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

Calcium peroxide (CaO 2 ) is a stable hydrogen peroxide (H 2 O 2 ) carrier, and the CaO 2 /Fe(II) system has been applied for treatment of various pollutants. It is commonly reported in the literature that hydroxyl radical (HO ) and superoxide radical anions (O 2 − ) are the two main reactive oxygen species (ROSs) generated in the CaO 2 /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 and O 2 − in the CaO 2 /Fe(II) system. Experimental conditions were optimized to investigate the production of HO and O 2 − . The results showed the influences of CaO 2 , Fe(II), and solution pH on HO and O 2 − generation, and the HO generation efficiency was reported for the first time. In addition, the ROSs generation pathways in the CaO 2 /Fe(II) system were elucidated. A strategy for enhancing HO 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 CaO 2 /Fe(II) for groundwater remediation.