Separation of ions using polyelectrolyte-modified nanoporous track-etched membranes

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Selective ion transport through nanopores is crucial for separation technologies.
• Charged surfaces within nanopores govern ion exclusion and transport.
• Track-etched membranes offer tunable pore structures for modification.

Purpose of the Study:

• To investigate ion transport and selectivity in track-etched membranes modified with polyelectrolyte multilayers.
• To evaluate the impact of surface charge and pore size on ion rejection.
• To model ion transport using the nonlinearized Poisson-Boltzmann equation.

Main Methods:

• Fabrication of track-etched membranes with poly(styrene sulfonate) (PSS) and poly(allylamine) (PAH) films.
• Measurement of ion selectivity and rejection using pressure-driven transport.
• Application of the nonlinearized Poisson-Boltzmann equation for pore size analysis.

Main Results:

• PSS-modified pores showed Br(-)/SO4(2-) selectivity of ~3.4, with 85% SO4(2-) rejection.
• PSS/PAH-modified pores exhibited K(+)/Mg(2+) selectivity >10 and >97.5% Mg(2+) rejection at low ionic strength.
• Modeled pore diameter was 8.4 ± 2.1 nm, smaller than predicted by hydraulic measurements, indicating constrictions.

Conclusions:

• Polyelectrolyte modification effectively tunes nanopore charge and size for selective ion separation.
• Electrostatic exclusion and pore size reduction are key mechanisms for high ion rejection.
• Streaming potentials contribute to differential ion rejection based on mobility.