Cascaded compression of size distribution of nanopores in monolayer graphene

Ultrafast Fabrication of Nanoporous, Atomically Thin Membranes Based on Wafer-Scale Graphene

Membrane separation technologies are garnering significant attention in both industry and academia due to their potential for energy savings and operational effectiveness. Among the promising materials for membranes, wafer-scale single-crystal graphene emerges as an exceptional candidate due to its ultraflat surface, superior mechanical strength, and chemical stability, making it ideal for the top-down fabrication of nanoporous separation membranes. Despite these promising properties, the slow etch rate of copper and the low transfer efficiency of wafer-scale graphene membranes pose challenges to their large-scale application. In this work, we present an innovative method for the rapid fabrication of nanoporous atomically thin membranes (NATMs) using wafer-scale graphene. We utilized argon plasma to treat the graphene wafers. Subsequently, a nonsolvent-induced phase inversion process using poly(vinylidene fluoride) (PVDF) was employed to create a porous support layer on a large scale. By wetting the PVDF with ethanol before etching the copper, we not only facilitated accelerated etchant diffusion during copper etching, but also introduced size-selective defects that enhance the separation performance. Our approach increases the etch rate of copper by 115 times compared to conventional transfer methods while maintaining the selectivity of the NATMs. Remarkably, the entire fabrication process can be completed on a 4 in. wafer within 1 h. This novel transfer method represents a significant advancement in overcoming the challenges of efficient graphene transfer without sacrificing the separation properties of graphene, thereby bringing graphene-based films closer to practical, real-world applications.

Biomimetic ion channels with subnanometer sizes for ion sieving: a mini-review

The remarkable ion selectivity of biological systems has inspired the development of artificial ion channels with Ångström-scale precision, expanding their potential applications in ion separation, energy conversion, and water purification. This mini-review systematically examines fundamental ion-sieving mechanisms operating at the subnanoscale, highlighting advanced fabrication strategies involving synthetic ion channels on lipid bilayers and solid-state ion channels. We further explore membrane material innovations spanning zero-dimensional nanopores to three-dimensional crystalline frameworks, emphasizing structure-function relationships in channel design. The discussion concludes with critical perspectives on scalability challenges and future research directions, outlining pathways toward next-generation sustainable ion sieving technologies.

Fast water transport and ionic sieving in ultrathin stacked nanoporous 2D membranes

Atomically thin nanoporous 2D membranes, featuring unique sieving characteristics for molecules and ions, have significant potential for seawater desalination. However, they face a common trade-off between permeability and selectivity. Here, we report an ultrathin stacked nanoporous graphene membrane (SNGM) created by layering atomically thin graphene nanomesh. This design achieves highly efficient and selective sieving of water molecules and ions. The SNGMs showcase in-plane nanopores for optimal size-exclusive water input and output, and interlayer 2D nanochannels between adjacent graphene nanomesh membranes for rapid water transport and precise ion/molecular sieving. The resulting SNGMs effectively address the trade-off between water permeability and ion selectivity in conventional desalination membranes, delivering a water permeability of ∼ 1-2 orders of magnitude higher than that of commercial membranes, while maintaining a comparable ion rejection ratio (>95% for NaCl). This advance marks a significant leap forward in adopting 2D nanoporous membranes for desalination technology.

Scalable Bottom-Up Synthesis of Nanoporous Hexagonal Boron Nitride (h-BN) for Large-Area Atomically Thin Ceramic Membranes

Nanopores embedded within monolayer hexagonal boron nitride (h-BN) offer possibilities of creating atomically thin ceramic membranes with unique combinations of high permeance (atomic thinness), high selectivity (via molecular sieving), increased thermal stability, and superior chemical resistance. However, fabricating size-selective nanopores in monolayer h-BN via scalable top-down processes remains nontrivial due to its chemical inertness, and characterizing nanopore size distribution over a large area remains extremely challenging. Here, we demonstrate a facile and scalable approach of exploiting the chemical vapor deposition (CVD) process temperature to enable direct incorporation of subnanometer/nanoscale pores into the monolayer h-BN lattice, in combination with manufacturing compatible polymer casting to fabricate centimeter-scale nanoporous atomically thin ceramic membranes. We leverage diffusive transport of analytes including size-selective Ficoll sieving to characterize subnanometer-scale and nanoscale defects that manifest as pores in centimeter-scale h-BN membranes, overcoming previous limitations in large-area characterization of nanoscale defects in h-BN. Our approach opens a new frontier to advance atomically thin membranes to 2D ceramic materials, such as h-BN via facile and direct formation of nanopores, for size-selective separations.

