A unique method for dopamine-cross-linked graphene nanoplatelets within polyethersulfone membranes (GNP-pDA/PES) for enhanced mechanochemical resistance during NF and RO desalination

This work presents unique mixed matrix membranes (MMMs) prepared from polydopamine-crosslinked graphene nanoplatelets (GNP-pDA) within polyethersulfone (PES) to enhance mechanochemical properties. This was done to enhance the membrane's resistance to chlorine attack, and fouling or scaling. Firstly, dopamine (DA) and GNPs were reacted via ultrasonication and added into the PES polymer solution. This was followed by the membranes being prepared via phase inversion at pH 8.5. This allowed for the polymerisation of DA and subsequent crosslinking of the GNPs in the matrix of the forming membrane. The chemical changes due to this process were investigated using Fourier transform infra-red spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Consequently, membrane mechanical strength was enhanced as determined by tensile strength analysis (TSA). Membrane morphology was studied by scanning electron microscopy (SEM) analysis, exhibiting an even film on the membrane surface, cross-sectional structure, and uniform dispersion of the GNP-pDA. The nanocomposite membranes fabricated via this novel method presented an enhanced contact angle of 54 degrees. Additionally, tensile strength was improved from 3.22 to 24.5 MPa, and pure water permeate fluxes (PWP) were reduced with decreasing pore size to 21.1 L.m(-2).h(-1). The rejection of salts NaCl and MgSO4 were enhanced to 99.85 and 99.95%, respectively. The membranes also presented lux recoveries of 93% after chlorine exposure as a direct result of the chemical reinforcement.