Exceptionally fast water desalination at complete salt rejection by pristine graphyne monolayers

Carbon-Based Nanocomposite Membranes for Membrane Distillation: Progress, Problems and Future Prospects

The development of an ideal membrane for membrane distillation (MD) is of the utmost importance. Enhancing the efficiency of MD by adding nanoparticles to or onto a membrane's surface has drawn considerable attention from the scientific community. It is crucial to thoroughly examine state-of-the-art nanomaterials-enabled MD membranes with desirable properties, as they greatly enhance the efficiency and reliability of the MD process. This, in turn, opens up opportunities for achieving a sustainable water-energy-environment nexus. By introducing carbon-based nanomaterials into the membrane's structure, the membrane gains excellent separation abilities, resistance to various feed waters, and a longer lifespan. Additionally, the use of carbon-based nanomaterials in MD has led to improved membrane performance characteristics such as increased permeability and a reduced fouling propensity. These nanomaterials have also enabled novel membrane capabilities like in situ foulant degradation and localized heat generation. Therefore, this review offers an overview of how the utilization of different carbon-based nanomaterials in membrane synthesis impacts the membrane characteristics, particularly the liquid entry pressure (LEP), hydrophobicity, porosity, and membrane permeability, as well as reduced fouling, thereby advancing the MD technology for water treatment processes. Furthermore, this review also discusses the development, challenges, and research opportunities that arise from these findings.

Exploring the Potential of Chemically Modified Graphyne Nanodots as an Efficient Adsorbent and Sensitive Detector of Environmental Contaminants: A First Principles Study

In this study, we investigated the reactivity of γ-graphyne (Gp) and its derivatives, Gp-CH3, Gp-COOH, Gp-CN, Gp-NO2, and Gp-SOH, for the removal of toxic heavy metal ions (Hg+ 2, Pb+ 2, and Cd+ 2) from wastewater. From the analysis of the optimized structures, it was observed that all the compounds exhibited planar geometry. The dihedral angles (C9-C2-C1-C6 and C9-C2-C1-C6) were approximately 180.00°, indicating planarity in all molecular arrangements. To understand the electronic properties of the compounds, the HOMO (EH) and LUMO (EL) energies were calculated, and their energy gaps (Eg) were determined. The EH and EL values ranged between - 6.502 and - 8.192 eV and - 1.864 and - 3.773 eV, respectively, for all the compounds. Comparing the EH values, Gp-NO2 exhibited the most stable HOMO, while Gp-CH3 had the least stable structure. In terms of EL values, Gp-NO2 had the most stable LUMO, while Gp-CH3 was the least stable. The Eg values followed the order: Gp-NO2 < Gp-COOH < Gp-CN < Gp-SOH < Gp-CH3 < Gp, with Gp-NO2 (4.41 eV) having the smallest energy gap. The density of states (DOS) analysis showed that the shape and functional group modifications affected the energy levels. Functionalization with electron-withdrawing (CN, NO2, COOH, SOH) or electron-donating (CH3) groups reduced the energy gap. To specifically target the removal of heavy metal ions, the Gp-NO2 ligand was selected for its high binding energy. Complexes of Gp-NO2-Cd, Gp-NO2-Hg, and Gp-NO2-Pb were optimized, and their properties were analyzed. The complexes were found to be planar, with metal-ligand bond distances within the range of 2.092→3.442 Å. The Gp-NO2-Pb complex exhibited the shortest bond length, indicating a stronger interaction due to the smaller size of Pb+ 2. The computed adsorption energy values (Eads) indicated the stability of the complexes, with values ranging from - 0.035 to -4.199 eV. Non-covalent interaction (NCI) analysis was employed to investigate intermolecular interactions in Gp-NO2 complexes. The analysis revealed distinct patterns of attractive and repulsive interactions, providing valuable insights into the binding preferences and steric effects of heavy metals.