Graphene Nanopore Fabrication and Applications

Graphene is a revolutionary material with excellent optical, electrical and mechanical properties and has garnered significant attention in the realm of nanopore technology. Devices incorporating graphene nanopores leverage the material's atomic thickness to enhance detection precision in solid-state nanopores. These nanopores exhibit high spatial resolution and ion selectivity, making them promising sensors for biomolecular detection. Additionally, their unique characteristics suggest their considerable potential for applications in material separation and osmotic power generation. In recent years, several literature reviews on graphene nanopores have been published; however, some have not fully addressed certain important aspects, such as the depth of theoretical analysis, the extent of coverage on technological advancements, and the exploration of potential applications. This paper reviews current fabrication methods, including "top-down" etching and "bottom-up" synthesis, highlighting their advantages and limitations. We also summarize diverse applications of graphene nanopores, such as in biomolecule detection and water desalination. Our findings emphasize the need for a deeper exploration of these aspects, advancing the field by showcasing the broader potential of graphene nanopores in addressing various technological challenges.

Scaling Behavior and Conductance Mechanisms of Ion Transport in Atomically Thin Graphene Nano/Subnanopores

Ion transport through atomically thin nano/subnanopores, such as those in monolayer graphene, presents challenges to traditional ion conduction models, primarily due to extreme confinement effects and hydration interactions. Under these conditions, existing models fail to account for conductance behaviors at the nano- and subnanometer scales. In this study, we perform a combined experimental and theoretical investigation of ion transport in monolayer graphene nano/subnanopores across varying salt concentrations. We introduce a conductance model that accurately predicts the observed scaling behavior by addressing the interaction between counterions and the edges of atomically thin pores, where counterion movement is constrained by the pore's structure. This model also quantifies the hydration energy barrier, highlighting the impact of the hydration shell structures on ion transport efficiency. Our findings reveal that hydrated potassium ions traverse these pores with higher efficiency than previously estimated, offering new insights into ion transport mechanisms under atomic-scale confinement.

Protein-Enabled Size-Selective Defect-Sealing of Atomically Thin 2D Membranes for Dialysis and Nanoscale Separations

Atomically thin 2D materials present the potential for advancing membrane separations via a combination of high selectivity (from molecular sieving) and high permeance (due to atomic thinness). However, the creation of a high density of precise nanopores (narrow-size-distribution) over large areas in 2D materials remains challenging, and nonselective leakage from nanopore heterogeneity adversely impacts performance. Here, we demonstrate protein-enabled size-selective defect sealing (PDS) for atomically thin graphene membranes over centimeter scale areas by leveraging the size and reactivity of permeating proteins to preferentially seal larger nanopores (≥4 nm) while preserving a significant amount of smaller nanopores (via steric hindrance). Our defect-sealed nanoporous atomically thin membranes (NATMs) show stability up to ∼35 days during size-selective diffusive separations with a model dialysis biomolecule fluorescein isothiocyanate (FITC)-Ficoll 70 in phosphate buffer saline (PBS) solution as well as outperform state-of-the-art commercially available dialysis membranes (molecular-weight-cutoff ∼3.5-5 kDa and ∼8-10 kDa) with significantly higher permeance for smaller solutes KCl (∼0.66 nm) ∼5.1-6 × 10-5 ms-1 and vitamin B12 (B12, ∼1.5 nm) ∼2.8-4 × 10-6 ms-1 compared to small protein lysozyme (Lz, ∼4 nm) ∼4-6.4 × 10-8 m s-1, thereby allowing unprecedented selectivity for B12/Lz ∼70 and KCl/Lz ∼1280. Our work introduces proteins as nanoscale tools for size-selective defect sealing in atomically thin membranes to overcome persistent issues and advance separations for dialysis, protein desalting, small molecule separations/purification, and other bioprocesses.

Emerging Advances around Nanofluidic Transport and Mass Separation under Confinement in Atomically Thin Nanoporous Graphene

Membrane separation stands as an environmentally friendly, high permeance and selectivity, low energy demand process that deserves scientific investigation and industrialization. To address intensive demand, seeking appropriate membrane materials to surpass trade-off between permeability and selectivity and improve stability is on the schedule. 2D materials offer transformational opportunities and a revolutionary platform for researching membrane separation process. Especially, the atomically thin graphene with controllable porosity and structure, as well as unique properties, is widely considered as a candidate for membrane materials aiming to provide extreme stability, exponentially large selectivity combined with high permeability. Currently, it has shown promising opportunities to develop separation membranes to tackle bottlenecks of traditional membranes, and it has been of great interest for tremendously versatile applications such as separation, energy harvesting, and sensing. In this review, starting from transport mechanisms of separation, the material selection bank is narrowed down to nanoporous graphene. The study presents an enlightening overview of very recent developments in the preparation of atomically thin nanoporous graphene and correlates surface properties of such 2D nanoporous materials to their performance in critical separation applications. Finally, challenges related to modulation and manufacturing as well as potential avenues for performance improvements are also pointed out.

