Graphene-like Structures Research Articles

Zr3C2O2 MXene as promising candidate for NH3 sensor with high sensitivity and selectivity at room temperature

MXene materials have attracted extensive attention due to their graphene-like structures and promising future applications in many fields. The gas adsorption behavior of NH3, NO, H2S, N2, H2, O2 and CO on Zr3C2O2 are investigated by using first principles simulations. The calculated adsorption energies and charge transfers indicate that Zr3C2O2 could be a promising candidate as room-temperature NH3 gas sensing material due to its high selectivity, superb sensitivity and short recovery time. The factors influencing the gas sensing behavior of MXenes are analyzed. The results show that the gas sensing performance of MXenes can be modulated by altering the interaction between the gas molecules and the substrate through the surface functional group, transition metal, and the biaxial strains. This study could guide the feasibility of using monolayer Zr3C2O2 as NH3 gas sensor in further experimental applications and provide an effective way to tailor MXene series in compliance with various applications.

Interface tweaking of perovskite solar cells with carbon nitride-based 2D materials

Two-dimensional van der Waals layered materials display strong Coulomb interactions, which in turn give rise to large exciton binding energies. Tuning the interface is the basis of devices including optoelectrical, and their delineation is of paramount importance. The developed 2D-carbon nitrides, display graphene-like atomic structures, and the variation in synthetic protocols impact their properties. Engineering the interface with carbon nitride at hole transport layers and perovskite, can eliminate defective charge build-up and suppress the charge carrier recombination rate to induce accelerated photo-induced charge transfer. The fabricated solar cells with L-C3N4 or g-C3N4 interface layers gave an improved performance with boosted open-circuit voltage and fill factor. The developed interface layers avoid the direct contact of NiOx with perovskite, overcoming the possible instability of the active layer via iodide oxidation and deprotonation of cationic amines. The carbon nitride-based 2D materials will serve as an effective interfacial layer for long-term reliability in photovoltaics.

Influence of matrix recrystallization and nanofiller porosity on the interfacial properties of holey graphene-aluminium nanocomposites

Due to their excellent properties, graphene-like 2D structures have been widely used to reinforce aluminium nanocomposites. However, the interfacial behaviour presented by different types of holey graphenes and their reinforcing effect on the mechanical properties of the nanocomposites are still not completely clear. In this work, Molecular Dynamics simulations are used to investigate the interfacial behaviour between five different graphenes and an aluminium matrix (Al-graphene, Al-Phagraphene, Al-haeckelite, Al-N-holey-graphene (hG) and Al-B-hG). Using pull-out loading test, the influence of the 2D nanofillers porosity on the mechanical properties of the nanocomposites is assessed. Additionally, and regarding the aluminium matrix, two different cases were studied: (i) the aluminium matrix was not recrystallized and (ii) the aluminium matrix was melted and then recrystallized. It was found that the introduction of porous graphene improves the interfacial adhesion in the nanocomposites while the pull-out force and interfacial shear strength of the nanocomposites are significantly higher when the aluminium matrix is previously melted and then recrystallized.

Reversing silicon carbide into 1D silicon nanowires and graphene-like structures using a dynamic magnetic flux template.

A dynamic magnetic flux template (DMT) method was developed to reverse silicon carbide (SiC) into amorphous silicon nanowires (a-SiNWs) and graphene-like structures driven by both heating and a dynamic magnetic field. The DMT served as a growth template for silicon nanowires, exhibiting an elongated life-time as an anode in a Li-ion battery.

Nonlinear oscillations, chaotic dynamics, and stability analysis of bilayer graphene-like structures.

In this work, we have investigated the nonlinear oscillations and chaotic dynamics of perturbed bilayer graphene-like structures. The potential energy surface (PES) of bilayer graphene-like geometries is obtained by considering interactions of a co-aligned and counter-aligned arrangement of atoms. We studied the dynamics using the Poincaré surface of section for co-aligned hydrofluorinated graphene (HFG) and counter-aligned hexagonal boron nitride (h-BN) and generalized it for other systems using various choices of interaction parameters. The nature of the oscillations is understood via power spectra and the Lyapunov exponents. We found that the PES is very sensitive to the perturbation for all bilayer graphene-like systems. It is seen that the bilayer HFG system displays chaotic oscillations for strong perturbation, while for the h-BN system, the signature of chaos is found for weak perturbation. We have also generalized the work for perturbed bilayer graphene-like geometries, considering different interlayer interactions and the strength of perturbation. We found a signature of transition from regular to quasiperiodic and finally chaotic oscillations tuned via the strength of the perturbation for these geometries. The nature of the equilibrium points for bilayer graphene-like systems is analyzed via Jacobian stability conditions. We found three stable nodes for co-aligned HFG and counter-aligned h-BN systems for all interaction strengths. Though all other nodes are unstable saddle nodes, the signature of a local bifurcation is also found for weak perturbation.

