Acta Astronautica | 2021
Influence of vacuum environment on photocatalytic degradation of methyl red by TiO2 thin film
Abstract
Abstract Photocatalysis has the potential to solve the contamination problem for spacecrafts in orbit. The atmosphere surrounding photocatalysts affects their photocatalytic activity. In this paper, decomposition tests of methyl red (MR) under vacuum condition were conducted to investigate the effects of vacuum on basic photocatalytic activity of titanium dioxide (TiO 2 ). TiO 2 thin films were fabricated on quartz glass and indium-tin oxide (ITO) substrates by a sol–gel method. The TiO 2 samples, coated with MR, were irradiated with UV rays in vacuum, and their absorbance spectra were measured. Moreover, mass change of MR and gas chromatography mass spectrometry were measured using TiO 2 powder to investigate intermediate materials (IMs) generated from decomposed MR. In vacuum, TiO 2 /quartz glass could decompose MR to IMs but could not further decompose the IMs. To investigate which roles of H 2 O and oxygen molecules lead to this result, decomposition experiments, using TiO 2 /ITO and TiO 2 /ITO filled with oxygen vacancies, were performed. The results indicated that TiO 2 cannot decompose IMs in vacuum due to the lack of active oxygen species and/or radical chain reaction of oxygen molecules.