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Nitrogen-doped carbon nanomaterials have greater capacity and better cycling stability for Li-ion batteries as compared to undoped carbon materials. In situ near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in combination with quantum chemical modeling has been applied to determine the chemical states of the incorporated nitrogen after interaction with lithium. NEXAFS N K-edge spectra of nitrogen-doped porous carbon were measured before and after thermal deposition of Li vapors. The simulation and interpretation of NEXAFS data were carried out based on density functional theory calculations of initial and lithiated graphene fragments that contained different nitrogen species. The preferable interactions of Li with pyridinic and hydrogenated pyridinic nitrogen which are located at edges of atomic vacancies and graphene planes were revealed. [ABSTRACT FROM AUTHOR]

Graphene materials including porous few-layered graphenes are under focus of scientific community today. The great attention towards them is caused by their remarkable properties. Here, we use two different fluorinated graphite intercalation compounds with different fluorine content in their matrices to prepare thermally exfoliated fluorinated graphites and to investigate them in terms of their structural, spectroscopic and electrochemical properties as materials for use in supercapacitors. A higher temperature of low-fluorinated graphenes preparation resulted in higher exfoliation degree and higher gravimetric capacitance in supercapacitor appliances. More dramatic leap of gravimetric capacitance was observed after a treatment in a concentrated acid mixture of graphene material samples prepared at the highest temperature of thermolysis with highest exposition time. [ABSTRACT FROM AUTHOR]

A well-defined controlled selective edge functionalization of graphene oxide (GO) is of high interest because it allows tuning the chemical and physical properties of graphene oxide with minimal damage to the carbon at the basal plane. The present work reports a rapid one-step synthesis of edge fluorinated graphene oxide (FGO) from GO in an aqueous medium. A selective fluorination of the tertiary carbon at the edge of GO was achieved by chemoselective substitution of the carboxylic acid with fluorine in one hour following a decarboxylative fluorination technique using 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (SELECTFLUOR) and silver ion catalyst. The structure and composition of FGO were characterized by multiple analytical techniques, such as TEM, SEM, XRD, EDS, FTIR, XPS, Raman spectroscopy, etc. As observed in XPS and NMR analysis, the decarboxylative fluorination of GO resulted in the formation of covalent C–F bonds at the edge. The absence of the peak associated with the C–F group on the basal plane in 19F NMR clearly indicates the fluorination at the edge of GO. Most importantly, similar linewidth and spectral patterns in proton-decoupled 19F{1H} and proton-coupled 19F NMR spectra of FGO suggest that the fluorine atoms are bonded to the tertiary carbon atom. The selective functionalization of the tertiary carbon at the edges of GO achieved here, is unprecedented. The fluorine group at the edge of GO can act as a new reaction center for subsequent chemical modification. This simple edge-controlled fabrication method described here provides a facile pathway to fabricate multifunctional GO and expand their potential applications. [ABSTRACT FROM AUTHOR]

Highly defective carbon nanotubes (HD-CNTs) are fabricated by template carbonization of polydopamine nanofilm coated on mesoporous titanium nitride nanotube arrays. With introduction of mesoporous holes on the side walls from the template, HD-CNTs exhibit much improved electrochemical properties. An ideal Nernst behavior toward [Fe(CN)6]3−/4− redox couple was observed on the HD-CNTs, with a heterogeneous charge transfer rate constant k0 greater than 0.5 cm/s that is among the fastest kinetics of electrode materials. Sensitive determination of dopamine has been demonstrated in the presence of ascorbic acid and uric acid, with a linear range of 0.1–180 μM, a detection limit of 0.074 μM (S/N = 3) and a sensitivity of 555 µA mM−1 cm−2. The excellent electrochemical activity should be attributed to the large number of exposed edge planes on the carbon nanofilm, the free-standing highly conductive titanium nitride architecture that is beneficial for electron transfer, mesoporous morphology that promotes the mass transfer between the nanotubes, and effective ion-accessible surface area. [ABSTRACT FROM AUTHOR]

