Graphite-like Phase Research Articles

Revealing an Extended Adsorption/Insertion-Filling Sodium Storage Mechanism in Petroleum Coke-Derived Amorphous Carbon.

Amorphous carbon holds great promise as anode material for sodium-ion batteries due to its cost-effectiveness and good performance. However, its sodium storage mechanism, particularly the insertion process and origin of plateau capacity, remains controversial. Here, an extended adsorption/insertion-filling sodium storage mechanism is proposed using petroleum coke-derived amorphous carbon as a multi-microcrystalline model. Combining in situ X-ray diffraction, in situ Raman, theoretical calculations, and neutron scattering, the effective storage form and location of sodium ions in amorphous carbon are revealed. The sodium adsorption at defect sites leads to a high-potential sloping capacity. The sodium insertion process occurs in both the pseudo-graphite phase (d002 > 0.370nm) and graphite-like phase (0.345 ≤ d002 < 0.370nm) rather than the graphite phase, contributing to low-potential sloping capacity. The sodium filling into accessible closed pores forms quasi-metallic sodium clusters, contributing to plateau capacity. The threshold of the effective interlayer spacing for sodium insertion is extended to 0.345nm, breaking the consensus of insertion interlayer threshold and enhancing understanding of closed pore filling. The extended adsorption/insertion-filling mechanism explains the sodium storage behavior of amorphous carbon with different microstructures, providing theoretical guidance for the rational design of high-performance amorphous carbon anodes.

Construction of PEO@g-C3N4 supported ionic liquid membrane with interactive network structure for enhanced carbon capture efficiency

Polyethylene oxide (PEO) shows a high CO2-philic due to its dipolar-quadrupolar interaction with CO2 molecules. As a result, it is an excellent candidate for gas separation applications, yet it faces problems such as crystallization and low permeance. Herein, we show a versatile strategy to enhance gas permeation fluxes, which is mainly achieved by hindering the crystallization of PEO and the stacking of nanosheets. Specifically, graphite-like phase carbon nitride (g-C3N4) nanosheets are introduced and interaction networks (PGCN) are constructed by taking full advantage of the dipole-level quadrupole moment interactions between the ether-oxygen groups contained in PEO and CO2. In order to compensate the membrane surface defects for enhancing gas selectivity, we used the suspension coating method to create a PEO@g-C3N4 supported ionic liquid membrane (PGCN/ILX SILM) by coating IL on the surface of membrane. The results show that, when the IL concentration is 30 wt%, the PGCN/IL30 % membrane separates CO2/N2 with a CO2 permeance of 1396 GPU and an optimal selectivity of 58. While overcoming the “Trade-off” effect, it has demonstrated good thermal stability and long-term stable operation for 72 h. The development of this work will generate solutions for overcoming PEO crystallization and achieving efficient CO2 capture.

Bandgap modulations and promoted carrier separation in crystalline g-C3N4 thin films via chemical vapor deposition

The preparation of high-quality graphite-like phase carbon nitride (g-C3N4) films is challenging, which limits the potential optoelectronic and photocatalytic applications. Here, we report the growth of crystalline g-C3N4 films with thicknesses of approximately 100–200 nm on the indium tin oxide substrates by chemical vapor deposition. The films show high crystalline quality and uniformity as suggested by the appearance of interference fringes in the transmission spectra and the existence of exciton peak. The optimized growth conditions for high-quality g-C3N4 films deposition have been obtained through combined optical characterizations and detailed electronic structure analyses using x-ray spectroscopies. The as-grown g-C3N4 films exhibit a bandgap value of 3.05 eV as well as an enhanced fluorescence lifetime of ∼12.43 ns. By adding thiourea to the melamine precursors, N vacancies have been formed in the main heptazine structure, achieving the modulation of the bandgap and the promoted carrier separation. This work provides guidelines for understanding the property–structure relationships during g-C3N4 film deposition. The deposition of high crystallinity g-C3N4 films therein further extends the applications in the fields of optoelectronic and photocatalytic devices.

