Abstract
Ion rectification is the asymmetrical conduction of ions through a system under different polarities of applied potentials. In this article we report the finding of a novel form of ion rectification in graphene oxide (GO) and reduced graphene oxide (RGO) films which act as an ensemble array of nanochannels. Rectification is imparted by introducing geometric asymmetry in fluidic inlets to the counter-ion selective nanochannels of GO/RGO which creates asymmetry in the enrichment/depletion effects at the macro-/nano-interface. The devices are made simply by cutting a GO or RGO film into a trapezoid and sealing the film within a Polydimethylsiloxane block so that fluid may only enter through one of two inlets. These devices exhibit rectification ratios larger than 20 (in 1 mM NaCl) while operating at modest voltages [−1 V, +1 V].
Highlights
Microfluidic technologies have the potential to revolutionize analytical sciences by reducing the volume requirement for fluids, providing faster response time-scales, and simplifying large scale parallelization.[1,2] Several technologies are very mature and some are commercially available, fluidic systems combining micro- and nano-structures are still in their infancy[3,4] underlining that several scientific phenomena that traverse these scales are yet to be fully understood
Ion-channels have the ability to respond to electric fields leading to changes in ion current flowing through the channel
The mechanism of rectification observed here differs from those reported in the following ways: the surface charge on graphene oxide (GO)/reduced GO (RGO) is uniformly distributed throughout the film so ignoring the edge effects, one can say that the surface potential is uniform throughout the film, the electrolyte is symmetrical at either end and the nanochannel’s characteristic dimension is reasonably uniform throughout the films
Summary
Microfluidic technologies have the potential to revolutionize analytical sciences by reducing the volume requirement for fluids, providing faster response time-scales, and simplifying large scale parallelization.[1,2] Several technologies are very mature and some are commercially available, fluidic systems combining micro- and nano-structures are still in their infancy[3,4] underlining that several scientific phenomena that traverse these scales are yet to be fully understood. In such an environment the fluidic properties of ionic solutions deviate from that of the bulk, exhibiting surface charge dependent ionic conduction and in more complex systems rectification of ion currents.[7,8,9]
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