Recent Research Progress of Porous Graphene and Applications in Molecular Sieve, Sensor, and Supercapacitor

Porous graphene, including 2D and 3D porous graphene, is widely researched recently. One of the most attractive features is the proper utilization of graphene defects, which combine the advantages of both graphene and porous materials, greatly enriching the applications of porous graphene in biology, chemistry, electronics, and other fields. In this review, the defects of graphene are first discussed to provide a comprehensive understanding of porous graphene. Then, the latest advancements in the preparation of 2D and 3D porous graphene are presented. The pros and cons of these preparation methods are discussed in detail, providing a direction for the fabrication of porous graphene. Moreover, various superior properties of porous graphene are described, laying the foundation for their promising applications. Owing to its abundant morphology, wide distribution of pore size, and remarkable properties benefited from porous structure, porous graphene can not only promote molecular diffusion and electron transfer but also expose more active sites. Consequently, a serious of applications containing gas sieving, liquid separation, sensors, and supercapacitors, are presented. Finally, the challenges confronted during preparation and characterization of porous graphene are discussed, offering guidance for the future development of porous graphene in fabrication, characterization, properties, and applications.

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.

Simultaneous Manipulation of Membrane Enthalpy and Entropy Barriers towards Superior Ion Separations

Sub-nanoporous membranes with ion selective transport functions are important for energy utilization, environmental remediation, and fundamental bioinspired engineering. Although mono/multivalent ions can be separated by monovalent ion selective membranes (MISMs), the current theory fails to inspire rapid advances in MISMs. Here, we apply transition state theory (TST) by regulating the enthalpy barrier (ΔH) and entropy barrier (ΔS) for designing next-generation monovalent cation exchange membranes (MCEMs) with great improvement in ion selective separation. Using a molecule-absorbed porous material as an interlayer to construct a denser selective layer can achieve a greater absolute value of ΔS for Li+ and Mg2+ transport, greater ΔH for Mg2+ transport and lower ΔH for Li+ transport. This recorded performance with a Li+/Mg2+ perm-selectivity of 25.50 and a Li+ flux of 1.86 mol ⋅ m-2 ⋅ h-1 surpasses the contemporary "upper bound" plot for Li+/Mg2+ separations. Most importantly, our synthesized MCEM also demonstrates excellent operational stability during the selective electrodialysis (S-ED) processes for realizing scalability in practical applications.

Art etching of graphene

The growth of graphene on a metal substrate using chemical vapor deposition (CVD), assisted by hydrocarbons such as CH4, C3H8, C2H6, etc. leads to the formation of carbon clusters, amorphous carbon, or any other structure. These carbon species are considered as unwanted impurities; thus a conventional etching step is used simultaneously with CVD graphene growth to remove them using an etching agent. Meanwhile, art etching is a specific method of producing controlled non-Euclidean and Euclidean geometries by employing intricate and precise etching parameters or integrated growth/etching modes. Agents such as H2, O2, CH4, Ar, and others are applied as art etching agents to support the art etching technology. This technique can generate nanopores and customize the properties of graphene, facilitating specific applications such as nanodevices, nanosensors, nanofilters, etc. This comprehensive review investigates how precursor gases concurrently induce graphene growth and art etching during a chemical vapor deposition process, resulting in beautifully etched patterns. Furthermore, it discusses the techniques leading to the creation of these patterns. Finally, the challenges, uses, and perspectives of these non-Euclidean and Euclidean-shaped art etched graphene geometries are discussed.

Nanofluidic Ionic Memristors

Living organisms use ions and small molecules as information carriers to communicate with the external environment at ultralow power consumption. Inspired by biological systems, artificial ion-based devices have emerged in recent years to try to realize efficient information-processing paradigms. Nanofluidic ionic memristors, memory resistors based on confined fluidic systems whose internal ionic conductance states depend on the historical voltage, have attracted broad attention and are used as neuromorphic devices for computing. Despite their high exposure, nanofluidic ionic memristors are still in the initial stage. Therefore, systematic guidance for developing and reasonably designing ionic memristors is necessary. This review systematically summarizes the history, mechanisms, and potential applications of nanofluidic ionic memristors. The essential challenges in the field and the outlook for the future potential applications of nanofluidic ionic memristors are also discussed.

Degree of disorder-regulated ion transport through amorphous monolayer carbon

Nanopore technology, re-fueled by two-dimensional (2D) materials such as graphene and MoS2, controls mass transport by allowing certain species while denying others at the nanoscale and has a wide application range in DNA sequencing, nano-power generation, and others. With their low transmembrane transport resistance and high permeability stemming from their ultrathin nature, crystalline 2D materials do not possess nanoscale holes naturally, thus requiring additional fabrication to create nanopores. Herein, we demonstrate that nanopores exist in amorphous monolayer carbon (AMC) grown at low temperatures. The size and density of nanopores can be tuned by the growth temperature, which was experimentally verified by atomic images and further corroborated by kinetic Monte Carlo simulation. Furthermore, AMC films with varied degrees of disorder (DOD) exhibit tunable transmembrane ionic conductance over two orders of magnitude when serving as nanopore membranes. This work demonstrates the DOD-tuned property in amorphous monolayer carbon and provides a new candidate for modern membrane science and technology.

