Synthesis Of Nitrogen-doped Carbon Nanotubes Research Articles

Supramolecular preorganization synthesis of nitrogen-doped carbon nanotubes functionalized by Brønsted acidic ionic liquid for microwave-assisted production of promising furanic derivatives

Brønsted acidic ionic liquids functionalized nitrogen-doped carbon nanotubes catalysts, [C4SO3HN][OTf]-NCNTs (OTf = SO3CF3), are synthesized by an additive-free supramolecular preorganization-thermal condensation route followed by chemical modification. By controlling the molar composition of carbon–nitrogen based monomers, sequence of the monomers and thermal condensation temperature, the tubular morphology and porosity properties of the catalysts are well-adjusted. The [C4SO3HN][OTf]-NCNTs are successfully applied in the reactions of great relevance to the development of sustainable bio-economy, namely, microwave-assisted production of 5-hydromethylfurfural (HMF) and furfural (FFR) from the dehydration of fructose and xylose, and the important reaction parameters including microwave irradiation temperature and time as well as solvent are considered. Co-operation of strong Brønsted acidity, unique tubular nanostructures and microwave heating approach finally endows [C4SO3HN][OTf]-NCNTs the enhanced dehydration reactivity and selectivity, in which the [C4SO3HN][OTf]-NCNTs800-2 with perfect tubular nanostructures displays the highest HMF yield (82.6%, 15 min in THF media) and FFR yield (56.2%, 45 min in DMSO media). The [C4SO3HN][OTf]-NCNTs also exhibit good catalytic reusability, attributing to covalent bonding of the [C4SO3HN+][OTf−] units onto NCNTs frameworks; meanwhile, the formation of considerable amount of humins at the surface of the catalysts is effectively inhibited by using microwave heating mode.

Theophylline-regulated pyrolysis synthesis of nitrogen-doped carbon nanotubes with iron-cobalt nanoparticles for greatly boosting oxygen reduction reaction

At present, construction of economical, efficient and stable electrocatalysts for oxygen reduction reaction (ORR) is critical to alleviate the energy shortage. Theophylline (THP) can be easily extracted from natural plants, whose nitrogen atoms can chelate with metal ions. With assistance of THP, FeCo alloy was confined in N-doped carbon nanotubes (FeCo/NCNTs-800) by one-step pyrolysis of a mixture of the metal precursors, g-C3N4 and THP. The resulting FeCo/NCNTs-800 showed a better ORR performance (onset potential, Eonset = 1.09 V; half-wave potential, E1/2 = 0.87 V) than commercial Pt/C (50 wt%) in a 0.1 M KOH solution, with a limiting current density as high as –5.54 mA cm−2. This work offers a feasible strategy for developing transitional bimetal-based carbon catalysts in alkaline fuel cells.

Supramolecular Preorganization Synthesis of Nitrogen-Doped Carbon Nanotubes Functionalized by Brønsted Acidic Ionic Liquid for Microwave-Assisted Production of Promising Furanic Derivatives

Supramolecular Preorganization Synthesis of Nitrogen-Doped Carbon Nanotubes Functionalized by Brønsted Acidic Ionic Liquid for Microwave-Assisted Production of Promising Furanic Derivatives

A metal–organic framework derived cobalt oxide/nitrogen-doped carbon nanotube nanotentacles on electrospun carbon nanofiber for electrochemical energy storage

