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Abstract: Two lamellar organosilica films made up of stacks of head-to-head and head-to-tail alkyl bilayers were synthesized by a UV-driven polymerization of n-C18H37SiCl3 and n-C18H37Si(OCH3)3, respectively. In addition to thermogravimetry and small-angle X-ray scattering, the characterization of these multilayer systems was focused on a variety of multinuclear solid-state NMR methods (1H, 29Si, 13C, 2D WISE). The chemical structure of the siloxane interlayer, the alkyl chain conformation and thermal stability were systematically investigated and compared. Through its marked sensitivity to molecular motion, solid-state NMR was used to investigate the effect of interdigitation on alkyl chain dynamics. [Copyright &y& Elsevier]

Nucleophilic opening of bis-epoxide 1 derived from d-mannitol by organolithium species in the presence of boron trifluoride etherate allows the synthesis of enantiopure polyhydroxy tetrahydrofurane skeletons with aromatic moieties in the pseudo-anomeric position. ortho-Lithiation and transmetalation are the most appropriate conditions for the preparation of the organometallic derivatives where halogen–metal exchange is unfavorable. [Copyright &y& Elsevier]

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]

The impact of crystal size on the transition orthorhombic ↔ monoclinic phase in MFI -type purely silica zeolites is investigated between 293 and 473 K using 29 Si MAS NMR and powder X-ray diffraction. Three silicalite-1 zeolites are synthesized: a material constituted of micron-sized crystals, pseudospherical nanometer-sized crystals and hierarchical porous zeolites with a mesoporous network created by the use of a gemini-type diquaternary ammonium surfactant giving nanosheet zeolites. Our results show for the first time that the orthorhombic ↔ monoclinic phase transition already known for micron-sized particles also occurs in nanometer-sized zeolite crystals whereas our data suggest that the extreme downsizing of the zeolite crystal to one unit cell in thickness leads to an extinction of the phase transition. [ABSTRACT FROM AUTHOR]

Here, using liquid crystals as template, an EISA (evaporation-induced self-assembly) method has been used to synthesize amorphous mesostructured alumina. The effect of the synthesis parameters such as the presence of a chelating agent, the amounts of both porogen agent and alumina precursor on the materials properties have been investigated in details. Under the optimum conditions, after Soxhlet extraction, the obtained Al 2 O 3 presents an HMS (Hexagonal Molecular Sieves) structure and a high specific surface area (≈400 m2/g) with a mesopore size distribution centered around 8.3 nm. Investigation of the thermal stability shows that the crystallization into γ-Al 2 O 3 of the amorphous alumina walls delimiting mesopores begins after heating at 800 °C. We have also demonstrated that half of the carbon present in the as-synthesized material can be removed by washing with water or ethanol at room temperature instead of Soxhlet extraction. On the basis of SAXS, XRD and N 2 adsorption-desorption analyses, we have shown that when treated into boiling water or exposed to water vapor the alteration of the mesostructure occurs quickly. Its collapse has been attributed to the crystallization of the amorphous alumina walls into aluminum hydroxides, mainly boehmite, upon the hydration of the alumina. Dual mesoporous alumina have been also obtained from micelles through a cooperative templating mechanism at low P123 amount and in the presence of citric acid. In that case both mesopores networks adopt a wormhole-like mesostructure. [Display omitted] • Mesostructure preserved until 900 °C. • Amorphous mesostructured Al 2 O 3 thermally stable up to 800 °C. • Porogen agent partially removed by water or ethanol at room temperature. • Framework collapses due to aluminum hydroxides crystallization in presence of water. • Dual mesoporous alumina prepared at low amount of porogen agent in presence of citrate. [ABSTRACT FROM AUTHOR]

