Electrochemically Self-Doped TiO2 Nanotube Arrays for Efficient Visible Light Photoelectrocatalytic Degradation of Contaminants

• Self-doped TNTs photocatalyst is prepared by electrochemical reduction.
• Self-doped TNTs photoelectrodes show an enhanced photoelectrochemical activity.
• Self-doping can enhance both the absorption in visible region and electrical conductivity of the TNTs.
• Self-doping can decrease the Rct between the solid-electrolyte interface.

In this study, a simple electrochemical reduction approach is reported to enhance the photoelectrochemical performance of TiO2 nanotube arrays towards degrading water contaminants such as Rhodamine B, phenol and E. coli K-12. The results obtained from X-ray diffraction and X-ray photoelectron spectroscopy demonstrate that oxygen vacancies i.e., Ti3+ self-doping, were formed in the lattices of TiO2 nanotube arrays during the electrochemical reduction process of pristine TiO2 nanotube arrays at different negative potentials ranging from −1.2 to −1.5 V. Comparing the pristine TiO2 nanotube arrays, the treatment TiO2 nanotube arrays samples by electroreduction process were found to be showing enhanced photoelectrocatalytic activity in the UV and visible regions in the entire potential window tested. Further, the photocurrent density of self-doped TiO2 nanotube arrays sample prepared at −1.3 V was 250% higher than that of the pristine TiO2 under visible-light illumination. Impedance analysis revealed that the electrical conductivity of the nanotubes significantly enhanced after self-doping. The photoelectrocatalytic activity of the self-doped TiO2 nanotube increased dramatically due to the enhanced electrical conductivity and absorption in the visible light region, as well as an accelerated charge transfer rate between the interface of solid and electrolyte.