Average Number Of Layers Research Articles

Supramolecular structure and thermal transformations of modified resinous-asphaltene substances

A detailed study of the supramolecular structure of high molecular weight resinous-asphaltene substances (RAS) and the study of their stability to thermal-oxidative degradation processes in the presence of surfactants is a promising scientific direction and can become the basis for the development of additional oil treatment processes and, as a result, the intensification of thermal transformations of oil dispersed systems (ODS). In the work it has been established that the maximum modifying effect, which consists in reducing the amount of asphaltenes by 8–11 % and increasing the concentration of resins, saturated and aromatic hydrocarbons in the composition of the dispersion medium, is achieved by the interaction of ODS with octadecylpropylenediamine, alkyldiamine with the content of ethoxylated groups n = 3–6 and butyl coconut fatty alcohol ester with n = 10. This fact is due to a change in the geometric parameters of asphaltene nanoaggregates due to the adsorption of these surfactants on their surface. Thus, against the background of an increase in the interplanar distances of condensed aromatic layers dm from 3.66 to 3.85 Å and values of the intrachain distance from 5.71 to 5.80 Å, the average diameter of aromatic layers decreases by 0.67–2.36 Å and the average height of their pack by 1.52–2.64 Å, while the average number of layers in a pack is 5. Estimation of the results of thermal analysis indicates that the RAS thermograms have a similar form with three endoeffects with minima in the ranges of ~ 34.7–37.7 °C (I); 325.7–339.3 (II) and 434.8–438.7 °С (III) and one exoeffect with a maximum of ~ 460.5–475.3 °С (IV). With a decrease in the factor of crystallinity and aromaticity of RAS, their resistance to the processes of thermo-oxidative degradation in the temperature region of coke formation increases. The energy of thermal-oxidative destruction for modified systems by surfactants exceeds by 21.6 kJ/mol of this indicator for unmodified RAS and is 62.07 ÷ 66.13 kJ/mol.

Few-layered-graphene - Si3N4 composite powders prepared by decomposition of methane onto a Si3N4 powder bed: Control of the average number of layers in the graphene stack

The chemical vapor deposition of carbon is performed onto a commercial silicon nitride powder bed. This produces few-layered-graphene (FLG) films or islands on the Si3N4 particles. The samples are characterized by several techniques including Raman spectroscopy, scanning and transmission electron microscopy. The experimental parameters of the methane (CH4) decomposition (temperature, CH4 concentration, dwell time) are correlated to the average number of graphene layers (N). Complete coverage of the Si3N4 particles is achieved for FLG with N controlled in the range 5–12, corresponding to 4–12 wt%. of carbon. Below that, for stacks with N = 3–4, the coverage of the surface by FLG islands is not total. The value found for the activation energy of CH4 conversion into carbon shows that island-growth is favored over layer-growth. A macroscopical method based on a carbon proportion evaluation gives an approximation of both the coverage ratio and the average number of layers in the stack.

Sustainable and cost-effective edge oxidized graphite/PEDOT:PSS nanocomposites with improved electrical conductivity

Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is a soft and conjugated polymer whose conductive properties can be properly tuned through doping with various additives or solvents, preserving its excellent processability. In this work PEDOT:PSS was combined with a cost-effective graphite derivative named Edge Oxidized Graphite (EOG) for developing a nanocomposite with improved electrical conductivity, with respect to the pristine PEDOT:PSS, through an easy and environmentally friendly doping process. Firstly, the EOG powders, produced by a green oxidation process of graphite, were deeply characterized through Fourier transform infrared (FT-IR), Thermogravimetric (TGA), and Wide-angle X-ray scattering (WAXD) analysis, showing that this nanofiller has oxygenated functional groups on the sheet edges. The quality and the stability of the EOG dispersions within PEDOT:PSS were investigated at different carbon-filler concentrations, up to high loading of 25 %wt/V of EOG through rheological analyses, demonstrating pseudo-plastic behavior and excellent long-term stability of the inks due to the absence of inhomogeneities and aggregates over time; in fact, the same inks were tested under the same rheological conditions after 21 days, showing the same viscosity trend for all EOG concentrations (%wt/V). Transmission electron microscopy (TEM) and (Scanning Electron microscopy) SEM investigation of spin-coated samples onto glass substrates were performed to morphologically evaluate the nanocomposites and estimate the average size of the sheets, particularly the mean length of 1.2 μm and an approximated thickness of 26 nm of the EOG sheets dispersed into the polymer matrix (PEDOT:PSS) was determined, while WAXD analysis allowed to identify the average layer number of the EOG sheets, obtaining thus, a direct measurement of the EOG sheets aspect ratio equal to 45. Finally, sheet resistance tests showed that the increasing concentration of EOG leads to a significant improvement in the electrical conductivity of the nanocomposites, from 1.1 S/cm for pristine PEDOT:PSS to 21.9 S/cm for nanocomposites with the highest EOG content (25 %wt/V). This work demonstrates the successful development of nanocomposite based on PEDOT:PSS doped with carbon-based filler synthesized through a green and cost-effective process, promoting their use in the production of bio/electrochemical sensors or optoelectronic devices.

