Manganese (Mn) oxides can oxidize dissolved organic matter (DOM) and alter its chemical properties and microbial degradability, but the compound selectivity for oxidation and oxidative alterations remain to be determined. We applied ultra-high mass spectrometry to catalogue the macromolecular composition of Suwannee River fulvic acid (SRFA) before and after oxidation by a Mn oxide (d‑MnO2) at pH 4 or 6. Polycyclic aromatic hydrocarbons, polyphenols and carbohydrates were more reactive in reducing d-MnO2 than highly unsaturated and phenolic compounds (HuPh) and aliphatics, but highly abundant HuPh contributed the most (~ 50 %) to the overall reduction of d-MnO2. On average, oxidized species had higher molecular weights, aromaticity, carbon unsaturation degree, nominal oxidation state of carbon, and oxygen and nitrogen contents, but were lower in hydrogen content compared to unoxidized species. The oxidation decreased those molecular indices and oxygen and nitrogen contents but increased the hydrogen content, with stronger changes at lower pH. This DOM oxidation on polar mineral surfaces was more selective, but shared similar selectivity rules as adsorption. The abiotic oxidation resembles microbial oxidative degradation of organic matter, and Mn oxide‑oxidizable carbon may be a useful index for detection and identification of labile organic carbon.
This study was supported by China Scholarship Council (CSC) and was published on Environmental Science & Technology, entitled “Macromolecular Characterization of Compound Selectivity for Oxidation and Oxidative Alterations of Dissolved Organic Matter by Manganese Oxide” . Dr. Jianchao Zhang from School of Earth System Science, Tianjin University is the first author of the publication.
Article information: Jianchao Zhang, Amy M. McKenna, Mengqiang Zhu*. Macromolecular Characterization of Compound Selectivity for Oxidation and Oxidative Alterations of Dissolved Organic Matter by Manganese Oxide. Environmental Science & Technology. 2021. 55, 11, 7741-7751 https://doi.org/10.1021/acs.est.1c01283
