Amorphous Carbon Matrix Research Articles

Crosslinking-induced spontaneous growth: A novel strategy for synthesizing sandwich-type graphene@Fe3O4 dots/amorphous carbon with high lithium storage performance

Graphene/Fe3O4 hybrids have long been regarded as promising anode materials for lithium-ion batteries but remain significant bottlenecks of inhomogeneous/large Fe3O4 particle size and agglomeration during the repeated lithiation/dethiation process. By carefully selecting a metallo-organic molecule of ferrocene as the building block, a novel methodology has been explored herein for the preparation of sandwich-type graphene@Fe3O4 dots/amorphous carbon (G@Fe3O4/C) hybrids via a Friedel–Crafts crosslinking-induced spontaneous growth process. As prepared, ultra-small Fe3O4 dots of 2–3 nm are distributed uniformly in the amorphous carbon matrix coated on the surface of graphene. The ultralow size of Fe3O4 dots is able to minimize the volume change and Li+ migrating distance, while the carbon matrix and graphene framework prevent Fe3O4 dots from aggregation and offer a superior conductive skeleton along with a flexible framework to buffer the volume changes. In addition, the well-developed pore structure can accommodate the large volume change and facilitate the electrolyte diffusion/transfer, thereby increasing the ion accessible surface area, especially at high charge–discharge rates. Consequently, G@Fe3O4/C presents excellent lithium storage performances, including a highly reversible capacity of 1241 mAh g−1, an outstanding cycling stability after 200 cycles (1055 mAh g−1) and a superior high-rate capability (724 mAh g−1 at 5 A g−1).

Photocatalytic activity of a new composite material of Fe (III) oxide nanoparticles wrapped by a matrix of polymeric carbon nitride and amorphous carbon

ABSTRACTPolymeric carbon nitride was synthesized from urea and doped with Cu and Fe to act as co-catalysts. The material doped with Fe was a new composite material composed of Fe(III) oxides (acting as a co-catalyst) wrapped by the polymer layers and amorphous carbon. Furthermore, the copper doped material was described in a previous report. The photocatalytic degradation of the azo dye direct blue 1 (DB) was studied using as photocatalysts: pure carbon nitride (CN), carbon nitride doped with Cu (CN-Cu) and carbon nitride doped with Fe (CN-Fe). The catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), by X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller method (BET), etc. The adsorption phenomenon was studied using the Langmuir and Freundlich models. For the kinetic study, a solution of 500 mg L−1 of DB1 was treated with each catalyst, visible light and H2O2. The dye concentration was measured by spectrophotometry at the wavelength of 565 nm, and the removal of the total organic content (TOC) was quantified. BET analysis yielded surface areas of 60.029, 20.116 and 70.662 m2g−1 for CN, CN-Cu and CN-Fe, respectively. The kinetics of degradation were pseudo-first order, whose constants were 0.093, 0.039 and 0.110 min−1 for CN, CN-Cu and CN-Fe, respectively. The total organic carbon (TOC) removal reached the highest value of 14.46% with CN-Fe.

Correlation study of nanocrystalline carbon doped thin films prepared by a thermionic vacuum arc deposition technique

The synthesis of Ag, Mg and Si nanocrystalline, embedded in a hydrogen-free amorphous carbon (a-C) matrix, deposited by a high vacuum and free buffer gas technique, were investigated. The films with compact structures and extremely smooth surfaces were prepared using the thermionic vacuum arc method in one electron gun configuration, on glass and silicon substrates. The surface morphology and wettability of the obtained multifunctional thin films were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and free surface energy (FSE) by See System. The results from the TEM measurements show how the Ag, Mg and Si interacted with carbon and the influence these materials have on the thin film structure formation and the grain size distribution. SEM correlated with EDX results reveal a very precise comparative study, regarding the quantity of the elements that morphed into carbides nanostructures. Also, the FSE results prove how different materials in combination with carbon can make changes to the surface properties.

MoO2 nanosheets embedded in amorphous carbon matrix for sodium-ion batteries.

