Identification and Analysis of the Intermediates from Photodegradation of 3,3′-diamino-4,4′-azoxyfurazan (DAAF) by SERS and HPLC–MS/MS

Understanding the structural changes and degradation mechanisms of organic pollutants is critical in environmental research. In this work, a xenon lamp was used as an analog light source to simulate the effect of sunlight on 3,3′-diamino-4,4′-azoxyfurazan (DAAF) in aqueous solution. Combining high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC–MS/MS), surface-enhanced Raman spectroscopy (SERS) with density functional theory (DFT), the degradation intermediates and mechanisms of DAAF were investigated. The sequential breakdown of the –NH2 and –O–N= bonds, followed by the removal of atomic O from –N=N(O)–, was emphasized and investigated using two-dimensional correlation spectroscopy (2D-COS) and SERS spectra. Three intermediates with mass-to-charge ratios (m/z) 181, 251 and 180 were identified and characterized by integrating experimental SERS data with DFT-calculated Raman spectra based on structures hypothesized from MS spectra. The findings from HPLC–MS and SERS not only corroborate each other but also provide a foundation for a detailed examination of the DAAF degradation process.