Nanostructured Hybrid Silica by 'Liquid Crystal Templating' of ionic precursors

Une série de précurseurs contenant des sous-structures organo-ioniques à base d'entités imidazolium, guanidinium, ammonium et zwitterionique ainsi que des précurseurs neutres contenant des sous-structures amido-thiol, amine-thiol et amine a été synthétisée. Ces précurseurs ont été utilisés pour la synthèse de matériaux silices hybrides nanostructurés par voie template. La formation de matériaux nanostructurés a été réalisée par des réactions d'hydrolyse-polycondensation par l'utilisation de différents agents de structuration. Ce travail avait pour but la détermination des principaux facteurs influençant la structuration des matériaux. Ainsi, nous avons préparé une série d'ionosilicates nanostructurés par une nouvelle méthode de structuration qui met en jeu des interactions spécifiques entre des paires d'ions ‘précurseur cationique - surfactant anionique' et ‘précurseur anionique - surfactant cationique'. Cette approche a permis d'accéder aux matériaux originaux de type PMO ionique. Finalement, nous avons utilisé pour la première fois des surfactants de guanidinium comme ‘template' dans la synthèse des silices ioniques nanostructurées de morphologie sphérique. Les matériaux nanostructurés contenant des sous-structures amine, amine-thiol, ammonium et zwitterionique développés au cours de ce travail présentent des surfaces spécifiques élevées et une bonne accessibilité des sites organiques. Ces propriétés font de ces matériaux des systèmes de choix pour des applications en catalyse ou en séparation.A series of precursors containing organo-ionic substructures such as imidazolium, guanidinium, ammonium and zwitterionic entities and several neutral precursors containing thiol-amide, thiol-amine and amino groups were successfully synthesized. These precursors were used for the synthesis of nanostructured silica hybrid materials containing ionic substructures via soft templating approaches. The formation of structured materials was achieved using template directed hydrolysis polycondensation procedures in the presence of various structure directing agents. The goal of this study was the determination of the parameters influencing the structuring of the materials. Thus, we prepared a series of nanostructured ionosilicates using a new method of structuring that is based on specific interactions between ‘cationic precursor - anionic surfactant' and ‘anionic precursor - cationic surfactant' ion pairs. This new strategy allowed the synthesis of ionic 'periodic mesoporous organosilicas'. At the end of this thesis, we used a new ‘guanidinium' type template in the preparation of nanostructured i-silica hybrid materials with a spherical morphology. Nanostructured ionosilicates bearing amine, amino-thiol, ammonium and zwitterionic substructures prepared in this work present high specific surface areas and a high accessibility of the organic functional sites. Due to these features, these materials have large potential in the fields of catalysis and separation

Guanidinium vs. ammonium surfactants in soft-templating approaches: Nanostructured silica and zwitterionic i-silica from complementary precursor-surfactant ion-pairs

International audienceWe investigated the behaviour of guanidinium and ammonium surfactants as structure directing agents in template directed hydrolysis-polycondensation processes. For this purpose, a series of guanidinium surfactants was synthesized from long chain substituted primary amines. In a first series of experiments, we compared nanostructured silicas obtained via template directed hydrolysis-polycondensation reactions of TEOS in the presence of either guanidinium or ammonium based surfactants. We observed that typical MCM-41-type silicas displaying 2D hexagonal architecture were obtained in the presence of ammonium surfactants such as cetyl-trimethylammonium bromide (CTAB). In contrast, the use of guanidinium surfactants led to the formation of hollow silica spheres or spherical silica nanoparticles. In a second time, we investigated the use of ammonium and guanidinium surfactants in the formation of periodic mesoporous organosilicas containing ionic groups (i-silica). We studied in particular template directed hydrolysis-polycondensation reactions of zwitterionic ammonium sulfonate and ammonium carboxylate precursors. We observed that both reactions involving the ammonium-sulfonate precursor yielded structured i-silicas. In contrast, hydrolysis-polycondensation reactions of the ammonium carboxylate precursor afforded structured materials only in the presence of the guanidinium surfactant, whereas amorphous materials were obtained in the presence of CTAB. This result reflects specific surfactant-precursor interactions and suggests that the nature of both surfactant and precursor are determinant for the formation of i-silica materials displaying regular architectures on a mesoscopic length scale

