Photonic titanium dioxide film obtained from hard template with chiral nematic structure for environmental application

International audienceIn the present work, mesoporous TiO 2 with a photonic structure was elaborated using cellulose nanocrystals (CNCs) as a biotemplate by two-step hard template methods. This strategy enables to replicate the chiral nematic (CN) structure of the photonic films (biotemplate) in TiO 2 films. A series of iridescent CNCs films with different weight ratios of silica/CNCs composite photonic films were prepared via evaporation induced self-assembly (EISA) method. The films showed iridescent color and tuneable Bragg reflection wavelengths by solely changing the ratio between the silica and the CNCs biotemplate. Polarized optical microscopy (POM) performed on hydride SiO 2 /CNCs films showed a birefringence and typical fingerprint of chiral nematic structure. This birefringence was also observed for TiO 2 films obtained using SiO 2 films as a hard template, which suggested the transfer of the chiral nematic structure in TiO 2 materials. Afterwards, their optical, morphological and electronic properties were studied by scanning electron microscope (SEM), POM, energy-dispersive X-ray spectroscope (EDX) and time resolved microwave conductivity (TRMC). The photocatalytic activities were evaluated by following the phenol degradation using high performance liquid chromatography (HPLC). The results showed that the structuration of the TiO 2 film using a chiral nematic SiO 2 film as hard template enhances the photocatalytic performance compared to non-structured mesoporous TiO 2

A liquid-crystalline hexagonal columnar phase in highly-dilute suspensions of imogolite nanotubes

International audienceLiquid crystals have found wide applications in many fields ranging from detergents to information displays and they are also increasingly being used in the 'bottom-up' self-assembly approach of material nano-structuration. Moreover, liquid-crystalline organizations are frequently observed by biologists. Here we show that one of the four major lyotropic liquid-crystal phases, the columnar one, is much more stable on dilution than reported so far in literature. Indeed, aqueous suspensions of imogolite nanotubes, at low ionic strength, display the columnar liquid-crystal phase at volume fractions as low as B0.2%. Consequently, due to its low visco-elasticity, this columnar phase is easily aligned in an alternating current electric field, in contrast with usual columnar liquid-crystal phases. These findings should have important implications for the statistical physics of the suspensions of charged rods and could also be exploited in materials science to prepare ordered nanocomposites and in biophysics to better understand solutions of rod-like biopolymers

A compact photoreactor for automated H2 photoproduction: Revisiting the (Pd, Pt, Au)/TiO2 (P25) Schottky junctions

The configuration and geometry of chemical reactors underpins the accuracy of performance evaluation for photocatalytic materials and, accordingly, the development and validation of thermodynamic and kinetic model reactions. The lack of accurate photonic, mass, and heat transport profiles for photochemical reactors hinder standardization, scale-up, and ultimately comparison between different experiments. This work proposes two contributions at the interface between engineering of chemical process and materials science: (A) an automated compact stainless-steel photoreactor with 40 cm3 and 65 cm2 of volume and area, respectively, for hydrogen photoproduction as a model reaction and (B) the synthesis, characterization, and performance of TiO2 Schottky junctions, using Pd, Pt, or Au nanoparticles (ca. 0.5, 1, 2 wt% loadings each) to validate the operation of the reactor. A photonic profile methodology is implemented to the studied reactor to obtain the local light absorption profile, opening up for evaluation of the local quantum yield calculation for the selected materials. A combination of transmission electron microscopy, (X-ray/ultraviolet) photoelectron/electron, energy loss/infrared spectroscopies, X-ray scattering, inductively coupled plasma atomic emission spectroscopy, and ultraviolet–visible spectrophotometry is employed to determine the distinctive surface and bulk properties to build structure–function correlations. The (Pd, Pt, Au)/TiO2 Schottky junction exhibits H2 production rates slightly higher than previous studies, with quantum yields almost 2-fold higher than reported values. These results, demonstrate that the proposed novel geometry of the photoreactor improves the photonic, heat, and mass profiles. An in-depth analysis of the Au plasmon was investigated coupling electron energy loss spectroscopy, UV–vis, and transmission electron microscope, resulting in insightful information about the Au NP mode at the TiO2 interface

Structural resolution of inorganic nanotubes with complex stoichiometry.

