Cross-linking modification with diamine monomers to enhance desalination performance of graphene oxide membranes

Two kinds of diamine molecules, including 1, 4-cyclohyxanediamine (CDA) and p-phenylenediamine (pPDA), were used as cross-linking for modification of graphene oxide (GO) nanosheets to prepare three-dimensional graphene oxide framework (GOF). Thereafter, graphene oxide composite membranes (GOCMs) were prepared on the polydopamine (PDA) modified α-Al₂O₃ tubes via vacuum filtration of GOF suspension. The separation performance of the GOCMs was tested for seawater desalination by pervaporation. The cross-linking modification, membrane thickness, operation temperature, feed concentration and PDA modification of α-Al₂O₃ tube have great effect on the separation performance of the GOCMs. Attributing to the enhancement of d-spacing and surface hydrophilicity after CDA modification, the CDA-based GOCM (CDA-GOCM) shows a higher water flux (20.1 kg m⁻² h⁻¹ with ion rejection of 99.9%) for desalination of 3.5 wt% seawater at 90 °C, which is higher than that of GO membrane (11.4 kg m⁻² h⁻¹ with ion rejection of 99.9%). However, since the hydrophilicity of the GO markedly decreases after pPDA modification, the pPDA-based GOCM (pPDA-GOCM) show a lower water flux (10.7 kg m⁻² h⁻¹ with ion rejection of 99.8%) at 90 °C. Further, the CDA-GOCM prepared on the PDA-modified α-Al₂O₃ tubes displays high stability for desalination of 3.5 wt% seawater.