Magnesium Ion Gated Ion Rejection through Carboxylated Graphene Oxide Nanopore: A Theoretical Study

While nanoporous graphene oxide (GO) is recognized as one of the most promising reverse osmosis desalination membranes, limited attention has been paid to controlling desalination performance through the large GO pores, primarily due to significant ion leakage resulting in the suboptimal performance of these pores. In this study, we employed a molecular dynamics simulation approach to demonstrate that Mg2+ ions, adhered to carboxylated GO nanopores, can function as gates, regulating the transport of ions (Na+ and Cl-) through the porous GO membrane. Specifically, the presence of divalent cations near a nanopore reduces the concentration of salt ions in the vicinity of the pore and prolongs their permeation time across the pore. This subsequently leads to a notable enhancement in salt rejection rates. Additionally, the ion rejection rate increases with more adsorbed Mg2+ ions. However, the presence of the adsorbed Mg2+ ions compromises water transport. Here, we also elucidate the impact of graphene oxidation degree on desalination. Furthermore, we design an optimal combination of adsorbed Mg2+ ion quantity and oxidation degree to achieve high water flux and salt rejection rates. This work provides valuable insights for developing new nanoporous graphene oxide membranes for controlled water desalination.

Prediction of 2D group-11 chalcogenides: insights into novel auxetic M2X (M = Cu, Ag, Au; X = S, Se, Te) monolayers

Two-dimensional (2D) auxetic materials have recently attracted considerable research interest due to their excellent mechanical properties and diverse applications, surpassing those of three-dimensional (3D) materials. This study focuses on the theoretical prediction of mechanical properties and auxeticity in 2D M2X (M = Cu, Ag, Au; X = S, Se, Te) monolayers using first-principles calculations. Our results indicate that the dynamically stable monolayers include low-energy α-Cu2S, α-Cu2Se, α-Cu2Te, β-Ag2S, β-Ag2Se, α-Ag2Te, β-Au2S, β-Au2Se and α-Au2Te. These M2X monolayers possess positive Poisson's ratios (PR) ranging from 0.09 to 0.52, as well as Young's moduli ranging from 19.92 to 35.42 N m-1 in x and y directions. Specially, α-Cu2S exhibits the lowest negative PR in θ = 45° × n (n = 1, 2, 3, 4) directions. The Poisson's function (PF) can be adjusted by increasing tensile strains. The β-phase monolayers exhibit positive PF with a linear change. Interestingly, the transition from positive to negative PF occurs in the α-Cu2S and α-Ag2Te monolayers at strains greater than +3% and +4%, respectively, while the α-Cu2Se, α-Cu2Te and α-Au2Te monolayers maintain positive PF within the range of 0% to +6% strains. Furthermore, taking α-Cu2S (α-Cu2Te) as an example, the mechanism underlying negative (positive) PF is demonstrated to involve increased (decreased) bond angles, decreased thickness, and weakened (enhanced) d(M)-p(X) orbital coupling. The findings of this study not only enrich the family of 2D group-11 chalcogenides but also provide insights into their mechanical properties, thereby expanding their potential applications in mechanics.

Two-Dimensional Carbon Graphdiyne: Advances in Fundamental and Application Research

Graphdiyne (GDY), a rising star of carbon allotropes, features a two-dimensional all-carbon network with the cohybridization of sp and sp² carbon atoms and represents a trend and research direction in the development of carbon materials. The sp/sp²-hybridized structure of GDY endows it with numerous advantages and advancements in controlled growth, assembly, and performance tuning, and many studies have shown that GDY has been a key material for innovation and development in the fields of catalysis, energy, photoelectric conversion, mode conversion and transformation of electronic devices, detectors, life sciences, etc. In the past ten years, the fundamental scientific issues related to GDY have been understood, showing differences from traditional carbon materials in controlled growth, chemical and physical properties and mechanisms, and attracting extensive attention from many scientists. GDY has gradually developed into one of the frontiers of chemistry and materials science, and has entered the rapid development period, producing large numbers of fundamental and applied research achievements in the fundamental and applied research of carbon materials. For the exploration of frontier scientific concepts and phenomena in carbon science research, there is great potential to promote progress in the fields of energy, catalysis, intelligent information, optoelectronics, and life sciences. In this review, the growth, self-assembly method, aggregation structure, chemical modification, and doping of GDY are shown, and the theoretical calculation and simulation and fundamental properties of GDY are also fully introduced. In particular, the applications of GDY and its formed aggregates in catalysis, energy storage, photoelectronic, biomedicine, environmental science, life science, detectors, and material separation are introduced.