A self-templated metal–organic framework (MOF)-based idea at low temperature, with no need of external reducing gas and additional precursors, offers a simple approach for direct synthesis of N-CNT-based controlled and organized nano-assemblies with the essence of MOF. • A new way of growing nitrogen-doped carbon nanotube (N-CNT) from self-templated metal–organic framework. • Low cost of production, controlled assembly and confinement of metallic nanoparticles. • Well-organized N-CNT/Co 3 O 4 nanotentacles on electrospun carbon nanofiber in a 3D array. • Promising performance of as-prepared material for electrochemical energy storage. Carbon nanotubes (CNTs) and their nanocomposites have been a promising choice for next-generation technologies. However, synthesis of CNT-based controlled assembly, one of the worthy aspects of advanced nanomaterials, has rarely been reported. Synthesis of CNTs at low temperature and incorporation of active nanoparticles (NPs) are other current issues. Herein, synthesis of nitrogen-doped CNTs (N-CNTs) embedded with very small Co 3 O 4 NPs is reported, for the first time, in the form of organized nanotentacles on electrospun carbon nanofiber (CNF) in a 3D array, at relatively low temperature with no need of external reducing gas and precursors, by self-templated metal–organic framework (MOF)-based approach. Self-templated MOF acts not only as a single source for CNTs, N-doping and small Co 3 O 4 NPs ensuring a large specific surface area, high porosity, and even distribution of constituents but also owes an additional advantage of orienting the pre-designed controlled morphology. The as-constructed 3D Co 3 O 4 /N-CNTs@CNF, for supercapacitors, exhibits a promising performance. This idea of growing N-CNTs in pre-designed shape of self-templated MOF by just heating to relatively low temperature with no need of reducing gas, additives and expensive and complicated instruments, offers a new approach for creating metallic constituent incorporated CNT-based pre-designed a varieties of controlled nanoassemblies with the essence of MOF.

Effects of Ionic Liquid and Biomass Sources on Carbon Nanotube Physical and Electrochemical Properties

The ongoing research toward meeting global energy demands requires novel materials from abundant renewable resources. This work involves an investigation on nitrogen-doped carbon nanotubes (N-CNTs) synthesized from relatively low-cost and readily available biomass as carbon precursors and their use as electrodes for supercapacitors. The influence of the ionic liquid 1-butyl-3-methylimidazolium chloride, or its combination with either sugarcane bagasse or cellulose (IL-CNTs, ILBag-CNTs, and ILCel-CNTs, respectively), in the synthesis of N-CNTs and the resultant effect on their physical and electrochemical properties was studied. Systematic characterizations of the N-CNTs employing transmission electron microscopy (TEM), thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), elemental analysis, nitrogen sorption analysis, cyclic voltammetry, and electrochemical impedance spectroscopy were performed. TEM data analysis showed that the mean outer diameters decreased, in the order of IL-CNTs > ILBag-CNTs > ILCel-CNTs. The N-CNTs possess only pyridinic and pyrrolic nitrogen-doping moieties. The pyridinic nitrogen-doping content is lowest in IL-CNTs and highest in ILCel-CNTs. The N-CNTs are mesoporous with surface areas in the range of 21–52 m2 g−1. The ILCel-CNTs had the highest specific capacitance of 30 F g−1, while IL-CNTs has the least, 10 F g−1. The source of biomass is beneficial for tuning physicochemical properties such as the size and surface areas of N-CNTs, the pyridinic nitrogen-doping content, and ultimately capacitance, leading to materials with excellent properties for electrochemical applications.

ZIF-67 derived nitrogen doped CNTs decorated with sulfur and Ni(OH)2 as potential electrode material for high-performance supercapacitors

Herein we report the synthesis of nitrogen-doped carbon nanotubes (NC) based sulfide (S) and nickel hydroxide (NH) supported on nickel foam as a novel electrode material for the supercapacitors (abbreviated as Co/NC/S@NH). A class of zeolitic imidazolate frameworks, ZIF-67 (Co), is initially grown to synthesize nanotubes directly on the nickel foam (NF). The anion exchange reactions are performed for the growth of sulfide and nickel hydroxide on ZIF-67 (Co) derived carbon nanotubes. In the structural analysis, X-ray diffraction confirmed the successful in-situ growth of carbon nanotubes. Transmission electron microscopy was employed to confirm the formation of NC-based sulfide and nickel hydroxide. The Co/NC/S@NH, hierarchical hybrid electrode, exhibited improved capacitance of 1636 F/g at 1 A/g (982 C/g or 273 mA/h) with exceptional cyclic stability. The Co/NC/S@NH showed capacity retention of 94% over 5,000 cycles. The enhanced electrochemical performance of the synthesized electrode is due to the improved redox reactions and direct growth of nitrogen-doped carbon nanotubes on 3D nickel foam which act as "superhighways" for electron transportation. Moreover, the sulfur ions could hinder the collapse of a structure by the intercalation among layers, whereas the extremely hydroxylated surface of Ni(OH)2 nanosheets could promote accessibility of ions to the electrolyte which decreases the resistance of electrodes which agreed with the finding from electrochemical impedance spectroscopy.

