Physico-chemical Control over the Single- or Double-Wall Structure of Aluminogermanate Imogolite-like Nanotubes Antoine Thill,* ,†,⊥ Perrine Maillet, † Be ́ atrice Guiose, † Olivier Spalla, †,⊥ Luc Belloni, † Perrine Chaurand, ‡,⊥ Me ́ lanie Auffan, ∥,⊥ Luca Olivi, § and Je ́ rôme Rose ∥,⊥ † CEA Saclay, IRAMIS, Laboratoire Interdisciplinaire sur l’Organisation Nanome ́ trique et Supramole ́ culaire, 91191 Gif-sur-Yvette cedex, France ‡ Aix-Marseille University, CEREGE, UMR 6635, 13545 Aix-en-Provence cedex 4, France § ELETTRA, Synchrotron Light Source, 34012 Trieste, Italy ∥ CNRS, CEREGE, UMR 6635, 13545 Aix-en-Provence cedex 4, France ⊥ International Consortium for the Environmental Implications of Nanotechnology, iCEINT, http://www.i-ceint.org, France * S Supporting Information ABSTRACT: It is known that silicon can be successfully replaced by germanium atoms in the synthesis of imogolite nanotubes, leading to shorter and larger AlGe nanotubes. Beside the change in morphology, two characteristics of the AlGe nanotube synthesis were recently discovered. AlGe imogolite nanotubes can be synthesized at much higher concentrations than AlSi imogolite. AlGe imogolite exists in the form of both single-walled (SW) and double-walled (DW) nanotubes, whereas DW AlSi imogolites have never been observed. In this article, we give details on the physicochemical control over the SW or DW AlGe imogolite structure. For some conditions, an almost 100% yield of SW or DW nanotubes is demonstrated. We propose a model for the formation of SW or DW AlGe imogolite, which also explains why DW AlSi imogolites or higher wall numbers for AlGe imogolite are not likely to be formed. ■ INTRODUCTION Achieving perfect control over the morphology of nanoparticles is the everyday job of many researchers around the world. This goal is essentially motivated by the fact that the different morphologies strongly influence the properties of the final products such as for carbon nanotubes or quantum dots. Among the vast family of available nanoparticles, imogolite is a clay nanotube for which perfect control of the diameter is possible. Imogolites were first observed in volcanic soils. 1 They are natural aluminosilicate nanotubes having the general formula (OH) 3 Al 2 O 3 SiOH with a 2 nm external diameter and up to micrometers in length. The local structure of imogolite has been proposed by Cradwick et al. in 1972, 2 and since then it has been widely characterized using multiscale approaches like X-ray diffraction (XRD), 3 solid-state nuclear magnetic resonance (NMR), 4,5 infrared spectroscopy (IR), 6 and trans- mission electron microscopy (TEM). 2,3,7 The local structure proposed by Cradwick et al. consists of a Gibbsite sheet curved by the adsorption of orthosilicate tetrahedra into the vacancies of the aluminum dioctaedral layer. Control of the imogolite diameter has been achieved by replacing silicon with germanium atoms. 8 The difference in nanotube diameter is explained by the local structure of the imogolite. Indeed, the adsorption of the SiO 4 or GeO 4 tetrahedra is responsible for the curvature of the Gibbsite layer, the Si−O and Ge−O bonds of the tetrahedra being stretched when covalently linked by three Si−O−Al or Ge−O−Al bonds in the dioctahedral layer. This size mismatch is responsible for the creation of a spontaneous curvature of the Gibbsite layer. 9 This has been confirmed recently by Konduri et al. both for AlSi imogolite and for AlGe imogolite using molecular modeling. 10,11 Their Received: October 17, 2011 Published: January 31, 2012 Article pubs.acs.org/JACS © 2012 American Chemical Society 3780 dx.doi.org/10.1021/ja209756j | J. Am. Chem. Soc. 2012, 134, 3780−3786