Structure and electronic properties of carbon onions

Electron paramagnetic resonance as a tool to determine the sodium charge storage mechanism of hard carbon

Hard carbon is a promising negative electrode material for rechargeable sodium-ion batteries due to the ready availability of their precursors and high reversible charge storage. The reaction mechanisms that drive the sodiation properties in hard carbons and subsequent electrochemical performance are strictly linked to the characteristic slope and plateau regions observed in the voltage profile of these materials. This work shows that electron paramagnetic resonance (EPR) spectroscopy is a powerful and fast diagnostic tool to predict the extent of the charge stored in the slope and plateau regions during galvanostatic tests in hard carbon materials. EPR lineshape simulation and temperature-dependent measurements help to separate the nature of the spins in mechanochemically modified hard carbon materials synthesised at different temperatures. This proves relationships between structure modification and electrochemical signatures in the galvanostatic curves to obtain information on their sodium storage mechanism. Furthermore, through ex situ EPR studies we study the evolution of these EPR signals at different states of charge to further elucidate the storage mechanisms in these carbons. Finally, we discuss the interrelationship between EPR spectroscopy data of the hard carbon samples studied and their corresponding charging storage mechanism.

Recent advances in nanobiosensors for sustainable healthcare applications: A systematic literature review

The need for novel healthcare treatments and drugs has increased due to the expanding human population, detection of newer diseases, and looming pandemics. The development of nanotechnology offers a platform for cutting-edge in vivo non-invasive monitoring and point-of-care-testing (POCT) for rehabilitative disease detection and management. The advancement and uses of nanobiosensors are currently becoming more common in a variety of scientific fields, such as environmental monitoring, food safety, biomedical, clinical, and sustainable healthcare sciences, since the advent of nanotechnology. The identification and detection of biological patterns connected to any type of disease (communicable or not) have been made possible in recent years by several sensing techniques utilizing nanotechnology concerning biosensors and nanobiosensors. In this work, 2218 articles are drawn and screened from six digital databases out of which 17 were shortlisted for this review by using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) technique. As a result, this study uses a systematic methodology to review some recently developed extremely sensitive nanobiosensors, along with their biomedical, point-of-care diagnostics (POCD), or healthcare applications and their capabilities, particularly for the prediction of some fatal diseases based on a few of the most recent publications. The potential of nanobiosensors for medicinal, therapeutic, or other sustainable healthcare applications, notably for ailments diagnostics, is also recognized as a way forward in the manifestation of future trends.

Size-Dependent Thermal Stability and Optical Properties of Ultra-Small Nanodiamonds Synthesized under High Pressure

Diamond properties down to the quantum-size region are still poorly understood. High-pressure high-temperature (HPHT) synthesis from chloroadamantane molecules allows precise control of nanodiamond size. Thermal stability and optical properties of nanodiamonds with sizes spanning range from <1 to 8 nm are investigated. It is shown that the existing hypothesis about enhanced thermal stability of nanodiamonds smaller than 2 nm is incorrect. The most striking feature in IR absorption of these samples is the appearance of an enhanced transmission band near the diamond Raman mode (1332 cm−1). Following the previously proposed explanation, we attribute this phenomenon to the Fano effect caused by resonance of the diamond Raman mode with continuum of conductive surface states. We assume that these surface states may be formed by reconstruction of broken bonds on the nanodiamond surfaces. This effect is also responsible for the observed asymmetry of Raman scattering peak. The mechanism of nanodiamond formation in HPHT synthesis is proposed, explaining peculiarities of their structure and properties.

