Bamboo-like Carbon Nanotubes Research Articles

H2O2-based selective oxidations by divanadium-substituted polyoxotungstate supported on nitrogen-doped carbon nanomaterials

Abstract In this work, we present a new methodology for the preparation of highly active, selective, leaching-tolerant and recyclable catalysts on the basis of polyoxometalates (POM) and nitrogen-doped carbon nanomaterials. A divanadium-substituted γ-Keggin phosphotungstate [γ-PW10O38V2(μ-O)(μ−OH)]4− (PV2), was immobilized on two types of supports – N-doped carbon nanofibers (N-CNFs) having herring-bone packing of graphite layers and bamboo-like N-doped carbon nanotubes (N-CNTs). Two series of catalysts have been prepared and characterized by elemental analysis, N2 adsorption, TEM, XPS and FTIR techniques. Their catalytic performance was assessed in the liquid-phase selective oxidation of two representative organic substrates, 2,3,6-trimethylphenol and cyclohexene, with aqueous H2O2 as the green oxidant. The presence of nitrogen in the supports ensures strong binding and quasi-molecular dispersion of POM on the carbon surface, which is crucial for the catalytic performance and catalyst stability. The catalysts reveal truly heterogeneous nature of the catalysis and can be easily recovered and reused without loss of the catalytic performance. The morphology of the support has a significant impact on the catalytic performance: the supported PV2 catalysts prepared using N-CNTs are more active and, in general, more selective than the catalysts prepared with N-CNFs.

Effect of fuel structure on synthesis of carbon nanotubes in diffusion flames

Carbon nanotubes (CNTs) were synthesized on nickel nitrate coated nickel foam in co-flow diffusion flames. Two different fuel structures, methane and ethylene, were used to synthesize CNTs. The effect of fuel structure on CNTs was systematically studied. Results showed that carbon nanomaterials, including nanotubes and nanofibers, were successfully synthesized in all conditions in methane flames, while, in ethylene flames, bamboo-like CNTs were synthesized in limited conditions. It was also found that carbon nanomaterials synthesized in ethylene flames had more defects than that of in methane flames. In addition, metal nickel nanoparticles acted as catalysts in the synthesis of CNTs, and carbon nanomaterials diameter was dependent on the catalyst particle size. Flame-synthesized CNTs were based on the vapor-liquid-solid mechanism, and a “recursive growth mechanism” for CNTs growth was proposed, which would be more conducive to the understanding of CNTs growth mechanism. This method offers another possibility for low-cost, large-scale synthesis of carbon nanomaterials.

Electrochemical sensors based on functionalized carbon nanotubes modified with platinum nanoparticles for the detection of sulfide ions in aqueous media

Vertically aligned carbon nanotube (CNT) arrays were synthesized by thermal chemical vapor deposition (CVD) on stainless steel substrates coated by cobalt nanoparticles as catalyst. Morphological and elemental analyses conducted by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) revealed that bamboo-like CNTs were blocked by Co nanoparticles at the tips. The fabricated nanotubes underwent functionalization by electrochemical oxidation in sulfuric acid, and the subsequent structural studies, as well as Fourier transform infrared (FTIR) spectroscopy confirmed that the tips of functionalized CNTs were opened while oxygenated functional groups were generated at the sidewalls and tube endings. In order to enhance the catalytic performance of the functionalized CNT-based electrodes, platinum nanoparticles were deposited on nanotubes by the potentiostatic and pulse potential electrodeposition processes, and the optimum operating parameters in both techniques were determined. The catalytic activities of these two electrodes towards methanol oxidation were determined by cyclic voltammetry (CV) testing, and a superior electrocatalytic activity and poisoning tolerance were detected for the electrode prepared by pulse deposition. The sensing performance of the pulse plated Pt/CNT electrode for the electrochemical detection and oxidation of dissolved sulfide ions was investigated. A sensitivity of $$0.632\, \upmu \hbox {A }\upmu \hbox {M}^{-1 }\hbox {cm}^{-2 }$$ and a detection limit of $$0.26~\upmu \hbox {M}$$ were obtained, indicating the enhanced capabilities of the developed sensor as a promising candidate for various industrial and environmental applications. Vertically aligned carbon nanotubes (CNTs) were synthesized by thermal chemical vapor deposition (CVD), and were subsequently functionalized by 10 cycles of electrochemical oxidation in sulfuric acid solution. CNT-based electrodes were modified by pulse plated platinum nanoparticles. The catalytic performance of the designed electrode towards methanol oxidation was investigated, and its sensing performance for the electrochemical detection of dissolved sulfide ions was explored.

