Graphitic Carbon Surfaces Research Articles

A Reactive Molecular Dynamics Simulation Study of the Mechanical Response of Amorphous Sulfur–Graphitic Carbon Composite Cathodes

The study explores the use of a composite, graphitic carbon (GC) – sulfur (S) based cathode in laminated structural batteries. Specifically, failure by delamination is studied with regards to the applicability of a double-walled tube architecture obtained by coating the inner surfaces of hollow carbon nanofibers with sulfur. Differences between the material responses of various LiXS (X ∈ (0, 2)) compounds under bulk-like and interface confined conditions are discussed in terms of the shear response of physically and chemically bonded interfaces, formed with non-functionalized and H/OH/O-functionalized GC surfaces. The study indicates that only a chemically bonded interface with non-functionalized GC yields bulk-compatible mechanical behavior, with the exception of concentrations of X ∈ (0.8, 1.1). To strengthen the interface at low Li concentrations, at which a pronounced inhomogeneity in mass density in terms of interface debonding occurs, a modified transition layer was tested. The results indicate a distinct improvement in terms of homogeneity of mass density and plastic strain localization. The effect of delithiation at high rates on the interface structural stability is investigated at different concentrations of Li in structures of initially uniform Li distribution. According to the results, delamination failure is likely to occur.

Integrating nitrogen-doped graphitic carbon with Au nanoparticles for excellent solar energy absorption properties

A novel excellent carbon-H2O nanofluid, nitrogen-doped graphitic carbon, has been discovered and prepared by using a facile metal-organic frameworks (MOFs) derived synthesis method. The obtained ZIF-8 (ZIF denotes zeolitic imidazolate framework) derived nitrogen-doped graphitic carbon (ZNG) analogs have high specific surface area of 580.2 m2 g−1 and show broad band absorption across the visible and near-infrared region. Au nanoparticles with the size of 2–5 nm are facilely and successfully deposited on the surface of nitrogen-doped graphitic carbon (Au/ZNG) via an impregnation-reduction method. The photothermal conversion tests indicate that both ZNG-H2O and Au/ZNG-H2O nanofluids show better photo-thermal performance and more awesome dispersion stability in water than conventional carbon nanofluids such as graphene and nitrogen-doped carbon nanotubes. Just as expected, Au/ZNG nanofluid shows obvious enhancement in photo-thermal performance due to the synergistic effect of the localized surface plasmon resonance (LSPR) Au nanoparticles and ZNG. This novel ZNG/water nanofluid is very attractive in working fluids for direct absorption solar collectors.

Transformation of carbon-encapsulated metallic Co into ultrafine Co/CoO nanoparticles exposed on N-doped graphitic carbon for high-performance rechargeable zinc-air battery

In this work, Co-MOFs microrod structures were firstly fabricated using Co2+ source and trimesic acid (H3BTC) as reaction precursors by a simple solvothermal method, followed by pyrolysis treatment at 900 °C in N2 atmosphere to obtain metallic Co encapsulated into graphitic carbon structure (Co@C) with an average Co particle size of 7.7 ± 0.2 nm excluding large-sized Co particles (>20 nm) and a surface area of 184 g cm−2. Interestingly, ultrafine Co/CoO nanoparticles with an average size of 1.8 ± 0.2 nm anchored on graphitic carbon surface (Co/CoO-C) can be obtained through further acid/alkali rinsing treatment of the as-prepared Co@C using HNO3 and NH3·H2O aqueous solutions respectively, followed by thermal treatment at 900 °C in N2 atmosphere. The formation of Co/CoO-C with a surface area of 247 g cm−2 can be ascribed to the dissolution and reorganization process of carbon-encapsulated metallic Co under acid/alkali rinsing and post-thermal-treatment conditions. As the electrocatalyst, Co/CoO-C exhibits superior bifunctional electrocatalytic activities of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media, notably better than ORR and OER activities of Co@C. The characterization results show that Co-Nx and N doping can be found in both Co@C and Co/CoO-C due to triethylamine (TEA) as solvent providing N source during Co-MOFs synthesis, which are catalytic active species toward electrocatalytic oxygen reactions. Furthermore, the highly exposed ultrafine Co/CoO on graphitic carbon surface can provide more catalytic active sites for high-performance ORR and OER, while carbon-encapsulated metallic Co in Co@C is incapable of directly contacting the electrolyte (only influencing shell-layer carbon function work) with limitedly improved electrocatalytic performance. The fabricated Co/CoO-C with superior bifunctional ORR and OER activities as air cathode material was assembled into a rechargeable zinc-air battery, exhibiting high power density and long-term stability. Our work provides an approach to transform low catalytic active electrocatalyst to high catalytic active one for renewable energy applications.

