Amorphous Carbon Nanoparticles Research Articles

Facile synthesis of stable colloidal suspension of amorphous carbon nanoparticles in aqueous medium and their characterization

In this study, amorphous carbon nanoparticles (CNPs) with an average diameter of 2.2 nm were synthesized by reducing dextrose (C6H12O6) with sodium hydroxide in an aqueous medium. The amorphous CNPs formed stable colloidal suspensions in water owing to the presence of hydrophilic functional groups on the nanoparticle surfaces. The amorphous CNPs exhibited ultraviolet (UV)-visible absorption (λabs) at 267 nm and emission (λem) at 453 nm under UV irradiation; thus, the colloidal suspension appeared sky-blue in color under UV irradiation. The amorphous CNPs were paramagnetic with weak magnetization at room temperature and exhibited small longitudinal (r1) and transverse (r2) water proton relaxivities of 0.036 and 0.068 s−1mM−1, respectively. The amorphous CNPs exhibited no cellular toxicity up to the measured carbon concentration of 500 μM and presented fluorescence microscopy images on a micrometer scale, thus demonstrating their utility in fluorescence bio-imaging applications.

Percolating Metallic Structures Templated on Laser-Deposited Carbon Nanofoams Derived from Graphene Oxide: Applications in Humidity Sensing

Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation of amorphous carbon nanoparticles into porous nanostructures. We report the use of a pulsed infrared laser to prepare CNF from a graphene oxide (GO) target material. Electron microscopy shows that the films consist of dendritic strings that form web-like three-dimensional structures. The conductivity of these structures can be modified by using the CNF as a nanostructured scaffold for gold nanoparticles deposited by sputter coating, controllably increasing the conductivity by up to 4 orders of magnitude. The ability to measure the conductivity of the porous structures allows electrochemical measurements in the environment. Upon decreasing humidity, the pristine CNF exhibits an increase in resistance with a quick response and recovery time. By contrast, the gold-sputtered CNF showed a decrease in resistance, indicating modification of the doping mechanism due to water adsorption. The sensitivity to humidity is eliminat...

Formation of Amorphous Carbon Nanoparticles by the Laser Electrodispersion Method

Experimental results on the laser ablation of the highly oriented pyrolytic graphite by using light pulses of an Nd:YAG laser (pulse width 25 ns, pulse energy 220 mJ) are presented. Analysis of the surface profile of the carbon target shows that the target material melts in the course of the laser ablation. As a result of ablation, a coating consisting of carbon nanoparticles about 10 nm in size is formed on the substrate placed at a distance of 4 cm from the target. It is assumed that such particles are formed as a result of the electrodispersion of carbon droplets detached from the target surface and charged to an unstable state in the laser plasma plume. Raman spectra of the coatings indicate that the carbon nanoparticles being formed have an amorphous structure.

Interface design of graphene/copper composites by matrix alloying with titanium

The attainment of intimate and strong interface is critical for promoting the load transfer ability and strength of graphene/metal composites. Herein, we reported an interface design strategy by matrix-alloying with Ti for in-situ interfacial carbide formation in reduced graphene oxide (RGO)/CuTi composites. It was demonstrated that both Ti8C5 nanolayers and Ti8C5 nanoparticles were in-situ formed at the local interface of RGO/CuTi composite, which played a “rivet” role in enhancing the interfacial bonding between the RGO and CuTi matrix. At 1.5vol% RGO loading, compared to RGO/Cu composite without alloying, the RGO/CuTi composite exhibited a higher enhancement in tensile strength (57.7% vs. 37.5%) and a lower reduction in coefficient of thermal expansion (−10.9% vs. −3.9%). The formed interfacial Ti8C5 nanolayers and Ti8C5 nanoparticles were proposed to originate from the amorphous carbon nanolayers and amorphous carbon nanoparticles on the surface of RGO, respectively. This study provides new insights into the interface design and carbide formation mechanism of advanced graphene/Cu composites with enhanced mechanical/thermal properties.

