Electrochemical preparation and characterization of surface-fluorinated TiO2 nanoporous film and its enhanced photoelectrochemical and photocatalytic properties

In recent years, surface fluorination of TiO2 has been demonstrated to be an efficient method for improving its photocatalytic (PC) reactivity toward some pollutants. In this paper, a new and simple method for surface fluorination and porosity-creating of TiO2 is Presented. The sample was prepared by anodization of TiO2 in HF aqueous solutions formed by direct thermal oxidization of titanium sheet. The preparation conditions were optimized. The prepared samples were characterized by scanning electron microscopy (SEM), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL). The photoelectrochemical (PEC) and photocatalytic (PC) properties of the samples were also investigated. SEM and Raman showed that the anodization made the TiO2 nanoporous, which consequently increased markedly the specific surface area, but did not change the bulk crystal structure under a certain preparation condition. DRS analysis revealed that the light absorption was decreased after electrochemical etching. The band gap energy narrowed from 3.15 to 3.04 eV. The surface fluorination of the etched-TiO2 was evidently supported by XPS. Highly enhanced PEC performance and PC activities for the degradation of target pollutants, phenol, methylene blue, and reactive brilliant red on the etched-TiO2 were observed. The possible reasons for such an improvement were studied in detail by a combination of the abovementioned methods and (photo) electrochemical techniques. It is mainly attributed to the enhanced specific surface area, negative-shifted appearing energy band edges, decreased surface recombination centers, and/or favorable charge transfer rate. The F-containing TiO2 electrode has an excellent stability against fluoride desorption.