Amorphous Carbon Nanospheres Research Articles

Catalytic Graphitization by Nickel Nitrate and Characterization on Palm Oil Solid Waste Graphite

Abstract Catalytic graphitization of biomass has been extensively studied. The conventional graphitization method uses high temperatures and non-renewable carbon sources. Temperatures below 1000°C was used in biomass graphitization. The aim of this study is to how these variables affect the structural and morphological properties of the graphite materials produced. In graphite production process, catalyst impregnation is followed by heat treatment. The graphitization process starting with amorphous carbon nanospheres, is investigated by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) studies. XRD was used to examine the graphitization behavior of palm oil solid waste. Based on the result, the position of the 2 theta peak intensity on the XRD graph of the Ni graphitized sample is extremely near to that on the XRD graph of the raw material and carbon sample. The morphological changes that occur in the SEM images for materials graphitized with nickel nitrate are characterized by structures comparable to those that occur in carbon samples. The circular structures in the graphitized sample are anisotropic and structured without orientation bias.

Surface-Pore-Modified N-Doped Amorphous Carbon Nanospheres Tailored with Toluene as Anode Materials for Lithium-Ion Batteries.

The surface modification of amorphous carbon nanospheres (ACNs) through templates has attracted great attention due to its great success in improving the electrochemical properties of lithium storage materials. Herein, a safe methodology with toluene as a soft template is employed to tailor the nanostructure, resulting in ACNs with tunable surface pores. Extensive characterizations through transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption/desorption isotherms elucidate the impact of surface pore modifications on the external structure, morphology, and surface area. Electrochemical assessments reveal the enhanced performance of the surface-pore-modified carbon nanospheres, particularly ACNs-100 synthesized with the addition of 100 μL toluene, in terms of the initial discharge capacity, rate performance, and cycling stability. The interesting phenomenon of persistent capacity increase is ascribed to lithium ion movement within the graphite-like interlayer, resulting in ACNs-100 experiencing a capacity upswing from an initial 320 mAh g-1 to a zenith of 655 mAh g-1 over a thousand cycles at a rate of 2 C. The findings in this study highlight the pivotal role of tailored nanostructure engineering in optimizing energy storage materials.

SnO2 coated carbon nanospheres: Facile preparation and electrochemical performances as anode materials for lithium ion batteries

In this work, the SnO2/C nanocomposites as the anode material for lithium ion batteries (LIBs) were successfully prepared by ultrasonic dispersing of the hydrothermally-synthesized carbon nanospheres in SnCl2 solution and aging for a period of time and then calcination of the dried intermediates in an inert atmosphere. As demonstrated by the experimental results, the obtained SnO2/C nanocomposites were composed of SnO2 nanocrystals (∼10 nm) coated uniformly on the surface of amorphous carbon nanospheres with diameters ranging from 200 nm to 240 nm. The electrochemical test results show that the prepared SnO2/C nanocomposites exhibited higher reversible capacity than the carbon nanospheres, and better cycling performance than the SnO2 nanocrystals. The enhanced electrochemical performance of SnO2/C nanocomposites could be due to the fact that the coupling of SnO2 nanocrystals and carbon nanospheres could not only effectively improve the mobility of charge carriers, but also effectively inhibit the collapse of the SnO2 structure at the expense of a part of the capacity, thus resulting in better structural stability of the SnO2/C nanocomposites.

Description of Photodegradation Mechanisms and Structural Characteristics in Carbon@Titania Yolk-Shell Nanostructures by XAS.

Carbon@titania yolk-shell nanostructures are successfully synthesized at different calcination conditions. These unique structure nanomaterials can be used as a photocatalyst to degrade the emerging water pollutant, acetaminophen (paracetamol). The photodegradation analysis studies have shown that the samples with residual carbon nanospheres have improved the photocatalytic efficiency. The local electronic and atomic structure of the nanostructures are analyzed by X-ray absorption spectroscopy (XAS) measurements. The spectra confirm that the hollow shell has an anatase phase structure, slight lattice distortion, and variation in Ti 3d orbital orientation. In situ XAS measurements reveal that the existence of amorphous carbon nanospheres inside the nano spherical shell inhibit the recombination of electron-hole pairs; more mobile holes are formed in the p-d hybridized bands near the Fermi surface and enables the acceleration of the carries that significantly enhance the photodegradation of paracetamol under UV-visible irradiation. The observed charge transfer process from TiO2 hybridized orbital to the carbon nanospheres reduces the recombination rate of electrons and holes, thus increasing the photocatalytic efficiency.

