A comparative study of the effects of In2O3 and SnO2 modification on the photocatalytic activity and characteristics of TiO2

In this study, we investigated the photocatalytic activities of In2O3-, SnO2-, and In2O3/SnO2-doped titanium dioxide (ITO–TiO2) samples prepared through a sol–gel approach from InCl3, SnCl4, and titanium tetraisopropoxide (TTIP) precursors, respectively. These ITO–TiO2 samples were characterized using X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV–vis spectroscopy, photoluminescence, and Brunauer–Emmett–Teller techniques. Herein, we compare the physical properties and photocatalytic activities of ITO–TiO2 samples having different In/Sn ratios. After calcination at 500 °C, In2O3 and SnO2 were present as either minor phases or In2xSnyO3x+2y structures, or they were incorporated into the TiO2 network. The ITO–TiO2 samples exhibited multimodal mesopores, whereas the undoped TiO2 displayed a monomodal pore size distribution. The ITO–TiO2 sample calcined at 500 °C and featuring an In/Sn molar ratio of 1:19 at a doping level of approximately 15% exhibited the highest activity for the photodegradation of phenol under simulated solar light illumination. We ascribe this superior photocatalytic activity to the simultaneous influence of (i) the presence of the rutile phase in an appropriate quantity, (ii) the high specific surface area, (iii) the enhanced hydrophilicity, and (iv) the high driving force for the photoexcited electrons to be transferred from TiO2 to ITO.

► SnO2 displays stronger doping effect on boosting the photocatalytic activity of TiO2 than In2O3.
► SnO2 doping creates more graphite-like matter and octahedral vacancies, causing a higher visible absorbance than In2O3 doping.
► Conduction band edges of In2O3, SnO2 and their composites (In2xSnyO3x+2y) are positioned below that of TiO2, causing efficient charge transfer.
► The ITO–TiO2 sample with an In/Sn molar ratio of 1/19 at a doping level around 15% exhibited the highest activity.