Self-Regulating Cross-Linked Graphene Oxide Membranes with Stable Retention Properties over a Wide pH Range

To extend the effective working range of porous membranes is highly desirable for membrane applications. Here, graphene oxide (GO) based membranes capable of retaining stable retention properties with varying pH are reported. The self-adjustable properties of GO based membranes are realized by coupling with pH-responsive polyacrylic acid (PAA) molecules via a facile vacuum filtration process. With decreasing pH, the shrinkage of the molecular chains of PAA decreases the interlayer spacing of PAA/GO membranes, which compensates for the weakened Donnan effect in acidic conditions, leading to the stable retention properties of the membranes over a wide pH range. With PAA introduced, the laminated structure of the membranes is well preserved while the membrane thickness is slightly increased. PAA endows the membranes with obvious self-alteration of pore structure in response to the change of pH. Nanofiltration performance measurements show that the dye retention properties of GO membranes decrease sharply when the pH changes from 9 to 1. However, the rejection rates of PAA/GO membranes could be well retained or even increased in acidic conditions. This work demonstrates that PAA is an effective pH-sensitive modification material for fabricating GO-based membranes with stable retention properties under varying pH.