Large-area ultra-thin GO nanofiltration membranes prepared by a pre-crosslinking rod coating technique

The figure a shown the schematic diagram of the pre-crosslinking rod-coating technique. First, GO and PPD underwent a crosslinking reaction for 180 min at 60℃ using DMF as the solvent to generate amide bonds, resulting in the formation of a pre-crosslinked GO-PPD solution (2 mg/ml). The main reaction involved the epoxy ring-opening reaction between the amine in PPD and the epoxy group in GO, resulting in a hydroxyl group and secondary amine. [Display omitted] •A large-area GO NF membrane was prepared by Pre-Crosslinking Rod Coating Technique.•The obtained GO-PPD NF membrane showed superior 99% rejection rate for dyes.•The permeability of GO-PPD NF membrane was 10 times that of non-crosslinking GO NF membrane. In existing separation membranes, it is difficult to quickly produce large-area graphene oxide (GO) nanofiltration membranes with high permeability and high rejection, which is the bottleneck of industrialization. In this study, a pre-crosslinking rod-coating technique is reported. A GO-P-Phenylenediamine (PPD) suspension was obtained by chemically crosslinking GO and PPD for 180 min. After scraping and coating with a Mayer rod, the ultra-thin GO-PPD nanofiltration membrane with an area of 400 cm2 and a thickness of 40 nm was prepared in 30 s. The PPD formed an amide bond with GO to improve its stability. It also increased the layer spacing of GO membrane, which could improve the permeability. The prepared GO nanofiltration membrane had a 99 % rejection rate for dyes such as methylene blue, crystal violet, and Congo red. Meanwhile, the permeation flux reached to 42 LMH/bar, which was 10 times that of the GO membrane without PPD crosslinking, and it still maintained excellent stability under strongly acidic and basic conditions. This work successfully solved the problems of GO nanofiltration membranes, including the large-area fabrication, high permeability and high rejection.