Systematic Investigation on the Surfactant‐Assisted Liquid‐Phase Exfoliation of MoS2 and WS2 in Water for Sustainable 2D Material Inks

MoS2 and WS2 have gathered significant attention due to their tunable properties and wide range of applications. Liquid‐phase exfoliation (LPE) is a facile method to prepare 2D MoS2 and WS2. Currently, the principally employed solvents for LPE of MoS2 and WS2 are expensive and toxic, and have high boiling points. These drawbacks encourage to find more sustainable alternatives to the liquid medium used for the preparation of 2D material inks. Water is the best option, but surfactants are necessary for LPE in water, since MoS2 and WS2 are hydrophobic. Organic molecules with amphoteric character such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium hexadecyl sulfonate (SHS) are selected as suitable candidates for the role. However, the study of these surfactants used in LPE is barely systematically reported. In this work, a detailed investigation is presented on their impact on the LPE of MoS2 and WS2, which are representatives of transition‐metal dichalcogenides. By characterizing and qualifying the products from average number of layers, it is found that all the surfactants work efficiently to exfoliate MoS2 and WS2 into few layers, and SHS stabilizes the 2D layers better than the other two. However, in terms of yield and relative surfactant concentration, a real trade‐off is not identified between maximized quantity of exfoliated materials and minimized surfactant concentration, which prompts to select the colloidal ink based on the specific further needs for processing.

Novel approach for modification of graphene oxide using continuous wave-laser obtained from surgical laser diode

The present investigation employs a modified version of Hummer's method to synthesise graphene oxide (GO), which is subsequently subjected to treatment with a continuous-wave (CW) laser derived from surgical laser diodes for the purpose of performing minimally invasive surgery for 30 s to yield laser-modified GO. XRD analysis was used to look at how CWlaser changed the sizes of crystallites, the distance between planes, and the average number of layers. The study examined the FTIR spectra of graphite oxidation and modification using a CW laser. Changes in the G band, D band, and 2D peaks in the Raman spectra showed disorder and multiple layers. The variations in negative zeta potential were used to analyse colloidal stability in graphite, GO, and laser-modified GO. Different types of dynamic light scattering techniques were used to study electrophoretic mobility, Brownian motion, and electrical double layers. The obtained results exhibited a high degree of agreement with the findings derived from the FTIR spectra. This work examined dielectric and impedance spectroscopy to assess relaxation behaviour that deviates from the Debye model. By fitting curves to the data, we evaluated the dielectric constant, loss, and conductivity. Graphite to laser-modified GO via GO lowered the real component of the dielectric constant at any frequency.

A study of screen-printed electrodes modified with MoSe2 and AuNPs-MoSe2 nanosheets for dopamine sensing

