A mechanistic study of photo-oxidation of phenol and AB92 by AgBr/TiO2

The energy levels of semiconductors can be modified so that they selectively interact with any desirable chemicals. In this study, AgBr/TiO2 is used for selective oxidation of two well-known organic pollutants, phenol and acid blue 92, in the visible and ultraviolet regions. The results show that phenol is only degraded in the ultraviolet, but acid blue 92 can be degraded in both ultraviolet and visible regions. In the ultraviolet region, phenol is degraded by OH radicals, produced by the hole in the valence band of TiO2. In the visible region, the holes generated by the valence band (VB) of AgBr play the main role in acid blue 92 degradation. However, they are not strong enough to oxidize phenol. Also, periodic DFT calculations are performed to study electronic structures of AgBr and TiO2 and elucidate their different photo-oxidation mechanisms. Theoretical data indicates that the reduction potential of a hole in the valence band of AgBr could not generate OH radicals, and thus is unable to oxidize phenol in the visible region. On the other hand, the reduction potential of a valence band hole in TiO2 is more positive and could readily generate OH radicals to degrade phenol in the ultraviolet region. This study implies that AgBr/TiO2 can selectivity oxidize compounds with lower oxidizability, when exposed to the visible region, and higher oxidizability, when the ultraviolet region is applied.