Conjugated cationic dye modulates the ion-confined partitioning of anions/cations in graphene membrane to enhance seawater desalination

Obtaining low-salinity water from seawater via nanofiltration technology has emerged as a crucial solution to solve the freshwater scarcity. Graphene nanofiltration membrane exhibits revolutionary potential but faces serious challenges, primarily insufficient structural stability and poor rejection for small salt ions. Herein, reduced graphene oxide (rGO)/Dye composite membranes with positively charged surfaces by intercalating π-conjugated cationic dye molecules into rGO membranes through π-π interaction and electrostatic interactions were successfully fabricated. The introduction of dye molecules not only regulates the interlayer spacing but also achieves electrostatic-induced ion-confined partitioning, effectively inhibiting the co-transport of cation-anion pairs to enhance the salt rejection performances. The optimized membrane demonstrated remarkable rejection of 85.3 % for NaCl and 91.4 % for Na 2 SO 4 with high permeance due to the interlayer spacing modulation and ion-confined partitioning in nanochannels. Notably, those membranes exhibited exceptional chemical and mechanical stability during long-term nanofiltration operation involving high-salinity solution, mixed feed solution, and actual seawater. Transmembrane mass transfer experiments further confirmed that rGO/Dye composite membranes effectively suppress cation-anion pair co-transport, thereby increasing mass transfer resistance for salt ions. This study presents a novel strategy for designing high-performance desalination nanofiltration membranes through the synergistic regulation of nanochannels and surface charge characteristics.