Polymer brush-modified graphene oxide membrane with excellent structural stability for effective fractionation of textile wastewater

Conventional graphene oxide (GO) desalination membranes generally experience severe structural deterioration due to physical swelling. The strong surface negativity of the membrane also synchronously influences the diffusion/transport behaviors of all the solutes, leading to a low solute-solute selectivity. To address these issues, a novel poly (styrenesulfonic acid- co -4-vinylpyridine) brush-modified GO nanosheet (PB-GO) is designed and synthesized via atom transfer radical polymerization (ATRP) and is then employed to fabricate the GO membranes by a vacuum filtration approach, followed by chemical crosslinking with glutaraldehyde (GA). The sulfonate groups of the polymer enable excellent water dispersibility, while the pyridine groups are locally protonated under appropriate conditions, leading to the neutralization of the surface charge of the PB-GO nanosheets. The best performing membrane had a PB-GO mass loading of 0.3 g m −2 (PB-GO-0.3). In addition to a high water permeability of 30.3 ± 4.2 L m −2  h −1 bar −1 , this membrane also exhibits ultralow rejection of Na 2 SO 4 (<6.9%) over a wide concentration range (1.0–20.0 g L −1 ) in a cross-flow operation mode, due to the suppressed charge repulsion effect. However, the typical dye molecules, e.g. Congo red, direct red 23, and direct red 80, could be effectively rejected (>98.3%) based on the size exclusion effect. As a result, the PB-GO-0.3 membrane provides a high solute-solute selectivity of 58.18, which far exceeds that of commercial and other reported nanofiltration membranes. Overall, we provide a facile strategy for designing a polymer brush-functionalized GO membrane for effective dye/salt fractionation to treat textile wastewater.