Prospects of 2D graphdiynes and their applications in desalination and wastewater remediation

Water is an indispensable part of human life that affects health and food intake. Water pollution caused by rapid industrialization, agriculture, and other human activities affects humanity. Therefore, researchers are prudent and cautious regarding the use of novel materials and technologies for wastewater remediation. Graphdiyne (GDY), an emerging 2D nanomaterial, shows promise in this direction. Graphdiyne has a highly symmetrical π-conjugated structure consisting of uniformly distributed pores; hence, it is favorable for applications such as oil-water separation and organic-pollutant removal. The acetylenic linkage in GDY can strongly interact with metal ions, rendering GDY applicable to heavy-metal adsorption. In addition, GDY membranes that exhibit 100% salt rejection at certain pressures are potential candidates for wastewater treatment and water reuse via desalination. This review provides deep insights into the structure, properties, and synthesis methods of GDY, owing to which it is a unique, promising material. In the latter half of the article, various applications of GDY in desalination and wastewater treatment have been detailed. Finally, the prospects of these materials have been discussed succinctly.

Recent advances on graphyne and its family members as membrane materials for water purification and desalination

Graphyne and its family members (GFMs) are allotropes of carbon (a class of 2D materials) having unique properties in form of structures, pores and atom hybridizations. Owing to their unique properties, GFMs have been widely utilized in various practical and theoretical applications. In the past decade, GFMs have received considerable attention in the area of water purification and desalination, especially in theoretical and computational aspects. More recently, GFMs have shown greater prospects in achieving optimal separation performance than the experimentally derived commercial polyamide membranes. In this review, recent theoretical and computational advances made in the GFMs research as it relates to water purification and desalination are summarized. Brief details on the properties of GFMs and the commonly used computational methods were described. More specifically, we systematically reviewed the various computational approaches employed with emphasis on the predicted permeability and selectivity of the GFM membranes. Finally, the current challenges limiting their large-scale practical applications coupled with the possible research directions for overcoming the challenges are proposed.

Understanding the performance of graphdiyne membrane for the separation of nitrate ions from aqueous solution at the atomistic scale

A molecular dynamics simulation study is conducted to investigate the capability of the pristine graphdiyne nanosheet for nitrate ion separation from water. The removal of nitrate ion contaminants from water is of critical importance as it represents an environmental hazard. The graphdiyne is a carbon-based membrane with pore density of 2.4 × 10¹⁸ pores/m² and incircle radius of 2.8 Å. We show that the efficient water flow is accurately controlled through fine regulation of the exerted hydrostatic pressure. The high water permeability of 6.19 L.Day^-1cm^-2MPa^-1 with 100% nitrate ions rejection suggests that the graphdiyne can perform as a suitable membrane for nitrate separation. The potential of mean force analysis of the single water molecule and nitrate ion indicated the free energy barriers for nitrate of about 4 times higher than that of water molecules. The results reveal the weak interaction of the water molecules and the membrane which aid to high water flux.

Ion Hydration under Nanoscale Confinement: Dimensionality and Scale Effects

How ions are hydrated in nanoconfined spaces is crucial for understanding many natural phenomena and practical applications, such as biological functionalities and energy conversion devices. In real systems, nanoconfinement shows structural diversity, but the influence of dimensionality and scale on ion hydration remains considerably unrevealed. Here, we study ion hydration under various confinements by systematic molecular dynamics simulations. In a given dimension, the structure and dynamics of water molecules in the first hydration shell are altered to a degree inversely correlated with the confinement scale, as long as there is no central bulk-like region. Further comparison of ion hydration among different dimensional systems shows that this scale effect becomes more pronounced in systems with lower dimensionality, due to a more significant water layering effect and lower probability for ions to stay away from confining surfaces. These findings provide a qualitatively new understanding of ion transport in biological channels and are instrumental for the design of functional nanofluidic devices.

