Photoelectrocatalytic Degradation of C.I. Basic Blue 9 in Water under UV and Visible Light Illumination using Copper/Sulfur Co-doped Titanium Dioxide Nanotubes

Titanium dioxide has long been investigated for its excellent photocatalytic activity under UV illumination. However, its sluggish activity under visible light illumination remains a challenge. Doping titanium dioxide with transition metals and non-metals was done in the past to improve its catalytic properties, yet the expensive synthesis protocols involved in doping titanium dioxide limit its applications. Herein, a one-pot approach of doping titanium dioxide nanotubes was used. In particular, the Cu/S-TiNTs electrode was synthesized by electrochemical anodization using an electrolyte solution spike with CuSO₄. The resulting nanostructured Cu/S-TiNTs electrode was used as a photoanode for the photoelectrocatalytic degradation of synthetic dye solution (50 ppm C.I. Basic Blue 9 in deionized water) in a 125-mL reactor. The Cu/S-TiNTs were shown to be catalytically active under both ultraviolet and visible light. Co-doping pristine TiNTs with copper and sulfur significantly enhanced the photoelectrocatalytic degradation rates of BB 9. Cu/S-TiNTs achieved 67% faster degradation rate (k₁ = 1.5054 ± 0.0193 x 10^-2 min^-1) compared to pristine TiNTs (k₁ = 8.9106 ± 0.0647 x 10^-3 min^-1) under visible light illumination. At the end of 60 minutes, the Cu/S-TiNTs were able to degrade 59.69% of the initial dye concentration under visible light compared to 45.43% degradation using pristine TiNTs. The synthesized photoanodes demonstrated good reusability and stability after several cycles of use, even at a low dopant loading. These findings bring us closer to the possible large-scale adaptation of advanced oxidation processes, such as photoelectrocatalysis, for environmental remediation of recalcitrant organic compounds in wastewater.