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Understanding the expansion modes of single-walled carbon nanotubes on catalysts


Understanding the growth modes of single-walled carbon nanotubes on catalysts
Aberration-corrected ETEM characterization of SWCNTs grown from an intermetallic Co7W6 catalyst. (A and B) Time-sequential ETEM pictures of SWCNT cap nucleated from stable intermetallic Co7W6 catalysts at 1000°C below CH4 (50 Pa). Inset: The FFT of the seeded Co7W6 catalyst alongside the [1 1¯ 0] course. (C) Scheme displaying an SWCNT cap nucleating from the atomic fringe of Co7W6 (001). The Co7W6 nanocrystal is alongside the [1 1¯ 0] course. (D and E) Different cap and SWCNT grown on the floor of Co7W6 catalysts captured by ETEM. FFT patterns of SWCNT and Co7W6 catalyst derived from TEM picture (E). Simulated (16,0) SWCNT and Co7W6 [ 1¯5¯ 1] had been additionally proven (E). Credit score: Science Advances (2022). DOI: 10.1126/sciadv.abq0794

Insights into the catalyst structure-function relationship of single-walled carbon nanotubes (SWCNTs) can present an outlook to their development mechanisms. In a brand new report now printed in Science Advances, Feng Yang and a analysis staff in molecular science, chemistry, supplies genome engineering and physics in China used an in-situ aberration-corrected environmental transmission electron microscope (ETEM) to disclose the results of the state and construction of catalysts.

The staff linked the completely different development modes to the distinct chiral selectivity of single-walled carbon nanotubes grown on non-metallic and intermetallic catalysts. The outcomes can present perception to design catalysts for chirality-regulated development of single-walled carbon nanotubes.

Heterogenous catalysis

The function of catalyst construction and efficiency is significant for heterogeneous catalysis. As an illustration, the lively websites of nanocatalysts are regarded as precursors resulting in the excessive selectivity of small molecules. The chiral construction of bigger single-walled carbon nanotube molecules is extra complicated and require two chiral indices for his or her identification.

Pure single-walled carbon nanotubes have distinctive properties and great software potential throughout next-generation electronics and biosensing purposes. To be able to rationally design artificial processes of chirality-specific single wall carbon nanotubes, it is important to know how such buildings grew from a catalyst nanoparticle.

Relying on the properties of catalysts and the circumstances of chemical vapor deposition concerned, single walled carbon nanotubes can both bear a vapor-liquid-solid (VLS) or vapor-solid-solid (VSS) course of. The VLS course of can catalyze the decomposition of carbon precursors, resulting in the dissolution of molten catalysts, nucleation and additional development of single-walled carbon nanotubes. The VSS course of is comparable, though the catalyst stays stable, whereas carbon diffusion is prone to be completely different.

The function of catalysts could be evaluated to find out the construction of single-walled carbon nanotubes, and it is a vital matter in analysis. Researchers had beforehand used environmental transmission electron microscopy (ETEM) as an efficient instrument to immediately visualize catalysts and nanotube development.

Understanding the growth modes of single-walled carbon nanotubes on catalysts
Ex situ TEM characterization of SWCNTs grown from catalysts. (A to C) Ex situ TEM pictures of SWCNTs grown with Co7W6 (A), Co (B), and Cu (C) catalysts. (D) The statistic ex situ TEM measurements of SWCNT diameter as a operate of catalyst dimension. A complete of 48 and 18 SWCNTs had been noticed from Co7W6 and monometallic (Cu and Co) catalysts, respectively. The carbon feeding circumstances for Co7W6 catalysts marked with (i) to (iv) are Ar–ethanol/H2 50:30 (i), 200:50 (ii), 200:150 (iii), and CH4/H2 200:20 (iv) cm3 min−1. Error bars come up from the uncertainty (5%) of the TEM measurements. Credit score: Science Advances (2022). DOI: 10.1126/sciadv.abq0794

On this work, Yang et al introduced a complete evaluation of the expansion of single walled carbon nanotubes on intermetallic and monometallic catalysts to research the tube-catalyst dimension correlation. They used an ETEM to detect nucleation and studied the expansion of nanotubes on catalyst nanoparticles to know the state and construction of catalysts and the expansion mode of single-walled carbon nanotubes in intermetallic buildings.

ETEM investigations of SWCNTs grown from intermetallic catalysts

To arrange the intermetallic tungsten cobalt (W-Co) catalyst, Yang et al used W-Co polyacid cluster precursors. The staff studied the expansion of single-walled carbon nanotubes on the intermetallic catalysts at 1,000 levels C with a picture decision on the angstrom degree. The metallic nanocrystals maintained a secure construction throughout the nucleation of the single-walled carbon nanotube cap.

