Low-Temperature Single-Wall Carbon Nanotubes Synthesis: Feedstock Decomposition Limited Growth

Abstract

We report on the lowest temperature of SWCNT growth using endothermic decomposition of CH4 gas on a specially activated alumina-supported Fe:Mo catalyst. However, the observed lowest growth temperature (560 °C) is higher than that reported previously for exothermic feedstock type. Our observation indicates that the decomposition threshold temperature of the feedstock limits the SWCNT growth. This study also suggests that, by using more active carbon feedstock or somehow facilitating its decomposition, one could enable the synthesis of SWCNT at an even lower temperature.

Understanding the “Activation” of the Nanocluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y] for Low Temperature Growth of Carbon Nanotubes

“…Later, Edgar et al [18], Jeon et al [19], Goss et al [20], Peng et al [21], demonstrated CNT growth by employing growth temperatures in the range of 880-1010°C without the use of additional catalyst promoters. The excessive growth temperatures required with FeMoC appear to counter previous work with Fe-Mo catalyst systems demonstrating CNT growth at temperatures as low as 550°C [22][23][24]. It should be noted that both Fe and Mo have been shown to be efficient catalysts both independently and as mixed metal nanoparticles [25][26][27][28][29][30]; thus, FeMoC should be ''active'' for CNT growth, but under the prior growth conditions studied it is not [16][17][18][19][20][21].…”

Threshold Barrier of Carbon Nanotube Growth

“…A deep understanding of the process may lead to experimental design for controlled CNT synthesis. A repeatable cycle of transforming two C atoms from feedstock into one 6-membered-ring (6MR) on the growth front (or the open end) of a CNT, which is attached to a catalyst particle surface, can be divided into three sequential steps: (i) catalytic decomposition of feedstock molecules, (ii) diffusion of the released C atoms to a nearby site of the CNT open end, and (iii) the direct incorporation of the C atoms into the tube wall [1][2][3][4]. Among the three steps, which one is the threshold step in CNT growth has been argued for a long time.…”

Reduction Kinetics of the Nanocluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y]

“…FeMoC samples were prepared by evaporating 1 mL of a concentrated FeMoC-EtOH solution resulting in * 20 mg samples. The samples were then placed in alumina pans and heated with a linear ramp rate (5,10,15, and 20°C/min) under a carrier gas flow of 70 mL/min. In addition to the multiple non-isothermal experiments an isothermal experiment at 850°C was performed to validate the kinetic analysis.…”

“…6 The SEM images of FeMoC reduction in 5% H 2 at a 500, b 750, c 900, and d 1100°C, using a 20°C/min heating rate Fig. 7 The conversion, a, of the TGA data at different heating rates (5,10,15, and 20°C/min) derived from Eq. (2) underlying approximations used for temperature integral, p(x), in Eq.…”

“…Of particular interest, are Fe-Mo nanoalloys used for catalytic chemical vapor deposition of carbon nanotubes (CNTs). The Fe-Mo catalyst system has proven itself to be excellent for CNT growth with reports demonstrating; ultra-long aligned CNT growth ([ 18.5 cm) [13], large area and ultra-highdensity CNT growth (160 SWCNTs/lm 2 ) [14], and CNT growth under a wide range of temperatures (450-1000°C) [15][16][17]. Preparation of Fe-Mo nanoalloys has been demonstrated by several chemical and physical methods, including thermal decomposition [18], solution phase wet chemical reduction [19], electrochemical synthesis [20], microwave synthesis [21], sono-chemical synthesis [22], chemical vapor condensation [23], and high-energy ball milling [24].…”