Abstract
A robust synthesis methodology for crystallizing nanoporous single-layer graphene hosting a high density of size-selective nanopores is urgently needed to realize the true potential of two-dimensional membranes for gas separation. Currently, there are no controllable etching techniques for single-layer graphene that are self-limiting, and that can generate size-selective nanopores at a high pore-density. In this work, we simulate a unique chemical vapor deposition based crystallization of graphene on Cu(111), in the presence of an etchant, to generate a high density (>1013 cm−2) of sub-nanometer-sized, elongated nanopores in graphene. An equilibrium between the growth rate and the etching rate is obtained, and beyond a critical time, the total number of the carbon atoms and the edge carbon atoms do not change. Using an optimal first-order etching chemistry, a log-mean pore-size of 5.0 ± 1.7 (number of missing carbon atoms), and a pore-density of 3 × 1013 cm−2 was achieved. A high throughput calculation route for estimating gas selectivity from ensembles of thousands of nanopores was developed. The optimized result yielded H2/CO2, H2/N2 and H2/CH4 selectivities larger than 200, attributing to elongated pores generated by the competitive etching and growth. The approach of competitive etching during the crystal growth is quite generic and can be applied to a number of two-dimensional materials.
Highlights
H2/C3H8 mixture separation factor exceeding the corresponding ideal selectivity
Using a kinetic Monte Carlo algorithm, we report a promising crystallization methodology capable of incorporating a high-density of size-selective, elongated nanopores in graphene in a scalable manner. This is achieved by subjecting a nanoporous graphene lattice to the chemical vapor deposition (CVD) conditions in the presence of an etchant (Fig. 1a)
To generate size-selective nanopores at a high pore-density, we introduce the concept of a competitive growth and etching of the nanoporous graphene lattice
Summary
Molecular simulations and transport calculations have shown that nanoporous graphene lattice, hosting size-selective nanopores at a high enough pore-density, exhibits ultrahigh gas permeance[15,16,17,20,21,22,23,24]. Using a kinetic Monte Carlo (kMC) algorithm, we report a promising crystallization methodology capable of incorporating a high-density of size-selective, elongated nanopores in graphene in a scalable manner. This is achieved by subjecting a nanoporous graphene lattice (typically obtained by conventional etching methods) to the chemical vapor deposition (CVD) conditions in the presence of an etchant (Fig. 1a). A high-throughput transport calculation from the ensemble of nanopores indicates that attractive separation selectivities (H2/CO2, H2/CH4 and H2/N2 > 50) at a high pore-density (>1013 cm−2) is possible by such approach
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