Photo-Fenton reaction at near neutral pH.

The photo-Fenton reaction, oxidation of photoproduced ferrous iron by hydrogen peroxide, produces reactive oxidants that may be important to degradation of biologically and chemically recalcitrant organic compounds in surface waters at circum-neutral pH. Sufficient Fe(II) for the photo-Fenton reaction was produced in situ at two field sites (pH 6.1-7.1) and during irradiations of model systems at pH 7.0 with Suwannee River fulvic acid (SRFA). Amorphous iron oxyhydroxide preparations were much more easily photoreduced than ferrihydrite (Ferr-90). The rate of the photo-Fenton reaction was measured as the difference in the H2O2 accumulation rate in irradiations without and with iron in model systems. Use of benzene as a probe for hydroxyl radical (OH) and nitrate photolysis as the OH source indicated that the yield of phenol from the reaction of benzene with OH is reduced in the presence of iron and SRFA. Even when this reduction in yield was accounted for, the rate of OH production from the Fenton reaction in the model systems was much smaller than the rate of the photo-Fenton reaction. These results indicate that OH is not the only oxidant produced by the photo-Fenton reaction in circum-neutral natural waters; however the photo-Fenton reaction could still be significant for contaminant degradation.