Insights into reactive species generation and organics selective degradation in Fe-based heterogeneous Fenton-like systems: A critical review

Currently, iron (Fe)-based heterogeneous Fenton-like processes have been widely employed for treating organic pollutants in wastewater. During such processes, organic pollutants are usually attacked by the generated reactive species and thus decomposed into some intermediates, further CO2 and H2O. Therefore, a comprehensive understanding of reactive species generation and utilization is significant for achieving the selective and effective degradation of organic pollutants in complicated water matrix. Herein, on the basis of the comprehensive literature survey, this review briefly analyzes the H2O2 activation mechanism over surface active sites of Fe catalysts, including surface Fe sites, oxygen vacancies, and electron distribution-polarized micro-areas, from the points of reactive species generation. Meanwhile, the guidelines for improving the Fenton-like performance of Fe catalysts are proposed based on this information. Furthermore, the selective oxidation of organic pollutants by generated reactive species, including high-valent iron oxo species (Fe(IV) = O/Fe(V) = O), hydroxyl radical (•OH), superoxide radical (•O2−), and singlet oxygen (1O2) are discussed with emphasis on the existing form and chemical characteristics of reactive species. Finally, the existing challenges and the prospects for water treatment are proposed from mechanism research and practical application aspects. We hope this review can provide a deeper understanding of the fundamentals of Fe-based heterogeneous Fenton-like reaction, and help readers to select a suitable Fenton-like system for practical applications.