Graphene-like Materials Research Articles

The low-cost g-C3N4/CuS electrode for QDSCs prepared with low-temperature solid-state method

The graphene-like carbon nitride (graphitic C3N4, g-C3N4) and CuS composite materials were prepared via a facile low-temperature solid-state method as the eco-friendly and low-cost counter electrodes (CEs) for quantum dot sensitized solar cells (QDSCs). Compared with the former complex processing, low-temperature solid-state method is simple and easy towards mass production. Based on XRD, SEM, EDX and TEM results, it was confirmed that g-C3N4 constructed a transport network for electron transfer, while distributed CuS played a catalytic role to contact with polysulfide electrolyte in reduction reaction at CE/electrolyte interface. Electrochemical Impedance Spectroscopy, Mott-Schottky and CyclicVoltammetry tests were performed for the electrochemical properties of composite counter electrodes with various C3N4/CuS ratio. The CE sample (CN/10CuS) with appropriate ratio possessed lower interface impedance, more catalytic active sites and better stability, and power conversion efficiency (PCE) of QDSCs with CN/10CuS CEs reached 5.05% under one sun, which is comparable to g-C3N4/CuS CE prepared with other routes in the same conditions.

Effect of pH and Concentration of Dopamine Solution on the Deposited Polydopamine Film and the Prepared Graphene-like Material

In this study, according to the acquired polydopamine deposition rates, polydopamine films with equal thickness were prepared under different conditions on SiO2 substrates. Subsequently, we investigated the influence of dopamine solution pH and concentration on the formation of surface aggregates of the deposited polydopamine films. Assumptions were made to explain how pH and concentration execute their effects. Based on the optimized parameters, a continuous and smooth polydopamine film with a thickness of about 14 nm and a roughness of 1.76 nm was fabricated on a silicon dioxide substrate, through the deposition for 20 minutes in a dopamine solution with a concentration of 1.5 mg/mL and a pH of 8.2. The prepared polydopamine film was then employed as a precursor and subjected to a high-temperature process for the carbonization and graphitization of the film. Raman spectroscopy analysis indicated that the resulting graphene-like film had fewer structural defects in comparison with previous works and the results of XPS indicated that most of the carbon atoms were bound into the cross-linked honeycomb lattice structure. The prepared graphene-like material also exhibited high electrical conductivity and satisfying mechanical elasticity.

Synthesis of graphene-like material derived from biomass from agricultural waste and its application in Cu (II) removal

Synthesis of graphene-like material derived from biomass from agricultural waste and its application in Cu (II) removal

CO2 Capture and Gas Storage Capacities Enhancement of HKUST-1 by Hybridization with Functionalized Graphene-like Materials.

The role of graphene related material (GRM) functionalization on the structural and adsorption properties of MOF-based hybrids was deepened by exploring the use of three GRMs obtained from the chemical demolition of a nanostructured carbon black. Oxidized graphene-like (GL-ox), hydrazine reduced graphene-like (GL), and amine-grafted graphene-like (GL-NH2) materials have been used for the preparation of Cu-HKUST-1 based hybrids. After a full structural characterization, the hybrid materials underwent many adsorption-desorption cycles to evaluate their capacities to capture CO2 and store CH4 at high pressure. All the MOF-based samples showed very high specific surface area (SSA) values and total pore volumes, but different pore size distributions attributed to the instauration of interactions between the MOF precursors and the specific functional groups on the GRM surface during MOF growth. All the samples showed a good affinity toward both gases (CO2 and CH4) and a comparable structural stability and integrity (possible aging was excluded). The trend of the maximum storage capacity values of the four MOF samples toward CO2 and CH4 was HKUST-1/GL-NH2 > HKUST-1 > HKUST-1/GL-ox > HKUST-1/GL. Overall, the measured CO2 and CH4 uptakes were in line with or higher than those already reported in the open literature for Cu-HKUST-1 based hybrids evaluated in similar conditions.

Properties and Characterization Techniques of Graphene Modified Asphalt Binders.