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation.

Glassy carbon electrodes were functionalized with redox-active moieties by condensation of o-phenylenediamine derivatives with o-quinone sites native to graphitic carbon surfaces. Electrochemical and spectroscopic investigations establish that these graphite-conjugated catalysts (GCCs) exhibit strong electronic coupling to the electrode, leading to electron transfer (ET) behavior that diverges fundamentally from that of solution-phase or surface-tethered analogues. We find that (1) ET is not observed between the electrode and a redox-active GCC moiety regardless of applied potential. (2) ET is observed at GCCs only if the interfacial reaction is ion-coupled. (3) Even when ET is observed, the oxidation state of a transition metal GCC site remains unchanged. From these observations, we construct a mechanistic model for GCC sites in which ET behavior is identical to that of catalytically active metal surfaces rather than to that of molecules in solution. These results suggest that GCCs provide a versatile platform for bridging molecular and heterogeneous electrocatalysis.

Magnetic porous Fe3O4/carbon octahedra derived from iron-based metal-organic framework as heterogeneous Fenton-like catalyst

The synthesis of effective and recyclable Fenton-like catalyst is still a key factor for advanced oxidation processes. Herein, magnetic porous Fe3O4/carbon octahedra were constructed by a two-step controlled calcination of iron-based metal organic framework. The porous octahedra were assembled by interpenetrated Fe3O4 nanoparticles coated with graphitic carbon layer, offering abundant mesoporous channels for the solid-liquid contact. Moreover, the oxygen-containing functional groups on the surface of graphitic carbon endow the catalysts with hydrophilic nature and well-dispersion into water. The porous Fe3O4/carbon octahedra show efficiently heterogeneous Fenton-like reactions for decomposing the organic dye methylene blue (MB) with the help of H2O2, and nearly 100% removal efficiency within 60 min. Furthermore, the magnetic catalyst retains the activity after ten cycles and can be easily separated by external magnetic field, indicating the long-term catalytic durability and recyclability. The good Fenton-like catalytic performance of the as-synthesized Fe3O4/carbon octahedra is ascribed to the unique mesoporous structure derived from MOF-framework, as well as the sacrificial role and stabilizing effect of graphitic carbon layer. This work provides a facile strategy for the controllable synthesis of integrated porous octahedral structure with graphitic carbon layer, and thereby the catalyst holds significant potential for wastewater treatment.

Enhanced photocatalytic hydrogen production of restructured B/F codoped g-C3N4 via post-thermal treatment

Restructured B/F codoped carbon nitride (r-CN-B/F) with enhanced photocatalytic H2 evolution was prepared by post-thermal treatment of B/F codoped carbon nitride (CN-B/F), which is obtained from direct condensation doping using ionic liquid as doping dopant. Characterization results show that B and F doped in the skeleton and surface layer of CN material respectively. It is found that the post-annealing strategy makes for compact interlayer accumulation and large surface area for doped CN. In particular, decreased surface graphitic carbon, increased B doping content and optimized conjugate aromatic ring structure of catalyst after post-sintering treatment are favorable for the photo-generated charge transfer and separation, thereby, the photocatalytic H2 production of r-CN-B/F was much enhanced. This study demonstrates a facile way for optimizing the polymeric structure of heteroatom doped semiconductor materials.