Molybdenum selenide nanosheets (MoSe2-NS) were synthesized by liquid-phase exfoliation (LPE) technique and successive liquid cascade centrifugation (LCC) at two different centrifugation rates (1.5 and 5 krpm). By this technique's combination, we were able to prepare MoSe2 nanosheets with different geometric characteristics (i.e., average number of layers <N> and average lateral length <L>). Increasing the centrifugation speed from 1.5 krpm to 5 krpm leads to a decrease in number of layers (down to nL = 2 – 4, with the presence of sparse monolayer flakes) and average lateral size of NS from 280 nm to 180 nm, as confirmed combining optical and morphological analysis. Modified screen-printed carbon electrodes (SPCE) with the as prepared MoSe2-NS were fabricated and applied for the determination of dopamine (DA) as an electroactive model analyte in the concentration ranging from 0.5 to 80 µM. DA is an important neurotransmitter for human beings and its deficiency can bring out various health diseases like Parkinson's and brain disorders, thus the development of simple DA sensors is highly demanding. Results demonstrated the better performances of the modified MoSe2 (5 krpm)/SPCE sensor compared to bare SPCE and the MoSe2 (1.5 krpm)/SPCE. With the objective to improve the electroanalytical performances toward dopamine, AuNPs-MoSe2-NS hybrid composite was also prepared, mixing AuNPs obtained by a green-reduction method with the MoSe2-NS. The developed AuNPs-MoSe2 (5 krpm)/SPCE sensor resulted the most promising with further improved sensitivity as compared to MoSe2/SPCE.

Sonication-assisted liquid exfoliation and size-dependent properties of magnetic two-dimensional α-RuCl3

Originating from the hexagonal arrangement of magnetic ions in the presence of strong spin orbit coupling, α-RuCl3 is considered as model system for the Kitaev-Heisenberg model. While the magnetic properties of α-RuCl3 have been studied in bulk single crystals or micromechanically-exfoliated nanosheets, little is known about the nanosheets’ properties after exfoliation by techniques suitable for mass production such as liquid phase exfoliation (LPE). Here, we demonstrate sonication-assisted LPE on α-RuCl3 single crystals in an inert atmosphere. Coupled with centrifugation-based size selection techniques, the accessible size- and thickness range is quantified by statistical atomic force microscopy. Individual nanosheets obtained after centrifugation-based size selection are subjected to transmission electron microscopy to confirm their structural integrity after the exfoliation. The results are combined with bulk characterisation methods, including Raman and x-ray photoelectron spectroscopy, and powder diffraction experiments to evaluate the structural integrity of the nanosheets. We report changes of the magnetic properties of the nanomaterial with nanosheet size, as well as photospectroscopic metrics for the material concentration and average layer number. Finally, a quantitative analysis on environmental effects on the nanomaterial integrity is performed based on time and temperature dependent absorbance spectroscopy revealing a relatively slow decay (half-life of ∼2000 h at 20 °C), albeit with low activation energies of 6–20 kJ mol−1.

Enhanced molecular sieving performance of thick graphene membranes self-assembled from weakly-oxidized graphene nanosheets

Graphene oxide (GO)-based membranes have attracted extensive attention in water purification but still face great challenge due to their poor service life. To overcome this issue, weakly oxidized graphene nanosheets have been chemically exfoliated from natural graphite via a newly-developed strategy for preparing layer-tunable graphene. When an 80 μm-thick graphene membrane is assembled from the graphene nanosheets with an average layer number of 3, it exhibits a high rejection rate of 99.9 % for Rhodamine B and a water flux of up to 3452.6 L m−2 h−1 bar−1. This should be ascribed to the unique hierarchically nanochannel structure within the membrane. This finding may provide a new insight into the design and fabrication of the thick membrane having excellent sieving performance. Furthermore, the rejection rate of RB can be maintained at 99.9 % even after 24 cycles of filtrations, demonstrating a superior service performance for the membrane.

The effect of the density difference between supercritical CO2 and supercritical CH4 on their adsorption capacities: An experimental study on anthracite in the Qinshui Basin

