Enhanced Visible-Light Photoelectrochemical Conversion on TiO₂ Nanotubes with Bi₂S₃ Quantum Dots Obtained by in Situ Electrochemical Method

A new greener strategy to incorporate Bi₂S₃-mercaptopropionic acid (MPA) quantum dots (QDs) onto TiO₂ nanotube (NT) films was developed, using <i>in situ</i> electrochemical synthesis with a graphite/sulfur powder macroelectrode (cathode) and cavity cell. Simultaneously, the obtained QDs were adsorbed on TiO₂ NTs, for the photoelectrochemical cell (PEC) assays. After the electrochemical synthesis, different thermal post-treatments were performed for growth and crystallization of obtained nanocrystals. The obtained TiO₂–Bi₂S₃ nanostructured composites were characterized by UV–vis, diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Photoelectrochemical tests were carried out, where TiO₂ NTs/Bi₂S₃ QDs with 15 min post-treatment at 90 °C presented a greater photocurrent density, when irradiated with visible light (427–655 nm region, 10 mW.cm^–2) and compared to pristine TiO₂ NTs. Such performance can be attributed to the synergetic effect caused by the good interface between TiO₂ NTs/Bi₂S₃ QDs, promoted by the electrochemical method of synthesis employed. The proof of concept evidenced in this work can be potentially extended for the sensitization of TiO₂ NTs with other semiconductors for PEC hydrogen generation and solar cell applications