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Charge Regulation at a Nanoporous Two-Dimensional Interface.

Mandakranta Ghosh¹, Moritz A Junker¹, Robert T M van Lent¹

¹Soft matter, Fluidics and Interfaces, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands.

|February 8, 2021

Summary

This study reveals nanoporous graphene

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Area of Science:

Materials Science
Surface Chemistry
Electrochemistry

Background:

Nanoporous graphene exhibits pH-dependent surface charge.
Understanding surface charge is crucial for applications in separation and sensing.
Previous studies have not fully characterized the surface charge behavior of nanoporous graphene across a wide pH range.

Purpose of the Study:

To investigate the pH-dependent surface charge of nanoporous graphene.
To determine the point of zero charge (isoelectric point) of the graphene surface.
To elucidate the influence of support materials on membrane potential measurements.

Main Methods:

Membrane potential measurements across nanoporous graphene.
Streaming current measurements to determine zeta potential.
Numerical simulations to model support effects.
Analysis using a 1-pK model for surface charge characterization.

Main Results:

Observed a sign reversal in membrane potential and zeta potential around pH 4-4.2.
Determined a representative pK of 4.2 for the graphene surface.
Simulations showed PET support can cause significant deviation (up to 85%) from ideal Nernst potential.

Conclusions:

Nanoporous graphene exhibits amphoteric surface behavior with a point of zero charge near pH 4.2.
The surface charge is accurately described by a 1-pK model.
Support material effects must be considered in membrane potential studies of nanoporous materials.