Abstract
This study achieved a nanocomposite structure of nickel oxide (NiO)/titanium dioxide (TiO2) heterojunction on a TiO2 film surface. The photocatalytic activity of this structure evaluated by decomposing methylene blue (MB) solution was strongly correlated to the conductive behavior of the NiO film. A p-type NiO film of high concentration in contact with the native n-type TiO2 film, which resulted in a strong inner electrical field to effectively separate the photogenerated electron-hole pairs, exhibited a much better photocatalytic activity than the controlled TiO2 film. In addition, the photocatalytic activity of the NiO/TiO2 nanocomposite structure was enhanced as the thickness of the p-NiO film decreased, which was beneficial for the migration of the photogenerated carriers to the structural surface.
Highlights
In recent decades, the photocatalytic degradation of organic and inorganic pollutants using oxide semiconductor-based materials had been extensively studied [1,2,3,4,5]
The best photocatalytic activity that corresponded to a rate constant of 0.0304 min−1 was obtainable from the Ni film deposited onto the TiO2 film surface and rapidly annealed at 550 °C for 1 min under oxygen ambient
Thin Ni metal was deposited onto TiO2 film and rapidly oxidized at 450 °C, 550 °C and 650 °C, respectively, for 1 min under oxygen ambient to result in a surface with the nickel oxide (NiO)/TiO2 nanocomposite structure
Summary
The photocatalytic degradation of organic and inorganic pollutants using oxide semiconductor-based materials had been extensively studied [1,2,3,4,5]. RuO2/TiO2 mesoporous heterojunction exhibited a significant enhancement in the photocatalytic activity due to the improved separation of photogenetrated electron-hole pairs resulting from the internal electric field. Since the TiO2 material is a well-known n-type material, nickel oxide (NiO) which shows a p-type semiconducting nature with a high band gap of about 3.86 eV [26], it is expected to be a promising candidate on contact to TiO2 since an additive pathway associated with the formation of an inner electrical field between the heterojunction which is favorable for the separation of the photo-generated electrons and holes to different semiconductors in the p-NiO/n-TiO2 heterojunction structure, can be achieved. Evidence of the separation of the photo-generated electron-hole pairs achieved from these NiO/TiO2 nanocomposite structures was determined from the on-off process of the photocurrent response. The thickness of the NiO film in the NiO/TiO2 nanocomposite structure was varied in order to understand the resulting photocatalytic activity influenced by the diffusion of the photogenerated carriers in the NiO film to the structural surface
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