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

Abstract

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).

Gas phase oxidation of n-decane and PCE by photocatalysis using an annular photoreactor packed with a monolithic catalytic bed coated with P25 and PC500

“…In the absence of any synergistic effect between the anatase and rutile mixed TiO 2 phases, it is accepted that anatase is much more active than rutile in the PCO of organic compounds in water and air [43]. Even considering that the smaller crystal size of PC500 (Table 1) may foresee higher density in surface defects [19] reducing the electron-hole recombination time, which ultimately results in lower photocatalytic efficiencies, the larger surface area of PC500 in comparison to P25 which may be related to the higher adsorption capacity may justify the superior activity of PC500 [34,43,44].…”

“…The superior photocatalytic activity of PC500 was attributed to its higher specific surface area (SSA). Taranto et al [19] also reported a slight higher photocatalytic activity of P25 over PC500 in the degradation of methanol and n-octane as gas-phase model pollutants. In another study conducted by Águia et al [13], ten distinct commercially available photocatalysts were incorporated into a water-based exterior paint aiming NO photoabatement.…”

Evaluation of a solar/UV annular pilot scale reactor for 24h continuous photocatalytic oxidation of n-decane

“…This relates to the specific surface areas of PC500 and P25 powders (Table 1). Although the crystal size of PC500 is smaller than that of P25 (which may foresee higher density in surface defects [29] and reduce electron-hole recombination time), the larger surface area of PC500 may be related to the higher adsorption capacity, and can justify the superior photocatalytic activity of PC500 [28,30,31].…”

Comparison of the photoelectrochemical oxidation of methanol on rutile TiO2 (001) and (100) single crystal faces studied by intensity modulated photocurrent spectroscopy

“…Methanol was chosen as a typical model substance for organic pollutants. [27][28][29] The IMPS measurements have been performed in aqueous electrolytes under variation of the methanol content and the electrode potential, which are expected to be the factors most strongly influencing charge transfer and recombination at the surface. The results reveal quite significant differences between the two surfaces concerning the dominating mechanism of photooxidation, leading to significantly different rate constants for water and methanol photooxidation.…”