Influence of TiO2 hydrophilicity on the photocatalytic decomposition of gaseous acetaldehyde in a circulated flow reactor

The raw titania pulp was heated from 350 up to 700 °C and the impact of TiO2 properties on the photocatalytic decomposition of acetaldehyde under UV–Vis light was investigated. The physico-chemical parameters such as BET surface area, extent of surface hydroxylation, phase composition and size of TiO2 crystallites, were measured. It appeared that low-hydroxylated TiO2 prepared at 400 °C with relatively high BET surface area (106 m2/g) and the crystallized anatase phase was the most active for the acetaldehyde decomposition. High hydroxylation of TiO2 surface and the presence of amorphous TiO2 slowed down the photocatalytic process in the gas phase. On the other hand, high concentration of OH groups on TiO2 surface favored the generation of a high amount of OH radicals in an aqueous environment under UV irradiation. A sufficient amount of hydroxyl groups adsorbed on TiO2 surface is needed to facilitate electron–hole separation and OH radicals formation. On the other hand, an excessive content of these groups results in the creation of a barrier for adsorption of acetaldehyde and thus deteriorates photocatalytic process. Additionally, the high concentration of hydroxyl groups on TiO2 surface could accelerate recombination of radicals and reduce its photocatalytic efficiency in the gas phase.