Enhanced oxidation of methoxy phenols at micromolar concentration photosensitized by dissolved natural organic material

The rate coefficients for the photosensitized oxidation of various phenols in aqueous solutions containing dissolved natural organic material increased in some cases with decreasing phenol concentration. For 3,4-dimethoxyphenol and 4-methoxyphenol at initial concentration going from 10 to 1.0 μM, the rate coefficients increased by a factor of 5 in a humic acid solution and by a factor of 2 in a fulvic acid solution and a lake water. For 2,4,6-trimethylphenol, 4-methylphenol and phenol at initial concentration going from 15 to 2.5 μM, they increased by a factor < 2 in the humic acid solution and were constant in the fulvic acid solution and the lake water. We suggest that the methoxy phenols, which are known to easily reduce oxidants, readily react with a class of photo-oxidants whose lifetime is expected to be > 100 μs. Thereby the long-lived photo-oxidants seem to be scavenged by the phenols themselves.