Highly Interconnected Cellulose Acetate Ultrafiltration Membranes via Interfacial Hydration-Induced Phase Separation for Ultrafast Water Purification

Abstract

Ultrafiltration is essential for ensuring water security, yet commercial ultrafiltration membranes remain constrained by the permeability-selectivity trade-off. While extensive research has focused on designing the selective skin layer, such improvements in permeance have neared a bottleneck due to the often-overlooked hydraulic resistance arising from the underlying sponge-like layer. Here, we propose a generalizable interfacial hydration-induced phase separation strategy to reconstruct the internal transport channels within the sponge-like layer of biodegradable cellulose acetate (CA) ultrafiltration membranes, enhancing permeance without sacrificing selectivity. Specifically, highly polar nanoclusters (TCZ), formed in situ via multidentate coordination between tannic acid-modified cellulose nanocrystals (TC) and Zr4+ ions, preferentially anchor within the sponge-like layer through strong interfacial interactions with the CA matrix. Acting as localized hydration seeds, these nanoclusters attract and enrich water molecules to establish water-rich microenvironments through strong hydrogen-bonding interactions, promoting local liquid–liquid demixing and driving the formation of highly interconnected, low-tortuosity water-transport pathways throughout the sponge-like layer. The resulting CTCZ membranes exhibit high water permeance (752.29 L m–2 h–1 bar–1), representing a 10-fold increase over the CA membrane, with high rejection (>96%) for typical water contaminants. Notably, this strategy can also be extended to mainstream polyvinylidene fluoride and poly(ether sulfone) matrices, yielding 13-fold and 21-fold permeance enhancements, respectively. Large-area NW-CTCZ membranes fabricated via a roll-to-roll process demonstrate reliable long-term stability in surface water purification. Furthermore, life-cycle and economic analyses confirm that the CTCZ membranes, as eco-friendly and cost-effective candidates, offer a scalable and sustainable approach for water treatment.