Graphene-like Sheets Research Articles

Molecular simulation using transfer-learned potentials for the disordered nanoscale structure of nitrogen-doped nanoporous carbons

Machine learning (ML)-based molecular dynamics (MD) simulations of the formation of a class of N-doped nanoporous carbons are performed to assess their disordered partially graphitized nanoscale structure. The study is motivated by the effectiveness of so-called nitrogen assembly carbons (NACs) for catalysis applications. Benchmark simulations for pure-C disordered graphitic systems reveal the importance of reliably capturing the vdW component of the potentials in order to accurately describe the tendency for layering of disordered graphene-like sheets. In our modeling, this is achieved by a transfer learning strategy incorporating features of the energetics from the optB88-vdW DFT functional into potentials initially trained with a less expensive functional, thereby providing a superior description of the pure-C systems. Generation from MD simulations of realistic partially graphitized structures is significantly more challenging for N-doped versus for pure C systems. However, such structures are achieved by a tailored MD simulation protocol mimicking the experimental synthesis process and in particular incorporating an annealing and subsequent quenching stages. Simulated PXRD patterns effectively reproduce the features of experimental observations for NACs, including the appearance of a prominent but broad (002) peak at around 25∘, and the development of another weaker feature associated with in-layer ordering of mixed C-N graphene-like sheets.

Facile fabrication of bismuth oxide anchored graphene oxide for the effective electrochemical sensing of diuron

BackgroundDiuron (DU), a weed controller widely used in the agricultural industry, prolonged conception of this agrochemical residue contaminated with environmental water bodies and soil sources could cause an acute impact on the human health system. This work utilized the electrochemical determination technique due to their rapid detection, outstanding sensitivity, and economical purpose. MethodsThe electrochemical behavior of DU at the γ-Bi2O3 microplates interconnected with sheet-like graphene oxide (GO) as a surface-modified electrode was scrutinized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The surface-modified γ-Bi2O3/GO/GCE elucidates superior electrocatalytic performance towards the irreversible oxidation response of diuron than the other surface-modified electrode in the phosphate buffer solution of 0.1 M. Significant findingsThe γ-Bi2O3/GO/GCE electrode displayed an extensive detection range of 0.1–631 µM with a 0.751 µM lower detection limit furthermore, noticeable 0.0280 µA µM-1 cm-2 sensitivity for diuron determination. In addition, the DPV experiment exposed that the γ-Bi2O3/GO/GCE electrode achieves stupendous selectivity, durability, and acceptable feasibility of the real-time samples.

Exploring the interlaminar toughening potential of carbon nanoparticles: Structural and size effects

This work explored the influence of the intrinsic structure and size of different carbon nanoparticles on the morphologies of their corresponding aggregated structures, as well as their interlaminar toughening effect in carbon fiber reinforced polymer composites. CNTs and Grs with different sizes were selected as building blocks of toughening layer, which were firstly well-dispersed into acetone and then spray-coated onto the surface of carbon fabrics. The results indicate that one-dimensional filamentous CNTs are prone to forming loose and porous layers, exhibiting better interlaminar toughening effects. On the contrary, the layers formed by two-dimensional sheet-like graphene are relatively dense at microscale, which weakens the interlaminar fracture toughness of the laminated plate. In addition, CNTs with short length have a larger BET surface area at nanoscale and form a porous layer at microscale, showing best interlaminar toughening efficiency.

