Green rust (GR) and glucose oxidase (GOX) based Fenton-like reaction: Capacity of sustainable release, promoted conversion of glucose through GOX-iron and pH self-adjustment

Methanol on the rocks: green rust transformation promotes the oxidation of methane

Shared coordination geometries between metal ions within reactive minerals and enzymatic metal cofactors hints at mechanistic and possibly evolutionary homology between particular abiotic chemical mineralogies and biological metabolism. The octahedral coordination of reactive Fe2+/3+ minerals such as green rusts, endemic to anoxic sediments and the early Earth's oceans, mirrors the di-iron reaction centre of soluble methane monooxygenase (sMMO), responsible for methane oxidation in methanotrophy. We show that methane oxidation occurs in tandem with the oxidation of green rust to lepidocrocite and magnetite, mimicking radical-mediated methane oxidation found in sMMO to yield not only methanol but also halogenated hydrocarbons in the presence of seawater. This naturally occurring geochemical pathway for CH4 oxidation elucidates a previously unidentified carbon cycling mechanism in modern and ancient environments and reveals clues into mineral-mediated reactions in the synthesis of organic compounds necessary for the emergence of life.

Atomic-Level Structural Differences between Fe(III) Coprecipitates Generated by the Addition of Fe(III) Coagulants and by the Oxidation of Fe(II) Coagulants Determine Their Coagulation Behavior in Phosphate and DOM Removal

In situ Fe(III) coprecipitation from Fe2+ oxidation is a widespread phenomenon in natural environments and water treatment processes. Studies have shown the superiority of in situ Fe(III) (formed by in situ oxidation of a Fe(II) coagulant) over ex situ Fe(III) (using a Fe(III) coagulant directly) in coagulation, but the reasons remain unclear due to the uncertain nature of amorphous structures. Here, we utilized an in situ Fe(III) coagulation process, oxidizing the Fe(II) coagulant by potassium permanganate (KMnO4), to treat phosphate-containing surface water and analyzed differences between in situ and ex situ Fe(III) coagulation in phosphate removal, dissolved organic matter (DOM) removal, and floc growth. Compared to ex situ Fe(III), flocs formed by the natural oxidizing Fe2+ coagulant exhibited more effective phosphate removal. Furthermore, in situ Fe(III) formed through accelerated oxidation by KMnO4 demonstrated improved flocculation behavior and enhanced removal of specific types of DOM by forming a more stable structure while still maintaining effective phosphate removal. Fe K-edge extended X-ray absorption fine structure spectra (EXAFS) of the flocs explained their differences. A short-range ordered strengite-like structure (corner-linked PO4 tetrahedra to FeO6 octahedra) was the key to more effective phosphorus removal of in situ Fe(III) than ex situ Fe(III) and was well preserved when KMnO4 accelerated in situ Fe(III) formation. Conversely, KMnO4 significantly inhibited the edge and corner coordination between FeO6 octahedra and altered the floc-chain-forming behavior by accelerating hydrolysis, resulting in a more dispersed monomeric structure than ex situ Fe(III). This research provides an explanation for the superiority of in situ Fe(III) in phosphorus removal and highlights the importance of atomic-level structural differences between ex situ and in situ Fe(III) coprecipitates in water treatment.

Co-Immobilization of Enzymes and Metals on the Covalent-Organic Framework for the Efficient Removal of Mycotoxins

Mycotoxin is an important contaminant in food and the environment. The conventional methods for detoxification of mycotoxins are plagued by high chemical consumption, secondary pollution, and specific equipment required. In this study, we propose a chemoenzymatic cascade reaction for mycotoxin removal in an effective and green manner using an enzyme-metal hybrid catalyst synthesized by compartmental co-immobilized glucose oxidase (GOx) and Fe₃O₄ nanoparticles (NPs) on a flower-shaped covalent organic framework (COF). The GOx-Fe₃O₄@COF hybrid catalyst exhibits excellent activity in mycotoxin removal due to the enrichment of mycotoxins in COF and the cooperative catalysis between GOx and Fe₃O₄ NPs. The degradation efficiency of aflatoxin B₁ (AFB₁) in the chemoenzymatic cascade reaction catalyzed by GOx-Fe₃O₄@COF is 3.5 times higher than that in the Fenton reaction catalyzed by Fe₃O₄@COF. The GOx-Fe₃O₄@COF hybrid catalyst is highly active in a wide pH range of 3.0-7.0, overcoming the limitation of the Fenton reaction that can only perform below pH 3.0. This study provides a powerful tool for the efficient removal of mycotoxins.