Molecular sieving through a graphene nanopore： non-equilibrium molecular dynamics simulation

Two-dimensional graphene nanopores have shown great promise as ultra-permeable molecular sieves based on their size-sieving effects. We design a nitrogen/hydrogen modified graphene nanopore and conduct a transient non-equilibrium molecular dynamics simulation on its molecular sieving effects. The distinct time-varying molecular crossing numbers show that this special nanopore can efficiently sieve CO_2 and H_2S molecules from CH_4 molecules with high selectivity. By analyzing the molecular structure and pore functionalization-related molecular orientation and permeable zone in the nanopore, density distribution in the molecular adsorption layer on the graphene surface, as well as other features, the molecular sieving mechanisms of graphene nanopores are revealed. Finally, several implications on the design of highly-efficient graphene nanopores, especially for determining the porosity and chemical functionalization, as gas separation membranes are summarized based on the identified phenomena and mechanisms.

Graphene nanopores toward DNA sequencing： a review of experimental aspects

Nanopores for DNA sequencing have drawn much attention due to their potentials to achieve amplification-free, low-cost, and high-throughput analysis of nuclei acids. The material configuration and fabrication of the nanopore has become one important consideration in the nanopore based DNA sequencing research. Among various materials, the newly emerged graphene has brought more opportunities to the development of sequencing technology because of its unique structures and properties. This review mainly focuses on the experimental aspects of graphene nanopore research including the nanopore fabrication methods and processes. Meanwhile, the challenges in the present graphene nanopore research including hydrophobicity, translocation velocity and noise are also addressed and discussed.

Molecular insights on Ca^(2+)/Na+separation via graphene-based nanopores:The role of electrostatic interactions to ionic dehydration

Ca^(2+)/Na+separation is a common problem in industrial applications,biological and medical fields.However,Ca^(2+)and Na+have similar ionic radii and hydration radii,thus Ca^(2+)/Na+separation is challenging.Inspired by biological channels,group modification is one of the effective methods to improve the separation performance.In this work,molecular dynamics simulations were performed to investigate the effects of different functional groups(COO,NH3+)on the separation performance of Ca^(2+)and Na+through graphene nanopores under an electric field.The pristine graphene nanopore was used for comparison.Results showed that three types of nanopores preferred Ca^(2+)to Na+,and Ca^(2+)/Na+selectivity followed the order of GE-COO(4.06)>GE(1.85)>GE-NH3+(1.63).Detailed analysis of ionic hydration microstructure shows that different nanopores result in different hydration factors for the second hydration layer of Ca^(2+)and the first layer of Na+.Such different hydration factors corresponding to the dehydration ability can effectively evaluate the separation performance.In addition,the breaking of hydrogen bonds between water molecules due to electrostatic effects can directly affect the dehydration ability.Therefore,the electrostatic effect generated by group modification will affect the ionic hydration microstructure,thus reflecting the differences in dehydration ability.This in turn affects the permeable and separation performance of cations.The results of this work provide perceptive guidelines for the application of graphene-based membranes in ion separation.

Controlled fabrication of freestanding monolayer SiC by electron irradiation

The design and preparation of novel quantum materials with atomic precision are crucial for exploring new physics and for device applications.Electron irradiation has been demonstrated as an effective method for preparing novel quantum materials and quantum structures that could be challenging to obtain otherwise.It features the advantages of precise control over the patterning of such new materials and their integration with other materials with different functionalities.Here,we present a new strategy for fabricating freestanding monolayer SiC within nanopores of a graphene membrane.By regulating the energy of the incident electron beam and the in-situ heating temperature in a scanning transmission electron microscope(STEM),we can effectively control the patterning of nanopores and subsequent growth of monolayer SiC within the graphene lattice.The resultant SiC monolayers seamlessly connect with the graphene lattice,forming a planar structure distinct by a wide direct bandgap.Our in-situ STEM observations further uncover that the growth of monolayer SiC within the graphene nanopore is driven by a combination of bond rotation and atom extrusion,providing new insights into the atom-by-atom self-assembly of freestanding two-dimensional(2D)monolayers.

