Volta Thomas T, Walters Stevie N, Martin Charles R
Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA.
Nanomaterials (Basel). 2024 Jul 16;14(14):1209. doi: 10.3390/nano14141209.
Under ideal conditions, nanotubes with a fixed negative tube-wall charge will reject anions and transport-only cations. Because many proposed nanofluidic devices are optimized in this ideally cation-permselective state, it is important to know the experimental conditions that produce ideal responses. A parameter called C, the highest salt concentration in a contacting solution that still produces ideal cation permselectivity, is of particular importance. Pioneering potentiometric studies on gold nanotubes were interpreted using an electrostatic model that states that C should occur when the Debye length in the contacting salt solution becomes equivalent to the tube radius. Since this "double-layer overlap model" (DLOM), treats all same-charge ions as identical point charges, it predicts that all same-charged cations should produce the same C. However, the effect of cation on C in gold nanotubes was never investigated. This knowledge gap has become important because recent studies with a polymeric cation-permselective nanopore membrane showed that DLOM failed for every cation studied. To resolve this issue, we conducted potentiometric studies on the effect of salt cation on C for a 10 nm diameter gold nanotube membrane. C for all cations studied were, within experimental error, the same and identical, with values predicted by DLOM. The reason DLOM prevailed for the gold nanotubes but failed for the polymeric nanopores stems from the chemical difference between the fixed negative charges of these two membranes.
在理想条件下，具有固定负管壁电荷的纳米管会排斥阴离子，仅传输阳离子。由于许多提出的纳米流体装置在这种理想的阳离子选择性透过状态下得到了优化，因此了解产生理想响应的实验条件非常重要。一个名为C的参数，即接触溶液中仍能产生理想阳离子选择性透过的最高盐浓度，尤为重要。对金纳米管的开创性电位研究是使用静电模型进行解释的，该模型指出，当接触盐溶液中的德拜长度等于管半径时，就会出现C值。由于这种“双层重叠模型”（DLOM）将所有同电荷离子视为相同的点电荷，它预测所有同电荷阳离子应该产生相同的C值。然而，阳离子对金纳米管中C值的影响从未被研究过。由于最近对聚合物阳离子选择性透过纳米孔膜的研究表明，DLOM对所研究的每种阳离子都不适用，这个知识空白变得很重要。为了解决这个问题，我们对直径为10 nm的金纳米管膜进行了盐阳离子对C值影响的电位研究。在所研究的所有阳离子中，C值在实验误差范围内是相同的，并且与DLOM预测的值一致。DLOM在金纳米管中适用而在聚合物纳米孔中不适用的原因源于这两种膜固定负电荷的化学差异。
