Abstract
In this study, we deposited TiO2 thin films onto borosilicate glass by ultrasonic spray pyrolysis at 350 and 450 °C. The aim of study is to determine the effect of deposition temperature on photocatalytic activity of TiO2 thin films and to investigate the performance of TiO2 thin films on photocatalytic degradation of methyl tert-butyl ether (MTBE), acetone, acetaldehyde, and heptane as functions of different operating parameters. TiO2 thin films deposited at 350 and 450 °C have a thickness value of 190 and 330 nm, respectively. All as-prepared TiO2 films possess an anatase crystalline structure. According to the X-ray photon spectroscopy (XPS) study, the TiO2 thin film deposited at 350 °C showed a higher amount of oxygen vacancies and hydroxyl groups on the film surface after UV treatment. The aged-TiO2 thin film deposited at 350 °C showed a water contact angle (WCA) value of 0° after 10 min UV irradiation, showing superhydrophilic surface behavior. The TiO2 film deposited at 350 °C exhibited the highest amount of conversion of MTBE (100%). The results also showed that TiO2 films are capable of photocatalytic degradation of MTBE (100%) and acetaldehyde (approx. 80%) in humid air conditions and high airflow rate. The visible-light-activity of TiO2 thin films was tested with 5 ppm MTBE and acetone. TiO2 thin films deposited at 350 °C with a surface area of 600 cm2 showed 60% of MTBE and 33% of acetone degradation under VIS light.
Highlights
Volatile organic compounds (VOCs) are the most common air pollutants, which are present in both indoor and outdoor air
The results showed that TiO2 films are capable of photocatalytic degradation of Methyl tert-butyl ether (MTBE) (100%) and acetaldehyde in humid air conditions and high airflow rate
The higher photocatalytic activity of TiO2 thin film deposited at 350 ◦ C can be ascribed to several factors including the surface morphology, higher level of oxygen vacancy defects, and OH− groups on the film surface compared to the samples deposited at 450 ◦ C (Table 1)
Summary
Volatile organic compounds (VOCs) are the most common air pollutants, which are present in both indoor and outdoor air. The most widely studied semiconductor materials as photocatalysts in air treatment systems are commercial TiO2 nanopowders such as P25, UV100, PC105, and PC500 and coatings prepared by those powders [8,9,10,11] These are expected to have a high photocatalytic activity for gas-phase pollutant degradation due to their large available surface area. The most common non-vacuum technique that was used to fabricate TiO2 thin films for photocatalytic applications is the sol–gel method (Supplementary Materials Table S1). Despite the several advantages of USP-synthesized thin films, no publications on the decomposition of VOCs such as acetone, acetaldehyde, and heptane on transparent TiO2 thin films fabricated by USP reporting their photocatalytic activity regarding the materials characteristics were found available; this study supplies more insights into this topic. MTBE, acetone, acetaldehyde, and heptane were individually used to evaluate the photocatalytic activity for gas-phase reactions in the multi-section plug-flow reactor
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