Nucleation and Growth Process of Water Adsorption in Micropores of Activated Carbon Revealed by NMR

Properties of liquids at solid interfaces play a central role in numerous important processes in nature. Nuclear magnetic resonance (NMR) is particularly useful for probing liquid/graphitic carbon interfacial properties. In particular, the nucleus-independent chemical shift (NICS) provides a sensitive measure of the distance between adsorbates and the graphitic carbon surface on the subnanometer scale, enabling NMR to acquire subnanometer scale spatial resolution. Here, by combining the information on thermodynamics obtained from in situ NMR-detected water isotherm and spatially resolved information on structure and dynamics obtained by NICS-resolved NMR, the microscopic process of water nucleation and growth inside the micropore of activated carbons is investigated. The formation of water clusters at surface sites, the cooperative growth process of pore bridging, and the final stage of horizontal pore filling are revealed in detail, demonstrating the potential of this comprehensive NMR approach for study...

Noncovalent immobilization and surface characterization of lanthanide complexes on carbon electrodes.

A new tripodal ligand featuring three appended pyrene moieties has been prepared for studies of noncovalent binding of lanthanide metal complexes to graphitic carbon surfaces. The ligand tightly binds lanthanide(iii) ions by encapsulation within a heptadentate coordination environment; the cerium, neodymium, samarium, and europium complexes (all with formal metal oxidation state of +3) have been synthesized and characterized. These compounds are readily immobilized on graphitic electrodes-this is driven by the presence of the pyrene moieties, as complexes of an analogous ligand without pyrene groups are not stably adherent to the surface. X-ray photoelectron spectra confirm the molecular identity of the pyrene-appended metal complexes upon immobilization, with unique signals appearing for the metal centers as well as all for all symmetry-related nitrogen atoms on the ligand. Consistent with these surface characterization data and studies of a soluble model compound, the surface-immobilized cerium(iii) complex is reversibly oxidized to cerium(iv) near -0.34 V vs. Fc+/0. Based on electrochemical data, this complex is stable for minutes to hours on the surface.

Nafion Induced Surface Confinement of Oxygen in Carbon-Supported Oxygen Reduction Catalysts

Surface confinement of oxygen inside layers of Nafion self-assembled on carbon-supported oxygen reduction reaction (ORR) catalysts was studied. It is demonstrated that oxygen accumulates in the hydrophobic component of the polymer remaining in contact with the carbon surface. The amount of surface confined oxygen increases with the degree of carbon surface graphitization, which promotes the self-assembly of the polymer. Planar macrocyclic ORR catalysts possessing a delocalized system of π electrons such as Co and Fe porphyrins and phthalocyanines have virtually no effect on the surface confinement of oxygen, in accordance with their structural similarity to graphitic carbon surfaces where they adsorb. Platinum particles in carbon-supported ORR catalysts with high metal contents (20%) disrupt the self-assembly of Nafion and virtually eliminate the oxygen confinement, but the phenomenon is still observed for low Pt loading (4.8%) catalysts.

Graphite-Conjugated Rhenium Catalysts for Carbon Dioxide Reduction.

