Maximization of photocatalytic activity of Bi₂S₃/TiO₂/Au ternary heterostructures by proper epitaxy formation and plasmonic sensitization

Ternary Bi₂S₃/TiO₂/Au heterostructure has been successfully synthesized by decorationg Au nanoparticls onto binary Bi₂S₃/TiO₂ heterostructure. Structural analysis suggests that the heterostructure consists of orthorhombic Bi₂S₃, tetragonal anatase TiO₂ and face centered cubic Au. The appearance of extra Raman peak at 123 cm⁻¹ and the modification of Raman peaks of Bi₂S₃ and TiO₂ phases indicates a significant molecular interaction during growth of TiO₂ nanocrystals (NCs) on the surface of Bi₂S₃ nanorods. Self assembly of nanorods triggered by oleic acid results in urchin like morphology of pure Bi₂S₃. The {011} facet of TiO₂ nanocrystals grow epiaxially on {013} facet of Bi₂S₃ nanorods. Periodic arrangement of (111) plane of Au and (011) plane of Bi₂S₃ favors epitaxial growth in Bi₂S₃/TiO₂/Au heterostructure. Unique design of the ternary heterostructure makes a preferable pathway for the photogenerated electrons by suppressing the electron-hole recombination. The observation of decreased electron spin resonance signal intensity based on spin label technique confirms the electron transfer from photoexcited heterostructure. Favorable energetic positions of conduction and valence band edges of semiconductors (Bi₂S₃ and TiO₂) and Fermi level of metal (Au) are the key factors to enhance the photo catalytic activity of ternary heterostructure. Plasmonic phenomenon of metal (Au) nanoparticles by changing their size and shape was also investigated to remove organic pollutants from waste water.