Insights into the role of in-situ and ex-situ hydrogen peroxide for enhanced ferrate(VI) towards oxidation of organic contaminants.

Recently, several studies have been conscious of the promotion effect of hydrogen peroxide (HO), a self-decay product of ferrate (Fe(VI)), on Fe(VI) to oxidize contaminations, but the pivotal activation mechanism has not been thoroughly evaluated. This work aims to compare and reveal the promoting mechanism of HO in Fe(VI) and Fe(VI)-HO processes, and to illustrate the practical use potential of Fe(VI)-HO system. Many lines of evidence verified the involvement of OH and O in pollutant degradation were excluded in Fe(VI) and Fe(VI)-HO systems, meaning that high dosage of HO cannot trigger an activation pathway different from in-situ HO. The better oxidation performance of the Fe(VI)-HO system than Fe(VI) alone was ascribed to the catalytic role of in-situ and ex-situ HO, which can directly and/ or indirectly facilitate the formation of Fe(IV) and Fe(V). Considering the structural similarity of peroxymonosulfate (PMS) and peroxydisulfate (PDS) with HO as well as their universality in water pollutant remediation, the oxidation properties and reactive oxidants of Fe(VI)-PMS and Fe(VI)-PDS processes were also examined. Besides, the Fe(VI)-HO system suffered from less restriction by inorganic ions and natural organic matter, and exhibited satisfactory pollutant removal effects in real water. Overall, this work provides a further and comprehensive cognition about the role of HO in Fe(VI) and Fe(VI)-HO systems.