Graphene Membranes Research Articles

The Graphene Squeeze-Film Microphone.

Most microphones detect sound-pressure-induced motion of a membrane. In contrast, we introduce a microphone that operates by monitoring sound-pressure-induced modulation of the air compressibility. By driving a graphene membrane at resonance, the gas, that is trapped in a squeeze-film beneath it, is compressed at high frequency. Since the gas-film stiffness depends on the air pressure, the resonance frequency of the graphene is modulated by variations in sound pressure. We demonstrate that this squeeze-film microphone principle can be used to detect sound and music by tracking the membrane's resonance frequency using a phase-locked loop. The squeeze-film microphone potentially offers advantages like increased dynamic range, lower susceptibility to pressure-induced failure and vibration-induced noise over conventional devices. Moreover, microphones might become much smaller, as demonstrated in this work with one that operates using a circular graphene membrane with an area that is more than 1000 times smaller than that of MEMS microphones.

Water compression induced ionic negative differential resistance in nanopores.

The mass transport behavior through nanoscale channels, greatly influenced by the structures and dynamics of nanoconfined water, plays an essential role in many biophysical processes. However, the dynamics of nanoconfined water under an external field and its effects are still not fully understood. Here, on the basis of molecular dynamics simulations, we theoretically show that the ionic current of [Bmim][PF6] through narrow pores in graphene membrane exhibits an ionic negative differential resistance effect-the ionic current decreases as the voltage increases over a certain threshold. This effect arises from the violation of traditional fluid dynamics as the assumption of continuity and homogeneity of fluids is no longer effective in ultrathin nanopores. The gradient of electric field around the atomic-thin layer produces a strong gradient force on the polarized water inside the nanopore. This dielectrophoretically compressed water leads to a hydrostatic force that repels ions from entering the nanopore. Our findings may advance the understanding of hydrostatic mechanism, which governs ion transport through nanopores.

Graphene Membrane for Water-Related Environmental Application: A Comprehensive Review and Perspectives

Graphene Membrane for Water-Related Environmental Application: A Comprehensive Review and Perspectives

Fabrication of flexible multifunctional graphene-based composite membrane with improved hydrophobicity and thermal conductivity characters for thermal management

The lifetime of electronic devices in complex environments is affected by the impact of high temperature water vapor on their performance. Equipping electronic devices with superhydrophobic properties and improved thermal conductivity will be the strategy of the future. In this paper, a surface material with high thermal conductivity and superhydrophobic properties is explored to address the problem of electronic device failure caused by heat and water vapor. To solve this problem, anti-temperature superhydrophobicity can be obtained by spraying alumina/nano-silicon carbide/thermoplastic elastomer composite powder (Al2O3/nano-SiC/SEBS) modified with 1 H,1 H,2 H,2H-perfluorooctyltriethoxysilane (POTS) on graphene membranes. A spherical Al2O3/nano-SiC composite superhydrophobic coating (ASS-GM) was formed on the surface of graphene-based composite membranes by spraying method. The results showed that the optimal ratio was m(Al2O3): m(SiC) = 8:1, and the static water contact angle of the coating was 162 ± 2.5°, and the surface energy was reduced. The ASS-GM significantly improves the thermal conductivity and superhydrophobicity of graphene-based composite membranes, achieving a double improvement in performance. The coating also offers excellent self-cleaning and antifouling properties compared to other materials. The ASS-GM is able to maintain a certain hydrophobicity angle (156 ± 1.5°) in harsh environments. This work provides practical applications for electronic coatings, which are important for improving the overall reliability and durability of electronic products.

Microstructural design of crown nanopores in graphene membrane for efficient desalination process

Designing a membrane with simultaneous high water permeability and desalination rate to overcome the trade-off presents a persistent and substantial challenge. In this paper, we employed molecular dynamics simulations to design the structure of the graphene crown ether reverse osmosis membrane and elucidate the relationship between the membrane's microscopic separation mechanism and its structure-activity.The results show that the water permeability through crown graphene nanopores exceeded that of the original graphene nanopores by an order of magnitude, and hundreds of times greater than that of the traditional reverse osmosis membrane. Additionally, the water permeation in multilayer crown graphene nanopores also surpassed that in monolayer original graphene nanopores. The water permeability exceeds 46.73 L/cm2/day/Mpa with 100 % salt rejection. Furthermore, the various sizes and shapes of graphene nanopores significantly influence water permeation. Within crown graphene nanopores, a narrow pore enables superior water permeation and salt rejection compared to a circular shape, unlike original graphene nanopores. Observed from MD simulation trajectories,this highly water permeation is caused by the hydrogen bonding between crown ether graphene and water molecules. First-principle calculations further confirm that water transport in graphene crown ether is energetically more favorable than in original graphene nanopores. Our findings support crown graphene membranes as promising candidates for seawater desalination.