Synthesis of nitrogen-doped carbon nanotubes directly on metallic foams as cathode material with high mass load for lithium-air batteries

Spray pyrolysis chemical vapor deposition was used to synthetize carbon nanotubes and nitrogen-doped carbon nanotubes directly on metallic foam substrates. Cathodes containing pristine and nitrogen-doped nanotubes with mass loads of 4.2 mg cm−2 were investigated for lithium-air batteries. Pristine nanotubes presented a maximum specific discharge capacity of 3320 mAh g − 1 in air, while nitrogen-doped nanotubes exhibited a maximum specific discharge capacity of 3934 mAh g − 1. These results demonstrate that is possible to deposit high amounts of carbon nanomaterials on metallic substrates and use them directly as electrode materials with high electrocatalytic activity for the cathode reaction for developing advanced energy storage devices.

Controllable synthesis of nitrogen-doped carbon nanotubes derived from halloysite-templated polyaniline towards nonprecious ORR catalysts

Halloysites were applied as the template to form halloysite/polyaniline core/shell hybrids through an oxidative polymerization route, where the amount of aniline monomer could be adjusted to precisely control the shell thickness of polyaniline. The pyrolysis process was then applied to ensure the carbonization of the polyaniline to form halloysite/nitrogen-doped carbon core/shell hybrids. Finally, halloysites were removed, resulting in the formation of nitrogen-doped carbon nanotube with a uniform morphology and a controlled shell thickness. The shell thickness and pyrolysis temperature of nitrogen-doped carbon nanotubes were optimized to improve the electrocatalytic performance involved in oxygen reduction reaction. The nitrogen-doped carbon nanotubes showed good electrocatalytic activities toward oxygen reduction reaction in 0.1 mol L−1 KOH aqueous solution, making them a promising cathode catalyst for alkaline fuel cell applications.

Hydrogenation of nitrobenzene over a composite catalyst based on zeolite supported N-doped carbon nanotubes decorated with palladium

A catalyst nanocomposite was synthesized based on zeolite supported nitrogen-doped carbon nanotubes (N-CNT) decorated with palladium nanoparticles. Zeolite beads impregnated with nickel nitrate solution were used as CCVD catalyst support during the synthesis of N-CNT. Then the zeolite supported N-CNT was decorated with palladium nanoparticles and the final nanocomposite was tested in nitrobenzene hydrogenation. The structure of the nanocomposite was characterized by SEM. The surface of the zeolite beads is extensively covered by N-CNT. The particle size distribution of the palladium nanoparticles on the surface of N-CNT is relatively homogenous (< 7 nm). The catalytic activity of the nanocomposite was the highest at 10 bar and 323 K while the achieved nitrobenzene/aniline conversion was 99.9% after 4 h of hydrogenation.

Physicochemical properties of nitrogen-doped carbon nanotubes from metallocenes and ferrocenyl imidazolium compounds