Determination of the atomic structure of inorganic single-walled nanotubes with complex stoichiometry remains elusive due to the too many atomic coordinates to be fitted with respect to X-ray diffractograms inherently exhibiting rather broad features. Here we introduce a methodology to reduce the number of fitted variables and enable resolution of the atomic structure for inorganic nanotubes with complex stoichiometry. We apply it to recently synthesized methylated aluminosilicate and aluminogermanate imogolite nanotubes of nominal composition (OH)3Al2O3Si(Ge)CH3. Fitting of X-ray scattering diagrams, supported by Density Functional Theory simulations, reveals an unexpected rolling mode for these systems. The transferability of the approach opens up for improved understanding of structure-property relationships of inorganic nanotubes to the benefit of fundamental and applicative research in these systems

Imogolite Nanotubes: A Flexible Nanoplatform with Multipurpose Applications

Among a wide variety of inorganic nanotubes, imogolite nanotubes (INTs) represent a model of nanoplatforms with an untapped potential for advanced technological applications. Easily synthesized by sol-gel methods, these nanotubes are directly obtained with a monodisperse pore size. Coupled with the possibility to adjust their surface properties by using straightforward functionalization processes, INTs form a unique class of diameter-controlled nanotubes with functional interfaces. The purpose of this review is to provide the reader with an overview of the synthesis and functionalization of INTs. The properties of INTs will be stated afterwards into perspective with the recent development on their applications, in particular for polymer/INTs nanocomposites, molecular confinement or catalysis

Phases transitions in clay minerals : impact of mineralogy and morphology : behaviour under flow and external fields

L’objectif de ce travail est d’étudier les transitions de phases sol-gel et isotrope-nématique dans des suspensions de smectites dioctaédriques en fonction de la morphologie et de la nature minéralogique des argiles. Bien que tous les systèmes étudiés présentent une transition sol-gel à de faibles fraction volumique, la transition cristal-liquide isotrope-nématique n’a pu être identifiée que dans le cas de suspensions de smectites ayant un déficit de charge tétraédrique. L’effet de la localisation de la charge sur le comportement colloïdal a été déterminée à l’aide de la diffusion des rayons X aux petits angles (SAXS) et par des mesures rhéologiques. La nature des interactions électrostatiques dans ces suspensions est purement répulsive et rejette l’idée d’une structure tridimensionnelle de type « château de carte ». Cependant, les smectites ayant un déficit de charge tétraédrique sont plus répulsives et ont des propriétés viscoélastiques plus faibles que celles ayant un déficit octaédrique. Il a également été montré que la dépendance en taille de particules de la position de la transition sol-gel était liée à une statistique de piégeage hydrodynamique des plaquettes d’argile. Finalement, l’application de champs externes (électrique et magnétique) a permis d’obtenir l’alignement de la phase nématique tandis que dans la phase isotrope, le champ électrique induit un ordre antinématique parfait. Afin de préserver l’ordre induit, ces suspensions ont été polymérisées sous champ permettant l’obtention de nanocomposites orientées et structurésThe aim of this work is to study sol-gel and isotropic-nematic phases transitions in suspensions of dioctahedral smectites depending on the morphology and mineralogical nature of clays. Although all the systems studied exhibit a sol-gel at low volume fraction, the liquid-crystalline isotropic-nematic transition could be identified only in the case of smectites with tetrahedral charge deficit. The effect of charge location on the colloidal behavior was determined using small-angle X-ray scattering (SAXS) and rheological measurements. The nature of electrostatic interactions in these suspensions is purely repulsive and rejects the idea of the so-called “house of card” network. However, smectites with a charge deficit located in the tetrahedron are more repulsive and their viscoelastic properties are lower than octahedrally substituted clays. It was also shown that the particle size dependence of the volume fraction corresponding to the sol-gel transition c was related to a simple statistical hydrodynamic trapping of clay platelets. Finally, the application of external fields (electric and magnetic) has resulted in the alignment of the nematic phase while in the isotropic phase, the electric field induces a perfect antinematic order. To preserve the induced alignment, these suspensions were polymerized under the field to obtain perfectly aligned and patterned nanocomposite

