Electrostatic interaction models for ion binding to humic substances
Electrostatic interaction models for ion binding to humic substances
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DOI：
10.1016/j.colsurfa.2004.10.139
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发表时间：
2005-09
期刊：
影响因子：
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通讯作者：
Takumi Saito;S. Nagasaki;Satoru Tanaka;L. Koopal
中科院分区：
文献类型：
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作者：
Takumi Saito;S. Nagasaki;Satoru Tanaka;L. Koopal
优选地，用不依赖于环境条件的热力学常数来描述与腐殖质(HS)结合的离子。为了解决这个问题，必须建立描述静电和特定相互作用的模型。利用给定的静电模型，不同盐浓度下 HS 的电荷/pH 曲线可以重新绘制为 HS 位置 (pHloc) 附近局部 pH 值的函数。如果模型合适，电荷/pHloc 曲线将合并成主曲线 (MC)。在本研究中，研究了五种静电模型以获得纯化的 Aldrich 腐植酸 (PAHA) 的 pHloc：刚性球 (RS)、离子渗透球、Donnan (NICA)、Donnan-EV 和 Donnan-EDL。 RS模型经过两个版本的测试；一种基于测量的流体动力学半径 (RS-ah)，另一种基于优化半径 (RS-aopt)。离子渗透球模型使用流体动力学半径并提供电势分布；使用球体内的径向平均值作为特征势。在 Donnan (NICA) 模型中，球体的体积 VD（其中 PAHA 的电荷被中和）通过 VD 和离子强度之间的约束进行优化，而在 Donnan-EV 模型中，通过将凝胶半径设置为 PAHA 的流体动力学半径与德拜长度之和来计算 VDis。 Donnan-EDL 模型使用流体动力学粒子半径，并基于 Donnan 模型和扩散双电层模型的组合。只有 RS-aopt、Donnan (NICA) 和 Donnan-EV 模型能够提供足够的 MC。 MC 的立场各不相同。这意味着静电相互作用和内在相互作用之间的区别是依赖于模型的，因此是任意的。 Donnan (NICA) 模型比其他两个模型具有实际优势，因为该模型不需要测量 HS 的大小。为了将离子结合数据常规拟合到包含静电的离子结合等温线方程，这一优点非常重要。
Preferably, the description of ion binding to humic substances (HSs) is done with thermodynamic constants that do not depend on the environmental conditions. To solve this problem, models have to be made that describe the electrostatic and specific interactions. With a given electrostatic model the charge/pH curves of HS at different salt levels can be re-plotted as a function of the local pH near the sites (pHloc) of HSs. If the model is appropriate, the charge/pHloccurves will merge into a master curve (MC). In this study five electrostatic models were investigated to obtain pHlocfor purified Aldrich humic acid (PAHA): rigid sphere (RS), ion-permeable sphere, Donnan (NICA), Donnan-EV, and Donnan-EDL. The RS model is tested in two versions; one based on the measured hydrodynamic radius (RS-ah) and the other on an optimized radius (RS-aopt). The ion-permeable sphere model uses the hydrodynamic radius and provides the potential distribution; as characteristic potential the radial average inside the sphere is used. In the Donnan (NICA) model the volume of the sphere, VD, in which the charge of PAHA is neutralized, is optimized with a constraint between VDand ionic strength, and in the Donnan-EV model VDis calculated by setting the radius of the gel as the sum of the hydrodynamic radius of PAHA and the Debye length. The Donnan-EDL model uses the hydrodynamic particle radius and is based on a combination of the Donnan model and the diffuse electrical double layer model. Only the RS-aopt, Donnan (NICA), and Donnan-EV models give adequate MCs. The positions of the MCs differ with respect to each other. This means that the discrimination between electrostatic and intrinsic interactions is model-dependent and therefore arbitrary. The Donnan (NICA) model has a practical advantage over the other two models because this model needs no measurements of the size of HS. For the purpose of the routine fitting of ion-binding data to an ion-binding isotherm equation that includes the electrostatics, this advantage is quite important.