Role of Subsurface Diffusion and Ostwald Ripening in Catalyst Formation for Single-Walled Carbon Nanotube Forest Growth

Abstract

Here we show that essentially any Fe compounds spanning Fe salts, nanoparticles, and buckyferrocene could serve as catalysts for single-walled carbon nanotube (SWNT) forest growth when supported on AlO(x) and annealed in hydrogen. This observation was explained by subsurface diffusion of Fe atoms into the AlO(x) support induced by hydrogen annealing where most of the deposited Fe left the surface and the remaining Fe atoms reconfigured into small nanoparticles suitable for SWNT growth. Interestingly, the average diameters of the SWNTs grown from all iron compounds studied were nearly identical (2.8-3.1 nm). We interpret that the offsetting effects of Ostwald ripening and subsurface diffusion resulted in the ability to grow SWNT forests with similar average diameters regardless of the initial Fe catalyst.

Bio-Inspired Supramolecular Chemistry Provides Highly Concentrated Dispersions of Carbon Nanotubes in Polythiophene

“…We attribute this specific XRD signal to the d -spacing arising from interactions among various CNT–U molecules. The resulting estimated distance between CNT–U molecules of approximately 4.9 Å corresponds to the distance in a π -stack [29]. Thus, we suggest that this distance is the axial distance between U moieties π -stacking on CNT–U; it is consistent with highly regular and extensive U modification on the CNTs.…”

“…The directional orientation in the AFM image reveals that the orientation of the CNT–U units could be regulated by manipulating the tactility for a selected noncovalent interaction. The regular arrays of CNT–U indicates strong organizing behavior through π -stacking between the U moieties of the CNT–U [12,13,14,28,29,33]. These interactions are presumably the same reversible interactions inferred from the DSC traces and the well-oriented π -stacks inferred from the XRD analysis.…”

“…In Figure 7b it appears that PAT had wrapped and interacted with CNT–U through the H-bonding forces depicted in Figure 7c. This magnified SEM image, focusing on the framed area, reveals a few nanosized PAT bundles attached to the fractured surface (despite the bundle orientation, with respect to the image plane, not being known) [29,30]. Figure 7c depicts the π -stacking interactions between the surface of CNT–U and the thiophene rings of PAT; the U···A multiple hydrogen bond interaction enhanced the dispersion of CNT–U in the PAT solution.…”

Controlling the diameter of aligned single-walled carbon nanotubes on quartz via catalyst reduction time

“…This causes an increase of particle size and number. Diffusion of iron into amorphous SiO 2 and Al 2 O 3 as well as the re-emergence of iron particles out of Al 2 O 3 was reported previously [32,37,38]. Due to comparable ion radii and crystal lattice of both oxides the interstitial diffusion between Fe 2 O 3 and Al 2 O 3 or Fe 2 O 3 and α-quartz seems possible, while it is less favorable for the β-quartz phase.…”

Pressure-induced evaporation dynamics of gold nanoparticles on oxide substrate

“…Size of Au nanoparticles can be gradually varied from 290 nm to ∼10 nm. In each stage, Au nanoparticle arrays have nearly identical size, demonstrating no inhomogeneous mass exchange among particles, like Ostwald ripening or other effects [52,53]. This might be due to relatively large distance between particles in this study, and the effect of the interaction between neighboring diffusion fields would be an interesting issue by altering the initial distance between particles on the substrate.…”