Graphene is a carbon-based nanomaterial used in various industries to improve the performance of hundreds of materials. For instance, graphene-like materials have been employed as asphalt binder modifying agents in pavement engineering. In the literature, it has been reported that (in comparison to an unmodified binder) the Graphene Modified Asphalt Binders (GMABs) exhibit an enhanced performance grade, a lower thermal susceptibility, a higher fatigue life, and a decreased accumulation of permanent deformations. Nonetheless, although GMABs stand out significantly from traditional alternatives, there is still no consensus on their behavior regarding chemical, rheological, microstructural, morphological, thermogravimetric, and surface topography properties. Therefore, this research conducted a literature review on the properties and advanced characterization techniques of GMABs. Thus, the laboratory protocols covered by this manuscript are atomic force microscopy, differential scanning calorimetry, dynamic shear rheometer, elemental analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Consequently, the main contribution of this investigation to the state-of-the-art is the identification of the prominent trends and gaps in the current state of knowledge.

Preparation of TiO2/WO3-corn straw based graphene-like composite and its low light catalytic hydrogen production performance and mechanism

In this paper, TiO2/WO3 corn straw graphene-like photocatalyst composite suitable for low light catalytic hydrogen production is prepared by one pot thermal synthesis method. The morphology and structural characteristics of TiO2/WO3 corn straw graphene-like compounds are analyzed. Based on the photoelectric characteristics and density functional theory simulation results, the energy band of TiO2/WO3 corn straw graphene-like composite material is reduced to 2.32 eV compared with pure TiO2 and WO3. The transfer rate of photogenerated carriers is accelerated, and the p-n heterostructure between TiO2 and WO3 interacts with graphene to promote the transfer of photogenerated electrons. Moreover, some photogenerated electrons reside on the graphene surface. Consequently, under low light irradiation, the efficiency of photogenerated electron transfer is increased and the hydrogen production performance is improved. The photocatalytic experiment showed that the hydrogen production rate of TiO2/WO3 corn straw graphene-like composite under low light irradiation is only 10% lower than that under visible light irradiation. Furthermore, the addition of graphene increases the specific surface area of the composite photocatalyst, which makes the composite material more adaptable to low light and improves its feasibility for industrial mass production.

Conductive Additives for Improving the Rate Capability of Cathode Materials in Secondary Lithium Batteries

Conductive additive, one of the most important components of a battery, is an indispensable key material in the high-current charging and discharging processes of lithium-ion batteries. The most fundamental reason for adding appropriate conductive additives in the electrode is to improve the poor conductive performance of the electrode-active material, reduce the internal resistance and polarization of the electrode, and improve the comprehensive performance of the battery. Herein, a graphene-like material with a unique two-dimensional morphology was proposed, as obtained by an efficient one-step electrochemical synthesis, which can provide a flexible plane-to-point conducting network to improve the electronic conductivity of cathode materials. Compared with the commercial conductive additive Super P, the NCM811 cathode material with ECGO can deliver a capacity of 147.3 mAh g–1 at a high rate of 2 C, and sulfur cathode retains 620 mAh g–1 after 200 cycles, corresponding to the capacity retention of 74%. Also, due to the presence of oxygen groups, ECGO is proposed as an effective conductive additive in Li-ion cathodes prepared by water-based processing. Therefore, the cathode materials with the ECGO conductive additive can contribute to reduce the interfacial resistance and increase the capability, showing great advantages compared to the commercial conductive additives.

Anomalous quantum oscillations in AA and AB bilayer graphene

We study the quantum oscillations in AA and AB graphene bilayers with broken intralayer P-symmetry in the presence of a gate voltage. We consider both doped (weakly) and undoped cases. The presence of a gate voltage leads to the appearance of an inverted band region in the spectrum of the bilayer, which results in additional peaks in the density of states oscillations. We demonstrate the existence of oscillations in the dielectric phase when the chemical potential is pinned within band gap. These effects are analyzed for different types of layer stacking in a bilayer. It is shown that the graphene bilayer is better suited for the experimental study of anomalous oscillations compared to narrow-gap topological insulator. It is worth mentioning that our results can be applied to other graphene-like bilayer materials, such as transition metal dichacolgenides bilayers.