Blue luminescent amorphous carbon nanoparticles synthesized by microplasma processing of folic acid

Environmentally friendly synthesis of carbon nanoprticles (C‐NPs) from folic acid (FA) is realized with the assistance of microplasma. TEM shows that the synthesized FA C‐NPs are amorphous and of diameter around 47 nm. The produced FA C‐NPs exhibit an excitation independent emission around 445 nm with the fluorescence quantum yield 13% at excitation wavelength of 370 nm. X‐ray photoelectron spectroscopy (XPS) shows the FA C‐NPs are composed of carbon (64.15%), nitrogen (6.04%), and oxygen (29.81%). Raman spectroscopy shows that the intensity ratio between the sp3and sp2hybridizations of Carbon is 0.35. UV‐Vis absorption, Fourier Transform Infrared Spectroscopy (FTIR), and Nuclear Magnetic Resonance (NMR) spectra provide a deep insight into the fluorescence of FA C‐NPs. With plasma processing of FA, carbon atoms are involved in sp2hybridization and amine (NH2), NH and COOH groups are converted into ROOCNHCOOR group. As a consequence, the electron donating ability of aromatic ring is enhanced, which plays an important role in the fluorescence of FA C‐NPs. Finally, the promising application of FA C‐NPs in bioimaging is also demonstrated by fluorescence labeling of MCF‐7 cancer cells.

Femtosecond Laser Filamentation in Gaseous Ethylene: Formation of Hydrogenated Amorphous Carbon

Photochemical reactions of gaseous ethylene in femtosecond laser filaments are studied. It is shown that hydrogenated amorphous carbon (a-C:H) films and nanoparticles are produced by the strong interactions with the intense laser fields (~1013 W/cm2). The laser field intensity is found to be an important parameter to determine the sp2/sp3 carbon ratio of the films and the size and number of nanoparticles.

Study of thermodynamic properties of carbon nanoparticles by the laser heating method

A new experimental approach to the analysis of thermodynamic properties of amorphous carbon nanoparticles synthesized via hydrocarbon pyrolysis behind shock waves is discussed. The proposed approach is based on the analysis of thermal radiation of nanoparticles heated by a laser pulse. The sublimation temperature of the carbon nanoparticles might be determined by the two-colour pyrometry; their sizes, by laserinduced incandescence; and the volume fraction of the sublimated substance, by the laser extinction method. The sublimation temperature depends on both the particle size and the temperature conditions of their formation. The value of surface energy for amorphous carbon nanoparticles was estimated.

Fabrication of Water Jet Resistant and Thermally Stable Superhydrophobic Surfaces by Spray Coating of Candle Soot Dispersion

A facile synthesis method for highly stable carbon nanoparticle (CNP) dispersion in acetone by incomplete combustion of paraffin candle flame is presented. The synthesized CNP dispersion is the mixture of graphitic and amorphous carbon nanoparticles of the size range of 20–50 nm and manifested the mesoporosity with an average pore size of 7 nm and a BET surface area of 366 m2g−1. As an application of this material, the carbon nanoparticle dispersion was spray coated (spray-based coating) on a glass surface to fabricate superhydrophobic (water contact angle > 150° and sliding angle < 10 °) surfaces. The spray coated surfaces were found to exhibit much improved water jet resistance and thermal stability up to 400 °C compared to the surfaces fabricated from direct candle flame soot deposition (candle-based coating). This study proved that water jet resistant and thermally stable superhydrophobic surfaces can be easily fabricated by simple spray coating of CNP dispersion gathered from incomplete combustion of paraffin candle flame and this technique can be used for different applications with the potential for the large scale fabrication.

Carbon-coated sepiolite clay fibers with acid pre-treatment as low-cost organic adsorbents

Carbon-nanoparticle-coated sepiolite hydrous-magnesium-silicate clay fibers are prepared by 220°C-autoclave hydrothermal carbonization of cellulose using 1.2-mol/L-hydrochloric-acid-pretreated sepiolite fibers. The deposited amorphous carbon nanoparticles (30–150 nm) nonuniformly and partially covering the sepiolite surface have surface functional groups (CH2, CH3, CC and CO), which enhance the organophilicity. Compared to a mixture of pristine sepiolite and hydrothermal carbon prepared without sepiolite, the carbon-coated sepiolite exhibits lower specific surface area but greater organic adsorption, due to the smaller pore size and particle size of the hydrothermal carbon coating compared to the hydrothermal carbon prepared without sepiolite. The acid pre-treatment decreases the sepiolite crystallinity and increases the deposited carbon content from 24.67 to 31.63 vol%, while increasing the specific surface area from 26.53 to 33.98 m2/g, increasing the fraction of phenol removed from 47.1% to 57.1%, and increasing the monolayer phenol adsorption capacity from 4.1 to 5.26 mg/g. Compared to the acid treated but uncoated sepiolite, the carbon coating decreases the density from 2.227 to 1.696 g/cm3 and decreases the specific surface area from 118 to 34 m2/g, but increases the fraction of phenol removed from 6.1% to 57.1%. The acid pre-treatment gives greater adsorption than the addition of acid to the hydrothermal process liquid.

