Formation of internal p-n heterojunction by wet-chemical doped anodic TiO2 nanotubes array for photocatalytic water splitting

초록

TiO2 nanotube is a widely used material as a photocatalyst with advantages of high catalytic activity, corrosion resistance, mechanical/chemical stability, and low recombination rate. Further, energy levels to evolve H2 and O2 are located between band gap of TiO2, so that TiO2 nanotube have been studied as a photocatalytic water splitting material. However, photoconversion performance of bare TiO2 is constrained by intrinsic wide bandgap, which does not allow absorption of visible light (approximately 3.2 eV). To solve the problem, several chemical methods are utilized to improve the photocatalytic performance of TiO2: chemical doping, heterojunction, composite, and activation of the surface are not only used for reduction of band gap, but also improvement of photocatalytic activity and absorption of visible light. In this study, we introduce the formation of internal p-n heterojunction in the anodic TiO2 nanotubes array by potential shock doping method: wet chemical doping method with anion precursor and high additional potential. During the doping of Pd by potential shock method, concentration of Pd is localized in the TiO2 nanotubes array. Besides, highly localized concentration of Pd makes n-type TiO2 to p-type TiO2 depending on the concentration of Pd so that p-n heterojunction is formed in the TiO2 nanotubes array during potential shock process. Anodic TiO2 nanotubes array with internal p-n heterojunction shows the highest photocatalytic water splitting performance among the TiO2-based photocatalysts (approximately 28 μL cm-2 h-1).