Graphitization Of Amorphous Carbon Research Articles

Single-atom silver induced amorphization of hollow tubular g-C3N4 for enhanced visible light-driven photocatalytic degradation of naproxen

In this work, a novel strategy for building single-atom silver-induced amorphous graphitic carbon nitride (g-C3N4) with a hollow tubular morphology is developed. By forming a tubular supramolecular gel, silver is successfully isolated by the nitrogen atoms in both melamine and nitrate anions, impeding agglomeration in the subsequent thermal polymerization. The high density of single-atom-dispersed silver (atomic ratio up to 11.6%) selectively breaks the hydrogen bonds in layered g-C3N4, leading to a fully amorphous structure. Silver-induced full amorphization not only enhances the visible light absorption of g-C3N4 but also accelerates charge transfer, endowing the as-prepared photocatalyst having the optimal silver content with 52 times higher surface area specific naproxen (NPX) removal activity than pure g-C3N4. Both density functional theory (DFT) calculations and steric effects are applied to explain the degradation pathway of NPX. The toxicity of NPX is reduced by sufficient irradiation. This work provides useful insights into the design and morphology control of single metal ion-dispersed g-C3N4 for environmental applications.

Understanding the Carbon-Bio Interface: Influence of Surface Chemistry and Buffer Composition on the Adsorption of Phospholipid Liposomes at Carbon Surfaces.

Surface active phospholipids are present in fluids of biological relevance, and their adsorption may condition and determine the response of carbon and nanocarbon surfaces when they are immersed in physiological media. In this work, the adsorption and assembly of liposomes at carbon interfaces were investigated to understand the effect of surface termination on the extent and mode of assembly of lipid aggregates. Liposomes of natural lipids were prepared from a mixture of phosphatidylcholine (PC) and phosphatidylserine (PS), and their hydrodynamic size and surface zeta potential were studied as a function of pH. Adsorption was investigated at graphitic amorphous carbon surfaces (a-C) and at these surfaces after oxidative treatments (a-C:O). Infrared surface spectroscopy experiments show that PC/PS liposomes adsorb at a-C surfaces exclusively, independently of pH, while no adsorption is observed at a-C:O materials. Nanogravimetry and fluorescence imaging experiments in solution indicate that adsorption at a-C occurs as supported intact vesicles. Interestingly, PC/PS adsorption at oxidized surfaces was observed only in the presence of a dication such as Ca2+, a behavior that was attributed to screening of surface-liposome repulsive electrostatic interactions. Vesicle rupture experiments show that lipids adsorb as monolayers on graphitic surfaces, whereas adsorbate structures correspond to bilayers in the case of oxidized carbons. These results therefore demonstrate a strong dependence of adsorbate structure on both carbon chemistry and buffer composition. These findings have important implications for the design of carbon nanoparticles, carbon electrodes, or carbon coatings for applications in biology and medicine.

Synthesis of Ag–Carbon–TiO2 composite tubes and their antibacterial and organic degradation properties

Ag–Carbon–TiO2 composite tubes were prepared by using polystyrene/AgNO3 composite fibers as a sacrifice template and a co-pyrolysis process. The Ag–Carbon–TiO2 tubes were characterized by SEM, TEM, X-ray diffraction, Raman spectrum, XPS, and UV–vis spectrum. The results showed that the Ag–Carbon–TiO2 tubes possessed uniform tubular structure with amorphous carbon, graphitic carbon, and Ag nanoparticles (AgNPs) distributing uniformly in TiO2. The Ag–Carbon–TiO2 tubes were confirmed high UV–vis light utilization and photocatalytic degradation efficiency to Rhodamine B due to the carbon doping, the surface plasmon resonance of AgNPs and the tubular structure, and the degradation of Rhodamine B reached 90% in 6 h. Meanwhile, they showed an excellent antibacterial effect on staphylococcus aureus, and the fatality rate of Ag–Carbon–TiO2 tubes to staphylococcus aureus reached 99.9% in 24 h when its concentration was higher than 4 mg/ml. The co-pyrolysis process could repress the AgNPs to grow to be large particles, which could be a key for the excellent antibacterial property. The research showed a promising strategy for preparing Ag–Carbon–TiO2 composite tubes by co-pyrolysis of PS composite electrospinning fibers, indicating their potential application in wastewater treatment and antibacterial materials.

