Single-layer Graphene Membranes Research Articles

Preparation of a membrane-sealed cell for studying catalyst nanoparticles in flowing gas with high vacuum x-ray photoelectron spectrometer.

Here a sealing-style x-ray photoelectron spectroscopy study of the surface of a 1.0 wt. %Ni/TiO2 nanoparticle catalyst in a flowing mixture of CO and O2 at 1bar was performed with a graphene membrane-sealed Si3N4 window-based miniature cell. We report the details on how a commercial Si3N4 window is modified before assembling a graphene membrane, how single-layer graphene membranes are transferred from their metal supports to the modified Si3N4 window, how a modified Si3N4 window covered with a double-layer graphene membrane is assembled onto a blank cell cap, how a nanoparticle catalyst is introduced to the cell cap and then the cell cap is installed onto a cell body to form a complete reaction cell, and how a complete cell is interfaced with a high vacuum chamber of an XPS system before an XPS study of 1.0 wt. %Ni/TiO2 catalyst surface in a flowing mixture for 0.2bar CO and 0.8bar O2 is performed. How the characterization of a catalyst using this type of graphene membrane-sealed Si3N4 window-based miniature cell is relevant to the finding of the actual surface chemistry of a catalyst during catalysis is discussed.

High rejection stacked single-layer graphene membranes for water treatment

Nowadays, the production of pure water from saltwater and wastewater is one of the most challenging issues. Polymeric materials represent, at the moment, the best solution for membranes technology but new materials with improved functionalities are desirable to overcome the typical limitations of polymers. In this work, graphene membranes with superior filtration properties are fabricated by stacking up to three graphene layers on a porous support and exploiting the intrinsic nanopores of graphene to filter diclofenac (drug), and methylene blue (dye). The rejection improves increasing the number of the stacked graphene layers, with the best results obtained with three graphene layers. Mass diffusion properties depend on the size of the probe molecule, consistently with the existence of intrinsic nanometer-sized pores within graphene. From the results of an in depth transmission electron microscopy analysis and molecular dynamics simulations it is inferred that graphene stacking results in a decrease of effective membrane pore sizes to about 13 Å diameter which corresponds to 97% rejection for diclofenac and methylene blue after one hour filtration.

Holes interaction of a graphene membrane under pressure for water desalination

Single-layer graphene is the basic structural element of several carbon allotropes, including graphite, fullerens and carbon nanotubes. The mechanical behavior of graphene has been intensely studied in the last years and it has been shown that it is significantly affected by the presence of structural holes, e.g., atom vacancies in the graphene lattice, which can dramatically reduce the failure strength. The presence of holes in the graphene lattice is nearly inevitable, either because of the production process or because of the environmental and operating conditions of the devices. Moreover, in some engineering applications, such as the desalination of sea water through a graphene filter, atom vacancies could be deliberately introduced to achieve new functionalities. Hence, the interaction between multiple holes becomes extremely important for the overall mechanical properties in a single-layer graphene. Here, we study the mechanical behavior of perforated single-layer graphene membrane through a molecular mechanics model, which is solved numerically using the Riks arc length method. We show that the distance between multiple holes in tensile tests determines a very different failure strength of the single-layer graphene. Finally, the effect of holes is also investigated in the case of out of plane deformation. Such analysis lays the foundations for the development of more sophisticated nano-materials that can achieve non-trivial mechanical functionalities through the presence of holes.

Design of Multi-Layer Graphene Membrane with Descending Pore Size for 100% Water Desalination by Simulation Using ReaxFF.

The performance of a desalination membrane depends on a specific pore size suitable for both water permeability and salt rejection. To increase membrane permeability, the applied pressure should be increased, which creates the need to improve membrane stability. In this research article, a molecular dynamics (MD) simulation was performed using ReaxFF module from Amsterdam Modeling suite (AMS) software to simulate water desalination efficiency using a single and multi-layer graphene membrane. The graphene membrane with different pore sizes and a multi-layer graphene membrane with descending pore size in each layer were designed and studied under different pressures. The stability of the membrane was checked using Material Studio 2019 by studying the dynamics summary. The single-layer graphene membrane was evaluated under pressures ranging from 100 to 500 MPa, with the salt rejection ranging from 95% to 82% with a water permeability of 0.347 × 10-9 to 2.94 × 10-9 (mm.g.cm-2s-1.bar-1), respectively. Almost 100% salt rejection was achieved for the multi-layer graphene membrane. This study successfully demonstrated the design and optimization of graphene membrane performance without functionalization.

