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Membranes are vital and touch every aspect of our daily lives. For instance, they ensure that clean or pure drinking water can be produced, or they can purify our air. However, there is no one-membrane material that can perform all these objectives, and they must be catered for each specific application. As more traditional membrane materials are either polymer based or inorganic/ceramic based, each application will require a different material that can use one or both of these components. Currently, much research is dedicated to combining both polymer and inorganic based materials to form hybrid membranes that could “have the best of both worlds”. The most common form of hybrid membranes are mixed matrix membranes, or MMM. However, their synthesis normally involves the direct addition of inorganic particles into an existing polymeric solution, leading to composite materials without strong interaction between organic and inorganic moieties. In this work, we explore the reversal of this process; that is, the formation of the polymeric component directly from the surface of these particles using surface-initiated atom-transfer radical polymerization, or si-ATRP. Such a method intends to provide a high intimacy between polymers and ceramics, and strong interconnection via covalent bonds. Using a latex based solution of these functionalized titania particles, we present two pathways, known as “Coating Onto” and “Grafting From” pathways, in which these latexes can be applied to larger, tubular membrane coatings. These latexes were first analyzed by TGA to determine their functionalization densities and degree of polymerization. SEM was then employed to visually assess the membrane surfaces to determine the final optimal conditions used for preliminary gas separation tests. [ABSTRACT FROM AUTHOR]

Abstract: We used a new synthesis of TiO2 anatase 6nm nanocrystals prepared at room temperature (Hegazy and Prouzet, 2012 [10]) to explore the influence of different physical-chemical parameters on photocatalysis, and bench-tested the material against two commercial powders made of either pure anatase (Sigma™), or composite anatase–rutile particles (P25 Degussa™). The initial as-synthesised material demonstrates a low photocatalytic activity, which is greatly improved after thermal activation as a result of improved crystallinity without any drastic change in crystal size. The influence of several other parameters was studied, the resulting tests being compared with commercial products. The cumulative improvement provided by these different parameters led finally to a material that exhibits a higher photocatalysis compared to commercial anatase, and similar to the commercial material usually used for reference (P25). This study, which can apply to other titania materials, illustrates how the post-treatment and process adaptation can help to optimise an initial material. [Copyright &y& Elsevier]

The photocatalytic properties of titanium dioxide depend not only on its electronic properties, but also on the material size and shape, which can increase interactions between the reactants and catalyst. Most studies to date show that reducing the particle size down to the nanoscale increases photocatalytic efficiency, as a result of a higher surface to volume ratio and because a larger proportion of the material is actually irradiated by light. We demonstrate that a multiscale shape design, which integrates surface roughness, particle shape, and 1D material processing and orientation, can favor photocatalytic properties in the solid-gas regime, especially mineralization (conversion into CO2), when the hierarchical 1D orientation of the material is combined with unidirectional gas flow. Several materials with hierarchical structure were prepared and characterized. They have been tested for the photocatalytic mineralization of gaseous acetone and compared with commercial catalysts. Our study reveals that a suitable combination of multiscale design and optimization of the material orientation and gas flow favors high mineralization. [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]