Degradation of 2,4-dichlorophenol and coupling into humic matter by oxidative biomimetic catalysis with iron-porphyrin

We evaluated the activity of a water-soluble iron-porphyrin as catalyst of an oxidative reaction of 2,4-dichlorophenol (2,4-DCP) in the presence of humic molecules, whereby the phenol disappearance should proceed through self-olygomerization and co-polymerization within humic matter. The catalyzed coupling reaction was conducted with H2O2 as oxidizing agent with and without humic matter (HA) and followed by High Performance Liquid Chromatography (HPLC), upon incubation in either dark or daylight conditions. UV- and Fluorescence-detected signals of reaction products separated by HPLC were collected and structurally characterized by GC–MS. The 2,4-DCP degradation by the catalyzed oxidative reaction without addition of HA was complete in both incubation conditions and showed reaction products such as dehalogenated and hydroxylated phenols, and dimers/trimers of the dechlorinated phenol. With the presence of HA, 2,4-DCP was degraded in the dark by only 75% of initial content, whereas degradation was again complete in daylight, which showed similar reaction products as in the dark. These results reveal that the catalyzed oxidative reaction in the presence of HA was less efficient in the dark, possibly because 2,4-DCP was protected from oxidation by absorption into humic hydrophobic domains. Conversely, photo-oxidation combined to chemical oxidation to enhance the coupling reactivity in daylight conditions, most likely through co-polymerization of 2,4-DCP in humic molecules. This work confirms the potentiality of an oxidative coupling reaction catalyzed by iron-porphyrin in co-polymerizing halogenated pollutants into humic matter and detoxifying the environment.

► Iron-porphyrin catalyzes oxidative coupling reactions of 2,4-DCP with HA.
► Catalyst without HA provides 99% of 2,4-DCP degradation either in dark or daylight.
► In dark with HA catalyst degrades only 75% of 2,4-DCP due to absorption in HA.
► In daylight with HA photo-oxidation pushes catalyst to degrade 99% of 2,4-DCP.
► 2,4-DCP is oxidatively co-polymerized in HA by iron-porphyrin catalyst.