Gas Separation Membranes with Atom-Thick Nanopores: The Potential of Nanoporous Single-Layer Graphene.

Gas separation is one of the most important industrial processes and is poised to take a larger role in the transition to renewable energy, e.g., carbon capture and hydrogen purification. Conventional gas separation processes involving cryogenic distillation, solvents, and sorbents are energy intensive, and as a result, the energy footprint of gas separations in the chemical industry is extraordinarily high. This has motivated fundamental research toward the development of novel materials for high-performance membranes to improve the energy efficiency of gas separation. These novel materials are expected to overcome the intrinsic limitations of the conventional membrane material, i.e., polymers, where a longstanding trade-off between the separation selectivity and the permeance has motivated research into nanoporous materials as the selective layer for the membranes. In this context, atom-thick materials such as nanoporous single-layer graphene constitute the ultimate limit for the selective layer. Gas transport from atom-thick nanopores is extremely fast, dependent primarily on the energy barrier that the gas molecule experiences in translocating the nanopore. Consequently, the difference in the energy barriers for two gas molecules determines the gas pair selectivity. In this Account, we summarize the development in the field of nanoporous single-layer graphene membranes for gas separation. We start by discussing the mechanism for gas transport across atom-thick nanopores, which then yields the crucial design elements needed to achieve high-performance membranes: (i) nanopores with an adequate electron-density gap to sieve the desired gas component (e.g., smaller than 0.289, 0.33, 0.346, 0.362, and 0.38 nm for H2, CO2, O2, N2, and CH4, respectively), (ii) narrow pore size distribution to limit the nonselective effusive transport from the tail end of the distribution, and (iii) high density of selective pores. We discuss and compare the state-of-the-art bottom-up and top-down routes for the synthesis of nanoporous graphene films. Mechanistic insights and parameters controlling the size, distribution, and density of nanopores are discussed. Fundamental insights are provided into the reaction of ozone with graphene, which has been successfully used by our group to develop membranes with record-high carbon capture performance. Postsynthetic modifications, which allow the tuning of the transport by (i) tailoring the relative contributions of adsorbed-phase and gas-phase transport, (ii) competitive adsorption, and (iii) molecular cutoff adjustment, are discussed. Finally, we discuss practical aspects that are crucial in successfully preparing practical membranes using atom-thick materials as the selective layer, allowing the eventual scale-up of these membranes. Crack- and tear-free preparation of membranes is discussed using the approach of mechanical reinforcement of graphene with nanoporous carbon and polymers, which led to the first reports of millimeter- and centimeter-scale gas-sieving membranes in the year 2018 and 2021, respectively. We conclude with insights and perspectives highlighting the key scientific and technological gaps that must be addressed in the future research.

Electronic interactions and stability issues at the copper-graphene interface in air and in alkaline solution under electrochemical control

A micro-electrochemical cell is sealed with a polymer-free single-layer graphene (SLG) membrane to monitor the stability of Cu nanoparticles (NPs) attached to SLG, as well as the interfacial electronic interactions between Cu NPs and SLG both in air and in a mildly alkaline aqueous solution under electrochemical control. A combination of techniques, including in-situ Kelvin probe force microscopy (KPFM) and ex-situ electron microscopy, are applied. When Cu NPs are metallic at cathodic potentials, there is a relatively bias-independent offset in the SLG work function due to charge transfer at the Cu-SLG contact. When Cu NPs are oxidized at anodic potentials, on the other hand, the work function of SLG also depends on the applied bias in a quasi-linear fashion due to electrochemical gating, in addition to charge transfer at the CuOx-SLG contact. Furthermore, Cu NPs were found to oxidize and detach from SLG when kept under anodic potentials for a few hours, whereas they remain adhered to SLG at cathodic potentials. This is attributed to water intercalation at the CuO-SLG interface associated with the enhanced hydrophilicity of positively polarized graphene, as supported by the absence of Cu detachment following oxidation by galvanic corrosion in air.