Anionic templating as a versatile method to access nanostructured ionosilicas from amine and ammonium precursors

International audienceThe synthesis of new functional ionosilicas via soft templating procedures is reported. Starting from functional amine and ammonium precursors, structured materials with regular architectures on a mesoscopic length scale can be obtained only in the presence of anionic structure directing agents. This 'anionic templating route' appears as a generally applicable method to access a large variety of structured ionosilicas containing cationic groups. However, differences concerning the texture and the morphological stability of the formed materials arise from the constitution of the used silylated precursors. The as-synthesized silica hybrid/surfactant nanocomposites obtained from amine precursors often display high order but only limited morphological stability. The ordered mesostructure of the nanocomposites collapsed during surfactant elimination and low-porous and non-structured ionosilica materials were finally obtained. In contrast, the use of trisilylated quaternary ammonium precursors yielded materials displaying high porosity combined with moderate structural regularity after surfactant elimination. Finally, the formation of ionosilicas with helicoïdal morphologies was observed starting from a chiral (1R,2R)-diaminocyclohexane-precursor. All these results show that the 'anionic templating route' is a versatile strategy allowing accessing structured materials which are not accessible following classical synthetic strategies, i.e. in the presence of cationic or non-ionic structure directing agents

Silices hybrides nanostructurées par 'Liquid Crystal Templating' de précurseurs ioniques

Une série de précurseurs contenant des sous-structures organo-ioniques à base d'entités imidazolium, guanidinium, ammonium et zwitterionique ainsi que des précurseurs neutres contenant des sous-structures amido-thiol, amine-thiol et amine a été synthétisée. Ces précurseurs ont été utilisés pour la synthèse de matériaux silices hybrides nanostructurés par voie template. La formation de matériaux nanostructurés a été réalisée par des réactions d'hydrolyse-polycondensation par l'utilisation de différents agents de structuration. Ce travail avait pour but la détermination des principaux facteurs influençant la structuration des matériaux. Ainsi, nous avons préparé une série d'ionosilicates nanostructurés par une nouvelle méthode de structuration qui met en jeu des interactions spécifiques entre des paires d'ions précurseur cationique - surfactant anionique' et précurseur anionique - surfactant cationique'. Cette approche a permis d'accéder aux matériaux originaux de type PMO ionique. Finalement, nous avons utilisé pour la première fois des surfactants de guanidinium comme template' dans la synthèse des silices ioniques nanostructurées de morphologie sphérique. Les matériaux nanostructurés contenant des sous-structures amine, amine-thiol, ammonium et zwitterionique développés au cours de ce travail présentent des surfaces spécifiques élevées et une bonne accessibilité des sites organiques. Ces propriétés font de ces matériaux des systèmes de choix pour des applications en catalyse ou en séparation.A series of precursors containing organo-ionic substructures such as imidazolium, guanidinium, ammonium and zwitterionic entities and several neutral precursors containing thiol-amide, thiol-amine and amino groups were successfully synthesized. These precursors were used for the synthesis of nanostructured silica hybrid materials containing ionic substructures via soft templating approaches. The formation of structured materials was achieved using template directed hydrolysis polycondensation procedures in the presence of various structure directing agents. The goal of this study was the determination of the parameters influencing the structuring of the materials. Thus, we prepared a series of nanostructured ionosilicates using a new method of structuring that is based on specific interactions between cationic precursor - anionic surfactant' and anionic precursor - cationic surfactant' ion pairs. This new strategy allowed the synthesis of ionic 'periodic mesoporous organosilicas'. At the end of this thesis, we used a new guanidinium' type template in the preparation of nanostructured i-silica hybrid materials with a spherical morphology. Nanostructured ionosilicates bearing amine, amino-thiol, ammonium and zwitterionic substructures prepared in this work present high specific surface areas and a high accessibility of the organic functional sites. Due to these features, these materials have large potential in the fields of catalysis and separation.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Surfactant-assisted ZnO processing as a versatile route to ZIF composites and hollow architectures with enhanced dye adsorption

