Polyphenol etched ZIF-8 modified graphene oxide nanofiltration membrane for efficient removal of salts and organic molecules

Multi-layer graphene oxide (GO) membranes show great perspective in vast fields due to special two-dimensional structure. However, pure GO membranes generally face main obstacles of low flux, weak interlayer interaction and poor stability, which hinder their wide application in separation. Introduction of nano-porous crystals into interlayer of GO nanosheets to form 3D/2D structure is a potential strategy to overcome these issues. In this study, novel polyphenol etched hollow MOF/GO composite membrane was first synthesized employing modified hollow metal organic frameworks with strong hydrophilicity and hollow structure by one-step etching-aided cross-linking method. MOF nanoparticles with hollow structure expanded interlayer spacing of GO nanosheets and brought about formation of additional water channels, significantly reducing water transfer resistance. Meanwhile, nano-porous crystal MOFs modified by phenolic materials were able to cross-link adjacent GO nanosheets via π–π interfacial interactions to achieve stable structure and increase anti-swelling property of membranes. The pores with abundant hydroxyl groups provided strong free energy barrier for ions at medium and low concentrations of ionic strength , therefore not only greatly improved membrane permeaselectivity, but also enhanced anti-fouling performance. The prepared eZIF-8/GO nanofiltration membrane exhibited excellent permeate flux of 16.4 L m −2  h −1 bar −1 , 382% higher than pure GO membrane, and competitive Na 2 SO 4 rejection of 86.3%. By simply adjusting GO loading to further reduce membrane thickness, the permeate flux reached up to 45.4 L m −2  h −1 bar −1 with high rejection more than 99% for organic molecules. These results indicate that novel MOF/GO composite membranes have broad application prospects in desalination and water treatment.