Interfacial carbonyl groups of propylene carbonate facilitate the reversible binding of nitrogen dioxide

Abstract

The interaction of NO₂ with organic interfaces is critical in the development of NO₂ sensing and trapping technologies, and equally so to the atmospheric processing of marine and continental aerosol. Recent studies point to the importance of surface oxygen groups in these systems, however the role of specific functional groups on the microscopic level has yet to be fully established. In the present study, we aim to provide fundamental information on the interaction and potential binding of NO₂ at atmospherically relevant organic interfaces that may also help inform innovation in NO₂ sensing and trapping development. We then present an investigation into the structural changes induced by NO₂ at the surface of propylene carbonate (PC), an environmentally relevant carbonate ester. Surface-sensitive vibrational spectra of the PC liquid surface are acquired before, during, and after exposure to NO₂ using infrared reflection–absorption spectroscopy (IRRAS). Analysis of vibrational changes at the liquid surface reveal that NO₂ preferentially interacts with the carbonyl of PC at the interface, forming a distribution of binding symmetries. At low ppm levels, NO₂ saturates the PC surface within 10 minutes and the perturbations to the surface are constant over time during the flow of NO₂. Upon removal of NO₂ flow, and under atmospheric pressures, these interactions are reversible, and the liquid surface structure of PC recovers completely within 30 min.