Chelation-competition interface engineering of polyphenol-derived coordination polymers for efficient emulsion separation.

Polyphenol-derived metal coordination polymers (MCPs) are promising for constructing hydrophilic and underwater antifouling membrane interfaces. However, conventional pH-regulated fabrication of MCPs is often accompanied by metal-ion hydrolysis, which consumes available metal ions and interferes with effective MCP formation. Herein, a triethanolamine (TEOA)-mediated chelation-competition strategy was developed to guide the in situ assembly of MCPs on separation membranes. TEOA modulated Fe3+ coordination and reactivity, while pre-adsorbed tannic acid (TA) subsequently displaced TEOA through competitive coordination to form Fe-TA MCPs. DFT calculations showed that the conversion from Fe-TEOA to Fe-polyphenol coordination was thermodynamically favorable (ΔG = -335.68 kJ/mol), supporting the proposed chelation-competition mechanism. The resulting FTC-PVDF exhibited superhydrophilicity, underwater superoleophobicity, and low oil adhesion. To leverage the low oil-droplet sliding angle, an inclined gravity-assisted cross-flow mode was further designed to facilitate oil-droplet migration and detachment. FTC-PVDF achieved a high permeance of 5300.5 L m-2∙h-1∙bar-1 and separation efficiencies above 99.5% for surfactant-stabilized emulsions. This work provides a chelation-competition interface-engineering route for regulating polyphenol-derived MCP formation and constructing high-permeance antifouling membranes for emulsion separation.