Graphitic Component Research Articles

In-plane electric field induced by cyano groups and graphitic carbon structure for enhancing photocatalytic hydrogen production of carbon nitride

Inducing an intrinsic driving force into a two-dimensional semiconductor plane to boost the separation and transfer of photoexcited electrons and holes near the photoexcited sites is an effective way of suppressing the recombination of photogenerated carriers. In this work, a photocatalyst (CN-g-C3N4-C) with in-plane continuous π-conjugated bonds was developed by introducing cyano groups (abbreviated as CN) and graphitic carbon (abbreviated as C) in the in-plane structure of carbon nitride (g-C3N4). Different from traditional interface modulation approaches based on the van der Waals forces or hydrogen bonds, chemical bonds are formed between the cyano groups and graphitic carbon component in the CN-g-C3N4-C atomic junction, which facilitate the efficient migration of photogenerated carriers. The ultra-thin porous lamellar structure of CN-g-C3N4-C not only shortens the carrier transfer distance, but also effectively increases the specific surface area. In the CN-g-C3N4-C plane, the strong in-plane electric field can drive the orderly transfer of photoexcited electrons and holes to the graphitic carbon end and the cyano group end, respectively, resulting in enhanced separation and transfer of the electrons and holes near the photoexcited sites. Due to its high charge carrier separation efficiency, CN-g-C3N4-C possesses excellent photocatalytic activity, and its hydrogen production rate is 14.8 times higher than that of pristine g-C3N4. This work provides an atomic-level strategy for designing efficient and economical photocatalysts.

Material Design and Optimisation of Electrochemical Li-Ion Storage Properties of Ternary Silicon Oxycarbide/Graphite/Tin Nanocomposites.

In this work, we present the characterization and electrochemical performance of various ternary silicon oxycarbide/graphite/tin (SiOC/C/Sn) nanocomposites as anodes for lithium-ion batteries. In binary SiOC/Sn composites, tin nanoparticles may be produced in situ via carbothermal reduction of SnO2 to metallic Sn, which consumes free carbon from the SiOC ceramic phase, thereby limiting the carbon content in the final ceramic nanocomposite. Therefore, to avoid drawbacks with carbon depletion, we used graphite as a substitute during the synthesis of precursors. The ternary composites were synthesized from liquid precursors and flake graphite using the ultrasound-assisted hydrosilylation method and pyrolysis at 1000 °C in an Ar atmosphere. The role of the graphitic component is to ensure good electric conductivity and the softness of the material, which are crucial for long term stability during alloying–dealloying processes. The presented approach allows us to increase the content of the tin precursor from 40 wt.% to 60 wt.% without losing the electrochemical stability of the final material. The charge/discharge capacity (at 372 mA g−1 current rate) of the tailored SiOC/C/Sn composite is about 100 mAh g−1 higher compared with that of the binary SiOC/Sn composite. The ternary composites, however, are more sensitive to high current rates (above 372 mA g−1) compared to the binary one because of the presence of graphitic carbon.

Fabrication of Partially Graphitic Biochar for the Removal of Diclofenac and Ibuprofen from Aqueous Solution: Laboratory Conditions and Real Sample Applications

In this study, partially graphitic biochar was synthesized using peanut shell biomass and potassium ferrate (K2FeO4) with a simple strategy and applied for the removal of two commonly used nonsteroid anti-inflammatory drugs (ibuprofen [IBU] and diclofenac [DCF]) from water. K2FeO4 0.1 M was found to be the suitable concentration for the conversion from pristine biochar to partially graphitic biochar. After modification, the scanning electron microscopy image revealed an extremely rough and heterogeneous surface of the modified biochar (PK01), while the HRTEM, X-ray diffraction, and Raman spectra analyses indicated the presence of graphitic component in PK01 structure. Characterization results indicated that the synthesized nanomaterial simultaneously possessed the properties of graphitic carbon and porous biochar with relatively large specific surface area (374.0 m2/g), as well as micro/mesopore structure. The effect of ambient conditions (contact time, temperature, and solution pH) on the adsorption processes of two contaminants was investigated. The experimental results suggested that the pseudo-second-order, Langmuir, and Freundlich models could well describe the attached behavior of IBU and DCF onto the adsorbent (PK01). In all experiments (single, binary, and real water sample systems), DCF exhibited higher adsorption capacity compared to that of IBU, due to the more H-bond acceptor of the DCF molecule compared with IBU. The H-bonding interactions could be the major driving force for the attachment of two adsorbates onto the adsorbent surface, followed by electrostatic attractions, and π-π EDA interactions. Based on the experimental results, PK01 can be suggested as a potential adsorbent for the removal of nonsteroidal anti-inflammatory drugs from water bodies.