Nitrogen doping of carbon nanomaterials has emerged as a method to develop novel material properties, though limitations in the form of extended treatment times, harsh chemical usage and limited total nitrogen content exist. Here, macroscopic ribbon-like assemblies of carbon nanotubes are functionalized with nitrogen using a simple direct current-based plasma–liquid system. This system utilizes the plasma-generated species in an ethanol:water solution with ethylenediamine as a nitrogen precursor for the nitrogen functionalization of the carbon nanotube assembly. These unique, plasma-generated species and pathways enable rapid and high levels of functionalization with the atomic concentration of nitrogen reaching 22.5%, with amine groups, pyrrolic groups and graphitic nitrogen observed in the X-ray photoelectron spectra, the highest ever achieved. This nitrogen content is demonstrated to be significantly higher than a comparative electrolysis process. This demonstrates that this plasma process enhances the availability of nitrogen from the ethylenediamine precursor, facilitating greater functionalization. [ABSTRACT FROM AUTHOR]

Alternative sources of neutron production other than nuclear fission reactions are important priorities in medical and nuclear applications due to costs, safety and ease of operation. In this work, 12 C and 13 C thick targets for neutron production through 12 C(d,n) 13 N and 13 C(d,n) 14 N , respectively, have been manufactured and characterized by different techniques. In order to evaluate the irradiation effects on these materials, the targets were irradiated with 150 keV proton beam. A complete characterization of these samples was performed using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, Auger electron spectroscopy, X-ray photoemission spectroscopy and Raman spectroscopy. The results of these studies allowed us to establish that even though the irradiated samples present microstructural and chemical structure changes on its surface, the 12 C and 13 C thick targets were stable and would maintain their performance after proton irradiation at a fluence of 2.0 × 10 18 ions/cm 2 and 3.7 × 10 18 ions/cm 2 , respectively. [ABSTRACT FROM AUTHOR]

5-hydroxymethylfurfural (HMF), as one of the most important renewable platform-chemicals, is a valuable precursor for the synthesis of biofuels and bio-products. In this work, hydrothermal carbon (HC), with a large specific surface area and plenty of oxygen-containing functional groups, was derived from sucrose via a hydrothermal method, which could facilitate the dispersion and anchoring of Ni. The selectivities to 2,5-bis(hydroxymethyl)furan (BHMF), 2,5-dimethyltetrahydrofuran (DMTHF), and 2,5-dimethylfuran (DMF) were tuned by modulating Ni nanoparticle sizes and Ni/NiO ratios. The yield of BHMF can reach 88% with its selectivity up to 94% on the reduced 10%-Ni/HC catalyst with big Ni particle size; while the total yield of DMF + DMTHF is up to 94.6% at full HMF conversion on the calcined 5%-Ni/HC catalyst with small Ni particle sizes and balanced Ni/NiO ratios; for the calcined Ni/HC catalysts, the synergistic effect between Ni(0), favoring H2 activation and hydrogenation, and NiO, facilitating the hydrogenolysis of C–O bonds, could promote the selective hydrogenolysis of HMF to biofuel production (DMF and DMTHF). [ABSTRACT FROM AUTHOR]

Silicon-based anodes are promising anode materials for lithium-ion batteries. However, during the charge–discharge processes, the huge volume change of silicon leads to the repeated formation of solid-electrolyte interphase layer, structure fracture and loss of electric contact, which seriously limits their practical applications. In this paper, a rational design combining graphite microsphere, silicon nanowire and porous carbon film is established, forming a micro-nanostructure that can effectively solve the above issues. Employing chemical vapor deposition method, silicon nanowire and polypyrrole are successively in situ synthesized on the graphite surface. After carbonizing the deposited composites, a porous carbon film and a silicon carbide layer locating between silicon and carbon film are obtained. It establishes a novel microstructure that possesses a strong bonding strength among interfaces of carbon film/silicon and silicon/graphite. Therefore, the porous carbon film/silicon nanowire/graphite microsphere composites anode exhibits a high capacity of 530 mA h g−1 at a current density of 0.2 C after 100 cycles. Significantly, the prepared composites anode could satisfy the practical application because their initial coulomb efficiency can reach to 80%. [ABSTRACT FROM AUTHOR]

