Iron promotion of the TiO2 photosensitization process towards the photocatalytic oxidation of azo dyes under solar-simulated light irradiation

The photocatalytic oxidation of the azo dye Orange-II (Or-II) using Fe loaded TiO2 (Fe–TiO2) was studied under ultraviolet (UV), visible (vis) and simultaneous UV–vis irradiations using a solar light simulator. Photocatalysts were characterized by means of XRD, SEM-EDX, FTIR and DRS. Fe3+ species, identified in XPS analyses, were responsible of the increased absorption of visible light. Moreover, DRS analyses showed a decrease in the bandgap due to Fe3+ loading. Photocatalystic tests proved that Fe modification enhanced the TiO2 photocatalytic activity towards Or-II photodegradation under simultaneous UV–vis irradiation. Even so, the performance of the Fe–TiO2 samples towards the photodegradation of phenol, under UV irradiation, was lower than TiO2 suggesting the recombination of the UV photogenerated electron–hole pair. Therefore, results evidence a Fe3+ promotion of the electron caption in the photosensitization process of TiO2 by Or-II acting as a sensitizer. Such process leads to the Or-II photooxidation under UV–vis irradiation by losing energy in electron transferring processes to sensitize TiO2, and, the formation of reactive oxygen species promoted by the injected electron to the TiO2 conduction band.

► Azo dye photooxidation occurs under strict combination of ultraviolet and visible irradiation of Fe–TiO2.
► Fe3+ enhances the TiO2 photooxidation of azo dyes while decreases that of phenol.
► UV irradiation leads to a decrease in photooxidation activity of Fe–TiO2 photocatalysts.