Air-gap-assisted solvothermal process to synthesize unprecedented graphene-like two-dimensional TiO2 nanosheets for Na+ electrosorption/desalination

Designing a high-performance capacitive deionization setup is limited due to the slow salt removal and charge storage capacities. Efforts are being made to replace traditional electrodes with advanced 2D materials. We introduce a simple method for synthesizing two-dimensional titanium dioxide graphene-like nanosheets via a unique air-gap-assisted solvothermal method. Crystalline 2D graphene-like anatase-TiO2 sheets of unprecedented quality were obtained by tuning the air gap in the solvothermal reactor. The 2D TiO2 synthesized by air-gap-assisted solvothermal process has shown an exceptionally high surface area of 934.5 m2/g compared to the pristine TiO2 (249.5 m2/g). The sheets were used as Faradaic electrodes in ion-electrosorption and their capacitive deionization capabilities were evaluated. The electrochemical conductivity was examined via an in situ investigation of Na+-ion migration and storage. The adsorption capacity of 2D TiO2 sheets increased with higher applied potential while keeping the adsorption time constant at 15 min. At adsorption potentials of –0.8 V, –1.0 V, and –1.2 V, desalting rates of 2.09, 2.18, and 2.20 mg g−1 min−1 resulted in adsorption capacities of 31.33, 32.73, and 33.023 mg g–1, respectively. The 2D TiO2 electrode demonstrated high electron-transfer rates, a large desalination capacity, and a rapid average desalting rate. The specific capacity of the 2D-layered TiO2 electrode was found to be about 45.68 F g−1. These results can be attributed to the large specific surface area, short ionic diffusion paths, numerous active adsorption sites, surface defects, and pseudocapacitance. This air-gap-assisted solvothermal method is expected to open new avenues for the synthesis of high-quality 2D materials.

Preparation and Tribological Behavior of Nitrogen-Doped Willow Catkins/MoS2 Nanocomposites as Lubricant Additives in Liquid Paraffin

In this study, willow catkins/MoS2 nanoparticles (denoted as WCMSs) have been prepared using a hydrothermal method. The WCMSs were modified with oleic acid (OA) to improve dispersion in base oil. The friction and wear properties of WCMSs in liquid paraffin (LP) for steel balls were investigated using a four-ball wear tester. The results have shown that at a high reaction temperature, willow catkins (being used as a template) and urea (being used as a nitrogen resource) can effectively decrease the wear scar diameters (WSDs) and coefficients of friction (COFs). At a concentration of 0.5 wt.%, the WSD and COF of steel balls, when lubricated using LP containing modified WCMS with urea, decreased from 0.65 mm and 0.175 of pure LP to 0.46 mm and 0.09, respectively. The addition of urea and hydroxylated catkins can generate a significant number of loose nano-sheets and even graphene-like sheets. The weak van der Waals forces, decreasing the shear forces that the steel balls must overcome, provide effective lubrication during rotation. On the other hand, the tribo-films containing MoS2, FeS, azide, metal oxides and other compounds play important roles in reducing friction and facilitating anti-wear properties.

New graphene-like metallic sheet is just an atom thick

New graphene-like metallic sheet is just an atom thick

Understanding Electrochemical Growth of Carbon Nanotubes from CO2

Previous works have pioneered the observation of carbon nanotube growth in molten LiCO3 electrolytes from CO2. However in many past works, several CO2-derived cathodic carbon morphologies were observed, which included carbon particles/spheres, graphite flakes, carbon nanofibers, CNTs, and graphene-like ultrathin carbon sheets. Moreover, these morphologies are often mixed, resulting in a low selectivity and difficult separation towards one single carbon morphology, and the factors leading to various morphologies are not currently well understood. In this talk, we will explore the fundamental growth mechanism to inform the broader long-term goal of improving the selectivity towards carbon nanotubes from CO2. This present work studied the cathodic growth of carbon nanotubes by utilizing a simple three-electrode configuration consisting of pure Li2CO3 electrolyte, pure transition metal foil cathodes, Pt anode, and homemade Ag/Ag2SO4 reference electrode to determine the impact of tunable parameters on the resulting electroreduction products.

