Molecular Evolution of Nitrogen Dioxide on a Nanostructured Gold Surface in the Atmosphere by In Situ Surface-Enhanced Raman Spectroscopy

Abstract

It has generally been believed that the interaction between nitrogen dioxide (NO2) and Au can occur only under ultralow temperature (<200 K) and vacuum conditions. The evolution process of NO2 on the Au surface and its products are still seriously controversial. Here, the molecular evolution of NO2 on a nanostructured Au surface in the atmosphere is studied by time-dependent in situ surface-enhanced Raman spectroscopy. According to the spectral measurements and density functional theory-based simulations, it has been found that when NO2 contacts the Au surface in the air with enough relative humidity (≳20%), chemisorbed NO2 species would be produced quickly, and after a short induction period (about 1 min), would evolve into NO[Au(NO3)4], which subsequently decomposes into O2 and NO, and/or deliquesce into the adsorbed NO2 and −OH as well as HNO3, depending on the temperature and the relative humidity. Further experiments show that the presence of O2 and H2O molecules is crucial to such molecular evolution of NO2 on the Au surface in the atmosphere. Finally, a H2O and O2-assisted reaction mechanism is proposed and nicely describes the molecular evolution of NO2 on the Au surface. This work provides sufficient spectral evidences for the molecular evolution of NO2 on the Au surface in the atmosphere, and offers a new insight into the interaction between NO2 and the Au surface.