Polyamide membranes with tannic acid-ZIF-8 for highly permeable and selective ion-ion separation

Highly permeable polyamide (PA) membranes with precise ion selection can be used for many energy-efficient chemical separations but are limited by membrane inefficiencies. Herein, polyphenol-mediated ZIF-8 nanoparticles with hydroxyl-rich hollow structure were synthesized by tannic acid tailored regulation. PA-based membranes with fast penetration, high retention, and precise Cl⁻/SO₄²⁻ selection were then synthesized through spatially and temporally controlling interfacial polymerization with modified ZIF-8 nanoparticles (tZIF-8) as aqueous phase additives or as interlayers. The effects of the embedding position of tZIF-8 on the structure, morphology, physicochemical properties, and performance of PA-based membranes were explored through a sequence of characterization techniques. The results revealed that the PA-based membrane with tZIF-8 embedded in the PA layer could achieve a high water permeance of 24.8 L m⁻² h⁻¹ bar⁻¹ with a high retention of 99.4 % Na₂SO₄ and a Cl⁻/SO₄²⁻ selectivity of 141, which was superior to most state-of-the-art PA-based membranes. Comparatively, the Cl⁻/SO₄²⁻ selection of the PA-based membrane with tZIF-8 embedded between the PA layer and the substrate was 136, while the water permeance was slightly enhanced to 28.2 L m⁻² h⁻¹ bar⁻¹. Excitingly, the resulting membranes all exhibit superior antifouling properties and stability. Our facile strategy for tuning membrane microstructures provides new ideals into the development of highly permeable and excellently selective PA-based membranes for precise ion sieving.