Bruno Boury

Polymorphs and colors of polydiacetylenes: a first principles study.

Polydiacetylenes (PDAs) are exceptional polymeric materials with pi-conjugated backbones. Several of them can undergo chromogenic transitions under a wide range of external stimuli. Herein we investigate the electronic structure and the resulting properties of model and experimental PDAs, by means of first principles condensed matter calculations. It is shown that torsional isomers with a twist of the lateral groups can be formed at small energetic costs. We also show the relationship that exists between these twists and the observed changes in the electronic and physical properties. In particular, the calculated changes in the absorption, Raman and NMR spectra agree with the color and property changes as observed experimentally. Therefore, these isomers are excellent models for the structures involved in the chromogenic transitions.

Nanostructured Silica-Based Organic–Inorganic Hybrid Materials—Evidence for Self-Organization of a Xerogel Prepared by Sol–Gel Polymerization

A hydrolytic polycondensation reaction of a rigid, rodlike nonmesomorphous precursor leads to an isotropic sol and then an anisotropic birefringent xerogel (see scheme). Optical and X-ray structural analyses demonstrate a short-range order and the possibility of a crystalline order.

Auto-organisation of hybrid organic–inorganic materials prepared by sol–gel chemistry

Silica-based hybrid organic–norganic materials prepared by sol–gel chemistry exhibit chemical and physical properties revealing their anisotropic organisation. Besides the opportunities that this phenomenon opens for the preparation of new materials, it also provides arguments to the chemist looking for a better comprehension and control of the organisation of solids.

Applications of bacterial cellulose as precursor of carbon and composites with metal oxide, metal sulfide and metal nanoparticles: A review of recent advances

This mini review is limited to very recent studies (last 5-10 years) on two major issues, concerning: the production and physical/chemical modification of bacterial cellulose (BC), and its transformation into carbon and integrated synthesis of metal oxides (TiO2, ZnO, Fe3O4, etc.), metal sulfide (ZnS, CdS, etc.) and metal nanoparticles (Au, Ag, Pt, Pd, etc.) within bacterial cellulose nanoribbons network. We believe that the crossover of these two domains could be of considerable interest in the view of improving the performance of materials prepared with bacterial cellulose. The diversity of these nanomaterials allows targeting of many very different properties/applications: electrochemical devices, catalysis and photocatalysis, sensors, etc. After an introduction to the most important chemical and physical characteristics of BC, production parameters, and its physical and chemical modifications, we review the use of BC as a precursor of inorganic materials like carbon and composites with metal or inorganic nanoparticles.

Structure of silica-based organic–inorganic hybrid xerogel

Abstract The short range order in hybrid xerogels obtained by hydrolysis of (MeO)3Si–CC–C6H4–CC–Si(OMe)3 was investigated by X-ray diffraction analysis. Results were correlated to spectroscopic data and porosity measurements. Aside from the signal related to the Si–O–Si units (q=1.60 A −1 ) , the signals at q 1 =0.55 A −1 and q 2 =1.12 A −1 were attributed to the presence of organic spacers and their organization within the material. These signals were found to be independent of the porosity of the material as measured by the BET method. Thus, changing the solvent or the concentration used at the polycondensation step leads apparently to a similar structure for the materials, representative of the same local order in the material although the porosity is very different. Copolycondensation with tetramethoxysilane (TMOS) results in a shift of the q1 broad peak towards small angles and a decay of the q2 signal when increasing TMOS ratio. An interpretation by a uniaxial swelling is proposed. Elimination of the organic group by chemical treatment and thermal treatment leads to silica xerogels. While no traces of the former organization were found in the case of chemical treatment, the presence of a signal at about 0.30 A−1 indicates the possibility of a residual organization in the case of the thermal treatment.