Implanting pyrazine ring into g-C3N4 for accelerating photocatalytic hydrogen evolution

It is of great significance to develop an efficient and stable photocatalyst for the photocatalytic decomposition of water to produce hydrogen. Within this paper, an effective and simple strategy was adopted to introduce pyrazine ring into graphite-like carbon nitride framework to realize efficient and stable hydrogen production process. After evaluation, the hydrogen production efficiency of the modified semiconductor material is 3.05 folds higher than the unmodified graphite-like phase carbon nitride, and an excellent stability performance was also achieved. It is proved that the light absorption ability of doped semiconductor composite nanomaterials was enhanced markedly by introducing 2-aminopyrazine into the carbon nitride structure. Meanwhile, the segregation efficiency of photo-induced carriers was obviously accelerated because the amino groups can work as hole trapping agents. Additionally, the introduced amino groups own Lewis alkalinity, which is in favour of the photoreduction. This work expands a new perspective of stable photocatalysts in the water split to produce hydrogen.

Analysis of degradation effect of carbon nitride nanomaterials in pollutant treatment

Abstract Photocatalytic technology is known as a green technology in solving energy problems and pollution problems, which can generate clean energy and degrade pollutants. In order to study the degradation performance of carbon nitride and its composites on air pollutants and water pollutants, this paper constructs TiO2/g-C3N4 composite photocatalysts by compositing graphite-like phase carbon nitride (g-C3N4) with titanium dioxide (TiO2) using titanium tetrachloride and melamine as raw materials in a water bath method. The physicochemical properties of the prepared complexes were analytically characterized by X-ray diffraction, UV-Vis diffuse reflectance, and X-ray photoelectron spectroscopy, and their degradation activities were examined and compared. The results of all the tests showed that the prepared 5 wt% TiO2/g-C3N4 nanocomposites performed better compared to other mass percentages of nanomaterials. The degradation of pollutants also resulted in better photocatalytic performance of the 5 wt% nanomaterials, with catalytic efficiencies of 54.2% and 99.5% for NO and methylene blue, respectively, at 30 min, and the good photocatalytic activity remained after five cycles.

Synergistic silver doping and N vacancy promoting photocatalytic performances of carbon nitride for pollutant oxidation and hydrogen production

Carbon nitride (C3N4) has attracted immense interest as a low-cost, non-toxic and naturally abundant raw material. However, graphite-like phase carbon nitride (g-C3N4) still suffers from poor visible light absorption, fast charge carrier recombination, slow electron mobility and relatively fewer surface-active sites. In this work, we synthesized silver-doped N vacancy-rich carbon nitride (AgCN) with convoluted ultra-thin lamellar layers from Ag precursors and melamine-cyanuric acid monomers using a self-assembly supramolecular strategy. AgCN exhibited excellent photocatalytic performance and stability. The introduction of N vacancies disrupted the off-domain π-bonds and weakened the conjugation effect of the triazine ring elements. The large specific surface area of the convoluted ultra-thin lamellar structure helps suppress the aggregation of active silver centers, and the Ag-N2C2 bond acts as a bridge for photoexcited charge transfer to promote the separation and transfer of photogenerated electron/hole pairs for surface redox reactions. As a result, AgCN exhibited excellent photocatalytic performance for photodegradation of rhodamine B (RhB) and hydrogen production (1.69 mmol g-1h−1), well outperforming the pristine CN. Density flooding theory (DFT) calculations revealed the improved conductivity and efficient separation of electron-hole pairs in AgCN at the excited state, generating superoxide radicals, singlet oxygen and holes.

Dielectric response and current-voltage characteristic of Mo-doped diamond-like carbon thin films at room temperature

