Insight on the generation of reactive oxygen species in the CaO2/Fe(II) Fenton system and the hydroxyl radical advancing strategy

Calcium peroxide (CaO2) is a stable hydrogen peroxide (H2O2) carrier, and the CaO2/Fe(II) system has been applied for treatment of various pollutants. It is commonly reported in the literature that hydroxyl radical (HO center dot) and superoxide radical anions (O-2(center dot-)) are the two main reactive oxygen species (ROSs) generated in the CaO2/Fe (II) system. However, many of the reported results were deduced from degradation performance rather than specific testing of radical generation. Thus, the specific generation of ROSs and the influence of system conditions on ROSs yield are still unclear. To our knowledge, this is the first study specifically focusing on the generation of HO center dot and O-2(center dot-) in the CaO2/Fe(II) system. Experimental conditions were optimized to investigate the production of HO center dot and O-2(center dot-). The results showed the influences of CaO2, Fe(II), and solution pH on HO% and O-2(center dot-) generation, and the HO center dot generation efficiency was reported for the first time. In addition, the ROSs generation pathways in the CaO2/Fe(II) system were elucidated. A strategy for enhancing HO center dot yield is developed, based on the continuously dosing Fe(II). This proposed strategy has implications for the effective application of in situ chemical oxidation employing CaO2/Fe(II) for groundwater remediation.