A mild molecular fusion route for the synthesis of polyhedral carbon nano-onions with high graphitization

Polyhedral carbon nano-onions (CNOs) compared with traditional quasi-spherical CNOs are more stable and have less defects, which will greatly broaden their potential applications. However, there still lacks of a suitable synthetic method. Here, we developed a simple molecular fusion route and templet growth method by which polyhedral CNOs can be successfully synthesized. Characterization of the polyhedral CNOs by transmission electron microscopy, x-ray diffraction and Raman spectroscopy indicates that they have an ultra-high degree of graphitization and a large cavity diameter of about 10 nm, which results in their low density of 1.42 g cm^-3. In addition, the deeper reaction mechanism of polyhedral CNOs growth was also elucidated. It was found that the channel structure and the absorption of the templet play the crucial role during the formation of polyhedral CNOs.

Application of carbon nano onions in the biomedical field: recent advances and challenges

Carbon nano onions (CNOs) are carbonaceous nanostructures composed of multiple concentric shells of fullerenes. These cage-within-cage structures remain as one of the most exciting and fascinating carbon forms, along with graphene and its derivatives, due to their unique chemical and physical properties. Their exceptional biocompatibility and biosafety make them an attractive choice in a wide range of areas, including biological systems. This nanomaterial displays low toxicity, high dispersity in aqueous solutions (upon surface functionalization), and high pharmaceutical efficiency. Even though CNOs were discovered almost simultaneously along with carbon nanotubes (CNTs), their potential in biomedical applications still appears unrealized. The existence of CNOs is equally important, just like any other carbon nanostructures such as CNTs and fullerenes, because they display the ability of carbon to form another unique nanostructure with wonderful properties. Therefore, this mini-review summarizes recent studies geared towards developing CNOs for various biomedical applications, including sensing, drug delivery, imaging, tissue engineering, and as a therapeutic drug. It concludes by discussing other potential applications of this unique nanomaterial.

Carbon Nanomaterials: Synthesis, Functionalization and Sensing Applications

Recent advances in nanomaterial design and synthesis has resulted in robust sensing systems that display superior analytical performance. The use of nanomaterials within sensors has accelerated new routes and opportunities for the detection of analytes or target molecules. Among others, carbon-based sensors have reported biocompatibility, better sensitivity, better selectivity and lower limits of detection to reveal a wide range of organic and inorganic molecules. Carbon nanomaterials are among the most extensively studied materials because of their unique properties spanning from the high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency fostering their use in sensing applications. In this paper, a comprehensive review has been made to cover recent developments in the field of carbon-based nanomaterials for sensing applications. The review describes nanomaterials like fullerenes, carbon onions, carbon quantum dots, nanodiamonds, carbon nanotubes, and graphene. Synthesis of these nanostructures has been discussed along with their functionalization methods. The recent application of all these nanomaterials in sensing applications has been highlighted for the principal applicative field and the future prospects and possibilities have been outlined.

Fluorescent Carbon Nano-onion as Bioimaging Probe

Concentrically arranged multilayered fullerenes exhibiting onion-like morphology are popularly known as carbon nano-onion (CNO) and are useful in bioimaging application. On the basis of the origin of the fluorescence, the CNO-based nanoprobes are classified into type I and type II. The type I CNO-based nanoprobe needs a secondary moiety such as organic dyes or an amine functionalization at its surface to induce the fluorescence. On the other hand, the emission in type II does not originate from such an external surface passivating agent. The CNO-based system not only shows structural similarity to the well-known multiwalled carbon nanotube but is also a bit more advantageous because of its low cytotoxicity. These features enable their prolonged use in the biological system for imaging purposes. In particular, we have covered the aspects of synthesis, surface functionalization, the origin of fluorescence, and biocompatibility. In addition, recent developments directed toward in vitro and in vivo imaging studies by utilizing CNO-based nanoprobes are summarized here.

Carbon Nano-onions: A Valuable Class of Carbon Nanomaterials in Biomedicine

The development of nanoscale materials is an important area of research as it provides access to materials with unique properties that can be applied to improve quality of life. Multi-layer fullerenes, also known as carbon nano-onions (CNOs) are an exciting class of nanostructures which show great versatility and applicability. They find applications in several fields of technology and biomedicine. This review highlights the potential advantages of CNOs for biomedical applications, which include but are not limited to bioimaging and sensing. Their good biocompatibility renders them promising platforms for the development of novel healthcare devices.