Shaped carbon nanomaterials (SCNMs) were synthesized via the chemical vapour deposition (CVD) technique by using typical metallocenes (ferrocene, nickelocene, cobaltocene, and ruthenocene), and more interestingly, by use of novel ferrocenyl imidazolium derivatives, containing -Cl (FcImCl), -NO2 (FcImNO2) and -CH3 (FcImCH3) substituents as catalysts. Acetonitrile was applied both as a carbon and nitrogen source at temperatures 800–900 °C. The SCNMs, namely, carbon nanotubes (CNTs), carbon spheres (CS), carbon fibres (CF) and amorphous carbons (ACs) were obtained in varying ratios depending on the catalyst and carbon sources. The ferrocenyl imidazolium catalysts produced nitrogen-doped CNTs (N-CNTs) with bamboo-like structures. The yields of various reactions were temperature-dependent, with the highest amount of N-CNTs obtained at 850 °C. In all samples, the composition was mainly of CS and N-CNTs except for nickelocene at 800 °C that gave CFs as a “minor” product. Ferrocene and nickelocene in acetonitrile produced well-aligned N-CNTs while cobaltocene and ruthenocene gave ‘spaghetti-like’ structures. In the case of ferrocenyl imidazolium catalyst, a coiled N-CNTs morphology was produced from FcImCl catalyst. Also, higher percentage of N-CNTs with traces of CS were obtained from the FcImCl and FcImCH3 catalysts in acetonitrile at 850 °C, while higher percentage of CS and AC were obtained for FcImNO2 catalyst. In all the catalysts, the use of acetonitrile promoted nitrogen-doping (samples with more disordered and with smaller outer-diameters). Thus, this study demonstrates that the synthesis of N-CNTs from nitrogen-containing ferrocenyl imidazolium compounds as catalyst sources, provided higher percentage of N-CNTs which can be suitable for various application.

Nitrogen-incorporated carbon nanotube derived from polystyrene and polypyrrole as hydrogen storage material

“Synthesis of nitrogen-doped carbon nanotubes from polymeric precursors (polystyrene and polypyrrole) by poly-condensation followed by carbonization under an inert atmosphere is reported. Three different carbonization temperatures (500 °C, 700 °C and 900 °C) were employed to synthesize three different carbon nanostructures with different morphologies. These were designated as NCNR-500 (nitrogen-doped carbon nanorods), NCBCT-700 (nitrogen-doped fused bead carbon nanotubes), and NCNT-900 (nitrogen-doped carbon nanotubes) according to morphology and carbonization temperature. Microstructure, morphology, porosity, and nitrogen content were characterized by several different techniques. The effects of carbonization temperature and the role of functional groups were also investigated. Total and excess hydrogen storage capacities of 2.0 wt% and 1.8 wt%, respectively, were measured at 298 K and 100 bar for the NCNT-900 material. This is higher than the capacities of the NCNR-500 and NCBCT-700 materials. NCNT-900 exhibited a porous structure with high specific surface area and total pore volume of 870 m/g and 0.62 cm3/g, respectively.

Straightforward synthesis of nitrogen-doped carbon nanotubes as highly active bifunctional electrocatalysts for full water splitting

The success of intermittent renewable energy systems relies on the development of energy storage technologies. Particularly, active and stable water splitting electrocatalysts operating in the same electrolyte are required to enhance the overall efficiency and reduce the costs. Here we report a precise and facile synthesis method to control nitrogen active sites for producing nitrogen doped multi-walled carbon nanotube (NMWNT) with high activity toward both oxygen and hydrogen evolution reactions (OER and HER). The NMWNT shows an extraordinary OER activity, superior to the most active non-metal based OER electrocatalysts. For OER, the NMWNT requires overpotentials of only 320 and 360mV to deliver current densities of 10 and 50mAcm−2 in 1.0M NaOH, respectively. This metal-free electrocatalyst also exhibits a proper performance toward HER with a moderate overpotential of 340mV to achieve a current density of 10mAcm−2 in 0.1M NaOH. This catalyst also shows high stability after long-time water oxidation without notable changes in the structure of the material. It is revealed that the electron-withdrawing pyridinic N moieties in the NMWNTs could serve as the active sites for OER and HER. Our findings open up new avenues for the development of metal-free electrocatalysts for full water splitting.

