First fluorine doping of In₂O₃ films and its crucial role in enhancing photocatalytic activity

We prepared In2O3 film on the wire mesh of stainless steel by a facile hydrothermal method followed by annealing. To enhance the visible-light-responsive photocatalytic activity of the prepared In2O3 film, we in-situ doped the element fluorine by adding FTO glass as the fluorine source during the hydrothermal process. The prepared In2O3 and F-doped In2O3 films were characterized by XRD, SEM, HRTEM, XPS, UV-vis spectra, PL, and electrochemical measurement. The results show that In2O3 octagonal pyramids of cubic phase were formed. The fluorine doping promoted to growth of In2O3 pyramids and porous In2O3 pyramids help to adsorb RhB dye molecules. Beside, the fluorine doping introduced a new impurity level between the VB and CB of In2O3, thereby, decreasing the bandgap value from 2.84 to 2.60 eV. As a result, it extended the visible light absorption range and more photoinduced electrons and holes can be excited under simulated sunlight. Moreover, the doping inhibited the recombination of photogenerated carriers. It is worth noting that the fluorine doping changed the surface state of In2O3 and enhanced the chemical adsorption of dissociated oxygen species. It finally made RhB dye molecules strongly adsorbed the surface of F-doped In2O3 film. The photocatalytic activity of the F-doped In2O3 film was increased by 7.6 times compared with the pristine In2O3 film because of the combined action of the above reasons. The importance of active groups for RhB photodegradation is O-2(center dot-) > h(+) > e(-) > center dot OH.