Defect-Healed Carbon Nanomembranes for Enhanced Salt Separation: Scalable Synthesis and Performance

Carbon nanomembranes (CNMs), with a high density of subnanometer channels, enable superior salt separation performance compared to conventional membranes. However, defects that occur during the synthesis and transfer processes impede their technical realization on a macroscopic scale. Here, we introduce a practical and scalable interfacial polymerization method to effectively heal defects while preserving the subnanometer pores within CNMs. The defect-healed freestanding CNMs show an exceptional performance in forward osmosis (FO), achieving a water flux of 105 L m-2 h-1 and a specific reverse salt flux of 0.1 g L-1 when measured with 1 M NaCl as draw solution. This water flux is 10 times higher than that of commercially available FO membranes, and the reverse salt flux is 70% lower. Through successful implementation of the defect-healing method and support optimization, we demonstrate the synthesis of fully functional, centimeter-scale CNM-based composite membranes showing high water permeance and a high salt rejection. Our defect-healing method presents a promising pathway to overcome limitations in CNM synthesis, advancing their potential for practical salt separation applications.

Depletion Strategies for Crystallized Layers of Two-Dimensional Nanosheets to Enhance Lithium-Ion Conductivity in Polymer Nanocomposites

The assembly of long-range aligned structures of two-dimensional nanosheets (2DNSs) in polymer nanocomposites (PNCs) is in urgent need for the design of nanoelectronics and lightweight energy-storage materials of high conductivity for electricity or heat. These 2DNS are thin and exhibit thermal fluctuations, leading to an intricate interplay with polymers in which entropic effects can be exploited to facilitate a range of different assemblies. In molecular dynamics simulations of experimentally studied 2DNSs, we show that the layer-forming crystallization of 2DNSs is programmable by regulating the strengths and ranges of polymer-induced entropic depletion attractions between pairs of 2DNSs, as well as between single 2DNSs and a substrate surface, by exclusively tuning the temperature and size of the 2DNS. Enhancing the temperature supports the 2DNS-substrate depletion rather than crystallization of 2DNSs in the bulk, leading to crystallized layers of 2DNSs on the substrate surfaces. On the other hand, the interaction range of the 2DNS-2DNS depletion attraction extends further than the 2DNS-substrate attraction whenever the 2DNS size is well above the correlation length of the polymers, which results in a nonmonotonic dependence of the crystallization layer on the 2DNS size. It is demonstrated that the depletion-tuned crystallization layers of 2DNSs contribute to a conductive channel in which individual lithium ions (Li ions) migrate efficiently through the PNCs. This work provides statistical and dynamical insights into the balance between the 2DNS-2DNS and 2DNS-substrate depletion interactions in polymer-2DNS composites and highlights the possibilities to exploit depletion strategies in order to engineer crystallization processes of 2DNSs and thus to control electrical conductivity.

Self-similarity study based on the particle sizes of coal-series diatomite

Coal-series diatomite (CSD) is widely distributed in China and has poor functional and structural properties and exhibits limited utilization of high value-added materials, resulting in a serious waste of resources and tremendous pressure on the environment. Moreover, due to differences in the mineralogical characteristics of CSD, different particle size scales (PSSs) have different functional structures and exhibit different self-similarities. In this study, we took CSD as the research object and PSS as the entry point and carried out a self-similarity study based on gas adsorption and an image processing method to illustrate the microstructures and self-similarities of different PSSs. The results showed that the pore structure of the CSD was dominated by mesopores and macropores and basically lacked micropores. The fractal dimensions were calculated with the Frenkel-Haisey-Hill (FHH) model and Menger model, and the DF1 values for - 0.025 mm and - 2 mm were 2.51 and 2.48, respectively, and the DM1 values were 3.75 and 3.79, respectively, indicating that the mesopore structure of the fine PSS was complex, whereas macropores were present in the coarse PSS. MATLAB was programmed to obtain grayscale thresholds, binarized images, grayscale histograms, three-dimensional (3D) reconstruction images and box dimensions, which enabled us to observe the microstructures and self-similarities of the CSD. Self-similarity studies based on particle sizes are very important for functional application of CSD.Please note that article title mismatch between MS and JS we have followed MS, kindly check and cofirm.Yes, I have checked and confirmed.Kindly check and confirm corresponding author mail id are correctly identified.Yes, I have checked and confirmed.