Search

Composite materials show improved properties compared to pristine materials, in particular when the filler is dispersed homogeneously in the matrix. For polymer–clay composites, different strategies exist to improve clay mineral dispersion in the polymer matrix. In this study, an innovative approach is suggested which consists of forming a talc-like structure directly in a polymer matrix using a silanized polymer as the silicon source. Poly(ethylene glycol) methyl ether of different average molar masses (Mn = 350, 500, 750, 1900 g mol−1) were functionalized with (3-isocyanatopropyl)triethoxysilane and added to the ethanolic solutions of magnesium nitrate. 1H–29Si CPMAS solid state NMR experiments revealed partial condensation of silane compounds, and FTIR analysis confirmed the presence of both Si–O and Mg–O bonds, but an additional proof of the Si–O–Mg bond is needed to prove the formation of such a structure. [ABSTRACT FROM AUTHOR]

Calcium oxalate phytoliths are one of the most prominent types of Ca speciation in the plant kingdom, and they store extensive amounts of carbon in crystalline form. Ca phytoliths were investigated in the root, trunk, and bark of Vitis vinifera Chasselas from a vineyard in Alsace, France. A multi-analytical approach was used, which included SEM coupled with EDX spectroscopy, XRD, XRF, TGA, and 13C-NMR spectroscopy. These techniques revealed that phytoliths are composed of crystalline calcium oxalate monohydrate (whewellite). The whewellite crystals exhibited mostly equant or short-prismatic habits in all of the three studied grapevine parts, but bipyramidal crystals also occurred. Raphide crystals were only observed in the root, where they were abundant. Instead of using wet chemical procedures to extract the mineral components from the organic parts of the biomass, a thermal treatment via calcination was chosen. The suitable temperature of calcination was determined through TGA experiments. The calcination of the biomass samples at 250 °C enhanced the amounts of Ca phytoliths in the residual chars. The thermal treatment, however, affected the appearance of the Ca oxalate crystals by producing surfaces that displayed macroporosity and by creating fractures. For calcination at both 300 °C and 350 °C, Ca oxalate lost a molecule of carbon monoxide to form Ca carbonate, and the modifications of the original crystal surfaces were more pronounced than those observed after thermal treatment at 250 °C. [ABSTRACT FROM AUTHOR]

This work is aimed at the development of synthetic approaches to luminescent hybrid organic–inorganic materials based on chemosensors bearing phosphonate anchoring groups for the detection of toxic metal ions in aqueous solutions. To that end, the sensing properties of phosphonate-substituted ruthenium(II) complex with (3-polyamino)phenanthroline Ru(N3P3phen) toward toxic metal ions in aqueous media at physiological pH was investigated and compared to those of the known selective chemosensor Ru(N2P2phen) for copper(II) ions. The Ru(N3P3phen) complex enables us to detect copper(II) by luminescence measurements and is much more sensitive (limit of detection (LOD) is 0.02 μM) than Ru(N2P2phen). The main advantage of the chemosensors Ru(N2P2phen) and Ru(N3P3phen) studied herein is the possibility to immobilize them on titanium oxide surfaces without extra-synthetic costs using phosphonate substituents as anchoring groups. After activation with TMSBr, both complexes were successfully grafted on hydrated mesoporous TiO2 (SBET = 650 m2 g−1) performing reactions in DMF solutions at room temperature. Strong covalent binding of chemosensors Ru(N2P2phen) and Ru(N3P3phen) to the mesoporous TiO2 support provides high chemical stability to the functionalized solids Ru(N2P2phen)@TiO2 and Ru(N3P3phen)@TiO2 but only one of them gives an optical response in the presence of copper(II) ions. The Ru(N3P3phen)@TiO2 material thus prepared allows for the luminescent detection of cupric ions in aqueous solutions displaying LOD lower than 10−13 M. Such a high sensitivity is unprecedented and cannot be obtained using soluble chemosensors in solutions. This solid-state sensor can be regenerated and reused at least three times. [ABSTRACT FROM AUTHOR]

Nanostructured silicon carbide (SiC) is an exceptional material with numerous applications, for example, in catalysis, biomedicine, high‐performance composites, and sensing. In this study, a fast and scalable method of producing nanostructured SiC from plant materials by magnesiothermic reduction via self‐propagating high‐temperature synthesis (SHS) route was developed. The produced biogenic material possessed a high surface area above 200 m2/g with a SiC crystallite size below 10 nm, which has not been done previously by SHS. This method enables affordable synthesis of the material plant‐based precursors in a reaction that only takes a few seconds, thereby paving a way for nanostructured SiC production in high volumes using renewable resources. The material was also functionalized with carboxylic acid and bisphosphonate moieties, and its use as metal adsorbent in applications such as wastewater remediation was demonstrated. [ABSTRACT FROM AUTHOR]

