Selective Gas Permeation in Defect-Engineered Bilayer Graphene

Abstract

Defective graphene holds great potential to enable the permeation of gas molecules at high rates with high selectivity due to its one-atom thickness and resultant atomically small pores at the defect sites. However, precise control and tuning of the size and density of the defects remain challenging. In this work, we introduce atomic-scale defects into bilayer graphene via a decoupled strategy of defect nucleation using helium ion irradiation followed by defect expansion using hydrogen plasma treatment. The cotreated membranes exhibit high permeability and simultaneously high selectivity compared to those singly treated by ion irradiation or hydrogen plasma only. High permeation selectivity values for H2/N2 and H2/CH4 of 495 and 877, respectively, are achieved for optimally cotreated membranes. The method presented can also be scaled up to prepare large-area membranes for gas separation, e.g., for hydrogen purification and recovery from H2/CH4 and H2/N2 mixtures.

Gas Separations using Nanoporous Atomically Thin Membranes: Recent Theoretical, Simulation, and Experimental Advances

“…used He + ion bombardment to perforate DLG. [ 154 ] The areal pore density reached 6.7 × 10 15 m −2 (average pore distance L D = 6.9 nm) when an irradiation dose of 10 15 ions cm −2 was used. In spite of the high areal pore density, the H 2 permeance through the perforated DLG was ≈3 × 10 −4 GPU (1 GPU = 3.35 × 10 −10 mol m −2 s −1 Pa −1 ), much lower than those through other NATMs or conventional polymeric membranes ( Figure ).…”

“…Figure 6. Compilation of experimentally measured H 2 /CH 4 and CO 2 /N 2 separation performances by NATMs in a selectivity-permeance Robeson plot.The experimental results are categorized according to the perforation methods used, including ion beam bombardment (some followed by additional chemical etching),[150][151][152][153][154]156,157] oxidative etching,[143,[158][159][160][161][162][163][164][165][166] and intrinsic defect formation during CVD [62,143,149,159,160,164,[167][168][169][170][171]. The Robeson upper bounds for polymers are plotted assuming 1 µm thickness [11].…”

A review of defect engineering, ion implantation, and nanofabrication using the helium ion microscope

“…Further work in this area has used Raman spectroscopy in combination with a model for defect activation to investigate the size and distribution of vacancy defects formed by broad-area illumination, using helium/neon ions and free-standing/supported monolayer graphene/MoS 2 [ 171 ]. Very recently, the fabrication of atomic-scale nanopores in bilayer graphene for selective gas permeation was reported using a combined approach of helium ion bombardment to nucleate the defects followed by treatment in hydrogen plasma to expand the pores to the desired size [ 172 ].…”

Investigation of Substrate Swell-Induced Defect Formation in Suspended Graphene upon Helium Ion Implantation

“…Controllable defect formation in suspended graphene has attracted widespread attention in the ionic/molecular selective transport applications, − including water purification, − seawater desalination, − gas separation, − and molecular detection. − The exposures to plasma and energetic ions/electrons induce the formation of defects by crystallographic modification and charge doping of integrated graphene devices with unique properties. ,,− The selective transport properties and quality of suspended graphene subjected to plasma exposure have been investigated to confirm the possibility of controllable defect patterning by plasma exposure. , Nevertheless, it is the exposure mechanism that obstructs graphene crystallographic modification with high precision and creates disordered pores and vacancies by exposing it to the plasma instead. On the other hand, the controllable pores and vacancies have been created in freestanding graphene by using transmission electron microscopy with energetic electrons, but limited in scale because an immense radiation dose is required for large-scale patterning applications. − The use of a focused helium ion beam can be a promising nanoscale patterning technology for controllable defect formation in freestanding graphene with little radiation dose. − The possibility of controllable defect formation under helium ion irradiation has been demonstrated by the quality of the graphene membrane using Raman spectroscopy. − Experimental results and simulations independently assess substrate influence on defect production upon helium ion irradiation, though these studies lack an understanding of the substrate influence on the energetic-ion–freestanding graphene interaction. − Recently, more insights into the effects of the substrate pore shape and its edge on the interaction between helium ions and suspended graphene are provided by a few experimental investigations. …”

“…13,15,24−33 The selective transport properties and quality of suspended graphene subjected to plasma exposure have been investigated to confirm the possibility of controllable defect patterning by plasma exposure. 13,15 Nevertheless, it is the exposure mechanism that obstructs graphene crystallographic modification with high precision and creates disordered pores and vacancies by exposing it to the plasma instead. On the other hand, the controllable pores and vacancies have been created in freestanding graphene by using transmission electron microscopy with energetic electrons, but limited in scale because an immense radiation dose is required for large-scale patterning applications.…”