MoO2 nanosheets embedded in the amorphous carbon matrix (MoO2/C) are successfully synthesized via a facile hydrothermal method and investigated as an anode for sodium-ion batteries. Because of the efficient ion transport channels and good volume change accommodation, MoO2/C delivers a discharge/charge capacity of 367.8/367.0 mAh g−1 with high coulombic efficiency (99.4%) after 100 cycles at a current density of 50 mA g−1.

Enhancing the nanoscratch resistance of pulsed laser deposited DLC films through molybdenum-doping

Pulsed laser deposition was used to grow DLC and molybdenum-doped DLC (DLC:Mo) films, with metal contents up to 3.2at.%, on silicon substrates. The microstructural details of the films were investigated using X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scan electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Residual stresses were quantified through curvature measurements while the nanoscale mechanical properties of the films were probed using an instrumented indentation platform in the nanoindentation and nanoscratch mode, respectively. The deposition conditions used in this study resulted in an amorphous carbon matrix with sp3 content of 77at.% and density of 2.9g/cm3. Molybdenum-doping reduced the percentage of sp3 hybridization within the amorphous carbon matrix and generated Mo-C bonds as detected through XPS. The increase in the molybdenum content reduced the residual stresses which can be related to the percentage reduction of the highly directional four-fold coordinated carbon atoms and the subsequent release of the strain energy in the system. Furthermore, the resistance to penetration of the DLC:Mo films was also reduced which again could be attributed to the severe graphitization of the amorphous carbon matrix. The effect of molybdenum on the coefficient of friction (COF) was of secondary importance with deviations from the COF of pure DLC on the order of ±12%. In contrast, all DLC:Mo films deposited herein exhibited higher critical loads to failure/delamination with DLC:Mo3.2at.% showing the highest enhancement (+87% compared to pure DLC). This improvement on the critical load to failure can be traced back to (a) the graphitization and softening of the amorphous carbon matrix that increased the ductility of the matrix, (b) the formation of the Mo-C bonds that can operate as obstacles to the micro-fracture processes and (c) the reduction of the residual stresses that increased the mechanical capacity of the film/substrate material system.

Encapsulated Vanadium-Based Hybrids in Amorphous N-Doped Carbon Matrix as Anode Materials for Lithium-Ion Batteries.

Recently, researchers have made significant advancement in employing transition metal compound hybrids as anode material for lithium-ion batteries and developing simple preparation of these hybrids. To this end, this study reports a facile and scalable method for fabricating a vanadium oxide-nitride composite encapsulated in amorphous carbon matrix by simply mixing ammonium metavanadate and melamine as anode materials for lithium-ion batteries. By tuning the annealing temperature of the mixture, different hybrids of vanadium oxide-nitride compounds are synthesized. The electrode material prepared at 700 °C, i.e., VM-700, exhibits excellent cyclic stability retaining 92% of its reversible capacity after 200 cycles at a current density of 0.5 A g-1 and attractive rate performance (220 mAh g-1 ) under the current density of up to 2 A g-1 . The outstanding electrochemical properties can be attributed to the synergistic effect from heterojunction form by the vanadium compound hybrids, the improved ability of the excellent conductive carbon for electron transfer, and restraining the expansion and aggregation of vanadium oxide-nitride in cycling. These interesting findings will provide a reference for the preparation of transition metal oxide and nitride composites as well.

Stress Writing Textured Graphite Conducting Wires/Patterns in Insulating Amorphous Carbon Matrix as Interconnects

This study reports a mechanical stress-based technique that involves scratching or imprinting to write textured graphite conducting wires/patterns in an insulating amorphous carbon matrix for potential use as interconnects in future carbonaceous circuits. With low-energy post-annealing below the temperature that is required for the thermal graphitization of amorphous carbon, the amorphous carbon phase only in the mechanically stressed regions transforms into a well aligned crystalline graphite structure with a low electrical resistivity of 420 μΩ-cm, while the surrounding amorphous carbon matrix remains insulating. Micro-Raman spectra with obvious graphitic peaks and high-resolution transmission electron microscopic observations of clear graphitic lattice verified the localized phase transformation of amorphous carbon into textured graphite exactly in the stressed regions. The stress-induced reconstruction of carbon bonds to generate oriented graphitic nuclei is believed to assist in the pseudo-self-formation of textured graphite during low-temperature post annealing.