Simulation of Tensile Behaviors of Bamboo-like Carbon Nanotubes Based on Molecular Structural Mechanics Approach Combining with Finite Element Analysis

A molecular structural mechanics approach combining with finite element analysis (MSM/ FEA) was applied to study the microstructure and tensile behaviors of bamboo-like carbon nanotubes (BCNTs). The mathematical model of tensile behaviors of BCNTs was established based on molecular structural mechanics theory. The deformations of BCNTs, with different diameters and compartments set based on the experimental investigation on BCNT structures synthesized by chemical vapor depositon, under tensile load, were analyzed with ANSYS programmed. Results show that the BCNTs have good tensile properties, and those Young’s modulus can reach 0.84 Tpa. Through the analysis, it can be found that the Young’s modulus of BCNTs depends on the diameters and the length of compartment, which is in good agreement with our experimental tests for the tensile performances of individual BCNT.

Ni@N-doped graphene nanosheets and CNTs hybrids modified separator as efficient polysulfide barrier for high-performance lithium sulfur batteries

Lithium-sulfur batteries (LSBs) have been regarded as one of the most promising energy storage systems to break through the upper limit of lithium-ion batteries. However, the rampant diffusions of soluble lithium polysulfides (LiPSs) in the electrolyte induced the shuttle effect between anode and cathode, resulting in low sulfur utilization, low energy efficiency and short cycling life. Herein, we prove the rational design and construction of Ni nanoparticles filled in vertically grown N-doped bamboo-like carbon nanotubes (CNTs) on graphene nanosheets (Ni@NG-CNTs) as efficient polysulfide barrier for high-performance LSBs. The unique design integrates graphene nanosheets and CNTs into hierarchical architectures with one-dimensional (1D) CNTs, two-dimensional (2D) ultrathin nanosheets and abundant carbon nanocages. This design provides large surface area for lithium polysulfides (LiPSs) adsorption, accelerates electron transport and enhances electrochemical redox of LiPSs. Benefiting from the unique structural features, the LSBs with the Ni@NG-CNTs as polysulfide barrier keep high reversible specific capacities of 309.1 and 265.0 mAh·g−1 at 5 and 10 C rates after 500 cycles. This work provides a new strategy for constructing self-assembled hybrids of CNTs and graphene nanosheets with abundant carbon nanocages for high-performance LSBs.

Ni/Ni3C core–shell nanoparticles encapsulated in N-doped bamboo-like carbon nanotubes towards efficient overall water splitting

A novel electrocatalyst of Ni/Ni3C core–shell nanoparticles embedded in bamboo-like N-doped carbon nanotubes has been successfully synthesized, which exhibits superior overall water splitting performance in alkaline solution.

Long-life Li–S batteries based on enabling the immobilization and catalytic conversion of polysulfides

A novel hierarchical mesoporous nitrogen-rich carbon nanospheres comprising one-dimensional (1D) bamboo-like carbon nanotubes encapsulating Fe3O4 nanoparticles synthesized are used as a high-efficiency host for lithium–sulfur batteries.

Synthesis and characterization of nanocarbon having different morphological structures by chemical vapor deposition over Fe-Ni-Co-Mo/MgO catalyst

Catalytic chemical vapor deposition (CCVD) is one of the most promising synthesis methods for economically producing large quantities of different nanocarbon structures. Here we report a systematic study of the synthesis conditions for the preparation of different nanocarbon morphological structures via acetylene decomposition over the surface of quaternary-metallic catalyst (Fe-Ni-Co-Mo) supported on MgO (Fe-Ni-Co-Mo/MgO). In particular, the effect of temperature, and the reaction time were investigated to optimize the yield, quality, size and graphitic crystallinity of the deposited carbon. The study showed a successful synthesis of: (i) a high-yield and quality bamboo-like multiwalled carbon nanotubes (b-CNT), (ii) hybrid graphene/carbon nanotubes (G/CNT), and (iii) multilayer graphene (MLG). The structures of the obtained products were characterized by HR-TEM, TGA, Raman spectroscopy, FTIR and X-ray diffraction. The results found seem essential for realizing the role of different synthesis parameters on the yield, quality, and morphology of the synthesized product.

