Detection of hot electron-driven photochemical reaction of steady- state NO2 gas molecules by surface–enhanced Raman spectroscopy

In this work, a steady-state detection method of 50 ppm of nitrogen dioxide NO2 gas in a polyethylene (PET) bag using surface-enhanced Raman spectroscopy (SERS) is reported for the first time. SERS was performed on different shapes of gold nanostructures, gold nanostars (GNS) and nanoporous gold film (NPG). In both, the vibrational modes assigned to the adsorbents of NO2 molecules such as NO2, NO, NO−3, N2O3, and N2O5 were detected. The generation of adsorbents is due to the photo-chemical reaction driven by the hot electrons generated at the surface of gold nanostructures. Our finding is supported by a finite element simulation excluding the plasmon-induced photo-thermal process due to the long duration of excitation compared to the duration of SERS measurement. The mechanism of NO2 photochemical reactions is explained, confirming the adsorption of NO2 molecules on the gold surface towards their oxygen atoms.