Microscopic Insight into Water Desalination through Nanoporous Graphene: The Influence of the Dipole Moment

Nanoporous graphene membranes with controllable pore size and chemical functionality may be one of the most desirable materials for water desalination. Herein, we investigate desalination performance of hydrogen-functionalized nanoporous graphene membranes. The charge values on hydrogen atoms (q_H) and carbon atoms at the pore rim are systematically adjusted. For q_H > 0, the flow rate decreases as q_H increases, whereas for q_H < 0, the flow rate tends to increase first and then decrease with increasing q_H, yielding a peak at ∼ -0.2 e. Moreover, nanopores with large dipole moments at the rim have little effect on the salt rejection. The calculated oxygen and hydrogen density maps, the potential of mean force for water molecule and salt ion passage through the nanopores, and the coordination number unveil the mechanisms underlying water desalination in nanoporous graphene. This work may inspire the design and improvement of two-dimensional membranes for water desalination.

Mechanistic studies on the anomalous transport behaviors of water molecules in nanochannels of multilayer graphynes

An in-depth understanding of directed transport behaviors of water molecules through nanoporous materials is essential for the design and development of next-generation filtration devices. In this work, we perform molecular dynamics (MD) simulations to explore transport properties of water molecules through nanochannels of multilayer graphyne with different pore sizes. Our simulation results reveal that the orientations of confined water molecules would periodically reverse between two opposite directions as they diffuse along the nanochannels, and such a transport mechanism shows similarities with water transport in aquaporin channels. Further, we observe that, for each orientation reversal, there is an obvious difference in the HB breaking frequency among the three graphyne systems, with an order of graphyne-4 > graphyne-5 > graphyne-3. Besides, the average HB number is found to display a periodic fluctuation with a pulse-like pattern along the diffusion direction, wherein the graphyne-4 system has the maximum fluctuation, while the graphyne-3 system has the minimum one. Such anomalous HB breaking frequency and average HB number fluctuation results finally lead to a nonmonotonic relationship between water diffusion rate and graphyne pore size, and the diffusion order follows graphyne-4 > graphyne-5 > graphyne-3. Herein, we provide a new insight into the transport mechanisms of water molecules through nanoporous materials and our findings open up opportunities for the design and development of high-performance graphyne-based membranes used for water purification and desalination.

Efficient Removal of Heavy Metals from Aqueous Solutions through Functionalized γ-Graphyne-1 Membranes under External Uniform Electric Fields: Insights from Molecular Dynamics Simulations

Carbon-based nanosheet membranes with functionalized pores have great potential as water treatment membranes. In this study, the separation of Hg²⁺ and Cu²⁺ as heavy metal ions from aqueous solutions using a functionalized γ-graphyne-1 nanosheet membrane is investigated by molecular dynamics simulations. The simulation systems consist of a γ-graphyne-1 nanosheet with -COOH or -NH₂ functional groups on the edge of pores placed in an aqueous solution containing CuCl₂ and HgCl₂. An external electric field is applied as a driving force across the membrane for the separation of heavy metal ions using these functionalized pores. The ion-membrane and water molecule-membrane interaction energies, the radial distribution function of cations, the retention time and permeation of ions through the membrane, the density profile of water and ions, and the hydrogen bond in the system are investigated, and these results reveal that the performance of -NH₂-functionalized γ-graphyne-1 is better than that of -COOH-functionalized γ-graphyne-1 in the separation of Cu²⁺, while the Hg²⁺ cations encounter a high energy barrier as they pass through the membrane, especially in the -COOH-functionalized pore, due to their larger ionic radius and the smaller pore size of this membrane.

Novel adjustable monolayer carbon nitride membranes for high-performance saline water desalination

In this study, via molecular dynamic simulations, we showed that the latest described graphene-like carbon nitride membranes, such as g-C₄N₃, g-C₆N₆, and g-C₃N₄ single-layers, can be used as high-performance membranes for water desalination. In addition to having inherent nanopores and extraordinary mechanical properties, the carbon nitride membranes have high water permeability and strong ion rejection (IR) capability. The important point about carbon nitride membranes is that the open or closed state of the pores can be changed by applying tensile stress and creating a positive strain on the membrane. The effect of the imposed pressure, the tensile strain, the ion concentration, and the effective pore size of the membranes are reported. It is demonstrated that, with the applied tensile strain of 12%, the g-C₆N₆ membrane is the best purification membrane, with a water permeability of 54.16 l cm^-2 d^-1 MPa^-1 and the IR of 100%. Its water permeability is one order of magnitude greater than other one-atom-thick membranes.

