Di Vincenzo J P, Sparks D L
Department of Chemistry, Middle Tennessee State University, Murfreesboro 37132, USA.
Arch Environ Contam Toxicol. 2001 May;40(4):445-50. doi: 10.1007/s002440010196.
Laboratory soil sorption experiments have been conducted on pentachlorophenol (PCP) at different pH values in an attempt to elucidate differences in sorption mechanisms between the charged and neutral species. Sorption of PCP on soil was investigated by maintaining pH 4 or 8 in batch sorption experiments. Pre-equilibration of the soil was necessary to maintain a constant pH over the course of the experiments. Additionally, a CaCO3-CO2/N2 buffered solution was necessary to maintain a pH of 8. Sorption of the neutral PCP species conformed to a linear isotherm model, while a Langmuir model provided the best fit for the charged species. Desorption of the neutral form was completely reversible over the sorption times studied but the charged species exhibited some resistance to desorption. Temperature effects on the distribution coefficients (Kd) were investigated and thermodynamic parameters were calculated. The ionized species showed a clear decrease in Kd with increasing temperature while the protonated species showed no apparent trend. Enthalpies (deltaHo), entropies (deltaSo), and free energies (deltaGo), support the conclusions that the neutral form of PCP partitions by hydrophobically binding to the soil while the charged form sorbs by a more specific exothermic adsorption reaction.
已经在不同pH值下对五氯苯酚（PCP）进行了实验室土壤吸附实验，以阐明带电和中性物种之间吸附机制的差异。通过在批量吸附实验中保持pH值为4或8来研究PCP在土壤上的吸附。在实验过程中，对土壤进行预平衡以保持恒定的pH值是必要的。此外，需要一种CaCO3-CO2/N2缓冲溶液来维持pH值为8。中性PCP物种的吸附符合线性等温线模型，而Langmuir模型对带电物种的拟合效果最佳。在所研究的吸附时间内，中性形式的解吸是完全可逆的，但带电物种表现出一定的解吸抗性。研究了温度对分配系数（Kd）的影响并计算了热力学参数。随着温度升高，离子化物种的Kd明显降低，而质子化物种没有明显趋势。焓（ΔHo）、熵（ΔSo）和自由能（ΔGo）支持以下结论：PCP的中性形式通过疏水结合分配到土壤中，而带电形式通过更特定的放热吸附反应吸附。