Exfoliated graphite as a heat-conductive frame for a new pelletized Fischer–Tropsch synthesis catalyst

The introduction of exfoliated graphite into pelletized Co-based catalysts affects in the most positive way both catalytic and physico-chemical properties. Unlike other carbons, the exfoliated graphite allows combination of extended surface with high thermal conductivity. An open-ended system of slit-type pores is revealed by X-ray tomography. Electron microscopy shows graphitic platelets forming an all-penetrating heat-conductive frame. Element distribution analysis shows that this catalyst cannot be considered as a cobalt-on-carbon catalyst since the graphitic component carries insignificant amount of cobalt and serves as a heat-conductive frame only. Thermal conductivity of a catalyst with graphite frame is 2 times higher than that of its industrial predecessor with Al metal frame and 30 times higher than that of a catalyst without heat-conductive additive. Testing in exothermal Fischer–Tropsch synthesis shows a favorable influence of the graphitic additive, i.e. such catalyst shows productivity of 455 g/kg/h at GHSV of 3000 h−1.

Gap-Tethered Au@AgAu Raman Tags for the Ratiometric Detection of MC-LR.

Establishing a simple and accurate assay for detecting Microcystin-LR (MC-LR) is of significant important for the environment and human health. Herein, we develop a ratiometric surface-enhanced Raman scattering (SERS) aptasensor based on internal standard (IS) methods for the sensitive and reproducible quantitative detection of MC-LR. Gap-tethered SERS-active Au@AgAu nanoparticles (NPs) are successfully prepared and the gap sizes are adjustable by simply adjusting the acidity. Gap-tethered Au@AgAu NPs exhibit gap-tunable amplified SERS activity and are served as SERS tags. The graphene oxide (GO)/Fe3O4 NPs demonstrate a unique and stable Raman band from the graphitic component, making them an ideal IS for quantitative Raman analysis. In principle, Au@gap@AgAu NPs are assembled with GO/Fe3O4 NPs depending on the π-π stacking interaction between GO and MC-LR aptamers. In the presence of MC-LR, Au@gap@AgAu NPs are dissociated from GO/Fe3O4 NPs due to the affinity of aptamer, leading to the changes of Raman intensity of SERS tags. Quantitatively, upon correction by the IS Raman signals, the limit of detection (LOD) is as low as 9.82 pM for MC-LR. The developed protocol provides a simple and rapid approach for the sensitive and quantitative detection of MC-LR and shows great promise for applications in complex systems.

Formation and Physicochemical Characteristics of Nano Biochar: Insight into Chemical and Colloidal Stability.

Nano biochar (N-BC) attracts increasing interest due to its unique environmental behavior. However, understanding of its formation, physicochemical characteristics, and stability of N-BC is limited. We therefore examined N-BC formation from bulk biochars (B-BCs) produced from peanut shell, cotton straw, Chinese medicine residues, and furfural residues at 300-600 °C. Carbon stability and colloidal processes of nano peanut shell biochars (N-PBCs) were further investigated. N-BCs formed from pore collapse and skeleton fracture during biomass charring, breakup due to grinding, and sonication. Amorphous fraction in B-BCs was more readily degraded into N-BCs than graphitic component. The sonication-formed N-PBCs contained 19.2-31.8% higher oxygen and fewer aromatic structures than the bulk ones, leading to lower carbon stability, but better dispersibility in water. Heteroaggregation of N-PBCs with goethite/hematite destabilized initially and then restabilized with increasing concentrations of N-PBCs. Compared with stacked complexes of N-PBCs-hematite, the association of goethite with N-PBCs could form interlaced heterostructures, thus shielding positive charges on goethite and causing greater heteroaggregation. These findings are useful for better understanding the formation of N-BCs and their environmental fate and behavior in soil and water.