Correlation effect between the capillary flow and evaporation rate of water in a 2-D photothermal membrane

To shed light on the correlation effect between the capillary flow and phase transition of water in photothermal evaporation, the non-equilibrium molecular dynamics (NEMD) simulations were employed to investigate the evaporation of water in Multilayered graphene oxide membranes. It was initially found that water molecules need to overcome strong energy barriers to migrate upward by layers before evaporation, with the energy barrier increasing with the reduction in nanogap, hydroxyl content, or increase in layer spacing of graphene sheets. The strong energy barrier accordingly results in dramatic sensible heat conversion and high evaporation temperature. It was shown that the enhanced temperature and hydrophilicity both weaken the hydrogen bond strength of water molecules confined in 2-dimensional channels, contributing to the reduced evaporation enthalpy. The preferential pathways in graphene channels or the weakened hydrogen bonds in hydroxyl-functionalized graphene of water molecules were found to be important influences on capillary flow energy consumption, leading to differences in evaporation energy supply. In combination with these effects, the evaporation rate could be increased by up to 2 folds and an interfacial enthalpy of evaporation below 1500 kJ kg−1 could be achieved by properly tuning the configuration and chemical properties of the graphene membrane. Our findings lay a theoretical foundation for providing a strategy to improve the interfacial evaporation performance in desalination.

Impact of titanium dioxide/graphene in polyvinylidene fluoride nanocomposite membrane to intensify methylene blue dye removal, antifouling performance, and reusability

AbstractThe development of efficient water purification technologies is a critical research focus driven by the crucial role of clean water sources for ecological sustainability. This study explores the strategic incorporation of nanoparticles within polyvinylidene fluoride (PVDF) membranes as a promising approach to enhance membrane performance for wastewater remediation. PVDF membranes containing varying ratios of graphene (GR) and titanium dioxide (TiO2) nanocomposites were fabricated via phase inversion method. Characterization techniques including XRD, FTIR, and FESEM‐EDX revealed that the 80% GR nanocomposite membrane exhibited desirable structural and functional properties with pronounced sponge‐like morphology and homogenous nanoparticle distribution. Fourier‐transform infrared spectroscopy and x‐ray diffraction analysis confirmed the 80% GR membrane retained PVDF crystallinity while uniquely eliminating TiO2 crystallinity. Subsequently, performance testing demonstrated the 80% GR nanocomposite membrane had the highest water flux and methylene blue dye rejection rates compared to other ratios and the pristine PVDF membrane. Both fabricated membranes exhibited sufficient reusability and antifouling properties. However, 80% GR ratio exhibited superior antifouling properties, indicating its potential as an optimal material for improving membrane hydrophilicity and overall water purification technologies. These findings underscore the strategic utility of GR‐TiO2 nanocomposites for enhancing PVDF membrane performance in sustainable wastewater treatment applications.

How Membrane Flexibility Impacts Permeation and Separation of Gas through Nanoporous Graphenes.

In recent years, extensive research has used molecular dynamics simulations to investigate gas separation through nanoporous graphene (NPG) membranes. However, most studies have considered graphene membranes as rigid, overlooking the impact of their inherent flexibility. This study systematically quantifies the effect of graphene flexibility on gas permeation by comparing the diffusion of various gases through flexible and rigid single-layer NPG models. The results demonstrate that flexibility notably increases permeance, particularly for gases with larger molecular diameters/pore size ratios, by allowing gas molecules greater mobility within the pore. Interestingly, the effect of flexibility boils down to the expansion of the average pore size, and the detail of the membrane's vibrational dynamics is of little importance in quantifying permeance. Our work shows that accounting for flexibility in molecular models improves the alignment of simulation results with experimental data, emphasizing the importance of considering membrane flexibility in predictive models of NPG membrane performance.

