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Abstract: The synthesis of tapered carbon nanotubes (TCNTs) by the thermal decomposition of poly(ethylene glycol) at 800°C using Ni as a catalyst is reported. The TCNTs consist of a 50nm diameter graphite tube terminated by a tapered tip, which is about 1μm in length and 20nm in diameter in the tip end. The catalyst particle contained in the tapered tip was found to be a cylindrical with a diameter of about 20nm. Electron microscopy revealed that the catalyst was a single crystal of NiCx and the graphene layers were grown in the [110] direction of the catalyst, forming TCNTs. The unique morphology of the catalyst particle played an important role in the formation of TCNTs. The field emission properties of the TCNTs exhibited a lower turn-on voltage (Eturn-on =3.2V/μm), lower threshold fields voltage (Ethreshold =5.2V/μm) and higher field-enhancement factor β than did multi-walled CNTs. [Copyright &y& Elsevier]

We report on a 20–40 s process for growing aligned, uniformed, high purity multi-walled carbon nanotubes (MWNTs) using an alcohol lamp burner. With an appropriate catalyst precursor concentration, MWNTs can be grown on a Co-coated 304 stainless steel mesh under incomplete combustion conditions at 680–700°C. The process provides a rapid, easy, economic and safe method for the formation of carbon nanotubes. We suggest that the proposed method be considered as an educational kit for college or high school level experiments. [ABSTRACT FROM AUTHOR]

Abstract: The fabrication of carbon nanocapsules and carbon nanotubes (CNTs) using an acetylene flame method was investigated. Carbon nanocapsules, a graphitic structure of nanoparticles with a hollow core, were synthesized using catalyst-free acetylene flames while CNTs were formed with the presence of cobalt-based catalysts in addition to acetylene flames. When the synthesis of these materials was carried out, the results showed that a massive amount of high-purity carbon nanocapsules with a particle size in the range of 15–30nm can be produced with the acetylene flame method. The CNTs produced were multi-walled carbon nanotubes measuring a few micrometers in length and 20–30nm in diameter. The acetylene flame method holds great potential for the cost-effective production of CNTs as well as carbon nanocapsules. [Copyright &y& Elsevier]

Lithium-oxygen batteries (LOBs) promise high energy density but suffer from catalyst-related issues. We've developed FeNi-NCNT/DrGO, a novel catalyst, by integrating iron-nickel nanoalloys (FeNi) embedded in nitrogen-doped carbon nanotubes (NCNTs) grafted onto defect-rich reduced graphene oxide (DrGO). The fabrication involved freeze-drying, defect engineering, and thermal treatments. The FeNi nanoalloy within the catalyst demonstrates outstanding bifunctional activity, while the NCNTs serve as an excellent electronic conduction medium and DrGO enables favorable ion transport. The 3D open-space architecture of this catalyst provides a rapid diffusion path for the electrolyte and room for accommodating discharge products. As a result, the LOBs with FeNi-NCNT/DrGO exhibits exceptional electrochemical performance, achieving a deep discharge capacity of 21,153.6 mAh g−1 and a high round-trip efficiency of 98.7% at 200 mA g−1. Moreover, it demonstrates excellent cycling stability, exceeding 100 cycles at 200 mA g−1 with a cut-off capacity of 500 mAh g−1. [Display omitted] • FeNi-NCNT/DrGO was formed by freeze-drying, ball milling, and thermal treatment. • The catalyst shows superior ORR, OER, conductivity, ion diffusion and Li 2 O 2 storage. • LOB with the catalyst shows a capacity of 21153 mAhg−1 and 98.74% efficiency. • LOB exceeds 100 cycles at 200 mA g−1 with a cut-off capacity of 500 mAh g−1. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable Zn-ion batteries (ARZIB) are promising candidates for next-generation batteries because of their high safety, low cost, and relatively high capacity. In this study, we developed hydrated and potassium-doped manganese dioxide (MO) nanowires mixed with carbon nanotubes (CNT) on a graphene substrate (hydrated KMO-CNT/graphene) for ARZIB. A simple polyol process using poly(ethyl glycol), KMnO 4 , CNT, and graphene was utilized to fabricate hydrated KMO-CNT/graphene. MnO 2 nanowires with diameters of 15–25 nm possess a high specific capacity with a short diffusion path. The intercalated K ions and hydrates in the layered MnO 2 nanowires maintained the MO structure during the charge and discharge processes, whereas carbon nanomaterials (CNT and graphene) enhanced the conductivity of the material. Consequently, hydrated KMO-CNT/graphene demonstrated good ARZIB performance. A high capacity of 359.8 mAh g–1 at 0.1 A g–1, and at a high current density of 3.0 A g–1, a capacity of 129 mAh g–1 with 77% retention after 1000 cycles, were achieved. • Hydrated and potassium-doped MnO 2 mixed with CNT on graphene substrate is synthesized. • Polyol process was conducted with PEG, KMnO 4 , CNT and graphene. • MnO 2 has a high capacity, intercalated K and H 2 O keep the structure of MnO 2 and CNT/graphene provide conductivity. • The hydrated KMO-CNT/graphene delivers high specific capacities of 359.8 mAh g–1 at 0.1 A g–1 and 129 mAh g–1 at 3.0 A g–1 with 77% retention. • The performance of ZIB reaches a high energy density of 410.36 Wh kg–1 at 109.93 W kg–1. [ABSTRACT FROM AUTHOR]

Abstract: Multiwalled carbon nanotubes (MWNTs) were synthesized using a chemical vapor deposition floating feed method in a vertical reactor. Effects of the preparation variables on the average diameter of carbon nanotubes were systematically examined using the fractional factorial design (FFD), path of the steepest ascent, and central composite design (CCD) coupled with the response surface methodology. From the FFD study, the main and interactive effects of reaction temperature, methane flow rate, and chamber pressure were concluded to be the key factors influencing the diameter of MWNTs. Two empirical models, representing the dependence of the diameter of carbon nanotubes at the vicinities around maximum (420nm) and minimum (15nm) on the reaction temperature and methane flow rate, were constructed in two independent CCD studies. These models, shown as contour diagrams, indicated that the diameter of carbon nanotubes generally increased with increasing reaction temperature and methane flow rate. Based on both models, the diameter of MWNTs from 15 to 420nm can be controlled precisely by using a continuous CVD fabrication method. [Copyright &y& Elsevier]

The aim of this study is to investigate the possibility of using a polymer material, polyvinyl alcohol (PVA), as an additional carbon source to fabricate carbon nanotubes using arc-discharge method. Experiments were carried out using a graphite anode filled with a mixture of PVA and iron group catalysts. The results indicated that PVA material not only can be used for the formation of carbon nanotubes but also for the formation of some novel carbonaceous structures such as spherical nanoparticles, beaded and sheet-like carbon nanostructures. Furthermore, we found that the catalyst content in the PVA filling mixture should be lower than 50 wt%. In addition, novel catalyst precursors, such as Fe2(SO4)3 · nH2O or Fe(NO3)3 · 9H2O, were employed to grow carbon nanotubes. The results showed that these catalyst precursors can be used to form carbon nanotubes if their filling content does not exceed 50 wt%. [Copyright &y& Elsevier]