Synthesis of Nearly Uniform Single-Walled Carbon Nanotubes Using Identical Metal-Containing Molecular Nanoclusters as Catalysts

Abstract

Uniform and small-diameter single-walled carbon nanotubes (SWNTs) have been produced using identical molecular nanoclusters containing Fe and Mo atoms with a defined molecular formula and a specific structure as catalysts in a chemical vapor deposition method. The average diameter of the SWNTs produced in these experiments is 1.0 nm with a standard deviation for the diameter distribution of 17%. The diameters of SWNTs were obtained by atomic force microscopy and Raman spectroscopy.

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

“…We show that the mechanism for FeMoC ''activation'' is due to the sufficient reduction of the metal oxide components. Consideration of prior reports, including our own, of using FeMoC as a single source molecular procatalyst precursor [16][17][18][19][20][21] suggest that their partial failures to perform as expected were due to insufficient activation or partial sublimation of the metal oxide resulting in a smaller than necessary catalyst size [45]. These reports underline the importance of the catalyst pre-treatment step in ''activating'' FeMoC and related pro-catalyst for growth of CNTs.…”

“…8, and clearly show MWCNT growth at all growth Fig. 9 The approximate CVD heating profile and conditions employed by a An et al [16], b Anderson et al [17], c Edgar et al [18], d Peng et al [21], and e, f this work. The CVD temperature profile is depicted by the red line, and the CVD conditions for air (blue), H 2 gas (green), inert gas (orange), and carbon precursor (black) are also depicted (Color figure online) temperatures tested.…”

“…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].…”

“…In the work by An et al [16], Anderson et al [17], and Edgar et al [18], FeMoC is heat treated C 700°C before reduction of the pro-catalyst occurs by either hydrogen or the carbon precursor. Catalyst pre-treatment at 700°C is important to note given that the sublimation point of bulk MoO 3 is * 700°C [41].…”

“…The first report of a molecular precursor for the growth of CNTs was by Liu and co-workers [16] . However, despite being set-up as an ideal precursor, it was found necessary to add a catalyst promoter (an external source of metal) to FeMoC to enable growth of CNTs, and then at only elevated temperatures (900°C, see Table 1).…”