Overcoming the trade-off in reverse osmosis membranes through homologous matching.

Abstract

The development of cellulose triacetate (CTA)-based reverse osmosis membranes offers a sustainable approach to alleviating the global freshwater crisis, yet overcoming the inherent permeability-selectivity trade-off remains a significant challenge. Herein, we propose a homologous matching strategy to address the trade-off by incorporating carbon dots (M-CDs) derived from m-phenylenediamine (MPD) into the interfacial polymerization process between CTA and polyamide (PA). Systematic characterization and molecular dynamics simulations reveal that M-CDs, which are structurally analogous to the MPD monomer, promote monomer diffusion, regulate cross-linking density, and refine the microstructure of the PA layer. At an optimal M-CDs concentration, the resulting membrane achieves simultaneous enhancements in both salt rejection (99.1% vs. 96.5%) and water flux (18.3 vs. 15.2 L·m^-2·h^-1), thus surpassing conventional CTA membranes. The incorporation of M-CDs results in a thinner, denser, and more hydrophilic barrier layer with reduced pore size and narrowed distribution, as confirmed by post-annealing structural analysis. Moreover, hydrogen bonding between M-CDs and MPD improves chlorine resistance, maintaining high performance even after exposure to 2000 ppm NaClO solution. Molecular dynamics further illustrate that M-CDs promote water cluster transport while hindering ion penetration, thereby effectively mitigating the trade-off. The innovative use of homologous carbon dots to optimize the CTA-PA interface through structural matching, offering inspiring avenues for developing advanced bio-derived desalination technologies.