Patrick Euzen

Size tailoring of oxide nanoparticles by precipitation in aqueous medium. A semi-quantitative modelling

Chemistry in aqueous solution is an easy and versatile method to form nanosized metal oxide particles. Considering our previous results on magnetite Fe3O4, anatase TiO2, brucite Mg(OH)2, and boehmite γ-AlOOH, we show that the strict control of the physicochemical conditions of the precipitation, essentially the acidity and ionic strength in the absence of complexing species, enables the tailoring of the particle size in the range 2–15 nm and, in some cases, of their morphology. We show that the variations in size and/or shape are tightly related to the variation of the electrostatic surface charge density of the particles, which induces a variation of the oxide-solution interfacial tension, and, consequently, a decrease of the surface energy. Such an effect enables the control of the surface area of the system. A semi-quantitative model is presented, which accounts for the effects observed for particles isotropic or anisotropic in shape.

Hexagonally organised mesoporous aluminium–oxo–hydroxide thin films prepared by the template approach. In situ study of the structural formation

Mesoporous organised aluminium oxide based thin films have been prepared by combining the dip-coating method, the sol–gel chemistry and the template approach. The oxide network is composed of aligned-with-the-surface cylindrical pores compacted in the 2D-hexagonal p6m space group. AlCl3 has been chosen as precursor and Brij 58 was used as structuring agent. Once deposited, films were treated to eliminate the organic surfactant and to stiffen the inorganic oxide structure. The final films are around 100 nm thick, exhibit an overall excellent optical quality, and undergo a contraction that transforms the hexagonal p6m original mesostructure into a centred rectangular c2m one, without significantly altering the degree of pore organisation. The structure was deduced from TEM and XRD in θ–2θ and transmission modes. The time-resolved formation of the film and the structure was simultaneously followed by in situ SAXS (synchrotron radiation) and interferometry. XRD, FTIR, 27Al NMR and RBS analyses allowed characterisation of the chemical composition of the present system at different stages of its evolution. This work shows that the meso-organisation is highly humidity dependent and that as-prepared hybrid films present a significant flexibility.