Carrageenan-assisted atomic layer deposition of TiO₂-rich antifouling interfaces on PVDF membranes for emulsion separation

Atomic layer deposition (ALD) is a powerful tool for engineering membrane interfaces, but its application to chemically inert polymeric membranes remains limited by sparse nucleation sites, discontinuous oxide growth, and poor pore-wall coverage. Herein, we develop a carrageenan-assisted ALD strategy to improve TiO₂ nucleation and promote TiO₂-rich interfacial deposition on nonpolar polyvinylidene fluoride (PVDF) porous membranes. ι-Carrageenan (ιCAR) serves as a sulfate ester-containing interfacial sensitization layer, whose sulfate ester groups interact favorably with TiCl₄ precursors and promote a denser and broader distribution of Ti-containing species along the membrane framework. Density functional theory (DFT) calculations show that, among the representative functional groups considered, the sulfate ester group has the strongest calculated interaction with TiCl₄ compared with hydroxyl and ether groups. The resulting M@ιCAR@TiO₂ membrane exhibits a hydrophilic TiO₂-rich interface while retaining the interconnected pore architecture. By virtue of a hydrated, negatively charged, and hierarchically rough interface, the optimized membrane delivers underwater superoleophobicity, stable cross-flow emulsion filtration, >99% oil rejection, permeate total organic carbon below 10 ppm, and a permeance recovery ratio of approximately 94.0%. This work provides a sustainable carrageenan-assisted interfacial sensitization strategy for ALD modification of inert polymer membranes and antifouling emulsion separation.