Effect of graphene functionalizing on the performance of NiMo/graphene in HDS and HDN reactions

In this research,to remove sulfur and nitrogen compounds from heavy naphtha,various nanocatalysts were prepared through supporting NiMo over nanoporous graphene and evaluated in hydrodesulfurization and hydrodenitrogenation reactions.The nanoporous graphene was initially functionalized in order to facilitate the metal being loaded on it.Three different methods were used to functionalize the nanoporous graphene.The NiMo/nanoporous graphene nanocatalysts were characterized by field emission scanning electron microscopy,Fourier transform infrared spectroscopy,X-ray diffraction,inductively coupled plasma optical emission spectrometry,temperature-programmed reduction,nitrogen adsorption-desorption isotherms and transmission electron microscopy techniques.Catalyst performance was evaluated in terms of conversions of sulfur,mercaptans(R-SH)and nitrogen compounds.It was found that the functionalized nanoporous graphene support could significantly enhance the catalytic performance in comparison with the industrial NiMo/alumina catalyst.Among the functionalized graphene supports,amine-functionalized graphene exhibited the best results.By using NiMo supported over amine-functionalized graphene,the conversions of total sulfur and R-SH reached 97.8%and 98.1%,respectively.

Engineering graphene for high-performance supercapacitors: Enabling role of colloidal chemistry

The high electrical conductivity and high specific surface area of graphene are traditionally regarded as the most intriguing features for its promise as the electrode material for supercapacitors. In this perspective, we highlight that from the engineering point of view, the unique colloidal chemistry of chemically functionalized graphene is the key property that has made graphene stand out as a promising nanoscale building block for constructing unique nanoporous electrodes for capacitive energy storage, We present several examples to demonstrate bow the non-covalent colloidal forces between graphene sheets can be harnessed to engineer the nanostructure of graphene-based bulk electrodes for supercapacitors based on both the electrical double layer storage and the redox reaction or pseudo-capacitance mechanisms. The colloidal engineering strategy can be extended to enable other nanomaterials to achieve high energy storage performance.

Template-directed fabrication of 3D graphene-based composite and their electrochemical energy-related applications

Graphene shows great potentials in electrochemical energy-related areas.To enhance its properties and corresponding electrochemical performance,recently,three-dimensional(3D)graphene-based materials especially monolithic porous graphene with encapsulated functional nanomaterials have arisen much research interest for electrochemical catalysis,lithium ion batteries(LIBs),lithium–sulfur batteries,supercapacitors,etc.With the enhanced structure properties such as interconnected graphene network,high volume-specific surface area and electronic conductivity,3D monolithic graphene is more suitable for the fabrication of composite electrode materials in real devices.In this article,we discuss recent development in fabricating monolithic 3D graphene and their composites using template-directed methods and their applications in electrochemical energy-related areas.

Recent advances in nanoporous graphene membrane for gas separation and water purification

Graphene is a one-atom-thick sheet of graphite comprising sp2-hybridized carbon atoms arranged in the hexagonal honeycomb lattices. By removing the honeycomb lattices and forming nanopores with specific geometry and size, nanoporous graphene has been demonstrated as a very high-efficiency separation membrane, due to the ultrafast molecular permeation rate for its one-atom thickness. This review focuses on the recent advances in nanoporous graphene membrane for the applications of gas separation and water purification, with a major emphasis on the molecular permeation mechanisms and the advanced fabrication methods of this state-of-the-art membrane. We highlight the advanced theoretical and experimental works and discuss the gas/water molecular transport mechanisms through the graphene nanopores accompanied with theoretical models. In addition, we summarize some representative membrane fabrication methods, covering the graphene transfer to porous substrates and the pore generation. We anticipate that this review can provide a platform for understanding the current challenges to make the conceptual membrane a reality and attracting more and more attentions from scientists and engineers.

