wiley-VCH Verlag GmbH: Weinheim, 2002, 1591-1676. (b) Wefers, K. Alumina Chemicals: Science And Technology Handbook; Hart L. D., Ed.; The American Ceramic Society: Westerville, OH, 1990; pp 13-22. (2) Misra, C. Industrial Alumina Chemicals; ACS Monograph 184; American Chemical Society: Washington, DC, 1986. (3) Gitzen, W. H. Alumina as a Ceramic Material; The American Ceramic Society: Coumbus, OH, 1970. (4) Levin, I.; Brandon, D. J. Am. Ceram. Soc. 1998, 81, 1995. (5) Husson, E.; Reppelin, Y., Eur. J. Solid State Inorg. Chem. 1996, 33, 1223. (6) Krokidis, X.; Raybaud, P.; Gobichon, A. E.; Rebours, B.; Euzen, P.; Toulhoat, H. J. Phys. Chem. B 2001, 105, 5121. (7) Nedez, C.; Ray, J.-L. Environmental Catalysys; Centi, G., Cristiani, S., Perathoner, S., Forzatti, P., Ed.; EFCE PublicationsSeries 112; Societa Chimica Italiana: Rome, Italy, 1995; pp 37-40. (8) Taylor, K. C: Catal. Rev.-Sci. Eng. 1993, 35, 457.
employed in petroleum refining9 and in the production of bulk and fine chemicals.10 However, the physical properties and potential applications of a given material do not depend only on its chemical composition and structure but also on its texture and shape. Indeed, materials chemists possess nowadays a set of efficient tools at hand, being able to smartly choose the texturing agents (surfactants, block copolymers, dendrimers, etc.), the starting mineral precursors (inorganic salts, metal alkoxides, NanoBuildingBlocks, etc.), and the reaction media (solvents, water contents, pH, complexing agents, aging conditions, etc.) to attempt a high control on the compatibility of the mineral and organic components, and the self-assembly processes at hybrid interfaces.11 More recently, organogelalors being able to reversibly form fibrous networks, with welldefined geometry and shape, have been used to shape and texture inorganic materials such as silica and titania based materials.12-20 (9) Kno¨zinger, H.; Ratnasamy, P. Catal. Rev.-Sci. Eng. 1978, 17, 31. (10) Shi, B.; Davis, B. H. J. Catal. 1995, 157, 359 (11) (a) Ozin, G. A. Chem. Commun. 2000, 419. (b) Dabbs, D. M.; Aksay, A. Annu. Rev. Phys. Chem. 2000, 51, 601. (c) Sa´nchez, C.; SolerIllia G. J. de A. A.; Ribot, F.; Lalot, T.; Mayer, C. R.; Cabuil, V. Chem. Mater. 2001, 13, 3061 (12) Ono, Y.; Kanekiyo, Y.; Inoue, K.; Hojo, J.; Nango, M.; Shinkai, S. Chem. Lett. 1999, 475. (13) Oishi, G K.; Ishi-i, T.; Sano, M.; Shinkai, S. Chem. Lett 1999, 1089. (14) Ono, Y.; Nakashima, K.; Sano, M.; Hojo, J.; Shinkai, S. Chem. Lett. 1999, 1119. (15) Kobyashi, S.; Hanabusa, K.; Susuki, M.; Kimura, M.; Shirai, H. Chem. Lett. 1999, 1077. (16) Kobyashi, S.; Hanabusa, K.; Hamasaki, N.; Kimura, M.; Shirai, H. Chem. Mater. 2000, 12, 1523.
10.1021/cm021247t CCC: $22.00 © 2002 American Chemical Society Published on Web 12/16/2002
Growth of Alumina-Based Fibers
Chem. Mater., Vol. 14, No. 12, 2002 5125 Table 1. Conditions for Samples Preparation (Molar Ratios, DDOA Concentration, Catalyst, and pH)
Figure 1. Molecular structure of DDOA (2,3-bis-n-decyloxyanthracene).