Enhanced reversible hydrogen storage performance of Mg-decorated g-C2N: First principles calculations

The graphene-like 2D material g-C2N owns superior properties for functional materials development, for instance, its ideal porosity can easily accommodate functional metal atoms, making itself more competitive for energy storage. In this study, density functional theory (DFT) computational studies were employed to solve the electronic structure of Mg-doped g-C2N, and furthermore its potential in hydrogen storage was systematically evaluated. Within our calculations, we found that partial charges of the doped Mg atoms can be successfully transferred to pyridinic N atoms. In one aspect, the Mg atoms can display higher electropositivity, and in another aspect, the N atoms own higher electronegativity. Such a change in electronic structure is favorable to enhance its hydrogen adsorption performance, as the H2 molecules in the vicinity of Mg and N atoms can be easily polarized, and thus the electrostatic attractions can be strengthened. In addition, multiple configurations of the Mg-doped g-C2N with adsorbed H2 molecules were presented also in this study, and we found that each 2 × 2 supercell unit possesses a high gravimetric surface area of 2863 m2/g, and can accommodate at most 44 H2 molecules with the adsorption energies ranging from −0.29 eV to −0.12 eV. With the decoration of Mg, its capacity of hydrogen storage can be as high as 8.03 wt%. The theoretical analysis presented in this study provides important chemical insights for energy materials design, with profound implications for improving the performance of 2D materials’ hydrogen.

Microstructural tailoring of porous few-layer graphene-like biochar from kitchen waste hydrolysis residue in molten carbonate medium: Structural evolution and conductive additive-free supercapacitor application

Biomass-derived graphene-like material is a promising candidate for supercapacitor electrodes, while it is critical to controllably convert biomass into structure-tunable graphene. Herein, few-layer graphene-like biochar (FLGBS) was successfully fabricated from waste biomass in molten carbonate medium. Molten carbonate acted as the effective catalyst for graphitizing and the liquid medium for microcrystal relinking to achieve the rearrangement of carbon structure. It was found that the stacking of graphene layer and formation of porous structure were influenced by the volume of reaction medium and biomass pre‑carbonation. Namely, increasing the dosage of molten K2CO3 was in favor to form few layer-type graphene structure, but excess dosage could destroy the nanopore structure to expand the aperture. In addition, pre‑carbonation at high temperature impeded the exfoliation of graphene layers. When FLGBSs were applied to fabricate conductive additive-free electrode, they displayed a superior supercapacitor performance (up to 237.4 F g−1 at 0.5 Ag−1). This excellent performance should be attributed to the large specific surface area, hierarchical pore structure and graphene-like structure. In short, this work could help to get insights into the structural evolution of biomass carbon to graphene-like biochar in molten carbonate medium and achieve the tailoring of microstructure for further application in energy storage.

Production of hydrogen and carbon in the petrochemical industry by cracking of hydrocarbons in the process of heat utilization in steel production

Preliminary calculations suggest that 530 million tons of hydrogen can be obtained from the utilization of heat from blast-furnace and converter processes in the global steel production, which is approximately 8 times higher than the current annual production of hydrogen (75 million tons).Mankind, already now, by introducing everywhere the technology of utilizing the heat of cooling steel for the pyrolysis of methane, can achieve an 8-fold excess of world hydrogen production.To date, the use of heat from metallurgical processes (steel) for methane pyrolysis using all available possibilities for the maximum high-quality and relatively cheap separation of methane into soot and hydrogen is an important tactical task. In the process of globally organized petrochemical production of hydrogen by cracking methane in the steelmaking process, it is possible to arrange the production of high-purity hydrogen and high-purity carbon for further synthesis of tubulenes, graphene-like and fullerene-like materials. However, the following tasks stand in the way of this problem: 1) careful study of the behavior of saturated hydrocarbons, including methane at near-critical parameters and supercritical parameters, 2) organization of the optimal process for removing soot (carbon) from a catalytic cracking processor, 3) profiling the optimal design of catalytic cracking – processor.

Highly NH3 Sensitive and Selective Ti3C2O2-Based Gas Sensors: A Density Functional Theory-NEGF Study.

Ammonia (NH3) detection at the early stage is an important precaution for human health and agricultural production. However, conventional sensing materials are difficult to achieve all the targeted operational performances such as low power consumption and high selectivity. MXenes are a type of graphene-like emergent material equipped with abundant surface sites benefiting gas-sensing applications. In the work, we discuss the sensing performance of Ti3C2O2 to anticipate harmful and polluting NH3 gases by density functional theory and nonequilibrium Green's function. The adsorption geometry, charge difference density, and partial density of states are discussed to understand the nature of interactions between gas molecules and Ti3C2O2. The theoretical results show that only NH3 adsorbs onto the nanosheet through chemisorption. Then, a two-electrode Ti3C2O2-based gas sensor device is built to unravel the transport properties. Current under different bias voltages indicates the Ti3C2O2-based sensor could maintain extremely high sensitivity, demonstrating that Ti3C2O2 has great potential for the NH3 sensor with high selectivity, excellent sensitivity, and low energy consumption. Upon external electric fields, the adsorption energy and charge transfer can be tuned effectively, suggesting that Ti3C2O2 is a versatile agent as an ammonia-sensing material.

