Enhancement mechanism of copper ions doped TiO2 substrates based on surface-enhanced Raman scattering

Abstract

Surface-enhanced Raman scattering (SERS) is considered as one of the most attractive analytical tools, and it is necessary to develop more semiconductor substrates. Herein, copper ions-doped TiO2 (Cu-TiO2) nanoparticles (NPs) with different doping ratios were synthesized by a sol-hydrothermal method and used as semiconductor SERS substrates to explore the possible enhancement mechanisms. The synthesized Cu-TiO2 NPs show a cubic crystalline structure of anatase with a small particle size at 8 nm. We discussed the SERS enhancement ability of Cu-TiO2 substrates using crystal violet (CV) used as a probe. It can be found that there is a charge transfer (CT) effect between CV molecules and Cu-TiO2 substrates. In addition, Cu-TiO2 substrates exhibit the most SERS enhancement with an enhancement factor (EF) up to 2.4 × 104 at the Cu2+ doping ratio of 3 %, with a detection limit of 5 × 10–7 M. The experiments demonstrated that Cu-TiO2 NPs can be used as SERS substrates because of the CT route among the valence band, the surface state energy level, and the lowest unoccupied molecular orbital, which facilitates the development of semiconductor SERS substrates and provides a new perspective in exploring SERS enhancement mechanisms.