Sp2-bonded Carbon Research Articles

Synthesis and application of Zn-doped polyaniline modified multi-walled carbon nanotubes as stimuli-responsive nanocarrier in the epoxy matrix for achieving excellent barrier-self-healing corrosion protection potency

Multi-walled carbon nanotubes (MWCNTs), which are one of the most favorable large aspect ratio hollow-cylindrical nanomaterials, have been considered for numerous advanced applications due to their exceptional thermal-mechanical and electrical characteristics. However, because of the high surface area and being susceptible to agglomeration, they suffered from low dispersion ability. Thus, functionalization with organic and inorganic materials is one of the promising solutions to their limitations. Due to the presence of sp2-bonded carbon atoms, they have no functionalities. One way to generate carboxylic functionalities on MWCNTs is their oxidation. Herein, this study reports the synthesis of a novel highly-oxidized multi-walled carbon nanotube (O-MWCNT) particles modified by the polyaniline (PANI) nanofibers and their performance in the epoxy-based nanocomposites for achieving passive/active anti-corrosion system with efficacious self-healing potency and barrier anti-corrosion characteristic. The O-MWCNT-PANI nanocomposite was then modified by the zinc metal cations to accomplish a smart self-healing anti-corrosion system. The total resistance of about 4000 ohm.cm2 was achieved in the extract with O-MWCNT-PANI-Zn, while the blank sample showed a resistance of about 1200 ohm.cm2 after three hours of immersion time. The most noticeable enhancement of the dual active-barrier protection was obtained in the scratched coatings with modified nano-inhibitors. The more log|Z|10 mHz values were reached, including 4.82 ohm.cm2 and 5.06 ohm.cm2, in O-MWCNT-PANI/EP and O-MWCNT-PANI-Zn/EP, respectively.

Interface Kinetics Assisted Barrier Removal in Large Area 2D-WS2 Growth to Facilitate Mass Scale Device Production.

Growth of monolayer WS2 of domain size beyond few microns is a challenge even today; and it is still restricted to traditional exfoliation techniques, with no control over the dimension. Here, we present the synthesis of mono- to few layer WS2 film of centimeter2 size on graphene-oxide (GO) coated Si/SiO2 substrate using the chemical vapor deposition CVD technique. Although the individual size of WS2 crystallites is found smaller, the joining of grain boundaries due to sp2-bonded carbon nanostructures (~3–6 nm) in GO to reduced graphene-oxide (RGO) transformed film, facilitates the expansion of domain size in continuous fashion resulting in full coverage of the substrate. Another factor, equally important for expanding the domain boundary, is surface roughness of RGO film. This is confirmed by conducting WS2 growth on Si wafer marked with few scratches on polished surface. Interestingly, WS2 growth was observed in and around the rough surface irrespective of whether polished or unpolished. More the roughness is, better the yield in crystalline WS2 flakes. Raman mapping ascertains the uniform mono-to-few layer growth over the entire substrate, and it is reaffirmed by photoluminescence, AFM and HRTEM. This study may open up a new approach for growth of large area WS2 film for device application. We have also demonstrated the potential of the developed film for photodetector application, where the cycling response of the detector is highly repetitive with negligible drift.

Dense as diamond: Pn-C10, a superhard sp3 carbon allotrope

We introduce a carbon allotrope with rhombic symmetry and a high crystal density reached 3.56 g/cm3, named Pn-C10, which was found using an unbiased particle-swarm structural-searching technique. This fully sp3-bonded carbon phase is dynamically and mechanically stable in its ground state. Results from our calculations reveal the excellent mechanical nature of Pn-C10 with a claimed shear modulus and Vickers hardness of 484 GPa and 88.45 GPa, respectively, which also suggested its slight anisotropy in elasticity. The predicted electronic band structure indicates that Pn-C10 is an indirect-bandgap material with a bandgap of 5.05 eV. Natural tiling analysis and simulations of x-ray diffraction and Raman spectra were performed to provide insights for further studies into Pn-C10 and other carbon phases.

