Interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials： A review

The heterogeneous Fenton reaction can generate highly reactive hydroxyl radicals（·OH）from reactions between recyclable solid catalysts and H2O2 at acidic or even circumneutral pH.Hence,it can effectively oxidize refractory organics in water or soils and has become a promising environmentally friendly treatment technology.Due to the complex reaction system,the mechanism behind heterogeneous Fenton reactions remains unresolved but fascinating,and is crucial for understanding Fenton chemistry and the development and application of efficient heterogeneous Fenton technologies.Iron-based materials usually possess high catalytic activity,low cost,negligible toxicity and easy recovery,and are a superior type of heterogeneous Fenton catalysts.Therefore,this article reviews the fundamental but important interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials..OH,hydroperoxyl radicals/superoxide anions（HO2./O2^-.）and high-valent iron are the three main types of reactive oxygen species（ROS）,with different oxidation reactivity and selectivity.Based on the mechanisms of ROS generation,the interfacial mechanisms of heterogeneous Fenton systems can be classified as the homogeneous Fenton mechanism induced by surface-leached iron,the heterogeneous catalysis mechanism,and the heterogeneous reaction-induced homogeneous mechanism.Different heterogeneous Fenton systems catalyzed by characteristic iron-based materials are comprehensively reviewed.Finally,related future research directions are also suggested.

Precursor-driven structural tailoring of iron oxychloride for enhanced heterogeneous Fenton activity

Iron oxychloride(FeOCl)is a unique layered material with tunable electronic properties.The conventional synthetic route of chemical vapor transition involves a thermodynamics-driven gas-solid interfacial reaction which often generates macroscopic crystals with stable facets.In this study,through analyzing the effects of the synthetic parameters on the FeOCl synthesis,we discovered the dominant contribution of theα-Fe_(2)O_(3)precursors on the chemical property of the FeOCl product,and subsequently developed a highly-controllable synthetic route of tailoring the FeOCl structures into small sizes and exposed high-energy facets via a facile and scalable mechanical-chemical approach.The synthesized products could be systematically tuned by the ball-milling conditions of theα-Fe_(2)O_(3)precursors.With increased milling time,the FeOCl crystallites demonstrated reduced sizes and more exposed(110)facets.Intriguingly,these smallsized FeOCl catalysts exhibited much faster Fenton-like kinetics than the pristine macroscopic FeOCl materials.Specifically,FeOCl catalysts with a 12-hour milling time showed nearly 39 times higher efficiency toward phenol degradation than the pristine FeOCl.The structure-reactivity relationship was further elucidated using the combinatory analysis via density functional theory calculation,electron paramagnetic resonance and radical quenching probe experiments.This work provides a rationale for tailoring the surface structures of FeOCl crystallites for potential applications in environmental catalysis.

Heterogeneous fenton oxidation of methylene blue with Fe-impregnated biochar catalyst

Fe-impregnated biochar(Fe-BC)as high-efficiency heterogeneous Fenton catalyst was synthesized and evaluated in detail for its catalytic activity,stability and reusability under various conditions.The optimal conditions for the Fenton oxidation of methylene blue(MB)as model dye were determined as 0.075 g/L H_(2)O_(2),0.5 g/L Fe-BC for 0.1 g/L MB,which resulted in optimum Dye:Fe_(cat):H_(2)O_(2) ratio of 1:5:0.75(on g/L basis)or[Dye]:[Fe_(total)]:[H_(2)O_(2)]molar ratio of 1:6.2:7.0 respectively.The effective degradation of MB was identified over a wider pH range,and even after four consecutive runs Fe-BC maintained above 95%MB removal rate within 3 min of treatment with low Fe release,indicating strong stability and reusability.Under the optimum Dye:Fe_(cat):H_(2)O_(2)(g/L)condition at initial pH 4,the Fe-BC achieved 99.9%removal efficiency of MB within 3 min in heterogeneous Fenton reaction(HEFR)with much less H_(2)O_(2) concentration and low catalyst dosage,demonstrat-ing its efficiency and cost-effectiveness compared to other Fenton reaction catalysts.The removal velocity of MB showed two rate steps:a fast first stage followed by a slow stage with the rate in the order of H_(2)O_(2)/Fe-BC⋙H_(2)O_(2)/biochar>biochar>H_(2)O_(2).Overall,the developed Fe-BC is more economical with strong stability and recyclability for use in HEFR for treating recalcitrant pollutants.