Laser-scribing fabrication of a disposable electrochemical device for forensic detection of crime facilitating drugs in beverage samples

A portable and disposable laser-scribed graphene (LSG) device was fabricated on polyetherimide (PEI) substrate for electrochemical detection of benzodiazepines (BZ) drugs such as diazepam (DZ) and midazolam (MZ) in commercial beverage samples. Morphological characterizations of the LSG material recorded by scanning electron microscopy (SEM) revealed the porous nature of the proposed electrochemical device, which contributed to the enhancement of the electroactive area. Besides, the structural and electrochemical characterizations performed by Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements revealed that the PEI-LSG material presents highly disordered graphene-like structures and high electron transfer features, respectively. The electrochemical detection of DZ and MZ was carried out by Square Wave Voltammetry (SWV), whose analytical curves exhibited two linear intervals in concentrations ranging from 2.5 μmol L−1 to 25.0 μmol L−1 and from 25.0 μmol L−1 to 100.0 μmol L−1 for both BZ. We obtained limits of detection (LOD) and quantification (LOQ) of 0.66 and 2.18 μmol L−1 for DZ and 0.61 μmol L−1 and 2.01 μmol L−1 for MZ, respectively. The developed sensor was applied to detect DZ and MZ in commercial beverages such as juice, whisky, and sugarcane spirit samples to mimic potential forensic evidence of drug-facilitated crimes. The recoveries ranged from 97.1% to 117.2% for DZ and from 92.2% to 114.3% for MZ. In addition, the proposed method presented high manufacturing reproducibility (relative standard deviation (RSD) = 2.18% for DZ and RSD = 3.82% for MZ, n = 8 sensors) and adequate selectivity, highlighting the potential of PEI-LSG sensor as an excellent alternative method for forensic detection of crime facilitating drugs in commercial beverage samples.

Calcium as an innovative and effective catalyst for the synthesis of graphene-like materials from cellulose

Pyrolysis of lignocellulosic biomass (hard carbon) produces poorly graphitic biochar. In this study, nano-structured biochars were produced from microcrystalline cellulose using calcium as a non-conventional catalyst. Calcium is abundant, environmental-friendly and widely accessible. Graphitization of calcium-impregnated cellulose was carried out at 1800 °C, a temperature below 2000 °C where the graphitization usually occurs. XRD, Raman spectroscopy, high-resolution TEM together with the in-house numerical tool developed enable the quantification of the graphene fringes in the biochars. The non-impregnated cellulose biochar was composed of short and poorly stacked graphene fringes. The impregnation with 2 wt.% of calcium led to the conversion of the initial structure into a well-organized and less defective graphene-like one. The graphene-like structures obtained were composed of tens of stacked graphene fringes with a crystallite size up to 20 nm and an average interlayer spacing equal to 0.345 nm, close to the reference value of standard hexagonal graphite (0.3354 nm). The increase of the calcium concentration did not significantly improve the crystallite sizes of the graphene-like materials but rather drastically improved their rate. Our results propose a mechanism and provide new insights on the synthesis of graphene-like materials from bio-feedstocks using calcium where the literature is focused on transition metals such as iron and nickel among others. The decrease of the graphitization temperature below 2000 °C should lower the production cost as well as the environmental impact of the thermal graphene-like materials synthesis using biomass. This finding should stimulate further research in the field and broaden the application perspectives.

First-principles investigation of interaction between the atomic oxygen species and carbon nanostructures

