pubs.acs.org/cm Published on Web 03/25/2010 r 2010 American Chemical Society 2466 Chem. Mater. 2010, 22, 2466–2473 DOI:10.1021/cm902883p Formation and Growth Mechanisms of Imogolite-Like Aluminogermanate Nanotubes C. Levard, † J. Rose,* ,† A. Thill, § A. Masion, † E. Doelsch, ‡ P. Maillet, § O. Spalla, § L. Olivi, ^ A. Cognigni, ^ F. Ziarelli, r and J.-Y. Bottero † † CEREGE, Aix-Marseille University, CNRS, IRD, Coll  ege de France, Europ ^ ole M editerran een de L’Arbois, BP 80, 13545 Aix en Provence, France, ‡ CIRAD, Environmental Risks of Recycling Research Unit, 34398 Montpellier, France, § CEA Saclay, IRAMIS, Laboratoire Interdisciplinaire sur l’Organisation Nanom etrique et Supramol  eculaire, 91191 Gif sur Yvette, France, ^ ELETTRA, Synchrotron Light Source, 34012 Trieste, Italy, and r Spectropole, F ed eration des Sciences Chimiques CNRS-FR1739, av. Escadrille Normandie Ni emen, 13397 Marseille cedex 20, France Received September 15, 2009. Revised Manuscript Received January 12, 2010 The growth mechanisms of imogolite-like aluminogermanate nanotubes have been examined at various stages of their formation. The accurate determination of the nucleation stage was examined using a combination of local- (XAS at the Ge-K edge and 27 Al NMR) and semilocal scale technique (in situ SAXS). For the first time, a model is proposed for the precursors of the nanotubular structure and consist in rooftile-shaped particles, up to 5 nm in size, with ca. 26% of Ge vacancies and varying curvatures. These precursors assemble to form short nanotubes/nanorings observed during the aging process. The final products are most probably obtained by an edge-edge assembly of these short nanotube segments. Introduction Over the past two decades, there has been an increasing interest in non-carbon-based nanotubes, because of their unique properties, in terms of chemical reactivity, optical properties, and a high specific surface area. The literature generally considers that the first synthesis of an inorganic nanotube (tungsten disulfide) was performed in 1992 by Tenne et al. 1-3 Since this date, numerous protocols to obtain other inorganic nanotubes have been developed, including template processes, 4,5 reverse micellar systems, 6 vapor depositions, 7 and electrochemical reactions. 8 Never- theless, imogolite (Al 2 SiO 7 H 4 ) nanotubes were success- fully synthesized even sooner, in 1977. 9 Imogolite is a natural mineral formed in volcanic soils. It consists of a single-walled aluminosilicate nanotube with inner and outer diameters of 1 and 2 nm, respectively, and a length ranging from a few tens to several hundreds of nano- meters. The wall of the imogolite nanotube is composed of a curved gibbsite (Al(OH) 3 ) layer on the outer surface and silicate tetrahedra linked to six aluminum octahedra inside the tube. 10 It was observed in natural systems for the first time in 1962, 11 and its structure was well- characterized 10 years later using X-ray diffraction (XRD). 10 The synthesis of imogolite nanotubes involves a simple hydrolysis step followed by a growth step at 95 °C. 9,12 This very simple synthesis protocol is in con- trast to the far-more-complicated multiple-step processes generally implemented in nanofabrication and, thus, explains the great interest for imogolite nanotubes. However, almost all current imogolite synthesis proto- cols are not suited to readily yield significant amounts of material. Indeed, since the initial concentration of re- agents lies in the millimolar range, 9 the synthesis of only 1 g of imogolite involves processing an initial reaction volume of at least 10 L. In a recent study, larger nanotube amounts could be obtained, but at the cost of a consider- ably longer growth step. 13 Such drawbacks hinder the transition from the laboratory scale to the pilot/industrial scales, thereby diminishing the interest in the develop- ment of the applications for imogolite nanotubes. Efforts to control and improve reaction yield, length, and dia- meter of the nanotubes requires the knowledge of the growth mechanisms of the nanotubes, i.e., identifying the *Author to whom correspondence should be addressed. Tel.: (þ33) 442 97 15 29. E-mail: rose@cerege.fr. (1) Tenne, R.; Margulis, L.; Genut, M.; Hodes, G. Nature 1992, 360, 444. (2) Remskar, M. Adv. Mater. 2004, 16(17), 1497. (3) Tenne, R. Nature Nanotechnol. 2006, 1, 103. (4) Mayya, K. S.; Gittins, D. I.; Dibaj, A. M.; Caruso, F. Nano Lett. 2001, 1(12), 727. (5) Wang, C. C.; Kei, C. C.; Yu, Y. W.; Perng, T. P. Nano Lett. 2007, 7, 1566. (6) Lisiecki, I.; Sack-Kongehl, H.; Weiss, K.; Urban, J.; Pileni, M. P. Langmuir 2000, 16(23), 8802. (7) Liu, Z. W.; Bando, Y. Adv. Mater. 2003, 15(4), 303. (8) Zhao, A. W.; Meng, G. W.; Zhang, L. D.; Gao, T.; Sun, S. H.; Pang, Y. T. Appl. Phys. A 2003, 76(4), 537. (9) Farmer, V. C.; Fraser, A. R.; Tait, J. M. J. Chem. Soc., Chem. Commun. 1977, 462. (10) Cradwick, P. D. G.; Farmer, V. C.; Russel, J. D.; Masson, C. R.; Wada, K.; Yoshinaga, N. Nat. Phys. Sci. 1972, 240, 187. (11) Yoshinaga, N.; Aomine, S. Soil Sci. Plant Nutr. 1962, 8(3), 22. (12) Yang, H.; Wang, C.; Su, Z. Chem. Mater. 2008, 20(13), 4484. (13) Levard, C.; Masion, A.; Rose, J.; Doelsch, E.; Borschneck, D.; Dominici, C.; Ziarelli, F.; Bottero, J.-Y. J. Am. Chem. Soc. 2009, 131, 17080.