Bimetallic Mn and Co encased within bamboo-like N-doped carbon nanotubes as efficient oxygen reduction reaction electrocatalysts

The development of oxygen reaction reduction (ORR) electrocatalysts that are low-cost, highly-active and have long-term stability for use in energy conversion and storage applications such as fuel cells and metal-air batteries is very important. In this paper, a facile one-step pyrolysis method was used to prepare bamboo-like N-doped carbon nanotubes (BNCNTs) as effective ORR electrocatalysts. Manganese and cobalt salts were used as the metal precursors, and urea was the C and N source. The resulting catalysts were characterized by the scanning electron microscopy, high resolution-transmission electron microscopy, X-ray photoelectron spectroscopy, Raman microscopy and X-ray power diffraction. The BNCNTs contained Mn and Co nanoparticles that were coated with graphitic carbon. The electrochemical performances of the catalysts in alkaline media were evaluated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The BNCNTs prepared with a Mn to Co molar ratio of 1:1 at 800 °C had the best catalytic activity. The reaction followed a quasi-4 electron reaction pathway with a smaller Tafel slope (57.5 mV dec−1) than that of the commercial Pt/C (72.8 mV dec−1). In addition, the limiting current density, durability and methanol crossover resistance were all superior to those of Pt/C. The above results indicate that Mn/Co-BNCNTs-800 is an active electrocatalyst with earth-abundant non-precious elements for ORR.

Development and Application of Carbon-Layer-Stabilized, Nitrogen-Doped, Bamboo-Like Carbon Nanotube Catalysts in CO2 Hydrogenation.

Nitrogen‐doped, bamboo‐like carbon nanotubes (BCNTs) were synthesized from butylamine by catalytic chemical vapor deposition (CCVD method). The nanotubes were oxidized by H2SO4/HNO3 treatment and used to prepare calcium alginate gelled BCNT spheres. These beads were first carbonized and then Pd, Rh and Ni nanoparticles were anchored on the surface of the spheres. These systems were then applied as catalysts in CO2 hydrogenation. The BCNT support was examined by Raman spectroscopy, dynamic light scattering (DLS) and X‐ray photoelectron spectroscopy (XPS). The prepared catalysts were characterized by HRTEM and SEM. The oxidation pretreatment of BCNTs was successful, with the electrokinetic potential of the water‐based dispersion of BCNTs measuring −59.9 mV, meaning the nanotube dispersion is stable. Pyridinic and graphitic types of incorporated nitrogen centers were identified in the structure of the nanotubes, according to the XPS measurements. The Pd‐containing BCNT sphere catalyst was the most efficient in the catalytic studies. The highest conversion was reached on the Pd catalyst at 723 K, as well as at 873 K. The difference in the formation rate of CO was much less at 873 K between the Pd and Rh compared to the 723 K values. Accordingly, the application of Pd‐containing BCNT/carbon‐supported catalyst favored the generation of CO. However, the Ni‐BCNT/carbon catalyst leads to the formation of CH4 as the major product.

Synthesis And Characterization Of Bamboo-like Multi-walled Carbon Nanotubes By Alcohothermal Process

Bamboo-like multi-walled carbon nanotubes have been synthesized by an alcohothermal approach between cobaltocene and absolute ethanol at 500 °C. The as-obtained product is characterized by FESEM, TEM, HRTEM and Raman spectroscopy. The results show that the sample consists of a large number of nanotubes with a range of outer diameters from 50 to 100 nm, inner diameter of about 25~50 nm and several micrometers in length. These nanotubes consist of a linear chain of hollow compartments that are spaced at nearly equal separation of 20 nm for an about 50 nm diameter nanotube. A possible growth mechanism of the bamboo-like carbon nanotubes has been proposed based on the observation of Co particles embedded at the nanotubes’ tips.

Amorphous Molybdenum Sulfide on Three-Dimensional Hierarchical Hollow Microspheres Comprising Bamboo-like N-Doped Carbon Nanotubes as a Highly Active Hydrogen Evolution Reaction Catalyst

Novel amorphous-MoSx-coated three-dimensional (3D) hierarchical hollow microspheres comprising one-dimensional bamboo-like N-doped carbon nanotubes (BNCNT/MoSx-HM) are developed as a highly active electrocatalyst for the hydrogen evolution reaction (HER). The 3D hierarchical microspheres are easily prepared via the growth of bamboo-like N-doped CNTs (BNCNTs) on both the inner and outer surfaces of Co3O4–MgO/carbon hollow microspheres, which are prepared by spray pyrolysis, followed by uniform MoSx coating of the surface. Metallic Co nanocrystals play a key role in the growth of BNCNTs, acting as catalysts for their nucleation. Owing to the electrostatic attraction between the N-doped sites in BNCNTs and the thiomolybdate precursor anions, few-layered amorphous MoSx catalysts are well deposited on BNCNT surfaces, even at low temperature. The 3D hierarchical hollow structure facilitates electrolyte access, and the synergistic effect between the MoSx catalyst material with ample active sites and the conducti...