Investigation of Vacuum Annealing Temperature Effects on the Microstructure Properties of DC-PECVD Grown Diamond Nanoparticles

In this study, nanodiamonds (NDs) coatings were grown on gold-coated silicon substrates by a DC-plasma enhanced chemical vapor (DC-PECVD) deposition technique using CH4 plus H2 as the feedstock. The effect of annealing temperature under vacuum environment on the characteristics of the resulting coatings were investigated experimentally by means of Raman spectroscopy, Atomic Force Microscopy (AFM), X-ray diffraction pattern (XRD) and field emission scanning electron microscopy (FE-SEM). Results show that by adjusting annealing temperature up to 200 °C, the internal compressive stress, the amount of aromatic ring and the size of the sp2-bonded carbon decreases in NDs coatings. It has been found that by further increasing annealing temperature up to 300 °C, the degree of graphitization of NDs coatings is increased and graphitic clusters become larger in grain boundaries. In addition, the high concentration and homogenous distribution of particles sizes of the diamond nanocrystals were obtained on the surfaces of the annealed sample at 100 °C. Our experimental results can be beneficial guidance to the production of NDs coatings with the desired attributes.

Incorporation of nitrogen in diamond films – A new way of tuning parameters for optical passive elements

This paper investigates the impact of nitrogen incorporation in diamond films for the construction of an interferometric sensor to measure displacement. Diamond films with different nitrogen levels (0–5%) were deposited on silicon substrates by microwave plasma enhanced chemical vapor deposition. The structural characteristics of these samples are characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), confocal micro-Raman spectroscopy, and electron energy loss spectroscopy (EELS). The homogeneous and continuous surface morphology of the films is observed through SEM. In the micro-Raman and electron energy loss spectroscopy studies, it is evident that there is a formation of sp2-bonded carbon phases due to the increase in the concentration of nitrogen. This investigation gives a strong basis for utilizing these diamond films as reflective layers in fiber-optic devices. The interferometric measurement setup is constructed as a Fabry-Pérot interferometer. The nitrogen incorporated films are proved to be useful as mirrors as they achieve a measurement signal with high contrast. The achieved visibility values for the investigated samples are higher than 94% in the range of 40–100 μm.

Influence of structural evolution on sliding interface for enhancing tribological performance of onion-like carbon films via thermal annealing

The onion-like carbon (OLC) possesses a micro-spherical structure with a diameter of approximately 7 nm consisting of 0.35 nm-spaced carbon layers, and the OLC film is capable of providing excellent solid lubrication performances because of the high content of sp2-bonded carbon phase. However, the unfavorable durability severely restricts the lubrication application in practice. For the purpose of addressing this issue, heat treatment is employed to improve the lubrication robustness of the loose OLC film. The wear resistance was significantly improved with a duration of 60,000 sliding cycles at least when the OLC-coated samples were annealed at 600 °C in vacuum. Furthermore, the systematic analyses, particularly providing deep insights into the microstructural characterization, indicate that the structural reinforcement of OLC and the net-like adhering structures formed on the steel substrates annealed at specific temperature can effectively promote lubrication characteristics in two different stages. We propose that annealing treatment can improve the stability of micro-spherical OLC structures, thereby increasing the duration of lubrication. The evolution mechanism of OLC structures at the sliding interface is the key factor for maintaining the lubrication duration in dry contact.

Combined Voltammetric Measurement of pH and Free Chlorine Speciation Using a Micro-Spot sp2 Bonded Carbon-Boron Doped Diamond Electrode.

