Laurence Rozes

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.

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.

Engineering the Optical Response of the Titanium-MIL-125 Metal− Organic Framework through Ligand Functionalization

Herein we discuss band gap modification of MIL-125, a TiO2/1,4-benzenedicarboxylate (bdc) metal-organic framework (MOF). Through a combination of synthesis and computation, we elucidated the electronic structure of MIL-125 with aminated linkers. The band gap decrease observed when the monoaminated bdc-NH2 linker was used arises from donation of the N 2p electrons to the aromatic linking unit, resulting in a red-shifted band above the valence-band edge of MIL-125. We further explored in silico MIL-125 with the diaminated linker bdc-(NH2)2 and other functional groups (-OH, -CH3, -Cl) as alternative substitutions to control the optical response. The bdc-(NH2)2 linking unit was predicted to lower the band gap of MIL-125 to 1.28 eV, and this was confirmed through the targeted synthesis of the bdc-(NH2)2-based MIL-125. This study illustrates the possibility of tuning the optical response of MOFs through rational functionalization of the linking unit, and the strength of combined synthetic/computational approaches for targeting functionalized hybrid materials.

New photoactive hybrid organic–inorganic materials based on titanium-oxo-PHEMA nanocomposites exhibiting mixed valence properties

Transparent monoliths made of new interpenetrating networks based on titanium-oxo-poly(hydroxyethyl methacrylate) (PHEMA) nanocomposites are obtained through one pot synthesis with low shrinking and show a strong laser-induced darkening activity.

Mechanical Properties of SiO2-PMMA Based Hybrid Organic-Inorganic Thin Films

Nano-indentations using a Berkovich indenter were performed in order to analyze the mechanical properties of hybrid organic-inorganic coatings. This technique allows to measure low load deformations and therefore to estimate quantitatively mechanical properties of the coatings. The elastic modulus and the hardness were determined on the basis of the load-displacement curve. We report results obtained for class II hybrid coatings based on SiO2-PMMA prepared by sol-gel process. The effects of coating composition were investigated.

Use of Functional Dendritic Macromolecules for the Design of Metal Oxo Based Hybrid Materials

The elaboration of porous materials by using metal alkoxides (Ce(O-iPr)4, Ti(OR)4) as inorganic precursors and acid functionalised dendrimers as organic templates is reported. Chelation by COOH groups present at the dendrimer surface was used to control the reactivity of the metal oxide precursors, creating at the same time anchoring points for the nucleation of a gel phase. The bicontinuous gels resulting after solvent evaporation present a “sponge-like” structure with pore size ranging from 10 to 30 nm. The effect of the metal/dendrimer ratio, the sol preparation procedure and aging conditions were studied by XRD, FTIR, TEM, SEM and BET.

New hybrid core–shell star-like architectures made of poly(n-butyl acrylate) grown from well-defined titanium oxo-clusters

New hybrid star-like macromolecular objects have been designed from an inorganic multifunctional platform following two routes. The first one consists of the direct introduction of polymer arms at the surface of the titanium oxo-cluster [Ti16O16(OEt)32] by alkoxide exchange. The second approach corresponds to the growth by Atom Transfer Radical Polymerization (ATRP) of n-butyl acrylate from the macroinitiator [Ti16O16(OEt)26(OCH2CCl3)6]. By crossing different characterization techniques and methodologies (single crystal X-ray diffraction, 13C and 17O NMR and 1H DOSY NMR spectroscopy, Size Exclusion Chromatography), evidence of the formation of such macromolecular compounds is reported.

Fast and continuous processing of a new sub-micronic lanthanide-based metal–organic framework

Processing strategies for the synthesis of hybrid materials stand as relevant ways to modulate the particle size and morphology. We present herein the use of a continuous high temperature–high pressure (HT–HP) process for the synthesis of a new cerium based metal–organic framework (MOF). The HT–HP harsh thermodynamic synthesis conditions lead to MOF nanostructures exhibiting the same phase as for microparticles obtained under conventional batch solvothermal conditions but in exceptional much shorter residence times, opening avenues towards production scaling-up. The HT–HP process also tailors down the size of the particles, which still presents a major issue for most MOF applications.

Nano-building block based-hybrid organic–inorganic copolymers with self-healing properties

New dynamic materials, that can repair themselves after strong damage, have been designed by hybridization of polymers with structurally well-defined nanobuilding units. The controlled design of cross-linked poly(n-butyl acrylate) (pBuA) has been performed by introducing a very low amount of a specific tin oxo-cluster. Sacrificial domains with non-covalent interactions (i.e. ionic bonds) developed at the hybrid interface play a double role. Such interactions are strong enough to cross-link the polymer, which consequently exhibits rubber-like elasticity behavior and labile enough to enable, after severe mechanical damage, dynamic bond recombination leading to an efficient healing process at room temperature. In agreement with the nature of the reversible links at the hybrid interface, the healing process can speed up considerably with temperature. 1H and 119Sn PFG NMR has been used to evidence the dynamic nature of these peculiar cross-linking nodes.

Design of Hybrid Organic-Inorganic Nanocomposites Synthesized Via Sol-Gel Chemistry

Abstract Among other soft chemistry processes, sol-gel chemistry offers a versatile access to chemically designed new hybrid organic-inorganic materials. Two approaches to synthesize hybrids are presented: the hydrolysis of organo functional metal alkoxides or the assembly of nanobuilding blocks.