Research Of Preparation And Photocatalytic Water Splitting Performance Of TiO₂ Nanotube Arrays And α-Fe₂O₃ Thin Films

Both TiO2 and Fe2O3 are n-type semiconductors, which can be used in photocatalytic water splitting. TiO2 with a wide band gap of 3.2 eV can only absorb UV light which is just about 5% of solar energy. However, about 47% of solar energy is visible light. Fe2O3 with a narrow band gap of 2.2 eV can absorb UV light and visible light. Whereas, the photocatalytic water splitting efficiency of Fe2O3 is still lower than the theoretical value. The reason is that α-Fe2O3 suffers from the short lifetime and short diffusion distance of charge carriers. In this work, TiO2 nanotube arrays (TNTAs) and α-Fe2O3 thin films were prepared and then they were modified through different methods. Further, the photocatalytic water splitting performance of modified TNTAs and modified α-Fe2O3 thin films was explored.Firstly, the TNTAs on Ti foils were prepared by anodization and the influence of water content on anodizing current-time curves and morphology of TNTAs was explored. Besides, the measured current-time curves were fitted with a theoretical formula to obtain the theoretical current-time curves. According to the theoretical curves, the total current can be separated into the ionic current and electronic current. Based on this, a new mechanism for the formation of TNTAs has been proposed.Secondly, the TNTAs with different lengths were prepared by changing anodizing time and then they were used as the electrodes for photocatalytic water splitting. The optimized parameters of preparing TNTAs under potentiostatic condition were determined by investigating the influence of length of TNTAs on photocatalytic water splitting. According to the experimental results,60 min was the best anodizing time for preparing TNTAs.Thirdly, the α-Fe2O3 thin films were prepared by cyclic voltammetry electrodeposition and galvanostatic electrodeposition. The α-Fe2O3 thin films with better performance of photocatalytic water splitting were prepared under galvanostatic electrodeposition. In addition, the surface plasmon resonance effect of Au nanoparticles and surface passivation by atomic layer deposition of Al2O3 was integrated to enhance the photocatalytic water splitting performance of α-Fe2O3 thin films. The experimental results suggested that the combination of surface plasmon resonance and surface passivation contributed to a 78% increase in photocurrent of modified electrodes. Further, the results were verified by finite-difference time-domain (FDTD) method.Finally, to utilize wide range of solar light from UV light to visible light, the TNTAs were decorated with α-Fe2O3 nanoparticles to prepare α-Fe2O3/TNTAs composite materials by different methods such as potentiostatic electrodeposition, successive ionic layer adsorption reaction method and cyclic voltammetry electrodeposition. The results demonstrated that α-Fe2O3 nanoparticles were only loaded on the outer surface of TNTAs via the methods of potentiostatic electrodeposition and successive ionic layer adsorption reaction. Moreover, the photocatalytic water splitting performance of α-Fe2O3/TNTAs composite materials was poor. While, the α-Fe2O3 nanoparticles were successfully inserted into the interior of nanotubes by cyclic voltammetry electrodeposition. Further, there was a 36% increase in the rate of photocatalytic degradation of methylene blue even though the photocatalytic water splitting performance was still poor.