Chemical vapor infiltration of photocatalytically active TiO2 thin films on glass microfibers

Abstract : Due to the high diffusivity of the chemical species, chemical vapor infiltration (CVI) is a suitable process for the conformal coverage of objects with large dimensions and complex shape geometry. Its large scale capacity and high reproducibility have made the technique favorable for the deposition of non-oxide ceramics. There are few works on other materials and metal-organic compounds are rarely used as molecular precursors. In this study we focus on the deposition of anatase thin films on substrates with large surface area (microfibers) for photocatalytic air treatment systems. Titanium tetra-isopropoxide (TTIP) was used as precursor without additional oxygen source. Using low mole fractions (26-124×10−5) and low deposition temperatures (300-400 °C), a relatively good thickness uniformity was obtained along the reactor axis. Infiltration experiments were achieved in this temperature range and under 1 Torr for high TTIP diffusivity (110-146 cm2 s−1) and low initial Thiele modulus (0.11-0.13) values. Photocatalytic activity of TiO2 coated glass microfiber samples depends on the film morphology, average thickness and infiltration efficiency. It is shown that this later parameter plays a major role due to the increase of active surface area.