Different soil humus fractions are structurally distinct from each other molecularly, however, the relationship between their microscopic molecular structures and the macroscopic reduction of Cr(VI) is still unknown, especially for the humin fraction. In this study, different humus fractions (HA, humic acid; HMi, humin linked to iron oxides; HMc, humin linked to clay; and HMr, humin residue) were sequentially extracted from a typical black soil and well characterized. It was found that HA, HMi and HMc were the same type of humus with similar molecular structures, while HMr was structurally different from the other fractions with a high cellulose content. The removal rate of Cr(VI) in solution decreased with progressive humus fractionation, namely, HA > HMi > HMc > HMr. Based on the two-dimensional correlation spectroscopic analysis (2DCOS) of the FTIR data, the changing functional groups of all humus fractions during reacting with Cr(VI) followed a similar order: carboxyl > phenol > hydroxyl > methyl > methylene. According to the correlation analysis, Cr(VI) reduction rates by different humus fractions were mainly determined by the content of phenol (R² = 0.99) instead of carboxyl (R² = 0.28). Except for HMr, the Cr(VI) reduction rates of different humus fractions were also positively correlated with surface and bulk polarity (R² = 0.98 and 0.99) but not with aromaticity or aliphaticity (R² = 0.21).

不同的土壤腐殖质组分在分子结构上是彼此不同的，但是，它们的微观分子结构与宏观Cr（VI）还原之间的关系仍然未知，尤其是对于腐殖质组分而言。在这项研究中，从典型的黑色土壤中依次提取了不同的腐殖质组分（HA，腐殖酸，HMi，与氧化铁连接的腐殖质，HMc，与粘土连接的腐殖质和HMr，腐殖质残留物），并进行了很好的表征。发现HA，HMi和HMc是具有相似分子结构的相同类型的腐殖质，而HMr与具有高纤维素含量的其他级分在结构上不同。溶液中Cr（VI）的去除率随腐殖质分级分离而降低，即HA> HMi> HMc> HMr。基于FTIR数据的二维相关光谱分析（2DCOS），与Cr（VI）反应期间所有腐殖质组分的官能团变化的顺序相似：羧基>酚>羟基>甲基>亚甲基。根据相关分析，不同腐殖质组分对Cr（VI）的还原率主要取决于苯酚（R ²  = 0.99）而不是羧基（R ²  = 0.28）。除HMr外，不同腐殖质组分的Cr（VI）还原率也与表面和体积极性呈正相关（R ²  = 0.98和0.99），而与芳香性或脂族性（R ²  = 0.21）则不相关。