Graphene Analogues Research Articles

Molecular dynamics study of the interactions between a hydrophilic polymer brush on graphene and amino acid side chain analogues in water.

We perform all-atom molecular dynamics simulations of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes in aqueous solutions of isobutane, propionamide, and sodium propionate. These solutes are side chain analogues to leucine, glutamine, and glutamic acid, respectively. We compute the Gibbs energy profile of the solute's adsorption to the polymer brush and decompose it into the contributions from the steric repulsion, van der Waals interaction, and Coulomb interaction to reveal the energetic origin of repulsion or attraction of the solute by the polymer brush. The Henry adsorption constant is the amount of adsorption normalized by the concentration in aqueous solution. We examine the dependence of this quantity on the grafting density and chain length. Our results suggest that the concurrent primary and ternary adsorption mechanism may be more important than previously expected when the solute is hydrophobic.

Untapped potential of 2D charge density wave chalcogenides as negative supercapacitor electrode materials.

Two-dimensional (2D) materials have opened new avenues for the fabrication of ultrathin, transparent, and flexible functional devices. However, the conventional inorganic graphene analogues are either semiconductors or insulators with low electronic conductivity, hindering their use as supercapacitor electrode materials, which require high conductivity and large surface area. Recently, 2D charge density wave (CDW) materials, such as 2D chalcogenides, have attracted extensive attention as high performance functional nanomaterials in sensors, energy conversion, and spintronic devices. Herein, TaS2 is investigated as a potential CDW material for supercapacitors. The quantum capacitance (CQ) of the different TaS2 polymorphs (1T, 2H, and 3R) was estimated using density functional theory calculations for different numbers of TaS2 layers and alkali-metal ion (Li, Na and K) intercalants. The results demonstrate the potential of 2H- and 3R-polymorphs as efficient negative electrode materials for supercapacitor devices. The intercalation of K and Na ions in 1T-TaS2 led to an increase in the CQ with the intercalation of Li ions resulting in a decrease in the CQ. In contrast, Li ions were found to be the best intercalant for the 2H-TaS2 phase (highest CQ), while K ion intercalation was the best for the 3R-TaS2 phase. Moreover, increasing the number of layers of the1T-TaS2 resulted in the highest CQ. In contrast, CQ increases upon decreasing the number of layers of 2H-TaS2. Both 1T-MoS2 and 2H-TaS2 can be combined to construct a highly performing supercapacitor device as the positive and negative electrodes, respectively.

Doubling down on borophene electronics.

A double-layer borophene — a boron analogue of the double-layer graphene — has been synthesized, expanding the phase space and potential applications of two-dimensional boron.

Asymmetric janus functionalities induced changes in structural, electronic, optical characteristics of MXenes Ta4C3Tx

MXenes, novel discovered two–dimensional (2D) graphene analogues materials, have attracted continuous and tremendous attention in many application fields because of their excellent physiochemical properties and high performance in multifunctional applications. In present work, the changes of structural, electronic, and optical properties in the functional MXenes Ta4C3Tx are elucidated by using the first principles based on the density functional theory (DFT). It is confirmed that the functional layer (OH, F, O) has a significant effect on the optical properties of Ta4C3. Functional layers lead to the strong anisotropy in dielectric function, especially for asymmetry Janus Ta4C3–HOF. In the infrared region (photon energy <1.6 eV), the monolayer Ta4C3O2 has highest values of absorption coefficients and reflectivity. The transmitting mechanism of Ta4C3T2 are attributed to the thickness variation which affected by functional Janus atoms, further affect the sp2-hybridized of carbon. Symmetric O atoms passivated Ta4C3O2 has considered to be a better photothermal conversion material than pristine Ta4C3 in the infrared region.

ϕ-Phosphorene sheets as adsorbing medium for dichloromethane and tetrachloroethylene molecules – a DFT outlook

Phosphorene, the phosphorus analogue of graphene exhibits various allotropes. One of the next-generation semiconductors is ϕ-phosphorene sheets (ϕ-PNS) with an energy band gap of 1.128 eV. We used ϕ-PNS as a base substrate to adsorb dichloromethane and tetrachloroethylene molecules, the prominent toxic vapours that evolved in textile industries. Based on the adsorption energy, charge transfer, and variation in average energy gap, the adsorption attributes of ϕ-PNS are explored. Besides, owing to dichloromethane and tetrachloroethylene adsorption on ϕ-PNS, the electronic properties get changed. The electron density difference, band structure, and projected density of states upon molecular adsorption of dichloromethane and tetrachloroethylene on ϕ-PNS are studied. The outcome supports that ϕ-PNS can be used as a chemical nanosensor towards dichloromethane and tetrachloroethylene.