Nanofibrillar biochar from industrial waste as hosting network for transition metal dichalcogenides. Novel sustainable 1D/2D nanocomposites for electrochemical sensing

Industrial wastes have become elective sustainable sources to obtain materials for electronic/electroanalytical purposes; on the other hand, easy and green strategies to include semiconductor 2D graphene-like materials in conductive networks are highly required.In this work, 1D/2D nanocomposites (NCs) based on nanofibrillar biochar (BH) from paper industry waste and transition metal dichalcogenides (TMDs: MoS2, WS2, MoSe2, and WSe2), were prepared in water via liquid phase exfoliation (LPE) using sodium cholate as bioderived surfactant. The TMD amount in the NCs has been carefully optimized, searching for the best compromise between electron transfer ability and electroanalytical performances. Four different water-dispersed BH-TMD NCs have been selected and comprehensively studied from the electrochemical point of view and morphologically characterized. The BH-TMDs potentiality have been demonstrated in model solutions and real samples towards different analytes of biological and agri-food interest. The most performing NCs have been selected and used for the simultaneous determination of the neurotransmitters dopamine (DP) and serotonin (SR), and the flavonoids quercetin (QR) and rutin (RT), obtaining good linearity (R2 ≥ 0.9956) with limits of detection ranging from 10 to 200 nM. Reproducible quantitative recovery values (90–112%, RSD ≤6%, n = 3) were obtained analyzing simultaneously DP and SR in synthetic biological fluid and drugs, and QR and RT in food supplements, proving the usability of the proposed materials for real analyses.This work proves that BH-nanofibers act as a sustainable conductive hosting network for 2D-TMDs, allowing full exploit their electroanalytical potential. The proposed BH-TMD NCs represent a sustainable, affordable, and captivating opportunity for the electrochemical and (bio)sensoristic field.

Synthesis of ultra-thin graphene-like nanosheets from lignin based on evaporation induced self-assembly for supercapacitors

Graphene-like carbon materials are widely used in power devices due to their excellent structural characteristics. In this study, ultra-thin graphene-like nanosheets (LGLNs) with rich surface wrinkles were prepared by classical evaporation induced self-assembly (EISA) using lignin biomass as carbon precursor, followed by chemical activation with KHCO3. The obtained LGLN900 material calcined at 900 °C had a thickness of ca. 3 nm, a large specific surface area of 2886 m2 g−1 with a high specific pore volume of 2.10 cm3 g−1. In addition, a large number of wrinkles on the surface of LGLN900 endows its effective compression resistance. When the LGLN900 material was used as electrode material of supercapacitor, a high specific capacitance of 388 F g−1 was obtained at 0.2 A g−1 current density in 6 M KOH aqueous solution, and 269 F g−1 specific capacitance could be at remained at 40 A g−1. The supercapacitor assembled with LGLN900 afforded a specific energy density of (11.0–13.7) Wh kg−1 at a power density of (128.8–6465) W kg−1. This work provides a facile and green strategy for the synthesis of highly wrinkled ultra-thin graphene-like nanosheets from sustainable biomass resources, which should have wide applications in adsorption, catalysis and energy storage.

Terahertz cyclotron emission from two-dimensional Dirac fermions

Since the emergence of graphene, we have seen several proposals for the realization of Landau lasers tunable over the terahertz frequency range. The hope was that the non-equidistance of the Landau levels from Dirac fermions would suppress the harmful non-radiative Auger recombination. Unfortunately, even with this non-equidistance an unfavorable non-radiative process persists in Landau-quantized graphene, and so far no cyclotron emission from Dirac fermions has been reported. One way to eliminate this last non-radiative process is to sufficiently modify the dispersion of the Landau levels by opening a small gap in the linear band structure. A proven example of such gapped graphene-like materials are HgTe quantum wells close to the topological phase transition. In this work, we experimentally demonstrate Landau emission from Dirac fermions in such HgTe quantum wells, where the emission is tunable by both the magnetic field and the carrier concentration. Consequently, these results represent an advance in the realization of terahertz Landau lasers tunable by magnetic field and gate-voltage.

