Synthesis and modification of TiO2 nanomaterials for the degradation of pollutants by heterogeneous photocatalysis

Environmental pollution is one of the biggest challenges to overcome after the industrial revolution, in which the release of several hazardous substances in water bodies and in the atmosphere is constantly taking place. During the last years, the nocive effects of these pollutants have become more evident, affecting not only humankind but also different ecosystems and the weather. New technologies are therefore crucial to avoid clean water shortages and to mitigate the negative effects associated with air pollution. Among the advanced oxidation processes (AOPs), heterogeneous photocatalysis is a promising technology because it can be used at ambient conditions without adding additional reagents, allowing the complete mineralization of several organic and inorganic compounds. Particularly, TiO2 has demonstrated to have excellent photocatalytic properties, good stability to photocorrosion, and it is a low-cost material. Some industries have already demonstrated the economic viability of this material as photocatalyst, but for large-scale environmental applications there are still two main limitations to overcome: the low efficiency of the reaction due to high recombination rates of the charges photogenerated, and the need of using ultraviolet light to trigger the process, which makes it power consuming and expensive. During my Ph.D. studies, different approaches were tested in order to increase the photoefficiency of anodically grown TiO2 nanotubes for the degradation of pollutants by heterogeneous photocatalysis. First, the synthesis parameters and the morphology/crystalline structure of the photocatalyst were correlated, and their impact in the material photoactivity in liquid phase was evaluated. For the most important parameters (i.e. electrolyte composition and thermal treatment conditions), their influence in the photoactivity of the material was also evaluated in gas phase. Second, the functionalization of TiO2 nanotubes with noble metals nanoparticles (i.e. Au and/or Pt) was done in order to reduce the rate of charge recombination reactions. Finally, doping and codoping strategies, with nitrogen and transition metals (i.e. Ta or Nb), were tested to increase the light absorption properties of the nanotubes under the visible light.