Electrocatalytic and stoichiometric reactivity of 2D layered siloxene for high‐energy‐dense lithium–sulfur batteries

AbstractLithium–sulfur batteries (LSBs) have emerged as promising power sources for high‐performance devices such as electric vehicles. However, the poor energy density of LSBs owing to polysulfide shuttling and passivation has limited their further market penetration. To mitigate this challenge, two‐dimensional (2D) siloxene (2DSi), a Si‐based analog of graphene, is utilized as an additive for sulfur cathodes. The 2DSi is fabricated on a large scale by simple solvent extraction of calcium disilicide to form a thin‐layered structure of Si planes functionalized with vertically aligned hydroxyl groups in the 2DSi. The stoichiometric reaction of 2DSi with polysulfides generates a thiosulfate redox mediator, secures the intercalation pathway, and reveals Lewis acidic sites within the siloxene galleries. The 2DSi utilizes the corresponding in‐situ‐formed electrocatalyst, the 2D confinement effect of the layered structure, and the surface affinity based on Lewis acid–base interaction to improve the energy density of 2DSi‐based LSB cells. Combined with the commercial carbon‐based current collector, 2DSi‐based LSB cells achieve a volumetric energy density of 612 Wh Lcell−1 at 1 mA cm−2 with minor degradation of 0.17% per cycle, which rivals those of state‐of‐the‐art LSBs. This study presents a method for the industrial production of high‐energy‐dense LSBs.

Electrophoretically deposited L-cysteine functionalized MoS2@MWCNT nanocomposite platform: a smart approach toward highly sensitive and label-free detection of gentamicin

The exploitation of antibiotics has caused many side effects on the agriculture, environment, and human health. The existing methods have numerous shortcomings in determining gentamicin (GEN), a broad-spectrum antibiotic that causes nephrotoxicity and ototoxicity when found in excess. Here, an immunosensing platform to detect GEN using multiwalled carbon nanotubes (MWCNTs) and molybdenum disulfide (MoS2) nanocomposite, deposited electrophoretically on indium tin oxide (ITO) glass has been developed. A novel 2-D graphene analog MoS2@ MWCNTs nanocomposite was made via a facile and low-cost hydrothermal technique using l-cysteine to achieve remarkable electrochemical properties. Subsequently, a highly sensitive electrochemical immunosensor was fabricated by assembling monoclonal antibodies against gentamicin (anti-GEN) on a MoS2@MWCNTs modified ITO electrode. The hetero-nanostructure formed on the immunosensor surface appeared relatively good conductor for accelerating the electron transfer. GEN was determined on anti-GEN modified electrodes by utilizing the differential pulse voltammetry technique by measuring the difference in current owing to the transfer of electrons directly between the redox species and immunoelectrodes. Under optimal experimental conditions, the fabricated immunosensor had a wide linear detection range of 1 × 10−6–40 μg/mL, a high sensitivity of 13.55 μA (log μg/mL)−1 and a low limit of detection and limit of quantification of 0.039 μg/mL and 0.130 μg/mL, respectively. The developed immunosensor also exhibits high reproducibility, repeatability, and good selectivity against various interferences. This electrochemical immunosensor having MoS2 modified MWCNTs displays the excellent potential for the point-of-care device for GEN testing.

First-Principles Study of Linear and Nonlinear Optical Properties of Multi-Layered Borophene

Anisotropic materials are of great interest due to their unique direction-dependent optical properties. Borophene, the two-dimensional analog of graphene consisting of boron atoms, has attracted immense research interest due to its exciting anisotropic electronic and mechanical properties. Its synthesis in several structural polymorphic configurations has recently been reported. The present work reports the layer-dependent optical absorption and hyperpolarizabilities of the buckled borophene (δ6-borophene). The results, based on density functional theory, show that multilayer borophene is nearly transparent with only a weak absorbance in the visible region, reflecting its anisotropic structural characteristics. The static first-order hyperpolarizability significantly increases with the number of layers, due mainly to interactions among the frontier orbitals in multilayer borophene. Transparency in the visible region combined with enhanced nonlinear optical properties makes the multilayer borophene important for future photonics technologies.

