School of Environment, Tsinghua University, Beijing, 100084, PR China; School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao, 066004, PR China.
School of Environment, Tsinghua University, Beijing, 100084, PR China.
Chemosphere. 2021 Jan;263:127956. doi: 10.1016/j.chemosphere.2020.127956. Epub 2020 Aug 18.
Humification is greatly enhanced by metallic oxides in nature, and the related products are critical to various environmental processes. However, little is known about the interaction between metallic oxides and oxygen in promoting the oxidative polymerization of small organic molecules during the humification process. The synthesis of humic-like acids (HLAs) with MnO was performed in the presence and absence of oxygen, and the influence of oxygen and MnO on the composition evolution of amino-phenolic HLAs was illustrated. The results of ultraviolet-visible (UV-Vis) spectra of reaction mixtures associated with two-dimensional correlation spectroscopy (2D-COS) combined with the XPS spectra of N 1s content changes in HLAs demonstrated that MnO induced pyrrole-type nitrogen formation and enhanced darkening. Furthermore, MnO mainly acted as a catalyst, and oxygen activated the regeneration of MnO by oxidizing free manganese ions, thus substantially promoting the formation and accumulation of HLAs, whereas it decreased the reaction rate of HLAs formation. Moreover, carbon dioxide release was found during the process of the formation of fulvic-like acids (FLAs), and the reaction was oxygen-independent. Additionally, the formation and transformation of products without MnO do not obey kinetics equations, whereas the darkening reaction with MnO followed the pseudo-second-order and pseudo-zero-order kinetics equations. These findings provide new insights into the behaviours and fate of the oxygen-mediated humification process and related reaction products.
自然环境中的金属氧化物极大地促进了腐殖化作用，相关产物对于各种环境过程至关重要。然而，人们对于金属氧化物在促进腐殖化过程中小分子有机物的氧化聚合反应中的作用知之甚少。本研究在有氧和无氧条件下合成了含有 MnO 的类腐殖酸（HLA），并说明了氧气和 MnO 对氨基-酚基 HLA 组成演变的影响。反应混合物的紫外-可见（UV-Vis）光谱与二维相关光谱（2D-COS）结合 HLA 中 N 1s 含量变化的 XPS 光谱的结果表明，MnO 诱导吡咯型氮的形成并促进了暗化。此外，MnO 主要起催化剂的作用，氧气通过氧化游离锰离子来激活 MnO 的再生，从而显著促进 HLA 的形成和积累，而降低了 HLA 形成的反应速率。此外，在富里酸（FLA）形成过程中发现了二氧化碳的释放，且该过程与氧气无关。此外，没有 MnO 时产物的形成和转化不遵循动力学方程，而 MnO 存在时的暗化反应遵循拟二级和拟零级动力学方程。这些发现为了解氧气介导的腐殖化过程及相关反应产物的行为和命运提供了新的思路。
