Enhancing Polyvalent Cation Rejection Using Perfluorophenylazide-Grafted-Copolymer Membrane Coatings.

Area of Science:

• Materials Science
• Surface Chemistry
• Separation Science

Background:

• Surface modification is key to enhancing material properties, particularly for nanofiltration membranes used in water treatment.
• Altering membrane surface charge is a direct method to improve ion separation performance.

Purpose of the Study:

• To investigate the effect of grafting electrostatically varying copolymers onto commercial membrane surfaces.
• To enhance ion separation performance, specifically for divalent cations and anions, using perfluorophenylazide (PFPA) photochemistry.

Main Methods:

• Grafting of copolymers with varying charges (quaternary ammonium, sulfonate, zwitterion) onto commercial membrane surfaces.
• Utilizing perfluorophenylazide (PFPA) photochemistry for surface modification.
• Evaluating membrane performance in terms of divalent cation and anion separation.

Main Results:

• Sulfonated polymer coatings enhanced Coulombic exclusion of divalent anions due to increased negative charge.
• Positively charged ammonium coatings improved cation exclusion compared to the native membrane.
• Zwitterion polymer coatings, despite near-neutral charge, enhanced exclusion of both cations and anions via aperture sieving and dielectric effects, while reducing surface roughness and improving wettability.

Conclusions:

• Surface modification with charged and zwitterionic copolymers offers tunable control over nanofiltration membrane performance.
• PFPA photochemistry provides an effective route for grafting functional copolymers to enhance ion separation.
• These findings pave the way for advanced separation technologies for liquid streams based on size and charge exclusion.