Condensation of fac-Re(5,6-diamino-1,10-phenanthroline)(CO)3Cl to o-quinone edge defects on graphitic carbon surfaces generates graphite-conjugated rhenium (GCC-Re) catalysts that are highly active for CO2 reduction to CO in acetonitrile electrolyte. X-ray photoelectron and X-ray absorption spectroscopies establish the formation of surface-bound Re centers with well-defined coordination environments. GCC-Re species on glassy carbon surfaces display catalytic currents greater than 50 mA cm(-2) with 96 ± 3% Faradaic efficiency for CO production. Normalized for the number of Re active sites, GCC-Re catalysts exhibit higher turnover frequencies than that of a soluble molecular analogue, fac-Re(1,10-phenanthroline)(CO)3Cl, and turnover numbers greater than 12,000. In contrast to the molecular analogue, GCC-Re surfaces display a Tafel slope of 150 mV/decade, indicative of a catalytic mechanism involving rate-limiting one-electron transfer. This work establishes graphite-conjugation as a powerful strategy for generating well-defined, tunable, heterogeneous electrocatalysts on ubiquitous graphitic carbon surfaces.

Wettability of graphitic-carbon and silicon surfaces: MD modeling and theoretical analysis.

The wettability of graphitic carbon and silicon surfaces was numerically and theoretically investigated. A multi-response method has been developed for the analysis of conventional molecular dynamics (MD) simulations of droplets wettability. The contact angle and indicators of the quality of the computations are tracked as a function of the data sets analyzed over time. This method of analysis allows accurate calculations of the contact angle obtained from the MD simulations. Analytical models were also developed for the calculation of the work of adhesion using the mean-field theory, accounting for the interfacial entropy changes. A calibration method is proposed to provide better predictions of the respective contact angles under different solid-liquid interaction potentials. Estimations of the binding energy between a water monomer and graphite match those previously reported. In addition, a breakdown in the relationship between the binding energy and the contact angle was observed. The macroscopic contact angles obtained from the MD simulations were found to match those predicted by the mean-field model for graphite under different wettability conditions, as well as the contact angles of Si(100) and Si(111) surfaces. Finally, an assessment of the effect of the Lennard-Jones cutoff radius was conducted to provide guidelines for future comparisons between numerical simulations and analytical models of wettability.

Importance of Internal Porosity for Glucan Adsorption in Mesoporous Carbon Materials.

To better understand the adsorption of long-chain poly(1 → 4)-β-D-glucans on carbon surfaces as well as interactions responsible for this adsorption, we use a comparative study involving mesoporous carbon-silica composite materials that have been etched to varying degrees and all-atom molecular dynamics simulations. The materials synthesized as part of this etching study consist of an as-synthesized composite material (MCN-MSN), MCN-MSN-0.5 (composite materials consisting of 50% carbon by mass), MCN-MSN-0.3 (composite materials consisting of 70% carbon by mass), and MCN, in which silica etching was conducted using an aqueous ethanolic solution of either NaOH or HF. Data for the adsorption of long-chain glucans to these materials from concentrated aqueous HCl (37 wt %) solution demonstrate a direct relationship between the amount of β-glu adsorption and the magnitude of exposed carbon mesopore surface area, which systematically increases and is also accompanied by an increase in the mesopore size during silica etching. This demonstrates β-glu adsorption as occurring on internal carbon mesopores rather than exclusively on the external carbon surface. These experimental data on adsorption were corroborated by molecular dynamics (MD) simulations of β-glu adsorption to a graphene bilayer separated by a distance of 3.2 nm, chosen to correspond to the carbon mesopore diameter of the experimental system. Simulation results using a variety of β-glu solvent systems demonstrate the rapid adsorption of a β-glu strand on the graphitic carbon surface via axial coupling and are consistent with experimentally observed trends in fast adsorption kinetics. Solvent-mediated effects such as small-scale hydrophobicity and preferential interactions with ions are shown to play important roles in modulating glucan adsorption to carbon surfaces, whereas experimental data on hydrophobically modified silica demonstrate that hydrophobicity in and of itself is insufficient to cause β-glu adsorption from concentrated aqueous HCl solution.