Potential Heat Transfer Fluids (Nanofluids) for Direct Volumetric Absorption-Based Solar Thermal Systems

Nanoparticle dispersions or more popularly “nanofluids” have been extensively researched for their candidature as working fluid in direct-volumetric-absorption solar thermal systems. Flexibility in carving out desired thermophysical and optical properties has lend the nanofluids to be engineered for solar thermal and photovoltaic applications. The key feature which delineates nanofluid-based direct absorption volumetric systems from their surface absorption counterparts is that here the working fluid actively (directly) interacts with the solar irradiation and hence enhances the overall heat transfer of the system. In this work, a host of nanoparticle materials have been evaluated for their solar-weighted absorptivity and heat transfer enhancements relative to the basefluid. It has been found that solar-weighted absorptivity is the key feature that makes nanoparticle dispersions suitable for solar thermal applications (maximum enhancement being for the case of amorphous carbon nanoparticles). Subsequently, thermal conductivity measurements reveal that enhancements on the order of 1–5% could only be achieved through addition of nanoparticles into the basefluid. Furthermore, dynamic light scattering (DLS) and optical measurements (carried out for as prepared, 5 h old and 24 h old samples) reveal that nanoclustering and hence soft agglomeration does happen but it does not have significant impact on optical properties of the nanoparticles. Finally, as a proof-of-concept experiment, a parabolic trough collector employing the amorphous carbon-based nanofluid and distilled water has been tested under the sun. These experiments have been carried out at no flow condition so that appreciable temperatures could be reached in less time. It was found that for the same exposure time, increase in the temperature of amorphous carbon based nanofluid is approximately three times higher as compared to that in the case of distilled water.

Fabrication of Optical Gap Selective Amorphous Carbon Photocatalyst for Hydrogen Production under Irradiation with Visible Light

Si-added amorphous carbon (a-C) nanoparticles with particle diameter of 12.6 nm were synthesized using radio frequency (r.f.) plasma-enhanced chemical vapor deposition method equipped with porous aluminum plate in plasma. The optical gap of Si-added a-C particles with Si/(Si + C) ratio of 0.51 was 1.92 eV. Band edges of this nanoparticles was estimated to be as follows: i) conduction band edge was located over the standard potential of H+/H2 and ii) valence band edge was located under the standard potential of O2/H2O. From X-ray photoemission spectra, it was clarified that the part of tri-s-triazine structure with higher adsorption property toward water was introduced into nanoparticle with optical gap of 1.92 eV by adding graphitic-carbon nitride (g-C3N4) in a source material. The photo-oxidation measurement of indigo carmine adsorbed on Si-added a-C nanoparticles with tri-s-triazine structure was carried out. As a result, indigo carmine was decomposed at a rate of 0.0197 µmol/h under UV irradiation. This result indicates that Si-added a-C nanoparticle can be applied to photocatalyst for reduction of water (estimated quantum efficiency of 0.049 %). It was experimentally demonstrated that the proposed Si-added a-C nanoparticles are tailor-made photocatalyst material that enables us to adjust band edge and surface functionalities for photo-oxidation (reduction) reactant.

Morphology, Microstructure, and Hydrogen Content of Carbon Nanostructures Obtained by PECVD at Various Temperatures

Carbon nanostructures were obtained by acetylene injection into an argon plasma jet in the presence of hydrogen. The samples were synthesized in similar conditions, except that the substrate deposition temperatures TD were varied, ranging from 473 to 973 K. A strong dependence of morphology, structure, and graphitization upon TD was found. We obtained vertical aligned carbon nanotubes (VA-CNTs) at low temperatures as 473 K, amorphous carbon nanoparticles (CNPs) at temperatures from about 573 to 673 K, and carbon nanowalls (CNWs) at high temperatures from 773 to 973 K. Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, elastic recoil detection analysis, X-ray photoelectron spectroscopy, and Raman spectroscopy were used to substantiate the differences in these material types. It is known that hydrogen concentration modifies strongly the properties of the materials. Different concentrations of hydrogen-bonded carbon could be identified in amorphous CNP, VA-CNT, and CNW. Also, the H : C ratios along depth were determined for the obtained materials.