Carbon transformations in rapidly solidified nickel–carbon ribbon

We report the structural transformations of carbon via the melt spinning and subsequent annealing of nickel-carbon alloys. We attained metastable solid solubility of carbon in nickel ribbon by achieving a rapid solidification rate of up to 1.6 × 106 K/s. Excess carbon atoms were found to be dissolved in the nickel lattice causing up to 1.4% strain for an alloy spun at 70 m/s tangential wheel speeds. High temperature heat treatments led to precipitation of carbon from the nickel lattice on the ribbon free surfaces but also led to growth of spherical precipitates within the nickel matrix, an effect consistent with bulk diffusion-driven Ostwald ripening. Carbon was excavated from the ribbons via chemical dissolution of the metal and characterized by electron microscopy and Raman spectroscopy. We found that the microstructure of carbon precipitated from the rapidly quenched ribbon could be tuned by varying the carbon content from 4 to 12 at. % in the precursor and annealing the ribbon at temperatures that ranged from 400 to 1200 °C. Via the step-wise variation of these two parameters, we sequentially transformed amorphous carbon nanospheres with a high BET surface area of 203 m2/g into thick, highly crystalline flakes of graphite that conformed to the shape of the as-spun ribbon.

Formation of monodispersed carbon nanospheres by pulsed laser irradiation of HOPG

Monodispersed carbon-based nanostructures in the diameter range of 40–50 nm have been produced by pulsed laser irradiation. A pulsed ultraviolet laser light (308 nm) was used to irradiate Highly Oriented Pyrolytic Graphite surfaces with power densities of the order 108 W cm−2. Scanning Electron Microscope images have exhibited a homogenous size distribution of amorphous carbon nanospheres as confirmed by the ID/IG ratio of the Raman spectra. It is shown that the presence of hydrogen acts as a nucleating agent for the carbon nanospheres observed at the outer region of a shockwave induced by the laser pulses at the point of impact. The effect of the energy density, the number of pulses applied to the sample, and the hydrogen flow rate are investigated to elucidate the phase transition from surface graphite-to-carbon nanospheres. Using analytical approaches, we establish the thermodynamic variables (temperature and pressure) corresponding to the laser pulses that drive the structural transformation in hydrogen.

Dynamic mechanical contact behaviours of amorphous nanoparticles subjected to high-speed impact

ABSTRACT The dynamic mechanical contact behaviours between nanoparticles, are of importance for designing advanced nanodevices. In this work, dynamic mechanical response between amorphous nanospheres has been probed by using fully atomistic molecular dynamics simulations. We confirm that the contact radius is greater than Hertzian predictions and the correlation between contact radius and number of atoms in contact still obeys linear relationship largely. It has been discovered that typical yield strength σ-Young's modulusE0 relationship (σ = E0/10) still holds for amorphous carbon nanospheres. Contact radius is characteristics of staircase-shaped hike with increasing normal displacement, but the magnitude of contact radius is prone to approach the Hertzian prediction with increasing the particle size. At the atomic level, the correlation between contact radius and number of contacting atoms exhibits weak dependence on particle size for small-sized nanoparticles, but for large-sized particles the number of contacting atoms plays dominant role in governing the contact radius.

Amorphization of carbon nanotubes in water by electron beam radiation

It is commonly assumed that carbon nanotubes (CNT's) are chemically stable in aqueous environments. Consequently, there has been significant interest in using them in applications where water is abundant, including agricultural fertilization, oil spill remediation, water treatment, food processing, and medicine. Indeed, despite outstanding questions regarding their toxicity, CNT's are already being employed commercially in some of these fields. Here, we use environmental transmission electron microscopy to show that when CNT's are subjected to electron beam radiation in the presence of water, amorphous carbon nanospheres, films, and globules can be synthesized. The type of amorphous carbon synthesized depends upon the surface functionality of the CNT's and the amount of water present. Nanospheres are formed in smaller amounts of water from unmodified CNT's, while amorphous films and globules form in large amounts of water from unmodified, polyethylene-glycol-functionalized, and carboxylic-acid-functionalized CNT's. Changes to the size, shape, and electron orbital hybridization of the CNT's due to amorphization increase their risk of toxicity to humans and the environment in applications, including all of those mentioned earlier, where CNT's are being employed alongside ionizing radiation. Our discovery of these amorphous transformations marks the first sub-atomic-resolution environmental observations of CNT's in water.

