Observation of Surface Coverage-Dependent Surface-Enhanced Raman Scattering and the Kinetic Behavior of Methylene Blue Adsorbed on Silver Oxide Nanocrystals

Abstract

We report the study of surface-enhanced Raman scattering (SERS) and photocatalytic reactions of methylene blue (MB) adsorbed on cubic silver oxide (c-Ag₂O) nanocrystals. The SERS activities of MB observed on c-Ag₂O are surface coverage-dependent. According to the SERS selection rules, the strong intensities of the C-S-C and C-N-C bending modes imply that the MB molecules are adsorbed on the c-Ag₂O surface with a near-perpendicular position. On the other hand, if these modes are weak, MB assumes a near-parallel position to the c-Ag₂O surface. Under the "perpendicular" condition, the photocatalytic reaction rate of MB observed on c-Ag₂O surfaces is first order at a high surface coverage, whereas under the "parallel" condition, the observed rate is zero order at a low surface coverage. The SERS intensity trends and the kinetic behavior of MB on c-Ag₂O are correlated.