Structure et croissance de nanotubes de Ge-imogolite simple et double-paroi

Imogolites are natural materials discovered during the sixties in japanese volcanic soils. Their structure is analogue to carbone nanotubes. Imogolite synthesis, described since 1977, gives nanotubes whose dimensions are well defined and monodisperse. Recently, it has been shown that it is possible to synthesize analogues containing germanium in concentration conditions that are much higher than classical silicium imogolites. That's why we have chosen this material to study the preparation of mesoporous materials from the assembly of anisotropic nanoparticles. Thanks to a SAXS and TEM characterization of these nanotubes, we have demonstrated that these analogues can present two types of tubular structures: a classical single-walled nanotube structure but also a double-walled one that had never been observed before. Moreover, the high concentration used in this synthesis has allowed us to precise the structure of the synthesis precursors called protoimogolites. We have indentified the parameter that control the type of the structure formed and then we have studied the growth mechanism of these nanotubes. Finally, the first temptatives about nanotubes organization when they are in high concentration have shown self assembly processes that are encouraging for further developments of applications.Les Imogolites (OH)3Al2O3Si(OH) sont des minéraux naturels découverts en 1962 dans des sols volcaniques japonais qui présentent une structure analogue à celle des nanotubes de carbone. Leur synthèse, décrite depuis 1977, permet l'obtention de tubes bien calibrés et monodisperses. La récente mise en évidence de la possibilité de synthétiser des analogues au germanium en grande quantité en a fait un matériau de choix dans le cadre de mon sujet de thèse visant à préparer des matériaux mésoporeux à base de nanoparticules anisotropes. Lors de la caractérisation de ces imogolites par diffusion de rayons X aux petits angles (SAXS) et microscopie électronique en transmission (MET) et à force atomique (AFM), nous avons montré que ces analogues d'Imogolite sont bien des nanotubes, mais qu'ils existent sous deux formes : des tubes à paroi unique mais également des tubes à paroi double jamais observés à ce jour. La concentration importante utilisée pour cette synthèse a également permis de mieux définir l'espèce précurseur de ces nanotubes appelée proto-imogolite et mal connue jusqu'ici. Après une identification du paramètre déterminant la formation de l'une ou l'autre des structures, nous avons étudié en détail le mécanisme et la cinétique de croissance de ces imogolites. Enfin, des premiers tests sur l'organisation de ces nanotubes en forte concentration ou au sein de microgouttes permettent d'observer leur tendance à s'organiser, propriété prometteuse pour le développement futur d'applications

Structure et croissance de nanotubes de Ge-imogolite simple et double-paroi

Les Imogolites (OH)3Al2O3Si(OH) sont des minéraux naturels découvert en 1962 dans des sols volcaniques japonais qui présentent une structure analogue à celle des nanotubes de carbone. Leur synthèse, décrite depuis 1977, permet l obtention de tubes bien calibrés et monodisperses. La récente mise en évidence de la possibilité de synthétiser des analogues au germanium en grande quantité en ont fait un matériau de choix dans le cadre de mon sujet de thèse visant à préparer des matériaux mésoporeux à base de nanoparticules anisotropes. Lors de la caractérisation détaillée de ces imogolites par SAXS et microscopie TEM/AFM, nous avons montré que ces analogues d'Imogolite sont bien des nanotubes, mais qu'ils existent sous deux formes : des tubes à paroi unique mais également des tubes à paroi double jamais observés à ce jour. La concentration importante utilisée pour cette synthèse a également permis de mieux définir l'espèce précurseur de ces nanotubes appelée proto-imogolite et mal connue jusqu ici. Après une identification précise du paramètre déterminant la formation de l une ou l autre des structures, nous avons étudié en détail le mécanisme et la cinétique de croissance de ces imogolites. Enfin, des premiers tests sur l organisation de ces nanotubes en forte concentration ou au sein de microgouttes permettent d observer leur tendance à s organiser, propriété prometteuse pour le développement futur d applicationsPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Physico-chemical Control over the Single- or Double-Wall Structure of Aluminogermanate Imogolite-like Nanotubes

