Molecular transformation of petroleum compounds by hydroxyl radicals produced upon oxidation of reduced nontronite
Geochimica et Cosmochimica Acta(2024)
摘要
At redox interfaces, the interaction between oxygen and structural Fe(II) in minerals produces hydroxyl radicals (●OH); however, the specific reactivity and mechanisms of oxidation of complex petroleum compounds by ●OH remain poorly understood. This study investigates the interaction mechanisms between ●OH generated from reduced nontronite, an Fe-rich clay mineral (NAu-2), and petroleum compounds by employing a suite of wet chemistry, gas chromatography mass spectrometry and Fourier transform-ion cyclotron resonance-mass spectrometry, as well as theoretical calculations. The results showed that the intrinsic structure, composition, solubility, and adsorption of petroleum molecules onto reduced NAu-2 significantly influenced their reactivity with ●OH. Specifically, the aromatic fraction of a crude oil sample exerted a minimal influence on the oxidation rate of structural Fe(II) in reduced NAu-2, but enhanced the production of ●OH by generating environmentally persistent free radicals. ●OH reacted more with water-soluble dissolved organic matter from oil compared to polar compounds. The newly generated molecules by ●OH exhibited a preference for the insoluble (polar) phase. The oxidation of petroleum hydrocarbons by ●OH was mediated through hydrogen atom abstraction and radical adduct formation, followed by dehydrogenation, hydroxylation, and carboxylation reactions. Consequently, the abundance of oxygen-containing compounds in polar compounds increased. However, specific oxidation pathways differed depending on the nature of petroleum compounds. Our results provide insights that oxidation of petroleum compounds by ●OH is vital for mitigating the negative impacts from hydrocarbon contamination and for evaluating the role of these processes in the carbon cycle in redox-active environments.
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关键词
Nontronite,Petroleum compounds,Hydroxyl radicals,Reactivity,Oxidation mechanisms
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