Graphene oxide (GO) membranes are robust and continue to attract great attention due to their fascinating properties, despite their potential issues regarding stability and selectivity in aqueous-phase processing. That being said, however, the functional moieties of GO could be used for membrane surface modification, while ensuring simultaneous removal and recycling of industrial organic dyes. Herein, we present a versatile porous structured polyvinylidene fluoride-graphene oxide (PVdF-GO) nanofibrous membranes (NFMs), prepared by using simple and straightforward electrospinning approach for selective separation and filtration. The GO nanosheets were distributed homogeneously throughout the PVdF nanofiber, regulating the surface morphology and performance of PVdF-GO NFM. The PVdF-GO NFMs possesses high mechanical strength and surface free energy (SFE), consequently resulting high permeation and filtration efficiency as compared to PVdF NFM. The selectivity (99%) toward positively charged dyes based on electrostatic attraction, while maintaining rejection (100%) for negatively charged dye from mixed solutions highlight the role of GO in PVdF-GO NFM, owing to uniform pores and negatively charged surface. In addition, the actual efficiency of NFMs could be recovered easily up to three consecutive filtration cycles by regeneration, thereby assuring high stability. The high permeation, purification and filtration efficiency, good stability and recycling of PVdF-GO NFMs are promising for use in practical water purification and applications, particularly for selective filtration and recycling of dyes.
The synthesis, multilevel structural features, adsorption performance and environmental applications of graphene nanosheets and 2D/3D graphene-based macrostructure material were summarized.
Synthetic membranes often suffer ubiquitous fouling as well as a trade-off between permeability and selectivity. However, emerging materials which are able to mitigate membrane fouling and break the permeability and selectivity trade-off are urgently needed. A novel additive, GO-PEI, bearing a positive charge and hydrophilic nature was prepared by the covalent grafting of polyethylenimine (PEI) molecules with graphene oxide (GO) nanosheets, which later was blended with bulk poly(ether sulfone) (PES) to fabricate the graphene containing nanocomposite membranes (NCMs). Strong π-π interactions contributed to the uniform dispersion of GO-PEI nanosheets in bulk PES to form the asymmetric structure of NCM without leaching. The ratio of the GO-PEI additive regulated the surface charge and hydrophilicity of NCMs. To filter charged proteins, the designed NCM exhibited a high permeability (flux) and high selectivity (retention) while showing resistance to fouling by the charged proteins, which could be attributed to the asymmetric structure and composition of the NCM that the porous internal and surface composited with the GO-PEI additive was responsible for the NCM's high flux; thereafter, the electrostatic attraction of the NCM surface to the charged pollutant enhanced the solute/water selectivity; finally, the synergistic effect of the hydrophilic and charged functional groups of the GO-PEI contributed to the formation of a dense hydration layer on the membrane surface thereby reducing membrane fouling. The NCM functionalized with the GO-PEI additive demonstrated potential for high-performance pollutant removal in water and wastewater treatments.
Graphene oxide membranes with tunable water channels and stability for ion rejections were fabricated by the blade casting technique and cation intercalation.
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