In situ preparation of compounds using silanized mPEG inspired by talc-like structures.

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.

Natural water defluoridation by adsorption on Laponite clay.

Safe drinking water is a necessity for every human being, but clean water is scarce and not easily available due to natural geochemical factors or industrial pollutant activity. Many issues involving water quality could be greatly improved using clays as adsorbents. We highlight for the first time, the uptake of fluoride from natural water by Laponite, synthetic hectorite clay, in raw and modified state. A series of batch adsorption experiments were carried out to evaluate the adsorption potential of the different parameters. The optimized parameters were: contact time, adsorbent dose and pH. It was found that fluoride uptake from natural water was better using raw Laponite and inorganic-modified Laponite than using organic-modified Laponite clays. Adsorbents were characterized before and after fluoride adsorption by X-ray diffraction, X-ray fluorescence, FTIR, thermo gravimetric analyses and 19F solid state NMR spectroscopy. The experimental data showed that both Langmuir and Freundlich models fitted an adsorption isotherm well. Thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were calculated. These parameters indicated that fluoride adsorption onto Laponite was nonspontaneous and endothermic in temperature range between 25 and 45 °C.

Hierarchical Zeolites as Catalysts for Biodiesel Production from Waste Frying Oils to Overcome Mass Transfer Limitations.

Hierarchical crystals with short diffusion path, conventional microcrystals and nanocrystals of ZSM-5 zeolites were used for biodiesel production from waste frying oils and were assessed for their catalytic activity in regard to their pore structure and acidic properties. Produced zeolites were characterized using XRD, nitrogen adsorption-desorption, SEM, TEM, X-ray fluorescence, and FTIR. Pore size effect on molecular diffusion limitation was assessed by Thiele modulus calculations and turnover frequencies (TOF) were used to discuss the correlation between acidic character and catalytic performance of the zeolites. Owing to the enhanced accessibility and mass transfer of triglycerides and free fatty acids to the elemental active zeolitic structure, the catalytic performance of nanosponge and nanosheet hierarchical zeolites was the highest. A maximum yield of 48.29% was reached for the transesterification of waste frying oils (WFOs) using HZSM-5 nanosheets at 12:1 methanol to WFOs molar ratio, 180 °C, 10 wt % catalyst loading, and 4 h reaction time. Although HZSM-5 nanosponges achieved high conversions, these more hydrophilic zeolites did not function according to their entire acidic strength in comparison to HZSM-5 nanosheets. NSh-HZSM5 catalytic performance was still high after 4 consecutive cycles as a result of the zeolite regeneration.

Grafting Diels-Alder moieties on cellulose nanocrystals through carbamation.

The Diels-Alder reaction is a promising click chemistry for the design of advanced materials from cellulose nanocrystals (CNCs). Transferring such chemistry to cellulose nanocrystals requires the precise grafting of reactive Diels-Alder moeities under heterogeneous conditions without compromising the nanocrystals morphology. In this study toluene diisocyanate is used as a spacer to graft Diels-Alder moieties viz the furyl and protected maleimido moieties onto cellulose nanocrystals. A factorial experimental design reveals that reaction time and reactant molar ratio positively affect the grafting efficiency, as evidenced by FTIR and CHNS elemental analysis. The surface degree of substitution was analyzed via CHNS elemental analysis and XPS and found to range between 0.05 to 0.30, with a good agreement between the two techniques. 13C CP/MAS NMR confirmed that the grafted moieties and CNCs are intact after reaction. Side reactions were also observed and their impact on performing controllable click chemistry between cellulose nanocrystals is discussed.

Amorphous mesostructured zirconia with high (hydro)thermal stability.

Here, combining the evaporation-induced self-assembly (EISA) method and the liquid crystal templating pathway, mesostructured amorphous zirconium oxides have been prepared by a soft templating method without addition of any heteroelement to stabilize the mesopore framework. The recovered materials have been characterized by SAXS measurements, nitrogen adsorption-desorption analysis and X-ray diffraction (XRD). The obtained mesostructured zirconia exhibits a high thermal stability. An in situ XRD study performed as a function of temperature shows that the amorphous ZrO2, obtained after removal of the pore templating agent (pluronic P123), begins to crystallize in air from 420 °C. Amorphous mesostructured ZrO2 also presents a high hydrothermal stability; these materials are not degraded after 72 hours in boiling water.

Combining a ligand photogenerator and a Ru precatalyst: a photoinduced approach to cross-linked ROMP polymer films.

Although metathesis photoinduced catalysis is now well established, there is little development in thin film preparation using photochemically activated ring-opening metathesis polymerization (ROMP). Herein, a N-heterocyclic carbene (NHC) photogenerator (1,3-bis(mesityl)imidazolium tetraphenylborate) is combined with an inactive metathesis catalyst ([RuCl2(p-cymene)]2) to generate under UV irradiation an active catalyst (p-cymene)RuCl2 (NHC), that is capable of producing in a single step cross-linked copolymer films by ROMP of norbornene with dicyclopentadiene. The study shows that the photoinitiated catalytic system can be optimized by increasing the yield of photogenerated NHC through a sensitizer (2-isopropylthioxanthone), and by choosing [RuI2(p-cymene)]2 as precatalyst to provide a long-term photolatency. The cross-linked polymer structure is investigated by a range of techniques including gel content measurement, FT-IR and solid-state 13C NMR spectroscopy, TGA and DSC, which reveal a cross-linking mechanism proceeding through both metathesis and olefin coupling.

