Laure Michelin

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.

Thick mesostructured films via light induced self-assembly

As an alternative to solvent evaporation, we show that UV light can serve as a stimulus to promote self-assembly during the formation of surfactant-templated silica films. Despite practical and conceptual advantages, the Light Induced Self-Assembly (LISA) route has been poorly described in comparison with its evaporation induced analogue. In this article, we give an exhaustive overview of the potentiality of this photoinduced process using a range of PEO-b-PPO-b-PEO amphiphilic triblock copolymers, and investigating systematically the structural (29Si MAS NMR, XRD) and textural properties (TEM, N2 sorption) of the resultant worm-like mesostructured films. Practically, UV irradiation is applied directly to isotropic micrometric films consisting of a nonhydrolyzed alkoxide-amphiphilic copolymer-photoacid generator mixture, obviating the addition of solvent and water. Photoliberation of Bronsted photoacid generates on demand hydrophilic silica species, driving the micellization of the copolymer. The process is single-step and fast, yielding transparent mesostructured films within a few seconds. A target addressed in this feature is to investigate the film structural evolution resulting from the UV irradiation by in situ Fourier transformed infrared analysis (FTIR). Without the interference of solvent, this powerful technique provides a new perspective on the course of the sol–gel process in mesostructured films. For the first time, hydrolysis is assessed kinetically as well as the silica network condensation and the water content of the film.

Influence of the porous texture of SBA-15 mesoporous silica on the anatase formation in TiO2–SiO2 nanocomposites

Two series of TiO2–SiO2 composites have been prepared by post-synthesis impregnation of a TiO2 precursor onto SBA-15 silica matrices and subsequent thermal treatment at 400 °C in air. The influence of the textural properties of the SBA-15 and the TiO2 content was evaluated upon the dispersion of TiO2 and its crystallization in anatase. The morphology of the samples before and after impregnation was observed by electronic microscopy while the textural and structural properties were evaluated by different techniques such as XRD, nitrogen sorption manometry, and Raman spectroscopy. The quantity of crystallized anatase in the composites was determined by XRD quantification using an internal standard. The bandgap energy (Eg) of the composites was evaluated by diffuse reflectance spectroscopy and the results show that Eg decreases as a function of the titania content. The photoactivity of the prepared materials was evaluated by following the degradation of methyl orange (MO) in water under UV irradiation. For the same amount of catalyst, the MO degradation rate in the presence of the composites containing 28 and 44 wt% of crystallized anatase was found to be similar to the one in the presence of commercial fully crystallized anatase.

Insights into the Formation and Properties of Templated Dual Mesoporous Titania with Enhanced Photocatalytic Activity

The one pot synthesis of dual mesoporous titania (2.3 and 7.7 nm) has been achieved from a mixture of fluorinated and Pluronic surfactants. The small and large mesopore networks are templated, respectively, by a fluorinated-rich liquid crystal and a Pluronic-rich liquid crystal, which are in equilibrium. After calcination at 350 °C, the amorphous walls are transformed into semicrystalline anatase preserving the mesoporous structure. Results concerning the photodegradation of methyl orange using the calcined photocatalysts highlight that the kinetic rate constant (k) determined for the dual mesoporous titania is 2.6 times higher than the k value obtained for the monomodal ones.

The relationship between mineral contents, particle matter and bottom ash distribution during pellet combustion: molar balance and chemometric analysis

This paper aims to identify the correlation between the mineral contents in agropellets and particle matter and bottom ash characteristics during combustion in domestic boilers. Four agrifood residues with higher mineral contents, namely grape marc (GM), tomato waste (TW), exhausted olive mill solid waste (EOMSW) and olive mill wastewater (OMWW), were selected. Then, seven different pellets were produced from pure residues or their mixture and blending with sawdust. The physico-chemical properties of the produced pellets were analysed using different analytical techniques, and a particular attention was paid to their mineral contents. Combustion tests were performed in 12-kW domestic boiler. The particle matter (PM) emission was characterised through the particle number and mass quantification for different particle size. The bottom ash composition and size distribution were also characterised. Molar balance and chemometric analyses were performed to identify the correlation between the mineral contents and PM and bottom ash characteristics. The performed analyses indicate that K, Na, S and Cl are released partially or completely during combustion tests. In contrast, Ca, Mg, Si, P, Al, Fe and Mn are retained in the bottom ash. The chemometric analyses indicate that, in addition to the operating conditions and the pellet ash contents, K and Si concentrations have a significant effect on the PM emissions as well as on the agglomeration of bottom ash.

