Anisotropic superhydrophobic graphene aerogel with radial superelasticity and axial superstiffness for efficient on-demand oil–water separation

Abstract

Graphene aerogels possess unique advantages for treating oil–water mixtures, but their fragile mechanical properties hinder further development, and their separation mechanisms remain unclear. Herein, a superhydrophobic silane-crosslinked graphene oxide/polyvinyl alcohol aerogel (Si-GPA) was prepared by directional freeze-drying of a graphene oxide/polyvinyl alcohol (GO/PVA) suspension and vapor-phase deposition of methyltriethoxysilane (MTES) for efficient on-demand oil–water separation, and its separation mechanism was revealed through computational fluid dynamics (CFD) simulations. With the binding of PVA polymer chains and the cross-linking of MTES monomers, the Si-GPA exhibits excellent anisotropy, radial superelasticity (over 50 000 cycles at 50% strain), and axial superstiffness (freezing direction) (more than 20 000 times its own weight), which are the best-known results to date. The Si-GPA utilizes its superelasticity to adsorb floating oil on the sea surface and oil droplets in oil-in-water emulsions, while employing its superstiffness to filter water-in-oil emulsions in pipelines for on-demand oil–water separation. More importantly, the Si-GPA overcomes the trade-off between flux and efficiency, enabling the separation of water-in-oil emulsions with water droplet sizes several times smaller than its pore size under gravity alone, and with ultra-high flux (4350 L m⁻² h⁻²) and ultra-high purity (99.9%), 1–2 times higher than those of 2D superwetting separation membranes that require external pressure. Additionally, visualization analysis based on simulation modeling reveals the emulsion coalescence filtration mechanism of the Si-GPA. Therefore, mechanically robust superhydrophobic graphene aerogels have enormous potential in oil–water separation applications.