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Title: Oxygen-promoted catalyst sintering influences number density, alignment, and wall number of vertically aligned carbon nanotubes

A lack of synthetic control and reproducibility during vertically aligned carbon nanotube (CNT) synthesis has stifled many promising applications of organic nanomaterials. Oxygen-containing species are particularly precarious in that they have both beneficial and deleterious effects and are notoriously difficult to control. In this paper, we demonstrated diatomic oxygen's ability, independent of water, to tune oxide-supported catalyst thin film dewetting and influence nanoscale (diameter and wall number) and macro-scale (alignment and density) properties for as-grown vertically aligned CNTs. In particular, single- or few-walled CNT forests were achieved at very low oxygen loading, with single-to-multi-walled CNT diameters ranging from 4.8 ± 1.3 nm to 6.4 ± 1.1 nm over 0–800 ppm O 2, and an expected variation in alignment, where both were related to the annealed catalyst morphology. Morphological differences were not the result of subsurface diffusion, but instead occurred via Ostwald ripening under several hundred ppm O 2, and this effect was mitigated by high H 2 concentrations and not due to water vapor (as confirmed in O 2-free water addition experiments), supporting the importance of O 2 specifically. Further characterization of the interface between the Fe catalyst and Al 2O 3 support revealed that either oxygen-deficit metal oxide ormore » oxygen-adsorption on metals could be functional mechanisms for the observed catalyst nanoparticle evolution. Finally, taken as a whole, our results suggest that the impacts of O 2 and H 2 on the catalyst evolution have been underappreciated and underleveraged in CNT synthesis, and these could present a route toward facile manipulation of CNT forest morphology through control of the reactive gaseous atmosphere alone.« less
Authors:
ORCiD logo [1] ;  [2] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ; ORCiD logo [6] ; ORCiD logo [3] ; ORCiD logo [1]
  1. Yale Univ., New Haven, CT (United States)
  2. Univ. of Michigan, Ann Arbor, MI (United States)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  4. Duke Univ., Durham, NC (United States)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  6. Johns Hopkins Univ., Baltimore, MD (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-711500
Journal ID: ISSN 2040-3364
Grant/Contract Number:
AC52-07NA27344; AC02-05CH11231; 1120187; 1552993
Type:
Accepted Manuscript
Journal Name:
Nanoscale
Additional Journal Information:
Journal Volume: 9; Journal Issue: 16; Journal ID: ISSN 2040-3364
Publisher:
Royal Society of Chemistry
Research Org:
Yale Univ., New Haven, CT (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY
OSTI Identifier:
1376047