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 Na2SO4 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.