Mechanical strength of a nanoporous bicrystalline h-BN nanomembrane in a water submerged state

Due to superior water permeability, structural stability, and adsorption capability, h-BN nanosheets are emerging as an efficient membrane for water desalination. In order to cater to the demand for potable water, large size membranes are required to maintain a high desalination rate from water purification systems. These large size membranes usually contain polycrystals with an offset in their mechanical properties from pristine h-BN nanosheets. In this article, molecular dynamics based simulations were performed in conjunction with a hybrid interatomic potential (reactive force field, TIP3P, and Lennard Jones) to simulate the mechanical strength of nanoporous single and bicrystalline h-BN nanosheets under water submerged conditions. The interaction between the atomic configuration of grain boundary atoms and nanopores in the presence of water molecules helps in investigating the viability of defective h-BN nanomembranes for underwater applications. Higher dislocation density enhances the mechanical strength of nanoporous bicrystalline h-BN nanosheets containing twin nanopores, which makes them a better substitute for water submerged applications as compared to the pristine nanosheets. The mechanical strength of nanoporous single crystalline h-BN nanosheets deteriorates with an increase in the number of nanopores, whereas a contrasting trend was observed with bicrystalline h-BN nanosheets.

A novel T-C3N and seawater desalination

A structurally stable stacked multilayer carbonitride is predicted with the aid of ab initio calculations. This carbonitride consists of C3N tetrahedra, and is similar to T-carbon and thus named T-C3N. Its 2-dimensional (2D) monolayer is also carefully investigated in this work. The studies on electronic properties reveal that bulk and 2D T-C3N are insulators with a 5.542 eV indirect band gap and a 5.741 eV direct band gap, respectively. However, the monolayer T-C3N exhibits an excellent uniform porosity. Its 5.50 Å pore size is perfect for water nanofiltration. The adsorption and permeation of water molecules on the monolayer T-C3N are investigated. Its promising potential application in highly efficient nanofiltration membranes for seawater desalination is discussed.

Multiscale Design of Graphyne-Based Materials for High-Performance Separation Membranes

By varying the number of acetylenic linkages connecting aromatic rings, a new family of atomically thin graph-n-yne materials can be designed and synthesized. Generating immense scientific interest due to its structural diversity and excellent physical properties, graph-n-yne has opened new avenues toward numerous promising engineering applications, especially for separation membranes with precise pore sizes. Having these tunable pore sizes in combination with their excellent mechanical strength to withstand high pressures, free-standing graph-n-yne is theoretically posited to be an outstanding membrane material for separating or purifying mixtures of either gases or liquids, rivaling or even dramatically exceeding the capabilities of current, state-of-art separation membranes. Computational modeling and simulations play an integral role in the bottom-up design and characterization of these graph-n-yne materials. Thus, here, the state of the art in modeling α-, β-, γ-, δ-, and 6,6,12-graphyne nanosheets for synthesizing graph-2-yne materials and 3D architectures thereof is discussed. Different synthesis methods are described and a broad overview of computational characterizations of graph-n-yne's electrical, chemical, and thermal properties is provided. Furthermore, a series of in-depth computational studies that delve into the specifics of graph-n-yne's mechanical strength and porosity, which confer superior performance for separation and desalination membranes, are reviewed.

Graphynes for Water Desalination and Gas Separation

Selective transport of mass through membranes, so-called separation, is fundamental to many industrial applications, e.g., water desalination and gas separation. Graphynes, graphene analogs yet containing intrinsic uniformly distributed pores, are excellent candidates for highly permeable and selective membranes owing to their extreme thinness and high porosity. Graphynes exhibit computationally determined separation performance far beyond experimentally measured values of commercial state-of-the-art polyamide membranes; they also offer advantages over other atomically thin membranes like porous graphene in terms of controllability in pore geometry. Here, recent progress in proof-of-concept computational research into various graphynes for water desalination and gas separation is discussed, and their theoretically predicted outstanding permeability and selectivity are highlighted. Challenges associated with the future development of graphyne-based membranes are further analyzed, concentrating on controlled synthesis of graphyne, maintenance of high structural stability to withstand loading pressures, as well asthe demand for accurate computational characterization of separation performance. Finally, possible directions are discussed to align future efforts in order to push graphynes and other 2D material membranes toward practical separation applications.

