Ce ion surface-modified TiO2 aerogel powders: a comprehensive study of their excellent photocatalytic efficiency in organic pollutant removal

Titanium dioxide aerogel (TiAP) powders were prepared by lyophilization of peroxo-polytitanic gels followed by annealing at 800 degrees C to obtain an anatase structure. The surface modification of TiAP was performed for the first time by low amounts of Ce ions (in the range of 0.0025 to 0.025 wt%) using a wet impregnation method. The photocatalytic activity of the aerogel samples was investigated for the removal of different organic pollutants (i.e., Rhodamine B, phenol and caffeine) and the results were compared with the reference P25. Both TiAP and Ce ion surface-modified TiAP (Ce/TiAP) have exhibited better degradation efficiencies for the removal of pollutants than P25, especially for Ce/TiAP with an enhancement in the degradation efficiencies of +18% and +37% for the removal of caffeine and Rhodamine B, respectively. These results have been partly explained by the high active surface area of Ce/TiAP compared to TiAP as well as its better photoelectrochemical properties which have shown, for instance, similar to 10% increased incident photon-to-electron conversion efficiency at 360 nm. Interestingly, the energetic position of the valence band maximum of Ce/TiAP is shifted from 3.2 eV to 2.8 eV (compared to TiAP), thus improving the generation of reactive oxygen species (ROS), especially hydroxyl radicals. Indeed, the presence of HO is confirmed by electron paramagnetic resonance, and fluorescence spectroscopy and their photoinduced generation are enhanced in the case of Ce/TiAP. Finally, the surface modification of TiAP by cerium ions led not only to better photoinduced properties, thus limiting the electron-hole pair recombination, but also to the improvement of ROS generation via different plausible mechanisms.