Characterization of Activated Carbon from Eggshell Membranes Prepared Using Sodium Acetate and Zinc Metal Activation

The eggshell membranes of ducks and hens were carbonized or activated with 4 wt% sodium acetate or zinc at 400-600°C. The carbonized or activated products were characterized by SEM-EDS, TEM, FTIR and XRD. It was found that the suitable activation temperature for eggshell membranes is 500°C with 30.03-35.26% yield. The activation performance of CH3COONa for eggshell membrane activated carbon production was higher than that of Zn metal. The CO3-2, Ca-O, C=C, Na-O and C-O functional groups have been formed on the surface of eggshell membrane activated carbon materials during both CH3COONa and Zn activation. Furthermore, CaO, MgO, Na2O and ZnO have also accumulated on eggshell membrane activated carbon materials with high content and regular dispersion. It was shown that the particles on the duck eggshell membrane activated carbon formed with Zn had weaker attachment on the surface than for duck eggshell membrane activated carbon formed with CH3COONa at same temperature. The XRD and TEM results revealed that the eggshell membrane activated carbons consist of an amorphous carbon matrix with some disordered graphite carbon matrix, spherical particles and nanofiber.

SnO2/TiO2 nanocomposites embedded in porous carbon as a superior anode material for lithium-ion batteries

With the objective of improving the capacity and cycling stability of SnO2-based anode materials, a new material of SnO2/TiO2 nanocomposites dispersed at porous carbon was synthesized via a route of absorption and carbonization by using Ti-MOF (MIL-125) as both titanium and carbon sources and SnCl2 as tin source. The composite shows micro-/nano-scale combined configuration: a monodisperse sub-micro cylinder structure formed by well-dispersed SnO2 and TiO2 nanoparticles in amorphous carbon matrix. Benefiting from the synergistic effect of TiO2 nanoparticle and amorphous carbon on maintaining the robust architecture as well as the uniform and stable nano-sized particles, the composite exhibits excellent performance as anode material for lithium-ion batteries: a high specific capacity of 1177mAhg−1 and 88.7% capacity retention after 100 cycles at 100mAhg−1, and a stable capacity of 487 at high current density of 2Ag−1.

One-pot synthesis of Li3VO4@C nanofibers by electrospinning with enhanced electrochemical performance for lithium-ion batteries

Electrospinning is firstly used to one-pot synthesis of Li3VO4@C nanofibers in a large scale. Although with the presence of organic sources in synthesis process, the pure phase Li3VO4 with superior nanofibrous morphology is still successfully obtained through adjusting different heat treatment processes and different vanadium sources. The prepared Li3VO4@C nanofibers exhibit a unique structure in which nanosized Li3VO4 particles are uniformly embedded in amorphous carbon matrix. Compared with Li3VO4/C powder, Li3VO4@C nanofibers display enhanced reversible capacity of 451mAhg−1 at 40mAg−1 with an increased initial coulombic efficiency of 82.3%, and the capacity can remain at 394mAhg−1 after 100 cycles. This superior electrochemical performance can be attributed to its unique structure which ensures a high reactivity by nanosized Li3VO4, more stable electrode/electrolyte interface by carbon encapsulation, improved electronic conductivity and buffered volume changes by flexible carbon matrix. The electrospinning technology provides an effective method to obtain high performance Li3VO4 as a promising anode material for lithium-ion batteries.