On the Performance of Vertically Aligned Graphene Array Membranes for Desalination.

In this paper, we perform molecular dynamics simulations to investigate the performance of multilayer graphene slit membranes. Graphene slit membranes at a critical slit size have been found to be promising desalination membranes. In this contribution, it is shown that multilayer slit membranes have the potential to provide significantly better permeability while retaining outstanding salt rejection. Improved permeability of the membrane is achieved by using slits of widths larger than the critical slit size required to reject salt through size exclusion, and desalination of sea water is performed by increased resistance to salt passage through the multilayering. To facilitate the design process of future multilayer membranes, we analyze the flow resistance of the membrane as a combination of electrical resistors in series and show that this analogy works for membranes where the layers possess the same slit size, as well as membranes with layers of different slit sizes. Comparing with single layer graphene membranes, it was shown that it is possible to obtain 55% improvement in permeability without loss in salt rejection capabilities through multilayering. This opens up possibilities for membrane designers to be free from the restrictions of using a single layer graphene slit membrane with a fixed slit width.

Rapid Gas Transport from Block-Copolymer Templated Nanoporous Carbon Films

Porous carbon films, attributed to their superior thermal and chemical robustness, are attractive for a number of applications. In the context of molecular separation, a major focus has been on films where the effective pore diameter is lower than 1 nm, e.g., carbon molecular sieves. Only a handful of reports are available on carbon films hosting 2–3 nm size pore channels where gas transport mainly takes place by Knudsen diffusion in contrast to activated transport. Recently, we reported nanoporous carbon (NPC) films, by the pyrolysis of phase-separated block-copolymer/turanose films, as a gas-permeable mechanical reinforcement for crack-free synthesis of single-layer graphene membranes. However, a dedicated study on the nanostructure and transport properties of the standalone NPC film has been missing. Herein, we show that the NPC film has a perforated lamellar (PL) nanostructure where molecular transport is limited by an interlamellar spacing of ∼2 nm. The unique PL nanostructure of the NPC film originates from its precursor, i.e., a block-copolymer stabilized by hydrogen bonding with a carbohydrate additive, where the latter also acts as the main carbon-forming agent. This nanostructure is highly sensitive to the carbohydrate/block-copolymer ratio and gives way to a lacey structure below a ratio of 2:1. The transport of gases through the interlamellar spacing takes place predominantly in the Knudsen regime, determined by their molecular mass. Attributed to a thickness of 100 nm, the film yields extremely rapid gas transport with a H2 permeance over two million gas permeation units (GPU) and H2/CO2 selectivity over 4.5 in a temperature range of 25–300 °C. These properties make the NPC film a promising membrane support and a good choice for the mechanical reinforcement for high-permeance two-dimensional membranes for gas separation.

New leak element based on transfer-free single-layer graphene membrane

In this work, a new leak element based on transfer-free single-layer graphene was developed. The single-layer graphene was synthesized on Cu foil and small holes of about 10 μm were drilled on Cu foil to reveal graphene membrane. The conductance of He, N2 and Ar through the graphene leak element was measured based on the difference method. The results imply that various gases exhibit molecular flow regime under pressures ranging from vacuum up to 105 Pa, and the conductance of the transfer-free graphene is about two orders of magnitude smaller than that of the wet-transferred graphene. The difference of conductance may result from the generation of micron-sized cracks and tears on graphene surface during wet-transfer process. The transfer-free single-layer graphene developed in this work is an excellent material for low-permeation leak element.

Direct Chemical Vapor Deposition Synthesis of Porous Single-Layer Graphene Membranes with High Gas Permeances and Selectivities.

Single-layer graphene containing molecular-sized in-plane pores is regarded as a promising membrane material for high-performance gas separations due to its atomic thickness and low gas transport resistance. However, typical etching-based pore generation methods cannot decouple pore nucleation and pore growth, resulting in a trade-off between high areal pore density and high selectivity. In contrast, intrinsic pores in graphene formed during chemical vapor deposition are not created by etching. Therefore, intrinsically porous graphene can exhibit high pore density while maintaining its gas selectivity. In this work, the density of intrinsic graphene pores is systematically controlled for the first time, while appropriate pore sizes for gas sieving are precisely maintained. As a result, single-layer graphene membranes with the highest H2 /CH4 separation performances recorded to date (H2 permeance >4000 GPU and H2 /CH4 selectivity >2000) are fabricated by manipulating growth temperature, precursor concentration, and non-covalent decoration of the graphene surface. Moreover, it is identified that nanoscale molecular fouling of the graphene surface during gas separation where graphene pores are partially blocked by hydrocarbon contaminants under experimental conditions, controls both selectivity and temperature dependent permeance. Overall, the direct synthesis of porous single-layer graphene exploits its tremendous potential as high-performance gas-sieving membranes.