Ordered Hybrids from Template-Free Organosilane Self-Assembly

Despite considerable achievements over the last two decades, nonporous organic-inorganic hybrid materials are mostly amorphous, especially in the absence of solvothermal processes. The organosilane self-assembly approach is one of the few opportunities for creating a regular assembly of organic and inorganic moieties. Additionally, well-established organosilicon chemistry enables the introduction of numerous organic functionalities. The synthesis of periodically ordered hybrids relies on mono-, bis-, or multisilylated organosilane building blocks self-assembling into hybrid mesostructures or superstructures, subsequently cross-linked by siloxane Si-O-Si condensation. The general synthesis procedure is template-free and one-step. However, three concurrent processes underlie the generation of self-organized hybrid networks: thermodynamics of amphiphilic aggregation, dynamic self-assembly, and kinetically controlled sol-gel chemistry. Hence, the set of experimental conditions and the precursor structure are of paramount importance in achieving long-range order. Since the first developments in the mid-1990s, the subject has seen considerable progress leading to many innovative advanced nanomaterials providing promising applications in membranes, pollutant remediation, catalysis, conductive coatings, and optoelectronics. This work reviews, comprehensively, the primary evolution of this expanding field of research.

Hydrolysis/Polycondensation in the Solid State: Access to Crystalline Silica-Based Hybrid Materials

Mild solid/gas or solid/liquid reactions can be used to prepare crystalline organosilicates, a class of silica-based hybrid materials, from the corresponding solid chlorosilanes. Hydrolysis and polycondensation in the solid state lead to the formation of the highly anisotropic organosilicates.

Adjusting the Porosity of a Silica‐Based Hybrid Material

Precise control of the porosity of silica-based hybrid materialsis the topic discussed here. One approach in particular—the copolycondensation of two precursors followed by selective removal of one of the organic spacers (see Figure) —is highlighted. Using this technique, microporous hybrid xerogels are produced that have a high specific surface area and a highly hydrophobic surface.

Generation of porosity in a hybrid organic-inorganic xerogel by chemical treatment

A hybrid xerogel of 1,4-bis(trimethoxysilylethynyl)benzene was prepared by using a sol-gel process. Chemical treatment of this material was performed under mild conditions in order to remove the organic group using fluoride anion as a catalyst. Experimental procedures were carried out using different solvents, acidities and counter-cations in order to modify the nucleophilic power of F-. Characterization of the residues was done by elemental analysis, spectroscopy (29Si NMR), thermal analysis, pycnometry, surface area measurement and SAXS. The efficiency of the chemical treatment is related to the solvation of the F- anion. It was possible to demonstrate that elimination of the organic part occurs at the same time as a reorganization of the silica network. This reorganization is the result of two competitive F--catalyzed chemical reactions: a redistribution and a polycondensation process known in solution and which take place in the solid. These processes account for the textural characteristics of the final material and may efface the organization of the organic spacers in the hybrid xerogel. These results demonstrate the limitations of silica as a molecular imprinting material and open a new approach to porous silica with adjustable pore size.

The layered double hydroxide route to Bi–Zn co-doped TiO2 with high photocatalytic activity under visible light

In this work, a co-doped Bi-Zn-TiO₂ photocatalist is synthesized by an original synthesis route of layered double hydroxide followed by heat treatment at 670 °C. After characterization the photocatalyst efficiency is estimated by the photo-discoloration of an anionic dye (indigo carmine) under visible light and compare to TiO₂-P25 as reference material. In this new photocatalyst, anatase and ZnO wurtzite are the only identified crystalline phase, rutile and Bi₂O₃ being undetected. Moreover, the binding energy of Bi determined (XPS analysis) is different from the one of Bi in Bi₂O₃. Compared to TiO₂-P25, the absorption is red shifted (UV-vis DRS) and the Bi-Zn-TiO₂ photocatalyst showed sorption capacity toward indigo carmine higher than that TiO₂-P25. The kinetics of the photo-discoloration is faster with Bi-Zn-TiO₂ than with TiO₂-P25. Indeed, a complete discoloration is obtained after 70 min and 120 min in the presence of Bi-Zn-TiO₂ and TiO₂-P25 respectively. The identification of the responsible species on photo-discoloration was carried out in the presence of different scavengers. The study showed that the first responsible is h(+) specie with a moderate contribution of superoxide anion radical and a minor contribution of the hydroxyl radical. The material showed high stability after five uses with the same rate of photo-discoloration.