UV aerosol synthesis: a one-step route to silica, organic-silica and surfactant/silica nanostructured materials

Aerosol flame technology has been used for decades to fabricate on an industrial scale a range of inorganic (nano)particles, including carbon blacks, titania, and fumed silica. Nevertheless, the high local temperatures inherent to this technique prevent direct organic functionalization or loading by organic derivatives, which is essential in many applications to achieve specific properties and optimal dispersion within an organic matrix. We describe herein a novel eco-friendly UV process allowing single-step manufacture of high-value silica and organosilica particles at ambient temperature. Atomized alkoxysilane precursor droplets are produced within an annular photoreactor including 6 fluorescent UV lamps (maximum emission: 312 nm), and photocondensed continuously after a 1 min single pass. Droplet condensation is controlled by the release of a photoacid catalyst localized in the droplets, affording spherical polydisperse powder particles with a mean diameter ranging around 400–700 nm. In the presence of an amphiphilic block copolymer template, a silica/surfactant mesostructured film was deposited using this UV aerosol technology, resulting in a wormlike mesoporous structure after calcination.

Non-symmetrical bis-silylated precursor can (also) self-direct the assembly of Silsesquioxane films

Symmetric α,ω-bis-silylated precursors are the standard building blocks of self-assembled bridged silsesquioxanes, a unique class of robust ordered nanomaterials prepared by sol-gel process without external surfactant. We report an unprecedented approach based on the utilization of a dissymmetric bis-silylated precursor, 1,2-bis(trimethoxysilyl)decane (1), in which the two alkoxy groups are carried by adjacent methylene groups. Extensive characterization—based on X-ray diffraction, real-time fourier transform infrared, electron and optical microscopy, 29Si solid-state nuclear magnetic resonance, thermogravimetry, and molecular modeling—shows surprisingly that such non-symmetrical precursor is highly conducive to achieve highly ordered lamellar mesostructure, able to sustain temperature up to 120 °C. To emphasize the effect of the alkoxy group functionality and position, comparison is made systematically with analogous silsesquioxanes derived from bis-(2) and mono-silylated (3) precursors. The sol-gel polymerization of 1 is unique by its ability to produce a homogeneous film possessing structural characteristic on multiple scales: uniform microcrystallites consisting of nanolamellar organosilica hybrid material. The most likely mesostructure consists of bilayers of slightly interpenetrated trans C8H9 chains, with a single central siloxy-hydrocarbon chain (Si2O(OH)4-C2H3)n. To permit a good lateral chain packing, the hydrocarbon chain of two adjacent silicon atoms point in opposite directions.Graphical abstract

Surfactant-directed synthesis of mesoporous films made single-step by a tandem photosol-gel/photocalcination route

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 ...

Synthesis of hierarchical ZSM-48 nano-zeolites

Hierarchical zeolites are known to offer fast mass transfer along with size and shape selectivity compared to their conventional micron-sized zeolite counterparts. We report here the successful synthesis and characterization of a hierarchical ZSM-48 zeolite (*MRE-type structure) using a specific gemini-type surfactant that acts as dual functions template to generate at the same time micropores and mesopores. The Si/Al molar ratio of the starting gel seems to influence the nature of the obtained zeolitic phase. Pure hierarchical ZSM-48 zeolites were only obtained at a high Si/Al molar ratio of the starting gel (Si/Al = 31 to 50). The catalytic properties of these acidic catalysts were then tested in ethanol transformation into hydrocarbons.