Calcium ion-sodium alginate double cross-linked graphene oxide nanofiltration membrane with enhanced stability for efficient separation of dyes

Graphene oxide (GO)-based membranes formed by stacking layered graphene oxide nanosheets have great application prospects for dye separation of textile wastewater. This paper proposes a simple vacuum-assisted method to prepare a double-crosslinked composite graphene oxide nanofiltration membrane (Ca/GO-SAx) by adding sodium alginate (SA) and calcium ions. This method adjusts the nanochannels of the membrane, expands the interlayer spacing, improves the water permeability, and increases the water flux from 10.14 L m(-2) h(-1) bar(-1) to 38.90 L m(-2) h(-1) bar(-1), which is 384% of the original GO membrane. Importantly, the Ca/GO-SA3 composite membrane has excellent dye separation performance, achieving more than 99% removal of multiple dyes (congo red, crystal violet, methylene blue). Furthermore, the structure of the Ca/GO-SA3 composite membrane is more compact and orderly, and the stability is obviously enhanced. It not only repels other cations in different chloride salt solutions, keeps the interlayer spacing stable, but also maintains excellent dye separation performance after being immersed in harsh aqueous solutions for one month. These findings demonstrate a simple and practical method to prepare GO nanofiltration membranes with a two-dimensional layered structure to achieve the purification treatment of textile wastewater.