Capucine Sassoye

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.

A sustainable aqueous route to highly stable suspensions of monodispersed nano ruthenia

Highly stable suspensions of monodispersed ruthenia nanoparticles have been prepared via a sustainable aqueous oxidative pathway. The nanoparticles (2 nm) have been thoroughly characterized by TEM, XRD, XPS, MS-TGA and thermodiffraction. The addition of hydrogen peroxide in the RuCl3 solution provokes a fast oxidation of Ru(III) ions into Ru(IV). This increases the rate of the hydrolysis/condensation reactions and further promotes the nucleation over the growth of the particles. The very high stability conditions of the colloidal suspension have been studied. This aqueous one-step process, which uses no organic solvent or toxic pollutant additive, is quick and produces calibrated ruthenia nanoparticles in high yields. It presents a green alternative to the preparation and use of ruthenia. As examples, two applications are presented. In the first, RuO2 coatings have been tested for their electrical capacitance. In the second, RuO2/TiO2 catalysts, prepared from the controlled deposition of ruthenia nanoparticles on TiO2 particles, have been proven to be highly effective for the production of methane from CO2.

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.

Selective CO2 methanation on Ru/TiO2 catalysts: unravelling the decisive role of the TiO2 support crystal structure

The catalytic hydrogenation of CO2 is a relevant strategy for mitigating CO2 emissions and its applicability relies on our ability to prepare catalysts that are highly active under mild conditions. Understanding and improving these tailored catalysts requires innovative materials synthesis routes and advanced methods of characterization. In this study, mono-dispersed 2 nm RuO2 nanoparticles were prepared as a stable colloidal suspension and deposited onto different titania supports by impregnation. Supported RuO2 nanoparticles are homogeneously dispersed at the surface of the titania supports. Then, upon annealing and reduction, metallic Ru nanoparticles are obtained, which are active in the hydrogenation of CO2 to CH4. However, depending on the crystal structure of the different TiO2 supports (anatase, rutile, and a mixture of both), the catalysts exhibited drastically diverse catalytic performances. An array of characterization tools (N2-physisorption, H2-chemisorption, HR-TEM, STEM-HAADF, 3D tomographic analysis, XRD, and XPS) was used to unravel the origin of this support effect. It appeared that catalytic behaviour was related to profound morphological changes occurring during the annealing step. In particular, advanced electron microscopy techniques allow visualisation of the consequences of RuO2 nanoparticle mobility onto titania. It is shown that RuO2 sinters heavily on anatase TiO2, but spreads and forms epitaxial layers onto rutile TiO2. On anatase, large Ru chunks are finally obtained. On rutile, the formation of a particular “rutile-TiO2/RuO2/rutile-TiO2 sandwich structure” is demonstrated. These phenomena – along with the relative thermal instability of the supports – explain why the catalysts based on the commercial P25 titania support outperform those based on pure crystalline titania. The study opens new perspectives for the design of highly active CO2 methanation catalysts.

A new open-framework fluorinated gallium phosphate with large 18-ring channels (MIL-31)

A new open-framework fluorinated gallium phosphate (MIL-31) containing the Ga9(PO4)9(H2O)(OH)(OH,F)4 5− anion was hydrothermally synthesized by using long alkyl chain diamines (C9 and C10) as structure-directing agents; its crystal structure is built up from hexameric units and exhibits large one-dimensional hexagonal channels delimited by 18-rings.

Titanium Oxo-Clusters: Vesatile Nano-Objects for the Design of Hybrid Compounds

The description of three titanium oxo-clusters and their use as inorganic components of hybrid organic-inorganic materials are reported. The first approach consists to add titanium oxo-clusters, [Ti 6 O 4 (C 6 H 5 COO) 8 (OPr n ) 8 ], in an ORMOCER⊗ based hybrid medium. Nano-sized titanium oxo-clusters combined with the chemical nature of the components, allow the tuning of the optical properties, especially the refractive index. The second approach consists to associate functionalized titanium oxo-clusters to elaborate hybrid materials with perfectly defined inorganic domains. The more relevant example of titanium oxo-cluster to build hybrid networks from nano-building blocks is the oxo-cluster [Ti 16 O 16 (OEt) 32 ]. Indeed, the nature and the number of functional groups at the surface of these metallic oxo-clusters can be tuned in order to generate cross-linking agents of organic polymers. The studies of the structure-property relationships of the resulting nanocomposites have been investigated. Finally the structure of a purely carboxylate oxo-clusters is briefly described. This new family of stable oxo-clusters opens the way for the production of original hybrid compounds.