Improvement of Fe2+/peroxymonosulfate oxidation of organic pollutants by promoting Fe2+ regeneration with visible light driven g-C3N4 photocatalysis

The Fe2+/peroxymonosulfate (PMS) process always faced the major drawbacks of slow Fe2+ regeneration, re -agent waste and strict pH requirement. Significant synergy was found by combining the visible light driven g-C3N4 photocatalysis with Fe2+(or Fe3+)/PMS at very low amount of reagent dosages. The synergistic mechanisms were investigated systematically. It was found that visible light played a minor role and the photoelectrons excited from g-C3N4 played the dominant role in the fast regeneration of Fe2+, and iron species should be the dominant activator for PMS compared with g-C3N4 in the combined process. For the complete degradation of 0.01 mM Bisphenol A (BPA), the consumption of PMS and Fe2+ in the combined process accounted for only 1/27 and 1/198 as that consumed in Fe2+/PMS process. The O-2(center dot-), O-1(2) and Fe(IV) were found to be the dominant reactive species in Fe2+/PMS, while center dot OH was more preferably and continuously produced in the combined process. Moreover, the combined process showed significant advantages to maintain high efficiency over a wide pH range (3.0 similar to 8.5) and to degrade pollutants with high concentrations. Stronger mineralization capability was also achieved by the combined process than the inclusive processes. Two degradation pathways of BPA degra-dation were proposed based on identifying the intermediates.