Deep unmineable coals are considered as economic and effective geological media for CO2 storage and CO2 enhanced coalbed methane (CO2-ECBM) recovery is the key technology to realize CO2 geological sequestration in coals. Anthracite samples were collected from the Qinshui Basin and subjected to mercury intrusion porosimetry, low-pressure CO2 adsorption, and high-pressure CH4/CO2 isothermal adsorption experiments. The average number of layers of adsorbed molecules (ANLAM) and the CH4/CO2 absolute adsorption amounts and their ratio at experimental temperatures and pressures were calculated. Based on a comparison of the density of supercritical CO2 and supercritical CH4, it is proposed that the higher adsorption capacity of supercritical CO2 over supercritical CH4 is the result of their density differences at the same temperature. Lastly, the optimal depth for CO2-ECBM in the Qinshui Basin is recommended. The results show that: (1) the adsorption capacity and the ANLAM of CO2 are about twice that of CH4 on SH-3 anthracite. The effect of pressure on the CO2/CH4 absolute adsorption ratio decreases with the increase of pressure and tends to be consistent. (2) A parameter (the density ratio between gas free and adsorbed phase (DRFA)) is proposed to assess the absolute adsorption amount according to the supercritical CO2/CH4 attributes. The DRFA of CO2 and CH4 both show a highly positive correlation with their absolute adsorption amounts, and therefore, the higher DRFA of CO2 is the significant cause of its higher adsorption capacity over CH4 under the same temperature and pressure. (3) CO2 adsorption on coal shows micropore filling with multilayer adsorption in the macro-mesopore, while methane exhibits monolayer surface coverage. (4) Based on the ideal CO2/CH4 competitive adsorption ratio, CO2 storage capacity, and permeability variation with depth, it is recommended that the optimal depth for CO2-ECBM in the Qinshui Basin ranges from 1000 m to 1500 m.

Effect of Temperature on the Graphitizability and Electrochemical Properties of a Quang Ninh Natural Anthracite Used As Anode in Li/Na-Ion Batteries

In this research, natural anthracite coal (ATC) originated from Vang Danh - Quang Ninh province in Viet Nam was firstly chemically purified and then calcined in inert gas (Ar) at 800 oC for different periods (t = 2, 3 and 6 h) to remove all the impurities and enrich the carbon content. The purity and graphitized structure of treated coal proved significantly while evaluating its structural parameters (the lateral crystallite size - La, stacking crystallite height - Lc, the average number of layers per carbon crystallite - Naverage, and the average number of carbon atoms per aromatic lamellae - n)1, 2 and morphology. After purification step, ATC possesses relatively high carbon content (96.0%) and its impurities were mostly removed. The structure of heat-treated ATC samples is like hard carbon. Besides, its graphene interlayer spacing is larger than that of graphite. These features seem to be potential for application of ATC as negative electrode materials for both Li and Na rechargeable batteries.In batteries testing, using ATC calcined at 800 oC for 3 hours as anode material in lithium half-cell exhibited a quite good specific capacity (170.1 mAh g-1), which is much higher than the value obtained for commercial hard carbon (162.2 mAh g-1). Moreover, Coulombic efficiency of ATC is almost absolute (99.8%). In sodium half-cell, the sample calcined at 800 oC for 2 hours gave much smaller specific capacity of 130.5 mAh g-1 than hard carbon one (280 mAh g-1). Nevertheless, Coulombic efficiency of ATC anode in lithium half-cell and sodium half-cell throughout 100 cycles remained absolutely at 99.6%, while their values for hard carbon anode were 99.9% and 99.7%, respectively. References Abou-Rjeily, J.; Laziz, N. A.; Autret-Lambert, C.; Outzourhit, A.; Sougrati, M.-T.; Ghamouss, F., Towards valorizing natural coals in sodium-ion batteries: impact of coal rank on energy storage. Scientific Reports 2020, 10 (1), 1-10.Manoj, B.; Kunjomana, A., Study of stacking structure of amorphous carbon by X-ray diffraction technique. Int. J. Electrochem. Sci 2012, 7 (4), 3127-34. Acknowledgement This work is supported by Viet Nam National University Ho Chi Minh City (VNUHCM) under grant number B2020-18-06

FDD LTE Performance Simulation Based on Massive Antenna Array

There are two methodologies to realize 3D MIMO for FDD LTE, MU-MIMO-based virtual beam (VB), and four-cell soft-split cell (SSC), which beamforms four logical cells in one physical sector, and this paper is aimed at figuring out which brings more performance between VB and SSC. In the first place, brief introduction for the mechanism of VB and SSC are presented. Subsequently, detailed systematic simulations based on WINNER II are carried out based on different traffic models (low load, medium load, and high load) and user distribution is also considered. For accurate evaluation on the performance gain of VB and SSC, 4T4R solution is also simulated as the benchmark, which is widely deployed to improve the capacity of FDD LTE by operators. Based on the simulation of results of the subsequent KPIs, cell throughput, average cell throughput, average UE throughput, and average layer number, VB and SSC effectively increase single-cell capacity and user experience in high load scenario compared with 4T3S solution and VB can bring more gain.

