Humic substances (HSs) have great retention effects on pentachlorophenol (PCP) migration in subsurface environment, but the adsorption mechanism of PCP by HSs with various aromatic/aliphatic moieties and acidic functional groups in the presence of Cr(VI) is still unclear. In this study, the adsorption mechanism of PCP by undissolved humic acid (HA) and humin (HM) extracted from peat, black soil, lignite and coal was investigated under the presence of Cr(VI). According to the results, HA samples had much lower adsorption capacity for hydrophobic PCP than HM samples due to their higher contents of hydrophilic polar oxygen-containing functional groups. In respect to PCP adsorption mechanism, the molecular unsaturation of HSs associated with humification degree was found to be the determinant instead of polarity. Notably, after reacting with Cr(VI), significant decreasing of PCP adsorption quantities occurred on HSs extracted from lignite and coal with higher degrees of unsaturation (H/C < 0.64), while HSs extracted from peat and black soil with lower degrees of unsaturation (H/C > 0.83) kept almost unchanged, which can be attributed to the much higher reactivity of aromatic domains of HSs for Cr(VI) reduction compared with aliphatic moieties. This indicated that the adsorption mechanism of PCP by HSs with higher and lower degrees of unsaturation might be respectively driven by π-π interaction and hydrophobic interaction. This study highlighted the diverse adsorption mechanisms of PCP on HSs with different degrees of humification, and emphasized the coexisting Cr(VI) only have significant effect on PCP adsorption by HSs with higher humification degrees instead of the lower ones.

腐殖质（HSs）对五氯苯酚（PCP）在地下环境中的迁移有很大的保留作用，但在Cr（VI）存在下，具有各种芳香族/脂肪族部分和酸性官能团的HSs对PCP的吸附机制尚不清楚。在本研究中，研究了在 Cr(VI) 存在下从泥炭、黑土、褐煤和煤中提取的未溶解腐殖酸 (HA) 和腐殖质 (HM) 对五氯苯酚的吸附机理。根据结果​​，由于亲水性极性含氧官能团含量较高，HA 样品对疏水性 PCP 的吸附能力比 HM 样品低得多。关于PCP吸附机制，发现与腐殖化程度相关的HSs的分子不饱和度是决定因素而不是极性。值得注意的是，在与 Cr(VI) 反应后，从褐煤和煤中不饱和度较高(H/C < 0.64)提取的HSs上PCP吸附量显着下降，而从泥炭和黑土中提取的不饱和度较低(H/C > 0.83)中的HSs几乎保持不变，这可归因于与脂肪族部分相比，HSs 的芳香族域对 Cr(VI) 还原的反应性要高得多。这表明具有较高和较低不饱和度的HSs对PCP的吸附机制可能分别由π-π相互作用和疏水相互作用驱动。本研究强调了 PCP 在不同腐殖化程度的 HSs 上的多种吸附机制，并强调共存的 Cr(VI) 仅对腐殖化程度较高的 HSs 对 PCP 的吸附作用显着，而不是较低的。