Do, 20.02.2020 13:15

Titanium oxide-based nanostructures as photocatalysts for purification of waste water

Dr. Sc. Andreja Gajovic

Head of the Laboratory for Energy Conversion Materials and Sensors

Divison of Materials Physics

Rudjer Boskovic Institute, Zagreb, Croatia

Increasing awareness of harmful consequences of persistent organic pollutants in water makes development of cheap and stable photocatalysts for their degradation one of significant goals in an environmental engineering. Materials based on nanostructured TiO2 are among the most prominent materials for the last 40 years. However, one of the main limitations for the application of TiO2 in photocatalysis is a wide energy bandgap (Eg = 3.2 eV for anatase, 3.02 for rutile), so its application is limited to UV light radiation. In order to increase the efficiency of the TiO2 nanostructures for the photocatalysis, it is essential to expand the spectral range in which the photocatalyst is active, and to prolong exited electron-hole pairs lifetime. Therefore, different approaches to modifications of the synthesized nanoparticles of TiO2 were applied. In this talk, the photocatalytic degradation of water pollutant by using different modified TiO2-based nanostructured photocatalysts will be presented, as well as the strategies used for the improvement of their photocatalytic activity in the UV light region as well as broadening of their photocatalytic activity in the visible and near IR light. The synthesis of TiO2 nanostructures (nanotubes and nanoparticles) was obtained by anodization of Ti in organic electrolyte, hydrothermal syntheses, and by pulsed laser ablation (PLA). Surface modification and decoration of NTs with Ag nanoparticles was done by photo-reduction, with FeOOH/Fe2O3 by hydrothermal synthesis, while with Cu-based compounds by spin-coating of copper acetylacetonate in 2-propoxyethanol. The additional processing in reduction atmosphere was occasionally applied. The structure of photocatalysts were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEM and TEM), while the photocatalytic degradation was studied using different model pollutants from simple dyes as methylene blue, or caffeine to serious industrial and pharmaceutic pollutants as 1H-benzotriazole or salicylic acid. It was shown that the photocatalytic activity of studied nanostructures was considerably increased by optimization of the TiO2-based materials bandgap to obtain absorption in the visible and near-IR regions of the solar irradiation. That was achieved by decoration with Ag, FeOOH/Fe2O3, or Cu-based compound nanoparticles, and/or due to the defects obtained in the reduction atmosphere. The improvement of photocatalytic properties of TiO2 nanoparticles prepared by PLA were obtained by increase of the active surface by decreasing the size of TiO2 photocatalyst nanoparticles and by introducing some content of TiO2 of Magneli phases during PLA synthesis. The shift of the photocatalytic activity in the visible and near-IR regions of the spectrum would allow the work of photocatalytic reactors for purification of the water using only sun light without appliance of additional UV lamps. The photocatalytic properties of the synthesized photocatalysts will be discussed considering the morphology, crystal structure and influence of modification and decoration.