Polymeric loose nanofiltration membranes based on water-soluble carbon nitride for efficient organics/salts separation

Loose nanofiltration (LNF) membranes with a remarkable water permeability are highly promising for the fractionation of organics and salts in the treatment of industrial wastewater. In this study, a novel polymeric membrane with high organics/salts separation efficiency and high water permeability was constructed by interfacial polymerization (IP) between water-soluble cyanocarbon nitride (WCN) and trimesoyl chloride (TMC) monomer. We revealed that the hydrophilic nature of WCN could slow down the polymerization of cyano and chlorine groups by inhibiting the diffusion of WCN into organic phase, forming a thin polymeric membrane with a loose structure on the polyethersulfone (PES) substrates. With a hydrophilic and charged surface, the polymeric membrane exhibited high rejection toward negatively charged organic molecules, while maintained good permeability to salt ions. The membrane demonstrated a high water permeability of 41.6 L m- 2 h- 1 bar- 1 , which was 4 times higher than that of conventional polyamide membranes. Additionally, it exhibited a high separation factor (S) of 1418 in the filtration of methyl blue/NaCl mixtures, surpassing the performance of state-of-the-art loose nanofiltration (LNF) membranes reported in the literature. This study provides a new strategy of tailoring the structure of carbon nitride to develop high-performance LNF membranes for water treatment.