Nonvolatile Memristive Devices Based on In Situ Functionalized Layered rGO-MoS2 Nanocomposites

Hybrid composites comprised of layered two-dimensional (2D) materials have attracted growing attention, especially in large-area electronics. Herein, we exploit the synergistic interfacial effect of molybdenum disulfide (MoS2) grafted reduced graphene oxide (rGO) and study the memristive characteristics of the layered hybrid rGO-MoS2 nanocomposites (NCs). The synthesized materials are analyzed using optical, structural, elemental, and morphological techniques. The average number of layers (∼6 to 10) is estimated from the intense X-ray diffraction peak of the polycrystalline materials. The intercalation of rGO in the rGO-MoS2 NCs results in an increased energy bandgap compared to pristine MoS2. The photoluminescence study exhibits dominant blue emission due to the restoration of the sp2-hybridized carbon domain in the reduced sheets. The surface topography of the NCs shows a 3D flower-like structure with multiple nano-petals interconnected in the form of nanosheets. The average diameter of the flower-shaped particles is calculated to be ∼258 and ∼301 nm for MoS2 and rGO-MoS2, respectively. The crossbar devices (ITO/rGO-MoS2/Cu) in a sandwich configuration (thickness ∼700 nm) are fabricated, displaying stable and repeatable bipolar resistive switching characteristics. The trapping and de-trapping of the charge carriers at the rich sulfur vacancies are responsible for bipolar memory behavior.

Investigation of the structural characteristics of vitrinites of some coals of the Kuznetsk Basin

In this work, the structural parameters of vitrinites of coal of various degrees of metamorphism were investigated by X-ray diffraction methods. Vitrinite concentrates were obtained from coal of the Kuznetsk Basin by the method of fractional analysis of coals, according to which the studied fuel is stratified into fractions in liquids of different densities. The following X-ray structural parameters were analyzed: the number of carbon atoms in the lamellae (natC), the longitudinal size of the lamellae, the height of their stacking (La and Lc), the number of polyaromatic layers in the stack (N), and the packing density of the lamellae (ρ). It was shown that in vitrinite concentrates, an increase in all analyzed structural parameters (Lc, La, natC, N, ρ) is observed with an increase in the degree of metamorphism, at the same time, a decrease in the value of the interplanar distance (d002) is observed. The performed X-ray diffraction studies showed that the average number of layers in a package and carbon atoms per monolayer in the samples of vitrinite concentrates of bituminous coals of high stages of metamorphism (Ro, r = 1.41%) varies from 7 to 8 and 14-15, respectively. A correlation was found between the linear nature of the number of arene layers and the height of their packing. The results obtained are in good agreement with the literature data given for coals of various deposits.

Study of the molecular structure of hexane-insoluble asphaltenes in coal tar pitch

A comprehensive study of the functional-group composition and structure of hexane-insoluble asphaltenes of coal tar pitch was carried out by methods of chemical elemental analysis, nuclear magnetic resonance (NMR), IR spectroscopy, scanning electron microscopy, X-ray diffraction (XRD), thermal analysis in combination with chromatography-mass spectrometry. It is shown that a hypothetical macromolecule of asphaltenes can be considered as a set of condensed aromatic nuclei of the peri-condensed type of 7 rings, which have alkyl substituents and connecting bridges consisting on average of 2 carbon atoms. The ratio of various structural units in the asphaltene powder is as follows: for one S-containing structure there are 4-5 N-and 1.3-1.7 O-containing structures. Sulfur atoms are contained in thiophene-like, thermally stable fragments of the structure and pass into the coke residue without decomposition. Oxygen is contained in thermally unstable carboxyl and phenolic groups, which decompose with the release of CO2, as well as in the composition of aromatic ethers that pass into the coke residue. The crystallographic characteristics of ordered structures formed by macromolecules of asphaltenes are studied. The average diameter of the packets is La of about 0.66 nm, with a thickness of Lc ≈ 1.30 nm, the distance between individual layers is d002 ≈ 0.34 nm, the average number of layers in the packages is n ≈ 5-7 pieces. In this case, the crystallinity of asphaltene powders does not exceed 30%. The data obtained by different methods are in good agreement and more fully characterize the structure of macromolecules of asphaltenes of coal tar pitch.