Cauliflower-like MnO@C/N composites with multiscale, expanded hierarchical ordered structures as electrode materials for Lithium- and Sodium-ion batteries

MnO@C/N composite with expanded cauliflower-like morphology was prepared via one-pot L-tryptophan assisted hydrothermal method following by annealing in Ar atmosphere. The cauliflower structure was assembled by porous nanowires that composed of MnO nanoparticles wrapped by continuous N-doped amorphous carbon matrix. Superior electrochemical performances were obtained in both lithium/sodium ion batteries. And the reaction kinetics of MnO@C/N in lithium/sodium ion batteries were analyzed and compared. More than 837mAhg−1 could be retained after 300 cycles at 500mAg−1. And a high reversible capacity of 336mAhg−1 at 5000mAg−1 also demonstrate the excellent rate performance of MnO@C/N for LIBs. As to SIBs, 123mAhg−1 could be maintained after 200 cycles at 100mAg−1. The superior performances could be attributed to the peculiar porous micro-nano structure and N-doped amorphous carbon coating. The reaction kinetics results revealed that the capacitive-controlled capacity would dominate of the electrochemical performance in SIBs and the diffusion-controlled capacity could play a more important role in LIBs, due to the atom weight and size of Na+ is larger than Li+.

Temperature effects on formation of carbon-based nanomaterials from kraft lignin

The formation of carbon-based nanomaterials was investigated through heating iron nitrate promoted kraft lignin at different temperatures up to 600°C under argon gas at atmospheric pressure. High-resolution transmission electron microscopy and electron diffraction images showed that multi-layer turbostratic-structured graphene presented in samples heated at 600°C. X-ray diffraction results indicated that iron oxides nanoparticles started their formation as an amorphous carbon matrix at 300°C, and turned into α-Fe nanoparticles at 600°C. It is believed that the formation of observed multi-layer graphene materials is based on the dissolution and precipitation mechanism of carbonaceous gases from lignin decomposition acting as carbon sources and α-Fe working as the catalyst.

NiCoO2 nanosheets grown on nitrogen-doped porous carbon sphere as a high-performance anode material for lithium-ion batteries

NiCoO2 nanosheets grown on nitrogen-doped porous carbon spheres (NiCoO2@N-PCs) have been synthesized via a facile approach using gelatin nanospheres (GNSs) as the template, carbon and nitrogen sources. Due to the synergistic effect between the NiCoO2 nanosheets and N-PCs, the NiCoO2@N-PCs composite exhibits an ultrahigh discharge capacity of 978 mAh g−1 at a current density of 200 mA g−1 with minimal capacity loss even after 80 cycles. The superior properties of NiCoO2@N-PCs illustrate that amorphous carbon matrix could significantly improve the electrochemical performance of high-capacity metal oxide anode nanomaterials. Findings from this study suggest that these GNSs may be used to synthesize functional metal oxides, including MnO2, Fe2O3, CoO and NiO@N-PCs nanostructures.

Electrochemical Performances of MoO2/C Nanocomposite for Sodium Ion Storage: An Insight into Rate Dependent Charge/Discharge Mechanism

MoO2/C nanocomposite has been prepared by simultaneously reducing as-prepared MoO3 nanosheets and introducing an amorphous carbon matrix in the combination of facile hydrothermal and post-annealing processes. MoO2 nanoparticles are uniformly embedded in the carbon framework, resulting in porous nanostructured MoO2/C composite material. The MoO2/C electrodes exhibit varied electrochemical working mechanisms for sodium ion storage that is dependent on charge/discharge rates. At low charge/discharge rate conditions, MoO2/C nanocomposite shows dominant battery performances for sodium ion storage involving reversible conversion reaction of MoO2. The MoO2/C anode material can deliver high initial charge capacity of 557.2mAh/g at 0.1C (1C=600mA/g), along with good cycling stability in comparison with bare MoO2 material. At high rate situations, cyclic voltammetric (CV) results indicate distinct pseudocapacitive behaviors of MoO2/C materials when the scanning rate is higher than 0.5mV/s. Specific capacitances of 123.25, 85.47 and 49.90F/g can be obtained from CV measurements conducted at 1, 2 and 5mV/s, respectively. These electrochemical performances illustrate remarkable capabilities of MoO2/C nanocomposite as anode material for sodium ion storage involving varied conversion reactions and pseudocapacitive sodiation/desodiation reactions depending on charge/discharge rates.

