Direct quantification of negatively charged functional groups on membrane surfaces
Direct quantification of negatively charged functional groups on membrane surfaces
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DOI：
10.1016/j.memsci.2011.11.018
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发表时间：
2012-02
影响因子：
9.5
通讯作者：
A. Tiraferri;M. Elimelech
中科院分区：
文献类型：
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作者：
A. Tiraferri;M. Elimelech
表面电荷在基于膜的颗粒、大分子和溶解离子种类的分离中起重要作用。在这项研究中，我们提出了两种实验方法来确定在致密的聚合物膜表面的带负电荷的官能团的浓度。这两种技术包括将膜表面部分与化学探针相关联，然后对结合的探针进行定量。醋酸铀酰和甲苯胺蓝O染料分别通过络合作用和静电相互作用与膜官能团相互作用，被用作探针。相关探针的量使用液体闪烁计数的铀原子和甲苯胺蓝染料的可见光光谱进行定量。该技术进行了验证，使用自组装的单分子层的烷硫醇与已知量的带电部分。在各种条件下定量测定了手铸薄膜复合聚酰胺膜以及商业三乙酸纤维素和聚酰胺膜的带负电荷官能团的表面密度。使用这两种技术，我们测量了一个带负电荷的官能团密度为20- 30 nm − 2的手工铸造薄膜复合膜。膜的功能团的电离行为，确定从测量与甲苯胺蓝在不同的pH值，是一致的薄膜复合聚酰胺膜的已发表的数据。同样，商业膜上测得的电荷密度与以前的调查基本一致。这两种方法的相对简单性使它们成为量化各种表面（包括分离膜）的表面电荷浓度的有用工具。
Surface charge plays an important role in membrane-based separations of particulates, macromolecules, and dissolved ionic species. In this study, we present two experimental methods to determine the concentration of negatively charged functional groups at the surface of dense polymeric membranes. Both techniques consist of associating the membrane surface moieties with chemical probes, followed by quantification of the bound probes. Uranyl acetate and toluidine blue O dye, which interact with the membrane functional groups via complexation and electrostatic interaction, respectively, were used as probes. The amount of associated probes was quantified using liquid scintillation counting for uranium atoms and visible light spectroscopy for the toluidine blue dye. The techniques were validated using self-assembled monolayers of alkanethiols with known amounts of charged moieties. The surface density of negatively charged functional groups of hand-cast thin-film composite polyamide membranes, as well as commercial cellulose triacetate and polyamide membranes, was quantified under various conditions. Using both techniques, we measured a negatively charged functional group density of 20–30nm−2for the hand-cast thin-film composite membranes. The ionization behavior of the membrane functional groups, determined from measurements with toluidine blue at varying pH, was consistent with published data for thin-film composite polyamide membranes. Similarly, the measured charge densities on commercial membranes were in general agreement with previous investigations. The relative simplicity of the two methods makes them a useful tool for quantifying the surface charge concentration of a variety of surfaces, including separation membranes.