Transitions de phases dans les argiles : influence de la minéralogie et de la morphologie : comportement sous écoulement et sous champs

The aim of this work is to study sol-gel and isotropic-nematic phases transitions in suspensions of dioctahedral smectites depending on the morphology and mineralogical nature of clays. Although all the systems studied exhibit a sol-gel at low volume fraction, the liquid-crystalline isotropic-nematic transition could be identified only in the case of smectites with tetrahedral charge deficit. The effect of charge location on the colloidal behavior was determined using small-angle X-ray scattering (SAXS) and rheological measurements. The nature of electrostatic interactions in these suspensions is purely repulsive and rejects the idea of the so-called house of card network. However, smectites with a charge deficit located in the tetrahedron are more repulsive and their viscoelastic properties are lower than octahedrally substituted clays. It was also shown that the particle size dependence of the volume fraction corresponding to the sol-gel transition c was related to a simple statistical hydrodynamic trapping of clay platelets. Finally, the application of external fields (electric and magnetic) has resulted in the alignment of the nematic phase while in the isotropic phase, the electric field induces a perfect antinematic order. To preserve the induced alignment, these suspensions were polymerized under the field to obtain perfectly aligned and patterned nanocompositesL'objectif de ce travail est d'étudier les transitions de phases sol-gel et isotrope-nématique dans des suspensions de smectites dioctaédriques en fonction de la morphologie et de la nature minéralogique des argiles. Bien que tous les systèmes étudiés présentent une transition sol-gel à de faibles fraction volumique, la transition cristal-liquide isotrope-nématique n'a pu être identifiée que dans le cas de suspensions de smectites ayant un déficit de charge tétraédrique. L'effet de la localisation de la charge sur le comportement colloïdal a été déterminée à l'aide de la diffusion des rayons X aux petits angles (SAXS) et par des mesures rhéologiques. La nature des interactions électrostatiques dans ces suspensions est purement répulsive et rejette l'idée d'une structure tridimensionnelle de type « château de carte ». Cependant, les smectites ayant un déficit de charge tétraédrique sont plus répulsives et ont des propriétés viscoélastiques plus faibles que celles ayant un déficit octaédrique. Il a également été montré que la dépendance en taille de particules de la position de la transition sol-gel était liée à une statistique de piégeage hydrodynamique des plaquettes d'argile. Finalement, l'application de champs externes (électrique et magnétique) a permis d'obtenir l'alignement de la phase nématique tandis que dans la phase isotrope, le champ électrique induit un ordre antinématique parfait. Afin de préserver l'ordre induit, ces suspensions ont été polymérisées sous champ permettant l'obtention de nanocomposites orientées et structuré

Influence of the Al/Ge Ratio on the Structure and Self-Organization of Anisometric Imogolite Nanotubes

Synthetic imogolite-like nanotubes (INT) with well-defined diameters represent a considerable opportunity for the development of advanced functional materials. Recent progress has made it possible to increase their aspect ratio and unique self-organization properties were evidenced. We suggest that slight modification of the synthesis conditions may drastically affect the resulting liquid-crystalline properties. In this work, we investigate how the precursor’s [Al]/[Ge] molar ratio (R’) impacts the morphology and the colloidal properties of aluminogermanate INTs by combining a multi-scale characterization. While only double-walled nanotubes are found for R’ ≥ 1.8, the presence of single-walled nanotubes occurs when the ratio is lowered. Except for the lowest R’ ratio investigated (R’ = 0.66), all synthetic products present one-dimensional shapes with a high aspect ratio. Small-angle X-ray scattering experiments allow us to comprehensively investigate the colloidal properties of the final products. Our results reveal that a liquid-crystalline hexagonal columnar phase is detected down to R’ = 1.33 and that it turns into a nematic arrested phase for R’ = 0.90. These results could be useful for the development of novel stimuli-responsive nanocomposites based-on synthetic imogolite nanotubes