Quantitative morphometry of topological graphene-based aerogels and carbon foams by x-ray micro-computed tomography

In this work, we report quantitative morphometry of freeze-dried graphene-based aerogels (i.e., graphene aerogel-GA, nitrogenated GA-NGA, graphene-carbon nanotube hybrid-Gr-MWCNTs, carbon foam-CF, and CF-GA hybrid-CF-GA) and monoliths, prepared by hydrothermal and organic sol-gel methods, respectively. X-ray micro-computed tomography (XMCT) in combination with scanning and transmission electron microscopy allowed visualization of internal microstructures in three-dimensional space. Quantitative morphometry analysis through the reconstructed volume renderings from two-dimensional sliced images revealed hierarchical structures possessing interlaced thin sheets, honeycomb organization, and topological interconnected pore background domains. The influence of small-diameter functionalized multi-walled carbon nanotubes (MWCNTs) inclusions to graphene-like sheets and integration with CF is assessed through quantitative morphometry analysis in terms of volume-weighted pore size, wall thickness, and porosity levels. Hybrid composite porous solids elucidated cross-linking reinforced by a homogeneous distribution of CNTs into complex sheets of GA and CF matrices. A consistent trend impacting porosity and interconnectedness was found following NGA ≥ GA > CF > Gr-MWCNT2:1 > CF-GA > Gr-MWCNT3:1 > Gr-MWCNT5:1, from XMCT image processing and analyses in corroboration with physical properties and reliability. The experimental results provide insights and guide the design of characteristic porous carbonaceous and graphene-based functional nanomaterials for energy sciences, environmental engineering, and fundamental reactive transport of fluids.

Additive Manufacturing of Cu Using Graphene-Oxide-Treated Powder.

Additive manufacturing of Cu is interesting for many applications where high thermal and electric conductivity are required. A problem with printing of Cu with a laser-based process is the high reflectance of the powder for near-infrared wavelengths making it difficult to print components with a high density. In this study, we have investigated laser bed fusion (L-PBF) of Cu using graphene oxide (GO)-coated powder. The powder particles were coated in a simple wet-chemical process using electrostatic attractions between the GO and the powder surface. The coated powder exhibited a reduced reflectivity, which improved the printability and increased the densities from ~90% for uncoated powder to 99.8% using 0.1 wt% GO and a laser power of 500 W. The coated Cu powders showed a tendency for balling using laser powers below 400 W, and increasing the GO concentration from 0.1 to 0.3 wt.% showed an increase in spattering and reduced density. Graphene-like sheet structures could be observed in the printed parts using scanning electron microscopy (SEM). Carbon-filled inclusions with sizes ranging from 10-200 nm could also be observed in the printed parts using transmission electron microscopy (TEM). The GO treatment yielded parts with higher hardness (75.7 HV) and electrical conductivity (77.8% IACS) compared to the parts printed with reference Cu powder.

Fe3C-Decorated Folic Acid-Derived Graphene-like Carbon-Modified Separator as a Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) battery has been regarded as an important candidate for the next-generation energy storage system due to its high theoretical capacity (1675 mAh g−1) and high energy density (2600 Wh kg−1). However, the shuttle effect of polysulfide seriously affects the cycling stability of the Li-S battery. Here, a novel Fe3C-decorated folic acid-derived graphene-like N-doped carbon sheet (Fe3C@N-CS) was successfully prepared as the polysulfide catalyst to modify the separator of Li-S batteries. The porous layered structures can successfully capture polysulfide as a physical barrier and the encapsulated Fe3C catalyst can effectively trap and catalyze the conversion of polysulfide, thus accelerating the redox reaction kinetics. Together with the highly conductive networks, a cell with the Fe3C@N-CS-modified separator evinces superior cycling stability with 0.06% capacity decay per cycle at 1 C rate over 500 cycles and excellent specific capacity with an initial capacity of 1260 mAh g−1 at 0.2 C. Furthermore, at a high sulfur loading of 4.0 mg cm−2, the batteries also express superb cycle stability and rate performance.

Synthesis and Self-Assembly of Ultrathin Holey Graphdiyne Nanosheets for Oxygen Reduction Reaction.

