Turning gas hydrate nucleation with oxygen-containing groups on size-selected graphene oxide flakes

Gas hydrate is a promising alternative for gas capture and storage due to its high gas storage capacity achieved with only structured water molecules. Nucleation is the critical controlling step in gas hydrate formation. Adding an alien solid surface is an effective approach to regulate gas hydrate nucleation. However, how the solid surface compositions control the gas hydrate nucleation remains unclear. Benefiting from the fact that the surface compositions of graphene oxide (GO) can be finely tuned, we report the effect of functional groups of size-selected GO flakes on methane hydrate nucleation. The carbonyl and carboxyl of GO flakes showed a more prominent promotion for methane hydrate nucleation than the hydroxyl of GO flakes. Surface energy, zeta potential, Raman spectra, and molecular dynamics simulation analysis were used to reveal the regulation mechanism of the functional groups of size-selected GO flakes on methane hydrate nucleation. The GO flakes with abundant carbonyl and carboxyl exhibited higher charge density than those enriched in hydroxyl. The negatively charged GO flakes can induce water molecules to form an ordered hydrogen-bonded arrangement via charge-dipole interactions. Therefore, the water molecules surrounding the carboxyl and carbonyl showed a more ordered hydrogen-bonded structure than those around the hydroxyl of GO flakes. The ordered water arrangement, similar to methane hydrate cages, significantly accelerated methane hydrate nucleation. Our study shows how the surface chemistry of solids control gas hydrate nucleation and sheds light on the design of effective heterogeneous nucleators for gas hydrate.