Permeability of gas molecules through sub-nanometer nitrogen-terminated porous graphene membranes: A DFT study

We present a systematic theoretical investigation of gas permeability through single-layer nanoporous graphene membranes with N-terminated (pyridinic and mixed pyridinic/pyrrolic) pores for He, H2, N2, O2, CO, CO2, H2O, and CH4. Our study is based on density functional theory transition-state calculations and the kinetic theory of gasses. We systematically evaluate pores of varying sizes and shapes up to 5.7 Å in diameter. According to our findings, membranes with pores in the size regime (4.5 Å - 5.0 Å) may exhibit industrially acceptable permeance to several gas molecules and advanced selectivity. Notably, we found that, among a few others, a pore with the same topological features at the pore boundary as those of the characteristic pore of g-C3N4 carbon nitride, is particularly promising. In addition, membranes with larger pores, ∼5.5 Å - 5.7 Å, can effectively separate CH4 from the other molecules. Our findings support the advanced potential of single-layer graphene membranes with nitrogen-terminated sub-nanometer pores, for gas separation applications.

Precision defect integrated graphene as reliable support membrane for high-resolution cryo-transmission electron microscopy

Graphene is an excellent support film for high-resolution transmission electron microscopy (TEM) but its use with biological samples, notably in cryo-TEM, is hindered by its inherent hydrophobicity. Whereas surface treatments have been proposed to render graphene hydrophilic, they are often difficult to reproduce due to a lack of information on the structural changes that modify the wetting properties of graphene. This study aims to correlate the atomic structure of graphene with its wetting properties to allow a reproducible protocol to advance its application in cryo-TEM. We follow the change in the atomic structure of graphene as a function of low-energy hydrogen plasma treatment duration on monolayer graphene transferred onto TEM grids. With finely controlled plasma exposure, partial hydrogenation, monoatomic vacancies, and pores of a few nanometers are realized in the graphene. The introduction of defects (vacancies and pores) enables the formation of continuous layers of vitreous ice on TEM grids. Grids with defect-integrated graphene are reproduced and used in the vitrification of the mouse serotonin 5-HT3 receptor, a membrane protein. Single particle analysis of the membrane protein on graphene compared to conventional holey carbon film give insight into the strengths and discretions in using graphene membrane for protein structural studies.

High-Yield Large-Scale Suspended Graphene Membranes over Closed Cavities for Sensor Applications.

Suspended membranes of monatomic graphene exhibit great potential for applications in electronic and nanoelectromechanical devices. In this work, a "hot and dry" transfer process is demonstrated to address the fabrication and patterning challenges of large-area graphene membranes on top of closed, sealed cavities. Here, "hot" refers to the use of high temperature during transfer, promoting the adhesion. Additionally, "dry" refers to the absence of liquids when graphene and target substrate are brought into contact. The method leads to higher yields of intact suspended monolayer chemical vapor deposition (CVD) graphene and artificially stacked double-layer CVD graphene membranes than previously reported. The yield evaluation is performed using neural-network-based object detection in scanning electron microscopy (SEM) images, ascertaining high yields of intact membranes with large statistical accuracy. The suspended membranes are examined by Raman tomography and atomic force microscopy (AFM). The method is verified by applying the suspended graphene devices as piezoresistive pressure sensors. Our technology advances the application of suspended graphene membranes and can be extended to other two-dimensional materials.

Pyridinic nitrogen-substituted graphene membranes for exceptional CO2 capture

Pyridinic nitrogen-substituted graphene membranes for exceptional CO2 capture

2D Carbonaceous Materials for Molecular Transport and Functional Interfaces: Simulations and Insights.

