Revealing Critical Pore Structure for Ultrafast Solvent Transport in Multilayer Nanoporous Graphene Membrane: Combined Experimental and Simulation Study

Nanoporous graphene has been recently employed in ultrafast organic solvent nanofiltration (OSN) membranes, where the nanopores effectively enhance solvent permeance by providing additional diffusion pathways while maintaining excellent molecular sieving properties due to their narrow interlayer spacing. However, the impact of nanoporous graphene structure on molecular transport has not been thoroughly explored. In this study, we revealed how the nanopore structure of graphene influences molecular transport properties of multilayer nanoporous graphene membranes with a combination of experimental and computational analysis. We prepared pore-tuned multilayer nanoporous graphene membranes by combining different reduction methods of graphene oxide (GO) with microwave treatment for the OSN experiment. To minimize the influence of functional groups and defective structure on the solvent transport, the microwave treatment was conducted to recover the crystallinity of graphene while maintaining the pore structure. The molecular dynamic study was conducted on graphene pores of different sizes and functionalities, permeating various organic solvent molecules. Overall, highly crystalline multilayer graphene membranes show ultrafast organic solvent permeability particularly in the range of 1.2 x 10-4 to 4.6 x 10-4 L m-1h-1 bar-1 for 2-propanol (IPA) with narrow molecular cut-off at 500 Da, far surpassing the upper bound of reported OSN membrane. Importantly, it is revealed that pore size predominantly determines organic solvent permeance, and significant enhancement was observed in pores larger than 2 nm regardless of the edge functionality, while molecular sieving was primarily governed by interlayer spacing. These findings can provide insights for designing nanoporous two-dimensional materials for ultrafast membrane fabrication beyond graphene.