Ion separation and water purification by applying external electric field on porous graphene membrane

Using molecular dynamics （MD） simulations, a porous graphene membrane was exposed to external electric fields to separate positive and negative ions from salt-water and to produce fresh water. It was observed that, by increasing the strength of the applied electric field, ion separation improved noticeably. In addition, to obtain fresh water, the designed system included two graphene membranes, which are exposed to two external electric fields in opposite directions. Ion rejection was found to be greater than 93% for the electric field of 10 mV/A and higher. This atomic-level simulation increases the understanding of electric field effects on desalination using multilayer graphene membranes and can be helpful in designing more efficient membranes.

Microelectrode glucose biosensor based on nanoporous platinum/graphene oxide nanostructure for rapid glucose detection of tomato and cucumber fruits

A microelectrode glucose biosensor based on a three-dimensional hybrid nanoporous platinum/graphene oxide nanostructure was developed for rapid glucose detection of tomato and cucumber fruits.The nanostructure was fabricated by a two-step modification method on a microelectrode for loading a larger amount of glucose oxidase.The nanoporous structure was prepared on the surface of the platinum microelectrode by electrochemical etching,and then graphene oxide was deposited on the prepared nanoporous electrode by electrochemical deposition.The nanoporous platinum/graphene oxide nanostructure had the advantage of improving the effective surface area of the electrode and the loading quantity of glucose oxidase.As a result,the biosensor achieved a wide range of 0.1-20.0 mmol/L in glucose detection,which had the ability to accurately detect the glucose content.It was found that the three-dimensional hybrid nanostructure on the electrode surface realized the rapid direct electrochemistry of glucose oxidase.Therefore,the biosensor achieved high glucose detection sensitivity 11.64μA·L/(mmol.cm^(2)),low detection limit(13μmol/L)and rapid response time(reaching 95%steady-state response within 3 s),when calibrating in glucose standard solution.In agricultural application,the as-prepared biosensor was employed to detect the glucose concentration of tomato and cucumber samples.The results showed that the relative deviation of this method was less than 5%when compared with that of high-performance liquid chromatography,implying high accuracy of the presented biosensor in glucose detection in plants.

Preparation of Nanoporous Carbon/Graphene Composites and Its Application in Direct Methanol Fuel Cell

Nanoporous carbon/graphene composites （NCGC） are synthesized via one-step hydrothermal approach com- bining carbonization, where phenol and formaldehyde are used as carbon sources and triblock copolymers F 127 as template. Transmission electron microscopy （TEM） and nitrogen adsorption measurements show that the synthe- sized NCGC samples possess high surface area over 400 m2·g-1 and mesoporous structures with interconnected pores. The electrochemical studies demonstrate that Pt catalyst with NCGC as support exhibits better eletrocatalytic activity for methanol oxidation as compared to the catalyst taking widely-used VulcanXC-72 as support. In addition, the potential formation mechanism of NCGC is discussed.

Recent progress on three-dimensional nanoarchitecture anode materials for lithium/sodium storage

High-performance batteries with high density and low cost are needed for the development of largescale energy storage fields such as electric vehicles and renewable energy systems.The anode with threedimensional(3D)nanoarchitecture is one of the most attractive candidates for high-performance lithiumion batteries(LIBs)and sodium-ion batteries(SIBs)due to its efficient electron/ion transport and high active material mass loading.Although some important breakthroughs have been made in 3D nanoarchitecture anode materials,more improvements are still needed for high cycling stability and high energy density.Herein,the latest research progress of 3D nanoarchitecture anode materials for LIBs and SIBs is reviewed,including nanoporous metal,nanoporous graphene,and their derived foams.Specifically,the storage properties of Li/Na ions,the kinetics of ion/electron transport,and specific chemical interactions are discussed based on the structure design.In addition,the research strategies and structural characteristics of 3D nanoarchitecture anode materials are summarized,providing a reference for the further development of LIBs and SIBs.Meanwhile,the future research directions of LIBs and SIBs have also prospected.