In Situ Growth of NiFe Alloy Nanoparticles Embedded into N-Doped Bamboo-like Carbon Nanotubes as a Bifunctional Electrocatalyst for Zn-Air Batteries.

Developing low-cost catalysts for electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with superior performance in an alkaline solution is of significance for large-scale applications in aqueous zinc-air batteries (ZABs). Herein, we describe the in situ design of embedded NiFe nanoparticles into the N-doped bamboo-like carbon nanotube (NBCNT) with high catalytic performance and stability. The obtained NiFe@NBCNT hybrid exhibits a high electrochemical activity and stability with an unexpectedly low overpotential of ∼195 mV for OER at 10 mA cm-2 and an onset potential at 1.03 V for ORR, superior to the state-of-the-art Pt/C and RuO2 catalysts. Additionally, compared to the mixture of Pt/C and RuO2 cathodes, the ZAB based on the NiFe@NBCNT cathode displays a lower overpotential (0.80 V), higher stable round-trip efficiency (58.3%), and improved power density for 200 cycles at 10 mA cm-2. Apparently, the obtained results indicate that the NiFe@NBCNT hybrid is proven to be one of the best nonnoble metal catalysts for achieving commercial implementation of rechargeable ZABs.

On an easy way to prepare highly efficient Fe/N-co-doped carbon nanotube/nanoparticle composite for oxygen reduction reaction in Al–air batteries

Developing an efficient and low-cost oxygen reduction reaction (ORR) catalyst is the key to realize the commercialization of metal–air batteries. Fe/N-co-doped carbon materials (Fe–N–C) are regarded as one of the most promising oxygen reduction reaction (ORR) catalysts to replace expensive and unstable Pt/C in metal–air batteries. In this work, a new kind of Fe/N-co-doped special carbon nanotube/nanoparticle hybrid catalyst was obtained by using cheap precursors, i.e., ketjenblack EC-600JD (KB), melamine and iron nitrate via a facile high-temperature pyrolysis treatment. The catalyst shows a comparative oxygen reduction reaction (ORR) catalytic activity and better stability than commercial 20 wt% Pt/C in the same test conditions. The outstanding performance results from the doping of Fe and N, which could effectively increase the active sites. Furthermore, a special bamboo-like carbon nanotube is generated due to the catalysis of Fe source. The catalyst exhibits good performance in Al–air batteries. The maximum power density can reach to 300 mW cm−2 with the cell voltage of about 1 V and the current density of 300 mA cm−2.

Fe-doped CoSe2 nanoparticles encapsulated in N-doped bamboo-like carbon nanotubes as an efficient electrocatalyst for oxygen evolution reaction

The utilization of clean and unlimited hydrogen energy is an attractive avenue to tackle the crises of energy and environmental pollution, and exploring high-active, earth-abundant and stable electrocatalysts for the oxygen evolution reaction (OER) is critical to the practicability for electrochemical water splitting. Herein, a nanohybrid with Fe-doped CoSe2 nanoparticles embedded in N-doped bamboo-like carbon nanotubes (denoted as FCS@N-CT) is prepared through simple pyrolysis followed by the selenization employing easily available raw materials for the first time. The received FCS@N-CT shows excellent electrocatalytic comprehensive properties for OER in 1 M KOH solution, comparable to and even surpassing the fresh RuO2. Specifically, it requires an overpotential of only 330 mV to deliver a current density of 10 mA cm−2, and achieves higher current density than that of RuO2 with elevating the potential over 1.652 V vs. reversible hydrogen electrode. More strikingly, FCS@N-CT exhibits a smaller Tafel slope and much better durability than those of RuO2. The remarkable electrocatalytic performance of FCS@N-CT can be ascribed to the unique nanostructure featuring abundant active sites, the favorable conductive network for rapid charge transfer, the synergistic effect between FCS and N-CT, along with the protection of FCS by carbon layers for strong robustness under catalytic conditions.

FeCo-Doped Hollow Bamboo-Like C-N Composites as Cathodic Catalysts for Zinc-Air Battery in Neutral Media

