Search

Titanium dioxide thin films were fabricated by anodisation of titanium foils in 1 mol/L of trichloroacetic acid under varying anodising parameters (voltage, current density and time) in order to determine the optimal processing conditions for maximal photocatalytic performance. The conditions used were a) voltage of 100 V with current densities of 10 and 20 mA/cm2 and b) voltage of 200 V with current densities of 40 and 60 mA/cm2; the anodising times were 1, 3, 5, 10, and 20 minutes for both sets of conditions. The mineralogical, microstructural, structural, and photocatalytic performance were evaluated using laser Raman microspectroscopy, glancing angle X-ray diffraction, scanning electron microscopy, focused ion beam milling, transmission electron microscopy and methylene blue degradation under UV irradiation. Anodisation tests illustrated that the voltage increased with time for all conditions: however at the higher current densities (40 and 60 mA/cm2), dielectric breakdown occurred and this caused a voltage drop and caused detachment of the film as seen from the FIB and TEM images. Even though Raman Microspectroscopy showed that anatase was present in all the samples, GAXRD analysis was only able to reveal the presence of anatase in only two samples. White to grey spots were observed to be present on every sample except sample 1 (anodised at 1 min, 100 V, and 10 mA/cm2) and these were determined to be either rutile or amorphous phase. SEM images showed that the numbers of depressions and delaminations increased with anodisation time and current density, and these observation confirmed that arcing occurred during the anodisation process. The thicknesses of the anodised samples were observed to increase with increase in the current densities as well. The photocatalytic performance was evaluated in terms of the degradation of methylene blue solution under UV irradiation. The results showed that the samples anodised at 40 and 60 mA/cm2 showed better performance than the ones anodised at 10 and 20 mA/cm2 owing to the difference in their microstructural characteristics The results showed that the microstructural effect was the major factor affecting the performance, rather than the mineralogy of the films. With increase in the anodisation time, current density, and voltage to higher values, the films grew thicker and arcing took place. The resultant volumetric and thermal stresses caused delaminations, formation of depressions, and detachment of the partially delaminated regions. These changes resulted in the surface having a rough texture and this increased the effective surface area, and thereby the number of active sites, for photocatalytic reactions and this was responsible for the enhancement of performance for these samples.