Abstract：
Dissolved Organic Matter (DOM) is easily adsorbed and transformed by soil minerals and is an important redox-active component of soil and sediment. However, the effects of the molecular weight of DOM on the interface between MnO2 and DOM remain unclear. Herein, fulvic acid (FA) from peat was size-fractionated into four molecular weight fractions (FA>10kDa, FA5-10kDa, FA3-5kDa, and FA<3kDa) and then reacted with δ-MnO2 in this study. The affinity of FA for MnO2 varied significantly with different molecular weights, and large molecular weight FA was more easily adsorbed by MnO2. After 30 h of reaction, the highest mineralization rate was for FA>10kDa (42.39 %), followed by FA5-10kDa (28.65 %), FA3-5kDa (25.58 %), and FA<3kDa (20.37 %), consistent with the results of adsorption. The stronger reducing ability of the large molecular weight fraction of FA to MnO2 was mainly attributed to hydrophobic functional groups, promoting adsorption by MnO2 and the exposure of more active sites. The main active species involved in the mineralization of FA were •OH and Mn4+ through the quenching experiment. Our findings confirm that the large molecular weight fractions of FA play a crucial part in the adsorption and redox reactions of MnO2. These results may help evaluate the performance of different molecular characteristics of FA in the biogeochemical cycles of MnO2 in the soil environment.
摘要：
溶解性有机质（DOM）易被土壤矿物吸附和转化，是土壤和沉积物中重要的氧化还原活性成分。然而,DOM分子量对MnO2与DOM界面的影响尚不清楚。在这里，泥炭中的富里酸（FA）被大小分级为四个分子量部分（FA>10kDa，FA5-10kDa,FA3-5kDa,和FA<3kDa），然后在本研究中与δ-MnO2反应。FA对MnO2的亲和力随分子量的不同而显著变化,大分子量FA更容易被MnO2吸附。反应30小时后，矿化率最高的是FA>10kDa(42.39%)，其次是FA5-10kDa（28.65%），FA3-5kDa(25.58%),FA<3kDa（20.37%），与吸附结果一致。大分子量FA对MnO2的还原能力较强主要归因于疏水性官能团。促进MnO2的吸附和更多活性位点的暴露。通过淬火实验，参与FA矿化的主要活性物种是•OH和Mn4。我们的发现证实，FA的大分子量部分在MnO2的吸附和氧化还原反应中起着至关重要的作用。这些结果可能有助于评估FA的不同分子特征在MnO2在土壤环境中的生物地球化学循环中的表现。
