Differential reactivity of rutile and anatase TiO2 nanoparticles: synthesis and surface states of nanoparticles of mixed valence Magnéli oxides
Résumé
Magnéli phases TinO2n-1 (3 < n ≤ 10) are mixed Ti 4+ /Ti 3+ oxides with high electrical conductivity. When used for water remediation or electrochemical energy storage and conversion, they are nanostructured and exposed to various environments. Therefore, understanding their surface reactivity is of prime importance. Such studies have been hindered by carbon contamination from syntheses. Herein we address this synthetic and characterization challenge through a new approach towards 50 nm carbon-free Ti4O7 and Ti6O11 nanoparticles. To do so, we take advantage of the different reactivities of rutile and anatase TiO2 nanoparticles versus H2, to use the former as precursors of TinO2n-1 and the latter as diluting agents. This approach is combined to silica templating in order to restrain particles growth. The surface reactivity of the Magnéli nanoparticles under different atmospheres was then evaluated quantitatively with synchrotron radiation-based X-ray photoelectron spectroscopy, highlighting oxidized surfaces with lower conductivity than the core. This finding sheds a new light on the charge transfer occuring in these materials.
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