▎ 摘　　要

Atomically thin porous graphene as a selective layer Is believed to be a promising candidate to exhibit superior gas separation performance. While small-area graphene membranes have been successfully fabricated, crack-free and large-area graphene transfer onto the porous substrate remains a great challenge. Large defects, up to micron-scale, can emerge during the conventional graphene transfer techniques. In this work, we improved transfer-free graphene membrane fabrication through small pore introduction into copper foil. We apply the typical photolithography process to establish a patterned mask on the backside of the graphene-covered copper foil followed by a chemical etching process to drill small-sized pores into the copper foil, with pore sizes varying between 200 nm and 4 mu m. To measure the membrane performance, He/CH4 separation is carried out. The observed selectivity similar to 3.5 shows 28% enhancement in comparison to the membrane prepared through the transfer step (similar to 2.5). The maximum measured selectivity achieved in this work is higher compared to the Knudsen selectivity (2), which can confirm the molecular-sieving-based selective gas transport through the angstrom-size intrinsic defects of the graphene film. In addition to the high permeance (1.19 x 10(-5) mol/m(2).s.Pa) achieved through the graphene-based membrane, its selectivity also exceeds the Robeson upper bound for polymeric membranes, proving the higher performance acquired compared to other polymeric membranes. The enhancement in transfer-free graphene membrane quality can bring us one step closer to realizing graphene's full potential and developing large-area and crack-free graphene membranes.