Quantitative study on graphitization and optical absorption of CVD diamond films after rapid heating treatment

Slightly graphitization might be incurred on CVD diamond films when suffering instantaneous high temperature thermal shock. In this paper, phase transitions of CVD free-standing diamond films have been studied experimentally at the temperature range of 1500–1800 °C through a plasma rapid heating process. Raman spectra and X-ray photoelectron spectra (XPS) are compared and discussed for the purpose of measuring the percentage of graphitic carbon component in CVD diamond films after heat treatment at different temperatures. An obvious optical degradation took place in both visible and infrared bands with the increased treating temperature. The result indicates that graphitization is dominated along grain boundaries rather than in internal grains. In addition, the nitrogen related absorption peaks were not covered by the enhanced optical absorption background, which was caused by the opaque graphitic carbon formed at high temperature. Nitrogen concentrations have also been evaluated for these graphitized diamond films and there is no evidence to show the movement or aggregation of nitrogen atoms.

Novel Ni-Cr-C alloys with chromium carbide whiskers

We study the phases forming in the Ni–Cr–C three-component system appearing during powder mixture baking at 1200–1300 °C followed by fast cooling under increasing the concentration of a graphitic component (up to 5 wt%). The resulting multiphase new alloys show distinctive crystalline Cr3C2 rods with 1–10 micrometer diameters. The whisker regions in alloys have an extremely high hardness from 2200 up to 3200 HV (comparable to the highest hardness of nano whiskers and coatings with the presence of chromium carbide nanoinclusions). We formulate a sol–gel chemistry mechanism of rod formation via carbon diffusion into Cr and CrxCy through a softened Ni-C particle on the Cr particle and the top of growing whisker. It explains discovered correlation between whisker diameters and Ni-particle sizes.

Stable and unique graphitic Raman internal standard nanocapsules for surface-enhanced Raman spectroscopy quantitative analysis

Graphitic nanomaterials have unique, strong, and stable Raman vibrations that have been widely applied in chemistry and biomedicine. However, utilizing them as internal standards (ISs) to improve the accuracy of surface-enhanced Raman spectroscopy (SERS) analysis has not been attempted. Herein, we report the design of a unique IS nanostructure consisting of a large number of gold nanoparticles (AuNPs) decorated on multilayered graphitic magnetic nanocapsules (AGNs) to quantify the analyte and eliminate the problems associated with traditional ISs. The AGNs demonstrated a unique Raman band from the graphitic component, which was localized in the Raman silent region of the biomolecules, making them an ideal IS for quantitative Raman analysis without any background interference. The IS signal from the AGNs also indicated superior stability, even under harsh conditions. With the enhancement of the decorated AuNPs, the AGN nanostructures greatly improved the quantitative accuracy of SERS, in particular the exclusion of quantitative errors resulting from collection loss and non-uniform distribution of the analytes. The AGNs were further utilized for cell staining and Raman imaging, and they showed great promise for applications in biomedicine.

