Designing Pyridinium‐Catalyzed Interfacial Polymerization for High‐Performance Acid‐Resistant Nanofiltration Membranes

ABSTRACT The “acyl ∼ amine” interfacial polymerization is widely studied to synthesize polyamide membranes, which, despite broad separation applications, suffer from poor acid stability. Cyanuric chloride (CC) can react with amines to form acid‐stable C─N bonds, yet its third chloride atom is unreactive at room temperature, thus hindering the synthesis of selective membranes by interfacial polymerization. This work reported a pyridinium‐catalyzed interfacial polymerization (PCIP) strategy to significantly improve CC's reactivity and synthesize high‐performance, acid‐resistant membranes. We designed a new monomer bearing triple pyridines, which were converted to positively charged pyridiniums during their interfacial polymerization with CC. These pyridiniums effectively reduce the electron density of CC rings via their electron‐withdrawing capacity, and improve CC's substitution reactivity by orders of magnitude, thereby enabling the rapid (1 min) synthesis of a large‐area (∼0.5 m 2 ) membrane. The membrane is stable in 2 M H 2 SO 4 , showing one of the highest separation performances (permeance: ∼16.8 L m −2 h −1 bar −1 ; selectivity: ∼12.8) among previous CC‐based membranes, combined with ∼4 times higher efficiency in lithium and cobalt recovery from LiCoO 2 spent batteries.