Fe@B6H6 aggregates: from simple building blocks to graphene analogue

We suggest the possibility to build graphene analogue with the planar hexacoordinate wheel-type Fe@B6H6 cluster as the building block through studying theoretically the geometry, stability, and electron structure of its dimer and trimer as well as the dimerization of the two trimers. Employing the dehydrogenation route to polymerization, we can obtain the hexagonal boron sheet that are partly and uniformly filled by Fe atoms in the center of the holes, achieving uniform chemical doping and a very large hexagonal-hole density. Thus, we may offer a novel cluster-assembled material for experimental chemists to construct graphene analogue.

Honeycomb Boron on Al(111): From the Concept of Borophene to the Two-Dimensional Boride.

A great variety of two-dimensional (2D) boron allotropes (borophenes) were extensively studied in the past decade in the quest for graphene-like materials with potential for advanced technological applications. Among them, the 2D honeycomb boron is of specific interest as a structural analogue of graphene. Recently it has been synthesized on the Al(111) substrate; however it remains unknown to what extent does honeycomb boron behave like graphene. Here we elucidate the structural and electronic properties of this unusual 2D material with a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and DFT calculations. We demonstrate that in contrast to graphene on lattice-mismatched metal surfaces, honeycomb boron cannot wiggle like a blanket on Al(111), but rather induces reconstruction of the top metal layer, forming a stoichiometric AlB2 sheet on top of Al. Our conclusions from theoretical modeling are fully supported by X-ray absorption spectra showing strong similarity in the electronic structure of honeycomb boron on Al(111) and thick AlB2 films. On the other hand, a clear separation of the electronic states of the honeycomb boron into π- and σ-subsystems indicates an essentially 2D nature of the electronic system in both one-layer AlB2 and bulk AlB2.

Germanene structure enhancement by adjacent insoluble domains of lead

Growth of Xene, referred to as the analog of graphene made of atoms other than carbon, with higher lattice quality and more intrinsic electronic structures, is an important challenge to the development of two-dimensional (2D) materials. We report an approach using Pb-atom deposition to striped-phase (SP) germanene grown on Ag(111) to trigger it to a quasifreestanding phase (QP). Using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM), we demonstrate that the 2D monatomic Pb layer, instead of being on top, grows side-by-side with QP germanene, not only driving the SP-to-QP transition but further enhancing the lattice order of QP as revealed by the dramatic evolution of LEED-spot shape and uniform STM-imaged array of moir\'e patterns. Originally oriented at 30\ifmmode^\circ\else\textdegree\fi{} to Ag(111), the QP germanene transits first to a narrow distribution of rotations then to two sharp domains at \ifmmode\pm\else\textpm\fi{}3\ifmmode^\circ\else\textdegree\fi{} from 30\ifmmode^\circ\else\textdegree\fi{}, while the monoatomic Pb domains twist from \ifmmode\pm\else\textpm\fi{}4.3\ifmmode^\circ\else\textdegree\fi{} to \ifmmode\pm\else\textpm\fi{}9.5\ifmmode^\circ\else\textdegree\fi{} with respect to Ag(111). The analysis of higher-order coincidence for both layers on Ag(111) is in complete agreement with LEED results and reveals a picture of two insoluble monatomic layers driving each other to a more optimal configuration. Moreover, the corresponding density of states measured by scanning tunneling spectroscopy for quality-enhanced QP germanene exhibits a clear V-shape distribution at the energy \ensuremath{\sim}0.4 eV above Fermi level, indicating the Fermi-Dirac cone, which agrees with our density functional theory calculation.

Modeling the optical properties of twisted bilayer photonic crystals

We demonstrate a photonic analog of twisted bilayer graphene that has ultra-flat photonic bands and exhibits extreme slow-light behavior. Our twisted bilayer photonic device, which has an operating wavelength in the C-band of the telecom window, uses two crystalline silicon photonic crystal slabs separated by a methyl methacrylate tunneling layer. We numerically determine the magic angle using a finite-element method and the corresponding photonic band structure, which exhibits a flat band over the entire Brillouin zone. This flat band causes the group velocity to approach zero and introduces light localization, which enhances the electromagnetic field at the expense of bandwidth. Using our original plane-wave continuum model, we find that the photonic system has a larger band asymmetry. The band structure can easily be engineered by adjusting the device geometry, giving significant freedom in the design of devices. Our work provides a fundamental understanding of the photonic properties of twisted bilayer photonic crystals and opens the door to the nanoscale-based enhancement of nonlinear effects.