XRD, NMR, and EPR study of polycrystalline micro‐ and nano‐diamonds prepared by a shock wave compression method

We report on XRD, NMR, and EPR study of commercial micro‐ and nano‐diamonds of the SSX series fabricated by a shock wave compression method. XRD data analysis shows that SSX samples consist of nanometer cubic diamond domains intermixing with stacking faults and twins. We show that as‐received samples reveal a graphitic component, which may be removed by additional purification. Crushing the initial microdiamond powder into submicron and nanometer sizes does not result in noticeable variations of the XRD, NMR, and EPR parameters. This finding is explained by the fact that SSX diamonds are polycrystalline aggregates consisting of numerous nanocrystallites of ∼20–25 nm in size. Therefore, soft crushing of these aggregates diminishes their size, but leaves constituting nanocrystallites and their intrinsically facet surfaces mainly untreated. With that some modification of the outer nanocrystallite surface on crushing is observed.

Dielectric properties of single crystalline diamond wafers with large area at microwave wavelengths

In this paper, we present first measurements, carried out at microwave wavelengths, aiming to characterize the dielectric properties of large size single crystalline diamond (SCD) wafers. While the sizes of the SCD wafers are still not sufficient for practical use, we obtained good optical property results. The sample with both sides polished shows a dielectric loss tangent tanδ as low as or possibly lower than a polycrystalline diamond sample with high quality. Results show the importance of surface treatment, especially on the boundaries of the composed SCD chips even without any graphitic component in the diamond wafers.

X-ray Photoelectron Spectroscopy of the Passive Surface of Nickel-Carbon Electrocatalysts after Polarisation in Sulfuric Acid

Thin films of nickel-carbon prepared by d.c. magnetron sputter deposition have previously been shown to exhibit passivity against corrosion as well as electrocatalytic activity towards the hydrogen oxidation reaction of the low-temperature acidic fuel cell. Pure nickel dissolves rapidly under such conditions. X-ray photoelectron spectroscopy (XPS) of Ni-C films containing between 13 and 64 at.% Ni, and polarized at +0.15 V(SHE) in 1.5M H2SO4 at room temperature demonstrates that this passivity is not due to oxide formation, but rather to the presence of the carbon component. XPS identifies the Ni component as being in the metallic state, both before and after polarization in acid. The carbon component comprises a range of phases, with a graphitic or graphenic component being responsible for passivation.

Nitrogen Incorporation of Nanostructured Amorphous Carbon Thin Films by Aerosol-Assisted Chemical Vapor Deposition

Nanostructured pure a-C and nitrogen doped a-C: N thin films with small particle size of, ~50 nm were obtained by Aerosol-assisted CVD method from the natural precursor camphor oil. Five samples were prepared for the a-C and a-C: N respectively, with the deposition temperatures ranging from <TEX>$400^{\circ}C$</TEX> to <TEX>$600^{\circ}C$</TEX>. At high temperature, the AFM clarifies an even smoother image, due to the increase of the energetic carbon ion bombardment at the surface of the thin film. An ohmic contact was acquired from the current-voltage solar simulator characterization. The higher conductivity of a-C: N, of <TEX>${\sim}{\times}10^{-2}Scm^{-1}$</TEX> is due to the decrease in defects since the spin density gap decrease with the nitrogen addition. Pure a-C exhibit absorption coefficient, <TEX>${\alpha}$</TEX> of <TEX>$10^4cm^{-1}$</TEX>, whereas for a-C:N, <TEX>${\alpha}$</TEX> is of <TEX>$10^5cm^{-1}$</TEX>. The high <TEX>${\sigma}$</TEX> value of a-C:N is due to the presence of more graphitic component (<TEX>$sp^2$</TEX> carbon bonding) in the carbon films.

Solvent-based preferential deposition of functionalized carbon nanotubes on substrates

