Review on spinel ferrites-based materials (MFe2O4) as photo-Fenton catalysts for degradation of organic pollutants

In recent years, the removal of organic pollutants in water has become a research hotspot for the scientific community. Advanced oxidation processes (AOPs) are effective ways to remove organic pollutant in water. Among them, the photo-Fenton process, as a simple, efficient, and clean catalytic method, has been widely applied. In the process of exploring photo-Fenton catalysts, spinel ferrites (MFe2O4, M = Cu, Co, Ni, Zn, Mn, etc.) has attracted more and more attentions because of its rich surface active sites, low price, better light-corrosion resistance, and outstanding recoverability. However, the relatively narrow band gap easily causes the rapid recombination of photo-generated electron-hole pairs, which seriously hinders the high catalytic activity of MFe2O4 catalysts. To improve the catalytic effect of MFe2O4 materials in wastewater treatment, this paper summarizes the problems faced in the photo-Fenton process when pure MFe2O4 as catalysts and it is found that the catalytic activity may be determined by the crystal field stabilization energy. Most importantly, the effective ways to improve the catalytic performance are discussed in detail, including element doping and coupling with carbon-based materials. And a possibility is proposed that the formation of n-type semiconductors by multi-electron doping is beneficial to promote Fe2+/Fe3+ cycle. Additionally, the order of factors affecting the degradation performance is determined in practical application, which will lay a foundation for the design of MFe2O4-based catalysts in the future.