The Role of Lattice Defects on the Optical Properties of TiO(2) Nanotube Arrays for Synergistic Water Splitting

[Image: see text] In this study, we report a facile one-step chemical method to synthesize reduced titanium dioxide (TiO(2)) nanotube arrays (NTAs) with point defects. Treatment with NaBH(4) introduces oxygen vacancies (OVs) in the TiO(2) lattice. Chemical analysis and optical studies indicate that the OV density can be significantly increased by changing reduction time treatment, leading to higher optical transmission of the TiO(2) NTAs and retarded carrier recombination in the photoelectrochemical process. A cathodoluminescence (CL) study of reduced TiO(2) (TiO(2–x)) NTAs revealed that OVs contribute significantly to the emission bands in the visible range. It was found that the TiO(2) NTAs reduced for a longer duration exhibited a higher concentration of OVs. A typical CL spectrum of TiO(2) was deconvoluted to four Gaussian components, assigned to F, F(+), and Ti(3+) centers. X-ray photoelectron spectroscopy measurements were used to support the change in the surface chemical bonding and electronic valence band position in TiO(2). Electron paramagnetic resonance spectra confirmed the presence of OVs in the TiO(2–x) sample. The prepared TiO(2–x) NTAs show an enhanced photocurrent for water splitting due to pronounced light absorption in the visible region, enhanced electrical conductivity, and improved charge transportation.