This work demonstrates the use of an sp2-bonded carbon microspot boron doped diamond (BDD) electrode for voltammetric measurement of both pH and analyte concentration in a pH-dependent speciation process. In particular, the electrode was employed for the voltammetric detection of pH and hypochlorite (OCl-) in unbuffered, aerated solutions over the pH range 4-10. Knowledge of both pH and [OCl-] is essential for determination of free chlorine concentration. The whole surface of the microspot BDD electrode was found active toward the voltammetric oxidation of OCl-, with OCl- showing a characteristic response at +1.5 V vs SCE. In contrast, it was only the surface integrated quinones (Q) in sp2-bonded carbon regions of the BDD electrode that were responsible for the voltammetric pH signal. A Nernstian response for pH (gradient = 63 ± 1 mV pH-1) was determined from proton coupled electron transfer at the BDD-Q electrode, over the potential range -0.4-0.5 V vs SCE. By measuring both OCl- and pH voltammetrically, over the pH range 4-10, the OCl- oxidative current was found to correlate extremely well with the predicted pH-dependent [OCl-] speciation profile.

Quantification of the carbon bonding state in amorphous carbon materials: A comparison between EELS and NEXAFS measurements

The quantitative determination of the carbon hybridization is critical for establishing processing-structure-properties relationships for carbon-based materials, including amorphous carbon coatings. While several techniques have been employed to characterize the amount of sp2 and sp3 carbon in these materials, direct comparisons between analytical results are limited. Here, we compare near edge X-ray absorption fine structure (NEXAFS) spectra of a silicon- and oxygen-containing hydrogenated amorphous carbon (a-C:H:Si:O) coating acquired in synchrotron-based scanning transmission X-ray microscopy (STXM) mode with electron energy loss spectra (EELS) obtained from the same a-C:H:Si:O lamella. While the fractions of sp2 carbon computed from STXM and EELS spectra are in close agreement, the comparison of NEXAFS spectra acquired in STXM mode with NEXAFS spectra collected in partial electron yield mode on a flat a-C:H:Si:O surface indicated that the destructive preparation of thin lamellae for STXM analyses induces variations in the structure of a-C:H:Si:O, namely the breakage of carbon-silicon and carbon-hydrogen bonds, a change in ordering of sp2-bonded carbon, and an increase in the sp2 carbon fraction. These findings can help scientists in the careful interpretation of spectroscopic results obtained from the analysis of samples made of metastable materials after the destructive preparation of specimens for analytical purposes.

Identification of Mechanistic Subtleties that Apply to Voltammetric Studies at Boron-Doped Diamond Electrodes

The α-[S2W18O62]4–/5– and α-[S2W18O62]5–/6– polyoxometalate (POM) reduction processes at boron-doped diamond (BDD) disk electrodes in acetonitrile (0.50 M [n-Bu4N][PF6]) have been investigated using large-amplitude Fourier transformed alternating current (FTAC) voltammetry. The origins of subtle differences in experimental data and simulated data modeled assuming the Butler–Volmer relationship with ion-paring implicitly included, planar diffusion and a uniform surface are considered. Parameters estimated are the apparent heterogeneous electron-transfer kinetics (kapp0′), apparent formal reversible potential (Eapp0′), and apparent charge transfer coefficient (αapp′). The electrode kinetic parameters, in contrast to theoretical predictions of the model employed, are dependent on frequency, POM concentration, and the data analysis method. Reasons for nonconformance to the model include the adsorption of POM on graphite-like sp2-bonded carbon impurities, limitations in the availability of charge carriers in BDD, and the method of incorporating ion pairing when slow electrode kinetics apply. Masking of the sp2 carbon-rich (edge) region of the BDD disk provided FTAC voltammetric data that complied much more closely with the simulated data. Nevertheless, data analysis still produces a concentration dependence in the estimated kapp0′ values, which is considered in terms of the assumption of an infinite number of charge carriers. Conclusions derived from this study are likely to be generally applicable to electrode kinetic investigations at BDD electrodes.