Tribo-mechanical properties of reactive magnetron sputtered transition metal carbide coatings

Hard and wear resistant coatings are useful to enhance the functional properties and improve the lifetime of mechanical components. This study proposes a relationship between microstructure and tribo-mechanical properties of TiC, CrC, ZrC and WC transition metal carbide coatings. In these coatings, an amorphous carbon (a-C) matrix phase coexists with a crystalline TMC phase. Superior wear resistance of ZrC coatings followed by the TiC coating was observed and this was explained by improved crystallinity and a-C phase present in coatings. Wear mechanisms were proposed by chemical analysis of wear tracks using micro Raman spectroscopy and energy dispersive X-ray spectroscopy.

Fe2C Nanocrystals Encapsulated in an Active Amorphous Carbon Matrix As High Performance Electrodes for Lithium-Ion Batteries

A Fe2C nanocrystals encapsulated into a nitrogen and sulfur dual doped carbon matrix (Fe2C@C) was first synthesized by a simultaneous polymerization-precipitation technique followed with a high temperature pyrolysis process. This method can lead to an effective and homogenous distribution of core/shell Fe2C nanoparticles into the carbon matrix. The optimized material was applied as an anode for a lithium-ion battery, which showed a high capacity, excellent rate performance, and good cycling capability. It delivered a high specific capacity of 657.7 mA h g-1 at a current density of 0.2 A g-1, and even at a very high current density at 6 A g-1, the electrode still retained a very high specific capacity of 509.1 mA h g-1. After 150 cycles of charge/discharge at a current density of 1 A g-1, no capacity decay was observed which presents itself a promising high performance anode for LIBs. Also, the presence of Fe2C can greatly stabilize the structure of the electrode and the electrode process for the lithiation/delithiation of LIBs. Figure 1

Influence of the nickel oxide nanoparticles content on the electrical properties of carbon/nickel nanocomposites

Carbon/nickel nanocomposites were prepared using the sol–gel method after the incorporation of nickel oxide (NiO) nanoparticles with different mass ratio between 2 and 10% in organic matrix based on pyrogallol–formaldehyde (PF). The obtained materials (C/Ni) were the subjected of heat treatment under inert atmosphere at 650 °C during 2 h. The X-ray diffraction (XRD) showed the presence of metallic Ni phase in amorphous carbon matrix. The electrical conductivity increases with the concentration of NiO at room temperature and exhibits a percolation phenomenon which is confirmed by transmission electron microscopy (TEM) images. The evolution of the dc conductivity in the temperature range between 80 and 300 K of the C/Ni nanocomposites is explained by the three dimensions variable range hopping transport model (3D-VRH) and the nearest neighbor hopping (NNH). The voltage–current V(I) characteristic presents a negative differential resistance (NDR) at room measurement temperature for a low content of NiO. The NDR phenomen is due to the discontinuity of temperature in the interface atmosphere-sample. The ac conductance shows the dominance of three models depending on the content of NiO: the correlated barrier hopping (CBH), the small polaron hopping (SPH) and the hopping conduction mechanisms.

Experimental and computational analysis of carbon molecular sieve membrane formation upon polyetherimide pyrolysis

Carbon molecular sieve membranes (CM) are typically synthesized through pyrolysis of polymers, and are suitable for gas separation under high pressure conditions due to their high selectivity and mechanical strength. There is a lack of knowledge of the mechanisms of membrane formation during pyrolysis, which would be of fundamental importance to a better understanding and precise control of the process. In this work, we investigate the process of CM formation upon pyrolysis of polyetherimide. A carbon membrane was synthesized on a ceramic support and characterized by different techniques, demonstrating the conversion of the polymeric precursor into a porous and predominantly amorphous carbon structure, containing embedded graphitic domains. The membrane showed effective molecular sieve performance as demonstrated in gas permeation tests. Reactive molecular dynamics simulations were carried out to explore the mechanisms of the polymer→CM transformation at the atomistic level. The simulations show that the continuous reaction among the reactive radicals formed upon polymer pyrolysis along with atomic rearrangements spontaneously led to the formation of a nanoporous amorphous carbon matrix, containing interconnected graphitic domains throughout the structure, as observed in the experiments. These results are expected to be of great help to the development of techniques for controllable synthesis of CMs.