Electrochemical synthesis of carbon nano onions

Electrochemical synthesis of hollow and solid carbon nano onions from simple aromatic compounds in acetonitrile on a platinum plate electrode by a multi-potential steps method.

Pulsed direct current field-induced thermal stability and phase transformation of nanodiamonds to carbon onions

The pulsed DC field-induced thermal stability of nanodiamonds (NDs) and their transformation to carbon onions lack detailed understanding. In this study, a comprehensive study was conducted, analyzing the thermal stability of NDs and the optimum conditions required for the formation of carbon onions, using spark plasma sintering (SPS) utilizing ON-OFF DC pulse energizing. X-ray diffraction, Raman spectroscopy and electron microscopy were employed to monitor the phase transformation. Experimental results showed that NDs could almost remain stable until 950 °C under 60 MPa pressure. As the temperature was increased, amorphous carbon appeared on the surface of NDs, and then, graphitization began. At 1300 °C, lamellar graphite structures were formed and kept stable with increasing holding time, but no carbon onion was found. The optimum parameters for the synthesis of carbon onions from NDs via SPS are the temperature of 1400 °C and holding time of 15 minutes under a pressureless condition. The pressureless condition during the SPS processing creates a more favourable environment for the ND graphitization and curling into spherical carbon onions. The existence of pressure during the SPS processing can improve the thermal stability of NDs, delay the initial temperature for the graphitization transition of NDs and inhibit the graphite layer curling to form carbon onions.

Onion-Like Carbon Nanostructures: An Overview of Bio-Applications

This article presents a brief review of the knowledge concerning onion-like carbons (OLCs). These nanostructures are some of the most fascinating carbon forms due to their unusual structure and physico-chemical properties. Generally, OLCs consist of a hollowspherical fullerene core surrounded by concentric graphitic layers with increasing diameter. Nevertheless, they can have different size, shape and type of core, which determine their physicochemical properties. In this article, we review the most important literature reports in this area and briefly describe these nanostructures, their physical and chemical properties and their potential uses with a focus on biomedicine.

A Review of Carbon Nanomaterials' Synthesis via the Chemical Vapor Deposition (CVD) Method

Carbon nanomaterials have been extensively used in many applications owing to their unique thermal, electrical and mechanical properties. One of the prime challenges is the production of these nanomaterials on a large scale. This review paper summarizes the synthesis of various carbon nanomaterials via the chemical vapor deposition (CVD) method. These carbon nanomaterials include fullerenes, carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, carbide-derived carbon (CDC), carbon nano-onion (CNO) and MXenes. Furthermore, current challenges in the synthesis and application of these nanomaterials are highlighted with suggested areas for future research.

Effect of Reaction Temperature on Structure, Appearance and Bonding Type of Functionalized Graphene Oxide Modified P-Phenylene Diamine

In this study, graphene oxides with different functionalization degrees were prepared by a facile one-step hydrothermal reflux method at various reaction temperatures using graphene oxide (GO) as starting material and p-phenylenediamine (PPD) as the modifier. The effects of reaction temperature on structure, appearance and bonding type of the obtained materials were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results showed that when the reaction temperature was 10–70 °C, the GO reacted with PPD through non-covalent ionic bonds (–COO⁻H₃⁺N–R) and hydrogen bonds (C–OH…H₂N–X). When the reaction temperature reached 90 °C, the GO was functionalized with PPD through covalent bonds of C–N. The crystal structure of products became more ordered and regular, and the interlayer spacing (d value) and surface roughness increased as the temperature increased. Furthermore, the results suggested that PPD was grafted on the surface of GO through covalent bonding by first attacking the carboxyl groups and then the epoxy groups of GO.