Influence of hydrogen supply on Mo(C,N) films synthesized by plasma-enhanced chemical vapor deposition using bis(tert‑butylimido) bis(dimethylamido) molybdenum

Complex composites of Mo(C,N) are deposited at temperatures of 150 °C and a working pressure of 1.3 Pa by plasma-enhanced chemical vapor deposition using bis(tert‑butylimido) bis(dimethylamido) molybdenum as precursor, argon as carrier gas to transport the vapors of the liquid metal–organic precursor at 80 °C, and hydrogen gas as reactant. The effect of hydrogen as reactive gas in the deposition process is investigated. For plasma generation in the plasma cleaning and deposition process, pulsed DC plasma is utilized at a negative voltage of 600 V with a frequency of 150 kHz and a pulse reversal time of 1 μs. As a result, hydrogen ambient decreases the depositio rate and surface roughness and increases the hardness of the films. Under the flow rate condition of hydrogen gas over 300 sccm, the hardness reaches high values over 26 GPa, and the adhesion is over 30 N. X-ray diffraction spectroscopy measurements reveal hexagonal phased molybdenum carbide as the preferred crystallization of the Mo(C,N) films, and nanocrystalline molybdenum nitride is mixed with the molybdenum carbide. Analysis of the chemical binding of the Mo(C,N) films by X-ray photoelectron spectroscopy and Raman spectroscopy shows that the dominant binding state is the molybdenum carbide, amorphous graphitic carbon and carbon nitride composites are identified from the evaluation of the binding energy of carbon atoms.

Temperature dependence of catalytic activity in graphene synthesis for Sn nanoparticles

Graphene synthesis at lower temperatures is quite important for a wider range of practical applications. Sn, which is recently found as a promising catalyst for the low-temperature graphene growth, is taken as the study material in this work. Based on the detailed transmission electron microscopy (TEM) observation, we found that catalytic activity of Sn nano-particles is highly temperature dependent which was observed during graphitization of amorphous carbon. For this study, C–Sn composite nanofibers were prepared on an edge of a carbon foil by the Ar+ ion irradiation with simultaneous supply of Sn. As-fabricated C–Sn composite nanofibers were observed to be the amorphous C nanofibers (CNFs) in which the Sn nanoparticles dispersed. The as-prepared samples were annealed at 180–250 °C in a vacuum and were characterized using Raman spectra and high-resolution TEM to study the graphitization process. The graphitization started to occur at an annealing temperature of 180 °C, which is much lower than the graphitization temperature for bulky Sn. Based on the detailed TEM observation of annealed samples, a model to explain the graphitization mechanism at such a low temperature was proposed.

Atomic structure and electronic structure of disordered graphitic carbon nitride

Random networks of sp2 bonded amorphous graphitic carbon nitride (g-CN) have been created by density functional molecular dynamics calculations. A direct molecular dynamics approach was found to create a network with too many like-atom bonds so that an indirect method via an h-BN random network is used. The resulting network possesses the local units of melems found in the crystalline g-C3N4 lattice. The networks have the electron affinity and ionization potential values compatible with photocatalytic water splitting. They are found to possess too many defects so that the band gap is smaller than found experimentally.

Green synthesis of fluorescent carbon quantum dots from Eleusine coracana and their application as a fluorescence ‘turn-off’ sensor probe for selective detection of Cu2+