Understanding the growth modes of single-walled carbon nanotubes on catalysts
Aberration-corrected ETEM characterization of SWCNTs grown from stable and molten Co catalysts. (A to D) Aberration-corrected ETEM pictures of SWCNT and cap nucleated from stable (A to C) and molten (D) Co catalysts at 600°C. (E) Statistic ETEM measurements of tube diameter as a operate of catalyst dimension. A complete of 30 interfaces had been noticed at 600°C. Error bars come up from the uncertainty (5%) of the TEM measurements. (F) Schemes displaying two development modes of SWCNTs from stable and molten catalysts. Credit score: Science Advances (2022). DOI: 10.1126/sciadv.abq0794

The outcomes confirmed how the vapor-solid-solid (VSS) course of led to carbon atom migration to the floor of the stable nanocrystal catalyst to nucleate, resulting in the expansion of a nanotube. This course of is completely different from the vapor-liquid-solid (VLS) course of, which facilitates carbon dissolution into the catalyst. The nanoparticles exhibited numerous catalyst morphology.

The staff credited the outcomes to the much less environment friendly carbon feeding mechanisms through the VSS course of than by means of the VLS course of, which led to bigger catalyst particles to facilitate the expansion of single-walled carbon nanotubes.

Understanding the growth modes of single-walled carbon nanotubes on catalysts
Statistical evaluation of SWCNTs and caps nucleating from completely different planes of Co and Co7W6 catalysts from TEM. (A) Distribution of 21 SWCNTs/caps nucleating from completely different Co crystal planes and 12 (12,6) SWCNTs nucleating from the (0 0 12) airplane of Co7W6. The corresponding atomic crystal planes of fcc and hcp Co are additionally proven. (B) Correlation between lively Co aspects and diameter of SWCNTs/caps. Credit score: Science Advances (2022). DOI: 10.1126/sciadv.abq0794

Extra characterizations of the SWCNTs

The scientists performed chemical vapor deposition-based development of single-walled carbon nanotubes in transmission electron microscopy (TEM) grids of skinny movies to carry out TEM evaluation. They measured the diameters of the carbon nanotubes and the scale of the catalyst nanoparticles hooked up on the tubes. They additional analyzed the nucleation of single-walled carbon nanotubes from cobalt catalysts in environmental transmission electron microscopy at 600 levels Celsius. The cobalt nanoparticles maintained a crystallized-solid state.

The in-situ observations of cobalt catalysts had been according to the TEM outcomes, the outcomes demonstrated the varied development modes of VLS and VSS mechanisms. Yang et al additional analyzed the chiral selectivity of single-walled carbon nanotubes and the impact of carbon feeding circumstances on chiral selectivity below these two development modes.

Understanding the growth modes of single-walled carbon nanotubes on catalysts
Chiral angle distribution of SWCNTs grown on completely different catalysts. (A to C) Raman spectra of SWCNTs grown from Co7W6 catalysts at 1050°C. Excitation wavelength: 532 nm. (D to L) Chiral angle distributions of SWCNTs grown from Co7W6 (D to F), Co (G to I), Fe (J), Ni (Okay), and Cu (L) catalysts at 1050°C. The carbon feeding circumstances are indicated in every panel: Ar by means of the ethanol bubbler is 200, 100, and 50 cm3 min−1; the H2 feeding fee is mounted at 40 cm3 min−1. Credit score: Science Advances (2022). DOI: 10.1126/sciadv.abq0794

Outlook

On this approach, based mostly on a collection of experimental characterizations, Feng Yang and colleagues confirmed how single-walled carbon nanotubes grew from molten catalysts. Through the examine outcomes, the diameters of the ensuing nanotubes trusted the scale of the corresponding catalyst nanoparticles.

The work highlights a collaborative impact of catalysts and kinetics to offer rise to the selective development of single-walled carbon nanotubes (SWCNTs). The staff envision structure-regulated development of SWCNTs sooner or later, by rigorously assessing the interfacial construction between the catalyst nanocrystal and the nucleated nanotube for improved kinetic development.

Extra info:
Feng Yang et al, Development modes of single-walled carbon nanotubes on catalysts, Science Advances (2022). DOI: 10.1126/sciadv.abq0794

Feng Yang et al, Chirality-specific development of single-walled carbon nanotubes on stable alloy catalysts, Nature (2014). DOI: 10.1038/nature13434

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