Graphdiyne (GDY) is a fascinating graphene-like 2D carbon allotrope comprising sp and sp2 hybridized carbon atoms. However, GDY materials synthesized by solution-phase methods normally come as thick and porous films or amorphous powders with severely disordered stacking modes that obstruct macroscopic applications. Here, a facile and scalable synthesis of ultrathin holey graphdiyne (HGDY) nanosheets is reported via palladium/copper co-catalyzed homocoupling of 1,3,5-triethynylbenzene. The resulting freestanding 2D HGDY self-assembles into 3D foam-like networks which can in situ anchor clusters of palladium atoms on their surfaces. The Pd/HGDY hybrids exhibit high electrocatalytic activity and stability for the oxygen reduction reaction which outperforms that of Pt/C benchmark. Based on the ultrathin graphene-like sheets and their unique 3D interconnected macrostructures, Pd/HGDY holds great promise for practical electrochemical catalysis and energy-related applications.

Fabrication of phosphorus-mediated MoS2 nanosheets on carbon cloth for enhanced hydrogen evolution reaction

Molybdenum sulfide (MoS2) as a graphene-like sheet material has attracted wide attention owing to the potential for hydrogen evolution reaction (HER). However, the large-scale application of MoS2 is still difficult due to the inherent poor conductivity and insufficient active edge sites. Herein, we develop a simple method to grow P-doped MoS2 nanosheets on carbon cloth for high efficiency HER. The 2D carbon cloth can prevent the stacking of MoS2 nanosheets and improve the conductivity with the doping of P atoms. As a result, the P–MoS2/CC-300 shows the excellent electrocatalytic activity with an overpotential of 81 mV at 10 mA cm−2 and the lower Tafel slope of 98 mV/dec. Furthermore, it also shows the good electrocatalytic durability for 15 h. This work provides an opportunity for the design of excellent and robust MoS2-based catalyst via structural engineering and doping method.

Graphene-like sheets supported Fe–Co layered double hydroxides nanoflakes as an efficient electrocatalyst for both hydrogen and oxygen evolution reaction, A green investigation

Herein, a nanohybrid material containing graphene-like sheets (GS) and Fe–Co layered double hydroxides nanoflakes (LDHs) was synthesized via simple two-step processes and named Fe–Co LDHs/GS. The Fe–Co LDHs/GS nanohybrid was characterized by various techniques. Fe–Co LDHs nanoflakes were grown on GS in Fe–Co LDHs/GS nanohybrid. The electrochemical surface area of Fe–Co LDHs/GS nanohybrid was obtained 0.05 cm2 based on the Randles-Sevcik equation. The Fe–Co LDHs/GS nanohybrid was applied as an electrocatalyst of HER and OER in a 1.0 M KOH. The electrochemical performance of Fe–Co LDHs/GS nanohybrid was surveyed by several electrochemical methods, and long-term electrochemical stability. The onset potential, overpotential at 10 mA cm−1 current density, and Tafel slope for the Fe–Co LDHs/GS nanohybrid were obtained −0.33 V, −0.43 V (vs. RHE), and 122 mV dec−1, respectively. The Fe–Co LDHs/GS nanohybrid has long-term stability over 35 h in alkaline media toward HER. Furthermore, the onset potential, overpotential at 10 mA/cm, and Tafel slope for the Fe–Co LDHs/GS nanohybrid were obtained as 1.52 V, 1.60 V (vs. RHE), and 44 mV dec−1, respectively. The Fe–Co LDHs/GS nanohybrid has long-term durability over 10 h in alkaline media toward OER.