Two-dimensional materials with intrinsic auxeticity: progress and perspectives

Materials with a negative Poisson's ratio, termed auxetic materials, will expand (contract) in the transverse direction when they are stretched (compressed) longitudinally. They provide exciting prospects for enhancing mechanical properties and a wide range of promising applications. Driven by the current demand for nano-devices with specific functionalities, research studies on two-dimensional auxetic materials with an intrinsic negative Poisson's ratio are intensively simulated. Herein, we summarize the recent efforts and progress in material discovery and property characterization on two-dimensional auxetic materials. We categorize the rich variety of the proposed two-dimensional auxetic materials based on their structures and whether they have been synthesized experimentally. The underlying mechanisms for forming a negative Poisson's ratio as well as the modulation of negative Poisson's ratio are discussed. Finally, we close by assessing the challenges and perspectives faced by future research and development of this compelling class of materials.

Applications of Graphdiyne on Optoelectronic Devices

Graphdiyne (GD) is a novel two-dimensional carbon material composed of sp and sp²-hybridized carbon atoms. This kind of carbon allotrope has attracted more and more attention not only because of the distinctive porous structure but also because of its intriguing electronic properties such as high mobility and conductivity, good field emission properties, and tunable natural band gap. In this review, some representative applications of GD on a variety of optoelectronic devices are described. Starting from the methods of introducing GD into the devices, we analyze the interactions between GD and other device components, summarize the general mechanism of how GD improves performance of the devices, and provide a glimpse into the future of GD at the end.

Graphyne and Its Family: Recent Theoretical Advances

Graphyne and its family are new carbon allotropes in 2D form with both sp and sp² hybridization. Recently, the graphyne with different structures have attracted great attentions from both experimental and theoretical communities, especially because the first successful synthesis of graphdiyne, which is a typical member of the graphyne family. In this review, recent theoretical progresses in the research of the graphyne family are summarized. More specifically, we systematically introduce the structural, mechanical, band, electronic transport, and thermal properties of graphyne and its family, as well as their possible applications, such as gas separation, water desalination and purification, anode material for ion battery, H₂ storage, and catalysis application. Several related theoretical methods are also reviewed. The coexistence of sp and sp² hybridization and the unique atom arrangement of the graphyne family members bring many novel properties and make them promising materials for many potential applications.

Acetylenic linkage dependent electronic and optical behaviour of morphologically distinct ‘-ynes’

We have critically examined the key role of acetylenic linkages (–CC–) in determining the opto-electronic responses of the dynamically stable tetragonal (T) ‘-ynes’ with the help of density functional theory.

Graphynes: indispensable nanoporous architectures in carbon flatland

Theoretical design and experimental realization of novel nanoporous architectures in carbon membranes has been a success story in recent times. Research on graphynes, an interesting class of materials in carbon flatland, has contributed immensely to this success story. Graphyne frameworks possessing sp and sp2 hybridized carbon atoms offer a variety of uniformly distributed nanoporous architectures for applications ranging from water desalination, gas separation, and energy storage to catalysis. Theory has played a pivotal role in research on graphynes, starting from the prediction of various structural forms to the emergence of their remarkable applications. Herein, we attempt to provide an up-to-date account of research on graphynes, highlighting contributions from numerous theoretical investigations that have led to the current status of graphynes as indispensable materials in carbon flatland. Despite unsolved challenges in large-scale synthesis, the future appears bright for graphynes in present theoretical and experimental research scenarios.

Graphene and its derivatives as biomedical materials: future prospects and challenges

