Core-shell graphene oxide-polymer hollow fibers as water filters with enhanced performance and selectivity

Extraction of proteins from blood biological fluids requires the removal of large aggregates or cells by membrane filtration. However, conventional filters, based on simple size exclusion, do not allow to remove small molecules such as antibiotics. Here, we demonstrate that a graphene oxide (GO) layer can be firmly immobilized either inside or outside polyethersulfone-polyvinylpirrolidinone hollow fibers (PES) modules and that the resulting core-shell structure inherits the microfiltration ability of PES and the adsorption selectivity of GO. GO nanosheets were deposited on fiber surface by filtration of a GO suspension through a PES cartridge (cut-off 0.1-0.2 μm), then fixed on it by thermal annealing at 80°C, rendering them insoluble. The filtration cut-off, retention selectivity and efficiency of the resulting inner and outer modified hollow fibers (HF-GO) were tested by performing filtration on water spiked with bovin serum albumin (BSA, 66KDa, ≈15 nm sized), monodisperse polystyrene nanoparticles (50 nm and 300 nm sized), water contaminated with two quinolonic antibiotics (ciprofloxacin and ofloxacin) and rhodamine B (RhB). These tests showed that microfiltration capability of PES was retained by HF-GO, in addition the GO coating can capture the molecular contaminants while letting through BSA and smaller Polystyrene nanoparticles. XRD and adsorption experiments show the separation mechanism does not rely only on a physical size exclusion but it involves interaction among GO coating and solute molecules.