Herein we have reported the effect of molybdenum (Mo) doping and acetylene (C2H2) gas flow rate, during deposition, on the electrical properties of diamond like carbon (DLC) films. The frequency dependent dielectric response of the undoped and doped DLC films has been discussed in details. Mo doping also increases the dielectric constant value owing to interfacial polarization and the corresponding change with C2H2 gas flow rate has been attributed to the formation of sp2 bonding over sp3 bonding, favoring the emergence of a graphite-like phase. The ac conductivity of DLC films has been observed to increase with frequency following a power law behavior. However, with 29 % Mo doping we have noticed two plateau regions having different slopes which has been explained on the basis of the jump relaxation model (JRM). The theoretical fitting of the experimental data indicates occurrence of ionic conduction along with polaron hoping. The dc contribution part (σdc) of the measured ac conductivity is found to vary with the acetylene (C2H2) gas flow dependent sp2 bonding formation. The σdc is extracted to be 2351 S/m for the 29 % Mo doped DLC films. From the Nyquist plot in impedance spectroscopy single relaxation phenomena have been observed for the no or low Mo doping but with 29 % Mo doping both the grain and grain boundary effect are prominent. This also suggests the presence of sp2 hybridization and formation of dangling bonds between the metal carbide and DLC film. From the current voltage characteristics, the development of high sp2 bonding and high electron injection into the DLC matrix with subsequent change in nature of the DLC from semiconducting to metallic with high Mo doping has been reported. From the capacitance voltage characteristics study it has been found that either increase in acetylene gas flow during deposition or Mo doping increases the space charge and trap carrier densities.

Atomic understanding of elastic-plastic deformation and crack evolution for single crystal AlN during nanoscratch

Single crystal aluminum nitride (AlN) as a new generation of ultra-wide band gap semiconductor materials is the preferred substrate material for high power, high RF devices, but single crystal AlN is hard and difficult to process. To obtain high-quality substrate requires comprehensive understanding of the material deformation and removal mechanism. In this paper, the molecular dynamics simulation method is used to scratch the AlN on the (0001) plane. Set up multiple sets of scratch depths to study the elastic-plastic deformation, material removal mechanism and crack evolution of single crystal AlN. The simulation results show that with the increase of scratch depth, the single crystal AlN workpiece undergoes elastic deformation to continuous plastic deformation and then to brittle fracture. The deformation mode in the elastic stage is phase-change, from wurtzite-structure to graphite-like (GL) phase. The plastic deformation of single crystal AlN is achieved by dislocations moving on the basal and pyramidal planes, and horizontally extended stacking faults. There is almost no subsurface damage below the stacking faults. When the scratch depth exceeds 6 nm, the material will undergo brittle fracture, and the fracture surface is the cleavage surface {10-10} of single crystal AlN.

STUDY OF COAL TAR PITCH MORPHOLOGY AND STRUCTURE

The morphology and structure of the mesophase in the series: coal tar pitch (CTP) - α-fraction of CTP - carbonised α-fraction after heating to 1200 °C, were studied by scanning electron microscopy, X-ray phase and X-ray structural analysis. The X-ray structural parameters were determined: longitudinal and transverse dimensions of the lamellae and the thickness of packages, the distance between the lamellae and the number of lamellae in the formed packages. It is shown that the two-dimensional structures of carbon mesophase are ordered into three-dimensional packages during the formation of semi-coke under CTP heating. It is established that the carbon structure of CTP and its α-fraction is represented by the turbostratic and graphite-like phases. The sizes of the packages formed by the lamellae during structuring in the transverse direction in the studied samples are of the order of 18-25 Å, in the longitudinal direction 46-63 Å, the average distance between the lamellae in the studied samples is 3.46-3.52 Å.

Decomposition of fullerite during the high-temperature heating

X-ray diffraction, scanning electron microscopy, Mossbauer and Raman spectroscopy have been used for studying structural changes arising due to the thermal decomposition of fullerite C60/70 at heating to 1600 °C in CO medium. The scheme of the structural changes of fullerite at the initial graphitization temperatures is given. It is shown that the thermal disordering of fullerite with the formation of a fullerite-like amorphous phase is observed at heating above 900 °C. The subsequent ordering of carbon takes place at the temperature of 1600 °C with the formation of a graphite-like amorphous phase. The graphitization process proceeds with the formation of turbostratic carbon and crystalline graphite with a low degree of ordering. The nature of the formation of carbon substructures is considered. Carbon structural changes are accompanied by morphological changes. Comparative studies of changes in the structure of soot, graphite and glass-like carbon during heating have been presented. The catalytic effect of Fe on the processes of the disordering of initial fullerite is considered. It is shown that in the Fe presence the temperature of the phase transition ‘fullerite-graphite’ decreases from 1600 to 760 °C. Graphite, formed after the Fe3C decomposition, is characterized by a higher degree of ordering.

