Clément Sanchez

Applications of hybrid organic–inorganic nanocomposites

Organic–inorganic hybrid materials do not represent only a creative alternative to design new materials and compounds for academic research, but their improved or unusual features allow the development of innovative industrial applications. Nowadays, most of the hybrid materials that have already entered the market are synthesised and processed by using conventional soft chemistry based routes developed in the eighties. These processes are based on: a) the copolymerisation of functional organosilanes, macromonomers, and metal alkoxides, b) the encapsulation of organic components within sol–gel derived silica or metallic oxides, c) the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures, etc. The chemical strategies (self-assembly, nanobuilding block approaches, hybrid MOF (Metal Organic Frameworks), integrative synthesis, coupled processes, bio-inspired strategies, etc.) offered nowadays by academic research allow, through an intelligent tuned coding, the development of a new vectorial chemistry, able to direct the assembling of a large variety of structurally well defined nano-objects into complex hybrid architectures hierarchically organised in terms of structure and functions. Looking to the future, there is no doubt that these new generations of hybrid materials, born from the very fruitful activities in this research field, will open a land of promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology, medicine for example as membranes and separation devices, functional smart coatings, fuel and solar cells, catalysts, sensors, etc.

Hybrid organic–inorganic materials: a land of multidisciplinarity

Organic-inorganic hybrids appear as a creative alternative for obtaining new materials with unusual features. This is related to their diphasic structures, leading to multifunctional materials. The low-temperature processes which are used to synthesize such structures provide a wide versatility in the design of the compounds. The potentiality of the chemistry is to play on the structure of these mixtures and dissociate the various contributions in tailoring both phases and controlling the interfaces. In this paper, a review of some chemistry pathways to hybrid materials is presented. The nature of the bonds between organic and inorganic phases is used to divide them in two major families: class I corresponds to materials with weak interphase bonding, while class II corresponds to materials where both phases are chemically grafted. Applications of these materials in the fields of optics, iono-electronics, mechanics, biology and others are expected. Some applications are reviewed, with respect to the versatility of the synthetic procedure. Most of the properties of these new high-technology materials are dependent on their structural and chemical composition as well as on the dynamical properties inside the blends.

Chemical modification of alkoxide precursors

Abstract The chemical reactivity of metal alkoxides offers a broad range of possibilities for chemical modification of these molecular precursors. The whole hydrolysis-condensation process may then be completely different leading to new products. An analysis is presented concerning some of the most common chemical additives used in the sol-gel process. Their role is explained in terms of chemical reactivity. The most important parameters appear to be the reactivity of the new ligand towards hydrolysis, the charge distribution in the new molecular precursor and the coordination numbers of the metal atom.

Hydrolysis of titanium alkoxides: modification of the molecular precursor by acetic acid

Monolithic TiO 2 gels can be reproducibly obtained when the hydrolysis of titanium alkoxides is performed in the presence of acetic acid. This carboxilic acid does not act only as an acid catalyst, but also as a ligand and changes the alkoxide precursor at a molecular level therefore modifying the whole hydrolysis condensation process. Infra-red experiments show that bidentate acetates replace OR groups and are directly bounded to the titanium. Both, chelating and bridging acetates, are observed, leading to Ti(OR) x (Ac) y . oligomers. Hydrolysis of this new molecular precursor removes first (OR) groups and bridging acetates. Chelating acetates are still observed in the gel. They can only be removed upon heating above 200 °C.

A New Photoactive Crystalline Highly Porous Titanium(IV) Dicarboxylate

Titanium is a very attractive candidate for MOFs due to its low toxicity, redox activity, and photocatalytic properties. We present here MIL-125, the first example of a highly porous and crystalline titanium(IV) dicarboxylate (MIL stands for Materials of Institut Lavoisier) with a high thermal stability and photochemical properties. Its structure is built up from a pseudo cubic arrangement of octameric wheels, built up from edge- or corner-sharing titanium octahedra, and terephthalate dianions leading to a three-dimensional periodic array of two types of hybrid cages with accessible pore diameters of 6.13 and 12.55 A. X-ray thermodiffractometry and thermal analysis show that MIL-125 is stable up to 360 degrees C under air atmosphere while nitrogen sorption analysis indicates a surface area (BET) of 1550 m(2) x g(-1). Moreover, under nitrogen and alcohol adsorption, MIL-125 exhibits a photochromic behavior associated with the formation of stable mixed valence titanium-oxo compounds. The titanium oxo cluster are back oxidized in the presence of oxygen. This photochemical phenomenon is analyzed through the combined use of Electron Spin Resonance (ESR) and UV-visible absorption spectroscopies. The photogenerated electrons are trapped as Ti(III) centers, while a concomitant oxidation of the adsorbed alcohol molecules occurs. This new microporous hybrid is a very promising candidate for applications in smart photonic devices, sensors, and catalysis.