Abstract: Whereas the hegemony of the Fischer–Tropsch synthesis is well established for the valorization of methane in the case of important gas fields, the methane dehydro-aromatization reaction remains an interesting solution to convert methane obtained as by-product of oil extraction and thus fight against flaring and global warming. Until now, it was generally accepted that the molybdenum is anchored on the Brønsted acid sites of the zeolite as (Mo2O5)2+ species. The molybdenum performs the dehydrogenation and coupling of CH4 to ethylene which is consecutively oligomerized to benzene over the Brønsted acid sites. In the present work, we bring evidence that this picture is actually more complicated than it seems. The Si/Al ratio of the zeolite, and consequently the density of available Brønsted acid sites, plays a dramatic role on the anchoring mode of the molybdenum and on its catalytic activity. [Copyright &y& Elsevier]

Abstract: Mass transfers of various molecules in multiphasic food products lead to quality modification and thus require the use of edible films or coatings in-between the foodstuff. Consequently, it is important to assess the barrier properties and efficiencies of edible films as well as to determine the diffusivities of the migrants. Translational diffusion of a reference molecule such as fluorescein, determined by the fluorescence recovery after photobleaching (FRAP) method, displays a threshold of a critical water content inducing an increase of the molecular mobility, and demonstrates that multiple populations of a single molecular specie can be involved in different diffusion kinetics. Further investigations at a molecular scale through high resolution solid state nuclear magnetic resonance (NMR) enables to go deeper into the understanding of the interactions involved in such a system, in particular on the identification of the possible binding sites of the diffusant on the polymer and on the overall effect of interactions on the polymer organization. Therefore, the appraisal of transport properties in foods by means of reference molecules constitutes a relevant approach to use in combination with molecular investigation of physicochemical interactions with the diffusing substances. [Copyright &y& Elsevier]

Abstract: Binderless beta zeolite has been anchored on a silicon carbide foam with a monolithic shape. The catalytic activity of the resulting composite was evaluated for a Friedel–Crafts reaction carried out in a fixed-bed configuration: the benzoylation of anisole to p-methoxybenzophenone. The results obtained were compared with those of a commercial beta zeolite. Significantly higher product yields along with a stable activity were obtained with the BEA/SiC composite. It has been suggested that the opened structure of the β-SiC foam and the absence of any binder allow a fast desorption of the p-ketone which is the main product of the reaction but also the major source of deactivation due to strong adsorption and/or coke formation inside the microporosity of the zeolite. [Copyright &y& Elsevier]

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]

A UV photoinduced cross-linking of non-modified commercial poly(disulfide) resins (Thioplast) is reported via the air oxidative photocoupling of terminal thiol functions. Catalyzed by a photogenerated guanidine base (TBD), this step-growth photopolymerization is useful to maximize disulfide functions content. The mechanism proceeds through thiol deprotonation into thiolate anions, further oxidized into thiyl radicals, eventually dimerizing into disulfide cross-links. Starting with a detailed structural characterization of the thiol-terminated resin, photooxidative kinetics are studied under exposure to a polychromatic medium-pressure Hg arc using Raman and infrared spectroscopy. The effects of irradiance, film thickness, photobase concentration, resin molar mass, and content of an additional polythiol monomer (reactive diluent) have been investigated. In an effort of upscaling, irradiation under a 365 nm LED panel has enabled the fast preparation of 1.5 μm thick cross-linked poly(disulfide) coatings in a matter of minutes. Capitalizing on the ability of residual thiol groups to react with silver cations, a post-functionalization has been successfully performed, leading to films exhibiting at their surface stable thiolate-silver bonds as proved by X-ray photoelectron spectroscopy. Despite the well-established biocide action of silver ions, no antibacterial action has been evidenced by confocal fluorescence microscopy because of insufficient release. [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]

