Degradation of 1-naphthylamine by a UV enhanced Fe2+/peroxymonosulfate system: A novel pH-dependent activation pathway

• Fe 2+ /PMS/UV-C exhibited efficient degradation of 1-Naphthylamine (1-NA) to CO 2 and H 2 O. • Fe 3+ can trigger formation of colored precipitate at pH below the pKa of 1-NA. • UV/Fe 2+ and NaOH activations promote favorable performance at low and high pH. • Oxidation and reduction of 1-NA into O and O–H / –COOH intermediates. This study demonstrated an Advanced Oxidation Process (AOPs) by the activation of Peroxymonosulfate (PMS) through Fe 2+ and UV for the degradation of 1-naphthylamine (1-NA). A series of processes including Fe 2+ /PMS, Fe 2+ /UV, PMS/UV, Fe 2+ /PMS/UV and direct photolysis by UV-A, UV-B, UV-C were examined. Comparatively, the Fe 2+ /PMS/UV process was highlighted to have the most remarkable degradation efficiency with 100% 1-NA removal within 20 min. The total organic carbon (TOC) removal can achieve 83.5% (mineralization rate = 0.08 g TOC/min) by 1.5 h under higher Fe 2+ /PMS dosage. The superior performance was ascribed to the activation of PMS into exclusive sulfate radicals (SO 4 •– ) and hydroxyl radicals ( • OH). The optimal Fe 2+ /PMS ratio, pH level, and UV wavelength were determined to be [Fe 2+ : PMS] 0 = 1: 2, wavelength = 254 nm, pH = 2.98. This process was observed to be a pH dependent process. A rise of degradation efficiency was observed once the pH was adjusted to above the pKa of 1-NA and was rationalized by the NaOH activation of PMS. Pigments were observed in different conditions and were justified by spectrophotometric analysis. By proposing GC/MS and LC/MS analysis, lawsone and juglone were identified as the major product. The oxidation reaction initiated by SO 4 •– and • OH has contributed a dominant role in the process, nevertheless, the redox cycle introduced by Fe 2+ /Fe 3+ can contribute the reduction of diol to quinone intermediates, which can accelerate the degradation ultimately.