Graphene and its derivatives possess some intriguing properties, which generates tremendous interests in various fields, including biomedicine. The biomedical applications of graphene-based nanomaterials have attracted great interests over the last decade, and several groups have started working on this field around the globe. Because of the excellent biocompatibility, solubility and selectivity, graphene and its derivatives have shown great potential as biosensing and bio-imaging materials. Also, due to some unique physico-chemical properties of graphene and its derivatives, such as large surface area, high purity, good bio-functionalizability, easy solubility, high drug loading capacity, capability of easy cell membrane penetration, etc., graphene-based nanomaterials become promising candidates for bio-delivery carriers. Besides, graphene and its derivatives have also shown interesting applications in the fields of cell-culture, cell-growth and tissue engineering. In this article, a comprehensive review on the applications of graphene and its derivatives as biomedical materials has been presented. The unique properties of graphene and its derivatives (such as graphene oxide, reduced graphene oxide, graphane, graphone, graphyne, graphdiyne, fluorographene and their doped versions) have been discussed, followed by discussions on the recent efforts on the applications of graphene and its derivatives in biosensing, bio-imaging, drug delivery and therapy, cell culture, tissue engineering and cell growth. Also, the challenges involved in the use of graphene and its derivatives as biomedical materials are discussed briefly, followed by the future perspectives of the use of graphene-based nanomaterials in bio-applications. The review will provide an outlook to the applications of graphene and its derivatives, and may open up new horizons to inspire broader interests across various disciplines.

Anomalous cation diffusion in salt-doped confined bilayer ice

The diffusive dynamics of aqueous electrolyte solutions in nanoconfined spaces has attracted considerable attention due to their potential applications in desalination, biosensors and supercapacitors. Here we show by molecular dynamics simulations that lithium and sodium ions diffuse at a rate at least an order of magnitude higher than that of water molecules when the ions are trapped in an ice bilayer confined between two parallel plates. This novel picture is in sharp contrast to the prevailing view that the diffusion rate of ions is comparable to or even lower than that of water in both bulk and confined solutions. The predicted high ion mobility stems from frequent lateral hopping of ions along the coordination sites inside the hydrogen-bonding network connecting the two water layers of the ice bilayer. This anomalous diffusion should provide new insights into the physics of confined aqueous electrolytes.

Corrugated graphene layers for sea water desalination using capacitive deionization

The effect of the electric field and surface morphology of corrugated graphene (GE) layers on their capacitive deionization process is studied using molecular dynamics simulations. Deionization performances are evaluated in terms of water flow rate and ion adsorption and explained by analysing the water density distribution, radial distribution function and distribution of the ions inside the GE layers. The simulation results reveal that corrugation of GE layers reduces the water flow rate but largely enhances ion adsorption in comparison to the flat GE layers. Such enhancement is mainly due to the adsorption of ions on the GE layers due to the anchoring effect in the regions with wide interlayer distances. Moreover, it reveals that the entrance configuration of the GE layers also has a significant effect on the performance of deionization. Overall, the results from this study will be helpful in designing effective electrode configurations for capacitive deionization.

Seawater desalination using pillared graphene as a novel nano-membrane in reverse osmosis process: nonequilibrium MD simulation study

Herein, the applicability and efficiency of two types of pillared graphene nanostructures, namely, (6,6)@G and (7,7)@G, were investigated as membranes in reverse osmosis seawater desalination using extensive nonequilibrium molecular dynamics simulations.

Water transport and desalination through double-layer graphyne membranes

Double-layer graphyne sheets with carefully chosen layer spacing are promising candidates as membranes in reverse osmosis desalination.

Fundamental transport mechanisms, fabrication and potential applications of nanoporous atomically thin membranes

Graphene and other two-dimensional materials offer a new approach to controlling mass transport at the nanoscale. These materials can sustain nanoscale pores in their rigid lattices and due to their minimum possible material thickness, high mechanical strength and chemical robustness, they could be used to address persistent challenges in membrane separations. Here we discuss theoretical and experimental developments in the emerging field of nanoporous atomically thin membranes, focusing on the fundamental mechanisms of gas- and liquid-phase transport, membrane fabrication techniques and advances towards practical application. We highlight potential functional characteristics of the membranes and discuss applications where they are expected to offer advantages. Finally, we outline the major scientific questions and technological challenges that need to be addressed to bridge the gap from theoretical simulations and proof-of-concept experiments to real-world applications.

Multiscale molecular simulations on interfacial adsorption and permeation of nanoporous graphynes

Unique interfacial adsorption and permeation on nanoporous graphynes have been revealed by a multiscale simulation strategy.