Novel nanocapsules with Co–TiC twin cores and regulable graphitic shells for superior electromagnetic wave absorption

The synthesis of nanometer materials with unique structures and compositions has proven successful towards the attenuation of electromagnetic (EM) waves. However, it is still a challenge to form special nanostructures by integrating magnetic/dielectric loss materials into one particle due to the difficulties in coupling the heterogeneous components. Herein, we present the synthesis of novel nanocapsules (NCs) with Co–TiC twin cores encapsulated inside graphitic shells using an arc-discharge plasma method. The thickness of the graphitic shell could be controlled by quantitatively tuning the carbon source concentration. The optimal reflection loss (RL) values of the prepared NCs was −66.59 dB at 8.76 GHz with a low thickness of 2.56 mm. The bandwidth of RL ≤ −10 dB was up to 14.4 GHz, which almost covered the entire frequency band, namely, the S to Ku band (3.6 GHz to 18 GHz). This superior EM wave absorption was ascribed to the specific double-core shell nanostructures and effective impedance matching between the magnetic loss and dielectric loss originating from the combination of the magnetic Co and dielectric TiC/C.

Fabrication of Co–TiC@C nanocapsules via an arc discharge plasma method. Its optimum EM wave absorption was −66.59 dB at 8.76 GHz.

Catalysis by hybrid sp2/sp3nanodiamonds and their role in the design of advanced nanocarbon materials

Hybrid sp²/sp³nanocarbons, in particular sp³-hybridized ultra-dispersed nanodiamonds and derivative materials, such as the sp³/sp²-hybridized bucky nanodiamonds and sp²-hybridized onion-like carbons, represent a rather interesting class of catalysts still under consideration.

Electronic structure of multi-walled carbon fullerenes

Despite an enormous amount of research on carbon based nanostructures, relatively little is known about the electronic structure of multi-walled carbon fullerenes, also known as carbon onions. In part, this is due to the very high computational expense involved in estimating electronic structure of large molecules. At the same time, experimentally, the exact crystal structure of the carbon onion is usually unknown, and therefore one relies on qualitative arguments only. In this work we present the results of a computational study on a series of multi-walled fullerenes and compare their electronic structures to experimental data. Experimentally, the carbon onions were fabricated using ultrasonic agitation of isopropanol alcohol and deposited onto the surface of highly ordered pyrolytic graphite using a drop cast method. Scanning tunneling microscopy images indicate that the carbon onions produced using this technique are ellipsoidal with dimensions on the order of 10 nm. The majority of differential tunneling spectra acquired on individual carbon onions are similar to that of graphite with the addition of molecular-like peaks, indicating that these particles span the transition between molecules and bulk crystals. A smaller, yet sizable number exhibited a semiconducting gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels. These results are compared with the electronic structure of different carbon onion configurations calculated using first-principles. Similar to the experimental results, the majority of these configurations are metallic with a minority behaving as semiconductors. Analysis of the configurations investigated here reveals that each carbon onion exhibiting an energy band gap consisted only of non-metallic fullerene layers, indicating that the interlayer interaction is not significant enough to affect the total density of states in these structures.

Formation of carbon nanodots with different spin states in mechanically processed mixtures of ZnO with carbon nanoparticles: an electron paramagnetic resonance study

Mixtures of zinc oxide with carbon nanoparticles, ZnO + xC (x = 0.1%, 1% and 3% by weight), were subjected to mechanical processing (MP) in a hermetically sealed grinding chamber.