Selective production of singlet oxygen for harmful cyanobacteria inactivation and cyanotoxins degradation: Efficiency and mechanisms

Knowledge about the impact of singlet oxygen (1O2) on the characteristics and inactivation of harmful cyanobacterial organic matter is limited. In this study, the feasibility of using an improved single-iron doped graphite-like phase carbon nitride catalyst (FeCN) to activate peroxymonosulfate (PMS) catalytic production of 1O2 to inactivate four harmful cyanobacteria was investigated. The inactivation efficiencies at 30 min were 92.77%, 66.84%, 91.06%, and 93.45% for Microcystis aeruginosa (M. aeruginosa), Nodularia harveyana, Oscillatoria sp., and Nostoc sp., respectively. This was associated with adjusting experimental parameters, such as the FeCN and PMS doses and initial pH, to obtain the maximum 1O2 yield. The quenching experiment results and electron paramagnetic resonance spectra showed that 1O2 generated via the non-radical pathway might play a dominant role in inactivating harmful cyanobacteria and degrading harmful algal toxins (Microcystin-LR and Nodularin). In addition, the FeCN-PMS system not only effectively destroyed the integrity of harmful cyanobacterial cells but also effectively degraded cyanobacterial toxins, thereby preventing severe secondary contamination by cell rupture. A possible removal mechanism was proposed. This reveals the potential of 1O2 to simultaneously inactivate harmful cyanobacteria and degrade harmful cyanobacterial toxins.

An ultrasensitive hairpin sensor based on g-C3N4 nanocomposite for the detection of miRNA-155 in breast cancer patient serum.

Achieving the early diagnosis of breast cancer, through ultrasensitive detection of tumor marker miRNA-155, is a significant challenge. Therefore, an ultrasensitive hairpin electrochemical biosensor based on graphite-like phase carbon nitride composite was proposed. In this paper, poly(D-glucosamine) (PDG) was used as a stabilizer and reducing agent to prepare gold nanoparticles at room temperature, and then a graphite-like phase with a two-dimensional lamellar structure carbon nitride was further combined with it to obtain the poly(D-glucosamine)/gold nanoparticles/graphite-like phase carbon nitride nanocomposite (PDG/AuNPs/g-C3N4), in order to achieve the goal of signal amplification. The specific hairpin capture probe (HP) that recognized and bound miRNA-155 was then grafted. The hairpin biosensor showed a linear range of 0.1 fM-1pM with a detection limit of 0.05 fM using differential pulse voltammetry (DPV) electrochemical analysis. Furthermore, the excellent performance hairpin electrochemical biosensor had been applied to the detection of miRNA-155 in human serum samples with good recovery.

Effects of swift heavy ions at different fluencies on WC-6Co hard metal alloy

Tungsten carbide hard metal alloy with 6% by weight cobalt was studied before and after irradiation at different fluencies with 167 MeV132Xe ions. Raman spectroscopy, X-ray diffraction, neutron diffraction and positron lifetime spectroscopy were employed in order to assess the microstructural evolution in the material upon irradiation fluence increase. Analysis of the Raman spectrum for the pristine, non-irradiated material unveils that the surface is composed of a graphite-like phase and highly oxidized tungsten atoms spread in the carbon matrix. All characteristic peaks of tungsten carbide (WC) and possible cobalt phases are either missing or strongly overlapped in all Raman spectra. Bonding between tungsten and oxygen atoms broke upon irradiation and total deoxidation of the surface is detected for the two highest fluencies investigated at 5 × 1013 ions/cm2 and 3,83 × 1014 ions/cm2. Increasing the irradiation dose causes amorphization of the carbon phase on the surface accompanied by “up and down” trend of change in carbon cluster size. The Raman spectra analysis also unveils, that molecular nitrogen (N2) from the atmosphere penetrates the carbon matrix upon irradiation. The results from the X-ray and neutron diffraction reveal that the main phase in the material is δ-WC and also give information about changes of the lattice parameters with increasing fluence. Reorganization of the induced point defects to dislocation defects as a function of the irradiation dose is discussed, but no phase transition of the main δ-WC phase is detected. Steady increase of compressive internal stress with increasing irradiation dose is noted by XRD. The tendency is not monotonic and the stress leans towards saturation at the highest fluence, with the highest value of −5.26 GPa. The Positron lifetime spectroscopy measurements show the presence of short lifetime component ranging from 170 ps to 190 ps, interpreted as small vacancy clusters. The intensities of the different positron lifetime components vary with the irradiation dose non-monotonically.