ConspectusCarbon-based two-dimensional (2D) functional materials exhibit potential across a wide spectrum of applications from chemical separations to catalysis and energy storage and conversion. In this Account, we focus on recent advances in the manipulation of 2D carbonaceous materials and their composites through computational design and simulations to address how the precise control over material structure at the atomic level correlates with enhanced functional properties such as gas permeation, selectivity, membrane transport, and charge storage. We highlight several key concepts in the computational design and tuning of 2D structures, such as controlled stacking, ion gating, interlayer pillaring, and heterostructure charge transfer.The process of creating and adjusting pores within graphene sheets is vital for effective molecular separation. Simulations show the power of controlling the offset distance between layers of porous graphene in precisely regulating the pore size to enhance gas separation and entropic selectivity. This strategy of controlled stacking extends beyond graphene to include covalent organic frameworks (COFs) such as covalent triazine frameworks (CTFs). Experimental assembly of the layers has been achieved through electrostatic interactions, thermal transformation, and control of side chain interactions.Graphene can interface with ionic liquids in various forms to enhance its functionality. A computational proof-of-concept showcases an ion-gating concept in which the interaction of anions with the pores in graphene allows the anions to dynamically gate the pores for selective gas transport. Realization of the concept has been achieved in both porous graphene and carbon molecular sieve membranes. Ionic liquids can also intercalate between graphene layers to form interlayer pillaring structures, opening the slit space. Grand canonical Monte Carlo simulations show that these structures can be used for efficient gas capture and separation. Experiments have demonstrated that the interlayer space can be tuned by the density of the pillars and that, when fully filled with ionic liquids and forming a confined interface structure, the graphene oxide membrane achieves much higher selectivity for gas separations. Moreover, graphene can interface with other 2D materials to form heterostructures where interfacial charge transfers take place and impact the function. Both ion transport and charge storage are influenced by both the local electric field and chemical interactions.Fullerene can be used as a building block and covalently linked together to construct a new type of 2D carbon material beyond a one-atom-thin layer that also has long-range-ordered subnanometer pores. The interstitial sites among fullerenes form funnel-shaped pores of 2.0-3.3 Å depending on the crystalline phase. The quasi-tetragonal phases are shown by molecular dynamics simulations to be efficient for H2 separation. In addition, defects such as fullerene vacancies can be introduced to create larger pores for the separation of organic solvents.In conclusion, the key to imputing functions to 2D carbonaceous materials is to create new interactions and interfaces and to go beyond a single-atom layer. First-principles and molecular simulations can further guide the discovery of new 2D carbonaceous materials and interfaces and provide atomistic insights into their functions.

Self-assembled superstructure alleviates air-water interface effect in cryo-EM

Cryo-electron microscopy (cryo-EM) has been widely used to reveal the structures of proteins at atomic resolution. One key challenge is that almost all proteins are predominantly adsorbed to the air-water interface during standard cryo-EM specimen preparation. The interaction of proteins with air-water interface will significantly impede the success of reconstruction and achievable resolution. Here, we highlight the critical role of impenetrable surfactant monolayers in passivating the air-water interface problems, and develop a robust effective method for high-resolution cryo-EM analysis, by using the superstructure GSAMs which comprises surfactant self-assembled monolayers (SAMs) and graphene membrane. The GSAMs works well in enriching the orientations and improving particle utilization ratio of multiple proteins, facilitating the 3.3-Å resolution reconstruction of a 100-kDa protein complex (ACE2-RBD), which shows strong preferential orientation using traditional specimen preparation protocol. Additionally, we demonstrate that GSAMs enables the successful determinations of small proteins (<100 kDa) at near-atomic resolution. This study expands the understanding of SAMs and provides a key to better control the interaction of protein with air-water interface.

Modulation of Interlayer Nanochannels via the Moderate Heat Treatment of Graphene Oxide Membranes.

In response to the phenomenon of interlayer transport channel swelling caused by the hydration of oxygen-containing functional groups on the GO membrane surface, a moderate heat treatment method was employed to controllably reduce the graphene oxide (GO) membrane and prepare a reduced GO composite nanofiltration membrane (mixed cellulose membrane (MCE)/ethylenediamine (EDA)/reduced GO-X (RGO-X)). The associations of different heat treatment temperatures with the hydrophilicity, interlayer structure, permeability and dye/salt rejection properties of GO membranes were systematically explored. The results indicated that the oxygen-containing groups of the GO membrane were partially eliminated after heat treatment, and the hydrophilicity was weakened. This effectively weakened the hydration between the GO membrane and the water molecules and inhibited the swelling of the oxidized graphene membrane. In the dye desalination test, the MCE/EDA/RGO membrane exhibited an ultra-high rejection rate of over 97% for methylene blue (MB) dye molecules. In addition, heat treatment increased the structural defects of the GO membrane and promoted the fast passage of water molecules via the membrane. In pure water flux testing, the water flux of the membrane remained above 46.58 Lm-2h-1bar-1, while the salt rejection rate was relatively low.

