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 in situ 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.