Influence of crystallization temperature on fluorescence of n-diamond quantum dots

Nanodiamonds are popular biological labels because of their superior mechanical and optical properties. Their surfaces bridging the core and surrounding medium play a key role in determining their bio-linkage and photophysical properties. n-diamond is a mysterious carbon allotrope whose crystal structure remains debated. We study the influence of the crystallization temperature on the fluorescence properties of the colloidal n-diamond quantum dots (n-DQDs) with sizes of several nanometers. They exhibit multiband fluorescence across the whole visible region which depends sensitively on the crystallization temperature. Their surfaces turn from hydrophobic ones rich of sp2-bonded carbon into hydrophilic ones rich of carboxyl derivatives and hydroxyl groups as the crystallization temperature increases. The different surface states correlated with the surface structures account for the distinct fluorescence properties of the n-DQDs crystallized at different temperatures. These high-purity ultrasmall n-DQDs with tunable surface chemistry and fluorescence properties are promising multicolor biomarkers and lighting sources.

Functionalization of Bis‐Diazaphospholene P–P Bonds with Diverse Electrophiles

Phosphorus‐sp3 or ‐sp2 carbon bonds are readily formed by the reaction of bis‐diazaphospholenes with several classes of electrophiles. These reactions result in cleavage of the phosphorus–phosphorus bond and formation of functionalized diazaphospholenes. The reactions proceed rapidly, without catalysis. Experimental evidence with aryl and alkyl halides suggests the intermediacy of radicals in some cases, however other evidence suggests either radical or polar mechanisms may be operative for certain substrates, with a dependence on reaction conditions. In three cases, the product aryl diazaphospholenes have been shown to transfer the aryl substituent to electrophiles. These results reveal that diazaphospholene dimers are potent participants in radical chemistry with organic substrates at room temperature without requiring chemical initiators.

Electronic properties of fluorine/hydrogen adsorbed two-dimensional tetrahex-carbon: A first-principles study

A recently proposed two-dimensional (2D) carbon allotrope, tetrahex-carbon, draws scientific attention due to its remarkable electronic and mechanical properties. This 2D carbon structure consists of tetragonal and hexagonal rings, and exhibits excellent semiconductor properties including a finite direct band gap and high carrier mobility, suggesting potential applications in semiconductor devices. In this paper, the electronic properties of fluorine/hydrogen adsorbed tetrahex-C was investigated via first-principles density-functional theory calculations. It demonstrates that its band structure can be significantly tuned and could be metallic with dangling bonds from F/H adsorption. With increasing F/H adsorption density, it shows semiconducting behavior and the band gap is widening, mainly due to the sp2-bonded carbon being gradually converted to sp3 hybridization. It was also found that effective masses of charge carriers along the zigzag-direction can largely reduce through adsorption of F/H, leading to potentially enhanced carrier mobility. Tetrahex-C shows prominent anisotropicity and the tunability of effective masses through F/H adsorption is remarkably dependent on the crystal orientation. In addition, it was found that, the work function of the F-adsorbed tetrahex-C increases while electron affinity decreases, compared to the pristine one. However, the H-covered carbon film shows significant reductions of both work function and electron affinity.

Structure and Properties of Coatings in the Cr–B–C–N System Obtained Using a CrB2 Cathode by the Method of Pulsed Cathode-Arc Evaporation P-CAE in Ar, N2, and C2H4 Media

The technology of pulsed cathode-arc evaporation (P-CAE) has been successfully applied for coating deposition in the Cr–B–C–N system. The coatings had a structure typical for arc coatings with a significant fraction of the condensed droplet phase, but the formation of an adverse columnar morphology has been eliminated. The coatings contained crystallites of the h-CrB2 and с-CrN phases along with a large amount of the amorphous phase, the composition of which varied depending on the type of the working environment. The coatings obtained in argon demonstrated the highest hardness of 12 GPa, while those obtained in the C2H4 medium were characterized by the highest elastic-plastic properties (elastic recovery 72%). The friction coefficient of coatings deposited in Ar, N2, and C2H4 media was 0.7, 0.4, and 0.3, respectively. The phase of diamond-like carbon in the latter case resulted in a decrease in the friction coefficient due to high fraction of sp2-bonded carbon serving as a dry lubricant. The coatings of the optimal composition were resistant to high temperature oxidation in the temperature range 600–1000°С. At high temperatures, the oxidation process was followed by intensive diffusion of boron atoms in depth of the substrate.

