Photocatalytic behaviour of niobium-doped titanium dioxide nanoparticulate films for photodegradation of methylene blue / Nur Munirah Safiay

TiO2 nanostructures is one of the promising metal oxide semiconductors which has been used in many applications such as solar cells, sensors, photocatalysts, and even for medicines. Photocatalysis using nano-TiO2 is an excellent approach in overcoming the water pollution problems. However, there are some issues regarding TiO2 shortcomings in photocatalysis such as leaving behind residual by-products of TiO2 powder suspension that needed an after treatment and limited light absorption in the visible region. Therefore, this current study was performed to synthesize TiO2 photocatalyst on substrates and doping approach with niobium (Nb) was introduced to enhance the crystallinity and optical properties of TiO2. In this work, TiO2 nanoparticulate films have been synthesized on glass substrates at fixed molarity of 0.25 M. In this part, the annealing temperatures and coating cycles were varied from 400-600 °C and 1-9 cycles, respectively. Further, TiO2 were doped with Nb where the dopant concentrations were manipulated from 0 (undoped) to 9 at.% and the annealing temperatures were varied from 400-600 °C. Photocatalytic behaviour Nb-doped TiO2 nanoparticulate films for the photodegradation of Methylene Blue (MB) were also investigated. The structural, morphological and optical properties of the synthesized films were characterized via Field-Emission Scanning Electron Microscope (FESEM), X-ray diffraction (XRD) and ultraviolet-visible spectrophotometry (UV-Vis), respectively. The photocatalytic behavior of Nb-doped TiO2 nanoparticulate films was also measured by using UV-Vis. Results show that the optimization of pristine TiO2 nanoparticulate films at different annealing temperatures exhibited that the film annealed at 500 °C have the most uniform morphology, highly crystalline and has the highest absorptivity at 3.6 × 107 m-1 than the other samples. Meanwhile, the optimum coating cycles was 7 cycles owing to the film has the smallest nanoparticles size, smallest crystallite size at 13.4 nm and highest absorption at 3.7 × 107 m-1. Nb-doped TiO2 nanoparticulate films were synthesized and their photocatalytic behavior was investigated at 5 ppm of MB concentration and neutral pH. 5 at.% of Nb-doped TiO2 shows the highest absorption at 3.2 × 107 m-1 and the degradation of MB was also the highest at 95.9 % compared to the pristine TiO2 film which only degraded up to 53.4 %. The optimized annealing temperature for Nb-doped TiO2 nanoparticulate films was found to be at 550 °C and the percentage degradation of MB was 96.9 %. Further study on the effect of MB concentration and pH were investigated for the optimized Nb-doped TiO2 films. It was found that 5 ppm of initial MB concentration has the highest degradation performance of 90.6 % and the optimum pH of MB was found to be at pH 9 were the percentage degradation was 98.3 %. These remarkable increases in photocatalytic behavior of Nb-doped TiO2 nanoparticulate films were due to the increase in absorption where the absorbance was extended to the longer wavelength.