Block copolymer-templated mesoporous oxides

Block copolymers (BC) are indeed suitable and versatile templates for the creation of mesostructured and mesoporous materials. Great advances have been achieved in the last 3 years. Nowadays, it is possible to obtain highly controlled large-pore and highly stable mesostructured and mesoporous materials (silica, non-silica oxides, carbons,…) shaped as powders, films, monoliths or aerosols. This paper reviews mainly the synthesis of BC-templated mesostructured oxides, stressing in the physical, chemical and processing parameters, which have to be thoroughly controlled to reproducibly obtain mesoporous materials.

Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives

and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Design and properties of functional hybrid organic–inorganic membranes for fuel cells

This critical review presents a discussion on the major advances in the field of organic-inorganic hybrid membranes for fuel cells application. The hybrid organic-inorganic approach, when the organic part is not conductive, reproduces to some extent the behavior of Nafion where discrete hydrophilic and hydrophilic domains are homogeneously distributed. A large variety of proton conducting or non conducting polymers can be combined with various functionalized, inorganic mesostructured particles or an inorganic network in order to achieve high proton conductivity, and good mechanical and chemical properties. The tuning of the interface between these two components and the control over chemical and processing conditions are the key parameters in fabricating these hybrid organic-inorganic membranes with a high degree of reproducibility. This dynamic coupling between chemistry and processing requires the extensive use and development of complementary ex situ measurements with in situ characterization techniques, following in real time the molecular precursor solutions to the formation of the final hybrid organic-inorganic membranes. These membranes combine the intrinsic physical and chemical properties of both the inorganic and organic components. The development of the sol-gel chemistry allows a fine tuning of the inorganic network, which exhibits acid-based functionalized pores (-SO(3)H, -PO(3)H(2), -COOH), tunable pore size and connectivity, high surface area and accessibility. As such, these hybrid membranes containing inorganic materials are a promising family for controlling conductivity, mechanical and chemical properties (349 references).

Mechanical properties of hybrid organic–inorganic materials

Homogeneously dispersed organic–inorganic hybrid nanocomposites can be obtained by increasing the interfacial interactions between both components via the formation of hydrogen bonds or covalent bonds, by mixing various polymers or via the adequate choice of the inorganic precursors. The mechanical response of these advanced functional materials is an issue of paramount importance when industrial applications are targeted. Large progress in the understanding of the mechanical properties of O–I hybrids has been gained by testing these materials under different conditions (static and dynamic, low and large deformations up to fracture) and using specific techniques developed for the mechanical characterization of conventional materials such as polymers, glasses or ceramics. However, the mechanical properties of hybrid O–I materials are dependent on their micro- and nanostructures and on the nature and extent of the O–I interfaces. Consequently, predictable mechanical properties for hybrids still represent a major challenge for hybrid materials science. Industrial attraction for hybrid materials has been emphasized by the development of new functional coatings. An important issue is the interface between the film and the substrate since strong adhesion can be tailored and ensures that delamination of the film will be limited.

Sol-gel chemistry

Sol-gel chemistry involves nucleophilic reactions. The chemical reactivity of metal alkoxides toward hydrolysis, condensation and complexation mainly depends on the electronegativity of the metal atom, its coordination number and the steric hindrance of alkoxide groups. Silicon alkoxides are poorly reactive. Hydrolysis and condensation rates have to be enhanced by acid and base catalysis or nucleophilic activation. Transition metal alkoxides are usually too reactive. They have to be stabilized by complexation in order to avoid fast condensation. The molecular design of alkoxide precursors opens the way to tailor-made materials.