COFs Meet Graphene Nanoribbons

2D covalent organic frameworks (COFs) have received considerable attention because of their crystallinity, permanent porosity, and tunability, yet they exhibit low in-plane conductivity. In this issue of Chem, Fischer and co-workers report an approach for growing 2D COF thin films featuring high in-plane conductivity for potential use in organic electronics.

Penta-C20: A Superhard Direct Band Gap Carbon Allotrope Composed of Carbon Pentagon.

A metastable sp3-bonded carbon allotrope, Penta-C20, consisting entirely of carbon pentagons linked through bridge-like bonds, was proposed and studied in this work for the first time. Its structure, stability, and electronic and mechanical properties were investigated based on first-principles calculations. Penta-C20 is thermodynamically and mechanically stable, with equilibrium total energy of 0.718 and 0.184 eV/atom lower than those of the synthesized T-carbon and supercubane, respectively. Penta-C20 can also maintain dynamic stability under a high pressure of 100 GPa. Ab initio molecular dynamics (AIMD) simulations indicates that this new carbon allotrope can maintain thermal stability at 800 K. Its Young’s modulus exhibits mechanical anisotropy. The calculated ideal tensile and shear strengths confirmed that Penta-C20 is a superhard material with a promising application prospect. Furthermore, Penta-C20 is a direct band gap carbon based semiconducting material with band gap of 2.89 eV.

Chemical structure transformation during the later stage of plastic layers during coking using Synchrotron infrared microspectroscopy technique

During the coking process, the carbon structure of coal evolves after the re-solidification of the plastic layers to form a solid residue, i.e., semi-coke, which is known to determine the structure and quality of the final coke product. This paper reports the chemical structural transformations of Australian coking coals during the later stage of the plastic layers that may be related to the evolution of the carbon structures. The plastic layers and semi-coke/coke samples were prepared from four Australian coking coals of different ranks and vitrinite contents in a lab-scale coke oven. The Synchrotron attenuated total reflection Fourier transform infrared (ATR-FTIR) microspectroscopy (Synchrotron IR) was used in combination with the X-ray photoelectron spectroscopy (XPS) to investigate the changes in the chemical structure during coke formation. The Synchrotron IR, as a nondestructive analytical technique, proved to be a useful tool to examine the change in functional groups in the semi-coke samples. The XPS analysis was employed to study the conversion of sp2- and sp3-bonded carbons. The results suggested that a dramatic chemical structure change took place during the stages following the plastic layers through to the coke/semi-coke regions. The chemical structure changes were strongly impacted by the properties of the parent coals. The carbon structure changes observed in XPS spectra were in good agreement with the aromatic ring condensation degree, which was indicated by the ratio of out-of-plane aromatic CH to CC bonds in aromatic rings. The results showed that the carbon structure evolution took place during the later stages of the thermoplastic ranges, forming the semi-coke.

Development of an x-ray detector by polycrystalline diamond and its application in Z-pinch x-ray detection.

Large-grain-sized polycrystalline diamond films are fabricated by electron assisted chemical vapor deposition. A pure SP3 carbon bond in the cubic lattice structure is confirmed by Raman spectrum analysis. The grain size is on the order of several hundreds of μm or larger. Interlaced-finger electrodes are imprinted onto a 6 × 6 mm2 × 500 µm film to fabricate the x-ray detector. The width of every finger is 25 µm, and the distance between nearby fingers is 25 μm. Strong x ray irradiates when a pulsed current flows through a double-layer nested tungsten wire array in the Z-pinch. This diamond detector now works as one of the main x-ray detectors for the Z-pinch device. The diamond detector is calibrated using a plastic scintillator. The comparison between the signal measured by these two methods confirms that the large-grain-sized polycrystalline diamond is a good candidate for the detection of nanosecond pulsed x ray.

