Heterogeneous Fenton catalytic oxidation technology is a powerful method for degradation of various kinds of non-biodegradable pollutants at moderate condition. Heterogeneous Fenton as the evolution of homogeneous Fenton reaction, offer the advantage of allowing easier separation from treated water and reuse, and wider field of application. This article mainly reviews the development of various iron-based materials, such as zero-valent iron, iron oxides, iron (hydr)oxides, ferrihydrite and other iron compounds, as heterogeneous catalysts for degrading organic pollutants. The mechanisms of Fenton reaction are comprehensively illustrated, including the free radical mechanism and the high-valent iron mechanism. Particularly, the emphasis is to summarize the catalytic activity of different heterogeneous Fenton catalysts, and point out that the catalytic efficiency of heterogeneous Fenton catalyst is strongly affected by the surface oxidation state, specific surface area, kinds of doped transition metal and the crystalline phase of catalysts. The different ways to improve the catalytic efficiency of heterogeneous Fenton catalysts are also concluded as: reducing the size of catalysts to nano-scales, loading the catalysts onto carriers with high specific surface area, introducing transition metal (such as Ti, Co, Mn, Cr and V) into the structure of iron oxide. In addition, some novel catalysts such as ferrites are especially paid attention due to their high catalytic activity and stability. Finally, the prospects of the development of the heterogeneous Fenton catalytic oxidation technology is given. We believe that an ideal heterogeneous Fenton catalyst should possess high catalytic efficiency and H₂O₂ utilization, good chemical stability, effectiveness at extend pH range and the ability of easy to be recycled. Contents
1 Introduction
1.1 Homogeneous Fenton catalytic oxidation technol-ogy
1.2 Heterogeneous Fenton catalytic oxidation techno-logy
2 Advantages, applications and developments of iron compound-based heterogeneous catalysts
2.1 Magnetite (Fe₃O₄)
2.2 Hematite (α-Fe₂O₃)
2.3 Maghemite (γ-Fe₂O₃)
2.4 Goethite (α-FeOOH)
2.5 Akaganeite (β-FeOOH)
2.6 Lepidocrocite (γ-FeOOH)
2.7 Feroxyhyte (δ-FeOOH)
2.8 Ferrihydrite (Fe₅HO₈·4H₂O)
2.9 Other iron compounds
2.10 Zero valence iron (Fe⁰)
3 Conclusion and outlook