Metal-Phenolic Acid Networks Enable Nanofiltration Membranes for Rapid and Precise Molecular Separation

Molecular sieving membranes based on molecular depositionhaveattracted extensive attention over the past several decades. However,the building blocks are mainly limited to catechol-based compounds,which possibly result in complexity of the ultimate selective layer.It is still a great challenge to construct selective layers of molecularsieving membranes using other building blocks. Herein, composite nanofiltrationmembranes with metal-phenolic acid networks as the selectivelayers are first demonstrated for molecular sieving. Represented byFe(3+)-ferulic acid (FA) networks with a thicknessof about 100 nm, they are facilely constructed at the interface ofthe deposition solution and porous substrates through a coordinationinteraction between metal ions and ten kinds of organic ligands. Thecoordination mechanism is further elucidated by molecular dynamicssimulation. The resultant defect-free and robust composite membranesshow great potential in rapid and precise separation performance fordyes as well as mixtures of dyes and inorganic salt ions. The waterflux is as high as 87.7 L/(m(2) h bar), and the rejectionsfor methyl orange (MO, 327 Da) and methyl blue (MB, 800 Da) are about20.1% and 98.0%, respectively. The separation mechanism has also beendiscussed. In addition, the composite membranes have sufficient pHstability and long-term operation stability. The present system expandsthe toolbox of membrane building blocks and provides an approach tothe design and fabrication of composite separation membranes basedon metal-phenolic acid networks.