A facile, rapid and frugal approach was developed for the preparation of highly fluorescent carbon quantum dots (CQDs) by pyrolysis of Finger millet ragi (Eleusine coracana) as a carbon source. The optical properties of as-synthesized CQDs were analyzed by using UV-Visible and fluorescence spectroscopies. Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) showed the formation of CQDs that predominantly consists of carbonyl and hydroxyl groups which can provide more adsorption sites. The X-ray diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy indicated that the synthesized CQDs made of amorphous graphitic carbon like structure. The size distribution was in the range of 3–8 nm with a high abundance of 6 nm particles. The CQDs exhibited bright blue fluorescence emission (wavelength ∼425 nm) under UV-light with an excitation wavelength of 340 nm. Our study indicated that Cu2+ strongly quenched the fluorescent intensity of CQDs compared to other metal ions (Al3+, Ca2+, Mg2+, Ni2+, Pb2+, Mn2+, Cr3+ and Hg2+). There was a linear correlation between the quenching efficiency vs. concentration of Cu2+ ions in the range from 0 to 100 μM (R2 = 0.9918). Furthermore, CQDs have been applied in sensing of Cu2+ in real water samples with a detection limit (LOD) of 10 nM. In addition, density functional theory (DFT) calculations revealed that there was a strong interaction between CQDs with divalent metal ions whereas trivalent metal ions adsorbed weakly. Particularly, Ni2+ and Cu2+ formed a very strong bonding with CQDs compared to other divalent ions. The metal-CQDs complex structure was reported with optimized highest occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) energy gap. The nature of interaction and optical properties of the COOH-CQD’s have been studied with metal ion adsorbed on the surface. Charge analysis corroborated that there was a significant charge transfer between CQDs with Ni2+ and Cu2+. Our study revealed that Cu2+ preferentially get adsorbed on aromatic CC (π-bond) of CQDs whereas other divalent metals form σ-bond(s) with the CQDs. This observation further confirmed by the HOMO-LUMO band gap (Eg) and Frontier molecular orbital analysis.

Computational Predictions and Microwave Plasma Synthesis of Superhard Boron-Carbon Materials.

Superhard boron-carbon materials are of prime interest due to their non-oxidizing properties at high temperatures compared to diamond-based materials and their non-reactivity with ferrous metals under extreme conditions. In this work, evolutionary algorithms combined with density functional theory have been utilized to predict stable structures and properties for the boron-carbon system, including the elusive superhard BC5 compound. We report on the microwave plasma chemical vapor deposition on a silicon substrate of a series of composite materials containing amorphous boron-doped graphitic carbon, boron-doped diamond, and a cubic hard-phase with a boron-content as high as 7.7 at%. The nanoindentation hardness of these composite materials can be tailored from 8 GPa to as high as 62 GPa depending on the growth conditions. These materials have been characterized by electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, and nanoindentation hardness, and the experimental results are compared with theoretical predictions. Our studies show that a significant amount of boron up to 7.7 at% can be accommodated in the cubic phase of diamond and its phonon modes and mechanical properties can be accurately modeled by theory. This cubic hard-phase can be incorporated into amorphous boron-carbon matrices to yield superhard materials with tunable hardness values.

Facile Synthesis of Nitrogen‐Doped Mesoporous Hollow Carbon Nanospheres for High‐Performance Supercapacitors

AbstractWe report the facile preparation of nitrogen‐doped mesoporous hollow carbon nanospheres (N‐MHCNS) by directly carbonizing hollow polypyrrole nanospheres that are derived from in situ polymerization. Here, we use a novel soft template (PMMA‐PBMA‐PMAA) as the core. At 700 °C, the obtained N‐MHCNSs (denoted N‐MHCNS700) show superior electrochemical performance. In 1 M HCl electrolyte, N‐MHCNS700 exhibits a capacitance as high as 275.5 F g−1 at a current density of 1 A g−1 and a high rate capability, retaining 54.4 % of the initial capacitance at the current density of 20 A g−1. In addition, the specific capacitance of N‐MHCNS700 is approximately 100 % retained at a current density of 10 A g−1 after 5000 cycles, indicating amazing stable cycling performance. The excellent electrochemical performance can be derived from the amorphous graphitic carbon, hollow nanosphere structure, mesoporous properties, and nitrogen doping effect.

