Raman Investigation of Nanosized TiO₂: Effect of Crystallite Size and Quantum Confinement

Abstract

The influence of the TiO 2 particle size on the enhanced Raman spectroscopy properties was systematically investigated on the nanometer-size scale. We report on the enhanced Raman spectrum of 4-mercaptobenzoic acid adsorbed on TiO 2 nanoparticles. The results presented in this study highlight the major findings that the intensities of both the molecular lines and the phonon modes of TiO 2 are strongly size-dependent. The TiO 2 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 is observed, with a maximum near 10.9 nm and a subsequent decline at larger sizes. Moreover, we have investigated quantum confinement effects between TiO 2 and the adsorbed molecules and attribute this to a charge-transfer resonance, which is responsible for the Raman enhancement.