Solution-processed deposition of carbon nanotubes (CNTs) provides a cost-effective means to synthesize uniform vertically or horizontally aligned nanostructures on top of substrates. The efficacy of deposition depends on the solubility of CNTs in the solvent as well as the ordering of nanotubes relative to the substrates. These governing factors, which determine the specific morphologies of CNTs that are deposited, are determined by the molecular interactions between the CNTs and the substrate and solvent molecules. In an effort to mimic the conditions during solution-processed deposition of nanotubes on substrates, we employed molecular dynamics (MD) simulations to study systems comprising CNTs and commonly used solvents toluene and acetone sandwiched between silicon substrates. Both charged and uncharged substrates were simulated to evaluate the effect of electrostatic interactions between nanotubes and substrate on deposition. Comparison of simulated systems with pure and functionalized CNTs indicate that the presence of –COOH functional groups in CNTs is necessary for uniform deposition on substrates. Time-averaged distribution of the angles formed between the axes of the CNTs and that between the nanotubes and substrates demonstrate that functionalized carbon nanotubes (FCNTs) align parallel with the substrates to a greater extent when toluene is used as a solvent. Time-averaged density distributions obtained from our simulations illustrate that FCNTs tend to migrate towards the substrates, especially when the substrates have finite charge density. However, polar acetone molecules form layers on the substrates and thus lead to electrostatic shielding between nanotubes and substrates that hinders deposition. Hence, non-polar solvents such as toluene are more effective for deposition of nanotubes. Based on radial distribution functions (RDFs) and coordination numbers of various atoms of CNTs with respect to solvent atoms as well as with respect to that of other CNTs, we present a hypothesis that relative extent of coordination between solvent molecules and the functional groups and graphitic component of CNTs determine the solubility and the propensity of parallel alignment of FCNTs in solvents. Overall, results presented in this study provide fundamental insight to predict key factors for solution-processed deposition of well-ordered CNTs on silicon substrates.

Effect of Graphite Features on the Properties of Metal–Organic Framework/Graphite Hybrid Materials Prepared Using an in Situ Process

Metal-organic framework (MOF)/graphite hybrid materials were prepared using an in situ process. Graphites with various chemical and physical features were used, and HKUST-1 was selected as the MOF component. The samples (parent materials and hybrid materials) were characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Then they were tested as ammonia adsorbents in dynamic conditions. The results indicate that the functionalization of graphite is important to build the hybrid materials with synergistic properties. The lack of functional groups on graphite results in the formation of a simple physical mixture. Besides the surface chemistry of the graphitic component, the physical parameters (porosity and size of flakes) also seem to influence the formation of the hybrid materials. It is observed that the graphite particles disturb the formation of HKUST-1 and induce a different crystal morphology (more defects and increased surface roughness) than the one observed when MOF is formed in the absence of a substrate. The latter behavior causes less ammonia to be adsorbed on the hybrid materials than is expected for the simple physical mixture of HKUST-1 and graphite. The MOF structure collapses (in HKUST-1 and the hybrid materials) upon ammonia adsorption and leads to the formation of new species.

Influence of annealing on the microstructure and electrochemical properties of B-doped nanocrystalline diamond films

The annealing under different temperatures was performed on boron-doped nanocrystalline diamond films synthesized by hot filament chemical vapor deposition (HFCVD). The effects of annealing on the microstructure and electrochemical properties of films were systematically investigated. The results show that there are four peaks at 1157,1346,1470 and 1555 cm-1 in Raman spectra of the unannealed sample. When the films were annealed at temperatures above 800 ℃, there are only two peaks of D and G band, indicating that the hydrogen in grain boundaries significantly decreased. The area-integrated intensity ratio of D band to G band (ID/IG) reaches minimum value, revealing that the cluster number or cluster size of sp2 phase was reduced. The G peak position shifts to lower wave number, indicating an decrease in the ordering of graphitic component. The electrode exhibits the widest potential window and the highest oxygen evolution potential, and the quasi-reversible reaction occurs on the surface of the samples. The D peak is quite sharp and its intensity increases when the sample was annealed at 1000 ℃. The ID/IG value attains to the maximum value and the G peak position clearly shifts to higher value. The electrode exhibits the narrowest potential window and the lowest oxygen evolution potential, and the reversible electrochemical reaction occurs in the surface of the sample. The above results reveal that the cluster number or cluster size of sp2 phase, the amounts of trans-polyacetylene related to hydrogen in the grain boundaries, the disordering of graphitic components and the boron diffusion in the nanocrystalline diamond films give contributions to the complex change in electrochemical properties of the films with the annealing temperature increasing.

