Charge-Transfer-Induced Surface-Enhanced Raman Scattering on Ag-TiO2 Nanocomposites

In this paper, a series of silver-deposited TiO2 (Ag-TiO2) nanoparticles (NPs) with a varying content of Ag were prepared by a photoreduction method and were attempted to serve as SERS-active substrates for the first time. SERS signals of 4-MBA molecules adsorbed on Ag-TiO2 NPs were further enhanced considerably relative to those enhancements on pure TiO2 NPs. The surface-deposited Ag on TiO2 can inject additional electrons into molecules adsorbed on the TiO2 surface through the conduction band of TiO2 NPs because of plasmon resonance absorption of Ag under incident visible laser, besides the intrinsic TiO2-to-molecule charge-transfer (CT) contribution. The two contributions mentioned are responsible for the whole SERS intensity of the molecules adsorbed on Ag-TiO2 NPs. This work is valuable in developing nanosized TiO2 used as a promising, nontoxic and biologically compatible SERS-active substrate as well is in studying the CT mechanism between Ag and TiO2 for potential photoelectrochemical applications.