Photoelectrochemical determination of shallow and deep trap states of platinum-decorated TiO2 nanotube arrays for photocatalytic applications

A novel insight into the effect of Pt decoration on electrochemical and photoelectrochemical behavior of TiO2 nanotube arrays (TNA) was developed in this study. TNA samples were prepared via a two-step anodization of a titanium foil and decorated with Pt by a facile photodeposition method. The formation of metallic Pt were confirmed by X-ray photoelectron spectroscopy (XPS). On the basis of our calculations, the localized states and surface states induced by Pt deposition into the bandgap of titania nanotubes, play a dominant role in trapping/detrapping charge carriers and electron transfer to electrolyte. In Pt/TNAs the appropriate electrical connection between Pt nanoparticles and TNA induces sufficiently shallow traps in the vicinity of conduction band edge of TNA which creates a fast lane for electrons toward semiconductor/electrolyte interface and decreases the density of deep trap levels compared to the pristine TNA. However, there is an optimum amount for deposited Pt. Higher amount of optimum Pt can impose the monoenergetic deep trap levels which act as recombination centers