International audienceIt 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

Growth kinetic of single and double-walled aluminogermanate imogolite-like nanotubes: an experimental and modeling approach

International audienceAtomic Force Microscopy (AFM) and in situ Small Angle X-ray Scattering (SAXS) were used to investigate the evolution of the aluminogermanate imogolite-like nanotubes concentration and morphology during their synthesis. In particular, in situ SAXS allowed quantifying the transformation of protoimogolite into nanotubes. The size distribution of the final nanotubes was also assessed after growth by AFM. A particular attention was focused on the determination of the single and double walled nanotube length distributions. We observed that the two nanotube types do not grow with the same kinetic and that their final length distribution was different. A model of protoimogolites oriented aggregation was constructed to account for the experimental growth kinetic and the length distribution differences

Synthesis of Ge-imogolite: influence of the hydrolysis ratio on the structure of the nanotubes

International audienceThe synthesis protocol for Ge-imogolite (aluminogermanate nanotubes) consists of 3 main steps: base hydrolysis of a solution of aluminum and germanium monomers, stabilization of the suspension and heating at 95 degrees C. The successful synthesis of these nanotubes was found to be sensitive to the hydrolysis step. The impact of the hydrolysis ratio (from n(OH)/n(Al) = 0.5 to 3) on the final product structure was examined using a combination of characterization tools. Thus, key hydrolysis ratios were identified: n(OH)/n(Al) = 1.5 for the formation of nanotubes with structural defects, n(OH)/n(Al) = 2 for the synthesis of a well crystallized Ge imogolite and n(OH)/n(Al) > 2.5 where nanotube formation is hindered. The capability of controlling the degree of the nanotube's crystallinity opens up interesting opportunities in regard to new potential applications

Evidence of Double-Walled Al-Ge Imogolite-Like Nanotubes. A Cryo-TEM and SAXS Investigation

International audienceSince the discovery of carbon nanotubes (NTs), there has been great interest in the synthesis and characterization of similar shaped structures like inorganic nanotubes, nanorods, or nanowires.1 However, limitations such as purity, complexity of the protocol, low-yield production, and size polydispersity still remain major impediments for industrial-scale applications. In this context, synthetic imogolites appear as an exception. Imogolites are singlewalled aluminosilicate NTs of 2 nm diameter and up to 1 μm in length with the empirical formula (OH)3Al2O3SiOH2 whose structure has been determined using X-ray Diffraction (XRD),2 solid state Nuclear Magnetic Resonance (NMR), and Transmission Electron Microscopy (TEM).3 Imogolite analogues with the generic formula (OH)3X2O3YOH (where X ) Al, Ga, or In and Y ) C, Si, Ge, or Sn) have been considered, mainly from a theoretical point of view,4 to tailor these NTs to specific needs. However, to date, only Ge imogolite analogues5 have been successfully synthesized. Although early reports of their synthesis involved diluted (i.e., millimolar) conditions, these imogolite analogues were recently obtained from 100 times more concentrated solutions,6 thereby opening the route for large scale applications. These analogues have been described to be structurally identical to the Al-Si imogolite, except for a larger tube diameter (∼3.3 nm) and shorter length (less than 100 nm). In the present study, the structure of two sets of samples obtained following the synthesis protocol described by Levard et al.6 with initial Al concentrations of 0.25 and 0.5 M is obtained using different probes. Infrared spectroscopy (see Supporting Information (SI)) confirms that the local structure of the formed Al-Ge NTs is compatible with the one of imogolite. Their mesostructure has been examined by cryo-TEM and Small Angle X-ray Scattering (SAXS). We demonstrate here that Al-Ge imogolite-like NTs synthesized at 0.25 M are double-walled NTs with a low dispersion in diameter. SAXS data also suggest that the double-walled NTs consist of two concentric tubes of equal length and identical wall structure. At higher concentration (0.5 M), both SAXS and cryo-TEM data confirm the formation of single-walled NTs