Highly Visible-Light-Photoactive Heterojunction Based on TiO2 Nanotubes Decorated by Pt Nanoparticles and Bi2S3 Quantum Dots

A heterojunction with excellent visible light response and stability based on titanium dioxide nanotubes (TiO2 NTs), bismuth sulfide quantum dots (Bi2S3 QDs), and platinum nanoparticles (Pt NPs) is proposed. Both Pt NPs (3.0 ± 0.2 nm) and Bi2S3 QDs (3.50 ± 0.20 nm) are well distributed on the (i) top parts, (ii) inner walls, and (iii) outer walls of the TiO2 NTs. Visible-light-induced photoreaction was initialized by excitation of narrow band gap Bi2S3 QDs, followed by electron injection to the conduction band of TiO2, while Pt NPs acted as electron traps, enhacing O2–• generation. Phenol in the aqueous phase and toluene in the gas phase were efficiently degraded over Bi2S3–Pt NTs, even for wavelengths longer than 455 and 465 nm, respectively, while no degradation of model compounds was observed over pristine TiO2 NTs under the same irradiation conditions. Photocatalytic tests of phenol degradation in the presence of scavengers revealed that superoxide radicals were responsible for the visible-light degradation of organic compounds in the aqueous phase.