Indeed, organogelators are low-weight organic molecules capable to form, at very low concentrations (ca. 10-3 mol dm-3, less than 1% w/w) in a variety of solvents, thermoreversible physical gels exhibiting strongly anisotropic structures, mostly in the shape of fibers, but also as ribbons, platelets, or cylinders.21-24 Several families of organogelators such as aliphatic amide derivatives, saccharides, steroids, phthalocyanines, or 2,3-bis-n-decyloxyanthracene (DDOA) exist.25-28 They have been mostly classified according to the main forces occurring at the supramolecular level (H-bonding, van der Waals forces, dipole-dipole interactions, charge transfer, electrostatic interactions, coordination bonds, etc.) and being responsible for the organized stacking of the molecules into the gel phase. Using the organogelator approach, silica fibers and other siliceous materials presenting novel morphologies and textures have been synthesized by changing the nature of the organogelator: (i) hollow silica tubes presenting a “wrapped” aspect (similar to the lamellarlike pattern observed in spiculae); 19 (ii) tubular silicas presenting a rolled paperlike structure; 19,20 (iii) helical silica or hybrid fibers with chiral information transcribed by selecting templates with the adequate (R or S) configuration;17 (iv) using DDOA and DAP organogelators as templates, silica fibers having a double-scale porosity can also be obtained.29 These first results are indeed encouraging, as they strongly suggest that the use of organogelators as “templates” will make possible the elaboration of novel materials presenting complex and unique architectures exhibiting multiscale texturing with possible size scales ranging from the nanometer to a fraction of a millimeter. In this work, an anthracenic organogelator, DDOA (see Figure 1), has been employed as a structuredirecting agent to orient the condensation of alumina in the form of fibers. The reproducible production of high-surface, alumina-based fibers (amorphous or crystalline γ-Al2O3) exhibiting a bimodal porosity (at the meso- and macroscales) would be of great interest for (17) (a) Jung, J. H.; Ono, Y.; Hanabusa, K.; Shinkai, S. J. Am. Chem. Soc. 2000, 122, 5008. (b) Moreau, J. J. E.; Vellutini, L.; Wong Chi Man, M.; Bied, C. J. Am. Chem. Soc. 2001, 123, 1509. (18) Jung, J. H.; Ono, Y.; Shinkai, S. Angew. Chem., Int. Ed. 2000, 39, 1862. (19) Jung, J. H.; Ono, Y.; Shinkai, S. Langmuir 2000, 16, 1643. (20) Jung, J. H.; Ono, Y.; Shinkai, S. J. Chem. Soc., Perkin Trans. 2 1999, 1289. (21) van Esch, J. H.; Feringa, B. L. Angew. Chem., Int. Ed. 2000, 39, 2263. (22) Terech, P.; Furman, I.; Weiss, R. G.; Bouas-Laurent, H.; Desvergne, J. P.; Ramasseul, R. Faraday Discuss. 1995, 101, 345. (23) Scartazzini, R.; Luisi, P. L. J. Phys. Chem. 1988, 92, 829. (24) Wang, R.; Geiger, C.; Chen, L.; Swanson, B.; Witten, D. G. J. Am. Chem. Soc. 2000, 122, 2399. (25) Terech, P.; Weiss, R. G. Chem. Rev. 1997, 97, 3133. (26) Abdallah, D.; Weiss, R. G.; Adv. Mater. 2000, 17, 1237. (27) Amaike, M.; Kobayashi, H.; Shinkai, S. Bull. Chem. Soc. Jpn. 2000, 73, 2553 (28) Nakano, K.; Hishikawa, Y.; Sada, K.; Miyata, M.; Hanabusa, K. Chem. Lett. (Chemical Society of Japan) 2000, 1170. (29) Clavier, G.; Pozzo, J. L.; Bouas-Laurent, H.; Lie`re, C.; Roux, C.; Sanchez, C. J. Mater. Chem. 2000, 10, 1725.
DDOA final sample Al:EtOH:H2O concentration 1 2 3 B1 B2
1:20:5 1:20:5 1:20:5 1:20:5 1:20:5
10-2 M 10-2 M 10-2 M
catalyst (basic)
pHa
