Photocatalytic self-cleaning graphene oxide/ZnO hybrid membrane for ultrafast cyclic small organic molecule separation

Graphene oxide (GO) based membranes have attracted tremendous interest owing to their unique lamellar structure resulting in excellent molecular filtration. However, the expansion of interlayer spacing of GO nanoflakes in liquid solutions, particularly in aqueous solution, and the adsorption of foulants in the layered nanoconfinement as well as on the surface adversely affects the long-term performance of the membranes. In this work, one-dimensional zinc oxide (ZnO) nanorods were integrated with graphene oxide via in-situ crystallization. A fast thermal treatment was applied to partially reduce the graphene oxide nanoflakes and chemically ‘lock’ the newly formed ZnO nanorods during the final step of hybrid membrane fabrication. It was found that the partially reduced graphene oxide (rGO) provided excellent mechanical stability between the nanolayers and also very stable and efficient molecular sieving properties. Interestingly, the ZnO nanorods not only served as a space holder between neighbouring reduced graphene-oxide nanoflakes but also endowed the hybrid membrane with responsive photocatalytic self-cleaning properties, which has been considered one of the most promising approaches for energy-efficient environmental remediation. In water permeation tests, these graphene oxide-zinc oxides (P-rGO/ZnO) membranes exhibited ultrahigh permeance of 400 ± 21 L m⁻² h⁻¹ bar⁻¹, more than an order of magnitude higher than the conventional rGO membranes. In the meantime, these membranes exhibited excellent small organic molecule separation efficiencies with >98.8 ± 1.2% rejections toward direct red 80, rose bengal, reactive black 5, and trypan blue. More importantly, under ultraviolet–visible light irradiation, the membrane demonstrated highly efficient self-cleaning behaviour for fast organic dye decomposition, enabling excellent cyclic removal of pre-adsorbed dye molecules. Therefore, this intelligent self-cleaning hybrid membrane has great potential in wastewater purification, particularly for ultrafast small organic molecule removal.