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

Abstract

Molecular sieving membranes based on molecular deposition have attracted 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 molecular sieving membranes using other building blocks. Herein, composite nanofiltration membranes with metal–phenolic acid networks as the selective layers are first demonstrated for molecular sieving. Represented by Fe3+–ferulic acid (FA) networks with a thickness of about 100 nm, they are facilely constructed at the interface of the deposition solution and porous substrates through a coordination interaction between metal ions and ten kinds of organic ligands. The coordination mechanism is further elucidated by molecular dynamics simulation. The resultant defect-free and robust composite membranes show great potential in rapid and precise separation performance for dyes as well as mixtures of dyes and inorganic salt ions. The water flux is as high as 87.7 L/(m2 h bar), and the rejections for methyl orange (MO, 327 Da) and methyl blue (MB, 800 Da) are about 20.1% and 98.0%, respectively. The separation mechanism has also been discussed. In addition, the composite membranes have sufficient pH stability and long-term operation stability. The present system expands the toolbox of membrane building blocks and provides an approach to the design and fabrication of composite separation membranes based on metal–phenolic acid networks.