Some perspectives on nitrogen-doped carbon nanotube synthesis from acetonitrile and N,N′-dimethylformamide mixtures

This work reports on the influence of the ratio of sp3 (N,N′-dimethylformamide, DMF) to sp (acetonitrile) hybridised nitrogen within the carbon source used in the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) by means of the floating catalyst chemical vapour deposition method. The physicochemical properties of the N-CNTs were investigated by means of scanning and transmission electron microscopies, textural characteristics, powder X-ray diffraction, X-ray photoelectron spectroscopy, thermal gravimetric analysis and elemental analysis. When the two nitrogen sources were compared before mixing, it was found that sp3 hybridised nitrogen in DMF was a more effective source for the incorporation of nitrogen atoms (5.87%) than sp hybridised nitrogen in acetonitrile (3.49%). The number of walls within the N-CNT synthesised from the sp3 nitrogen source was tailored by changing the synthesis temperature. Overall, a 1:3 sp3:sp ratio produced N-CNTs with the highest nitrogen content of 9.38% and a general abundance of pyrrolic nitrogen moieties within the samples. The best synthesis temperature in terms of nitrogen content and largest composition of N-CNTs with least residual iron was found to be 900 °C. Varying ratio of sp3:sp hybridised nitrogen is suitable for tailoring the physicochemical properties of N-CNTs towards preferred applications.

Facile synthesis of nitrogen-doped carbon nanotubes encapsulating nickel cobalt alloys 3D networks for oxygen evolution reaction in an alkaline solution

Abstract Efficient oxygen evolution reaction (OER) catalysts are required to facilitate the large-scale exploitation of renewable energy resources and applications in electrochemical energy conversion technologies. Here, we show that metal alloy-based hybrids can provide higher electrocatalytic activity than their individual metal-based hybrids. In particular, NiCo alloys encapsulated within nitrogen-doped carbon nanotubes (NiCo@NCNTs) showed higher OER activities in an alkaline solution than the individual metal hybrids (Ni@NCNTs and Co@NCNTs), highlighting a synergy between the Ni and Co components. NiCo@NCNTs pyrolyzed at 800 °C displayed an overpotential of ∼41 mV at a current density of 10 mA cm −2 and were more stable than IrO 2 during 1000-cycle accelerated durability testing at a scan rate of 100 mV s −1 .

Preparation of nitrogen-doped carbon nanotubes with different morphologies from melamine-formaldehyde resin.

We report a facile method for the synthesis of nitrogen-doped carbon nanotubes (NCNTs) from melamine-formaldehyde (MR) resin using FeCl3 or supported FeCl3 as catalysts. The growth of NCNTs follows a decomposition-reconstruction mechanism, in which the polymer precursor would totally gasify during pyrolysis process and then transformed into carbon nanotubes. The morphology of the NCNTs could be adjusted via applying different catalyst supports and three kinds of carbon nanotubes with outer-diameter of 20-200 nm and morphologies of either bamboo-like or hollow interiors were obtained. Nitrogen atoms in the materials were mainly in the form of pyridinic and quaternary form while the formation of iron species strongly depended on the interaction between iron precursor and organic carbon/nitrogen sources. All MR resin derived NCNTs are efficient toward oxygen reduction reaction (ORR). NCNTs prepared using FeCl3 as catalyst showed the highest ORR activity with half-wave potentials of -0.17 V, which is comparable with commercial Pt/C. This is probably because of a close contact between MR resin and iron precursor could enhance the iron-ligand coordination strength and thus steadily improve the performance of the catalyst.

Microwave synthesis of nitrogen-doped carbon nanotubes anchored on graphene substrates

We report a fast and facile microwave technique to synthesize nitrogen-doped carbon nanotubes anchored on graphene substrates from azobis(cyclohexanecarbonitrile), a commodity chemical, commonly used as a radical initiator in polymerization reactions as the nanotube precursor. Micrometer-long, nitrogen-doped carbon nanotubes vertically anchored on graphene was obtained to produce mesoporous, hierarchical nanostructures. X-ray photoelectron spectroscopy reveals that nitrogen moieties exist as pyridinic and graphitic nitrogen. When applied as anodes in lithium-ion batteries, our materials exhibit a high capacity of 1342mAhg−1 even after prolonged cycling reflecting the ability of the three-dimensional network to accommodate the extreme volume changes occurring during the lithiation/delithiation reactions.