Direct conversion of waste tires into three-dimensional graphene

Approximately 1000 million used tires will emerge worldwide each year, and the quantity continually grows as the vehicle development. Numerous tires are inevitably discarded, and thus their disposal is a worldwide issue. Herein, we for the first time achieve to directly convert waste tires into 3D graphene through alkaline-assisted one-step pyrolysis process with no using any expensive chemical reagents and complex installations. By elevating the treatment temperature from conventional ∼800 °C to above 1000 °C, the generated potassium metal vapor will induce the carbon atom rearrangement, which facilitates the soft carbon components in the waste tire to convert into graphene-type structure. Our systematically study demonstrates the morphology evolution of waste tire from amorphous carbon nanospheres, monolithic carbon conglomeration, wrinkled graphene, and finally to vertical 3D graphene. The obtained 3D graphene exhibits a high electrical conductivity of 18.2 S cm−1, which is obviously two orders higher than the traditional active carbon. Profit from such a high conductivity and favorable hierarchical 3D graphene structure with rich porosity, the material can serve as a decent energy storage material. When used as a supercapacitor electrode, it exhibits excellent capacitive behaviors with both high rate performance and superstable cyclic life (retention of 95.9% after 10 000 cycles). This work not only propose a new protocol for high-value reuse of waste tires but also provides a potential low-cost feedstock for large scale production of graphene.

DMF-treated strategy of carbon nanospheres for high-efficient and selective removal of organic dyes

Designing adsorbents possessing high-efficient and selective adsorption performance is valuable for water pollution control, yet challengeable. Herein, a new N,N-dimethylformamide (DMF)-hydrothermal strategy was introduced to treat amorphous carbon nanospheres (CNPs) to make it possess a pH-sensitive and high selective adsorption behavior for organic dye. Excitingly, the surface electrical behavior of DMF-CNPs and CNPs are entirely different at pH 5.0, and thus in striking contrast to CNPs, DMF-CNPs exhibits a rapid removal of 70 mg L−1 cationic rhodamine B (at least 99% within 10 min), and also a pH-sensitive adsorption with a maximum adsorbability of 63.85 mg g−1 at pH 9.0 and a minimum value of 32.99 mg g−1 at pH 3.0. The DMF-CNPs's adsorption mechanism could be well explained the pseudo-second-order kinetic model and better fitted the Langmuir isotherm model with a high adsorption capacity of 56.56 mg g−1 at pH 6.5. The significantly improved adsorption performance of DMF-CNPs could be mainly ascribed to its doubled specific surface area, more positive charged active sites of oxygen-containing functional groups available for synergistic adsorption.

3D Laser Scribed Graphene Derived from Carbon Nanospheres: An Ultrahigh‐Power Electrode for Supercapacitors

AbstractLaser scribed graphene (LSG) electrodes hold great potential as supercapacitor electrodes. However, the rate performance of LSGs has been limited by the micropore‐dominated electrode structure. Here, a new method is proposed to prepare LSG electrodes with a 3D porous framework dominated by meso‐ and macro‐pores, a property that enables exceptional rate performance. The process uses amorphous carbon nanospheres (CNS) as precursors, which, after laser scribing, are transformed into highly turbostratic graphitic carbon electrodes (henceforth denoted as CNS‐LSG) with a 3D framework structure dominated by meso‐ and macro‐pores. When used as electrodes in conventional supercapacitor devices, the CNS‐LSG electrodes exhibit a high volumetric power density of 28 W cm−3, which is 28 times higher than that of current commercial activated carbon supercapacitors, and is the highest among all the reported laser scribed/induced graphene electrodes.

Graphene-size-tuned mechanical serration behaviors in nanocarbons

Two vastly different types of load-displacement responses observed in graphitic nanostructures under nano-compression are compared in terms of serration behaviors. Different from commonly encountered linear/nonlinear elastic deformation, a periodic serration behavior related to plastic flow is observed in amorphous carbon nanospheres. The true stress-strain relation exhibits a sole feature of type C serration, and comprehensive statistical, dynamical and fractal analyses further demonstrate a chaotic characteristic of dynamics for those serration events. When entering a quasi-steady flow stage, the elastic stress in each serration event could maintain a relatively stable level near ∼135 MPa, very close to the interlayer shear stress (ISS) of single crystalline graphite (∼140 MPa). This finding indicates the dependence of shear deformation on weak van der Waals interaction (elastic constant C44), instead of other structural factors associated with high elastic constants of graphite cells. Based on the experimental results, a microscale ISS-driven shearing mechanism is proposed. The local flexibility induced by small graphene lamellas may facilitate interfacial slip between neighboring domains with commensurate contact. Such slip mode may be responsible for the mechanical serration phenomenon in graphitic materials.