Graphitization of amorphous carbon by swift heavy ion impacts: Molecular dynamics simulation

Stable C-C bonds existing in several sp hybridizations place carbon thin films of different structural compositions among the materials most tolerant to radiation damage, for applications in extreme environments. One of such applications, solid state electron stripper foils for heavy-ion accelerators, requires the understanding of the structural changes induced by high-energy ion irradiation. Tolerance of carbon structure to radiation damage, thermal effects and stress waves due to swift heavy ion impacts defines the lifetime and operational efficiency of the foils. In this work, we analyze the consequences of a single swift heavy ion impact on two different amorphous carbon structures by means of molecular dynamic simulations. The structures are constructed by using two different recipes to exclude the correlation of the evolution of sp2-to-sp3 hybridization with the initial condition. Both initial structures contain approximately 60% of sp2-bonded carbon atoms, however, with different degree of clustering of atoms with sp3 hybridization. We simulate the swift heavy ion impact employing an instantaneous inelastic thermal spike model. The analysis of changes in density, bonding content and the number and size of carbon primitive rings reveals graphitization of the material within the ion track, with higher degree of disorder in the core and more order in the outer shell. Simulated track dimensions are comparable to those observed in small angle x-ray scattering measurements of evaporation-deposited amorphous carbon stripper foils irradiated by 1.14 GeV U ions.

Anthracite-Derived Dual-Phase Carbon-Coated Li3V2(PO4)3 as High-Performance Cathode Material for Lithium Ion Batteries.

In this study, low cost anthracite-derived dual-phase carbon-coated Li3V2(PO4)3 composites have been successfully prepared via a traditional solid-phase method. XRD results show that the as-prepared samples have high crystallinity and anthracite introduction has no influence on the LVP crystal structure. The LVP/C particles are uniformly covered with a dual-phase carbon layer composed of amorphous carbon and graphitic carbon. The effect of the amount of anthracite on the battery performance of LVP as a cathode material has also been studied. The LVP/C composite obtained with 10 wt % anthracite (LVP/C-10) delivers the highest initial charge/discharge capacities of 186.1/168.2 mAh g-1 at 1 C and still retains the highest discharge capacity of 134.0 mAh g-1 even after 100 cycles. LVP/C-10 also displays an outstanding average capacity of 140.8 mAh g-1 at 5 C. The superior rate capability and cycling stability of LVP/C-10 is ascribed to the reduced particle size, decreased charge-transfer resistance, and improved lithium ion diffusion coefficient. Our results demonstrate that using anthracite as a carbon source opens up a new strategy for larger-scale synthesis of LVP and other electrode materials with poor electronic conductivity for lithium ion batteries.

Fast microwave synthesis of hybrid graphite-amorphous carbon encapsulated Li3V2(PO4)3 as cathode for lithium ion batteries

Abstract In this article, carbon encapsulated Li 3 V 2 (PO 4 ) 3 cathode materials were successfully synthesized via a fast microwave heating method, using domestic microwave oven as reaction device, activated carbon as microwave absorbing agent and starch as carbon precursor. We aimed to use this facile and fast method to shorten the preparation time for Li 3 V 2 (PO 4 ) 3 /C material but maintain its high-rate capability as cathode in lithium ion batteries. X-ray diffraction (XRD), scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) were used to characterize crystal structure and morphology of the material. Results show that the Li 3 V 2 (PO 4 ) 3 encapsulated by hybrid graphite-amorphous carbon possesses pure crystal structure, relatively uniform particles and excellent specific capacities. When cycled at 0.5 C charge/discharge rate, the composite possesses 131.1 mAh g −1 of discharge capacity and still maintains excellent capacity retention (≈100%) over 250 cycles at 20C rate, implying it is a feasible strategy for preparing high-performance Li 3 V 2 (PO 4 ) 3 cathode for lithium ion batteries.

