Inherent rate constants and humidity impact factors of anatase TiO2 film in photocatalytic removal of formaldehyde from air

• Photocatalytic reaction rate constant as a function of I and humidity was built.
• The inherent (light intensity- and humidity-independent) rate constant was derived.
• Humidity effect on photocatalytic rate is quantified by humidity impact factor.
• The zero-sum effect of humidity in the medium humidity regime was observed.
• Three typical commercially UVC and UVA lamps were compared.

In photocatalytic oxidation (PCO) of volatile organic compounds (VOCs), even if using the same UV lamp, reaction rate constant of a photocatalyst denoted as k(I,H)Lampk(I,H)Lamp is still affected by operation conditions of light intensity (I) and humidity. It is of great significance to find characteristic parameters of photocatalysts, which excludes the effect of above-mentioned operation conditions and enables direct comparisons of photocatalysts. For this purpose, PCO of formaldehyde in synthetic air in a continuous-flow reactor over transparent films of anatase TiO2 was investigated using three commercially available UV lamps, i.e. UVC, UVA black (UVA1) and UVA white (UVA2). Thereby, inherent rate constant (kLampkLamp) that is only related to the wavelength of UV lamp but independent of light intensity and humidity was found. It suggested that a sequence of kLampkLamp under the three UV lamps, kUVCkUVC >> kUVA1kUVA1 ∼ kUVA2kUVA2, which, for instance, are 1.6, 0.33 and 0.26 cm2 s−1 mW−1 at low light intensity, respectively. Moreover, humidity impact factor (fH  ) is approximately 3, 0 and −0.4 in three regimes of low, medium and high humidity (LH, MH, and HH), respectively, which manifests positive, zero-sum and negative effects of humidity on the PCO reaction rate. The zero-sum effect of humidity in the MH regime was observed for the first time. Finally, a generalized and quantitative relationship to express k(I,H)Lampk(I,H)Lamp as a function of I and humidity was built.

Figure optionsDownload as PowerPoint slide