Fabrication of sub-nanometer pores on graphene membrane for ion selective transport

Abstract

The ability to sieve ions through nanopores with high throughput has significant importance in seawater desalination and other separation applications. In this study, a plasma etching process has been demonstrated to be an efficient way to produce high-density nanopores on graphene membranes with tunable size in the sub-nanometer range. Besides the pore size, the nanopore density is also controllable through adjusting the exposure time of the sample to argon or oxygen plasma. The plasma-treated graphene membranes can selectively transport protons, Na and Cl ions. Density function theory calculations uncover that the sp and vacancy-type defects construct different energy barriers for different ions, which allow the defected graphene membrane to selectively transport ions. Our study indicates that oxygen plasma etching can be used as a very convenient and efficient method for fabricating a monolayer filtration graphene membrane with tunable sub-nanometer pores.

Ion transport through a nanoporous C2N membrane: the effect of electric field and layer number

“…As expected, with an increase in electric eld, the currents of each ion nonlinearly increase due to the accelerated dehydration of the cation shell under the higher electric eld. 27,55,56 Notably, the current of the K + ion through a single nanopore in the C 2 N membrane is about 1.16/30 z 0.039 nA under E ¼ 0.15 V nm À1 , where 30 is the number of nanopores in the C 2 N membrane. It is approximately the same as that from a single pore in a graphene membrane (0.032 nA 57 ) under the same conditions.…”

Graphene Membranes: Transport Properties and Energy Applications

“…A variety of techniques can be used to create nanopores in graphene. This includes methods such as drilling pores through a focused ion [4][5][6][7][8][9][10] or electron beam [11][12][13], etching [14][15][16] chemical activation [17][18][19][20][21] and electrical pulses [22]. Focused ion beam (FIB) drilling is one of the most commonly used techniques to create porous graphene, [7,23] as it allows the formation of pores with broad diameters ranging from 10 nm to 1 µm [7,15,24,25].…”

“…acid etching [8] and combination of electron beam and ion beam [5], low-energy focused electron beam (<10 keV) and nitrogen-ions [27] to induce high density pores in graphene membrane, or gain better distribution of pore size. Etching methods include plasma etching, where high speed plasma is shot in pulses at the graphene drilling high density nanopores on to the graphene membrane [14,15]. For example, R. Karnik's group reported the use of oxygen plasma etching to create pores in graphene for selective gas permeance [6].…”

Single-File Water Flux Through Two-Dimensional Nanoporous Membranes

“…As a result of its one-atom-thick pore width, the frictional pressure loss can be minimized theoretically, and a superior water flux can be obtained [ 14 ]. Nanoporous single-layer graphene has been successfully fabricated by using an oxygen plasma etching process, allowing control of pore size [ 15 , 16 ]. It has been successfully used for desalination membranes by exhibiting nearly 100% salt rejection and high water flux up to 10 6 g/m 2 s [ 16 ].…”

“…High desalination performance is also demonstrated by performing molecular dynamics (MD) simulations [ 17 ]. In addition, nanoporous graphene membranes exhibited efficient molecular sieving for gas separation [ 18 , 19 ] and ion separation [ 15 , 20 ].…”