Influence of Morphology and Crystallinity on Surface Reactivity of Nanosized Anatase TiO2Studied by Adsorption Techniques. 1. The Use of Gaseous Molecular Probes

Various titanium dioxide nanoparticles were prepared by sol–gel method in order to obtain samples showing different sizes and morphologies. An original approach based on the adsorption of gaseous molecules from the gas phase was proposed to gain information about surface energy of nanosized TiO2anatase in terms of interfacial reactivity and heterogeneity. Argon, nitrogen, and ammonia were selected as such surface molecular probes. The mainly observed crystallographic faces of anatase particles were the {101} and {001} surfaces together with the {100} one. Their abundance was correlated with the energy distribution inferred from the local isotherms of argon adsorption in the low-pressure range. The acid character of the anatase surface was probed by nitrogen molecules, and, consequently, the location of polar sites on the particle surface could be determined in correlation with the argon adsorption domains. Moreover, the number and the strength of surface acid sites were evaluated with the aid of two-cycle adsorption of gaseous ammonia supplemented by appropriate flow microcalorimetry measurements. This molecular probe revealed significant differences among the samples depending on their crystal shape or face distribution.