This article reports on the systematic investigation of the influence of the TiO2 particle size on the enhanced Raman spectroscopy properties using the nanometer-size scale.
The focus was on the enhanced Raman spectrum of 4-mercaptobenzoic acid adsorbed on TiO2 nanoparticles. The major findings that the intensities of both the molecular lines and the phonon modes of TiO2 are strongly size-dependent. The TiO2 crystallite size estimated using the Scherrer equation varied from 6.8 to 14.2 nm; as a function of crystal size, a large increase in intensity was observed, with a maximum near 10.9 nm and a subsequent decline at larger sizes. Moreover, the study investigated quantum confinement effects between TiO2 and the adsorbed molecules, attributing this to a charge-transfer resonance, which is responsible for the Raman enhancement. (publisher abstract modified)