Probing buckling and post-buckling deformation of hollow amorphous carbon nanospheres: In-situ experiment and theoretical analysis

Amorphous carbon probably is the most-known and widely used carbon allotrope. However, unlike crystalline carbon such as graphene or carbon nanotubes, amorphous carbon generally is brittle and unable to sustain large mechanical deformation due to the inherent lack of long-rang order. In this work, we demonstrate a significant delay of failure on an amorphous carbon hollow nanosphere due to the buckling and post-buckling deformation of the spherical shell. Both in situ experiments and finite element analyses are conducted to probe deformation mechanism of buckling and post-buckling, suggesting a strong dependence of the shell thickness on the buckling process. A unified deformation energy-based mechanics model is developed to extract the critical buckling and post-buckling force, and shows good agreement with in situ experiments and finite element analyses. Extension of the model to inhomogeneous hollow nanospheres is also discussed and confirmed with finite element analyses.

Metal-Organic-Framework-Derived Carbon Nanostructure Augmented Sonodynamic Cancer Therapy.

Sonodynamic therapy (SDT) can overcome the critical issue of depth-penetration barrier of photo-triggered therapeutic modalities. However, the discovery of sonosensitizers with high sonosensitization efficacy and good stability is still a significant challenge. In this study, the great potential of a metal-organic-framework (MOF)-derived carbon nanostructure that contains porphyrin-like metal centers (PMCS) to act as an excellent sonosensitizer is identified. Excitingly, the superior sonosensitization effect of PMCS is believed to be closely linked to the porphyrin-like macrocycle in MOF-derived nanostructure in comparison to amorphous carbon nanospheres, due to their large highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap for high reactive oxygen species (ROS) production. The nanoparticle-assisted cavitation process, including the visualized formation of the cavitation bubbles and microjets, is also first captured by high-speed camera. High ROS production in PMCS under ultrasound is validated by electron spin resonance and dye measurement, followed by cellular destruction and high tumor inhibition efficiency (85%). This knowledge is important from the perspective of understanding the structure-dependent SDT enhancement of a MOF-derived carbon nanostructure.

Carbon-encapsulated metal nanoparticles deposited by plasma enhanced magnetron sputtering

Carbon-encapsulated gold nanoparticles (CEGNs) were synthesized by plasma enhanced magnetron sputtering using C2H2 and Ar mixtures as the precursor. The morphology, microstructure and optical property of the CEGNs were characterized using TEM, SEM, and UV–Vis absorption spectrum. The results show that the gold NPs with narrow size distribution ranging from 7 nm to 20 nm were encapsulated by amorphous carbon nanospheres. The fraction of C2H2 in the gas mixture of C2H2 and Ar seemed to have a significant influence on the gold particle size and distribution of the as-made CEGNs. As the fraction of the C2H2 increased from 5% to 10%, the average particle size decreased from about 13 nm to 7 nm and the carbon nanospheres with single gold NPs core evolved to the carbon chain with multi-cores. In addition, carbon-encapsulated silver nanoparticles (CESNs) were also prepared by the same method. This indicates that the plasma enhanced magnetron sputtering may be one of the best ways for the deposition of the carbon-encapsulated metal nanoparticles (CEMNs). The UV–Vis absorption spectra of the CEGNs and CESNs reveal strong absorption bands due to the surface plasma resonance of the nanoparticles, implying that the as-made CEMNs could be applied in optical limiting devices.

Rapid Formation of Diamond-Like Nano-Carbons in a Gas Bubble Discharge in Liquid Ethanol

This work demonstrates that diamond-like nano-carbons can be rapidly grown at atmospheric pressure and near ambient temperature in Ar gas bubble discharge in liquid ethanol. The method uses a discharge between point-to-plate electrodes immersed in ethanol, with plasma being generated inside Ar gas bubbles introduced through the needle electrode. The ethanol was dissociated at the liquid/gas interface into reactive species such as C2 and CH, which are the primary species responsible for diamond formation. A mixture of lonsdaleite nano-diamonds, amorphous carbon nano-spheres, and a graphitic carbon network, was formed. The rapid bubble movement distributes the reaction products almost immediately into the liquid phase, ensuring that nucleation of new material continues throughout the process. This simple, inexpensive and fast process avoids the elevated temperatures and extreme pressures of current methods.

