Titanium dioxide is a widely-investigated semiconductor photocatalyst due to its wide availability and low cost. Although it has been successfully used in the photocatalytic treatment of various organics in wastewater, it remains a challenge to modify its structure to achieve enhanced catalytic properties at a wider light spectrum. Doping with transition metals was seen to narrow its optical band gap yet synthesis routes have been largely limited to the use of high-end equipment. Herein we demonstrate the use of a simpler one-pot approach to synthesize nanoporous arrays of silver-doped titanium dioxide nanotubes (Ag-TiNTs) by double anodization of titanium sheets. The synthesized Ag-TiNTs have an average inner diameter of 58.68 nm and a wall thickness of 16.46 nm. ATR-FTIR spectroscopy revealed its characteristic peaks attributed to O-Ti-O bonds. Silver doping increased the lattice volume and crystallite size of anatase with a corresponding decrease in the degree of crystallinity due to the introduction of impurity Ag atoms in its tetragonal structure. Silver was homogeneously distributed across the nanotube surface at an average loading of 1.41 at. %. The synthesized Ag-TiNTs were shown to have a superior photoelectrocatalytic activity in degrading C.I. Basic Blue 9 under UV illumination with a pseudo-first-order kinetic rate of 1.0253 x 10-2 min-1. Most importantly, the Ag-TiNTs are photoelectrocatalytically-active even at a low Ag loading.

Highly-organized one-dimensional arrays of copper-doped titanium dioxide nanotubes (Cu-TiNTs) were synthesized in a one-pot approach by double anodization of titanium sheets. Field-emission scanning electron microscopy showed that Cu-TiNTs have an average inner diameter of 52.13 nm, a wall thickness of 14.28 nm, and a tube length of 0.6401 μm. Fourier-transform infrared spectroscopy confirmed the presence of characteristic O-Ti-O bond of TiO2. X-ray fluorescence spectroscopy confirmed copper-doping with an average dopant loading of 0.0248%. Even at this low dopant loading, Cu-TiNTs were shown to be photo-active in degrading Acid Orange 52 (AO 52) under UV light illumination. The kinetic profiles of AO 52 photoelectrochemical degradation were best described by the pseudo-first-order kinetic model (R2 ≥ 0.991) with kinetic constants 9.42 x 10-3 min-1 for Cu-TiNTs as compared to 6.04 x 10-3 min-1 for pristine TiNTs. Overall, doping pristine TiNTs with Cu was shown to enhance its photoelectrocatalytic properties in degrading textile dyes such as AO 52.