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Graphical abstract Highlights • Sustainable preparation of mesoporous silica. • ScCO 2 extraction of non-ionic templates. • Fast extraction of the organic template. • Improvement of material crystallinity. • Hydrothermal resistance of mesoporous silica. Abstract We report how we could circumvent two major drawbacks in the potential scale up synthesis of mesoporous silica via the surfactant-based templating route. First, burning the organic templates to free porosity is costly and not environmental friendly. Most of the mesoporous silica materials show also extremely poor resistance to hydrothermal environments. These drawbacks have certainly contributed to prevent these materials meet practical use, and hampered any possible large-scale manufacturing. Unlike previous reports that claimed that supercritical carbon dioxide (scCO 2) was ineffective in removing most of the organic templates, except amines, we describe how the unique synergy we achieved between scCO 2 extraction and our two-step synthesis of mesoporous silica with nonionic templates allowed us to overcome these drawbacks. We conducted different tests, and we report here the preparation of mesoporous materials with tunable pore size between 1 and 10 nm, structure varying from 3D wormhole to hexagonal, and hydrothermal resistance. [ABSTRACT FROM AUTHOR]

The formation of silicate/organic hybrid micelles is an important milestone in the two-step synthesis of mesoporous silica with polyethyleneoxide (PEO) nonionic structure directing agents (C.R. Chimie 8 (2005) 579). Unlike many inorganic/organic hybrid micelles, these objects have the inorganic component as a diffuse layer positioned at the periphery of the initial micelles and interacting with the hydrophilic polyoxyethylene palisade. We studied how this additional inorganic layer can modify the structure and dynamics of micelles prepared with different types of nonionic surfactants using steady-state and time-resolved fluorescence and dynamic light scattering. Our results show that these hybrid micelles still possess a versatile behavior, which allows them to adapt reversibly to temperature changes. This silicate layer tends to stabilize and consolidate the micelle structure, especially close to the cloud point of critical micelle temperature for polypropyleneoxide (PPO)-based triblock copolymers. Their internal structure is only slightly disturbed by the silicate layer, which reduces the molecular exchanges a little bit. Among other results, we managed to elucidate why mesoporous silica prepared with Pluronic P123, according to our synthesis, stands a dramatic structural change from wormhole to hexagonal structure at 40 °C. Our dynamic light scattering study shows that 40 °C is a critical temperature corresponding to a sphere-to-rodlike structural transition of hybrid micelles, which is not observed with pure micelles. [ABSTRACT FROM AUTHOR]

Abstract: The complete understanding of the properties of a material goes in close relationship with a correct description of their structure. This is particularly true for mesoporous silica that exhibits different shapes and sizes of the porous framework as well as different degrees of crosslinking of the silica network itself. These variations can affect drastically the specific properties of these materials as well as their hydrothermal resistance. Hydrothermal resistance and adsorption properties are governed by the surface structure, but the later parameter is not frequently studied because it can be difficult to characterize. Therefore a simple parameter such as surface roughness could be helpful in relating the properties of materials with their surface structure. The direct determination of surface roughness is impossible, but it has been demonstrated that a single mathematical parameter, the surface fractal dimension Ds, can be related within a certain limit with surface roughness. Here we demonstrate using nitrogen adsorption data that a correlation can be drawn between the values of the surface fractal dimension Ds used as a gauge of the surface roughness and the structural evolution of a series of mesoporous silicas. Among the different adsorption models for obtaining Ds that are available nowadays, we selected the one proposed by Avnir and Jaroniec. We demonstrate in this report that there exists a real correlation between the evolution of Ds, when applied to a series of samples prepared under different synthesis conditions, with the evolution of their structure and properties. By example, this study allowed us to link the range of hydrothermal resistance of different mesoporous silicas (e.g. the HMS, MSU, MCM, SBA families of silicas) with their surface roughness. Moreover, we found that HMS silica, a very resistant material toward hydrothermal treatment, exhibits actually the lowest surface roughness. We could demonstrate too how different synthesis parameters such as temperature, can modify this surface roughness, hence the final properties of the mesoporous silica. Finally, we show that this method can even be applied to water ellipsoporometry and help to follow the crystallization of thin layers of metal oxide. Bearing in mind that Ds is a parameter that can readily be determined using the existing software – based on different models – associated with most commercial adsorption equipment, we urge the broader use of the Ds parameter for the structural characterization of surface roughness in mesoporous materials and metal oxide thin layers. [Copyright &y& Elsevier]

Abstract: Magnetic behavior of molecular magnets-based nanocomposite materials was investigated as a function of the molecular materials’ concentration. These materials, made of transition metal ions connected via cyano-bridging ligands, Co3[Fe(CN)6]2, were synthesized simultaneously with MSU-type mesoporous silica as a confinement matrix. This synergetic synthesis led to Co3[Fe(CN)6]2 nanoparticles of ca. 2–3nm. Their magnetic properties were investigated as a function of their concentration. These analyses, including dc and ac vs temperature, as well as frequency measurements, reveal a superspin-glass like transition at low temperature. The aging and memory effects observed demonstrate that the superspin-glass behavior for nanocomposites containing the lowest amount of nanoparticles is due principally to spin frustration on the surface of the nanoparticles while for the nanocomposites containing the largest amount of nanoparticles, both surface spin-frustration and dipolar interparticle interactions influence the magnetic regime. [Copyright &y& Elsevier]

Abstract: We report the singular filtration properties of an ultrafiltration membrane made with mesoporous silica that exhibits cylindrical pores aligned mostly normal to the support. This membrane supported on tubular commercial macroporous alumina supports was prepared by the interfacial growth mechanism between stable silica–surfactant hybrid micelles made of the association of silica oligomers with polyethyleneoxide-based (PEO) surfactants and sodium fluoride, a well-known silica condensation catalyst [Boissière et al., An ultrafiltration membrane made with mesoporous MSU-X silica, Chem. Mater. 15 (2003) 460–463]. It appears that the combined effect of the silica nature of the membrane, whose surface charge can be easily adjusted by changing the pH and the non-connected cylindrical shape of the pores provides a new behavior in the retention properties, as proved by the filtration of polyoxyethylene polymers (PEO) with different molecular weights. Depending on the filtration conditions, a rejection rate of 80% and a steep cut-off at 2000Da can be obtained or, on the reverse, polymers three times bigger than the pore diameter can diffuse through the membrane. This new filtration mechanism, which opens up new modes of separation modes, is explained in the light of both topology of the porous network and pH-dependent interactions between PEO polymers and silica porous media. [Copyright &y& Elsevier]

Abstract: We report the preparation of a novel type of mesoporous silica of the MSU-type family. This material was prepared with Pluronic P123 copolymer in mild acidity according to a two-step process. Its structure was explored by X-ray diffraction, N2 isotherms, SEM and TEM. The TEM study was completed by a 3D tomography analysis that allowed us to obtain information on the morphology of the pore-and-void system. The powder is homogeneous and made of nanoparticles (200 nm in size) built by the folding of ribbons with hexagonally-packed pores (pore diameter of 8.6 nm). This folding creates microvoids in the particles that give rise to an additional porosity. The properties of adsorption/separation of this new type of silica were tested for HPLC. Although the powder was not optimized for this application, the first results on ungrafted silica appear equivalent to those obtained with a commercial HPLC silica powder. To cite this article: M.U. Martines et al., C. R. Chimie 8 (2005). [Copyright &y& Elsevier]