Effect of elastic deformations on direct polymorphic transformations in BN under pressure

This paper gives an investigation of the effect of shear deformation on direct transitions in BN under pressure. The transition of a hexagonal (graphite-like) phase h-BN into a cubic (“sphalerite”) c-BN through the intermediate rhombohedral phase r-BN, at a pressure P = 3.0 GPa, is shown. With shear deformation applied, the mechanism of h-BN transformation into the hexagonal (wurtzite) phase w-BN changes, and the following planes are parallel in the phases: for P = 5.0 GPa and deformation ε = 0° (001)h|| (001)w; and for P = 5.0 GPa and deformation ε ≅ 7.2 (001)h|| (100)w. The shear deformation at 6–17 GPa leads to the reverse transition of w-BN to h-BN and the observed orientation relationship is different from the one occurring at the thermal transformation of w-BN to h-BN (T ≅ 1600 K) at a pressure P = 0.1 MPa.

Synthesis, structure and electromagnetic properties of FeCoAl/C nanocomposites

Magnetic nanoparticles play an important role in rapidly developing advanced branches of science and industry, e.g. fabrication of magnetic storage media, synthesis of ferromagnetic liquids, medicine and chemistry. One problem faced in the usage of magnetic nanoparticles is their high chemical activity leading to oxidation in air and agglomeration. The chemical activity of magnetic nanoparticles stems from the contribution of their large specific surface to volume ratio. Carbon coating of nanoparticles reduces the interaction between nanoparticles. FeCoAl/C metal-carbon nanocomposites have been synthesized using IR pyrolysis of polymer / metal salt precursors. The effect of synthesis temperature (IR heating) in the range from 500 to 700 °C on the structure and composition of the nanomaterials has been studied. We show that the forming particles are the FeCoAl ternary solid solution with a FeCo based bcc lattice. An increase in the synthesis temperature from 500 to 700 °C leads to an increase in the coherent scattering region of three-component nanoparticles from 5 to 19 nm. An increase in the aluminum content from 20 to 30 % relative to Fe and Co results in an increase in the size of the nanoparticles to 15 nm but this also entails the formation of a Co based solid solution having an fcc lattice. An increase in the nanocomposite synthesis temperature and a growth of the relative Al content as a result of a more complete carbonization and the structure-building effect of metals reduce the degree of amorphousness of the nanocomposite carbon matrix and lead to the formation of graphite-like phase crystallites having an ordered structure. The effect of synthesis temperature and relative content of metals on the electromagnetic properties (complex dielectric and magnetic permeability) of the synthesized nanocomposites has been studied. Synthesis conditions affect the radio absorption properties of the nanocomposites, e.g. reflection loss (RL) in the 3—13 GHz range.

Synthesis, structure and electromagnetic properties of FeCoAl/C nanocomposites

Magnetic nanoparticles play an important role in rapidly developing advanced branches of science and industry, e.g. fabrication of magnetic storage media, synthesis of ferromagnetic liquids, medicine and chemistry. One problem faced in the usage of magnetic nanoparticles is their high chemical activity leading to oxidation in air and agglomeration. The chemical activity of magnetic nanoparticles stems from the contribution of their large specific surface to volume ratio. Carbon coating of nanoparticles reduces the interaction between nanoparticles. FeCoAl/C metal-carbon nanocomposites have been synthesized using IR pyrolysis of polymer/metal salt precursors. The effect of synthesis temperature (IR heating) in the range from 500 to 700 °C on the structure and composition of the nanomaterials has been studied. We show that the forming particles are the FeCoAl ternary solid solution with a FeCo based bcc lattice. An increase in the synthesis temperature from 500 to 700 °C leads to an increase in the coherent scattering region of three-component nanoparticles from 5 to 19 nm. An increase in the aluminum content from 20 to 30% relative to Fe and Co results in an increase in the size of the nanoparticles to 15 nm but this also entails the formation of a Co based solid solution having an fcc lattice. An increase in the nanocomposite synthesis temperature and a growth of the relative Al content as a result of a more complete carbonization and the structure-building effect of metals reduce the degree of amorphousness of the nanocomposite carbon matrix and lead to the formation of graphite-like phase crystallites having an ordered structure. The effect of synthesis temperature and relative content of metals on the electromagnetic properties (complex permittivity and permeability) of the synthesized nanocomposites has been studied. Synthesis conditions affect the radio absorption properties of the nanocomposites, e.g. reflection loss (RL) in the 3–13 GHz range.

