An Efficient Anthraquinone–Resin Hybrid Co‐Catalyst for Fenton‐Like Reactions: Acceleration of the Iron Cycle Using a Quinone Cycle under Visible‐Light Irradiation

Abstract

The Fenton reaction (H 2 O 2 +Fe 2 + /Fe 3 + ) has been widely used to oxidize organic compounds for various purposes, such as DNA damage by free radicals, [1] organic or inorganic synthesis, [2] and environmental detoxication. [3] As a versatile catalysis system, Fenton-like reactions have particular features: readily available and inexpensive reagents, extremely large rate constants (ca. 10 9 m À1 s À1 ), and a facile procedure. [4] The generally accepted free-radical-chain mechanism for the Fenton reactions is shown below, [5] and the slow reaction [Eq.(2)] is the rate-determining step.When Fenton reactions are used for rebating organic pollutants in water, if the cycle of iron species is not fast enough, or furthermore is not sustainable, the degradation rate and mineralization yield of pollutants would be very low and low-molecular-weight organic acids accumulate unavoidably during the degradation of organic substrates, thereby leading to the complete impedance of the whole reaction. [6] The acceleration of iron cycling and the more-efficient production of powerful HO· (E 0 = + +2.59 V vs. NHE; NHE = normal hydrogen electrode) as reactive species, to oxidize substrates in this chemical system, have become challenging goals for advanced oxidation processes (AOPs).In recent decades, the Fenton-like chemistry based on iron complexes of N-donor ligands has made a giant step towards significant acceleration of iron cycling. [7] Meunier and co-workers [7a] and Collins and co-workers [7b] have developed catalysts that use special iron complexes in the place of free Fe 2 + or Fe 3 + ions. These intricate catalysts resemble enzymes to some extent and show high catalytic activities for the degradation of organic pollutants. However, for the former, having an acetonitrile co-solvent in water as an axial ligand for the FePcS catalyst is needed; for the latter, the Fe-TAML catalyst is itself oxidatively degraded during recyclable use and even de-metalates in some standard buffers. [8] Our group has also reported some iron complexes that can activate H 2 O 2 under visible-light irradiation to effectively degrade organic pollutants in water without any co-solvent, albeit with relatively low activity. [9] Recently, an interesting study into attenuation of the Fenton reaction by iron chelation was reported, which is the reverse strategy to the above efforts for inhibiting oxidative stress; [10] moreover, tuning the Fenton-like reaction to inhibit or induce oxidative stress by UV-light-activated release of caged copper from a photolabile ligand was also reported. [11] Fenton reactions can be accelerated by UV-light illumination [3b, 12] but not by much-broader visible-light irradiation. This feature is because the absorption wavelength of Fe(OH) 2 + is less than 400 nm and general organic pollutants cannot absorb visible light. Visible-light irradiation comprises about 50 % of the sun's energy, and thus using visible light to accelerate the Fenton-like reactions is strongly desirable but remains a challenge. Herein, w...

Enhanced Generation of Reactive Oxygen Species under Visible Light Irradiation by Adjusting the Exposed Facet of FeWO4 Nanosheets To Activate Oxalic Acid for Organic Pollutant Removal and Cr(VI) Reduction

“…The presence of persistent organic pollutants, such as industrial dyes, antibiotics, and hexavalent chromium Cr­(VI), in the wastewater has caused great concern because of their incomplete elimination and persistent pollution of the environment. − Because of the large volume of industrial and municipal wastewater, advanced water treatment techniques are essential for maintaining healthy water circulation. Advanced water treatment techniques for organic pollutant degradation rely on the Fenton reaction (Fe 2+ /H 2 O 2 ) to generate • OH. − Nevertheless, in a traditional Fenton reaction system, the free ferrous ions can be quickly expended, and this process requires the addition of Fe 2+ .…”

Crystal‐Facet Engineering of Ferric Giniite by Using Ionic‐Liquid Precursors and Their Enhanced Photocatalytic Performances under Visible‐Light Irradiation

“…[45][46][47][48][49][50] However, it should be pointed out that the heterogeneous Fenton reaction itself is too slow, especially those containing Fe III oxides, due to the slow reduction of Fe III to Fe II (k = 0.001-0.1 m À1 S À1 ). [51][52] Therefore, most heterogeneous Fenton catalysts are used in an aqueous environment with the assistance of UV irradiation for the acceleration of the reaction, resulting in the need for specific equipment at additional cost. In this respect, it is well-understood that significant attention has been directed towards using solar-driven heterogeneous Fenton catalysts with a high catalytic activity and long-term stability.…”

“…Correspondingly, in a large number of studies in the past few decades, these heterogeneous catalysts have demonstrated their usefulness in treating various organic pollutants in an aqueous environment 45–50. However, it should be pointed out that the heterogeneous Fenton reaction itself is too slow, especially those containing Fe III oxides, due to the slow reduction of Fe III to Fe II ( k =0.001–0.1 M −1 S −1 ) 51–52. Therefore, most heterogeneous Fenton catalysts are used in an aqueous environment with the assistance of UV irradiation for the acceleration of the reaction, resulting in the need for specific equipment at additional cost.…”

One‐step preparation of Fe2O3/reduced graphene oxide aerogel as heterogeneous Fenton‐like catalyst for enhanced photo‐degradation of organic dyes

“…To overcome these drawbacks, heterogeneous Fenton‐like reaction has become an alternative technology, in which H 2 O 2 is converted to ⋅OH on solid catalyst surface. Among various catalysts, magnetic nanoparticles (NPs) are deeply studied owing to extensive source, high efficiency and magnetic separation ,. Unfortunately, magnetic NPs easily aggregate because of high surface energy and strong anisotropic dipolar interactions, which reduces their catalytic activity.…”