Abstract
TiO2 was placed in heat-treatment at the temperature of 400–500 °C under flow of hydrogen gas in order to introduce some titania surface defects. It was observed that hole centers in TiO2 were created during its heat treatment up to 450 °C, whereas at 500 °C some Ti3+ electron surface defects appeared. The type of titania surface defects had a great impact on the mechanism of acetaldehyde decomposition under irradiation of artificial visible light. Formation of O•− defects improved both acetaldehyde decomposition and mineralization due to the increased oxidation of adsorbed acetaldehyde molecules by holes. Contrary to that, the presence of electron traps and oxygen vacancies in titania (Ti3+ centers) was detrimental for its photocatalytic properties towards acetaldehyde decomposition. It was proved that transformation of acetaldehyde on the TiO2 with Ti3+ defects proceeded through formation of butene complexes, similar as on rutile-type TiO2. Formed acetic acid, upon further oxidation of butene complexes, was strongly bound with the titania surface and showed high stability under photocatalytic process. Therefore, titania sample heat-treated with H2 at 500 °C showed much lower photocatalytic activity than that prepared at 450 °C. This study indicated the great impact of titania surface defects (hole traps) in the oxidation of acetaldehyde and opposed one in the case of defects in the form of Ti3+ and oxygen vacancies. Oxidation abilities of TiO2 seem to be important in the photocatalytic decomposition of volatile organic compounds (VOCs) such as acetaldehyde.
Highlights
The photocatalytic purification of air from volatile organic compounds (VOCs) has been an interesting subject of study for many research groups [1–3]
We have proved that the presence of both oxygen vacancies and Ti3+ centers formed in TiO2 upon ammonia modification were detrimental for acetaldehyde decomposition [17]
Titania pulp was used as a source of TiO2, which was received from the Chemical factory “Police” S.A
Summary
The photocatalytic purification of air from volatile organic compounds (VOCs) has been an interesting subject of study for many research groups [1–3]. A. Fujishima published many papers related to the photocatalytic properties of TiO2 towards environmental cleanup [5–7]. Fujishima published many papers related to the photocatalytic properties of TiO2 towards environmental cleanup [5–7] They proposed the mechanism of acetaldehyde decomposition, which involved radical-initiated chain reactions with oxygen consumption [5]. They noticed that adsorbed molecules could react with photogenerated holes and contribute in the suppressing of recombination of free charges. They reported that formed holes (h+) mediated in the reaction of carbonyl radicals formation, according to the reaction [8]: CH3CHO + O2 + h+ → 2 CH3COOH + CH3CO + H+
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