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Dissolved natural organic matter (DOM) is a complex matrix of organic matter that is ubiquitous in natural aquatic environments. So far, substantial research has been conducted on the DOM adsorption on Mn oxides as well as the reduction processes of Mn oxides by DOM. However, little is known about the oxidative roles of DOM in oxidizing Mn2+(aq) to Mn(III/IV) oxide solids. Sunlight-driven processes can initiate the degradation of DOM accompanied by the formation of photochemically produced reactive intermediates, including excited triplet state DOM (3DOM*), hydroxyl radical (•OH), superoxide radical (O2•−), hydrogen peroxide (H2O2), and singlet oxygen (1O2). Further, in the presence of halide ions, reactive halogen species can be generated by reactions between 3DOM* and halide ions, and by reactions between •OH and halide ions. In this study, we found that the solution pH controlled the oxidation of Mn2+(aq) to Mn oxide solids during photolysis of DOM. Among the reactive oxygen species, Mn2+(aq) was found to be oxidized to Mn oxide solids mainly by O2•−. The DOM with different quantities of aromatic functional groups affected its oxidative capability. With the addition of bromide ions (Br−), Mn2+(aq) oxidation was promoted further by formation Br radicals, which can also oxidize Mn2+(aq) to Mn oxide solids. These findings can help us better understand the oxidative role of DOM in the formation of Mn oxide solids in organic-rich surface water. In addition, this study assists in comprehending the impacts of the photolytic reactions between DOM and halide ions and their resulting reactive oxygen and halogen species on the oxidation and reduction processes of other transition metal oxides in the environment.
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This content will become publicly available on June 3, 2026
Photochemically Induced Co-oxidation of Aqueous Manganese and Cobalt and the Formation of Cobalt-Incorporated Manganese Oxides
Manganese (Mn) oxides, widely found in aquatic and terrestrial environments, play crucial roles in natural ecosystems and in environmental processes. Previously, it was believed that naturally abundant Mn oxides originated through biotically mediated processes. However, we have revealed the significance of photochemically induced abiotic oxidation of Mn2+(aq) to Mn(IV) oxides. This study further elucidates the photochemically induced co-oxidation of aqueous Mn2+ and cobalt (Co2+), which leads to the predominant formation of Mn(IV)–Co(III) oxide nanosheets. Both pair distribution function analysis and X-ray absorption spectra provide evidence that Co2+ is mainly oxidized to Co(III) within the plane of the Mn oxide structure, where it forms double-edge-sharing arrangements. Additionally, the initial concentration of Co2+ greatly influences the extent of Co incorporation within the final Mn–Co oxides and Mn oxidation states. Increased Co incorporation correlates with a higher concentration of oxygen vacancies within the Mn oxide structures, which reduces their band gap and significantly influences the reactivity of Mn oxides, governing their ability to participate in pollutant degradation and redox transformations. This study advances our understanding of the mechanism of formation of Co-incorporated Mn oxides in the natural environment and provides insights into their occurrence in the natural environment and their applications in environmental processes.
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- Award ID(s):
- 2122070
- PAR ID:
- 10644494
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- Environmental Science & Technology
- Volume:
- 59
- Issue:
- 21
- ISSN:
- 0013-936X
- Page Range / eLocation ID:
- 10455 to 10466
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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