Improved water permeability and structural stability in a polysulfone-grafted graphene oxide composite membrane used for dye separation

Abstract Polysulfone (PSf)-grafted graphene oxide (GO) nanosheets (GO-g-PSf) were synthesized via a nucleophilic substitution reaction between hydroxyl groups of GO and chloromethyl groups of chloromethylated polysulfone (CMPSf). GO-g-PSf dispersion in N-methyl pyrrolidone (NMP) was employed to fabricate GO-g-PSf composite membranes for dye separation by a vacuum filtration self-assembly method using polyamide (PA) composite membranes as the supports. The chemical structure and morphology of GO-g-PSf nanosheets were characterized by XRD, FTIR, Raman, XPS and TEM analyses. The morphology and filtration performance of membranes with various GO and GO-g-PSf depositions were investigated. The GO-g-PSf composite membrane with a deposition rate of 31.8 μg cm−2 exhibited a much higher pure water flux (88.0 L m−2 h−1 (LMH)) than pure GO composite membrane (12.8 LMH) at 2 bar owing to the enlarged interlayer spacing between the GO-g-PSf nanosheets. Simultaneously, the rejection rate of the GO-g-PSf composite membrane reached 90.3% for acid black 1 (AB), 99.5% for Congo red (CR) and 99.8% for methyl blue (MB) dyes under a cross-flow process at 2 bar. Moreover, the water permeance of the GO-g-PSf composite membrane remained at 25.9 LMH bar−1 after 60 h of operation for CR separation. Notably, the GO-g-PSf composite membrane also exhibited improved structural stability after 2 h of ultrasonic irradiation due to the physical entanglement of PSf chains. This study provides a simple approach to enhancing the permeability and structural stability of GO-based membranes used for dye separation.