Microscopic Kinetics Pathway of Salt Crystallization in Graphene Nanocapillaries.

The fundamental understanding of crystallization, in terms of microscopic kinetic and thermodynamic details, remains a key challenge in the physical sciences. Here, by using insitu graphene liquid cell transmission electron microscopy, we reveal the atomistic mechanism of NaCl crystallization from solutions confined within graphene cells. We find that rock salt NaCl forms with a peculiar hexagonal morphology. We also see the emergence of a transitory graphitelike phase, which may act as an intermediate in a two-step pathway. With the aid of density functional theory calculations, we propose that these observations result from a delicate balance between the substrate-solute interaction and thermodynamics under confinement. Our results highlight the impact of confinement on both the kinetics and thermodynamics of crystallization, offering new insights into heterogeneous crystallization theory and a potential avenue for materials design.

Atomistic simulation of amorphization during AlN nanoindentation

Molecular dynamics simulation is used to study phase transformations during nanoindentation into the (0001) surface of monocrystalline AlN with wurtzite structure. With the indentation depth increasing, the following effects are observed consecutively: a Y-type tearing of the surface; nucleation and growth of a graphite-like phase; formation and flow of an amorphous phase; generation of tetragonal intermediate structure. Due to the symmetry of the crystal structure, a Y-type groove appears after the surface is torn under the force induced by the indenter. Later, graphite-like phase nucleates near the peak of the Y-type groove due to stress concentration, and then expands into the deformation zone where the normal force plays the dominant role. Subsequently, the normal force, exerted to the graphite-like phase, increases continuously and thus induces amorphization. The amorphous phase, appearing beneath the indenter, grows and flows laterally, and leads eventually to the generation of a tetragonal intermediate structure. The results are unaffected when the speed is varied in a wide range of 10–160 m/s.

Ab initio predictions of graphite-like phase with anomalous grain boundaries and flexoelectricity from collapsed carbon nanotubes.

Although large-radius carbon nanotubes (CNTs) are now available in macroscopic quantities, little is known about their condensed phase. Large-scale density functional theory calculations predict a low energy phase in which the same-diameter "dog-bone" collapsed CNTs form a graphite-like phase with complex, anomalous grain boundaries (GBs). The excess GB volume does not prevent the strong van der Waals coupling of the flattened CNT sides into AB stacking. The associated GB energetics is dominated by the van der Waals energy penalty and high curvature bending of the loop CNT edges, which exhibit reactivity and flexoelectricity. The large density and superior mechanical rigidity of the proposed microstructural organization as well as the GB flexoelectricity are desirable properties for developing ultra-strong composites based on large-radius CNTs.

Improvement in the tribocorrosion performance of CrCN coating by multilayered design for marine protective application

Steel structures significantly degrades owing to tribology and corrosion in aggressive marine environment and is unavoidable. Chromium nitride (CrN) based coatings material has aroused great interest as one of the most promising protective system in the marine equipment or its components. In the present study, we provided insights for the tribocorrosion mechanism of CrN and CrCN monolayers as well as CrN/CrCN multilayered coatings deposited on steel substrates via a multi-arc ion method. Field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM) revealed that the design of multilayer structure could interrupt the continuous growth of columnar crystals and making the coating denser. Furthermore, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) results confirmed the CrN/CrCN multilayered coating presented a high content of graphite-like phase and hard Cr-C compounds, which might play a key role enhancing lubrication and hardness. In particular, tribocorrosion tests in artificial seawater showed that the as-deposited CrN/CrCN multilayered coating could demonstrate significant improvement of tribocorrosion resistance compared to the CrN and CrCN monolayers coatings. The corresponded mechanisms were discussed in term of the coatings microstructure and tribocorrosion behaviors.