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-/SO42- separation by spatial and temporal control of interfacial polymerization via graphitic carbon nitride (g-C3N4). The g-C3N4 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)center dot h(-1)center dot bar(-1) with a Na2SO4 rejection of 99.4% and a Cl-/SO42- 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. Membranes with precise ion-ion separation are critical for sustainable water treatment. Here, authors demonstrated controlled construction of a nanofiltration membrane with fast permeation and high Cl-/SO42- selectivity by simultaneous spatial and temporal control of interfacial polymerization.

Automated summary

By controlling the spatial and temporal aspects of interfacial polymerization, a nanofiltration membrane with fast permeation and high Cl-/SO42- selectivity has been constructed. This membrane demonstrates ultra-permeability and excellent ion-ion separation, making it ideal for sustainable water treatment applications such as water purification and desalination.