Dust evolution, a global view: II. Top-down branching, nanoparticle fragmentation and the mystery of the diffuse interstellar band carriers.

The origin of the diffuse interstellar bands (DIBs), one of the longest-standing mysteries of the interstellar medium (ISM), is explored within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS). The likely nature of the DIB carriers and their evolution is here explored within the framework of the structures and sub-structures inherent to doped hydrogenated amorphous carbon grains in the ISM. Based on the natural aromatic-rich moieties (asphaltenes) recovered from coal and oil, the likely structure of their interstellar analogues is investigated within the context of the diffuse band problem. It is here proposed that the top-down evolution of interstellar carbonaceous grains, and, in particular, a-C(:H) nanoparticles, is at the heart of the formation and evolution of the DIB carriers and their associations with small molecules and radicals, such as C2, C3, CH and CN. It is most probable that the DIBs are carried by dehydrogenated, ionized, hetero-cyclic, olefinic and aromatic-rich moieties that form an integral part of the contiguous structure of hetero-atom-doped hydrogenated amorphous carbon nanoparticles and their daughter fragmentation products. Within this framework, it is proposed that polyene structures in all their variants could be viable DIB carrier candidates.

Electrically conductive gamma-alumina/amorphous carbon nano-composite foams

The templating method has always been considered an efficient method to design new morphologies for old materials. We have already demonstrated that it is possible to generate by templating method, a new class of alumina meso-foams showing peculiar conductive properties that strictly depend on the size of the bubbles generated by polymeric templating beads.In this work we definitively demonstrate by the “high resolution transmission electron microscopy” and by the “Energy Dispersive X-ray Spectrometry (EDS)” that the alumina meso-foams are actually composites of conductive amorphous carbon and γ-alumina nanoparticles. This evidence supports the hypothesis that the conductive properties of the meso-foams are mainly due to the un-combusted amorphous carbon imbedded in the alumina frame.We believe that our innovative approach based on in-situ carbon-composite formation, could be potentially extended to several other non-conductive oxides shaped through the old templating method.

Tribological modification of high-density polyethylene by using carbon soot from diesel combustion

Purpose The purpose of this paper is to explore the tribological properties of high-density polyethylene (HDPE) modified by carbon soot from the combustion of No. 0 diesel. Design/methodology/approach Carbon soot is characterized using X-ray diffraction, transmission electron microscopy and scanning electronic microscopy. The tribological properties of HDPE samples with carbon soot are investigated on a materials surface tester with a ball-on-disk friction pair. Findings The collected carbon soot mainly comprises amorphous carbon nanoparticles of 50-100 nm in diameter. The main wear behaviours of pure HDPE include abrasive wear and plastic deformation. After adding carbon soot nanoparticles to HDPE, HDPE wear decreases. The appropriate carbon soot content is 8 per cent in HDPE under the selected testing conditions. Compared with other HDPE samples, HDPE with 8 per cent carbon soot has higher melting temperature, lower abrasive wear and better wear resistance. The lubrication of HDPE with carbon soot is due to the formation of a transferring film composed of HDPE, amorphous carbon and graphite carbon. Originality/value The paper reveals the HDPE modification and lubrication mechanisms by using carbon soot from the combustion of diesel. Related research can perhaps provide a potential approach for the treatment of carbon soot exhaust emission.

Scalable and Cost-Effective Synthesis of Highly Efficient Fe2N-Based Oxygen Reduction Catalyst Derived from Seaweed Biomass.

A simple and scalable synthesis of a 3D Fe2N-based nanoaerogel is reported with superior oxygen reduction reaction activity from waste seaweed biomass, addressed the growing energy scarcity. The merits are due to the synergistic effect of the 3D porous hybrid aerogel support with excellent electrical conductivity, convenient mass transport and O2 adsorption, and core/shell structured Fe2N/N-doped amorphous carbon nanoparticles.