Superlyophilicity-Facilitated Synthesis Reaction at the Microscale: Ordered Graphdiyne Stripe Arrays

As a new member of carbon allotropes, graphdiyne is a promising material with excellent electronic performance and high elasticity, indicating the possibility of graphdiyne to serve as the building blocks in flexible electronics. However, precise positioning/patterning of graphdiyne is still a challenge for the realization of large-area and flexible organic electronic devices and circuits. Here, the direct in situ synthesis of patterning graphdiyne stripe arrays dominated by the superlyophilic grooved templates is reported, whereas the superlyophilicity of grooved templates plays a key role in allowing continuous mass transport of raw reactants into the microscale spacing. After the completion of cross-coupling reaction procedure, precisely patterned graphdiyne stripes can be generated accordingly. The size of graphdiyne stripe arrays is depending on the silicon substrate size (1 cm × 1.5 cm), and the layer thickness can be manipulated from just several nanometers to hundreds of nanometers by varying the primary concentration of hexaethynylbenzene monomers. As a proof-of-principle demonstration, a stretchable sensor based on the graphdiyne stripe arrays is performed to monitor the human finger motion. It is expected that this wettability-facilitated strategy will provide new insights into the controlled synthesis of graphdiyne toward promising flexible electronics and other optoelectronic applications.

The Dynamics of Water in Porous Two-Dimensional Crystals

Porous two-dimensional crystals offer many promises for water desalination applications. For computer simulation to play a predictive role in this area, however, one needs to have reliable methods for simulating an atomistic system with hydrodynamic currents and interpretative tools to relate microscopic interactions to emergent macroscopic dynamical quantities, such as friction, slip length, and permeability. In this article, we use Gaussian dynamics, a nonequilibrium molecular dynamics method that provides microscopic insights into the interactions that control the flows of both simple liquids and liquid water through atomically small channels. In simulations of aqueous transport, we mimic the effect of changing the membrane chemical composition by adjusting the attractive strength of the van der Waals interactions between the membrane atoms and water. We find that the wetting contact angle, a common measure of a membrane's hydrophobicity, does not predict the permeability of a membrane. Instead, the hydrophobic effect is subtle, with both static and dynamic effects that can both help and hinder water transport through these materials. The competition between the static and dynamical hydrophobicity balances an atomic membrane's tendency to wet against hydrodynamic friction, and determines an optimal contact angle for water passage through nonpolar membranes. To a reasonable approximation, the optimal contact angle depends only on the aspect ratio of the pore. We also find that water molecules pass through the most hydrophobic membranes in a punctuated series of bursts that are separated by long pauses. A continuous-time Markov model of these data provides evidence of a molecular analogue to the clogging transition, a phenomenon observed in driven granular flows.

Investigating the Potential of Single-Walled Aluminosilicate Nanotubes in Water Desalination

Water shortage has become a critical issue. To facilitate the large-scale deployment of reverse-osmosis water desalination to produce fresh water, discovering novel membranes is essential. Here, we computationally demonstrate the great potential of single-walled aluminosilicate nanotubes (AlSiNTs), materials that can be synthesized through scalable methods, in desalination. State-of-the-art molecular dynamics simulations were employed to investigate the desalination performance and structure-performance relationship of AlSiNTs. Free energy profiles, passage time distribution, and water density map were also analyzed to further understand the dependence of transport properties on diameter and water dynamics in the nanotubes. AlSiNTs with an inner diameter of 0.86 nm were found to fully reject NaCl ions while allowing orders of magnitude higher water fluxes compared to currently available reverse osmosis membranes, providing opportunities in water desalination.

Potential Interference of Protein-Protein Interactions by Graphyne

Graphyne has attracted tremendous attention recently due to its many potentially superior properties relative to those of graphene. Although extensive efforts have been devoted to explore the applicability of graphyne as an alternative nanomaterial for state-of-the-art nanotechnology (including biomedical applications), knowledge regarding its possible adverse effects to biological cells is still lacking. Here, using large-scale all-atom molecular dynamics simulations, we investigate the potential toxicity of graphyne by interfering a protein-protein interaction (ppI). We found that graphyne could indeed disrupt the ppIs by cutting through the protein-protein interface and separating the protein complex into noncontacting ones, due to graphyne's dispersive and hydrophobic interaction with the hydrophobic residues residing at the dimer interface. Our results help to elucidate the mechanism of interaction between graphyne and ppI networks within a biological cell and provide insights for its hazard reduction.