Filtered air (relative humidity ) 9-10%) containing methanol was flown through a cold plasma reactor connected to a photocatalytic reactor. The results showed a synergetic effect between the two purifying technologies, which is principally attributed to plasma-generated O 3 benefiting the photocatalytic process.

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We have investigated the effects of the TiO 2 type and coating method, two important factors for TiO 2 -based photocatalytic purification/deodorization of air. First, two TiO 2 powders (PC500 and 105) designed by Millennium Chemicals for photocatalysis were compared with Degussa P25 TiO 2 , a common reference, for removing methanol or n-octane in a flowing dry mixture of O 2 (20 v/v %) and N 2 . 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 O 2 + N 2 mixture in a batch reactor. Increasing the SiO 2 wt % from 20 to 50, at equal mass of TiO 2 + SiO 2 , 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).

Comparing the UV-A photocatalytic treatment of bioaerosols contaminated with different airborne microorganisms such as L. pneumophila bacteria, T2 bacteriophage viruses and B. atrophaeus bacterial spores, pointed out a decontamination sensitivity following the bacteria > virus > bacterial spore ranking order, differing from that obtained for liquid-phase or surface UV-A photocatalytic disinfection. First-principles CFD investigation applied to a model annular photoreactor evidenced that larger the microorganism size, higher the hit probability with the photocatalytic surfaces. Applied to a commercial photocatalytic purifier case-study, the CFD calculations showed that the performances of the studied purifier could strongly benefit from rational reactor design engineering. The results obtained highlighted the required necessity to specifically investigate the removal of airborne microorganisms in terms of reactor design, and not to simply transpose the results obtained from studies performed toward chemical pollutants, especially for a successful commercial implementation of air decontamination photoreactors. This illustrated the importance of the aerodynamics in air decontamination, directly resulting from the microorganism morphology.

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