Electrical transport through pelletized tablet of silicene-like quasi 2D crystalline silicon

Silicene, the silicon-based 2D analogue of graphene, is predicted to have many exotic properties. However, most of the theoretically predicted phenomena have not yet been experimentally verified. In this work, we have prepared silicene-like, quasi 2D nanostructures via topochemical exfoliation of layered silicide and hot-pressed the dried powders to form bulk pellets. Temperature dependent electrical transport characteristics of pelletized silicene were investigated and found to exhibit evidence of some theoretically predicted features. The current–voltage (I-V) characteristics of the pelletized samples are non-linear, asymmetric about V = 0 and bears clear signature of negative differential resistance (NDR). The heuristic study provides interesting insights into the transport properties of bulk pellets of silicene and opens up the possibility of many applications.

Comparison of group 14 elements in sp3 and sp2 environment by fragment structure energy analysis.

To explore the characteristics of group 14 elements in sp3 and sp2 hybrid environments systematically, the concept of fragment structure energy (FSE) was proposed through ab initio molecular orbital method. A fragment in this study means a building block of molecular structure and the energy of each kind of fragments (FSE) is obtained from the total electronic energy of different size of model compounds by just a simple algebraic method. The model compounds are the hydrogen-terminated diamond and graphene analogs as the typical compounds in the ideal sp3 - and sp2 -environment, respectively. As a result, the sp3 environment was found to be more stable than the sp2 for all the group 14 elements (C-Pb) in the ideal hybrid environment. Furthermore, a mixing effect of carbon and heavier group 14 elements (E=Si, Ge, Sn, and Pb) was investigated by comparing the E/C-alternately mixed- and the pure FSEs.

Eggshell membrane hydrolysate as a multi-functional agent for synthesis of functionalized graphene analogue and its catalytic nanocomposites

This paper demonstrates eggshell membrane protein hydrolysate (ESMH), a critical food waste worldwide, can be harnessed as a multifunctional agent for eco-friendly reduction and functionalization of graphene oxide (GO) based on its diverse and abundant functional groups. The resulting GO reduced and functionalized with ESMH (ESMH-RGO) exhibits an aqueous dispersibility and applicability as a 2-dimensional support for synthesis of catalytic Au nanoparticles (Au NPs) with a high density. The AuNPs synthesized on ESMH-RGO (AuNPs@ESMH-RGO) presents a high catalytic activity for conversion of environmental pollutant (4-nitrophenol) to an industrially useful raw material (4-aminophenol). Those results clearly indicate that ESMH has a strong potential in environmental and materials chemistry.

Carbon nitride of five-membered rings with low optical bandgap for photoelectrochemical biosensing

<h2>Summary</h2> As an analog of graphene, carbon nitrides have drawn increasing attention, ranging from artificial photosynthesis to synthetic organic chemistry. Notably, the most studied polymeric, C₃N₄, and other stoichiometric ones, such as C₃N₅, C₄N₃, and C₃N, are commonly employed repetitive units of six-membered rings. Building blocks of five-membered rings (FMRs) are also fascinating and prevalent from a fundamental point of view, but FMR-based carbon nitrides are scarcely reported. Here, we propose a stable FMR-based C₃N₂ and the kinetic-oriented synthesis method via a pre-stabilization strategy using abundant-available zeolitic imidazolate framework as a precursor. The FMR topological structure and the associated dangling bonds were disclosed in C₃N₂, leading to an interesting p-π conjugation and splitting molecular orbitals, which remarkably narrowed the optical bandgap unusually down to 0.81 eV. The as-obtained C₃N₂ was further successfully applied to real-time, dynamic, and quantitative photoelectrochemical biosensing for practical non-transparent biosamples under near-infrared light irradiation.

