Surface Enhanced Raman Spectroscopic Studies on Surface Plasmon Resonance Catalytic Activity of TiO<sub>2</sub>-Metal Nanocomposites

Abstract

The rapid recombination of carriers on plasmon metal nanoparticles leads to relatively low efficiency of traditional photocatalysts. The combination of a metal and a semiconductor allows to the separation of hot electrons and holes to improve photocatalytic efficiency. In this study, Au nanoparticles were integrated with semiconductor TiO2 nanoparticles of different sizes to improve the photocatalytic activity. Various techniques have been developed to study the mechanism of catalytic activity, the significance of band bending in the space-charge region within metal–semiconductor nanocomposites, and the built-in electric field. The results provide theoretical and experimental evidence for the design of a high-performance surface plasmon resonance (SPR) photocatalyst. To reveal the interface band structure, surface-enhanced Raman spectroscopy (SERS) was employed to analyze the band structure of the TiO2–metal composites. This approach was based on the electrochemical Stark effect and a molecular probe strategy, combined with X-ray photoelectron spectroscopy (XPS), Electrochemical impedance spectroscopy (EIS), and other techniques at the molecular level. The results demonstrated that charge transfer occurred spontaneously between the Au nanoparticles and TiO2, and that the TiO2–metal interface constitutes a Schottky barrier. Moreover, the size of the TiO2 nanoparticles affects the degree of band bending. Optimal state matching was achieved with TiO2 (60 nm)–Au, improving the photocatalytic activity of the nanocomposite. The photocatalytic coupling reaction of p-aminothiophenol (PATP) acted as a probe to study the catalytic performance of TiO2–metal nanocomposites. The results revealed that the introduction of TiO2 improves the SPR catalytic activity of Au, mainly through the efficient separation of electrons and holes at the TiO2–metal interface.