Substrate-specific mineralization and deactivation behaviors of TiO2 as an air-cleaning photocatalyst

Volatile organic compounds (VOCs) having the same number of carbon atoms with different functional groups were selected to investigate the substrate-specific mineralization and deactivation behaviors of TiO2. The mineralization rate of VOCs decreased in the order of n-propylaldehyde > n-propanol > > n-propylamine > npropanethiol > n-chloropropane, which indicates that the presence of heteroatoms significantly retards the mineralization rate. The mineralization of tested VOCs is closely related to the efficient production of aldehydes as intermediates. During the PCD, the formation of carbonaceous deposits on the TiO2 surface was observed, which was the most significant with n-propylamine, much less with other VOCs, and negligible with n-chloropropane. The repeated PCD cycles of n-propylamine and n-propanethiol caused the significant deactivation of TiO2, while those of other VOCs little reduced their PCD activity. The photocatalyst deactivation is associated with the deposition of non-volatile products on the TiO2 surface such as carbonaceous residues, ammoniums, and sulfates.