Influence of humidity on the photo-catalytic degradation of acetaldehyde over TiO2 surface under UV light irradiation

- Higher humidity level decreased the photo-catalytic mineralization of acetaldehyde.
- The total mineralization of acetaldehyde was majorly mediated by O2.
- Water vapor was competitively adsorbed on TiO2 surface with acetaldehyde and O2.
- Water molecules inhibited the adsorption of the acetaldehyde and O2.
- Active sites ensemble promoted the total mineralization of acetaldehyde.

We have studied the influence of water vapors on the activity of the photo-catalytic oxidation of acetaldehyde on the surface of TiO2 film under UV light (365 nm) irradiation. Photo-catalysis experiments were performed at atmospheric conditions under various humidity levels (0, 16.8, and 33.6 relative humidity%) using a high vacuum chamber equipped with online gas-chromatography as a batch-type reactor. Acetaldehyde and H2O molecules competitively adsorbed on the surface of TiO2 film and the increase in the humidity decreased both the acetaldehyde removal and CO2 evolution rates. The rate of CO2 evolution was even more influenced by the humidity level of the gas mixture compared to the acetaldehyde removal rate, particularly over the certain level of relative humidity. We evidenced that the total oxidation of acetaldehyde was majorly mediated by oxygen molecules rather than H2O vapor under our experimental conditions. It is suggested that photo-catalytic total oxidation of acetaldehyde was promoted by the presence of large active sites ensemble near the adsorbed acetaldehyde, which were available to oxygen. Increase of humidity level disturbed this large ensemble, resulting in the reduction of photo-catalytic degradation rate of acetaldehyde under UV light irradiation.

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