Abstract
Electrically conductive composite ultrafiltration membranes composed of carbon nanotubes have exhibited efficient fouling inhibition in wastewater treatment applications. In the current study, poly(vinyl-alcohol)-carbon nanotube membranes were applied to fed batch crossflow electroultrafiltration of dilute (0.1 g/L of each species) single and binary protein solutions of α-lactalbumin and hen egg-white lysozyme at pH 7.4, 4 mM ionic strength, and 1 psi. Electroultrafiltration using the poly(vinyl-alcohol)-carbon nanotube composite membranes yielded temporary enhancements in sieving for single protein filtration and in selectivity for binary protein separation compared to ultrafiltration using the unmodified PS-35 membranes. Assessment of membrane fouling based on permeate flux, zeta potential measurements, and scanning electron microscopy visualization of the conditioned membranes indicated significant resulting protein adsorption and aggregation which limited the duration of improvement during electroultrafiltration with an applied cathodic potential of -4.6 V (vs. Ag/AgCl). These results imply that appropriate optimization of electroultrafiltration using carbon nanotube-deposited polymeric membranes may provide substantial short-term improvements in binary protein separations.
Highlights
Carbon nanotubes (CNT) have drawn significant attention as an ideal conductive material to modify UF membranes [1, 2]
From the cross-sectional scanning electron microscopy (SEM) image of the PVA-CNT/PS-35 composite membrane (S3 Fig in S1 File), the thickness of the PVA-CNT thin film was determined to be approximately 6 μm compared to the 165 μm thickness of the commercial polysulfone membrane which agrees with previously reported measurements [5, 11]
Electroultrafiltration using a CNT-based composite ultrafiltration membrane was evaluated for its effectiveness in improving membrane performance during crossflow filtration of dilute single and binary protein solutions of α-lactalbumin and hen egg-white lysozyme (0.1 g/L of each species; pH 7.4; 4 mM ionic strength; 1 psi TMP)
Summary
Carbon nanotubes (CNT) have drawn significant attention as an ideal conductive material to modify UF membranes [1, 2]. Composite UF membranes combine the properties of good electrical conductivity, robust mechanical strength, and efficient filtration performance. Conducting membranes with tunable charged surfaces under an applied electrical potential take advantage of electrophoretic and electrostatic contributions to the transport of charged particles (Fig 1). Extensive work has been performed to develop and investigate the use of electrically conductive composite CNT-polymer composite UF membranes for water treatment [3,4,5,6,7,8].
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