Enhancing Separation Performance of PA Nanofiltration Membrane Through Polyelectrolyte PSS Interlayer and Surface...

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Thin-film composite (TFC) polyamide (PA) nanofiltration (NF) membranes are crucial for water purification.
• A significant challenge in TFC membrane development is the selectivity-permeability trade-off.

Purpose of the Study:

• To fabricate a novel three-layer structured NF membrane to overcome the selectivity-permeability trade-off.
• To enhance both water permeability and salt rejection simultaneously.

Main Methods:

• Fabrication of a three-layer NF membrane using poly (sodium 4-styrenesulfonate) (PSS) interlayer, a polyethyleneimine (PEI)-based PA separation layer, and a PEI-grafted top layer.
• Utilized interfacial polymerization (IP) and surface grafting techniques.
• Characterized membrane properties including surface charge, crosslinking degree, pure-water permeability (PWP), and salt rejections.

Main Results:

• The fabricated membrane (I-TFC-g) exhibited a positive surface charge and increased crosslinking degree.
• Achieved significantly higher rejection rates for divalent ions (e.g., 91% for MgCl2, 92% for MgSO4) via synergistic Donnan and size-exclusion mechanisms.
• The PSS interlayer increased PWP by 2.8 times compared to the non-layered membrane, reaching 7 L m⁻² h⁻¹ bar⁻¹.
• Demonstrated good long-term stability with high salt rejections for various salts (MgCl2, MgSO4, Na2SO4, NaCl).

Conclusions:

• A simple yet effective strategy was developed to enhance NF membrane performance.
• Simultaneous improvement in water permeability and salt selectivity was achieved.
• The novel three-layer structured membrane shows great potential for advanced water purification and reclamation.