Determination of the number of bromo groups and brominated positions of edges on carbon materials is essential for selective functionalization because the brominated positions influence their electronic structures. However, the determination is challenging because the analysis of introduced bromo groups on carbon materials is conventionally limited to quantitative analysis by X-ray photoelectron spectroscopy. In this work, infrared spectra (IR) of brominated aromatic compounds were analyzed experimentally and theoretically using reference aromatic compounds to verify that the calculated peak positions can be used to estimate the experimental peak positions of brominated aromatic compounds. IR spectra of brominated graphene nanoribbons (GNRs) with zigzag, armchair, and other edges were simulated as one of the carbon materials with clear edge structures. Their characteristic peak positions and tendencies of shifts were explained from the point of view of Mulliken charge, C–H and C=C length, and orbital hybridization. As the number of Br on GNRs increased, the peak positions basically shifted further, indicating that the density of Br and introduced positions of Br can be estimated from IR spectra. The detailed assignments obtained in this work will lead to selective functionalization of carbon materials. [ABSTRACT FROM AUTHOR]

Relative humidity (RH) sensors have been fabricated with polyaniline-encased multiwall carbon nanotube (MWCNT) matrix. MWCNT matrices were grown on oxidized Si substrates by catalytic chemical vapour deposition technique. The MWCNT matrices were made hydrophilic by acid treatment. The sensing properties of MWCNTs were improved by encasing the acid-treated MWCNT matrix with PANI. PANI was synthesized via in situ chemical oxidation technique using three acid dopants, named as 5-sulfosalicylic acid, 4-nitrobenzoic acid and hydrochloric acid (HCl). A growth time variation of the PANI was also performed from 1.5 to 2.5 h. The time-varying sensor resistance was recorded with RH change, and RH sensing properties of the corresponding sensors were investigated with the measured data. Doping variation exhibited that CNT–PANI sensor, fabricated with HCl dopant, showed the highest response (42.6% at 90% RH). Synthesis time variation of PANI from 1.5 to 2.5 h exhibited that with an increase in synthesis time, the sensor responsivities degraded from 42.6 to 19.5% at 90% RH. Excellent repeatability, linear response behaviour (R2 = 0.992), low hysteresis loss (± 2.68%) were exhibited by the fabricated RH sensing devices. A facile transfer technology was developed in order to transfer the MWCNT on PET substrate for fabrication of flexible RH sensor. A practical application on human respiration monitoring was demonstrated with the wearable and flexible RH sensors. The humidity sensing mechanism and electron transfer process were schematically explained with the aid of energy band diagram. [ABSTRACT FROM AUTHOR]

Nanodiamonds (NDs) were synthesized under atmospheric conditions by heating a precursor powder mixture consisting of naphthalene and a microwave (MW) absorbing material inside an ordinary MW oven for 10 min. Pyrolysis of naphthalene led to the formation of onion-like carbon particles which then converted to NDs after prolonged MW irradiation. Different carbon-based materials like graphite, carbon black, graphene, and carbon nanotubes were used as microwave radiation absorbers that assisted in the dissociation of naphthalene and formation of NDs. ND particles were formed in both isolated as well as aggregated forms. Size of the particles ranged from 2 to 700 nm. Scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy and thermogravimetric analysis were used to characterize the NDs present in the MW-synthesized product. The proposed MW-based ND synthesis technique is simple, fast, inexpensive, energy efficient and could be suitable for industrial scale production. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) are possible low-cost alternative to the current lithium ion batteries and hold great perspectives for large-scale renewable energy storage. However, the unavailability of appropriate anode material hinders the practical application of SIBs. Herein, we have examined the structural and electrochemical properties of perovskite Na0.5Bi0.5TiO3 (NBTO) and explored the possibilities of utilizing it as an anode component for Na ion batteries. The electrochemical measurement shows that the perovskite NBTO exhibits high sodium storage capability via alloying/de-alloying reaction, fast sodium storage kinetics, and a good cyclability. The perovskite Na0.5Bi0.5TiO3 delivers a high capacity of ~ 470 mAh g−1 at 100 mA g−1 and 230 mAh g−1 at 250 mA g−1, emerging as a new anode for SIBs. Furthermore, the perovskite Na0.5Bi0.5TiO3 can retain a capacity of ~ 215 mAh g−1 after 50 cycles at 100 mA g−1, which is comparable to several previous metal oxide anodes. In addition, the sodium storage behavior is investigated by ex situ XRD and XPS techniques. The high capacity and good rate capability suggest that the perovskite Na0.5Bi0.5TiO3 has great potential to serve as anodes for high-performing SIBs. [ABSTRACT FROM AUTHOR]

