Lanteri Y, Fievet P, Szymczyk A
Institut UTINAM, UMR CNRS 6213, Université de Franche-Comté, 16 Route de Gray, Besançon Cedex 25030, France.
J Colloid Interface Sci. 2009 Mar 1;331(1):148-55. doi: 10.1016/j.jcis.2008.11.014. Epub 2008 Dec 10.
The current work focuses on the application of the steric, electric, and dielectric exclusion (SEDE) model to the study of both the ion rejection rate and the membrane potential of a nanofiltration polyamide membrane. The aim of this study was to evaluate the performance of the SEDE model and to compare it with steric/electric exclusion theory. Experiments were conducted with CaCl(2) solutions at various concentrations. The SEDE model is a four-parameter model because the effective pore size (r(p)), the effective thickness-to-porosity ratio (Delta x/A(k)), the effective volume charge density of the membrane (X), and the dielectric constant of the solution inside the pores (epsilon(p)) have to be known to predict the rejection rate and the membrane potential. The first parameter was estimated from membrane potential measurements performed at high salt concentrations and the second from water permeability. In the case of single salt solutions, experimental rejection rates and membrane potentials can be described by a number of couples of values (X,epsilon(p)) because both electric and dielectric exclusion contribute to reject ions. A set of couples (X,epsilon(p)) were first estimated by fitting membrane potentials. One of the couples was found to provide a good description of experimental rejection rates as well. Results showed that the polyamide membrane is negatively charged in CaCl(2) solutions at natural pH and that the membrane charge increases with the salt concentration. A decrease in the effective dielectric constant inside the pores with respect to its bulk value was found. This is indirect evidence that dielectric exclusion plays a major role in the transport phenomena of the studied NF membrane. The standard steric/electric theory was also used to fit experimental rejection rates and membrane potentials, the effective volume charge density being the single adjustable parameter in this case. Unlike the SEDE model, the steric/electric exclusion theory was unable to account simultaneously for both rejection rate and membrane potential data by using a unique choice for X and epsilon(p). This highlights the global coherence of the SEDE model and the nonappropriateness of the description of transport in NF membranes by the classical steric/electric exclusion theory.
当前的工作聚焦于空间、静电和介电排斥（SEDE）模型在纳滤聚酰胺膜离子截留率和膜电位研究中的应用。本研究的目的是评估SEDE模型的性能，并将其与空间/静电排斥理论进行比较。使用不同浓度的CaCl₂溶液进行了实验。SEDE模型是一个四参数模型，因为要预测截留率和膜电位，必须知道有效孔径（r(p)）、有效厚度与孔隙率之比（Δx/A(k)）、膜的有效体积电荷密度（X）以及孔内溶液的介电常数（ε(p)）。第一个参数是通过在高盐浓度下进行的膜电位测量估算得出的，第二个参数是根据水渗透率估算得出的。在单盐溶液的情况下，由于静电排斥和介电排斥都有助于截留离子，实验截留率和膜电位可以用许多组（X，ε(p)）值来描述。首先通过拟合膜电位估算出一组（X，ε(p)）值。结果发现其中一组值对实验截留率也有很好的描述。结果表明，在自然pH值下，聚酰胺膜在CaCl₂溶液中带负电，且膜电荷随盐浓度增加而增加。发现孔内有效介电常数相对于其本体值有所降低。这间接证明了介电排斥在所研究的纳滤膜传输现象中起主要作用。标准的空间/静电理论也被用于拟合实验截留率和膜电位，在这种情况下有效体积电荷密度是唯一的可调参数。与SEDE模型不同，空间/静电排斥理论无法通过对X和ε(p)的唯一选择同时解释截留率和膜电位数据。这突出了SEDE模型的整体一致性以及经典空间/静电排斥理论对纳滤膜传输描述的不适用性。