Helium-graphene optical-acoustic converter of extreme ensitivity

The prospects for the use of single-layer graphene in the design of optical-acoustic converters (OAC) of a new generation are considered. It is shown that the limiting characteristics of transducers with single-layer graphene membranes can be obtained only in OACs constructed according to the Hayes scheme. The main characteristics of membranes – the main elements of OAC – are considered, and the physical properties of graphene, as the most preferred mate-rial for membranes, are analyzed. Estimates having been made show that the use of SLG gra-phene membranes makes it possible to create IR and THz radiation receivers with cells of the order of tens of microns with extremely high sensitivity. To achieve the maximum sensitivity, it is proposed to perform edge perforation of graphene membranes. A new design scheme of uncooled helium-graphene optoacoustic receivers with theoretically maximum sensitivity and speed and an operating range extended to helium temperatures is proposed. The de-scribed technical solutions can be used as the basis for the design of uncooled.

The effect of nanopores geometry on desalination of single-layer graphene-based membranes: A molecular dynamics study

The water desalination process using nanoporous single-layer graphene membranes is simulated through classical molecular dynamics. The effect of nanopores shapes on the capacity of the membrane for filtration of water is investigated. According to the results, the geometry of the nanopores considerably affects the performance of the membrane and can completely change the water flow rate and salt rejection. The results reveal that the effective area of the nanopores plays a critical role and for a better understanding of the impact of this parameter, aspect ratio and the equal diameter of noncircular pores based on different methods such as equal area, equal perimeter, and hydraulic diameter for each case are calculated. In the case of noncircular nanopores, the results indicate that aspect ratio and hydraulic diameter, as well as equal area method, can adequately capture the associated trends, while the equal perimeter method is unable to correctly predict them.

Efficient separation of small organic contaminants in water using functionalized nanoporous graphene membranes: Insights from molecular dynamics simulations

Small organic molecules, and specifically micropollutants, pose known hazards to human health, but their removal is particularly challenging in water treatment. Our work demonstrates promising single-layer nanoporous graphene (NPG) membranes with high water permeability and varying degrees of selectivity against common organic contaminants, using molecular dynamics (MD) simulations. Seven target organic molecules are considered—including methanol, urea, ethanol, 2-propanol, n-nitrosodimethylamine (NDMA), pyrrole, and phenol—to understand the molecular parameters that govern organic removal. We systematically study molecular transport dynamics and energetics through membranes having varying sizes of pores with hydrophobic (hydrogenated) and hydrophilic (hydroxylated) functionalizations. We find that NPG membranes with smaller, hydroxylated pores offer higher water/organic permselectivity compared to those with larger, hydrogenated pores, as they impede the transport of organics while facilitating the transport of water. Molecular size is the primary organic parameter that controls transport. Larger organic molecules have a greater affinity for the membrane and pore groups (interfacial-affinity sieving), but they are more hindered from entering the pore (pore-size sieving). There is a net decrease in transport with increased molecular size, which suggests that pore-size sieving is the governing mechanism for most of the molecular separations. We further find that traditional measures of organic hydrophobicity are not strong predictors of transport, as they correlate poorly with interfacial affinity, and the contribution of dehydration to the energy barrier of permeation is limited, though non-negligible. Finally, our simulations show that organic-pore interactions are not pressure independent: as flow rate is decreased, the effects of interfacial-affinity sieving become more pronounced. In short, this study establishes a comprehensive understanding of membrane and molecular parameters to guide the design of effective NPG membranes for organic contaminant removal, particularly in desalination and wastewater reuse.

Dynamic and weak electric double layers in ultrathin nanopores.

