Ethylenediamine-oxidized sodium alginate hydrogel cross-linked graphene oxide nanofiltration membrane with self-healing property for efficient dye separation

The filtration membrane formed by stacking graphene oxide (GO) nanosheets with two-dimensional layered structure and single-atom thickness has great application prospects for the purification of dye wastewater. In this study, GO was first grafted with ethylenediamine (EDA) to obtain EGO nanosheets, and then oxidized sodium alginate (OSA) was introduced. The aldehyde groups on the OSA molecular chain reacted with the active amino groups to form a hydrogel network structure between adjacent GO layers through Schiff base reaction. Afterwards, a hydrogel-supported layered modified GO nanofiltration membrane was obtained by vacuum-assisted filtration. By changing the addition amount of OSA molecules, the EGO-OSA3 composite membrane with the best performance was selected, which not only had a water flux 9.17 times that of the original GO membrane, but also did not sacrifice the separation performance of dyes. After mechanical damage, by adding a very small amount of OSA, the composite membrane could self-heal by the synergistic effect of dynamic Schiff base and hydrogen bonding interactions between OSA chains and EDA molecules. In addition, due to the stability of the membrane structure brought about by chemical cross-linking, the composite membrane still maintained excellent water purification performance after 100 h of operation.