One-step constructed ultrathin Janus polyamide nanofilms with opposite charges for highly efficient nanofiltration

Preparation of nanofiltration membranes (NFMs) with high rejection to both divalent cations and anions and simultaneous high water permeation is rather significant and highly desired. Herein, we engineered an ultrathin Janus polyamide (PA) separating layer with opposite charges in one step through the self-regulation process of low temperature interfacial polymerization (LTIP). The low temperature strategy plays a crucial role in optimizing the self-regulation process. It can reduce the transmission rate of aqueous monomers to the top reaction zone and thus the thickness of the reaction zone, resulting in an ultrathin Janus PA separating layer. Owing to the collaborative separation effect and reduced thickness of the Janus separating layer, our NFMs exhibit excellent comprehensive separation performance with high rejection to both divalent cations and anions and desirable water permeation, simultaneously, which exceeds the separation performance upper bound of state-of-the-art NFMs. Furthermore, these NFMs show outstanding anti-fouling performance owing to the uniform and smooth upper surface. The methodology reported here is easy to couple with current commercialized interfacial polymerization technology, making up-scaling feasible.