Nanoporous Graphene Research Articles

Ion Selectivity in Multilayered Stacked Nanoporous Graphene.

Nanoporous graphene is an ideal candidate for molecular filtration as it can potentially combine high permeability with high selectivity at molecular levels. To make use of graphene in filtration setups, the defects formed during its growth and during the transfer of graphene to the carrier support pose a challenge. These uncontrolled pores can be avoided by stacking graphene layers, and then, controlled pores can be initiated with oxygen plasma. Here, we show that two-layer stacks provide the best balance of defect coverage and high selectivity compared with other stacks. Using the electrical characterization of ionic solutions in the standard diffusion cell, we compare the ionic transport and ionic selectivity of up to three-layered stacks of graphene that have been plasma-treated. We find that there is a decrease in the ionic selectivity of a two-layered stack as one more layer of graphene is added. We provide a model for this occurrence. Our results will be helpful for making practical and high-performance filtration systems from two-dimensional materials.

Fabrication of nanoporous multilayer graphene nanoplatelets membrane for water desalination

In recent years, graphene-based membranes are extensively explored for desalination process to fulfil the pure water scarcity. Still, there is a noticeable gap in the research on a technique that simultaneously deposits a membrane and also generates pores in the flake of membrane. In this work, we demonstrated a one-step and scalable protocol i.e. a conventional atmospheric plasma spraying (APS) to fabricate a graphene nanoplatelets (GNP) membrane for water desalination application. Various characterization tools: FE-SEM, Raman, and TEM etc. utilized to evaluate the deposition of GNPs flakes and induced sub-nanometer pores in the large area GNP membrane. Plasma-sprayed GNP membrane showed impressive desalination performance in terms of water flux, salt rejection, and permeability around ~67 Lm−2 h−1, ~99 %, and ~ 115 Lm−2h−1bar−1 respectively at 0.6 bar of transmembrane pressure (TMP). This performance of the GNP membrane was attributed to the critical role of graphene in terms of its structures, including induced pores within graphene sheets and its functions. Our deposited GNP membrane is cost-effective and showed the applicability of conventional plasma spraying in the design of nanomaterials-based membranes for various water purification protocols.

Structural control of nanoporous frameworks consisting of minimally stacked graphene walls

This mini-review provides an in-depth analysis of the formation and post-processing of nanoporous graphene materials via methane chemical vapor deposition (CH4-CVD) using nanostructured metal oxide templates, including Al2O3, MgO, and SiO2. Initially, the formation of graphene sheets is discussed in terms of the role of CH4-CVD, the influence of templates, and the underlying mechanism for tailoring the structures of the graphene-based materials. Following this, the discussion extends to the post-graphene formation process. We focus on key steps, including template removal and graphene repair via zipping reactions at high temperatures. Additionally, we evaluate the conditions to prevent undesired structural transformations. The correlation between the structural features and transformations occurring during post-processing is also examined. The materials fabricated through these methods exhibit impressive properties of high porosity, minimal edge sites, superior oxidation resistance, and elasticity, positioning them as promising materials in various applications.

Bubbling resilient 3D free-standing nanoporous graphene with an encapsulated multicomponent nano-alloy for enhanced electrocatalysis.

The design and synthesis of highly durable and active electrocatalysts are crucial for improving the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). In this work, we present a novel dealloyed nanoporous PtCuNiCoMn multicomponent alloy with ligaments/pores ranging from 2-3 nm, which is in situ encapsulated in a three-dimensional, free-standing nanoporous nanotubular graphene network featuring a pore/tube diameter of ∼200 to 300 nm. This method allows precise control over the noble metal loading and alloy composition while preventing noble metal loss throughout the preparation process. The innovative bimodal nanoporous graphene/alloy structure, coupled with an open 3D spongy morphology, and optimized surface Pt electronic structure through multicomponent interaction, significantly enhances the activity for the HER/ORR, outperforming commercial Pt/C. Moreover, this design addresses the issues of Pt nanoparticle aggregation and detachment from carbon supports that typically exist in Pt/C-type catalysts, thereby substantially improving the catalytic durability, even under intense gas bubbling conditions.