Large-deformation and high-strength amorphous porous carbon nanospheres.

Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation.

Interconnected hollow carbon nanospheres for stable lithium metal anodes.

For future applications in portable electronics, electric vehicles and grid storage, batteries with higher energy storage density than existing lithium ion batteries need to be developed. Recent efforts in this direction have focused on high-capacity electrode materials such as lithium metal, silicon and tin as anodes, and sulphur and oxygen as cathodes. Lithium metal would be the optimal choice as an anode material, because it has the highest specific capacity (3,860 mAh g(-1)) and the lowest anode potential of all. However, the lithium anode forms dendritic and mossy metal deposits, leading to serious safety concerns and low Coulombic efficiency during charge/discharge cycles. Although advanced characterization techniques have helped shed light on the lithium growth process, effective strategies to improve lithium metal anode cycling remain elusive. Here, we show that coating the lithium metal anode with a monolayer of interconnected amorphous hollow carbon nanospheres helps isolate the lithium metal depositions and facilitates the formation of a stable solid electrolyte interphase. We show that lithium dendrites do not form up to a practical current density of 1 mA cm(-2). The Coulombic efficiency improves to ∼ 99% for more than 150 cycles. This is significantly better than the bare unmodified samples, which usually show rapid Coulombic efficiency decay in fewer than 100 cycles. Our results indicate that nanoscale interfacial engineering could be a promising strategy to tackle the intrinsic problems of lithium metal anodes.

Low-temperature graphitization of amorphous carbon nanospheres

The investigation by SEM/TEM, porosity, and X-ray diffraction measurements of the graphitization process starting from amorphous carbon nanospheres, prepared by glucose carbonization, is reported. Aspects studied are the annealing temperature in the 750–1000 °C range, the type of inert carrier gas, and time of treatment in the 2–6 h range. It is investigated how these parameters influence the structural and morphological characteristics of the carbon materials obtained as well as their nanostructure. It is shown that it is possible to maintain after graphitization the round-shaped macro morphology, a high surface area and porosity, and especially a large structural disorder in the graphitic layers stacking, with the presence of rather small ordered domains. These are characteristics interesting for various catalytic applications. The key in obtaining these characteristics is the thermal treatment in a flow of N2. It was demonstrated that the use of He rather than N2 does not allow obtaining the same results. The effect is attributed to the presence of traces of oxygen, enough to create the presence of oxygen functional groups on the surface temperatures higher than 750 °C, when graphitization occurs. These oxygen functional groups favor the graphitization process.

Growth of linked silicon/carbon nanospheres on copper substrate as integrated electrodes for Li-ion batteries

We report the growth of linked silicon/carbon (Si/C) nanospheres on Cu substrate as an integrated anode for Li-ion batteries. The Si/C nanospheres were synthesized by a catalytic chemical vapor deposition (CCVD) on Cu substrate as current collector using methyltrichlorosilane as precursor, a cheap by-product of the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermal gravimetry, Raman spectroscopy, nitrogen adsorption, inductively coupled plasma optical emission spectrometry, and X-ray photoelectron spectroscopy. It was found that the linked Si/C nanospheres with a diameter of 400-500 nm contain Si, Cu(x)Si, and Cu nanocrystals, which are highly dispersed in the amorphous carbon nanospheres. A CCVD mechanism was tentatively proposed, in which the evaporated Cu atoms play a critical role to catalytically grown Si nanocrystals embedded within linked Si/C nanospheres. The electrochemical measurement shows that these Si/C nanospheres delivered a capacity of 998.9, 713.1, 320.6, and 817.8 mA h g(-1) at 50, 200, 800, and 50 mA g(-1) respectively after 50 cycles, much higher than that of commercial graphite anode. This is because the amorphous carbon, Cu(x)Si, and Cu in the Si/C nanospheres could buffer the volume change of Si nanocrystals during the Li insertion and extraction reactions, thus hindering the cracking or crumbling of the electrode. Furthermore, the incorporation of conductive Cu(x)Si and Cu nanocrystals and the integration of active electrode materials with Cu substrate may improve the electrical conductivity from the current collector to individual Si active particles, resulting in a remarkably enhanced reversible capacity and cycling stability. The work will be helpful in the fabrication of low cost binder-free Si/C anode materials for Li-ion batteries.