Preparation And Comparative Study Of Thin-Film Photoelectrocatalytic Reactors Using TiO₂ Nanotube Electrode

Two thin-film photoelectrocatalytic (PEC) reactors have been developed and successfully applied to degrade Rhodamine B (RhB). The enhanced treatment efficiency achieved by thin-film PEC process was attributed to the reduced path length ofirradiation light source in the solution, so the irradiation light absorption by the solution was also significantly reduced. Also, the reactor setup was simplified and the mass transfer was promoted. Meanwhile a bias voltage was added to enhance the separation efficiency of electron-hole pairs and to improve the treatment efficiency. However the TiO₂ anode in our former work, which resulted in a plane structure, was prepared by sol-gel method. The surface morphology of TiO₂ influences the specific surface area, absorption rate of light and photocatalytic activity. Nowadays, TiO₂ nanotubes have been widely used in photocatalytic technology owing to large active surface area, outstanding performance in photocatalytic, convenient conduction channel, easy preparation and modification by loading other compounds. However in different kinds of reactors, whether the performance of TiO₂ nanotubes electrode is better than that of TiO₂ electrode with plane structure, is worthy to be investigated.In this work, a TiO₂ nanotubes electrode was prepared by anodization method on the titanium sheet. The nanotubes were arranged regularly and closely, and the specific surface area was 8.2 times larger than that of the sol-gel electrode. Due to larger specific surface area and smaller inner resistance, the photo-current response of TiO₂ nanotubes electrode was also better than the sol-gel electrode. In the conventional photocatalytic reactor without agitation, the TiO₂ nanotubes electrode had obviously better degradation ability than the sol-gel electrode, which agreed well with the photo-current response. The decolorization efficiency by the nanotubes electrode was not improved when agitation was added, while the efficiency by the sol-gel electrode was greatly improved, which meant that enhancing mass transfer was beneficial to photocatalytic degradation by the sol-gel electrode.A gradient sheet thin-film PEC reactor with TiO₂ nanotubes anode was assembled and used to degrade RhB. Compared with the sol-gel anode, the energy consumption of TiO₂ nanotubes anode in the optimal condition was less than the sol-gel electrode, and the photo-current response was better. Though TiO₂ nanotubes anode possessed larger surface area, there were no significant differences between the two types of TiO₂ electrodes when they were applied to degrade RhB in the thin-film PEC reactor. This was probably due to the specific structure of TiO₂ nanotube array. Because the TiO₂ nanotube is blind pore architecture and the tube can be easily sealed by the water, which will decrease the efficient surface area of TiO₂ nanotubes. A rotating disk thin-film PEC reactor with TiO₂ nanotubes anode was also assembled and used to degrade RhB. Compared with former results, TiO₂ nanotubes anode was able to obviously improve the degradation efficiency of RhB. The decolorization efficiency of TiO₂ nanotubes anode in photocatalytic process and PEC process reached 89% and 94%, which increased by 66% and 10%, respectively. In addition, RhB at high concentration levels was also able to be effectively treated by TiO₂ nanotubes anode.In order to improve the degradation efficiency of RhB by the gradient sheet thin-film PEC reactor, a porous TiO₂ electrode was prepared by adding PEG 2000 in the precursor solution of the sol-gel method, and then used to degrade RhB in the gradient sheet reactor. Compared with blank TiO₂ electrode (no PEG 2000 in the precursor solution), porous TiO₂ anode effectively improved the decolorization efficiency of RhB. Compared with TiO₂ nanotubes anode, the decolorization efficiency of RhB was improved at low and medium concentration (20-80 mg L-1). But the degradation ability of TiO₂ nanotubes anode was better at high concentration levels (100 mg L-1).