Synthesis of Binderless ZK-4 Zeolite Microspheres at High Temperature.

Binderless zeolite macrostructures in the form of ZK-4 microspheres were prepared using anion-exchange resin beads as shape-directing macrotemplates. The particles were synthesized under hydrothermal conditions at different temperatures and treatment times. The influence of the different synthesis parameters was investigated by X-ray diffraction, scanning electron microscopy, fluorescence X, nitrogen adsorption measurements and 29Si solid-state NMR. Fully crystalline spheres similar in size and shape to the original resin beads were obtained by a hydrothermal treatment at the highest temperatures (150⁻180 °C) for a short treatment time of 24 h. The synthesized microspheres showed to be promising in the molecular decontamination of volatile organic compounds (VOCs).

Block copolymer self-assembly in mesostructured silica films revealed by real-time FTIR and solid-state NMR.

Over the past ten years, understanding the self-assembly process within mesostructured silica films has been a major concern. Our characterization approach relies on two powerful and complementary techniques: in situ time-resolved FTIR spectroscopy and ex situ solid-state NMR. As model systems, three silica/surfactant films displaying various degrees of mesostructuration were synthesized using an amphiphilic block copolymer (PEO-b-PPO-b-PEO) via a UV light induced self-assembly process. The key idea is that the hydration state of the hydrophobic PPO chain is expected to be different depending upon whether the sample is amorphous (blend) or mesostructured (segregated). With real-time FTIR experiments, we show that the methyl deformation mode can act as a signature for the PPO microenvironment so as to trace the progressive copolymer self-association throughout the irradiation time. In (1)H solid-state NMR, the dependence of the (1)H chemical shift on the PPO hydration state has been exploited to evidence the extent of mesostructuration.

Photopatterning of multilayer n-alkylsilane films.

Surface photopatterning of organosilane self-assembled monolayers (SAM) has received increasing attention since its introduction 20 years ago. Herein we report for the first time a cost-efficient soft photopatterning technique affording amplified 3D multilayer structures. The essential chemistry relies on a spatially controlled photoacid-catalyzed hydrolysis and polycondensation of n-alkyltrimethoxysilane precursors (n-C(12)H(25)Si(OCH(3))(3),). Amphiphilic siloxane species are photogenerated locally and are able to self-assemble spontaneously into a long-range-ordered lamellar mesostructure.

Insights into photoinduced sol-gel polymerization: an in situ infrared spectroscopy study.

Photoacid-catalyzed sol-gel polymerization is now recognized as a powerful single-step synthetic approach to the synthesis of hybrid films, which can be distinguished from conventional sol-gel methods by higher reactivity and a solvent-free process. Despite its utility, 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 situ the hydrolysis-condensation reactions of oligomeric silicon alkoxides and the formation of byproducts. Systematic review and assessment of 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 independent phenomena: the intrinsic chemical reaction rates and the water vapor permeation into the film.

Self-organized poly(n-octadecylsilsesquioxane) films via sol-gel photopolymerization.

We describe a novel solvent- and water-free sol-gel process for n-octadecyltriclorosilane (C(18)H(37)SiCl(3)) film catalyzed by photogenerated Brönsted acids. Driven by hydrophobic van der Waals interactions, a photoinduced self-assembly process occurs to afford a long-range ordered lamellar mesostructure, characterized by X-ray diffraction and transmission electron microscopy. Real-time Fourier transform IR spectroscopy was instrumental to probe the fast hydrolysis kinetics and assess the change of conformational behavior of the alkyl chains during UV irradiation. A unique combination of different solid-state NMR techniques ((29)Si, (13)C, (1)H) provided an insight into the supramolecular organization of this hybrid film.

New insights in the formation of silanol defects in silicalite-1 by water intrusion under high pressure.

The "water-silicalite-1" system is known to act as a molecular spring. The successive intrusion-extrusion cycles of liquid water in small crystallites (6 × 3 × 0.5 µm(3)) of hydrophobic silicalite-1 were studied by volumetric and calorimetric techniques. The experiments displayed a decrease of the intrusion pressure between the first intrusion-extrusion cycle and the consecutive ones, whereas the extrusion pressures remained unchanged. However, neither XRD studies nor SEM observations revealed any structural and morphological modifications of silicalite-1 at the long-range order. Such a shift in the value of the intrusion pressure after the first water intrusion-extrusion cycle is attributed to the creation of silanol groups during the first water intrusion. Detailed FTIR and solid-state NMR spectroscopic characterizations provided a molecular evidence of chemical modification of zeolite framework with the formation of local silanol defects created by the breaking of siloxane bonds.

Pure silica chabazite molecular spring: a structural study on water intrusion-extrusion processes.

Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite show that the water-Si-CHA system displays real spring behavior. However, differences in pressure-volume diagrams are observed between the first and the other intrusion-extrusion cycles, indicating that some water molecules interact with the inorganic framework after the first intrusion. (29)Si and especially (1)H solid-state NMR showed the creation of new defect sites upon the intrusion-extrusion of water and the existence of two kinds of water molecules trapped in the supercage of Si-CHA: a first layer of water strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquidlike physisorbed water molecules undergoing interaction with the first layer. This hydrogen bonding scheme is also supported by X-ray powder diffraction.