Splitting and Flattening of Helical Carbon Nanofibers by Acid Treatment

Abstract

Helical carbon nanofibers (HCNFs), such as the carbon nanocoil (CNC) and the carbon nanotwist (CNTw), were synthesized by catalytic chemical vapor deposition using a substrate. HCNFs are classified into round and angular types according to the fiber cross-sections. When four types of HCNFs (round-type CNC and CNTw, angular-type CNC and CNTw) were acidified in a 30% hydrogen peroxide solution, only the angular type CNC was found to show a drastic shape change. The shape change observed was a splitting followed by a flattening of the angular type CNCs. The CNC was split into two or three thinner flat fibers. As a function of the treatment temperature, the weight of the CNCs decreased above 80 degrees C and the CNCs were etched effectively at 140 degrees C. The longer the reaction time the lower the weight of the CNCs, and the weight loss reached a saturation point when the reaction time was greater than 45 min at 140 degrees C. The splitting and flattening of the CNC occurred during the weight loss process. To analyze the CNC structure, electron tomography of the as-grown and acid-treated CNCs was obtained using a computerized tomograph system with transmission electron microscopy (TEM). The 3D-images were constructed using the TEM images collected at different tilt angles. The 3D image reconstructions showed that the CNCs had a tubular structure and were composed of several helical fibers which act as frames.

Synthesis of Nitrogen-Doped Carbon Nanocoils with Adjustable Morphology Using Ni—Fe Layered Double Hydroxides as Catalyst Precursors

“…It is well known that the catalyst composition plays a critical role in determining CNC morphology [19,20,22,23].…”

Syntheses and Electronic Applications of Helical Carbon Nanofibers

“…The weight loss and shape change of CNCs by acid treatment for 1 h were evaluated. (Yokota et al, 2010) The weight decreased as the temperature was increased. Furthermore, the weight decreased dramatically at 80-120ºC.…”

“…Syntheses and Electronic Applications of Helical Carbon Nanofibres 41 alloys (Fe-Cr-Mn-Mo, Fe-Cr-Ni-Mo (SUS513), Fe-Ni-Cr-Mo-Mn-Sn) (Yang et al, 2004), (Yang et al, 2005), Ni/SnO 2 (Hosokawa et al, 2007), Ni/Sn (Yokota et al, 2010), Cu-(Ni, Cr, Ti or Zn) (Takikawa et al, 2000), and Ni/Cu . According to our experimental results, it is possible to grow CNC and CNTw selectively by the combination of binary catalyst; CNC is synthesized by Fe-based catalyst, and CNTw synthesized by Ni-based catalyst.…”

High-Yield Synthesis of Helical Carbon Nanofibers Using Iron Oxide Fine Powder as a Catalyst

“…The low CNC purity is ascribed to the thickness of the carbon layer. Yokota et al [45] reported that the thickness of the carbon layer depends on the thickness of the catalyst film on the substrate.…”

“…We used a drop-coating method to deposit catalyst films on substrates, as reported in our previous study [44,45]. Although this method is convenient, the catalyst films tended to be thick under our experimental conditions.…”