Pure silica ITQ-7 zeolite of topology ISV synthesized in fluoride media possesses a 3D 12-membered-rings pore system. Originally the structure of ITQ-7 zeolite was solved and refined from a calcined sample in the highest possible space group symmetry P4 2 / mmc . This space group leads to only 5 independent silicon T sites for this structure. However, this high symmetry was not supported by solid state 29 Si MAS NMR spectroscopy. In this short communication, we show from a revised 29 Si solid state MAS NMR and Rietveld analyses, that lowering of the space group symmetry from P4 2 / mmc to P4 2 consolidates structure model and experimental data, in particular, the number of non equivalent crystallographic T sites passing from 5 to 16, is in agreement with 29 Si solid state NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: In sol–gel polymerization of alkoxysilane precursors, base catalysts are usually employed to introduce textural properties. Herein, we show the feasibility and interest of a photobase-catalyzed sol–gel reaction to afford silicate films. Our inorganic polymerization is solvent-free, single-step and UV activatable with a mixture of α-aminoacetophenone (photobase generator), benzophenone (photosensitizer) and triphenylphosphine (oxygen scavenger). To date, the present tricomponent photolatent system generating N-alkyl morpholine tertiary amines represents one of the most efficient photobase generators reported so far in sol–gel chemistry. A combination of spectroscopic and electron microscopy techniques enabled to investigate the fundamental chemistry underlying alkoxysilane photopolymerization: reaction mechanism, hydrolysis kinetics and siloxane microstructure. Systematic comparison with a photoacid-catalyzed process revealed also the impact of the photocatalyst nature on film texture, morphology and optical properties. [Copyright &y& Elsevier]

Photoacid-catalyzed sol–gel polymerization isnow recognizedas a powerful single-step synthetic approach to the synthesis of hybridfilms, which can be distinguished from conventional sol–gelmethods by higher reactivity and a solvent-free process. Despite itsutility, the mechanism is not yet understood, in particular what chemical,physical, and photochemical parameters determine the precise sequence,kinetics, and advancement of this UV inorganic photopolymerization.Here, using mainly transmission real-time Fourier transformed infrared(RT-FTIR) spectroscopy, we characterize in situthehydrolysis–condensation reactions of oligomeric silicon alkoxidesand the formation of byproducts. Systematic review and assessmentof numerous processing variables (relative humidity, film thickness,precursor structure, nature, and the concentration of photoacid generator)prove that the reaction kinetics are controlled by the two independentphenomena: the intrinsic chemical reaction rates and the water vaporpermeation into the film. [ABSTRACT FROM AUTHOR]

Abstract: An alternative to the Evaporation Induced Self Assembly (EISA) method is described as a fast and simplified approach towards mesoporous silica films. The sol–gel process is photochemically triggered with the aid of photoacid generator (PAG), thereby making mesostructuration independent of film deposition conditions, solvent evaporation and complex chemistry associated with a silica sol. The developed solvent-free synthesis uses non-ionic poly(ethylene oxide)-based surfactants and polydimethoxysiloxane, affording after UV irradiation a film with a wormhole porous framework, and a uniform pore size distribution. The disordered mesostructure was characterized by X-ray diffraction, N2 adsorption, 29Si solid-state NMR and transmission electron microscopy. [Copyright &y& Elsevier]

Abstract: The control of the inter-particle porosity in polycrystalline zeolite bodies remains a challenge. The present study reports on the preparation of centimeter-sized zeolite bodies (32×2mm pellets) with reduced inter-particle porosity. The bodies were prepared by assembling zeolite colloidal nanocrystals with monomodal particle size distribution and sub-colloidal aluminum hydroxide binder. A secondary growth treatment under hydrothermal conditions was performed in order to fill up the inter-particle voids and obtain polycrystalline zeolite materials with textural characteristics close to those of single zeolite crystals. Initial material, intermediates and ultimate product were studied with a combination of complementary methods revealing a substantial reduction even an elimination of the inter-particle porosity. Particular attention was paid to the chemical evolution of the binder and the migration of aluminum species, employing X-ray powder diffraction, 27Al-MAS, 27Al-3QMAS NMR and X-ray fluorescence spectroscopy analyses. Evidences for insertion of aluminum from the binder into the zeolite framework during secondary growth step were found. Consequently the ultimate pellets comprised aluminum-rich zeolite beta crystals and very low binder content. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of bridged polysilsesquioxane films was performed viaa photoacid-catalyzed sol–gel method using a series of three precursors with different organic moiety structures. [ABSTRACT FROM AUTHOR]

