Nanofiltration Using Graphene-Epoxy Filter Media Actuated by Surface Acoustic Waves

Abstract

We exploit the enhancement of liquid transport through a graphene-epoxy film actuated by surface acoustic waves to demonstrate effective and efficient nanoparticle filtration. Unlike previously reported findings using graphene films, the addition of silver epoxy to create a composite film allows higher excitation powers to be sustained over extended operation durations without disintegration of the film such that an increase in the liquid flow rate through the film by up to fourfold can be achieved. Counter to intuition that suggests that the epoxy would fill the interstitial voids between the layers that make up the graphene film so as to reduce the efficiency of liquid transport through the film, we show instead that the higher density and elastic stiffness of the composite film enhances the transmission of acoustic energy into the film that, in turn, leads to more efficient liquid transport through it. Filtration efficiencies above $99$% are obtained for 26-nm particles, decreasing to 99% for 10-nm and 5-nm particulates, which is a significant improvement compared to that obtained with a pure graphene film. While a decrease in filtration rate over time is observed (up to 50% over 3 h of continuous operation) typical to that of graphene and other filter media, the introduction of a simple backwash process allowed for up to 87% recovery of the initial filtration rate. The significant performance enhancement, namely the fourfold increase in throughput, filtration efficiencies of up to 99% for nanoparticles down to 5 nm, and the ability to sustain extended operation at higher powers without disintegration through such a facile and cost-effective modification to the film highlights its potential applicability in practical nanofiltration systems.