A thermodynamically favorable route to the synthesis of nanoporous graphene templated on CaO via chemical vapor deposition

Efficient CaO-catalyzed conversion of CH4 to graphene via CVD demonstrates a sustainable, cost-effective approach for nanoporous graphene synthesis.

Toward three-dimensionally ordered nanoporous graphene materials: template synthesis, structure, and applications

Precise template synthesis will realize three-dimensionally ordered nanoporous graphenes (NPGs) with a spatially controlled seamless graphene structure and fewer edges.

Optimization of Leaky Integrate-and-Fire Neuron Circuits Based on Nanoporous Graphene Memristors

Optimization of Leaky Integrate-and-Fire Neuron Circuits Based on Nanoporous Graphene Memristors

Tailoring giant quantum transport anisotropy in nanoporous graphenes under electrostatic disorder.

During the last 15 years bottom-up on-surface synthesis has been demonstrated as an efficient way to synthesize carbon nanostructures with atomic precision, opening the door to unprecedented electronic control at the nanoscale. Nanoporous graphenes (NPGs) fabricated as two-dimensional arrays of graphene nanoribbons (GNRs) represent one of the key recent breakthroughs in the field. NPGs interestingly display in-plane transport anisotropy of charge carriers, and such anisotropy was shown to be tunable by modulating quantum interference. Herein, using large-scale quantum transport simulations, we show that electrical anisotropy in NPGs is not only resilient to disorder but can further be massively enhanced by its presence. This outcome paves the way to systematic engineering of quantum transport in NPGs as a novel concept for efficient quantum devices and architectures.

Enhancing the seawater desalination performance of multilayer reduced graphene oxide membranes by introducing in-plane nanopores: a molecular dynamics simulation study.

In this study, using MD simulation, the effect of creating in-plane nanopores in a reduced graphene oxide (rGO) membrane and the formation of a reduced nanoporous graphene oxide (rNPGO) membrane is proposed to increase salt rejection and water flux. To this end, the desalination performance of r1NPGO, r2NPGO and r4NPGO membranes, which have 1, 2 and 4 pore(s), respectively, with a diameter of 0.9 nm and the r1NPGO-3 nm membrane, which has 1 pore with an approximate diameter of 3.0 nm, was investigated and compared from a molecular point of view. The simulation results show that in the rNPGO membranes, by increasing the number of pores from 1 to 4, water flux increases by ∼6 times compared to the rGO membrane. Meanwhile, upon increasing the pore size from 0.9 to 3.0 nm, water flux is enhanced by ∼16 times compared to the rGO membrane. The simulation results also demonstrate that the rGO membrane has two paths for water penetration, which are called the interlayer pathway and in-slit pathway. Moreover, pores in the rNPGO membranes provide another additional path for water transfer by shortening the lateral size of the membranes. This path is referred to as the in-pore pathway. By increasing the size of the pore in the r1NPGO-3 nm membrane, the contribution of the in-pore pathway increases and plays an important role. Furthermore, the simulation results show that in all rGO and rNPGO membranes, the interlayer space acts as a barrier for ions. Therefore, complete salt rejection is observed. Interestingly, by increasing the pore size in the r1NPGO-3 nm membrane, this membrane still maintains complete salt rejection. The observed phenomenon can be a result of very high water flux in this membrane. By increasing water flux, the presence of water molecules around Na+ and Cl- ions decreases. As a result, the formation of Na+Cl- ionic clusters is strengthened in such a way that these clusters do not have the ability to pass through large pores of 3.0 nm.