Inherently-Forced Tensile Strain in Nanodiamond-Derived Onion-like Carbon: Consequences in Defect-Induced Electrochemical Activation

We analyzed the nanodiamond-derived onion-like carbon (OLC) as function of synthesis temperature (1000~1400 °C), by high-resolution electron microscopy, electron energy loss spectroscopy, visible-Raman spectroscopy, ultraviolet photoemission spectroscopy, impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The temperature dependences of the obtained properties (averaged particle size, tensile strain, defect density, density of states, electron transfer kinetics, and electrochemical oxidation current) unanimously coincided: they initially increased and saturated at 1200 °C. It was attributed to the inherent tensile strains arising from (1) the volume expansion associated with the layer-wise diamond-to-graphite transformation of the core, which caused forced dilation of the outer shells during their thermal synthesis; (2) the extreme curvature of the shells. The former origin was dominant over the latter at the outermost shell, of which the relevant evolution in defect density, DOS and electron transfer kinetics determined the electrochemical performances. In detection of dopamine (DA), uric acid (UA) and ascorbic acid (AA) using the OLC as electrode, their oxidation peak currents were enhanced by factors of 15~60 with annealing temperature. Their limit of detection and the linear range of detection, in the post-treatment-free condition, were as excellent as those of the nano-carbon electrodes post-treated by Pt-decoration, N-doping, plasma, or polymer.

From the traditional way of pyrolysis to tunable photoluminescent water soluble carbon nano-onions for cell imaging and selective sensing of glucose

Water soluble photoluminescent carbon nano-onions were synthesized from vegetable ghee using traditional pyrolytic approach for imaging cells and selective-immediate detection of glucose via fluorescent “turn-off”/“turn-on” technique.

Carbon nano onions cross the blood brain barrier

Water soluble fluorescent carbon nano onions (wsCNO) cross the blood brain barrier (BBB) in the CADASIL murine model as well as in GBM induced mice.

Gigahertz Dielectric Polarization of Substitutional Single Niobium Atoms in Defective Graphitic Layers

We synthesize two Nb/C composites with an order of magnitude difference in the density of single niobium atoms substituted into defective graphitic layers. The concentration and sites of single Nb atoms are identified using aberration-corrected scanning transmission electron microscopy and density functional theory. Comparing the experimental complex permittivity spectra reveals that a representative dielectric resonance at ∼16  GHz originates from the intrinsic polarization of single Nb atom sites, which is confirmed by theoretical simulations. The single-atom dielectric resonance represents the physical limit of the electromagnetic response of condensed matter, and thus might open up a new avenue for designing electromagnetic wave absorption materials. Single-atom resonance also has important implications in understanding the correlation between the macroscopic dielectric behaviors and the atomic-scale structural origin.

Dispersion analysis of carbon nanotubes, carbon onions, and nanodiamonds for their application as reinforcement phase in nickel metal matrix composites

Low aspect ratios and sp³ hybridization of carbon nanoparticles benefit both, small agglomerate sizes in ethylene glycol and nickel composites.

Carbon nano-onions (multi-layer fullerenes): chemistry and applications

This review focuses on the development of multi-layer fullerenes, known as carbon nano-onions (CNOs). First, it briefly summarizes the most important synthetic pathways for their preparation and their properties and it gives the reader an update over new developments in the recent years. This is followed by a discussion of the published synthetic procedures for CNO functionalization, which are of major importance when elucidating future applications and addressing drawbacks for possible applications, such as poor solubility in common solvents. Finally, it gives an overview over the fields of application, in which CNO materials were successfully implemented.

Nickel nanoparticles effect on the electrochemical energy storage properties of carbon nanocomposite films

The growth of nanostructured nickel : carbon (Ni : C) nanocomposite thin films by the supersonic cluster beam deposition of nickel and carbon clusters co-deposited from two separate beam sources has been demonstrated. Ni : C films retain the typical highly disordered structure with predominant sp(2) hybridization, low density, high surface roughness and granular nanoscale morphology of cluster assembled nanostructured carbon, but display enhanced electric conductivity. The electric double layer (EDL) capacitance of Ni : C films featuring the same thickness (200 nm) and different nickel volumetric concentrations (0-35%) has been investigated by electrochemical impedance spectroscopy employing an aqueous solution of potassium hydroxide (KOH 1 M) as electrolyte solution. Evidence of increased electric conductivity, facilitated EDL formation and negligible porous structure modification was found as consequence of Ni embedding. This results in the ability to synthesize electrodes with tailored specific power and energy density by the accurate control of the amount of deposited Ni and C clusters. Moreover, nickel nanoparticles were shown to catalyze the formation of tubular onion-like carbon structures upon mild thermal treatment in inert atmosphere. Electrochemical characterization of the heated nanocomposite electrodes revealed that the presence of long range ordered sp(2) structures further improves the power density and energy storage properties.

