Aminal-Linked Covalent Organic Framework Membranes Achieve Superior Ion Selectivity

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• High-salinity wastewater presents a global challenge for water resource recycling and achieving zero discharge.
• Membrane technology offers a promising route for sulfate removal from chlor-alkali brine, but current membranes lack sufficient water permeance and ion selectivity.
• Efficient separation of monovalent and divalent salts is critical for effective wastewater treatment and resource utilization.

Purpose of the Study:

• To develop a novel covalent organic framework (COF) membrane with enhanced ion selectivity and water permeance for high-salinity wastewater treatment.
• To investigate the performance of an aminal-linked COF membrane in separating monovalent (NaCl) and divalent (Na2SO4) salts.
• To assess the potential of the developed membrane for industrial applications in wastewater resource utilization and zero discharge.

Main Methods:

• Assembly of a uniform covalent organic framework (COF) layer using 1,4-phthalaldehyde (TPA)-piperazine (PZ) via amidation with trimesoyl chloride (TMC).
• Fabrication of an aminal-linked COF membrane (sTPA-PZ) with subnanosized channels and a regular pore size of 7 Å.
• Testing the membrane's performance in water permeance, Na2SO4 rejection, and Cl-/SO42- separation using mixed-salt solutions.

Main Results:

• The chemically spliced TPA-PZ (sTPA-PZ) membrane demonstrated a high water permeance of 13.1 L m⁻² h⁻¹ bar⁻¹.
• Achieved a superior Na2SO4 rejection of 99.1% and a Cl-/SO42- separation factor of 66 for mixed-salt separation.
• Single-stage treatment of NaCl/Na2SO4 mixed-salt solutions yielded high NaCl purity (>95%) and a recovery rate of ≈60%.

Conclusions:

• The aminal-linked COF membrane exhibits excellent performance in monovalent/divalent salt separation, outperforming existing COF-based membranes.
• The developed membrane shows significant potential for industrial applications in wastewater resource utilization and achieving zero discharge goals.
• This work presents a new avenue for designing advanced angstrom-scale separation membrane materials.