Nitrogen-doped reduced graphene oxide – PVDF nanocomposite membrane for persulfate activation and degradation of water organic micropollutants

Abstract

Metal-free carbon-based polymer nanocomposite membranes were employed for the first time for activated persulfate oxidation in continuous mode of operation. For that purpose, reduced graphene oxide doped with nitrogen by using melamine as source (rGO-M) was included as catalytic active phase in a poly(vinylidene fluoride) matrix (PVDF). The performance of the resulting composite membrane (rGO-M-PVDF) was compared against that obtained with supported membranes prepared by simple filtration of rGO-M into a PTFE substrate. The uniform distribution of rGO-M within both the surface pores and cross-sectional channels of the composite rGO-M-PVDF membrane (with a thickness of 292 ± 20 μm) was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while its main structural features were studied by X-ray diffraction (XRD) and Raman spectroscopy. The quite good performance of this composite membrane was demonstrated by the degradation of three fluoroquinolone antibiotics at ppb level in ultrapure water (100 μg L−1 each), leading to average pollutant mass removal rates in the range 2.05–2.73 mg m−2 h−1. Conversions of the pharmaceuticals in the range 54–91% were obtained even after 24 h of operation in full continuous mode. Persulfate conversion was confirmed and high resistance to fouling was observed with this novel catalytic membrane. Average pollutant mass removal rates in the range 0.34–0.77 mg m−2 h−1 were obtained in preliminary experiments performed with surface water instead of ultrapure water, highlighting the need for additional studies on both water matrix effects and process optimization.