Water electrolysis with a conducting carbon cloth: subthreshold hydrogen generation and superthreshold carbon quantum dot formation

A conducting carbon cloth, which has an interesting turbostratic microstructure and functional groups that are distinctly different from other ordered forms of carbon, such as graphite, graphene, and carbon nanotubes, was synthesized by a simple one-step pyrolysis of cellulose fabric. This turbostratic disorder and surface chemical functionalities had interesting consequences for water splitting and hydrogen generation when such a cloth was used as an electrode in the alkaline electrolysis process. Importantly, this work also gives a new twist to carbon-assisted electrolysis. During electrolysis, the active sites in the carbon cloth allow slow oxidation of its surface to transform the surface groups from COH to COOH and so forth at a voltage as low as 0.2 V in a two-electrode system, along with platinum as the cathode, instead of 1.23 V (plus overpotential), which is required for platinum, steel, or even graphite anodes. The quantity of subthreshold hydrogen evolved was 24 mL cm(-2)  h(-1) at 1 V. Interestingly, at a superthreshold potential (>1.23 V+overpotential), another remarkable phenomenon was found. At such voltages, along with the high rate and quantity of hydrogen evolution, rapid exfoliation of the tiny nanoscale (5-7 nm) units of carbon quantum dots (CQDs) are found in copious amounts due to an enhanced oxidation rate. These CQDs show bright-blue fluorescence under UV light.

The mechanism of transforming diamond nanowires to carbon nanostructures

The transformation of diamond nanowires (DNWs) with different diameters and geometries upon heating is investigated with density-functional-based tight-binding molecular dynamics. DNWs of {100} and {111} oriented cross-section with projected average line density between 7 and 20 atoms Å(-1) transform into carbon nanotubes (CNTs) under gradual heating up to 3500-4000 K. DNWs with projected average line density larger than 25 atoms Å(-1) transform into double-wall CNTs. The route of transformation into CNTs clearly exhibits three stages, with the intriguing intermediate structural motif of a carbon nanoscroll (CNS). Moreover, the morphology plays an important role in the transformation involving the CNS as one important intermediate motif to form CNTs. When starting with [Formula: see text] oriented DNWs with a square cross-section consisting of two {111} facets facing each other, one interesting structure with 'nano-bookshelf' shape emerges: a number of graphene 'shelves' located inside the CNT, bonding to the CNT walls with sp(3) hybridized atoms. The nano-bookshelf structures exist in a wide range of temperatures up to 3,000 K. The further transformation from nano-bookshelf structures depends on the strength of the joints connecting shelves with CNT walls. Notably, the nano-bookshelf structure can evolve into two end products: one is CNT via the CNS pathway, the other is graphene transformed directly from the nano-bookshelf structure at high temperature. This work sheds light on the microscopic insight of carbon nanostructure formation mechanisms with the featured motifs highlighted in the pathways.

Nanodiamond graphitization: a magnetic resonance study

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) study of the high-temperature nanodiamond-to-onion transformation. (1)H, (13)C NMR and EPR spectra of the initial nanodiamond samples and those annealed at 600, 700, 800 and 1800 ° C were measured. For the samples annealed at 600 to 800 ° C, our NMR data reveal the early stages of the surface modification, as well as a progressive increase in sp(2) carbon content with increased annealing temperature. Such quantitative experimental data were recorded for the first time. These findings correlate with EPR data on the sensitivity of the dangling bond EPR line width to air content, progressing with rising annealing temperature, that evidences consequent graphitization of the external layers of the diamond core. The sample annealed at 1800 ° C shows complete conversion of nanodiamond particles into carbon onions.

