Abstract

Titanium dioxide nanotubes are regarded as one of the most important functional materials and due to their unique electronic properties, chemical stability and photocorrosion resistance, they find applications in, for example, highly efficient photocatalysis or perovskite solar cells. Nevertheless, modification of TiO2 nanotubes is required to overcome their main drawback, i.e. large energy bandgap (>3.2 eV) limiting their ability to capture solar light. In this work, we report the changes in optical and photoelectrochemical properties of well-separated TiO2 nanotubes that are tuned by varying the geometry of the material. The ordered tubular titania is formed via anodization in the presence of fluoride ions in diethylene glycol at elevated temperature. Length, inner diameter, wall thickness, and separation distance are described in function of synthesis parameters such as applied voltage and duration. The morphology and optical properties are characterized by means of scanning electron microscopy and UV–Vis spectroscopy techniques, respectively, while cyclic voltammetry, linear voltammetry and chronoamperometry are used to determine electrochemical/photoelectrochemical activity in different light conditions. The obtained results suggest a link between specific surface area, the width of the band-gap, and photoactivity, each of which could be individually optimised via anodization conditions. Moreover, the behaviour of the Mott-Schottky plot before and after 3 min of irradiation is studied indicating the positive shift of the flat band position and an increase in donor density values for all the obtained materials. The Mott-Schottky analysis was correlated with the linear voltammetry scans suggesting the important role of surface trapped holes. Presented in here results significantly supplement the current state-of-art regarding separated TiO2 nanotubes that are considered as not fully investigated and unappreciated class of titania materials which due to the exposure of inner and outer wall can be used for further modifications.

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Authors (7)