| TiO2nanotube array is one of the ideal materials for making UV detector because of its excellent photoelectric property, good physical and chemical stabilities and high specific surface area. In this study, highly ordered TiO2nanotube array electrodes with different phase composition and microstructure were fabricated by two-step anodization method in an electrolyte comprised of NH4F, H2O and ethylene glycol. The effect of the microstructure of TiO2nanotube array on photoelectric property was researched by photoelectrochemical measurement. The results are as follows:1. The heat treatment temperature can remarkably influence the crystallization degree and phase composition of TiO2nanotube array. When heated at300℃, the nanotube array is anatase. As heat temperature rise to400℃, some of the anatase nano-crystals begin to transform into rutile. The FE-SEM measurement results shows that heat temperature lower than400℃can not destroy the highly ordered structure of the nanotube array, but when temperature is higher than600℃, the nanotubes seriously crash and the holes of the nanotubes are blocked completely. According to the photoelectrochemical measurement results, the electrode heated at400℃shows the highest photocurrent.2. During anodization process, the etching of F-on the surface of Ti sheet can be promoted via improving anode voltage and F-concentration. This is beneficial to the formation of nanotube array. When the anode voltage is constant, the thickness of nanotube array is proportional to the anodizing time. The growth rate of nanotube is measured to be1.27μm/h under a40V of anode voltage. Furthermore, the water content of2wt%in electrolyte can efficiently improve the uniformity of nanotube array.3. The photoelectric properties of TiO2nanotube array are mainly depend on the tube diameter and length. Larger tube diameter can help the electrolyte efficiently inject into the tube to capture the photoinduced holes from TiO2/electrolyte interface, leading to a large photocurrent. However, excessive tube diameter will reduce the total surface area of nanotube array and result in a markedly decrease in photocurrent. In addition, though long nanotube is favorable to enhance the absorption intensity of UV light, the growth of tube length will increase the transport distance of photoinduced electrons, which can obviously improve the recombination probability of electron-hole pairs, so a bad photocurrent would be observed.4. In our study, the tube length, diameter and wall thickness of the nanotube array with strongest photocurrent are9.68μm,92.62nm and4.94run, respectively. Photocurrent action spectra show that the electrode exhibits highest photoelectric conversion efficiency when illuminated by UV light with wavelength at360nm. Furthermore, the positive bias voltage of0.4V can speed up the separation of photoinduced electron-hole pairs, which could efficiently decrease the electron-hole recombination probability and improve the photoelectric performance. Under this bias voltage, the electrode shows a strongest photocurrent of25.2uA, and its response time is less than1second, showing excellent UV photoelectric property. All measurement results indicate that TiO2nanotube array is very suitable for UV detector. |
PDF Full Text Request