• The following trends in the value of adsorption energies of triplet oxygen atoms on the carbon nanostructures were identified: diamond-like structures (sp 3 ) < graphene-like structures (sp 2 ) < fullerenes & nanotubes (sp 2 , pentagons, high curvature). • For the graphene flake and fullerene structures there are common precursors for carbon desorption in the form of CO/CO 2 molecules: (1) ether-ether-epoxy precursor and (2) epoxy-ether-epoxy. • Etching of sp 3 hybridized carbon structures can proceed faster than etching of sp 2 structures. • For graphene structure, unzipping process is more favorable than reduction process at lower temperatures. In this work we perform a systematic theoretical study of oxidation process of different carbon nanomaterials by atomic oxygen. In order to understand the atomistic mechanism of interaction between atomic oxygen and carbon nanostructures and to explain experimental results on their oxygen treatment, first-principles calculations were performed. Influence of spin state of the atomic oxygen on its interaction with different carbon nanostructures (finite size graphene flake, carbon nanotube, fullerene, diamondoid) was investigated. We found that the structure and stability of the adsorption complexes are determined by the oxygen spin state and depend on the carbon nanostructure morphology and hybridization. The atomistic mechanisms of chemical transformations driven by high local oxygen coverage, such as CO/CO 2 desorption and graphene unzipping, were investigated. Calculated barriers of CO 2 desorption allow to explain experimental data on thermal reduction of the oxidized carbon structures. In case of graphene, competition between channels resulting in CO 2 desorption and plane unzipping was observed. We found that for the temperatures ~400 K and lower unzipping process is favorable, since CO 2 desorption precursor formation proceeds through higher activation barrier (1.3 eV) and requires temperatures above 450 K.

Direct laser-assisted fabrication of turbostratic graphene electrodes: Comparing symmetric and zinc-ion hybrid supercapacitors

Lasers offer a versatile means towards the single-step, binder-free synthesis of three-dimensional graphene-like porous networks, providing an enticing alternative over energy intensive, multi-step traditional synthesis protocols creating unwanted waste streams. Here, we report on a novel laser-assisted method for the one-step preparation of the electrode component, not solely the active material, based on the simultaneous synthesis of turbostratic graphene-like structures on a carbon precursor and its transfer/deposition on the selected current collector. The performance of the graphene-based electrodes was electrochemically evaluated for both electric double layer capacitor (EDLC) and zinc-ion hybrid capacitor (ZIC) configurations. The performance of the EDLC devices was found to be superior to that of the current state-of-the-art devices prepared by laser-grown graphene. The ZIC exhibited higher areal energy density than the symmetric devices by one order of magnitude. The devices showed very low equivalent series resistance, good rate performance and high long-term cycling stability. Notably, the EDLC with the KOH electrolyte demonstrated an unexpected ∼20% increase in capacitance during the stability test of 10,000 cycles. This result was attributed to the substantial increase of oxygen content of the graphene electrodes, which act as sites for redox activity.

WAYS OF CHANGING THE STRUCTURAL-MORPHOLOGICAL, PHYSICO-CHEMICAL AND ELECT­RICAL PROPERTIES OF GRAPHENES

A literature analysis of sources on synthesis methods and their influence on the structural-morphological, physico-chemical, and electrochemical properties of graphene and graphene-like structures was carried out. It was established that these properties have a clear dependence on the synthesis method, starting materials, and the composition of the synthesis medium.&#x0D; The main ways of changing graphene's structural-morphological, physico-chemical and electrical properties are changes in the synthesis method and conditions that affect the formation of σ-bonds and π-bonds. The presence of these bonds regulates the number of graphene layers and the formation of van der Waals interactions between them, as well as the formation of edge structural defects responsible for electrokinetic and catalytic properties. Changing the gas medium to a liquid one greatly simplifies the synthesis of graphene. Still, in the case of a liquid nitrogen medium, simultaneously with a 2-dimensional structure, it is possible to form 3-dimensional particles up to tens of nanometers in size. Aqueous medium and plasma-arc synthesis methods are the most attractive for obtaining materials with electron-donor conductivity, which have attractive electrochemical and catalytic properties for use in chemical current sources and fuel cells. Using an aqueous environment requires mandatory further heat treatment at temperatures above 250 0C to se­parate chemisorbed water from the structure, which complicates the synthesis procedure. The advantage of the plasma-arc method for the synthesis of graphene and other carbon nanostructures is its ability to shorten the stages of the synthesis of graphene, the possibility of modifying them directly during the synthesis process by changing the environment, easy management, and obtaining a clean final pro­duct. In the modern practice, this method is limited to obtaining coatings on a solid carrier.

Two-dimensional anisotropic Dirac materials PtN4C2 and Pt2N8C6 with quantum spin and valley Hall effects

We propose two different two-dimensional topological Dirac materials, planar ${\mathrm{PtN}}_{4}{\mathrm{C}}_{2}$ and ${\mathrm{Pt}}_{2}{\mathrm{N}}_{8}{\mathrm{C}}_{6}$, which exhibit graphenelike electronic structures with linearly dispersive Dirac-cone states exactly at the Fermi level. Moreover, the Dirac cone is anisotropic, resulting in anisotropic Fermi velocities and making it possible to realize orientation-dependent quantum devices. Using first-principles electronic structure calculations, we have systemically studied the structural, electronic, and topological properties. We find that spin-orbit coupling opens a sizable topological band gap so that the materials can be classified as quantum spin Hall insulators as well as quantum valley Hall insulators. Helical edge states that reside in the insulating band gap connecting the bulk conduction and valence bands are observed. Our work not only expands the Dirac-cone material family, but also provides another avenue to search for more two-dimensional topological quantum spin and valley Hall insulators.

