Polyamide membranes with nanoscale ordered structures for fast permeation and highly selective ion-ion separation

Fast permeation and effective solute-solute separation provide the opportunities for sustainable water treatment, but they are hindered by ineffective membranes. We present here the construction of a nanofiltration membrane with fast permeation, high rejection, and precise Cl(-)/SO(4)(2-) separation by spatial and temporal control of interfacial polymerization via graphitic carbon nitride (g-C(3)N(4)). The g-C(3)N(4) nanosheet binds preferentially with piperazine and tiles the water-hexane interface as revealed by molecular dynamics studies, thus lowering the diffusion rate of PIP by one order of magnitude and restricting its diffusion pathways towards the hexane phase. As a result, membranes with nanoscale ordered hollow structure are created. Transport mechanism across the structure is clarified using computational fluid dynamics simulation. Increased surface area, lower thickness, and a hollow ordered structure are identified as the key contributors to the water permeance of 105 L m(2)·h(−1)·bar(−1) with a Na(2)SO(4) rejection of 99.4% and a Cl(-)/SO(4)(2-) selectivity of 130, which is superior to state-of-the-art NF membranes. Our approach for tuning the membrane microstructure enables the development of ultra-permeability and excellent selectivity for ion-ion separation, water purification, desalination, and organics removal.