Role of the Hydroxyl Groups Coordinated toTiO 2 Surface on the Photocatalytic Decomposition of Ethylene at Different Ambient Conditions.

The titania pulp—a semi product received from the industrial production of titania white—was submitted for the thermal heating at 400–600 °C under Ar and H₂ to obtain TiO₂ with different structure and oxygen surface defects. Heating of titania in H₂ atmosphere accelerated dehydration and crystallisation of TiO₂ compared to heating in Ar. TiO₂ prepared at 500 and 600 °C under H₂ had some oxygen vacancies and Ti³⁺ centres (electron traps), whereas TiO₂ obtained at 450 °C under H₂ exhibited some hole traps centres. The presence of oxygen vacancies induced adsorption of atmospheric CO₂. It was evidenced, that ethylene reacted with TiO₂ after UV irradiation. Formic acid was identified on TiO₂ surface as the reaction product of ethylene oxidation. Hydroxyl radicals were involved in complete mineralisation of ethylene. TiO₂ prepared at 500 °C under H₂ was poorly active because some active sites for coordination of ethylene molecules were occupied by CO₂. The most active samples were TiO₂ with high quantity of OH terminal groups. At 50 °C, the physically adsorbed water molecules on titania surface were desorbed, and then photocatalytic decomposition of ethylene was more efficient. TiO₂ with high quantity of chemisorbed OH groups was very active for ethylene decomposition. The acidic surface of TiO₂ enhances its hydroxylation. Therefore, it is stated that TiO₂ having acidic active sites can be an excellent photocatalyst for ethylene decomposition under UV light. [ABSTRACT FROM AUTHOR]