Selective Molecular Transport through Intrinsic Defects in a Single Layer of CVD Graphene

Abstract

We report graphene composite membranes with nominal areas more than 25 mm(2) fabricated by transfer of a single layer of CVD graphene onto a porous polycarbonate substrate. A combination of pressure-driven and diffusive transport measurements provides evidence of size-selective transport of molecules through the membrane, which is attributed to the low-frequency occurrence of intrinsic 1-15 nm diameter pores in the CVD graphene. Our results present the first step toward the realization of practical membranes that use graphene as the selective material.

Graphene membranes for water desalination

“…26,27 However, according to simulations, by the inclusion of pores of controlled size, density and functionality, graphene membranes can surpass current desalination membranes, showing orders of magnitude higher permeability and selectivity ( Figure 4). 28 Molecular dynamics simulations have predicted that nanoporous graphene, due to its extraordinary water flow rate (up to 66 l.cm − 2 .day −1 .MPa −1 ) and high (499%) salt rejection (depending on the pore size and chemistry), may be one of the most desirable materials for water desalination. 2 By comparison, a conventional RO membrane can offer same salt rejection efficiency but with a water permeability of only 0.01-0.05 l.cm −2 .day −1 .MPa −1 .…”

“…Regarding employing monolayer graphene membranes with intrinsic pores, O'Hern et al 28 transferred a monolayer of CVD graphene onto a porous polycarbonate substrate to fabricate a graphene composite membrane as large as 25 mm 2 . The intrinsic 1-15 nm diameter pores in the CVD graphene contributed to the size-selective transport of molecules through the membrane.…”

“…Ideally, a monolayer graphene membrane should possess only homogenously sized pores at high density. However, intrinsic and extrinsic defects formed during growth and graphene transfer processes, 28,47,48 respectively, act as leakage pathways and hinder the practical realization of graphene monolayer membranes. Accordingly, such defects must be sealed or blocked or molecular permeation through them should be hampered.…”

“…Mass transport measurements and electron microscopy indicated that this membrane includes nanometer-scale (~1 − 15 nm) intrinsic defects that formed during CVD on copper and large (~100 − 200 nm) tears that formed during graphene transfer. 28 The intrinsic defects were sealed by selectively filling with hafnia via atomic layer deposition (Figure 8). In addition, an interfacial polymerization process was adopted to seal large defects via deposition of nylon-6,6 within the defects.…”

“…This leakage-sealing process was evaluated by the diffusion of KCl across the membrane. 28 Although monolayer graphene mounted to a polycarbonate track etch membrane decreases the permeation of KCl to~65% of that across a bare polycarbonate track etch membrane, defect-free monolayer graphene can decrease this flux to zero. In this regard, the deposition of hafnia on graphene lowers the flux to~40% and subsequent interfacial polymerization further decreases it to~8% of that through a bare polycarbonate track etch membrane, showing a significant sealing ability for the graphene layer.…”