Phosphonium-defoliated GO nanosheets as micropore booster of carbon membrane to improve separation of tetracycline from isopropanol

This study developed a supported carbon membrane (CM) to conduct organic solvent nanofiltration (OSN). The OSN performance was tuned up by dispersing phosphonium-defoliated graphene oxide (PGO) as filler (0.3 wt%) in the precursor (bitumen) coating. PGO was synthesized through anchoring phosphonium (Ph3PBu+) ions to the oxygenated groups dangled on individual GO sheets that take up 49 wt% of PGO. As PGO experiences elimination of the pendant organic functional groups to form a graphene-like sheet through the course of pyrolysis and carbonization that converts the precursor coating to CM, the graphene-like sheets thus act to induce in-situ face-to-face stacking of the planar polyaromatic hydrocarbons (PAHs) generated from the pyrolysis of bitumen in nanoscale. PGO achieved a superior efficacy of induction than GO because of the defoliating role of phosphonium ion that assures a higher dispersity of graphene-like sheets in the precursor coating. This mechanism in the end casts a higher pore volume in membrane CMPGO than in CMGO (600 vs. 334 μl/g) primarily associating with the micro and meso pores inside the carbonaceous grains (~15–20 nm) that constitute the membrane. These tiny pores connect with the grain boundaries (3–5 nm) to form a porous network in the membrane. Moreover, the resultant membrane operates through a dual interaction model of adsorption and size screening. Membrane CMPGO manifests 99.2~94.2% retention of tetracycline (TC) from the permeate (isopropanol) with an average permeance of 32 L/m2·h·bar over 30 h, whereas the control, CMGO, shows progressive declining from 82% to 30% in 10 h. CMPGO was also evaluated by using the oppositely-charged dyes of different sizes to examine the effect of solute identity on percolation.

High-voltage aqueous symmetric supercapacitors based on 3D bicontinuous, highly wrinkled, N-doped porous graphene-like ultrathin carbon sheets

Biomass-derived 3D bicontinuous, highly-wrinkled, N-doped porous graphene-like ultrathin carbon sheets for high-performance aqueous symmetric supercapacitor.

Sodium hypophosphite-assist pyrolysis of coal pitch to synthesis P-doped carbon nanosheet anode for ultrafast and long-term cycling sodium-ion batteries

Sodium-ion battery has been considered as an ideal alternative to lithium-ion battery due to the abundant resource of sodium. Hard carbon stands a good chance among most carbons to be the most promising anode material for sodium-ion battery because of its randomly oriented graphite layers. However, the disordered graphite layers display sluggish kinetics of sodium ions thus the high-rate capability of hard carbon in sodium-ion battery is still a big challenge. In this study, extremely ultrafast P-doped carbon nanosheet anode with graphene-like wrinkles and sheet thickness of ca. 8 nm for sodium-ion battery was synthesized by pyrolysis of coal pitch with the assistance of sodium hypophosphite. The ultrathin sheet structure and P-doped property could render pseudocapacitive behavior, as a result, the resultant carbon nanosheet anode delivers high-rate capacity and also the long-term cycling stability (i.e., a high reversible capacity of 189 mA h g−1 at 2 A g−1 after 500 cycles, and an extraordinarily high capacity of 80 mA h g−1 at 20 A g−1 after 10,000 cycles).

Structural Evaluation of Coal-Tar-Pitch-Based Carbon Materials and Their Na+ Storage Properties

Linking to the S element hybrid strategies, S-doped carbon materials having different macrostructures and defect concentrations are prepared by using sulfur and coal-tar-pitch as raw materials in a carbonization temperature range of 700–1000 °C. The evaluations of macrostructure and surface characteristics are performed through XRD, TEM, Raman and XPS measurements. Through the linear fitting among the Na+ storage capacity with ID/IG and d002 values, the correlations of Na+ storage capacity with macrostructures and defects are respectively investigated in detail. It is observed that S-doped carbon materials exhibit storage capacity at 120 mAh/g after the charge-discharge is being carried out 2000 cycles at 2.0 A/g. Studies have shown that adsorptions of introduced defects on graphene-like carbon sheets mainly play the role to enhance the storage capacity, and the expanded carbonaceous lamellar spaces of highly disordered and pseudo-graphitic macrostructures provide the channels for fast transfer of Na+. Our studies are able to provide references for designs and fabrications of coal tar pitch based soft carbon materials as sodium-ion batteries (SIBs) anodes when using heteroatoms doping methods.

