Synthesis and Modification of TiO2 and WO3 Based Nanostructured Materials for Environmental Applications

TiO2 and WO3 based nanomaterials are highly attractive for various applications encompassing photocatalysis, electrochromic devices, dye sensitized solar cells, hydrogen production, and sensing applications due to their low cost, non-toxicity, high efficiency, chemical inertness and ability to be synthesized in various morphologies. TiO2 is the most intensely studied photocatalyst and a significant proportion of research focuses on improving its photocatalytic activity, which is innately limited due to its wide band gap and electron/hole recombination kinetics. The doping and co-doping of metals and non-metals into the crystal lattice of TiO 2 have proved to reduce the band gap and decrease the rate of electron/hole recombination. This band gap reduction results in absorptive red shifting, which may be utilized for visible light-driven photocatalysis and dye sensitized solar cells (DSSC). Although WO3 is a very promising material that has the capacity for absorbing in the visible spectrum, it pales in comparison to TiO2 in terms of efficacy and thus there are considerable opportunities for the improvement of its activity for various applications through its modification.;During my PhD study, mesoporous N-doped and N,W co-doped TiO2 photocatalysts were initially prepared with an exclusive anatase phase and high specific surface areas, utilizing a facile, reproducible and inexpensive solution combustion synthesis method. The atomic percentage of N was kept constant, whereas that of W was varied from 0.5% to 3% in order to evaluate the effects of the amount of W on the photocatalytic activities and other properties of the materials. It was observed that the N and W atoms were well incorporated into the titania lattice structure, which led to a significant red shift in the absorption edge of the co-doped TiO2, and concordantly, a dramatic narrowing of the band gap. Photodegradation studies of rhodamine B (RhB) dye on the various samples revealed that an enhancement of up to 14 fold in the reaction rate was observed with 1.5 at% W doped TiO2 as compared with commercial Degussa P25.;To enhance the activity of the TiO2 based materials we introduced a novel UV treatment approach. The UV treated electrodes exhibited a dramatic increase in the donor density of the TiO2 nanotubes by three orders of magnitude. For the UV treated electrodes the photocurrent was enhanced 15 fold and the photoelectrochemical activity was approximately 6.8 times higher than that of the untreated TiO2 nanotubes. This novel approach was also employed with the N, W co-doped mesoporous TiO2. Following the UV treatment, the photocatalytic activity of the co- doped samples was increased two-fold under UV light and a 12-fold under visible light. The increase in the activity of the TiO2 nanotubes and N, W co-doped samples may be attributed to the lowering of the band gap due to the formation of Ti3+ during the UV treatment process.