Abstract
A simple, inexpensive, and viable method for growing multiple heterostructured carbon nanotubes (CNTs) over the entire surface of Ni-Al bimetallic nanowires (NWs) in the gas phase was developed. Polymer-templated bimetallic nitrate NWs were produced by electrospinning in the first step, and subsequent calcination resulted in the formation of bimetallic oxide NWs by thermal decomposition. In the second step, free-floating bimetallic NWs were produced by spray pyrolysis in an environment containing hydrogen gas as a reducing gas. These NWs were continuously introduced into a thermal CVD reactor in order to grow CNTs in the gas phase. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectrometry analyses revealed that the catalytic Ni sites exposed in the non-catalytic Al matrix over the entire surface of the bimetallic NWs were seeded to radially grow highly graphitized CNTs, which resembled “foxtail” structures. The grown CNTs were found to have a relatively uniform diameter of approximately10±2 nm and 10 to 15 walls with a hollow core. The average length of the gas-phase-grown CNTs can be controlled between 100 and 1000 nm by adjusting the residence time of the free-floating bimetallic NWs in the thermal CVD reactor.
Highlights
Low-dimensional nanostructures such as nanoparticles, nanowires, and nanotubes have strong potential for use as building blocks in the assembly of various micro- or nanoscale functional devices [1, 2]
It is difficult to carry out the gas-phase synthesis and nanostructure control of heterostructured carbon nanotubes (CNTs)-metal composites for achieving continuous production of composites with relatively high purity, because the size and shape of the catalytic particles continuously change because of the competition between the coagulation and coalescence processes prior to or during the chemical vapor deposition- (CVD-) assisted growth of CNTs that is accompanied by relatively high temperature processes
The mean diameter (DNW) of electrospun bimetallic nitrate NWs with PVP templates was significantly decreased by calcination; in particular, DNW decreased from 305 ± 12 nm to 100 ± 14 nm
Summary
Low-dimensional nanostructures such as nanoparticles, nanowires, and nanotubes have strong potential for use as building blocks in the assembly of various micro- or nanoscale functional devices [1, 2]. Among the various low-dimensional functional materials, carbon nanotubes (CNTs) have drawn considerable attention from the viewpoint of design and controlled synthesis, since they offer the advantages of strong mechanical strength and high electrical/thermal conductivity. The assembly of functional CNTs on a substrate comprising complex metallic bulk-, micro-, or nanostructures can serve as a novel method for enhancing the mechanical, electrical, and thermal properties of CNT-based composite materials or devices [8–11]. There are various synthesis methods based on wet chemistry methods; these methods have been successfully developed for synthesizing complex heterostructured CNT-metal composites that have potential for applications in energy storage [12], catalysis [13], and sensors [14, 15]. It is difficult to carry out the gas-phase synthesis and nanostructure control of heterostructured CNT-metal composites for achieving continuous production of composites with relatively high purity, because the size and shape of the catalytic particles continuously change because of the competition between the coagulation and coalescence processes prior to or during the chemical vapor deposition- (CVD-) assisted growth of CNTs that is accompanied by relatively high temperature processes
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