Realizing precise ion separation in polyamide nanofiltration membranes via stage control reactions

Area of Science:

• Materials Science
• Chemical Engineering
• Membrane Science

Background:

• Thin-film composite nanofiltration membranes often exhibit a trade-off between ion selectivity and permeability.
• Interfacial polymerization (IP) faces challenges due to the structural constraints of single monomers.

Purpose of the Study:

• To decouple comonomer reactions during ultrafast IP using in situ-generated H+.
• To regulate the reaction sequence and monomer ratios for improved membrane performance.
• To design nanofiltration membranes with enhanced water permeance and ion selectivity.

Main Methods:

• Utilized in situ-generated H+ as equilibrium-shifting inducers for the enamine reaction during ultrafast IP.
• Employed polyethyleneimine and piperazine monomers to create the separation layer.
• Investigated staged-regulated membranes for ion separation in ultrahigh-salt solutions.

Main Results:

• Achieved a separation layer with large free volume, high-density homogeneity, well-tuned nanopores, and tailored charge distribution.
• Demonstrated high water permeance in the staged-regulated membrane.
• Reported a >1600% improvement in Mg2+/Li+ selectivity in ultrahigh-salt solutions compared to control membranes.

Conclusions:

• The stage control strategy precisely regulates IP for tailored nanofiltration membrane synthesis.
• This method offers flexibility in modulating membrane structure for specific applications.
• Decoupling comonomer reactions is key to overcoming the selectivity-permeability trade-off.