The effect of the introduction of heteroelement (Si, P, Al, Ge, Ga and Zr) by direct synthesis on the thermal stability of mesostructured titania prepared by the soft templating pathway has been investigated. All materials have been surfactant-extracted with EtOH and calcined at different temperatures up to 900 °C. Ti4+ can be partially substituted by most of the investigated heteroelements but they mainly form an oxide amorphous phase surrounding the titania anatase particles. Results obtained by SAXS, X-Ray diffraction, Raman spectroscopy and manometry nitrogen adsorption-desorption show that the crystallization of the amorphous titania into nanosized anatase particles and the transition from anatase to rutile occur at higher temperature with the addition of the heteroelement. Even if the lattice distortion introduced by the partial Ti4+ substitution can participate to this phenomenon, it is mainly due the «glass » effect induced by the presence of the heteroelement in the TiO 2 amorphous phase, which limits the growth of the nanosized anatase crystallites. However, when the crystallites reach a limit size, the collapse of the mesostructure occurs. With increasing the calcination temperature, the anatase titania particles become bigger and bigger, the transition from anatase to rutile takes place and the heteroelement can crystallize or be integrated in a crystalline phase. Among the considered heteroelements and by comparison with the bare mesostructured TiO 2 , the most beneficial effect is obtained in the presence of Si4+ and PO 4 3− for which the mesostructure collapse at higher temperature by about two hundred Celsius degrees. Al3+ and Ge4+ enhance the thermal stability by about a hundred Celsius degrees and Ga3+ or Zr4+ have no significant effect on the temperature at which the mesostructure collapses. Image 1 • Thermal stability of mesostructured TiO 2 enhanced by the addition of heteroelements. • Heteroelements form amorphous phase which embedded the anatase particles and inhibit their growth. • Limit size reached by anatase particles involves the collapse of the mesostructure. • Delay of the anatase to rutile transformation in the presence of heteroelements. • Partial substitution of titanium by the heteroelement. [ABSTRACT FROM AUTHOR]

In contrast with the conventional CoMoS/alumina catalyst, the use of amorphous mesostructured ZrO2 as support for the dispersion of the CoMoS active phase in deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene led to a higher promotion rate and a better sulfidation of the cobalt species. The CoMoS, dispersed over mesostructured amorphous ZrO2 as catalyst, also induced a modification of the main desulfurization way; in this case, a shift towards direct desulfurization selectivity was observed. This result was unexpected regarding the literature. Indeed, the hydrogenated route was observed for commercial zirconia. The designed catalysts are therefore more eco-friendly, since they consume less hydrogen. This implies a better use of the fossil resources. [ABSTRACT FROM AUTHOR]

• Solid-state nuclear magnetic resonance (NMR) reveals ordering in hybrid silica film. • Narrower 1H NMR lines reflect a better chemical uniformity of ordered structures. • Narrower 13C NMR lines translate a higher mobility of ordered structures. • Disorder-to-order transition is reflected by 1H transverse relaxation time. In the context of increasing use of nanostructured materials, finding innovative characterization methods able to assess precisely the level of ordering is essential. To this end, a range of model organic-inorganic copolymer-silica films is synthesized using poly(ethylene oxide)- b -poly(propylene oxide)- b -poly(ethylene oxide) amphiphilic triblock copolymer as supramolecular template. Upon increasing copolymer concentration (10–100 wt%), the order can be gradually enhanced from short-range to long-range as proved by conventional techniques such as X-ray diffraction and electron microscopy. To evaluate the level of mesoscopic organization, the same series of samples is also analyzed by solid-state nuclear magnetic resonance (NMR) spectroscopy. The disorder-to-order transition is probed by 1H and 13C magic angle spinning NMR spectra through the increase in chemical environment uniformity and chain mobility respectively, which both result from the self-assembly mechanism. 1H NMR relaxation measurements (T 2) using low-field NMR spectroscopy are instrumental to identify the threshold template concentration where ordering takes place. [ABSTRACT FROM AUTHOR]