Different strategies for the immobilization of copper complexes with 1,10-phenanthroline (phen) using the phosphonate anchoring group were investigated to prepare robust and porous heterogeneous catalysts. Homoleptic and heteroleptic copper(i) complexes with phen bearing the bis(trimethylsiloxy)phosphoryl anchoring group (Pphen-Si) at different positions of the phen backbone were prepared and covalently incorporated into titania (TiO2) xerogels by using the sol–gel process or grafted onto the surface of mesoporous TiO2 (SBET = 650 m2 g−1). Copper(i) bis(Pphen-Si) complexes were the only complexes that were successfully anchored onto the TiO2 surface because the heterogenization was often accompanied by the undesirable dissociation of copper complexes. Hybrid materials based on copper(i) chelates with one phen ligand were obtained following a two-step procedure involving the immobilization of Pphen-Si chelators and their successive complexation with copper(i) ions. Porous material, Cu/6b/SM/A, displaying a BET surface area of 243 m2 g−1 and bearing 0.57 mmol g−1 of the complex was synthesized according to this approach. Excellent catalytic performance of the reusable Cu/6b/SM/A material in the Sonogashira-type coupling and the Huisgen 1,3-dipolar cycloaddition was also demonstrated. This solid represents the first example of mesoporous TiO2-supported transition metal catalysts. [ABSTRACT FROM AUTHOR]

ABSTRACT This report introduces a novel UV-curing technology based on thiol-thiol coupling for polydisulfide network formation. Beginning with a model tris(3-mercaptopropionate) trithiol monomer and xanthone propionic acid-protected guanidine as photobase generator, a comprehensive characterization based on spectroscopic techniques supports the reaction of thiols into disulfides without side reactions. The best experimental conditions are described as regards to film thickness, irradiance, emission wavelength, and atmosphere composition. The results shed light on a step-growth photopolymerization mechanism involving two steps: first, the formation of thiyl radicals by thiolate air oxidation or/and thiol photolysis, and second, their recombination into disulfide. By varying thiol functionality and structure, oligomer chain length and monomer/oligomer ratio, the network architecture can be finely tuned. The molecular mobility of the polydisulfide network is crucial to high thiol conversion rates and yields as revealed by 1H T2 NMR relaxation measurements. Ultimately, spatial control enables the formation of a photopatterned poly(disulfide) film, used as next-generation high refractive index photoresist. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 117-128. [ABSTRACT FROM AUTHOR]

In view of their technological impact in materials chemistry, a simplified and more efficient synthetic route to mesoporous films is highly sought. We report, herein, a smart UV-mediated approach coupling in a one-stage process sol-gel photopolymerization and photoinduced template decomposition/ablation to making mesoporous silica films. Performed at room temperature with a solvent-free solution of silicate precursor and amphiphilic poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide) block copolymer, the synthesis relies on photoacid generation to induce the fast formation (≈10 min) of mesostructured silica/surfactant domains. Continuation of UV exposure for three additional hours enables subsequent and complete photodegradation of the polyether copolymer, resulting in ordered or disordered mesoporous silica film. One of the most attractive features is that the one-step procedure relies on a continuous illumination provided by the same conventional medium-pressure Hg-Xe arc lamp equipped with a 254 nm reflector to enhance the emission of energetic photons <300 nm. In addition to X-ray diffraction and transmission electron microscopy, time-resolved Fourier transform infrared spectroscopy has proved to be a powerful in situ technique to probe the different chemical transformations accompanying irradiation. Photocalcination strengthens the inorganic network, while allowing to preserve a higher fraction of residual silanol groups compared with thermal calcination. A polyether chain degradation mechanism based on oxygen reactive species-mediated photo-oxidation is proposed. [ABSTRACT FROM AUTHOR]

ABSTRACT Diphenyl iodonium hexafluorophosphate salt and N-alkyl morpholino acetophenone were shown to be effective photocatalyst generators for the cross-linking of α,ω-silanol terminated silicone oligomers. These two photoacid and photobase-induced polycondensation pathways provided an attractive and efficient alternative to toxic and expensive organometallic catalysts. The utility of this novel UV-curing process was demonstrated with a combination of time-resolved infrared spectroscopy to follow the fast reaction kinetics and solid-state 29Si nuclear magnetic resonance to investigate the polysiloxane network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39875. [ABSTRACT FROM AUTHOR]