Ghosh Mandakranta, Junker Moritz A, van Lent Robert T M, Madauß Lukas, Schleberger Marika, Lebius Henning, Benyagoub Abdenacer, Wood Jeffery A, Lammertink Rob G H
Soft matter, Fluidics and Interfaces, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands.
Fakultät für Physik und CENIDE, Universität Duisburg-Essen, 47057 Duisburg, Germany.
ACS Omega. 2021 Jan 20;6(4):2487-2493. doi: 10.1021/acsomega.0c03958. eCollection 2021 Feb 2.
In this work, we have studied the pH-dependent surface charge nature of nanoporous graphene. This has been investigated by membrane potential and by streaming current measurements, both with varying pH. We observed a lowering of the membrane potential with decreasing pH for a fixed concentration gradient of potassium chloride (KCl) in the Donnan dominated regime. Interestingly, the potential reverses its sign close to pH 4. The fitted value of effective fixed ion concentration ( ) in the membrane also follows the same trend. The streaming current measurements show a similar trend with sign reversal around pH 4.2. The zeta potential data from the streaming current measurement is further analyzed using a 1-pK model. The model is used to determine a representative pK (acid-base equilibrium constant) of 4.2 for the surface of these perforated graphene membranes. In addition, we have also theoretically investigated the effect of the PET support in our membrane potential measurement using numerical simulations. Our results indicate that the concentration drop inside the PET support can be a major contributor (up to 85%) for a significant deviation of the membrane potential from the ideal Nernst potential.
在这项工作中，我们研究了纳米多孔石墨烯的pH依赖性表面电荷性质。通过膜电位和流动电流测量对其进行了研究，两者均在不同pH值下进行。在唐南主导区域，对于固定浓度梯度的氯化钾（KCl），我们观察到随着pH值降低，膜电位降低。有趣的是，电位在接近pH 4时会反转其符号。膜中有效固定离子浓度（ ）的拟合值也遵循相同趋势。流动电流测量显示出类似趋势，在pH 4.2左右符号反转。使用1-pK模型对流动电流测量得到的zeta电位数据进行了进一步分析。该模型用于确定这些穿孔石墨烯膜表面的代表性pK（酸碱平衡常数）为4.2。此外，我们还通过数值模拟从理论上研究了PET支撑体在我们的膜电位测量中的影响。我们的结果表明，PET支撑体内的浓度下降可能是导致膜电位显著偏离理想能斯特电位的主要因素（高达85%）。
