Ultra-thin trinity coating enabled by competitive reactions for unparalleled molecular separation

Abstract

Advanced nanoporous membranes with outstanding permeance and exceptional molecular-separation efficiency are highly desirable for key industrial applications for alleviating the worldwide environmental/energy crisis. Herein, an ultra-thin trinity coating (∼33 nm) for unparalleled molecular separation is first built via covalent bond (CB)/coordination bond (COB) competitive reactions. The COBs generated among various polyphenols (PPhs), amino substances (ASs) and transition metal ions (TMIs) can limit Michael addition or Schiff base reactions for CB formation between PPhs and ASs during the mussel-inspired ternary coating process so as to elegantly engineer the trinity coating architecture on the porous substrate with ultra-thin thickness, excellent structural integration, high hydrophilicity and outstanding smoothness. Our molecular separation nanoporous membrane demonstrates ultra-high permeance (114 L m⁻² h⁻¹ bar⁻¹ for Bromothymol Blue (BTB) and 104 L m⁻² h⁻¹ bar⁻¹ for Congo Red (CR)) with complete rejection, which is much superior to that of state-of-the-art membranes and can realize the lower energy consumption of the membrane separation process. The CB/COB competitive reactions drastically enhanced the permeance of the trinity coated membrane by 533%, 238%, and 93% compared to that of the unary (pDA) and binary (pDA/PEI or pDA/Co²⁺) coated membranes. Meanwhile, the novel membrane with the perfectly tuned architecture by CB/COB competitive reactions possesses extraordinary dye/salt selectivity, tremendous acid/alkali–base stability and excellent anti-pollution capacity simultaneously. The new strategy for building an outstanding trinity coating via competitive reactions can pave a realistic way for fabricating unparalleled next-generation separation membranes.