Green and edible cyclodextrin metal-organic frameworks modified polyamide thin film nanocomposite nanofiltration membranes for efficient desalination

Abstract

Nanofiltration membranes are widely used in water treatment applications. However, their performance is often limited due to the trade-off between permeability and selectivity. To overcome this limitation, the incorporation of metal-organic frameworks (MOFs) into polyamide layers to prepare thin film nanocomposite polyamide membranes has been extensively investigated. However, these reported MOFs usually contain toxic heavy metal ions and ligands, posing the risk of leaching during the filtration process and being harmful to environment and even human health. In this work, γ-cyclodextrin and K+ were used to prepare green and edible cyclodextrin MOF (CD-MOF) nanoparticles. Furthermore, these CD-MOF nanoparticles were further loaded at the porous substrate surface to prepare polyamide nanofiltration membranes. The CD-MOF nanoparticles delay the diffusion of PIP molecules and leads to a thin PA layer. In addition, the rough substrate surface loaded with CD-MOF provide an uneven interfacial polymerization reaction interface. After the dissolvement of the CD-MOF nanoparticles, a wrinkled PA structure eventually formed. The PWP of the optimal membrane was 24.4 L m-2 h-1 bar-1, which was 502% higher than that of the controlled TFC membrane, and the Na2SO4 rejection was improved to 97.1%. More ordered surface and negative electrical properties increase the selectivity of divalent to monovalent ions. Compared to conventional TFC nanofiltration membranes, the novel TFN membrane successfully overcame the longstanding permeability and selectivity trade-off. The current work expands the potential of CD-MOF to be utilized in the fabrication of high-performance NF membranes.