Necrotic cell death caused by exposure to graphitic carbon‐coated magnetic nanoparticles

We synthesized graphitic carbon-coated magnetic nanoparticles (Fe@C NPs) and evaluated their physicochemical properties and mechanism of cytotoxicity in vitro. The structure of these nanocomposites consisted of an iron core encapsulated by a graphitic-carbon shell. The diameter of these Fe@C NPs was 81 ± 14 nm, and the thickness of the carbon layer encapsulating the core was 7.0 ± 0.5 nm. Inhibition of cell proliferation was induced by exposure to Fe@C NPs at doses above 50 μg mL(-1) . The exposed cells did not show increased activation of apoptosis biomarkers such as PARP, caspase-3, caspase-7, and caspase-9, and apoptosis-specific responses such as DNA laddering and annexin V binding to the cell membranes. In addition, the expression levels of autophagy-specific biomarkers such as ATG5 and LC3 after exposure were not enhanced, either. Instead, we observed increased release of lactate dehydrogenase in the culture media and red-fluorescent cell cytosol stained with ethidium homodimer I after the exposure. These results indicated enhanced cell membrane permeability after exposure to Fe@C NPs, probably caused by necrosis. The analysis of the regulatory molecules of cell cycling and proliferation, ERK, p53, and AKT, implied that cell cycle arrest was initiated and the cells were sensitized to necrosis. This necrotic cell death was also observed in carbon shells from Fe@C NPs obtained by removing the metal core. In conclusion, the graphitic carbon-encapsulated magnetic nanoparticles synthesized by one-pot synthesis induced necrotic cell death to human HEK293 cells, which was caused by graphitic carbon surface encapsulating the metal core.

Water Clusters on Graphitic Carbon Surfaces

In this review, we outline our computational efforts in understanding the interactions between water and various graphitic carbon surfaces based on quantum-mechanical level calculations. Among them, we have determined the geometry structures, electronic properties, and vibrational infrared and resonant Raman spectra of water clusters on graphene surface and single walled carbon nanotubes (SWCNTs). Specifically, we found that (1) the hexamer water cluster undergoes isomerization when interacting with a graphene surface, while the smaller water clusters maintain their cyclic or linear configurations, with little changes in their infrared peak positions and almost perfect graphene surfaces due to the physical adsorption of the water clusters; and (2) water molecules can form cylindrical crystalline structures, referred to as ice nanotubes, by hydrogen bonding under confinement within SWCNTs. Our computational results are expected to shed light on the graphene and SWCNTs studies and their applications in areas such as biology and materials science.

Carbon-coated carbon black as stable electrocatalyst support for polymer electrolyte membrane fuel cells.

The surface of commercial carbon black was modified by pyrolysis of acetonitrile in attempt to obtain the graphitic carbon coating layer. It was confirmed that the surface of carbon black was partially graphitized, having 0.23 of graphitization index and 1.87 nm of mean stack height. From the electrochemical oxidation test of carbon, the carbon-coated carbon black showed higher corrosion resistance than the untreated carbon black although the core of the carbon black support still remained untreated. When it was applied to the support for platinum electrocatalyst, the enhanced stability was observed. From those corrosion tests as well as XPS results, it can be suggested that the partially crystalline graphitic carbon surface facilitates the relatively more reduced surface of platinum.

Atomic Force Microscopy of Polymer Coated Graphitic Carbon Surfaces

A modified AFM technique was used to measure interactions between graphitic carbon black particles and, hence, compare effectiveness of dispersants for stable dispersions. The carbon black dispersions were prepared in water using three polymeric dispersants Triton X100, Triton X405 and Lugalvan BNO12. The surfactants were selected based on a previous study with PE/F103 without aromatic ring. That surfactant had attractive interactions emphasizing need for aromatic ring in anchoring group. Attractive interactions between surfaces were observed in water and in absence of polymers. Lack of any attractive interactions in the presence of polymers proved that the selected dispersants are effective stabilizers.