Single Nanoparticle Mass Spectrometry as a High Temperature Kinetics Tool: Sublimation, Oxidation, and Emission Spectra of Hot Carbon Nanoparticles.

In single nanoparticle mass spectrometry, individual charged nanoparticles (NPs) are trapped in a quadrupole ion trap and detected optically, allowing their mass, charge, and optical properties to be monitored continuously. Previous experiments of this type probed NPs that were either fluorescent or large enough to detect by light scattering. Alternatively, small NPs can be heated to temperatures where thermally excited emission is strong enough to allow detection, and this approach should provide a new tool for measurements of sublimation and surface reaction kinetics of materials at high temperatures. As an initial test, we report a study of carbon NPs in the 20-50 nm range, heated by 10.6 μm, 532 nm, or 445 nm lasers. The kinetics for sublimation and oxidation of individual carbon NPs were studied, and a model is presented for the factors that control the NP temperature, including laser heating, and cooling by sublimation, buffer gas collisions, and radiation. The estimated NP temperatures were in the 1700-2000 K range, and the NP absorption cross sections ranged from ∼0.8 to 0.2% of the geometric cross sections for 532 nm and 10.6 μm excitation, respectively. Emission spectra of single NPs and small NP ensembles show a feature in the IR that appears to be the high energy tail of the thermal (blackbody-like) emission expected from hot particles but also a discrete feature peaking around 750 nm. Both the IR tail and 750 nm peak are observed for all particles and for both IR and visible laser excitation. No significant difference was observed between graphite and amorphous carbon NPs.

Depletion of carbon nanotube depositions and tube realignment in the spreading of sessile drops

Abstract We studied spreading of drops of water and dilute alcohol on multiwall carbon nanotube (MWNT) depositions. These deposits consisted of individual arc-discharge synthesized MWNTs and irregular amorphous carbon nanoparticles on hydrophilically rendered silicon substrates. The mobile circular contact line of a spreading drop created an annular shape on the deposit, where some of the MWNTs and the amorphous nanoparticles in particular were largely depleted. The effect was strongly dependent on the hydrophilicity of the substrate. Most of the MWNTs were not only left within the annuli, but were also apparently reoriented by their interaction with the passing contact line. Our results imply the possibility of applications in quality improvement of nanotube depositions in terms of both tube orientation and cleanliness.

Conductive porous carbon film as a lithium metal storage medium

The Li metal anode boasts attractive electrochemical characteristics for use in rechargeable Li batteries, such as a high theoretical capacity and a low redox potential. However, poor cycle efficiency and safety problems relating to dendritic Li growth during cycling should be addressed. Here we propose a strategy to increase the coulombic efficiency of the Li metal electrode. Conductive porous carbon films (CPCFs) were prepared by distributing amorphous carbon nanoparticles within a polymer binder. This porous structure is able to provide enough conductive surfaces for Li deposition and dissolution, which reduce the effective current density. Moreover, the pores in these films enable the electrolyte to easily penetrate into the empty space, and Li can be densely deposited between the carbon particles. As a result, dendritic Li growth can be effectively prevented. Electrochemical tests demonstrate that the coulombic efficiency of the porous electrode can be greatly improved compared to that of the pure Cu electrode. By allowing for the development of robust Li metal electrodes, this approach provides key insight into the design of high-capacity anodes for Li metal batteries, such as Li-air and Li-S systems.

Exploring the potential of Raman spectroscopy for the identification of silicone oil residue and wear scar characterization for the assessment of tribofilm functionality

We applied a combination of Raman spectroscopy (RS) and cross-sectional transmission electron microscopy (X-TEM) to identify silicone oil residues and tribofilms at steel disc surfaces after tribological testing. Neither chemical cleaning nor mechanical removal of a 50µm thick surface layer produced a surface without any silicone residue. Nevertheless, long-term tribological properties are not affected due to silicone degradation which has been proved by Raman spectroscopy. Excellent anti-wear and anti-friction properties of a nanocomposite at severe stressing conditions correlated with the formation of a silica-based tribofilm containing amorphous and graphite-like carbon nanoparticles. Since reliable carbon quantification by analytical TEM is difficult, RS is a useful complementary method for carbon identification at wear scars.