On the forbidden graphene\u2019s ZO (out-of-plane optic) phononic band-analog vibrational modes in fullerenes

The study of nanostructures’ vibrational properties is at the core of nanoscience research. They are known to represent a fingerprint of the system as well as to hint the underlying nature of chemical bonds. In this work, we focus on addressing how the vibrational density of states (VDOS) of the carbon fullerene family (Cn: n = 20 → 720 atoms) evolves from the molecular to the bulk material (graphene) behavior using density functional theory. We find that the fullerene’s VDOS smoothly converges to the graphene characteristic line-shape, with the only noticeable discrepancy in the frequency range of the out-of-plane optic (ZO) phonon band. From a comparison of both systems we obtain as main results that: (1) The pentagonal faces in the fullerenes impede the existence of the analog of the high frequency graphene’s ZO phonons, (2) which in the context of phonons could be interpreted as a compression (by 43%) of the ZO phonon band by decreasing its maximum allowed radial-optic vibration frequency. And 3) as a result, the deviation of fullerene’s VDOS relative to graphene may hold important thermodynamical implications, such as larger heat capacities compared to graphene at room-temperature. These results provide insights that can be extrapolated to other nanostructures containing pentagonal rings or pentagonal defects.

Photonic analog of bilayer graphene

Drawing inspiration from bilayer graphene, this paper introduces its photonic analog comprising two stacked graphene-like photonic crystals, that are coupled in the near-field through spoof surface plasmons. Beyond the twist degree of freedom that can radically alter the band structure of the bilayer photonic graphene, the photonic dispersion can be also tailored via the interlayer coupling which exhibits an exponential dependence on the distance between the two photonic crystals. We theoretically, numerically, and experimentally characterize the band structures of AA- and AB-stacked bilayer photonic graphene, as well as for twisted bilayer photonic graphene with even and odd sublattice exchange symmetries. Furthermore, we numerically predict the existence of magic angles in bilayer photonic graphene, which are associated with ultra-flat bands resulted from interlayer hybridization. Finally, we demonstrate that the bilayer photonic graphene at a particular twist angle satisfying even sublattice exchange symmetry is a high-order photonic topological insulator. The proposed bilayer photonic graphene could constitute a useful platform for identifying new quantum materials and inspiring next-generation photonic devices with new degrees of freedom and emerging functionality.

Graphene analogue metal organic framework with superior capacity and rate capability as an anode for lithium ion batteries

Metal–organic frameworks (MOFs), are enormously versatile materials, have vast potential in electrochemical energy storage systems (ESS) owing to their extraordinary surface area, high electronic conductivity, and suitable porosity. Herein, we synthesize porous, 2D graphene analogue conductive metal–organic framework, Ni3(2,3,6,7,10,11-hexaaminotriphenylene)2 (designed as Ni-MOF) nanofilaments (NFs), and utilise it as a competitive active lithium-ion battery (LIB) anode material for the first time. The Ni-MOF NF electrode supply extraordinarily high reversible capacities of ~1,079, 917, 790, and 626 mAh g−1 at specific currents of 0.1, 1, 2, and 5 A g−1, correspondingly. After cycling at diverse specific currents varying from 0.1 to 50 A g−1 for ten cycles each and afterward up to 150 cycles at 0.1 A g−1, the Ni-MOF NF anode supply a capacity of 845 mAh g−1. The full cell of 2D Ni-MOF NFs anode couple with nickel cobalt manganese oxide (NCM622) cathode provide a large energy density of 423 W h kg−1 with highly stable cyclic behaviour. The full cell attained a 431 mAh g−1 of capacity even after 200 cycles at a high specific current of 1 A g−1. These outstanding performances demonstrate the high application potential of 2D Ni-MOF NFs as a next-generation LIB anode.

Quadratic Dirac point and valley topological phases in acoustic analogues of AB-stacked bilayer graphene

The concepts of Dirac point and valley have been extended to phononic crystals, inspired by the development of valleytronic materials. Usually, the valley topological phases are induced by opening the gap of the linear Dirac points. In this work, we investigate the valley topological phases by breaking the quadratic Dirac point in two-dimensional bilayer phononic crystals, as analogues of the AB-stacked bilayer graphene. The acoustic edge states exist at the zigzag boundary of a single valley phase, attributed to the integer valley Chern number. In the domain wall between two distinct valley phases, the numbers of the acoustic edge states double in both the zigzag and armchair boundaries. Our work provides a macroscopic platform to explore the intriguing properties of the bilayer graphene.