Making co-condensed amorphous carbon/g-C3N4 composites with improved visible-light photocatalytic H2-production performance using Pt as cocatalyst

Novel composites comprising amorphous carbon and graphitic carbon nitride (g-C3N4) were fabricated via facial one-step thermal condensation of glucose and urea precursors. The as-prepared composites were systematically characterized. The photocatalytic activity towards H2 production under visible light was examined. By fine-tuning the weight ratio of precursors, the composites exhibited enhanced photocatalytic activity. The photocatalytic H2 evolution rate of optimal composite was 212.8 μmol h−1g−1, about 10-fold larger than that of pure g-C3N4. The intimate interface between the amorphous carbon and g-C3N4 plays the key role for prolonging the charge carrier lifetime and accelerating the charge transfer kinetics, which benefit the photocatalytic performance. Besides, the enhanced photocatalytic performance is also attributed to the improved visible-light absorption and enlarged surface area. Apart from H2 production, the high-performance gC3N4based photocatalysts are potentially applicable for CO2 reduction, organic synthesis and environmental remediation.

An insight into the effect of calcination conditions on catalytic cracking of toluene over 3Fe8Ni/palygorskite: Catalysts characterization and performance

In this paper, the effect of calcination conditions on catalytic cracking of toluene over 3Fe8Ni/PG (PG: palygorskite) was investigated. The experimental parameters including the calcination temperature, time and atmosphere and reaction temperature were evaluated. The catalysts were characterized using X-ray diffraction (XRD), H2 temperature-programmed reduction (TPR), transmission electron microcopy (TEM) and Raman spectroscopy. The gas composition was analyzed by a gas chromatograph (GC). The results showed that 3Fe8Ni/PG catalyst exhibited a higher catalytic reactivity for catalytic cracking of toluene than that of thermal cracking over quartz. In consideration of the thermal stability and catalytic reactivity of catalyst, a proper calcination temperature and time should be employed in the preparation of 3Fe8Ni/PG catalyst. The 3Fe8Ni/PG reduced in hydrogen at 700°C for 2h showed the highest catalytic reactivity as evidenced by the toluene conversion of 100% at the reaction temperature of 550°C. The catalytic reactivity of 3Fe8Ni/PG reduced in hydrogen for toluene conversion was superior to that of 3Fe8Ni/PG calcinated in air, 3Fe/PG, and 8Ni/PG, which revealed that the awaruite (NiFe) was the active component for the decomposition of toluene. Moreover, steam reforming of toluene over 3Fe8Ni/PG catalysts suggested that 80% toluene conversion can be achieved and most of toluene was converted into H2 and CO. Both amorphous carbon and graphitic carbon species were formed on 3Fe8Ni/PG catalysts after the catalytic reaction. The D/G ratio (the relative intensity of D-band to G-band ratio) was positively correlated to the catalytic reactivity of 3Fe8Ni/PG catalysts.

The electric conductivity of composites based on various carbonaceous fillers and estimation of their percolation model parameters

We have studied the electric conductivity of composites with various carbonaceous fillers (multiwalled carbon nanotubes, colloidal graphite, and amorphous carbon) as a function of the filler content. The widths of critical regions of the percolation transition to the conducting state are determined and the percolation critical exponents are estimated. It is established that there is a tendency to increase in the width of transition region and values of critical exponents when the filler is varied in the following order: carbon nanotubes–colloidal graphite–amorphous carbon.

Electrical property improvement in Cu@graphitic-carbon nanocables

Nanocables of metallic copper nanowire cores coated with amorphous carbon (Cu@C NCs) and graphitic carbon (Cu@G NCs) were mass synthesized via a hydrothermal approach and a further carbonization process. TEM and other techniques revealed that ≈15nm thickness graphitic carbons uniformly encapsulated the well crystallized copper nanowires along the [110] direction. The electrical resistivity measurement indicated that the Cu@C NCs are insulating while the Cu@G NCs are conductive. In addition, the electrical resistivity of a single Cu@G NC was ≈1.6158×10−5Ωcm at room temperature, lower than that of Cu nanowires. This opens a door to broad applications in nanoelectronics.

Effect of Nitrogen and Hydrogen Gases on the Synthesis of Carbon Nanomaterials from Coal Waste Fly Ash as a Catalyst.