Hierarchical porous N-doped carbon (NPC) is prepared by pyrolysis of poly(methyl methacrylate) (PMMA) particles decorated by graphene oxide (GO) and polypyrrole (PPy) as precursors and used as anode for lithium-ion batteries. The composite precursors with different diameter and composition (PMMA/GO/PPy-A and B) were conveniently prepared by dispersion polymerization of methyl methacrylate in the presence of graphene oxide as stabilizer in aqueous medium, followed by addition of pyrrole and its oxidative polymerization. After pyrolysis, the resulting NPC composites with hierarchically structured macro- and mesopores exhibit high surface area (289–398 m2/g) and different N-doping levels (7.46 and 4.22 wt% of nitrogen content). The NPC with the highest N-doping level (7.46 wt%) shows high reversible capacities of 831 mAh/g at 74.4 mA/g (C/5) after 50 cycles and excellent rate performances. [ABSTRACT FROM AUTHOR]

One of the most suitable approaches for the production of inorganic nanotubes is by means of carbon nanotube (CNT) templates coated by atomic layer deposition (ALD). This approach is attractive because it has the potential of controlling the wall thickness down to the Angstroms level. However, it is a recognized fact that the chemistry of the substrate surface can delay the full coverage at the initial stages of the ALD coating process, mainly due to nucleation issues. This is an important issue that might restrict laying down homogeneous coatings within the ultrathin range, which is the foundation for producing self-supported inorganic nanotubes. Here, we explore the early stage of the TiO nucleation on CNT templates systematically functionalized with different chemical groups (COOH, OH) or N-doped. The effects of the functionalization on the nucleation process from tetrakis (dimethylamino) titanium and water were meticulously studied by means of transmission electron microscopy. Observations revealed grain-like growth of TiO over pristine, purified and -OH-functionalized CNTs. In contrast, COOH functionalization yielded good conformality, which was improved on N-doped CNTs. Results were confirmed by X-rays photoelectron spectroscopy analysis. We recommend either COOH or N-doped CNTs for the production of ultrathin TiO nanotubes. [ABSTRACT FROM AUTHOR]

In this work, a novel composite of CoO nanoparticle and carbon nano-onions (CNOs) is synthesized by using ionic liquid as carbon and nitrogen source through a facile carbothermic reduction followed by low-temperature oxidation method. The SEM and HRTEM images reveal that the CoO particles are homogenously embedded in the CNOs. Due to the unique nano-structure, the electrolyte contacts well with the active materials, leading to a better transfer of lithium ions. Moreover, the unique nano-structure not only buffers the volume changes but also facilitates the shuttling of electrons during the cycling process. As a result, the electrode made up of CoO/CNOs composite delivers favorable cycling performance (676 mAh g after 200 cycles) and rate capability (557 mAh g at the current of 1 C), showing a promising prospect for lithium-ion batteries as anode materials. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon nanotubes (N-CNTs) containing different nitrogen species were synthesized via a chemical vapour deposition technique. This was archived by use of ferrocene and ferrocenyl-2-(4-cyanophenyl)acrylonitrile as catalysts. The N-CNTs were acid-treated and then used as Pd nanoparticle supports (Pd/N-CNTs). Both N-CNTs and Pd/N-CNTs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and other spectroscopic techniques. The selective reduction of nitroarenes to anilines was used as a model reaction to test the effect of pyridinic- and pyrrolic-nitrogen species on the catalytic performance of Pd/N-CNTs. A larger number of pyridinic-nitrogens in the N-CNTs increased nitroarene conversion and enhanced the selectivity towards anilines as opposed to the pyrrolic-nitrogens. Also, pyridinic-nitrogens favoured the nucleation of Pd nanoparticles with higher surface areas than those nucleated in the presence of pyrrolic-nitrogens. Density functional theory calculations were employed to determine the band-gap energy and optimal geometry of Pd complexed to pyridine and pyrrole ligands. These results showed that the pyridine complex had a lower band-gap energy (5.804 eV) than the pyrrole complex (6.406 eV) implying that the former complex is more reactive than the later. Thus, the inclusion of pyridinic-nitrogens in the N-CNTs, used as support, favours Pd-catalyzed nitroarene reductions. [ABSTRACT FROM AUTHOR]

