Titanium dioxide is widely used as a photocatalyst, mostly in its pulverulent form. The use of powders presents the advantage of a great surface contact between the catalyst and reactants; however, it generates other problems : catalyst recovering, particles agglomeration...
We present two different syntheses routes leading to TiO₂ nanoscaled particles, arranged in a tubular shape or supported on carbon fibers. Particles were obtained either by impregnation of a carbon substrate in a precursor solution or by chemical vapor deposition of the precursor on the substrate, both followed by heating treatments.
The immersion of carbon fibers (rough felt - Mitsubishi, surface area 10 m² g^-1) in a 0.09 mol L^-1 TiCl₄ solution in n-hexane led to the formation of a 200 nm titanium oxichloride layer covering nearly the whole surface of the fibers. Its conversion into TiO₂ was achieved after hydrolysis (air - H₂O, 400C, 15 hours). The surface area of the resulting material was considerably increased and reached 700 m² g^-1. A complete oxidation of the carbon fibers occurred after calcination under air at 600C for 4 hours. The surface area of obtained TiO₂ tubes was 15 m² g^-1. X-ray diffraction analyses showed the presence of a mixture of both rutile and anatase varieties (ca. 90 wt. % of anatase).
The second synthesis route consists in the deposition of TiCl₄ on the fibers by CVD. When TiCl₄ was directly vaporized on the carbon fibers (Ar, 350C), a non adherent TiO₂ layer composed of nanoscaled particles (200 nm) was formed. The adhesion of the layer was reached by first covering the fibers by a POCl₃ layer (Ar, 350C) or by activation (H₂O - air, 350C) prior to the deposition of TiCl₄. After conversion (air, 400C), nanoscaled adherent TiO₂ particles (100 nm) covering the whole surface of the fibers were observed. Samples were characterized by SEM, EDS and XRD. They will find their main applications as photocatalysts or gas sensors.
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1. Synthesis of nanoscaled oxides and metals with various shapes : powder, tubes or plates.