Modeling and simulation of the capacitive NEMS pressure sensor based on suspended graphene membranes

Modeling and simulation of the capacitive NEMS pressure sensor based on suspended graphene membranes

Application prospects of graphene in environmental science

Nanomaterials and graphene, as cutting-edge materials, have play a crucial role in environmental governance. The introduction of nanomaterials brings new hope to environmental governance. Graphene not only improves the efficiency and cost-effectiveness of water treatment but also drives innovation and development in environmental technologies. This article provides a summary and analysis review starting from the characteristics of nanomaterials and Graphene, comprehensively reviewing Graphenes advantage in environmental technologies and discovered its application in this area. The research summarized the conclusion that Graphenes characteristics make it suitable for addressing environmental issues such as water pollution, its composites can play an important role in water treatment process including water purification, heavy metal adsorption, organic compound adsorption and removal through different preparation and reaction mechanisms. By introducing Nanopore structures and artificially designed stacking structures on graphene membranes, the permeation performance could be modulated and improved. By the way of physical and chemical adsorption, ion exchange, electrochemical and photocatalysis, Graphene and its oxide could be applied to remove heavy metal ion and organic substances from polluted water. The article also introduced the main preparation methods of Graphene and its potential secondary pollution problem. This article provides valuable insights for scientific research and engineering practices in environmental protection and sustainable development.

Enhanced Li+/Mg2+ separation via Ca2+-supported graphene membranes: Mechanistic insights from molecular dynamics simulations

Achieving the efficient separation of Li+ and Mg2+ ions remains a significant challenge. To address this issue, a Ca2+-supported graphene membrane was engineered and evaluated through molecular dynamics simulations. The separation mechanism of Li+/Mg2+ in the Ca2+-supported graphene membrane was investigated by analyzing the dehydration behavior as well as the interfacial interactions between ions and the graphene membrane. The Ca2+-supported graphene membrane exhibits well separation performance for Li+ and Mg2+ mixtures, and the separation efficiency of the Ca2+-supported graphene membrane for Li+/Mg2+ mixture increases first and then decreases with the increase of Ca2+ ion number inserted into the membrane. Li+ ions display heightened permeability and reduced ion rejection, which can be attributed to their relatively weaker interaction with the graphene sheets compared to Mg2+ ions, facilitating smoother penetration. Furthermore, Li+ ions are intended to form smaller sizes with Cl− ions at the entrances of the Ca2+-supported graphene membrane, mitigating size-related effects. Additionally, their weaker interactions with water molecules, facilitate the dehydration process of Li+ ions.

Enhanced through-plane thermal conductivity of graphene membranes by the interlayer microstructure manipulation: Multiscale numerical simulations and experimental verifications

Graphene, with ultrahigh in-plane thermal conductivity (IPTC), has been widely applied in the thermal dissipation of integrated circuits. However, the extremely low through-plane thermal conductivity (TPTC) of graphene limits its further application. In this work, a novel strategy was proposed to enhance the TPTC of graphene membranes (GNMs) by improving the interlayer bonding state through interlayer decoration with metal elements. Molecular dynamics simulations demonstrated that decoration with interlayer elements (Al, Ti, and Ni) enhanced the interfacial thermal conductance. This was attributed to interfacial chemical bonding through strong interfacial interactions (intensive electron localization) formed at the interface between metal and GN sheets as implied by the first principles calculations. Furthermore, the composite GNMs decorated with interlayer metal nanoparticles (Al, Ni, and Co) were prepared through co-reduction using thermal decomposition method. The corresponding TPTC was tested using time-domain thermoreflectance (TDTR) method which was much higher for the composite GNMs (175–400 W/m·K) than for pure GNM (∼140 W/m·K), and this was in consistent with the simulation results. Interlayer decoration, which enhanced the TPTC of GNMs, provides a novel and effective strategy for enhancing the overall thermal management performance of graphene-based materials in both vertical and horizontal directions.

Ab Initio Molecular Dynamics Investigation on the Permeation of Sodium and Chloride Ions Through Nanopores in Graphene and Hexagonal Boron Nitride Membranes.

Nanoporous membranes promise energy-efficient water desalination. Hexagonal boron nitride (h-BN), like graphene, exhibits outstanding physical and chemical properties, making it a promising candidate for water treatment. We employed Car-Parrinello molecular dynamics simulations to establish an accurate modeling of Na+ and Cl- permeation through hydrogen passivated nanopores in graphene and h-BN membranes. We demonstrate that ion separation works well for the h-BN system by imposing a barrier of 0.13 eV and 0.24 eV for Na+ and Cl- permeation, respectively. In contrast, for permeation of the graphene nanopore, the Cl- ion faces a minimum of energy of 0.68 eV in the nanopore plane and is prone toward blockade of the nanopore, while the Na+ ion experiences a slight minimum of 0.03 eV. Overall, the desalination performance of h-BN nanopores surpasses that of their graphene counterparts.