Facile preparation of dopamine mediated graphene oxide composite membranes with enhanced stability for nanofiltration: Structure, performance and stability

Stability is a key issue to improve the commercialization of graphene oxide (GO) membranes for aqueous separation. Herein, the effect of dopamine (DA) addition mass on the performance and stability of the DA-mediated GO membranes was systematically investigated. The d-spacing of GO/DA membranes increased from 0.78 to 1.02 nm with DA loading from 0 to 25%. The improvement of water flux for GO/DA membranes was ascribed to the increased hydrophilicity and enlarged d-spacing, but excessive crosslinkers contributed to the declining water flux. The Na₂SO₄ rejection of GO/DA membranes showed the opposite trend with variations of less than 10%. The 30-day immersed evaluation further validated that the stability of DA-mediated GO membrane improved with increasing DA addition. The spacing modulation and functional groups in the interlayer galleries contributed to the rejection performance and swelling of the GO membranes. The negligible effect of pharmaceutical adsorption on the d-spacing demonstrated the stability of the GO/25%DA membrane. The density functional theory (DFT)-based molecular simulations indicated the GO membranes could be crosslinked by the interaction of polydopamine with the oxygenated groups of GO nanosheets, and the hydration of the residual hydrophilic functional group or the bounded DA monomers of GO was responsible for the slight swelling effect.