Metal oxides can be used as hard sacrificial templates for the preparation of multifunctional core–shell MOF-based composites following reaction with an organic linker. This is a facile method, but often structures of well-defined shape are only obtained under narrow ranges of conditions, the shape can be lost completely and low levels of MOF conversion observed. Using the prototypical framework ZIF-8 we present an alternative surfactant-assisted surface passivation strategy where the ZnO precursor particles are first coated with a guanidinium-based amphiphile. The surfactant interacts strongly with the oxide surface and allows fine-tuning of the release of Zn(II) and ZIF-8 nucleation by the level of surface coverage permitting a range of well-defined ZnO@ZIF-8 core–shell architectures to be prepared including in water. Further, selective base-etching of the oxide core provides facile access to hollow ZIF-8 and yolk–shell structures. We also demonstrate enhanced dye adsorption and recovery from aqueous mixtures using ZnO@ZIF-8 composite microspher

Supramolecular templating of hierarchically porous metal–organic frameworks

This tutorial review summarises recent advances in the direct supramolecular templating of metal–organic frameworks (MOFs) with hierarchical porosity across the micro- and mesoporous regimes. These are set against the important synthetic considerations that need to be addressed to ensure that strong interactions between the MOF precursors and a stable template assembly allow the highest chance of success. The article is grouped by template type and each category is illustrated with key examples and, where reported, an evaluation of their enhanced properties arising from the hierarchical structuring of the porous networks

Magnetic MOF microreactors for recyclable size-selective biocatalysis

In this contribution we report a synthetic strategy for the encapsulation of functional biomolecules within MOF-based microcapsules. We employ an agarose hydrogel droplet Pickering-stabilised by UiO-66 and magnetite nanoparticles as a template around which to deposit a hierarchically structured ZIF-8 shell. The resulting microcapsules are robust, highly microporous and readily attracted to a magnet, where the hydrogel core provides a facile means to encapsulate enzymes for recyclable size-selective biocatalysi

Surface etching of HKUST-1 promoted via supramolecular interactions for chromatography

The addition of guanidinium-based surfactants to the synthesis of HKUST-1 reveals a novel surface patterning effect where meso- and macroscopic features appear on the MOF crystals. The size of the features increases with increasing alkyl chain length of the guanidinium amphiphiles, and their formation is strongly dependent on the presence of water which appears to more favourably etch the crystal surfaces when the surfactants are employed. The patterned crystals display intermediate type I/IV isotherms and the presence of the surface features have been evaluated for the chromatographic separation of styrene and ethylbenzene. Some degree of control over the interactions between the framework building blocks and the amphiphiles is afforded, and by simply changing the order of addition of the reactants the guanidinium surfactants promote the formation of HKUST-1 nanoparticles

Facile synthesis of magnetic macroporous polymer/MOF composites as separable catalysts

Design and synthesis of magnetic macroporous metal�organic frameworks (MOFs) have been of significant interest, in order to improve the catalytic efficiency and reusability. In this work, we prepared magnetic macroporous MOF composites based on as-prepared magnetic macroporous polyacrylamides (MMPam). Different MOFs with or without unsaturated coordinative metal sites, including HKUST-1, MOF-2, UiO-66, and Fe-MIL-101(-NH2) were grown on and within the MMPam matrices. The composites showed hierarchical porosity with both micro- and macropores, which facilitated substrate diffusion to increase the conversion for isomerization of α-pinene oxide from 62% in the case of pure HKUST-1 microparticles to 90% in the case of HKUST-1@MMPam. The magnetic property also endowed the composites with easy recovery and reasonable reusability.</p

Periodic mesoporous organosilica from zwitterionic precursors

International audienceMesoporous hybrid silica bearing zwitterionic species were synthesized via template directed hydrolysis-polycondensation reactions from zwitterionic ammonium-sulfonate precursors. The formation of nanostructured phases involves specific precursor-template interactions. The obtained materials are efficient heterogeneous catalysts in Biginelli reactions