Large-Area and Crack-free Helium-Sieving Graphene Membranes

Porous single-layer graphene is believed to be an ultimate molecular sieving membrane. One of the bottlenecks in scaling up graphene membranes is the transfer process in which capillary forces as well as the mechanical tensions imposed on the graphene film generate unwanted cracks and tears. Herein, we report a single-step fishing-free transfer technique for the fabrication of a helium-sieving graphene membrane using a spin-coating-assisted approach in which no capillary forces and mechanical tensions are exerted on the graphene film. The porous polysulfone (PS), which is synthesized in this method, is applied as both the graphene protective layer and the porous reinforcing support; thus, eliminating the fishing stage in which the graphene film is scooped onto a supporting substrate. The proposed technique yields a crack-free and large-area (similar to 1 cm(2)) graphene film on the porous polymer substrate. This technique also eliminates the issue with polymer residues remaining on the graphene surface during the transfer process. A relatively high gas molecular sieving performance (gas selectivity of 25, 24, and 1.1 for He/CH4, H-2/CH4, and He/H-2 separation, respectively) was obtained, which demonstrates the presence of sub-nanometer intrinsic defects as well as the absence of cracks and tears in the graphene membrane. Despite the low graphene porosity of 0.002%, agreeable He and H-2 permeance (up to 5.18 x 10(-8) mol m(-2) s(-1) Pa-1) was observed, which highlights the success of the developed technique used for the fabrication of graphene membrane in the current work.