Degradation and debromination of bromophenols using a free-base porphyrin and metalloporphyrins as photosensitizers under conditions of visible light irradiation in the absence and presence of humic substances

• H2TMPyP and ZnTMPyP were effective photosensitizers for degrading TrBP and TBBPA.
• 1O2 was a major photo-induced ROSs in the photodegradation of bromophenols.
• More than 95% of debromination had been achieved in the presence of ZnTMPyP.
• Inhibition of TrBP degradation by HSs can be due to competitive oxidation by 1O2.
• HSs with higher levels of aromatic parts strongly inhibited TrBP photodegradation.

The photodegradation and debromination of 2,4,6-tribromophenol (TrBP) and tetrabromobisphenol A (TBBPA) were investigated in the presence of a free-base porphyrin and metalloporphyrins as photosensitizers under conditions of visible light irradiation. Among the photosensitizers, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (H2TMPyP) and Zn(II)-tetrakis(N-methylpyridinium-4-yl)porphyrin (ZnTMPyP) were effective in the photodegradation of bromophenols. In particular, 96% of the debromination was achieved in the case of the ZnTMPyP photosensitization system for TBBPA after 24 h of irradiation. ESR spectra with a spin-trapping reagent indicated that singlet oxygen (1O2) was the major photo-induced reactive oxygen species. The presence of humic substances and natural organic matter, which are common components in landfill leachates, inhibited the photodegradation of TrBP via competitive oxidation by 1O2 when ZnTMPyP was used as a photosensitizer. The presence of humic acids, which contained higher levels of electron-rich moieties like aromatic carbons, strongly inhibited the photodegradation of TrBP. TrBP and TBBPA were ultimately decomposed to organic acids, such as maleic and fumaric acids, as evidenced by LC/TOF-MS analysis. Thus, the photoirradiation of H2TMPyP and ZnTMPyP can induce 1O2 generation, which is effective in the photodegradation and debromination of TrBP and TBBPA.

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