Molecular intercalated graphene oxide with finely controllable interlayer spacing for fast dye separation

Molecular intercalation has been widely used for graphene oxide (GO) nanosheets to control interlayer spacing (d-spacing). However, further research is necessary to refine and enhance the precision of d-spacing control. In this study, we demonstrate a versatile strategy to create chitosan (CS) intercalated GO (GO@CS) nanosheets, whose d-spacing can be finely controlled by numbers of linked CS unit. This means the concentration of CS solution directly influences d-spacing of GO, and we can get the desired d-spacing for various applications by modulating the CS concentration. This is benefited from the linear structure of CS ensuring a consistent molecular length. The simulation of molecular structures with different numbers of linked CS unit supports this model. Then, the nanofiltration membranes prepared by these GO@CS nanosheets show high hydrophilicity, strong chemical bonding force, and abundant negative charges, which enhances permeability (water permeance of 91 L m⁻² h⁻¹ bar⁻¹), stability, and anti-fouling ability during dye separation processes, even though they are ultrathin (∼70 nm). Notably, the contrasting filtration efficiencies observed for oppositely charged dye molecules indicate a great potential use in molecular sieving.