Routes to visible light active C-doped TiO2 photocatalysts using carbon atoms from the Ti precursors

In this work, different thermal treatments of titanium isopropoxide-derived photo-catalyst precursors, designed with the purpose of generating C-doped TiO2 photo-catalysts using carbon atoms present in the TiOx gel precursors as dopants, are presented. Specifically, these look at varying the standard calcination techniques using heat treatments in He (rather than calcination in air) and lower temperature calcinations (200 °C rather than 500 °C). The formed materials are characterised using N2 physisorption, XRD, UV–Visible spectroscopy and XPS and their activities in promoting the oxidation of 4-chlorophenol under visible-light-only conditions were analysed. The nature of carbon remaining on the (or in the) material is discussed found to be both surface graphitic carbon and carbon present in anionic dopant positions. The different contributions of each type of carbon to the catalytic photo-activity under visible light are discussed.

Thermodynamics of adsorption of 1,3,4-oxadiazole and 1,2,4,5-tetrazine derivatives from aqueous-organic solutions on the surface of porous graphitic carbon

The dynamic method was used under conditions close to equilibrium to study thermodynamics of the Henry adsorption of some 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from aqueous-acetonitrile and aqueous-methanol solutions on the surface of porous graphitic carbon (PGC) (Hypercarb™) in the column temperature range of 313 to 333 K. It is shown that dependences of logarithm of retention factor on inverse temperature for all heterocycles are approximated by linear functions with r2 ≥ 0.999. An increase is observed in absolute values of Gibbs energy and enthalpy change at adsorption from aqueous-organic solutions on PGC at an increase in surface area of adsorbate molecules and, on the contrary, a decrease is found in absolute values of entropy change at an increase in the van der Waals volume of molecules. Assumptions are made as to the possible causes of anomalously strong adsorption from solutions under dynamic conditions of planar heterocycles molecules in the range of extremely low PGC surface coverages. Linear correlation is found between the values of variation of Gibbs energy at adsorption from aqueous-acetonitrile and aqueous-methanol solutions.

Negative-ion production on carbon materials in hydrogen plasma: influence of the carbon hybridization state and the hydrogen content on H− yield

Highly oriented polycrystalline graphite (HOPG), boron-doped diamond (BDD), nanocrystalline diamond, ultra-nanocrystalline diamond and diamond-like carbon surfaces are exposed to low-pressure hydrogen plasma in a 13.56 MHz plasma reactor. Relative yields of surface-produced H− ions due to bombardment of positive ions from the plasma are measured by an energy analyser cum quadrupole mass spectrometer. Irrespective of plasma conditions (0.2 and 2 Pa), HOPG surfaces show the highest yield at room temperature (RT), while at high temperature (HT), the highest yield (∼3–5 times compared to HOPG surface at RT) is observed on BDD surfaces. The shapes of ion distribution functions are compared at RT and HT to demonstrate the mechanism of ion generation at the surface. Raman spectroscopy analyses of the plasma-exposed samples reveal surface modifications influencing H− production yields, while further analyses strongly suggest that the hydrogen content of the material and the sp3/sp2 ratio are the key parameters in driving the surface ionization efficiency of carbon materials under the chosen plasma conditions.

The adsorption of hetero- and alicyclic thiophene derivatives from water-acetonitrile solutions on the surface of porous graphitic carbon under high-performance liquid chromatography conditions

The adsorption of hetero- and alicyclic thiophene derivatives synthesized for the first time from water-acetonitrile solutions with various compositions on the surface of porous graphitic carbon was studied by the high-performance liquid chromatography method. The retention factor and Henry adsorption constant values and equilibrium constants of quasi-chemical reactions of the adsorption and solvation of the heterocyclic compounds studied were calculated using the Lanin-Nikitin equation. The influence of the structure of hetero- and alicyclic thiophene derivative molecules on their adsorption on the surface of porous graphitic carbon and solvation in water-acetonitrile solutions was discussed. The Lanin-Nikitin model was found to be more informative in the interpretation of the adsorption-chromatographic experiment data compared with the Snyder-Soczewinski and Scott-Kucera models.