Since the 1970s, palladium-catalysed carbon-carbon (C-C) bond formation has made a critical impact in organic synthesis. In early studies, homogeneous palladium catalysts were extensively used for this reaction with limitations such as difficulty in separation and recycling ability. Lately, heterogeneous palladium-based catalysts have shown promise as surrogates for conventional homogeneous catalysts in C-C coupling reactions, since the product is easy to isolate, while the catalyst is reusable and hence sustainable. Recently, a better part of these heterogeneous palladium catalysts are supported on carbon nanotubes (Pd/CNTs), that have shown superior catalytic performance and better recyclability since the CNT support imparts stability to the palladium catalyst. This review discusses the wide variety of surface functionalization techniques for CNTs that improve their properties as catalyst supports, as well as the methods available for loading the catalyst nanoparticles onto the CNTs. It will survey the literature where Pd/CNTs catalysts have been utilized for C-C coupling reactions, with particular emphasis on Suzuki-Miyaura and Mizoroki-Heck coupling reactions. It will also highlight some of the important parameters that affect these reactions. [ABSTRACT FROM AUTHOR]

In this work we present an ab initio study of electronic properties of one-dimensional (1D) core-shell nanostructures made of MS (MoS, WS) or BN armchair nanotube encapsulated carbon nanotubes (CNT). With local density approximation in density functional theory we calculate the band structure, carrier effective masses, various fundamental electrostatic features and optical absorption in such core-shell tubes. The carrier transport in these structures is important for nanoelectronics applications and is studied with the Green's function formalism. Simulations show a moderate indirect band gap in the core-shell CNT@MS tubes, while the CNT@BN shows metallic nature. The varying chirality of CNT strongly affects the carrier effective masses of the CNT@MS structure. Electron density is found to be much more localized near the atom cores and stronger in magnitude for the CNT@BN, while the W atoms show a more prominent electron-gas presence around them than Mo atoms as found in the electron localization functions. In the CNT@MS systems, the electrostatic difference potential indicates a drive to transfer charge from the metal to the S atoms in the shell. In terms of optical absorption, a strong and sharper peak is observed around 6 eV for the CNT@BN compared to a more broad absorption spectra of the CNT@MS. Metallic transmission spectra are seen for CNT@BN, while CNT@MS shows non-metallic transport but with a larger number of transmission states near Fermi level. The electronic and optical properties and its possible tuning in the core-shell structures can be useful in various applications such as shielded interconnects, logic switches and optoelectronics. [ABSTRACT FROM AUTHOR]

Microporous carbons are important in a wide variety of applications, ranging from pollution control to supercapacitors, yet their structure at the molecular level is poorly understood. Over the years, many structural models have been put forward, but none has been entirely satisfactory in explaining the properties of the carbons. The discovery of fullerenes and fullerene-related structures such as carbon nanotubes gave us a new perspective on the structure of solid carbon, and in 1997 it was suggested that microporous carbon may have a structure related to that of the fullerenes. Recently, evidence in support of such a structure has been obtained using aberration-corrected transmission electron microscopy, electron energy loss spectroscopy and other techniques. This article describes the development of ideas about the structure of microporous carbon, and reviews the experimental evidence for a fullerene-related structure. Theoretical models of the structural evolution of microporous carbon are summarised, and the use of fullerene-like models to predict the adsorptive properties of microporous carbons are reviewed. [ABSTRACT FROM AUTHOR]

Nitrogen-doped multi-walled carbon nanotubes (N-MWCNT) were synthesized by means of catalytic chemical vapor deposition technique using acetonitrile as carbon source material and ferrocene as catalyst. The structure of the synthesized N-MWCNT was characterized by means of microscopic (SEM, HRTEM) as well as spectroscopic (FTIR, Raman) techniques. Furthermore, the specific resistivity and the electrochemical properties of N-MWCNT were investigated and compared with those of pristine MWCNT. The results are discussed in terms of structural differences between pristine MWCNT and N-MWCNT. [ABSTRACT FROM AUTHOR]