The unique properties of aqueous electrolytes in ultrathin nanopores have drawn a great deal of attention in a variety of applications, such as power generation, water desalination, and disease diagnosis. Inside the nanopore, at the interface, properties of ions differ from those predicted by the classical ionic layering models (e.g., Gouy-Chapman electric double layer) when the thickness of the nanopore approaches the size of a single atom (e.g., nanopores in a single-layer graphene membrane). Here, using extensive molecular dynamics simulations, the structure and dynamics of aqueous ions inside nanopores are studied for different thicknesses, diameters, and surface charge densities of carbon-based nanopores [ultrathin graphene and finite-thickness carbon nanotubes (CNTs)]. The ion concentration and diffusion coefficient in ultrathin nanopores show no indication of the formation of a Stern layer (an immobile counter-ionic layer) as the counter-ions and nanopore atoms are weakly correlated in time compared to the strong correlation observed in thick nanopores. The weak correlation observed in ultrathin nanopores is indicative of a weak adsorption of counter-ions onto the surface compared to that of thick pores. The vanishing counter-ion adsorption (ion-wall correlation) in ultrathin nanopores leads to several orders of magnitude shorter ionic residence times (picoseconds) compared to the residence times in thick CNTs (seconds). The results of this study will help better understand the structure and dynamics of aqueous ions in ultrathin nanopores.

Techno-economic assessment of postcombustion carbon capture using high-performance nanoporous single-layer graphene membranes

High-performance membranes have emerged as an energy-efficient alternative to absorption-based postcombustion carbon capture. So far, the techno-economic analyses have been centered around the polymeric membranes. Recently, nanoporous single-layer graphene (NSLG) membranes have yielded large CO2 permeance, making them attractive for capture. Herein, we assess the techno-economic feasibility of NSLG-based capture using an optimized process. The most suitable system to achieve recovery and purity of 90% comprises a double-stage process with (i) recycle of 2nd stage retentate, and (ii) multi-staged vacuum pumps for the permeate, including roots pumps in series with liquid-ring pumps and intermittent condensers for water vapor. The high CO2 permeance of NSLG makes the vacuum process without feed compression more economically competitive, even if the area required is higher. Attractive capture penalties are estimated despite a conservative membrane cost (500 $/m2): 41.2 and 31.8 $/tonCO2 from wet feeds with CO2 concentration of 10% and 13.5%, respectively, corresponding to energy penalty of 1.53 and 1.24 MJ/kgCO2. For steel and cement industries where CO2 concentration is favorably high (25%) but electricity cost is also higher (0.10–0.20 $/kWh), the capture penalty ranges from 28.0 to 46.0 $/tonCO2. Overall, the analysis shows that NSLG membranes are competitive with state-of-the-art processes for postcombustion capture.

Predicting Gas Separation through Graphene Nanopore Ensembles with Realistic Pore Size Distributions.

The development of nanoporous single-layer graphene membranes for gas separation has prompted increasing theoretical investigations of gas transport through graphene nanopores. However, computer simulations and theories that predict gas permeances through individual graphene nanopores are not suitable to describe experimental results, because a realistic graphene membrane contains a large number of nanopores of diverse sizes and shapes. With this need in mind, here, we generate nanopore ensembles in silico by etching carbon atoms away from pristine graphene with different etching times, using a kinetic Monte Carlo algorithm developed by our group for the isomer cataloging problem of graphene nanopores. The permeances of H2, CO2, and CH4 through each nanopore in the ensembles are predicted using transition state theory based on classical all-atomistic force fields. Our findings show that the total gas permeance through a nanopore ensemble is dominated by a small fraction of large nanopores with low energy barriers of pore crossing. We also quantitatively predict the increase of the gas permeances and the decrease of the selectivities between the gases as functions of the etching time of graphene. Furthermore, by fitting the theoretically predicted selectivities to the experimental ones reported in the literature, we show that nanopores in graphene effectively expand as the temperature of permeation measurement increases. We propose that this nanopore "expansion" is due to the desorption of contaminants that partially clog the graphene nanopores. In general, our study highlights the effects of the pore size and shape distributions of a graphene nanopore ensemble on its gas separation properties and calls into attention the potential effect of pore-clogging contamination in experiments.

