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.

Factors influencing the photodegradation of Nnitrosodimethylamine in drinking water

In order to provide basic data for practical application,photodegradation experiment of Nnitrosodimethylamine(NDMA)in aqueous solution was carried out with a low-pressure Hg lamp.Effects of the initial concentration of NDMA,solution pH,dissolved oxygen,and the presence of humic acid on NDMA photodegradation were investigated.NDMA at various initial concentrations selected in this study was almost completely photodegraded by UV irradiation within 20 min,except that at 1.07 mmol/L,NDMA could be photodegraded almost completely in the acidic and neutral solutions,while the removal efficiency decreased remarkably in the alkaline solution.Dissolved oxygen enhanced the NDMA photodegradation,and the presence of humic acid inhibited the degradation of NDMA.Depending on the initial concentration of NDMA,NDMA photodegradation by UV obeyed the pseudo-first-order kinetics.Dimethylamine,nitrite,and nitrate were detected as the photodegradation products of NDMA.^(1)O_(2) was found to be the reactive oxygen species present in the NDMA photodegradation process by UV,based on the inhibiting experiments using tert-butanol and sodium azide.