Solar‐Photoactivated Nanoporous Graphene Aerogel Flowers for High‐Performance Supercapacitors

Supercapacitors are gaining popularity as potential energy‐storage devices due to their efficiency and environmentally sustainable features. Among the extensive range of 2D materials utilized in energy storage, graphene is particularly noteworthy for its exceptional physicochemical properties. Graphene aerogels (GAs) have great potential for supercapacitor application due to their porous structure and, as such, are widely researched. However, enhancing the capacity performance with easy and low‐energy processes is still facing challenges. Here, a facile, low‐cost, and environmentally friendly photoactivation method on GAs is proposed to address this problem. Nanoporous GA flowers with higher specific surface area are formed and the corresponding capacitance can be achieved to 264 F g−1. After 10 000 cycles at the current density of 10 A g−1, the measured electrode's cycle efficiency is found to be 80.9%, further emphasizing its remarkable performance. The unparalleled performance confirms the reliability of this method as compared to traditional activation methods while being cost‐effective and environmentally friendly.

Preanchoring Enabled Directional Modification of Atomically Thin Membrane for High-Performance Osmotic Energy Generation.

Salinity gradient energy is an environmentally friendly energy source that possesses potential to meet the growing global energy demand. Although covalently modified nanoporous graphene membranes are prospective candidates to break the trade-off between ion selectivity and permeability, the random reaction sites and inevitable defects during modification reduce the reaction efficiency and energy conversion performance. Here, we developed a preanchoring method to achieve directional modification near the graphene nanopores periphery. Numerical simulation revealed that the improved surface charge density around nanopores results in exceptional K+/Cl- selectivity and osmotic energy conversion performance, which agreed well with experimental results. Ionic transport measurements showed that the directionally modified graphene membranes achieved an outstanding power density of 81.6 W m-2 with an energy conversion efficiency of 35.4% under a 100-fold salinity gradient, outperforming state-of-the-art graphene-based nanoporous membranes. This work provided a facile approach for precise modification of nanoporous graphene membranes and opened up new ways for osmotic power harvesting.

Graphene crown pore for efficient heavy metal ion Removal: Protonated vs. Non-protonated

The rapid progression of industrialization has significantly intensified the contamination of water resources by heavy metal ions, thereby exacerbating the global challenge of water scarcity. Aiming at solving this pressing issue of worldwide freshwater scarcity, nanomaterial and nanotechnology show a pivotal alternative in wastewater treatment. In this study, we construct distinct graphene nanosheets with varying shaped and sized pores (named as graphene crown pores) and assess the protonation of the pore edges to the heavy metal ion removal capacity. Employing molecular dynamics (MD) simulations, we demonstrate that protonated graphene nanopores exhibit exceptional water permeability and outstanding ion rejection rates. Moreover, our free energy calculations confirm that water molecules encounter a lower energy barrier compared to ions when traversing through graphene crown pores. Furthermore, the non-protonated graphene pores allow faster water permeance while compromising the ion rejection, yielding a dissatisfactory performance of metal ion removal. Detailed analysis suggest that the protonated pore endows the pore with a positively charged center, obstructing the passage of heavy metal ions. Therefore, our findings not only propose the protonated graphene crown pores for efficient heavy metal ion removal but also reveal the corresponding molecular mechanism, which is useful for future application of such membranes for heavy metal ion removal.

Cascaded compression of size distribution of nanopores in monolayer graphene.

Monolayer graphene with nanometre-scale pores, atomically thin thickness and remarkable mechanical properties provides wide-ranging opportunities for applications in ion and molecular separations1, energy storage2 and electronics3. Because the performance of these applications relies heavily on the size of the nanopores, it is desirable to design and engineer with precision a suitable nanopore size with narrow size distributions. However, conventional top-down processes often yield log-normal distributions with long tails, particularly at the sub-nanometre scale4. Moreover, the size distribution and density of the nanopores are often intrinsically intercorrelated, leading to a trade-off between the two that substantially limits their applications5-9. Here we report a cascaded compression approach to narrowing the size distribution of nanopores with left skewness and ultrasmall tail deviation, while keeping the density of nanopores increasing at each compression cycle. The formation of nanopores is split into many small steps, in each of which the size distribution of all the existing nanopores is compressed by a combination of shrinkage and expansion and, at the same time as expansion, a new batch of nanopores is created, leading to increased nanopore density by each cycle. As a result, high-density nanopores in monolayergraphene with a left-skewed, short-tail size distribution are obtained that show ultrafast and ångström-size-tunable selective transport of ions and molecules, breaking the limitation of the conventional log-normal size distribution9,10. This method allows for independent control of several metrics of the generated nanopores, including the density, mean diameter, standard deviation and skewness of the size distribution, which will lead to the next leap in nanotechnology.