One-step hydrothermal synthesis of nitrogen-doped carbon nanotubes as an efficient electrocatalyst for oxygen reduction reactions.

A high amount of heteroatom doping in carbon, although favorable for enhanced density of catalytically active sites, may lead to substantially decreased electroconductivity, which is necessary for the electrochemical oxygen reduction reaction. Herein, a relatively low amount of nitrogen was successfully doped into carbon nanotubes (CNTs) by a hydrothermal approach in one step, and the synthesized nitrogen-doped CNT (CNT-N) materials retained most of the original, excellent characteristics, such as the graphitic structure, tubular morphology, and high surface area, of CNTs. The resultant CNT-N materials, although containing a relatively low amount of nitrogen doping, exhibited high electrocatalytic ORR activity, comparable to that of 20 wt% Pt/C; long durability; and, more importantly, largely inhibited methanol crossover effect.

Nitrogen-doped carbon nanotubes decorated silicon carbide as a metal-free catalyst for partial oxidation of H2S

Hierarchical metal-free catalyst based on the CVD synthesis of nitrogen-doped carbon nanotubes decorated silicon carbide (N-CNTs/SiC) macroscopic host structure has been prepared. The catalyst was evaluated in the partial oxidation of H2S by oxygen into elemental sulfur in a fixed-bed reactor. The catalytic results indicate that the N-CNTs/SiC catalyst exhibits an extremely high desulfurization performance even under severe reaction conditions such as low temperature, high space velocity and at low O2-to-H2S molar ratio. The high desulfurization performance was attributed to the high effective surface area of the catalyst along with a short diffusion length associated with the nanoscopic dimension of the carbon nanotubes. The N-CNTs/SiC catalyst also displays a high stability as a function of time on stream which could be attributed to the strong anchoring of the nitrogen doping within the carbon matrix. The extrudates shape of the SiC support allows the direct macroscopic shaping of the catalyst for use in conventional fixed-bed reactor without facing problems linked with catalyst handling, transportation and pressure drop across the catalyst bed as encountered with nanoscopic carbon-based catalyst.

Nitrogen-doped carbon nanotubes synthesized on metal substrates from a single precursor

We report the synthesis of nitrogen-doped carbon nanotubes (CNTs) by thermal chemical vapor deposition on metal substrates without additional catalyst or processing in the temperature range of 850–1000°C. Monoethanolamine was used as a source of both carbon and nitrogen. X-ray photoelectron spectroscopy revealed that the concentration of nitrogen atoms in the CNTs was 2.0–2.5%. Electron microscope images confirmed that the CNTs prepared in this temperature range all exhibited bamboo-like, corrugated structures. The crystallinity of the N-doped CNTs increased with synthesis temperature. This study suggests that simple, low cost synthesis of nitrogen-doped CNTs on metal substrates is feasible.

Initial Stages of Growth of Nitrogen-Doped Single-Walled Carbon Nanotubes

The dynamics of carbon and nitrogen atoms on the Fe55 nanoparticle is investigated by means of molecular dynamics simulations at the density-functional tight-binding level. A time range of at most 0.4 ns is covered in the molecular dynamics simulations. Different degrees of adatom coverage are considered. Nitrogen and carbon atoms express different dynamics. Adsorbed monomers and large fragments are rather immobile whereas dimers and trimers move fast. Nitrogen-containing fragments are less strongly bound to the iron cluster and are therefore more mobile than carbon-only fragments with equal amount of atoms. On the iron nanoparticle surface, five-membered rings are formed first and then six-membered rings. The present simulations provide insight into the atomistic mechanisms involved in the nanocatalyzed synthesis of nitrogen-doped carbon nanotubes. The tendency of nitrogen atoms as parts of carbon fragments to repel the iron surface is confirmed by performing short molecular dynamics simulations at the d...