Ionization behavior of nanoporous polyamide membranes.

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Global water scarcity demands advanced desalination technologies.
• Nanofiltration (NF) membranes are crucial for water purification.
• Understanding structure-property-performance relationships in NF membranes is essential for optimization.

Purpose of the Study:

• To investigate the ionization behavior of nanoporous polyamide selective layers in NF membranes.
• To elucidate the influence of ionization on membrane permeability and selectivity.
• To explore strategies for enhancing NF membrane performance through controlled ionization.

Main Methods:

• Fabrication of physically and chemically similar polyamide selective layers using layered interfacial polymerization.
• Assessment of location-dependent ionization of carboxyl and amine groups under varying pH conditions.
• Utilizing first-principles simulations to understand the underlying mechanisms of ionization behavior.

Main Results:

• Demonstrated location-dependent ionization of carboxyl groups: surface groups ionize at neutral pH, while interior groups require pH >9.
• Observed consistent amine ionization across the film, irrespective of location.
• First-principles simulations attributed anomalous carboxyl ionization to the low permittivity of nanoconfined water.
• Showcased a fourfold improvement in water-salt permselectivity through interior carboxyl ionization.

Conclusions:

• Nanoconfinement significantly influences the ionization behavior and transport properties of NF membranes.
• Interior charge density is a critical factor for enhancing the selectivity of polyamide membranes.
• Findings provide fundamental insights for designing next-generation desalination membranes with improved performance.