Tunable reduced graphene oxide nanofiltration membrane for efficient retention and separation of dye/salt based on molecular interactions

Effective retention and separation of mixed dyes are critical to treating textile wastewater. Graphene oxide (GO) is an ideal material for treating polluted water attributed to its unique structure and abundant oxygen-containing groups. However, GO still has some limitations, such as unstable performance, poor dye retention and no selective separation performance. Here, we report a weakly reduced graphene oxide (rGO) membrane that can modulate its water permeability and dye retention by controlling the reduction temperature. The water flux (84.35 L m- 2 h-1 bar-1) of rGO membranes decreased with increasing reduction temperature but the methylene blue (MB) dye rejection rate (99.09 %) increased with increasing reduction temperature. More interestingly, the rGO membrane has completely different dye rejection rates for MB and methyl orange (MO), allowing the separation of MB and MO mixtures, effectively replacing traditional column chromatography. In addition, we investigated the reasons for the different retention rates and selective separation of dyes by rGO membranes through reduction temperature, contact angle, interlayer distance, electrostatic interactions and molecular dynamics simulations. This work uses a non-expensive and low-energy method to prepare nanofiltration membranes that can be easily extended to construct other stable and efficient filtration membranes for the separation of different dyes and salts.