Surface zwitterionization of graphene oxide (GO) was firstly conducted by grafting poly(sulfobetaine methacrylate) (PSBMA) onto the GO surface via reverse atom transfer radical polymerization (RATRP). Then, a novel type of GO-PSBMA/polyethersulfone (PES) loose nanofiltration membrane (NFM) was constructed by mixing with modified GO composites via phase inversion. FTIR, XRD, TEM, XPS and TGA were applied to analyze the chemical composition and morphology, confirming a favorable synthesis of GO-PSBMA composites. Besides, the effect of the embedded GO-PSBMA nanoplates on the morphology and overall performance of the hybrid membranes was systematically investigated based on the SEM images, water contact angle, zeta potential, and fouling parameters. It was found that the water flux of the hybrid membrane was greatly enhanced from 6.44 L m⁻² h⁻¹ bar⁻¹ to 11.98 L m⁻² h⁻¹ bar⁻¹ when the GO-PSBMA content increased from 0 to 0.22 wt%. The antifouling tests revealed that the GO-PSBMA embedded membranes had an excellent antifouling performance: a high flux recovery ratio (ca. 94.4%) and a low total flux decline ratio (ca. 0.18). Additionally, the hybrid membranes exhibited a distinct advance in the mechanical strength due to the addition of highly rigid GO. Notably, compared with unmodified membranes, the hybrid membranes had a higher retention of Reactive Black 5 (99.2%) and Reactive Red 49 (97.2%), and a lower rejection of bivalent salts (10% for Na₂SO₄) at an operational pressure of 0.4 MPa, rendering the membranes promising for dye/salt fractionation.

Membrane-based nanotechnologies have gained growing attention in various separation fields due to advantages such as high energy efficiency and ecofriendliness. However, the limited and empirical design parameters of conventional membranes greatly slow down research progress on rapid and efficient molecular separations. Two-dimensional materials (2DMs) – e.g., graphene, MoS₂, MXene, metal–organic frameworks, and covalent organic framework nanosheets – are rapidly emerging in the development of membranes with high selectivity and permeability. The rational tunability and precise control of interlayer distances and/or nanoporous apertures of 2DMs enable 2DM-based membranes to achieve highly specific separations. Furthermore, the ultrathin structure of 2DMs offers minimal transport resistance and thus leads to extraordinary flux rates. This review briefly outlines recent approaches in the use of various 2DMs for membrane designs. Some remarkable performances of 2DM-based membranes and their separation mechanisms are also noted. Challenges and future directions toward molecular-level designs of membranes with 2DMs are additionally discussed.

A rational manipulation of the surface structures and properties of thin-film composite membranes is important to optimize their separation performance and service durability. In this study, a facile strategy is reported for fabricating electroneutral loose nanofiltration membranes based on the rapid co-deposition of biomimetic adhesive polydopamine and poly(ethylene imine) (PEI) by using CuSO₄/H₂O₂ as a trigger. Through this strategy, the surface properties and the filtration performance of the membranes can be easily tailored by the addition of PEI and CuSO₄/H₂O₂, as well as tuning the deposition time. UV, XPS, SEM, AFM, zeta potential, water contact angle and nanofiltration measurements were used to investigate membrane performance. Surface characterization revealed that overall enhanced surface properties including low roughness, favourable hydrophilicity, and relatively neutral charge can be achieved after the addition of PEI. The optimum membranes, with 1 h co-deposition of PDA and PEI, show an ultrahigh water permeability (26.2 L m⁻² h⁻¹ bar⁻¹), distinguished rejection for both negatively and positively charged dyes and a high permeation of divalent salts (>90%). Furthermore, the optimum membranes also show excellent operational stability in long-term nanofiltration operations in alkaline solution. This study provides an efficient and facile approach to tailor the membrane properties and structure for loose nanofiltration membranes.