Transitions de phases dans les argiles (influence de la minéralogie et de la morphologie)

L objectif de ce travail est d étudier les transitions de phases sol-gel et isotrope-nématique dans des suspensions de smectites dioctaédriques en fonction de la morphologie et de la nature minéralogique des argiles. Bien que tous les systèmes étudiés présentent une transition sol-gel à de faibles fraction volumique, la transition cristal-liquide isotrope-nématique n a pu être identifiée que dans le cas de suspensions de smectites ayant un déficit de charge tétraédrique. L effet de la localisation de la charge sur le comportement colloïdal a été déterminée à l aide de la diffusion des rayons X aux petits angles (SAXS) et par des mesures rhéologiques. La nature des interactions électrostatiques dans ces suspensions est purement répulsive et rejette l idée d une structure tridimensionnelle de type château de carte . Cependant, les smectites ayant un déficit de charge tétraédrique sont plus répulsives et ont des propriétés viscoélastiques plus faibles que celles ayant un déficit octaédrique. Il a également été montré que la dépendance en taille de particules de la position de la transition sol-gel était liée à une statistique de piégeage hydrodynamique des plaquettes d argile. Finalement, l application de champs externes (électrique et magnétique) a permis d obtenir l alignement de la phase nématique tandis que dans la phase isotrope, le champ électrique induit un ordre antinématique parfait. Afin de préserver l ordre induit, ces suspensions ont été polymérisées sous champ permettant l obtention de nanocomposites orientées et structurésThe aim of this work is to study sol-gel and isotropic-nematic phases transitions in suspensions of dioctahedral smectites depending on the morphology and mineralogical nature of clays. Although all the systems studied exhibit a sol-gel at low volume fraction, the liquid-crystalline isotropic-nematic transition could be identified only in the case of smectites with tetrahedral charge deficit. The effect of charge location on the colloidal behavior was determined using small-angle X-ray scattering (SAXS) and rheological measurements. The nature of electrostatic interactions in these suspensions is purely repulsive and rejects the idea of the so-called house of card network. However, smectites with a charge deficit located in the tetrahedron are more repulsive and their viscoelastic properties are lower than octahedrally substituted clays. It was also shown that the particle size dependence of the volume fraction corresponding to the sol-gel transition c was related to a simple statistical hydrodynamic trapping of clay platelets. Finally, the application of external fields (electric and magnetic) has resulted in the alignment of the nematic phase while in the isotropic phase, the electric field induces a perfect antinematic order. To preserve the induced alignment, these suspensions were polymerized under the field to obtain perfectly aligned and patterned nanocompositesNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Imogolite Nanotubes and Their Permanently Polarized Bifunctional Surfaces for Photocatalytic Hydrogen Production

Abstract To date, imogolite nanotubes (INTs) have been primarily used for environmental applications such as dye and pollutant degradation. However, imogolite's well‐defined porous structure and distinctive electro‐optical properties have prompted interest in the system's potential for energy‐relevant chemical reactions. The imogolite structure leads to a permanent intrawall polarization arising from the presence of bifunctional surfaces at the inner and outer tube walls. Density functional theory simulations suggest such bifunctionality to encompass also spatially separated band edges. Altogether, these elements make INTs appealing candidates for facilitating chemical conversion reactions. Despite their potential, the exploitation of imogolite's features for photocatalysis is at its infancy, thence relatively unexplored. This perspective overviews the basic physical‐chemical and optoelectronical properties of imogolite nanotubes, emphasizing their role as wide bandgap insulator. Imogolite nanotubes have multifaceted properties that could lead to beneficial outcomes in energy‐related applications. This work illustrates two case studies demonstrating a step‐forward on photocatalytic hydrogen production achieved through atomic doping or metal co‐catalyst. INTs exhibit potential in energy conversion and storage, due to their ability to accommodate functions such as enhancing charge separation and influencing the chemical potentials of interacting species. Yet, tapping into potential for energy‐relevant application needs further experimental research, computational, and theoretical analysis