Synthesis of Nitrogen-Doped Wood-Based Carbon Materials and Their Application for Oxygen Reduction

Recently, great attention has been focused on biomass-derived electrocatalysts for the oxygen reduction reaction (ORR). In the present study, the wood-derived nitrogen-doped carbon nanomaterials with graphene-like structures have been synthesized from wood biomass using a chemical activation method with NaOH to achieve a high specific surface area (SSA). Then, the activated carbon materials have been doped with nitrogen using dicyandiamide (DCDA) as a cheaper nitrogen precursor. The synthesized catalyst's morphology, structure, and composition have been characterized using TEM, XPS, Raman Spectroscopy, and ICP-OES. The activity of the prepared catalysts was evaluated for ORR in the 0.1 M KOH solution employing the rotating disk electrode (RDE) method. The nitrogen-doped carbon materials have been shown a high electrocatalytic activity and stability for the oxygen reduction reaction. The number of electrons transferred per O2 molecule is close to 4.0.AcknowledgmentThis project has received funding under the Baltic Research Programme project “Sustainably produced nanomaterials for energy applications (SuNaMa)” (No. S-BMT-21-12, LT08-2-LMT-K-01-055).

Perspective on plexciton based on transition metal dichalcogenides

Two-dimensional transition metal dichalcogenides (TMDCs) have outstanding physical advantages over graphene-like non-zero bandgap structures. It indicates that the monolayer TMDC material has significant light–material interaction, and it also implies that TMDCs have various application prospects in optoelectronic devices. The coupling of excitons and metal surface plasmons in monolayer TMDCs would affect the optical and electrical properties of the TMDC surface, and we revealed the improvement of surface catalytic reaction efficiency by plexcitons (coupling of excitons and plasmons) supported by recent experiments and theoretical reports. We also review the stress regulation on charge transfer excitons based on van der Waals (vdW) heterostructures composed of TMDCs, the special characteristics, and potential applications of coupling charge-transfer excitons with Ag plasmons in vdW and lateral heterostructures.

Melanin is a plenteous bioactive phenolic compound in date fruits (Phoenix dactylifera L.)

Date palm fruits (Phoenix dactylifera L.) were found to contain high levels of allomelanin (1.2–5.1%). The melanin is localized in the tanniferous cells between the inner and outer mesocarp tissues of the fruit. The melanin, extracted with 2 M sodium hydroxide, consisted of amorphous graphene-like granular structures of irregular shape and variable size. The date fruit melanin mainly comprises carbon (64.6%) and oxygen (30.6) but no nitrogen, and was thermally stable. It has radical scavenging (63.6–75.1 IC50, µg/mL), antimicrobial (250–1000 µg/mL), hypoglycemic (51.8–58.2%), and angiotensin-converting-enzyme inhibitory (65.8%) effects. The high level of melanin in date fruits highlights the importance of investigating its dietary intake and its impact on nutrition. This study also suggests that date fruit melanin can be a functional ingredient in foods, food packages, pharmaceuticals, and cosmetics.

Laser-assisted transformation of a phenol-based resin to high quality graphene-like powder for supercapacitor applications

Synthesis of high-quality graphene-like structures by means of an eco-friendly, cost effective, one-step and scalable method is highly sought after. Some of these traits have been successfully addressed in recent studies employing laser irradiation in the synthesis process, however, reports on laser-assisted high-quality graphene growth overwhelmingly rely on the rather costly polyimide precursor. In this study, we report laser-mediated synthesis of high-quality graphene powder, originating from a phenol-based resin. Raman spectroscopy and X-ray diffraction findings suggest turbostratic, i.e., rotationally faulted, stacking of graphene layers, while the porous structure of the produced material is revealed by scanning electron microscopy. X-ray photoelectron spectroscopy was employed to probe the chemical composition of the materials before and after irradiation, and revealed the high C/O ratio value (22.6) in the irradiated powder. Moreover, the potential of these graphene-like structures in energy storage applications are investigated in aqueous supercapacitors, using both three- and two- electrode configurations. The excellent conductivity is validated from both sheet resistance measurements 40Ohmsq-1 and the very low ohmic losses during galvanostatic charge discharge measurements. The two-electrode device showed a capacitance of 17.2 Fg−1 at 10 mVs−1, a fairly good rate performance 67% up to 200 mVs−1 and excellent cycling stability (87.2% after 20,000 cycles).

