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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: 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 present a general review on the synthesis of mesoporous silica obtained with nonionic surfactants and bloc-copolymers as templates. This silica, referred as MSU silica, was obtained by a two-step process that led to the formation of stable hybrid micelles after a first stage of assembling between silica and surfactants, followed by the fluoride-catalyzed condensation of silica. This process allows some unique features: the final pore size can be adjusted with some synthesis parameters such as temperature or amount of catalyst, the particle shape is spherical and in the micrometric range, different shapes and nanostructures can be achieved, including hexagonal-like frameworks. Finally, we demonstrate how an accurate control of the synthesis itself may allow us to adapt this synthesis for applications dedicated to separation processes, including liquid filtration of HPLC chromatography. To cite this article: É. Prouzet, C. Boissière, C. R. Chimie 8 (2005). [Copyright &y& Elsevier]

A novel technique combining inkjet printing (IJP), evaporation-inducedself-assembly (EISA), and click chemistry is implemented for elaboratingmesoporous silica-based multifunctional microdots arrays. The microdotsare in situ azide-functionalized with (3-azidopropyl)triethoxysilane(AzPTES). AzPTES is directly added to the initial sol before IJP andco-condenses with the silica precursor (TEOS) during the evaporation-inducedself-assembly (EISA) of micelles on the substrate. After extractingthe surfactants to release the porosity, model alkynes, namely propargylalcohol, methyl pent-4-ynoate, ethynylferrocene, and N-propargyl-4-amino-1,8-naphthalimide, are grafted by the azide–alkyneCuAAC click reaction. The demonstration is established that the clickreaction is nearly quantitative and occurs in the whole volume ofthe microdots attesting the accessibility of the azide groups. Byintegrating an alkyne-containing silylated precursor in a similarroute, azide-containing functional groups are anchored in the microdotsby click reaction. A demonstration of the multifunctionalization ofsuch microdots arrays is achieved by reacting clickable dyes on alternatealkyne- and azide-functionalized lines of microdots, as evidencedby confocal fluorescence microscopy. Such multifunctional mesoporoussilica microdots arrays offer promising perspectives for biosensingapplications. [ABSTRACT FROM AUTHOR]

A comparative study of the degradation in a model phosphatebufferedsaline (PBS) medium of mesoporous mixed silica–zirconia oxidesand hybrid organosilica materials is reported, and their thermodynamicand kinetic stability are discussed. Thin film morphology was usedto monitor the degradation rates of all these materials for the firsttime directly in liquid and undersaturated medium. The introductionof zirconium centers in mesoporous materials strongly inhibits degradationand allowed the self-limitation of soluble silica concentration inthe immediate environment of the vector. This avoids renucleationof potentially toxic silica small nanoparticles with uncontrolledsurface chemistry in the release medium. Chemical modifications (hybridationor zirconia doping) of mesoporous silica allow the fine-tuning ofits degradation from hours to days. Methylated thin films are highlystable when the functionalization ratio is high (50%). The hybridationby mercaptopropyl and aminopropyl moieties can be successfully performedwithout any high thermal treatment, allowing not only slowing downsilica dissolution but also opening the possibility to introduce inone-pot other thermally fragile molecules into the vector. Dissolutionrates K measured for the first time at different biologically relevanttemperatures follows an Arrhenius law: K= KoExp(−Ea/RT). Stabilities of these chemically modified silicas aremainly associated with a strong decrease of the pre-exponential factor K0of modified silicas. Counterintuitively, activationenergies Eadecrease with increasing thehybrid/silica or the zirconia/silica ratios. [ABSTRACT FROM AUTHOR]

Abstract: Solid-state NMR methods based on dipolar and J-derived experiments such as CP, MAS-J-HMQC and MAS-J-INEPT MAS have been developed in the frame of the {31P,29Si} spin pair. The potential of these techniques has been demonstrated using model compounds including crystalline silicophosphate phases (Si5O(PO4)6 and various SiP2O7 polymorphs). Spatial interactions as well as through-bond connectivities were established. Evaluation of isotropic 2 J P–O–Si coupling constants has been established by careful analysis of the HMQC and INEPT build-up curves under fast MAS. The efficiency of the 31P→ 29Si CP MAS experiment for the detailed characterization of Si–O–P mesoporous materials (at low temperature) was demonstrated. The incorporation of P atoms in the silica network has been proved unambiguously. Such materials could be appropriate for biocompatibility purposes. [Copyright &y& Elsevier]