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Membrane Charge Effects on Solute Transport in Nanofiltration: Experiments and Molecular Dynamics Simulations
Suwei Liu1, Zihao Foo2,3, John H Lienhard2
1Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208, USA.
Membranes
|June 25, 2025
Summary
Molecular dynamics simulations reveal how charged polyamide nanofiltration membranes purify water. Membrane charge concentration and pH significantly impact solute rejection, guiding future membrane design for enhanced water treatment.
Area of Science:
- Water purification
- Membrane science
- Physical chemistry
Background:
- Polyamide nanofiltration (NF) membranes are crucial for water purification.
- Molecular-level understanding of solute transport and rejection mechanisms in charged NF membranes is lacking.
- Solute charge interactions with membrane functional groups are key but poorly understood.
Purpose of the Study:
- To investigate the molecular mechanisms of solute transport and rejection in charged polyamide nanofiltration membranes.
- To examine the influence of membrane charge concentration (COO- and NH+2) and pH on ion transport.
- To elucidate the role of functional group distribution and steric effects on solute rejection.
Main Methods:
- Utilized molecular dynamics simulations to model single-solute transport through charged NF membranes.
- Varied membrane charge concentrations (COO- and NH+2) by adjusting pH conditions.
- Analyzed ion permeation, functional group interactions, and steric effects within membrane pores.
Main Results:
- Higher concentrations of negative membrane charges (higher pH) enhanced rejection of Na+ and Cl- ions.
- CaCl2 exhibited high rejection across all tested pH levels.
- Membrane functional group distribution significantly affected ion permeation; concentrated COO- groups at the surface reduced ion entry.
- Observed association of counter-ions with charged groups and easier passage of co-ions.
- Steric effects influenced transport when oppositely charged ions clustered in membrane pores.
Conclusions:
- Solute rejection is strongly dependent on membrane charge characteristics and pH.
- Functional group distribution and steric factors play critical roles in ion transport mechanisms.
- Findings provide molecular insights for designing advanced nanofiltration membranes with tailored solute rejection properties.
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