Various reducing and inert gases have been used in the catalytic chemical vapour deposition (CCVD) synthesis of carbon nanomaterials (CNMs). In this paper we report on the effects that hydrogen and nitrogen gases have on the production of CNMs from acetylene on fly ash catalysts. Parameters such as temperature and gas environments were investigated. Transmission electron microscopy (TEM) revealed that CNMs of various morphologies such as carbon nanofibers (CNFs) and carbon nanospheres (CNSs) were formed. When hydrogen was used the carbonaceous products were formed in higher yields as compared to when nitrogen was used. This could be due to the multifunctional roles that hydrogen plays as compared to nitrogen. Laser Raman and Mössbauer spectroscopy measurements revealed that three types of products were formed, namely: amorphous carbon, graphitic carbon and iron carbide. Significantly cementite (Fe3C) was identified as the main intermediate carbide species in the catalytic growth of well-ordered CNMs.

Direct laser writing of nanorough cell microbarriers on anatase/Si and graphite/Si

The formation of hierarchical structures consisting of microstripe barriers decorated with nanorough ablated materials prepared by direct laser writing is described. Linear features of circa 25μm width and 12μm height are achieved on amorphous and crystalline titania and graphitic carbon films deposited on silicon. Ablated protrusions build up barriers decorated by nanoscale Si-film reconstructions, as indicated by EDX maps and micro-Raman spectroscopy. Wettability tests show a dramatic change in water contact angle, which leads to almost full wetting after irradiation, irrespective of the original film composition. Fluorescence microscopy images of human mesenchymal stem cells cultured on 1D and 2D structures demonstrate the short term biocompatibility of the ablated surfaces. It is shown that cells adhere, extend and polarize on feature edges, independently of the type of surface, thus suggesting that the created nanoroughness is at the origin of the antifouling behavior. In particular, irradiated anatase and graphite surfaces demonstrate an increased performance of crystalline films for the creation of cell guiding and trapping devices. The results suggest that such laser processing of films may serve as a time-and-cost-efficient method for the design of few-cells analytical surfaces.

Growth of hybrid carbon nanostructures on iron-decorated ZnO nanorods

A novel carbon-based nanostructured material, which includes carbon nanotubes (CNTs), porous carbon, nanostructured ZnO and Fe nanoparticles, has been synthetized using catalytic chemical vapour deposition (CVD) of acetylene on vertically aligned ZnO nanorods (NRs). The deposition of Fe before the CVD process induces the presence of dense CNTs in addition to the variety of nanostructures already observed on the process done on the bare NRs, which range from amorphous graphitic carbon up to nanostructured dendritic carbon films, where the NRs are partially or completely etched. The combination of scanning electron microscopy and in situ photoemission spectroscopy indicate that Fe enhances the ZnO etching, and that the CNT synthesis is favoured by the reduced Fe mobility due to the strong interaction between Fe and the NRs, and to the presence of many defects, formed during the CVD process. Our results demonstrate that the resulting new hybrid shows a higher sensitivity to ammonia gas at ambient conditions (∼60 ppb) than the carbon nanostructures obtained without the aid of Fe, the bare ZnO NRs, or other one-dimensional carbon nanostructures, making this system of potential interest for environmental ammonia monitoring. Finally, in view of the possible application in nanoscale optoelectronics, the photoexcited carrier behaviour in these hybrid systems has been characterized by time-resolved reflectivity measurements.

Characterization of carbon ion implantation induced graded microstructure and phase transformation in stainless steel

Austenitic stainless steel 316L is ion implanted by carbon with implantation fluences of 1.2×1017ions-cm−2, 2.4×1017ions-cm−2, and 4.8×1017ions-cm−2. The ion implantation induced graded microstructure and phase transformation in stainless steel is investigated by X-ray diffraction, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy. The corrosion resistance is evaluated by potentiodynamic test. It is found that the initial phase is austenite with a small amount of ferrite. After low fluence carbon ion implantation, an amorphous layer and ferrite phase enriched region underneath are formed. Nanophase particles precipitate from the amorphous layer due to energy minimization and irradiation at larger ion implantation fluence. The morphology of the precipitated nanophase particles changes from circular to dumbbell-like with increasing implantation fluence. The corrosion resistance of stainless steel is enhanced by the formation of amorphous layer and graphitic solid state carbon after carbon ion implantation.