Uniformly dispersed nanocrystalline silver reduces the residual stress within diamond-like carbon hard coatings

Composite films containing silver (Ag) nanoparticles embedded in amorphous diamond-like carbon (Ag–DLC) matrix have been deposited on glass and Si (100) substrates using r.f. capacitatively coupled plasma chemical vapour deposition (rf-CVD). Ag content in the DLC films varies with the relative amount of argon in the methane and argon gas mixture during the plasma growth. The film thickness ranges from 50 nm to 105 nm. The sp2/sp3 ratio in the DLC films decreases with the incorporation of nanocrystalline silver. A considerable amount, of about 99% residual stress reduction in Ag–DLC films has been demonstrated through theoretical calculation with the help of experimental optical absorption spectra. The results are verified by experimental nano-mechanical property evolution using nano-indentation. The related residual compressive stress reduction in the Ag–DLC composite films is attributed to the addition of uniformly dispersed nanocrystalline silver nanoparticles in the DLC matrix and the corresponding relative sp2/sp3 ratio variation.

Cell survival and differentiation with nanocrystalline glass-like carbon using substantia nigra dopaminergic cells derived from transgenic mouse embryos.

Regenerative medicine requires, in many cases, physical supports to facilitate appropriate cellular architecture, cell polarization and the improvement of the correct differentiation processes of embryonic stem cells, induced pluripotent cells or adult cells. Because the interest in carbon nanomaterials has grown within the last decade in light of a wide variety of applications, the aim of this study was to test and evaluate the suitability and cytocompatibility of a particular nanometer-thin nanocrystalline glass-like carbon film (NGLC) composed of curved graphene flakes joined by an amorphous carbon matrix. This material is a disordered structure with high transparency and electrical conductivity. For this purpose, we used a cell line (SN4741) from substantia nigra dopaminergic cells derived from transgenic mouse embryos. Cells were cultured either in a powder of increasing concentrations of NGLC microflakes (82±37μm) in the medium or on top of nanometer-thin films bathed in the same culture medium. The metabolism activity of SN4741 cells in presence of NGLC was assessed using methylthiazolyldiphenyl-tetrazolium (MTT) and apoptosis/necrosis flow cytometry assay respectively. Growth and proliferation as well as senescence were demonstrated by western blot (WB) of proliferating cell nuclear antigen (PCNA), monoclonal phosphorylate Histone 3 (serine 10) (PH3) and SMP30 marker. Specific dopaminergic differentiation was confirmed by the WB analysis of tyrosine hydroxylase (TH). Cell maturation and neural capability were characterized using specific markers (SYP: synaptophysin and GIRK2: G-protein-regulated inward-rectifier potassium channel 2 protein) via immunofluorescence and coexistence measurements. The results demonstrated cell positive biocompatibility with different concentrations of NGLC. The cells underwent a process of adaptation of SN4741 cells to NGLC where their metabolism decreases. This process is related to a decrease of PH3 expression and significant increase SMP30 related to senescence processes. After 7 days, the cells increased the expression of TH and PCNA that is related to processes of DNA replication.On the other hand, cells cultured on top of the film showed axonal-like alignment, edge orientation, and network-like images after 7 days. Neuronal capability was demonstrated to a certain extent through the analysis of significant coexistence between SYP and GIRK2. Furthermore, we found a direct relationship between the thickness of the films and cell maturation. Although these findings share certain similarities to our previous findings with graphene oxide and its derivatives, this particular nanomaterial possesses the advantages of high conductivity and transparency. In conclusion, NGLC could represent a new platform for biomedical applications, such as for use in neural tissue engineering and biocompatible devices.