Phosphonates-enhanced production of reactive oxygen species by ferrous ion in the presence of oxygen: Effects and mechanisms

Due to their potential environmental hazards, the ongoing release of phosphonates into natural water bodies has sparked serious worries. Phosphonates are typically found as metal-phosphonate complexes in natural water and their complex with Fe2+ is predominant. In this study, we demonstrated that phosphonates could enhance reactive oxygen species (ROS) production upon complexation with Fe2+ in the presence of O2 (from the air). Using aminotris (methyphosphonic acid) (ATMP) as a model phosphonate, we thoroughly investigated the effects and mechanism of ROS production in the ATMP/Fe2+/O2 system. OH center dot-mediated oxidation was responsible for the transformation of co-existing contaminants. With oxygen (O-) and nitrogen (N-) in ATMP complexed with Fe2+, the redox potential of Fe2+/Fe3+ was significantly reduced, thus promoting OH center dot production. Further experiments identified OH center dot production followed the one-electron transfer pathway (O2 -> O2 center dot- -> H2O2 -> OH center dot). Due to the generation of OH center dot, 61.5% of phenol (10 mg/L) was degraded and a small fraction of ATMP underwent C-P bond cleavage. The phenomenon of ATMP-enhanced ROS production and co-existing pollutants degradation occurred throughout a wide pH spectrum from 3.0 to 10.0. This study not only clarified how ROS were produced in the ATMP/Fe2+/O2 system, but also provided new ideas for understanding the environmental behavior of phosphonates in promoting co-existing pollutants degradation.