Optical and Electrical Properties of Low-Dimensional Crystalline Materials: A Review

Low-dimensional materials have been revolutionary in both the technological and research fields over the last decades. Since the discovery of graphene in 2004, and thanks to the technological improvements in nanotechnology achieved during this last century, the number of low-dimensional materials under research and their potential applications have not stopped increasing. In this review, we present a comprehensive tour of the principal 2D and 1D materials that compose the current state of the art and also the technological applications derived from them. In both cases, the focus will be on their optical and electrical properties, as well as the potential applications on novel photonic, electronic, or optoelectronic devices. For 2D materials, we will focus on a brief review of graphene-like materials, giving more emphasis to graphene derivatives, hexagonal boron nitride, and transition metal dichalcogenides. Regarding 1D materials, we will aim at metallic and semiconductor nanowires. Nevertheless, interesting 2D and 1D materials are mentioned in each section. The topic will be introduced using the related origin of their unique capabilities as a common thread. At the same time, we will try to remark on the differences and similarities between both groups and their physical relationship.

Ultra-thin highly-wrinkled graphene-like nanosheets for supercapacitor electrodes via 4-nitrocatechol and solvent-induced self-assembly

Graphene-like carbon materials are in high demand due to their potential applications in power devices. However, conventional synthesis of graphene-like materials causes repacking to occur during high-pressure compression steps resulting in low surface areas and unfavorable structures for mass transfer. Herein, ultra-thin wrinkled graphene-like nanosheets (GNs) were prepared simply via classical evaporation induced self-assembly (EISA) of 4-nitrocatechol as carbon precursor. Combination of EISA and subsequent KHCO3 activation and calcination at 900 °C (GN-900) afforded materials with thicknesses of (2–3) nm, specific surface areas of 3300 m2 g−1 with specific pore volumes of 2.34 cm3 g−1 under optimum conditions. When GN-900 was evaluated as an electrode material, a specific capacitance of 367 F g−1 was achieved at 0.2 A g−1 current density in 6 M KOH aqueous solution with a rate capability of 228 F g−1 at 40 A g−1. Supercapacitors assembled with GN-900 had specific energy densities of 11.5 Wh kg−1 at power densities of 89.8 W kg−1. Moreover, capacitance retention was greater than 98% after 3000 cycles at 10A g−1. Materials prepared with the proposed methods in this study were determined to be structurally stable and to exhibit favorable electrochemical performance for present and near-future supercapacitor applications.

Optical excitations of graphene-like materials: group III-nitrides.

By using first-principles calculations, we have studied the electronic and optical characteristics of group III-nitrides, such as BN, AlN, GaN, and InN monolayers. The optimized geometry, quasi-particle energy spectra, charge density distributions, band-decomposed charge densities, and Van Hove singularities in density of states are described in the work using physical and chemical pictures and orbital hybridizations found in B-N, Al-N, Ga-N, and In-N chemical bonds. Moreover, the dielectric functions, energy loss functions, absorption coefficients, and reflectance spectra with electron-hole interactions of optical properties are successfully achieved. More importantly, the close relations between electronic and optical properties are successfully demonstrated. The theoretical framework will be useful to research other graphene-like materials.

Optical Biosensors Based on Graphene-Like Two-Dimensional Materials

Optical Biosensors Based on Graphene-Like Two-Dimensional Materials

Theoretical investigations of the electronic and optical properties of a GaGeTe monolayer.

Our study focused on exploring the electronic and optical characteristics of the GaGeTe monolayer using first-principles calculations. Our findings showed that this material has remarkable physical and chemical properties attributed to its unique band structure, van Hove singularities in the density of states (DOS), charge density distributions, and charge density differences. We also observed excitonic effects, multiple optical excitation peaks, and strong plasmon modes in the energy loss functions, absorption coefficients, and reflectance spectra, which contribute to its enriched optical response. Moreover, we were able to establish a close relationship between the orbital hybridizations of the initial and final states with each optical excitation peak. Our results suggest that GaGeTe monolayers hold great potential for various semiconductor applications, especially those involving optics. Furthermore, the theoretical framework we used can be applied to study the electronic and optical properties of other graphene-like semiconductor materials.