Chemical and structural properties of reduced graphene oxide\u2014dependence on the reducing agent

Graphene oxide (GO) prepared from graphite powder using a modified Hummers method and reduced graphene oxide (rGO) obtained from GO using different reductants, i.e., sodium borohydride, hydrazine, formaldehyde, sodium hydroxide and L-ascorbic acid, were investigated using transmission electron microscopy, X-ray diffraction, Raman, infrared and electron spectroscopic methods. The GO and rGOs’ stacking nanostructure (flake) size (height x diameter), interlayer distance, average number of layers, distance between defects, elementary composition, content of oxygen groups, C sp3 and vacancy defects were determined. Different reductants applied to GO led to modification of carbon to oxygen ratio, carbon lattice (vacancy) and C sp3 defects with various in-depth distribution of C sp3 due to oxygen group reduction proceeding as competing processes at different rates between interstitial layers and in planes. The reduction using sodium borohydride and hydrazine in contrary to other reductants results in a larger content of vacancy defects than in GO. The thinnest flakes rGO obtained using sodium borohydride reductant exhibits the largest content of vacancy, C sp3 defects and hydroxyl group accompanied by the smallest content of epoxy, carboxyl and carbonyl groups due to a mechanism of carbonyl and carboxyl group reduction to hydroxyl groups. This rGO similar diameter to GO seems to result from a predominant reduction rate between the interstitial layers. The thicker flakes of a smaller diameter than in GO are obtained in rGOs prepared using remaining reductants and result from a higher rate of reduction of in plane defects.

Green Preparation of Aqueous Graphene Dispersion and Study on Its Dispersion Stability.

The large-scale preparation of stable graphene aqueous dispersion has been a challenge in the theoretical research and industrial applications of graphene. This study determined the suitable exfoliation agent for overcoming the van der Waals force between the layers of expanded graphite sheets using the liquid-phase exfoliation method on the basis of surface energy theory to prepare a single layer of graphene. To evenly and stably disperse graphene in pure water, the dispersants were selected based on Hansen solubility parameters, namely, hydrophilicity, heterocyclic structure and easy combinative features. The graphene exfoliation grade and the dispersion stability, number of layers and defect density in the dispersion were analysed under Tyndall phenomenon using volume sedimentation method, zeta potential analysis, scanning electron microscopy, Raman spectroscopy and atomic force microscopy characterization. Subsequently, the long-chain quaternary ammonium salt cationic surfactant octadecyltrimethylammonium chloride (0.3 wt.%) was electrolyzed in pure water to form ammonium ions, which promoted hydrogen bonding in the remaining oxygen-containing groups on the surface of the stripped graphene. Forming the electrostatic steric hindrance effect to achieve the stable dispersion of graphene in water can exfoliate a minimum of eight layers of graphene nanosheets; the average number of layers was less than 14. The 0.1 wt.% (sodium dodecylbenzene sulfonate: melamine = 1:1) mixed system forms π–π interaction and hydrogen bonding with graphene in pure water, which allow the stable dispersion of graphene for 22 days without sedimentation. The findings can be beneficial for the large-scale preparation of waterborne graphene in industrial applications.

Исследование структурных характеристик витринитов некоторых углей Кузнецкого бассейна

The article is devoted to research of the main structural parameters of vitrinites of bituminous coals of various metamorphism degrees carried out by methods of X-ray phase and X-ray structural analysis. Vitrinite concentrates were obtained from coal of the Kuznetsk Basin. The main X-ray structural parameters were estimated: the number of carbon atoms in the lamellae (natC), the longitudinal size of the lamellae, and the height of their stacking (La and Lc), the number of polyaromatic layers in the package (N), and the packing density of the lamellae (ρ). It is shown in the work that in vitrinite concentrates, an increase in all analyzed structural parameters (Lc, La, natC, N, ρ) is observed with an increase in the degree of metamorphism, at the same time, a decrease in the value of the interplanar distance (d002) is observed. The XRD analysis showed that for the average number of layers in a package and carbon atoms per monolayer, in the samples of vitrinite concentrates of bituminous coals of high stages of metamorphism (Ro, r = 1.41%) varies from 7 to 8 and 14-15, respectively. It was found a correlation between the linear nature of the number of polyarene-layers and the height of their stacking. The results obtained were in good agreement with the literature data given for coals of various deposits.

