Abstract
Gas separation membranes based on single-layer-graphene are highly attractive because the size of graphene nanopores can be tuned to separate gases by the size-sieving mechanism. A prerequisite for this, the synthesis of high-quality polycrystalline single-layer graphene film by chemical vapor deposition (CVD), is extremely crucial. The quality of graphene in the context of membranes is reflected by the size and the density of the intrinsic vacancy defects, and is affected by the catalytic metal substrate and the CVD environment. Generally, expensive high-purity Cu foil is used to obtain gas-sieving performance from single-layer graphene. For the eventual scale-up of graphene membranes, it is highly attractive to use low-cost Cu foils, however, as we show here, these Cu foils are rough and graphene membranes derived from these foils do not yield gas-sieving performance. Herein, we conduct a systematic high-temperature annealing study on two separate, commercial, low-cost Cu foils leading to their transformation to Cu(111). The annealing process smoothened the Cu surface, decreasing the root mean square (RMS) surface roughness from over 200 nm to close to 100 nm. The RMS roughness on the individual Cu step, measured using the scanning tunneling microscopy (STM), was only 0.23 nm. The smooth, oriented Cu grains yielded single-layer graphene with a significantly lower defect density with ID/IG ratio decreasing from 0.18 ± 0.02 to 0.04 ± 0.01. Finally, single-layer graphene films, synthesized on the annealed low-purity Cu foil, yielded H2-selective membranes with H2 permeance reaching 1000 gas permeation units (GPU) in combination with attractive H2/CH4 and H2/C3H8 selectivities of 13 and 26, respectively.
Highlights
Single-layer graphene hosting subnanometer-sized nanopores have shown attractive gas separation performances by molecular sieving where separation takes places based on differences in size of the mole cule [1,2,3,4,5]
Single-layer graphene was synthesized on as-received Cu as well as Cu subjected to various annealing and polishing steps (Fig. 1a and b)
We investigated the effect of high-temperature annealing on the intrinsic vacancy-defects in chemical vapor deposition (CVD) graphene and subsequently the gas sieving performance
Summary
Single-layer graphene hosting subnanometer-sized nanopores have shown attractive gas separation performances by molecular sieving where separation takes places based on differences in size of the mole cule [1,2,3,4,5]. Khan et al reported that H2-sieving vacancy defects can be incorporated in graphene at lower CVD tem perature when benzene is chosen as the carbon precursor [23]. Most of these studies used expensive high-purity Cu foil with prohibitive cost for scaling-up graphene membranes. We demonstrate a facile crystallographic and morphological optimization protocol, applied to two different low-cost Cu foils, which successfully transforms them into smooth Cu(111) substrates, resulting in the synthesis of higher-quality single-layer graphene which led to hydrogen-sieving membranes. 100 nm, and on a single Cu step as low as 0.23 nm This treatment greatly improved the gas separation performance from the intrinsic defects of graphene membranes. The Cu(111) surface reduces the grain-boundary defects attributing to the fact that there is only a small mismatch (3–4%) between the lattice constants of the (111) facet of Cu and that of gra phene [24,25]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
