Photocatalytic Treatment of Air: Comparison of Various TiO2, Coating Methods, and Supports Using Methanol or n-Octane as Test Pollutant

We have investigated the effects of the TiO2 type and coating method, two important factors for TiO2-based photocatalytic purification/deodorization of air. First, two TiO2 powders (PC500 and 105) designed by Millennium Chemicals for photocatalysis were compared with Degussa P25 TiO2, a common reference, for removing methanol or n-octane in a flowing dry mixture of O2 (20 v/v %) and N2. Under the conditions used, the differences were very small. For methanol mineralization, PC500 (the highest surface area sample) was, however, more efficient, which is attributed to increased adsorption of methanal (main intermediate product). Second, PC500 and 105 coated on a fibrous tissue (Ahlstrom) using a silica binder were tested for removing methanol in the O2 + N2 mixture in a batch reactor. Increasing the SiO2 wt % from 20 to 50, at equal mass of TiO2 + SiO2, was detrimental but not markedly, and the interest of using PC500 preferentially to PC105 to mineralize methanol was confirmed. Third, experimental design was used to optimize the thickness and quality of P25 coatings on quartz (or similarly on aluminum), which were obtained by several dipping/drying steps followed by a final calcination. For the optimized coatings, methanol or n-octane disappearance (batch reactor) and mineralization reached a maximum for three dip-coating steps (ca. 0.6 μm coating thickness, likely corresponding to UV light maximum penetration depth).