Surface electrostatic potential transformation of nanodiamond induced by graphitization

The surface electrostatic potential of raw nanodiamonds is implied to be altered permanently during in the spontaneously occurred graphitization process by recent reports. With all-electron ab initio density functional theory methods, the intrinsic effect of graphitization on the electrostatic potential of nanodiamonds is investigated. It is exposed that while the graphitization process goes on, the dangling bonds on the (111) surface transfer into the inner side and subsequently the surface potential changes from negative to positive. Our results may be of great help in understanding the various electrostatic properties of nanodiamonds.

Preparation and characterization of composites that contain small carbon nano-onions and conducting polyaniline

Small multilayer fullerenes, also known as carbon nano-onions (CNOs; 5-6 nm in diameter, 6-8 shells), show higher reactivity than other larger carbon nanostructures. Here we report the first example of an in situ polymerization of aniline on phenyleneamine-terminated CNO surfaces. The green, protonated, conducting emeraldine polyaniline (PANI) was directly synthesized on the surface of the CNO. The functionalized and soluble CNO/PANI composites were characterized by TEM, SEM, DSC, Raman, and infrared spectroscopy. The electrochemical properties of the conducting CNO/PANI films were also investigated. In comparison with pristine CNOs, functionalized carbon nanostructures show dramatically improved solubility in protic solvents, thus enabling their easy processing for coatings, nanocomposites, and biomedical applications.

DIAMOND NANORODS FROM CARBON NANOTUBES BY HYDROGEN PLASMA TREATMENT

Single crystalline diamond nanorods with diameters of 4–8 nm and with lengths up to 200 nm have been synthesized by hydrogen plasma post-treatment of multiwalled carbon nanotubes. The diamond nanorods were identified to have a core-sheath structure with inner core being diamond crystal and outer shell being amorphous carbon. A growth mechanism for the diamond nanorods was proposed.

Hydrogen Stabilization of {111} Nanodiamond

Presented here are results of ab initio Density Functional Theory (DFT) structural relaxations performed on dehydrogenated and monohydrogenated nanocrystalline diamond structures of octahedral {111} and cuboctahedral morphologies, up to approximately 2nm in diameter. Our results in this size range show a transition of dehydrogenated nanodiamond clusters into carbon onion-like structures, with preferential exfoliation of the C(111) surfaces, in agreement with experimental observations. However, we have found that this transition may be prevented by hydrogenation of the surfaces. Bonding between atoms in the surface layers of the relaxed structures, and interlayer bonding has been investigated using Wannier functions.

Upcycling: converting waste plastics into paramagnetic, conducting, solid, pure carbon microspheres

The recent tremendous increase in the volume of waste plastics (WP) will have a harmful environmental impact on the health of living beings. Hundreds of years are required to degrade WP in atmospheric conditions. Hence, in coming years, in addition to traditional recycling services, innovative "upcycling" processes are necessary. This article presents an environmentally benign, solvent-free autogenic process that converts various WP [low density polyethylene (LDPE), high density polyethylene (HDPE), polyethylene terephthalate (PET), polystyrene (PS), or their mixtures] into carbon microspheres (CMSs), an industrially significant, value-added product. The thermal dissociation of these individual or mixed WP in a closed reactor under autogenic pressure ( approximately 1000 psi) produced dry, pure powder of CMSs. In this paper, the optimization of process parameters such as the effect of mixing of WP with other materials, and the role of reaction temperature and time are reported. Employing advanced analytical techniques, the atomic structure, composition, and morphology of as-obtained CMSs were analyzed. The room-temperature paramagnetism in CMSs prepared from waste LDPE, HDPE, and PS was further studied by electron paramagnetic resonance (EPR). The conducting and paramagnetic nature of CMSs holds promise for their potential applications in toners, printers, paints, batteries, lubricants, and tires.