Spray-Pyrolysis Synthesised TiO₂ Thin Films for Photocatalytic Air Treatment from Volatile Organic Compounds ^†

A wide range of mixtures of volatile organic compounds (VOCs), which are present in indoor air in low concentrations, can strongly affect human health. Therefore, the scientific interest in photocatalytic oxidation as a cost-effective and efficient technology for the removal of VOCs from indoor air is growing. The aim of the study was to deposit TiO₂ thin films by ultrasonic spray pyrolysis with different titanium isopropoxide (TTIP)/acetylacetone (AcacH) molar ratios in the spray solution. Other objectives were to determine the optimal TTIP:AcacH ratio and to study the ability of the film to purify air from VOCs under different experimental conditions. TiO₂ films were deposited onto the borosilicate glass at 350 °C and heat-treated at 500 °C for 1 h. The TTIP:AcacH molar ratio in spray solution varied from 1:1 to 1:20. At first, the photocatalytic activity of all obtained films was estimated by the degradation of 8.8 mM stearic acid (SA) deposited on top of the film [1]. In the second step of the studies, TiO₂ films were tested for the oxidation of VOCs (acetone, acetaldehyde, heptane and toluene) as separate pollutants in the concentration ranges 5–40 ppm [2] and as 9 ppm VOCs mixtures [3]. The oxidation of VOCs was studied in the gas-phase, multi-section reactor under ultraviolet and visible light. An increase in the amount of AcacH in the spray solution enhanced the photocatalytic performance of the films due to the carbon incorporation and changes in electronic structure. The reaction rate constant of SA oxidation on the film with the TTIP:AcacH molar ratio 1:8 was 10 times higher than that of the 1:3 film. The TiO₂ film with a molar ratio of 1:8 showed a promising ability in VOCs’ degradation, oxidizing up to 9 ppm VOCs mixtures at 1.5 min at catalyst surface areas of 600 cm² under ultraviolet, and up to 90% of the mixture under visible light.