Suspended nanoporous graphene produced by swift heavy ion bombardment

In the present work, Raman spectroscopy measurements and molecular dynamics simulations were used to investigate damage production in suspended single-layer graphene when irradiated by 23 MeV I, 3 MeV Cu and 18 MeV Cu beams. Despite the high energies of the used swift heavy ion beams, we found no evidence of ion track formation, i.e. all damage imparted to graphene was due to elastic collisions between ions and carbon atoms. Comparing experimental results with simulations, we conclude that a significant amount of energy (at least 40 % in the case of 23 MeV I irradiation) is dissipated away from graphene following the ion impact, and is a likely reason for the absence of ion tracks.

Modulation of transport at the interface in the microporous layer for high power density proton exchange membrane fuel cells

The proton exchange membrane (PEM) fuel cell is a device that demonstrates a significant potential for environmental sustainability, since it efficiently converts chemical energy into electrical energy. The microporous layer (MPL) in PEM fuel cells promotes gas transport and eliminates water. Nevertheless, the power density of PEM fuel cells is restricted by ohmic losses and mass transport losses in conventional MPLs. In this study, we enhanced the power density of proton exchange membrane (PEM) fuel cells through the identification of appropriate materials and the mitigation of mass transport losses occurring at the interface between the microporous layer and the catalyst layer. The incorporation of high electron conductivity, slip behavior at the interface between graphene and water, and rapid water evaporation facilitated by nanoporous graphene effectively address transport-related challenges. We evaluated two types of graphene as potential substitutes for carbon black in the microporous layer (MPL). The enhanced power density (up to 1.1 W cm−2) under all humidity conditions and reduced mass transport resistance (a 75 % reduction compared to carbon black MPL) make them promising candidates for next-generation PEM fuel cells. Furthermore, these findings provide guidance for controlling interfacial mass transport in colloidal systems.

Covalently Functionalized Nanopores for Highly Selective Separation of Monovalent Ions.

Biological ion channels possess prominent ion transport performances attributed to their critical chemical groups across the continuous nanoscale filters. However, it is still a challenge to imitate these sophisticated performances in artificial nanoscale systems. Herein, this work develops the strategy to fabricate functionalized graphene nanopores in pioneer based on the synergistic regulation of the pore size and chemical properties of atomically thin confined structure through decoupling etching combined with in situ covalent modification. The modified graphene nanopores possess asymmetric ion transport behaviors and efficient monovalent metal ions sieving (K+ /Li+ selectivity ≈48.6). Meanwhile, it also allows preferential transport for cations, the resulting membranes exhibit a K+ /Cl- selectivity of 76 and a H+ /Cl- selectivity of 59.3. The synergistic effects of steric hindrance and electrostatic interactions imposing a higher energy barrier for Cl- or Li+ across nanopores lead to ultra-selective H+ or K+ transport. Further, the functionalized graphene nanopores generate a power density of 25.3W m-2 and a conversion efficiency of 33.9%, showing potential application prospects in energy conversion. The theoretical studies quantitatively match well with the experimental results. The feasible preparation of functionalized graphene nanopores paves the way toward direct investigation on ion transport mechanism and advanced design in devices.

Topological descriptors, entropy measures and NMR spectral predictions for nanoporous graphenes with [14]annulene pores

AbstractPorous two‐dimensional (2D) nanographene structures are materials with vast potentials in several areas of research with varied applications. The porous structures of these 2D‐materials offer multiple applications in the field of nanochemistry including sequestration of toxic metal ions as they possess large surface areas, enhanced electrical and electronic properties, and high mechanical flexibility. Their porous structures facilitate the creation of highly efficient electrodes, which could significantly improve the performance of batteries and other energy storage technologies. Topological descriptors are powerful tools for characterizing their structures and predicting the properties of molecules and thus have a number of applications. We compute the analytical expressions for degree‐based and Szeged‐type topological descriptors and their information‐theoretic entropies. In addition, we perform a comparative analysis of the scaled bond‐wise entropies between nanoporous graphenes and rectangular kekulene structures with comparable sizes. Furthermore, we predict the C and proton NMR spectral patterns of these materials using graph‐theoretical techniques.