Fast chemical exfoliation of graphite to few-layer graphene with high quality and large size via a two-step microwave-assisted process

Scalable preparation of graphene with both large size and high quality is an important prerequisite for fully realizing its commercial use. Herein, we propose a high-efficient route for preparing few-layer graphene, in which the chemical exfoliation of graphite to ~100% few-layer graphene can be realized within only about 15 min by using a novel two-step microwave irradiation strategy. The as-obtained graphene sheets behave a few-layer feature (average layer number ≤5 layers) and possess large size (the average area size is up to 256.8 μm2). The graphene film prepared from the obtained graphene sheets exhibits an excellent electrical conductivity of up to 2.03 × 105 S m−1, among the highest ones reported so far for the graphene, suggesting the high quality of the prepared graphene. Most importantly, no water-washing and effluent-treatment are needed during the whole preparation process, which will greatly reduces the consumption of water resource and alleviates the environmentally detrimental impact caused by the effluent of used chemicals compared with those conventional chemical exfoliation routes. Benefiting from its simplicity, high-efficiency and high-quality, the present method will show great promise for the mass production of high-quality graphene sheets.

The novel and facile preparation of 2DMoS2@C composites for dye adsorption application

In this work, we proposed a convenient strategy for preparing the MoS2-based adsorbents by combining liquid-phase shear exfoliation and annealing. We selected carboxymethylcellulose sodium (CMC) as the additive to promote the exfoliation of bulk MoS2 in the pollution-free ethanol/water mixture system. The results showed that the addition of appropriate CMC increased the viscosity of the suspension and prevented 2D MoS2 nanosheets agglomeration to improve the shear-exfoliating effect. By optimizing the operating conditions, the average lateral dimension and average layer number of 2D MoS2 nanosheets were around 100 nm and around 4 layers, respectively. The composites of 2D MoS2 nanosheets and porous carbon (2DMoS2@C) were obtained after annealing the composites of 2D MoS2 nanosheets and CMC. Furthermore, the adsorption behaviors of 2DMoS2@C for the removal of rhodamine B (RhB) and methylene blue (MB) were investigated. Interestingly, the 2DMoS2@C exhibited superior performance towards MB removal than towards RhB removal because of the pore structure and dye molecular size. The theoretical adsorption capacity of 2DMoS2@C for MB removal calculated by the Langmuir isotherm model could get 272 mg/g. The adsorption mechanism of 2DMoS2@C was also analyzed in detail. This is a facile, efficient and economical method for preparing adsorbents based on 2D materials.

X-Ray Diffraction Evaluation of the Average Number of Layers in Thermal Reduced Graphene Powder for Supercapacitor Nanomaterial

Graphene oxide (GO) can be partially reduced to graphene-like sheets by removing the oxygen-containing groups and recovering the conjugated structure. In this work, the thermal reduction of GO powder has been carried out using back pumping vacuum pressures and investigated employing X-ray diffraction analysis. The experimental results of estimating the number of graphene layers on the reduced powder at various temperatures (200 – 1000 °C) have been reported. Electrical changes have been produced in a graphene oxide with the vacuum reduction process. This study has shown that the ideal processing temperature for reducing graphene oxide nanomaterial was about 400 °C. It has also been shown that at 600 °C the number of layers in the reduced nanomaterial increased. The internal series equivalent resistance (ESR) has been improved substantially with the vacuum thermal treatment even at temperatures above 400 °C. ESR was reduced from 95.0 to about 13.8 Ω cm2 with this processing. These results showed that the process can be applied to the reduction of graphene oxide to produce supercapacitor nanomaterials. The advantage of employing this method is that the processing is a straightforward and low cost thermal treatment that might be used for large amount of nanocomposite material.