Enhancing Nanofiltration Selectivity of Metal-Organic Framework Membranes Via a Confined Interfacial Polymerization Strategy.

Developmentof well-constructed metal-organic framework(MOF) membranes can bring about breakthroughs in nanofiltration (NF)performance for water treatment applications, while the relativelyloose structures and inevitable defects usually cause low rejectioncapacity of MOF membranes. Herein, a confined interfacial polymerization(CIP) method is showcased to synthesize polyamide (PA)-modified NFmembranes with MOF nanosheets as the building blocks, yielding a stepwisetransition from two-dimensional (2D) MOF membranes to polyamide NFmembranes. The CIP process was regulated by adjusting the loadingamount of piperazine (PIP)-grafted MOF nanosheets on substrates andthe additional content of free PIP monomers distributed among thenanosheets, followed by the reaction with trimesoyl chloride in theorganic phase. The prepared optimal membrane exhibited a high Na2SO4 rejection of 98.4% with a satisfactory waterpermeance of 37.4 L & BULL;m(-2)& BULL;h(-1)& BULL;bar(-1), which could be achieved by neitherthe pristine 2D MOF membranes nor the PA membranes containing theMOF nanosheets as the conventional interlayer. The PA-modified MOFmembrane also displayed superior stability and enhanced antifoulingability. This CIP strategy provides a novel avenue to develop efficientMOF-based NF membranes with high ion-sieving separation performancefor water treatment. Theproposed strategy of confined interfacial polymerizationenabled a stepwise transition from 2D lamellar membranes to polyamidemembranes, affording a novel candidate for a more efficient nanofiltrationprocess.