CoFe/N, S-C Featured with Graphitic Nanoribbons and Multiple CoFe Nanoparticles as Highly Stable and Efficient Electrocatalysts for the Oxygen Reduction Reaction.

The stability and activity of the catalysts are crucial for the oxygen reduction reaction (ORR) in fuel cells. Herein, CoFe/N, S-codoped biomass carbon (FB-CoFe-700) with graphitic nanoribbons and multiple CoFe nanoparticles was prepared through a facile thermal pyrolysis followed by an acid treatment process. The evolution of the growth of metal nanoparticles with the formation of graphite during the carbonization process was investigated. Inseparable from graphitic carbon-encased metal nanoparticles with the coexistence of graphitized nanoribbons and graphene-like sheets, FB-CoFe-700 exhibited a remarkable long-term electrocatalytic stability with 90.7% current retention after 50 000 s much superior to that of the commercially available Pt/C (20 wt %) in an alkaline medium. Meanwhile, FB-CoFe-700 displayed promising ORR catalytic activity (E0 = 0.92 V vs reversible hydrogen electrode (RHE), E1/2 = 0.82 V vs RHE, and n = 3.97) very similar to that of commercial Pt/C and outstanding methanol tolerance in an alkaline medium. This work is helpful for further development of nonprecious metal-doped carbon electrocatalysts with long-term stability.

Predicting the Number of Graphene-Like Layers on Surface for Commercial Fumed Nanodiamonds with Raman Spectra and Model Calculations.

Nanoscale carbon materials have a broad range of applications in the field of surface and material sciences. Each vibration mode of a Raman and Fourier transform infrared (FT-IR) spectra corresponds to a specific frequency of a bond in the core and surface of the crystal, thus it is highly sensitive to morphology, implying that every band is sensitive to the orientation of the bonds and the atomic weight at either end of the bond. Accordingly, in this study we apply transmission electron microscope (TEM), Raman spectroscopies, and model calculations to study the relative content of carbon-carbon (C-C) bonds to the anhydrous and weakly aggregated elementary nanoscale carbon particles of detonation nanodiamonds. One point of the Raman bands at approximately 1300 cm-1 established that there are highly uniform C-C bonds in a tetrahedral crystal field environment not unlike that of diamonds. Another point at approximately 1600 cm-1 would be a hexagonal graphene-like sheet. By analyzing the relative content of carbon bonds using the area of intensity of the Raman peaks and a simulation of crystal morphology, we suggest that the number of graphene surface layers would be monolayers in nanodiamonds, comprising two kinds of C-C bonds, one being sp₃ bonds of diamond in the core and the other being sp₂ bonds of graphene on the surface.

Synthesis and electrochemical performances of ternary nanocomposite SnO2@MoO3@graphene as high-performance anode material for lithium-ion batteries

Nano-grained SnO2@MoO3 are homogenously wrapped in sheet-like graphene to synthesize the SnO2@MoO3@graphene nanohybrid by hydrothermal and ball milling method. It is difficult to find other characteristic diffraction in the XRD patterns, analyzed together with XPS, Raman spectra and TEM image, which further show that a good recombination has occurred. Meanwhile, the SnO2@MoO3 hybrid uniformly dispersed in the graphene, can supply more active sites to store Li+ and prevent the ultrathin graphene nanosheets from stacking. Furthermore, the sheet-like graphene can alleviate the volume expansion in cycling and shorten the transmission path of the electron or Li+. Therefore, the SnO2@MoO3@graphene composite shows high invertible capacity of 1522.5 mAh g−1 at 0.2 A g−1 after 250 cycles with high coulombic efficiency increases from 72.25% in the first cycle to 97.6% in the fourth cycle and remains above 98.0% in the following cycles, superior rate capacity of 730.4 mAh g−1 at 5.0 A g−1 and outstanding long term cycling capacity of 609.3 mAh g−1 at 5.0 A g−1 after 1000 cycles. Thus, SnO2@MoO3@graphene nanocomposite is a confident anode material for next-generation lithium-ion batteries.