Charge Regulation at a Nanoporous Two-Dimensional Interface

Abstract

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 (C̅ R) 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.

Multifunctional graphene heterogeneous nanochannel with voltage-tunable ion selectivity

“…7 . It is difficult to obtain analytical solutions in nanochannels with complex structures, and thus numerical simulations with the finite element method were used here, which have also been successfully utilized in studying the ion transport in nanofluidics 9 – 11 , 22 , 27 , 30 – 32 , 39 , 40 , 61 – 68 , including not only PETNCs 39 , 40 , 63 – 66 but also nanopores in 2D materials 9 – 11 , 22 , 27 , 67 , 68 .…”

Electrical Circuit Modeling of Nanofluidic Systems

“…Since the average excess concentration, Σ s , is linear with the surface charge density [Equation ( 5)], the nanochannel resistance [R nano c 0 /Σ s in Equation (7)] is modified accordingly. Since Equation ( 2) is the exact solution to the PNP equations, it is relatively straightforward to incorporate SCR models [40,45,47] into the solution for R unit-cell by modifying Σ s . This is another added advantage of our theory.…”