Rational design of reverse osmosis membranes for boron removal: A counter-intuitive relationship between boron rejection and pore size

Owing to the toxicity of excess boron, developing reverse osmosis membranes that are capable of effectively removing boric acid, a boron specie commonly exists in seawater, is critical to advance water purification technology. To date, design principles of reverse osmosis membranes for boron removal have not yet been systematically explored. Using nanoporous graphene as a model system and by employing state-of-the-art molecular simulation techniques, this study discovers the critical role of the adsorptive competition of boric acid against water in the nanopores of membranes in their design. Specifically, the preferential adsorption of water onto the pore rims can be exploited to impede the permeation of boric acid, facilitating the size-exclusion effect for much improved boron rejection. Moreover, a well-balanced adsorptive competition is desired; water adsorption should not be too strong so that efficient water permeation can still be preserved. This results in membranes that are not only highly permeable but also capable of effectively removing boric acid. Detailed investigations on energetic, dynamics, and spatial distribution of water and boric acid as well as their free energy landscapes are also conducted for better understandings. Moreover, bilayer nanoporous graphene membranes with a heterogeneous design are identified to effectively block both boric acid and salt with a decent water permeation. Overall, the outcomes achieved herein can fundamentally guide the rational design of reverse osmosis membranes for more efficient and effective boron removal.

Ionic transport through a bilayer nanoporous graphene with cationic and anionic functionalization.

Understanding the ionic transport through multilayer nanoporous graphene (NPG) holds great promise for the design of novel nanofluidic devices. Bilayer NPG with different structures, such as nanopore offset and interlayer space, should be the most simple but representative multilayer NPG. In this work, we use molecular dynamics simulations to systematically investigate the ionic transport through a functionalized bilayer NPG, focusing on the effect of pore functionalization, offset, applied pressure and interlayer distance. For a small interlayer space, the fluxes of water and ions exhibit a sudden reduction to zero with the increase in offset that indicates an excellent on-off gate, which can be deciphered by the increasing potential of mean force barriers. With the increase in pressure, the fluxes increase almost linearly for small offsets while always maintain zero for large offsets. Finally, with the increase in interlayer distance, the fluxes increase drastically, resulting in the reduction in ion rejection. Notably, for a specific interlayer distance with monolayer water structure, the ion rejection maintains high levels (almost 100% for coions) with considerable water flux, which could be the best choice for desalination purpose. The dynamics of water and ions also exhibit an obvious bifurcation for cationic and anionic functionalization. Our work comprehensively addresses the ionic transport through a bilayer NPG and provides a route toward the design of novel desalination devices.

Bioinspired Large‐Area Atomically‐Thin Graphene Membranes

AbstractNanoporous graphene membranes are attractive for molecular separations, but it remains challenging to maintain sufficient mechanical strength during scalable fabrication and module development. Inspired by the composite structure of cell membranes and cell walls, a large‐area atomically thin nanoporous graphene membrane supported by a fiber‐reinforced structure with strong interlamellar adhesion is designed. Compared with other graphene‐based membranes of large scale, the fracture stress, fracture strength, and tensile stiffness of the composite membranes can be enhanced by a factor of 17, 67, and 94, respectively. This fiber‐reinforced structure also confers stability of the composite membrane to different curvature states and repeated bending processes after 10 000 times, which provides an opportunity for modularization. The breathable function of such membrane with an ultrahigh gas permeance (≈8.6–23 L m−2 d−1 Pa−1) and an ultralow water vapor transportation rate (WVTR) (≈23–129 g L m−2 d−1) is observed, superior to most commercial materials. This work provides a facile method to fabricate large‐area graphene membranes and paves the road to practical application in the membrane separation field for other 2D films.