Performance analysis of poly-, nano- and single-crystalline diamond-based photocathodes

The results of the external Quantum Efficiency (QE) measurements, in the range 150–210 nm, of Poly-, Nano- and Single-Crystalline Diamond (PCD, NCD and SCD) film photocathodes (PCs) are reported and discussed. The diamond films, grown by Microwave Plasma Assisted Chemical Vapour Deposition (MPACVD) technique, have been analyzed with the aim to define which characteristics enhance their QE. It has been found that NCD film PCs, generally showing a lower QE with respect to PCD ones, enhance their photoemission if a graphitic component is present in the film. Surface hydrogenation effects on the photoemissivity of PCs have been investigated. Comparative studies between the QE of an untreated and a hydrogenated-treated diamond film PC show that the hydrogenated sample exhibits Negative Electron Affinity (NEA) properties. An ageing test of 24 h air exposure shows a stability of the hydrogenated diamond PC higher than that of the CsI one. Moreover, the PC conditioning by means of H 2 plasma allows to recover almost completely the loss of PC QE due to ageing effect caused by the air exposure of a previously hydrogenated sample. The sensitivity of PCs depends strongly on the topography of diamond films.

Modern and fossil charcoal: aspects of structure and diagenesis

The structures and compositions of modern and fossil charcoal samples were compared in order to evaluate charcoal degradation processes in archaeological sites. Modern charcoal samples produced in campfires contain two major phases: graphite-like microcrystallites and a non-organized phase. These phases create a mosaic-like structure with differing relative proportions depending on the taxonomic source of the wood used. Fossil charcoal samples (Tel Dor, Israel: 3000 years BP and Kebara Cave, Israel: 40,000 years BP) also contained the graphite-like microcrystallites and the non-organized phases, but were clearly altered compared to modern charcoal. The graphite-like phase of the fossil charcoal has much higher electrical resistivity, and its ESR properties show that it has markedly altered surface electronic states. Infrared spectra show the presence of additional carboxylate groups. Oxidation has therefore altered the structure. This appears to be a “self-humification” process that affects the graphitic component, and probably the non-organized phase as well.

Carbon accumulation on Pt black from hydrocarbons of different structure

Pt black was subjected to deactivating treatments with 3 hydrocarbons: hexadiene (HD), hexane (nH) and neohexane (neoH) followed by measurements of XPS and UPS spectra. The binding energy of the Pt 4f peak remained unchanged after treatments. The carbon accumulation after HD treatment was greater than that after contact with nH or neoH. The carbon content and its chemical state was close to each other after both alkanes. The graphitic component was higher after HD treatment while slightly more ℌdisordered Cℍ was present after deactivation with nH, indicating no pronounced ℌ1 routeℍ of carbonization during neoH treatment.

Elastic modulus and structural evolution of diamond-like carbon films deposited by RF-PACVD

Dependence of the elastic modulus of diamond-like carbon (DLC) films on film thickness was investigated by the recently suggested free overhang method. The DLC films of thickness ranging from 50 to 1300 nm were deposited on Si (100) wafer by 13.56-MHz radio frequency plasma assisted chemical vapor deposition (RF-PACVD) process. In the free overhang method, the elastic modulus of thin film could be measured without considering the substrate effect since the substrate was completely excluded from the measurement. It was observed that the elastic modulus of the very thin film was smaller than that of the thick film in both cases where the ion energy was higher and lower than the optimum value for dense and hard DLC film deposition. However, at the optimum ion energy, the elastic modulus was independent of film thickness. Raman spectroscopy analysis showed that the change of elastic modulus in very thin DLC films was intimately related to the structural evolution which occurred in the initial stage of the film deposition. When the ion energy was lower than the optimum value, more polymeric component was deposited in the initial stage. On the other hand, a more graphitic component was involved in very thin films at an ion energy higher than the optimum value.