Ion Transport in a pH-Regulated Nanopore

Abstract

Fundamental understanding of ion transport phenomena in nanopores is crucial for designing the next-generation nanofluidic devices. Due to surface reactions of dissociable functional groups on the nanopore wall, the surface charge density highly depends upon the proton concentration on the nanopore wall, which in turn affects the electrokinetic transport of ions, fluid, and particles within the nanopore. Electrokinetic ion transport in a pH-regulated nanopore, taking into account both multiple ionic species and charge regulation on the nanopore wall, is theoretically investigated for the first time. The model is verified by the experimental data of nanopore conductance available in the literature. The results demonstrate that the spatial distribution of the surface charge density at the nanopore wall and the resulting ion transport phenomena, such as ion concentration polarization (ICP), ion selectivity, and conductance, are significantly affected by the background solution properties, such as the pH and salt concentration.

Transport mechanisms in nanopores and nanochannels: can we mimic nature?

“…This charge regulation effect not only affects nanochannels modified by pH-responsive polyelectrolytes but also systems where the inner walls have weak acid or basic groups. The later situation was analyzed by Yeh et al using numerical calculations [44] and analytical theory [45]. These works showed that charge regulation is coupled to the polarization concentration effect, which results in gradients of pH and degree of protonation along the axis of the pore [44].…”

“…The later situation was analyzed by Yeh et al using numerical calculations [44] and analytical theory [45]. These works showed that charge regulation is coupled to the polarization concentration effect, which results in gradients of pH and degree of protonation along the axis of the pore [44]. Figure 2e shows that the charge carriers inside the nanochannel at low pH are almost exclusively Cl À ions and, hence, the anion selectivity (current carried by the anions over the total current) is very high.…”

Energy Conversion From Salinity Gradient Using Microchip With Nafion Membrane

“…When the electrolyte was at higher pH value, the additional OH -were repelled by the cation-selective membrane, but might associate with H 2 O to form H 3 O 2 -28,29 . According to previously studies [30][31][32][33] , results indicated the spatial variation of surface charge density strongly depends on bulk concentration and pH value. The surface charge density increases with increasing the pH value due to the H + ion concentration is high in the Nafion membrane.…”

Electroviscous effect on the streaming current in a pH-regulated nanochannel

“…The pressure-driven flow is directed in the y-direction and E str is induced in the opposite flow direction. Note that the effect of ion concentration polarization [24,25], arising from the selective transport of ions in nanofluidics, is neglected, which is appropriate when the nanochannel is sufficiently long.…”