Magnetic Solid-Phase Extraction of Organic Compounds Based on Graphene Oxide Nanocomposites.

Graphene oxide (GO) is a chemical compound with a form similar to graphene that consists of one-atom-thick two-dimensional layers of sp2-bonded carbon. Graphene oxide exhibits high hydrophilicity and dispersibility. Thus, it is difficult to be separated from aqueous solutions. Therefore, functionalization with magnetic nanoparticles is performed in order to prepare a magnetic GO nanocomposite that combines the sufficient adsorption capacity of graphene oxide and the convenience of magnetic separation. Moreover, the magnetic material can be further functionalized with different groups to prevent aggregation and extends its potential application. Until today, a plethora of magnetic GO hybrid materials have been synthesized and successfully employed for the magnetic solid-phase extraction of organic compounds from environmental, agricultural, biological, and food samples. The developed GO nanocomposites exhibit satisfactory stability in aqueous solutions, as well as sufficient surface area. Thus, they are considered as an alternative to conventional sorbents by enriching the analytical toolbox for the analysis of trace organic compounds.

In Situ Construction of Hierarchical Diamond Supported on Carbon Nanowalls/Diamond for Enhanced Electron Field Emission.

The integration of sp2-/sp3-bonded carbon has aroused increasing attention on attaining a great electron field emission (EFE) performance. Herein, a novel hierarchical diamond@carbon nanowalls/diamond (D@C/D) architecture is facilely prepared through the growth of the hybrid carbon nanowalls/diamond (C/D) film followed by the in situ hydrogen plasma treatment using microwave plasma chemical vapor deposition. The hierarchical D@C/D architecture is composed of thin diamond nanoplatelets sandwiched into carbon nanowalls (CNWs) as the bottom layer and the thickened nanoplatelets constituted by diamond nanograins as the upper layer. The hydrogen plasma plays an effective role in the transformation of sacrificial sp2-bonded CNWs to sp3-bonded diamond, eventually leading to the template thickening of diamond nanoplatelets in the upper layer. Impressively, the D@C/D-90 film demonstrates much better EFE behaviors of low turn-on potential (Eo = 4.3 V μm-1), high current density (Je@8 V μm-1 = 20.81 mA cm-1), and superior long-term stability, in comparison with the pristine C/D film (Eo = 6 V μm-1, Je@8 V μm-1 = 0.33 mA cm-1). The enhanced EFE performance of the hierarchical D@C/D film is ascribed to the well-established graphite pathway for electrons transported from the bottom to the top and the increased diamond emitting sites with negative electron-affinity and robust nature at the top. This work will promote the development of the high-performance cathode EFE material based on hybrid sp2/sp3-bonded carbon, and the method proposed here also provides an effective strategy to construct a diamond nanostructure for various applications.

Dependence of Optimum Thickness of Ultrathin Diamond-like Carbon Coatings over Carbon Nanotubes on Geometric Field Enhancement Factor

The generation of a field emission (FE) cathode electron source has attracted wide attention for its miniaturization, high-frequency operability, and low energy consumption. However, the FE performance of cold cathodes is limited by poor current stabilities of carbon nanotube (CNT) emitters. Coating CNTs with sp3-bonded carbon coatings is considered as a successful approach to stabilize the FE currents. High-quality ultrathin diamond-like carbon (DLC) films, which serve as sp3 carbon coatings, are deposited uniformly on CNTs by filtered cathodic vacuum arc evaporation in this research. The thicknesses of DLC coatings and the field enhancement factors of pristine CNTs affect to a large extent the FE properties. An optimum coating thickness of DLC layers corresponding to the lowest threshold field exists due to space-charge-induced band bending, at which the depletion region of the DLC layer in equilibrium is maximized. The optimum coating thickness increases with the geometric field enhancement factor of p...