Revealing interfacial charge transfer in TiO2/reduced graphene oxide nanocomposite by surface-enhanced Raman scattering (SERS): Simultaneous a superior SERS-active substrate

Abstract The strong interface interaction, especially interfacial charge transfer (CT) behavior, in TiO 2 /reduced graphene oxide (TiO 2 /rGO) nanocomposite endows the advanced hybrid material with extensive availability in dye-sensitized solar cells, photocatalysis, etc. Thus, revealing and understanding of the interfacial CT process are a crucial and interesting issue, owing to its vital contributions to optoelectronic and electronic properties. In this work, the TiO 2 /rGO nanocomposites with anchoring of TiO 2 nanoparticles on rGO nanosheets have been fabricated, and a surface-enhanced Raman scattering (SERS) strategy with 4-mercaptobenzoic acid (4-MBA) as probe was performed to reveal the interfacial CT in the nanocomposites. There are obvious enhancements in the SERS intensity and the degree of CT (ρ CT ) in the 4-MBA/TiO 2 /rGO/4-MBA system compared with those of 4-MBA/TiO 2 and 4-MBA/TiO 2  + rGO/4-MBA (TiO 2  + rGO is a physical mixture of TiO 2 and rGO) due to the chemical interaction and the interfacial CT between TiO 2 and rGO in the nanocomposite. It is indicated that the interfacial chemical interaction in the nanocomposite is an essential requirement for occurrence of the interfacial CT. The interfacial CT process can be evaluated quantitatively by the ρ CT in SERS spectrum. The ρ CT shows an obvious increasing trend with the increase of rGO amount in TiO 2 /rGO nanocomposites, and then reaches a saturation when the amount of rGO is 1.0%. And also, to further understanding of this CT progress, the model of the CT mechanism has been proposed. Furthermore, as-prepared TiO 2 /rGO nanocomposite can also be served as an effective SERS-active substrate for the ultrasensitive detection of analytes. The minimum detectable concentration of 4-MBA on the TiO 2 /rGO substrate can reach to 1 × 10 −7  mol/L, which is comparable to a noble metal substrate. Even, for p -aminothiophenol target molecule whose SERS signals cannot almost be observed on the ordinary TiO 2 substrate, the minimum detectable concentration can reach to a value as low as 1 × 10 −8  mol/L on the TiO 2 /rGO substrate.