The current work explores the reaction mechanism of carbon contaminant photocatalytic decomposition on anatase TiO2 under starved oxygen conditions using Fourier-transform infrared spectroscopy (FTIR) and in situ X-ray photoelectron spectroscopy (XPS) coupled with a 375 nm UV laser diode. The reaction stoichiometry of reactions stimulated by UV photons at various irradiation intensities within the natural sunlight spectral range were estimated. The in situ FTIR spectral changes associated with a non-UV treated TiO2 sample and a 2-hour UV-treated TiO2 sample under evacuated conditions showed the decomposition of carbon contaminant species with the consumption of adsorbed water/hydroxyls and the formation of carboxyl (HO-C=O) carbon species and isolated surface hydroxyls. The UV photodecomposition of carbon species and the concomitant consumption of oxygen species was also observed by tracking the XPS spectral change of a UV-irradiated area compared to a dark reference spot on the same specimen. Eight different reaction cases at four different UV intensities within the natural sunlight spectral range, repeated twice each, were investigated using separate pieces of the same TiO2 media. The measured stoichiometry for the decomposition of carbon species and consumption of oxygen species ranged from 0.53 during the first 20 minutes of UV irradiation and increased to 0.65 with an average value of 0.59 and a standard deviation of 0.11. These data suggest that the reaction product and leaving group from the TiO2 surface is primarily CO2 during the first 20 minutes of initial reaction with perhaps a small fraction of CO toward the end of the reaction. A second-order dependence on the UV irradiation intensity was also observed, which potentially indicated the UV-induced desorption and diffusion of H2O/hydroxyls to the sample surface is the key step for the reaction mechanism.

XPS and FTIR investigation of UV-induced catalytic decomposition of carbon contaminants on anatase TiO2 in starved oxygen environments

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.