Real wastewater micropollutant removal by wood waste biomass biochars: A mechanistic interpretation related to various biochar physico-chemical properties

Emerging organic micropollutants (OMPs) are ubiquitous in waterbodies and not fully eliminated by wastewater treatment plants (WWTP). A proposed WWTP upgrade includes OMPs sorption by biochar rather than activated carbon (AC). Activated biochar (AB) and non-activated biochar (NAB) sorption performance towards 4 target OMPs (benzotriazole, sulfamethoxazole, carbamazepine, diclofenac) were evaluated in real-wastewater. Sorption processes are discussed in light of sorption mechanisms that depend both on OMP and on biochar physico-chemical properties. AB and AC have similar average sorption efficiency (45%), while NABs are much less efficient (<19%). OMPs sorption significantly correlates to SSA, inversely to H/C (indicating hydrophobic interaction with graphene-like structures) and to CEC or ash content (indicating H-bond or ternary surface complexation sorption mechanisms). This highlights the need to mix AB sources with different physico-chemical characteristics to sorb a large OMP spectrum within WWTPs. Production and use of ABs alleviate the negative environmental impact of ACs.

Zeolite templated carbon from Beta replica as metal-free electrocatalyst for CO2 reduction

Zeolite Templated Carbons (ZTCs) are a class of materials that feature the textural properties of the template zeolites and the high conductivity of graphene-like structures. These characteristics make ZTCs a valuable candidate for CO2 catalytic reduction. We report here for the first time that metal-free ZTCs obtained from Beta zeolite are a novel valuable energy material for the reduction of CO2 to formic acid, about 10 times better than a reference reduced graphene oxide catalyst. In addition, it is evidenced that the pristine ZTC contains a large amount of oxygen, an aspect largely underestimated in literature. A specific method to reduce this oxygen content was developed, that coupled to an in-depth characterization by multiple techniques of these materials, allows to understand the nature of the oxygen functionalities on ZTCs surface. Moreover, it was evidenced that the change of oxygenated species by combined thermal and NaBH4 treatment of ZTCs affects the catalytic behavior, leading to a remarkable increase in the performances compared to the pristine one. The comparison of the performances and characteristics of two ZTCs, obtained by different BEA nanostructures, allow to correlate better the modification of the type of oxygen species present in ZTCs to the catalytic behavior. The results open new perspectives for the catalytic application of deoxygenated ZTCs.

Erratum: Saddle point anomaly of Landau levels in graphenelike structures [Phys. Rev. B 104 , 035419 (2021)

Erratum: Saddle point anomaly of Landau levels in graphenelike structures [Phys. Rev. B <b>104</b> , 035419 (2021)

Superconducting LaP2H2 with graphenelike phosphorus layers

Novel structural building blocks in compounds could induce interesting physical and chemical properties. Although phosphorus tends to form very different motifs, the existence of lone pair electrons has always prevented the formation of graphenelike structures. Here, the application of first-principles swarm structural calculations has allowed us to predict the stability of pressure-induced hexagonal LaP2H2 containing graphenelike phosphorus, which derives from the trigonal bipyramid configuration of P atoms regulated by symmetric hydrogen bonds. LaP2 in LaP2H2 has the same configuration as MgB2, and P and H atoms form a three-dimensional framework as H3S. Interestingly, LaP2H2 shows a superconductivity dominated by the graphenelike phosphorus layer and its coupling with La atoms. On the other hand, LaP2H2 is not only superconducting at a lower pressure than the H-rich LaPH6, but it also shows a superconducting transition temperature three times higher. Our work provides an example which extends the landscape of conventional superconductors at lower pressures.

To the model description of electronic spectrum for the graphene-like Janus structures

Model of C-AB-D Janus structure as the compound formed by the interacting through atoms A and B dimers A-C and B-D, where A and B atoms are in the sites of two-dimensional hexagonal lattice and C and D atoms are on the opposite sides from AB list is proposed. In the scope of tight-binding theory and Green's function method general equation for the dispersion low is obtained. The particular cases of C-AA-D and A-AB-B compounds are considered and analytical expressions for their electronic spectra is fulfilled. The effect of the external mechanical deformation on the band parameters including effective masses is examined. Problem of the magnetic states in Janus compounds is discussed. Keywords: model of interacting dimers, electronic spectrum, effect of deformation, magnetic states.