Centimeter-scale gas-sieving nanoporous single-layer graphene membrane

High-permeance, molecular-sieving, nanoporous single-layer graphene (NSLG) membranes are highly promising for gas separation. However, the formation of cracks during the transfer of NSLG to a low-cost porous support is difficult to avoid. These cracks are detrimental to gas selectivity, and therefore, make the scale-up of the gas-sieving NSLG membranes challenging. To mitigate the crack formation on low-cost macroporous supports, herein, we demonstrate mechanical reinforcement of the graphene film with a two-layer composite carbon film. The bottom layer of the composite film is a 100-nm-thick block-copolymer film derived nanoporous carbon (NPC) film with a pore size of 20–30 nm. This layer makes an intimate contact with NSLG and prevents generation of crack. However, the NPC film by itself is not robust enough to cover the rough surface of low-cost macroporous supports and tends to generate occasional cracks. This is prevented by spin-coating a 500-nm-thick multi-walled carbon nanotube (MWNT) film, hosting pore size of 200–300 nm, on top of the NPC film. This imparts enough mechanical strength to NSLG/NPC film to be successfully suspended on a low-cost, macroporous, nonwoven metal wire mesh on a centimeter-scale while completely avoiding cracks. As a result, H2/CH4 and H2/CO2 selectivities of 11–23 and 5–8, respectively, higher than the corresponding Knudsen selectivities of 2.8 and 4.7, respectively, are obtained from the centimeter-scale NSLG membranes. The reinforced membranes are mechanically robust and can successfully withstand transmembrane pressure difference of 4 bar. When the MWNT film is directly coated on NSLG without using the intermediate NPC layer, the gas sieving behavior is not observed, likely due to the development of nanoscale cracks. This underlines the crucial role of the hierarchical pore structure in the composite carbon film in realizing the gas-sieving graphene membranes.

Hydrogen-sieving single-layer graphene membranes obtained by crystallographic and morphological optimization of catalytic copper foil

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.

Water desalination performance of h-BN and optimized charged graphene membranes

Water desalination using pressure-driven flow in hexagonal boron nitride (h-BN) and charged nanoporous graphene membranes are investigated using molecular dynamics (MD) simulations. Nanoporous h-BN membranes with pore diameters of 10.1 A, 12.2 A, and 14.7 A were selected to compare with the desalination performance of uncharged nanoporous graphene membranes with similar pore diameters. Salt rejection efficiency of uncharged graphene membranes is superior to that of h-BN, and the pressure drop for both materials exhibits the same inverse-cubic dependence on the pore diameter, regardless of the hydrophobic versus hydrophilic nature of graphene and h-BN, respectively. Charged graphene membranes with pore diameters of 15.9 A, 18.9 A, and 20.2 A were also considered, and 15.9 A pore diameter with total fixed charge of 12e was found to be the optimum setting for single-layer graphene membrane, resulting in 100% and 98% rejection efficiencies for Na+ and Cl− ions, respectively. The corresponding pressure drop is 51.8% lower than that obtained with 9.9 A pore diameter uncharged graphene with 100% salt rejection. To maintain perfect salt removal, 15.9 A pore diameter charged bilayer graphene membranes with 12e total charge on the first layer, and − 1e on the second one was simulated at different separation distances between the two membranes. The associated pressure drop is 35.7% lower than that obtained in 9.9 A pore diameter uncharged base-line case. These findings confirm the potential application of using charged bilayer nanoporous graphene membranes in improving the performance of reverse osmosis desalination systems.

Progress and control in development of single layer graphene membranes

Recent approaches in graphene transfer on different substrates and nanostructured surfaces have opened up new potential applications such as: pressure sensors, separation membranes, electrochemical sensors. Graphene single layer is a promising membrane material, due to chemically inert, large specific surface area with hydrophobic property. In this work, single layer graphene have been synthesized by CVD on copper catalyst and transferred by three different wet chemical transfer methods on Si/SiO2 holes of approximatively 7 μm diameter. The novelty of this study is the introduction of a vacuum step to help remove liquids from underneath the graphene layer while maintaining the structural integrity of the membrane. Raman spectroscopy was performed to analyze the number of layers and the quality of graphene. The morphology of the graphene transferred on the holes were examined using scanning electron microscopy (SEM).