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

This study demonstrated an Advanced Oxidation Process (AOPs) by the activation of Peroxymonosulfate (PMS) through Fe²⁺ and UV for the degradation of 1-naphthylamine (1-NA). A series of processes including Fe²⁺/PMS, Fe²⁺/UV, PMS/UV, Fe²⁺/PMS/UV and direct photolysis by UV-A, UV-B, UV-C were examined. Comparatively, the Fe²⁺/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 Fe²⁺/PMS dosage. The superior performance was ascribed to the activation of PMS into exclusive sulfate radicals (SO₄^•–) and hydroxyl radicals (^•OH). The optimal Fe²⁺/PMS ratio, pH level, and UV wavelength were determined to be [Fe²⁺: 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 SO₄^•– and ^•OH has contributed a dominant role in the process, nevertheless, the redox cycle introduced by Fe²⁺/Fe³⁺ can contribute the reduction of diol to quinone intermediates, which can accelerate the degradation ultimately.