Precious metal-free C-N composites possess great significance as replacements for Pt-based catalysts used as cathodes in fuel cells. Herein, we have fabricated the Fe/Co-doped C-N composite catalysts, marked as C-N, Co/C-N and Fe-Co/C-N, by direct pyrolysis of the dried suspensions consisting of cobalt/iron salt, dicyandiamide and glucose. For the Fe-Co/C-N catalyst, its morphological texture is characterized by Fe-Co nanoparticles and hollow bamboo-like nitrogen-doped carbon nanotubes (C-N nanotubes). The electroactivity of the prepared samples for oxygen reduction reaction (ORR) in a neutral medium has been investigated. The catalyst Fe-Co/C-N presents the highest ORR current density of 5.1 mA·cm−2 @0.8V (vs Ag/AgCl) in a neutral medium. A zinc-air battery in neutral KNO3 solution, assembled with zinc as the anode and carbon paper loaded by the prepared catalysts as the air electrode (cathode), displays excellent and stable discharge performance. The maximum power density of the Fe-Co/C-N catalyst is 32 mW·cm−2, and the continuous discharge time reaches 209, 155, 17 h at constant discharging current density of 25, 50 and 100 mA·cm−2 respectively. Simultaneously, the air electrode using the Fe-Co/C-N as the catalyst shows good cycle stability and repeatability. Results reveal that the Fe-Co/C-N is a very promising cathodic catalyst applied in neutral zinc-air battery.

Co-VN encapsulated in bamboo-like N-doped carbon nanotubes for ultrahigh-stability of oxygen reduction reaction.

The electrocatalytic activity of carbon-based non-precious metal composites towards oxygen reduction reaction (ORR) is far from that of the recognized Pt/C catalyst. Thus, it is necessary to exploit novel catalysts based on multicomponent carbon-based composites with both high activity and high stability. Herein, a bottom-up strategy was used for constructing bamboo-like N-doped graphitic CNTs with a few encapsulated Co and VN nanoparticles (namely, NGT-CoV) by adopting melamine as both a nitrogen source and a carbon source. During the synthesis, melamine initially coordinated with cobalt and vanadium ions and then decomposed into carbon nitride nanosheet structures. Simultaneously, cobalt ions/clusters were converted into metal nanocatalysts by the reduced gases that were generated, which further rearranged the carbon nitride nanostructures to form N-doped CNTs. The presence of vanadium species strengthened the electronic structure and increased the contents of Co and N species by enhancing the interactions among Co and N species. The optimized NGT-Co35V65-45-900 exhibited an Eonset of 0.92 V (vs. RHE), an E1/2 of 0.81 V (vs. RHE), and a Tafel slope of 66.1 mV dec-1 in the ORR. It also displayed much higher durability (a negative shift in E1/2 of only 11 mV after 10 000 cycles) and methanol tolerance than a commercial Pt/C catalyst. The excellent performance should be attributed to the high exposure level of active sites that originated from Co-N, VN and N-doped bamboo-like graphitic CNTs. Moreover, the skeleton composed of hollow graphitic ultra-long CNTs could not only provide smooth mass transport pathways but also facilitate fast electron transfer.

Apically Co-nanoparticles-wrapped nitrogen-doped carbon nanotubes from a single-source MOF for efficient oxygen reduction

Bamboo-like N-doped carbon nanotubes wrapping Co nanoparticles (Co@BNCNTs) derived from a single precursor Co-MOF exhibited remarkable ORR electrocatalytic performance with long-term durability, due to the synergetic interaction between the NCNTs and Co nanoparticles.

Nitrogen-doped bamboo-like carbon nanotubes as anode material for high performance potassium ion batteries

Nitrogen-doped bamboo-like carbon nanotubes enable a simple intercalation of K+ ions and provide enough spaces to accommodate volume change.

Hierarchical hollow microspheres grafted with Co nanoparticle-embedded bamboo-like N-doped carbon nanotube bundles as ultrahigh rate and long-life cathodes for rechargeable lithium-oxygen batteries

Rational design of efficient, affordable, and durable electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is essential for rechargeable lithium-oxygen (Li–O2) batteries. We present for the first time hierarchical hollow microspheres grafted with metallic Co-embedded bamboo-like N-doped carbon nanotube bundles (Co-b-NCNTs hollow microspheres) as oxygen electrodes for Li-air batteries. Hierarchical composite microspheres are prepared via a facile two-step process involving synthesis of Co3O4-MgO hollow microspheres by spray pyrolysis, followed by internal and external growth of bamboo-like NCNTs in the shells. During post-treatment, metallic Co and MgO nanoparticles play key respective roles in catalyzing in-situ growth of NCNTs and maintaining structural integrity of the composites. The hierarchical composite structure with Co and N doping not only provides ample active sites for the OER and ORR, but also sufficient space for storing produced Li2O2. Thus, Co-b-NCNTs hollow microspheres exhibit high initial round-trip efficiency, long-term cycling and ultrahigh rate performances when applied as oxygen electrodes for Li–O2 batteries. The initial discharge capacity and round-trip efficiency at a current density of 200 mA g−1 are 28,968 mA h g−1 and 78.2%, respectively. Specific capacities at cutoff capacities of 500 and 1000 mA h g−1 are stable for 201 and 157 cycles, respectively.