Carbon nanotubes (CNTs) offer unique properties that have the potential to address multiple issues in industry and material sciences. Although many synthesis methods have been developed, it remains difficult to control CNT characteristics. Here, with the goal of achieving such control, we report a bottom-up process for CNT synthesis in which monolayers of premade aluminum oxide (Al2O3) and iron oxide (Fe3O4) nanoparticles were anchored on a flat silicon oxide (SiO2) substrate. The nanoparticle dispersion and monolayer assembly of the oleic-acid-stabilized Al2O3 nanoparticles were achieved using 11-phosphonoundecanoic acid as a bifunctional linker, with the phosphonate group binding to the SiO2 substrate and the terminal carboxylate group binding to the nanoparticles. Subsequently, an Fe3O4 monolayer was formed over the Al2O3 layer using the same approach. The assembled Al2O3 and Fe3O4 nanoparticle monolayers acted as a catalyst support and catalyst, respectively, for the growth of vertically aligned CNTs. The CNTs were successfully synthesized using a conventional atmospheric pressure-chemical vapor deposition method with acetylene as the carbon precursor. Thus, these nanoparticle films provide a facile and inexpensive approach for producing homogenous CNTs.

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Published in C, v. 7, issue 4, 79.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

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This research was funded by NSF, grant number 2016484 under NSF PFI-RP.

Partial salary support for A.U. was provided by an internal seed grant from the University of Kentucky (UK) Energy Research Priority Area program. XPS data were collected at the UK electron microscopy center (EMC), which belongs to the National Science Foundation NNCI Kentucky Multiscale Manufacturing and Nano Integration Node, supported by ECCS-1542174.

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The following are available online at https://www.mdpi.com/article/10.3390/c7040079/s1, Table S1: Current methods of premade catalyst nanoparticles assembly used for CNTs growth; Figure S1: SEM images of spherical shaped aluminum oxide/hydroxide NPs. (A) Large size of aluminum oxide/hydroxide nanoparticles separated by centrifuge technique with 12,000 rpm, (B) Small size of nanoparticles remained in decanted solution. A few drops of nanoparticle solution was drop cast onto a silicon wafer and annealed at 400 °C for an hour before characterization; Figure S2: FTIR spectra of (A) pure oleic acid, (B) aluminum oleate, (C) aluminum oxide nanoparticles without annealing, and (D) aluminum oxide nanoparticles annealed at 700 °C; Figure S3: XPS spectra of aluminum oxide nanoparticles after annealing at 700 °C for 2 h. (A) Survey spectra that represent all the core level peaks, (B) Al 2p, and (C) O 1s; Figure S4: FTIR spectra of (A) pure oleic acid, (B) iron oleate, and (C) oleic acid coated iron oxide nanoparticles; Figure S5: XPS survey spectra of blank silicon oxide substrate that show all the core level peaks; Figure S6: XPS survey spectra of 11-phosphonoundecanoic acid (PNDA) film on silicon substrate showing all core level peaks; Figure S7: XPS spectra of PNDA attached silicon oxide substrate. (A) core level Si 2p peak, (B) core level P 2p peak, (C) core level O 1s peak, and (D) core level C 1s peak; Figure S8: XPS survey spectra of 11-phosphonoundecanoic acid film on alumina monolayer showing all core level peaks; Figure S9: XPS spectra of PNDA attached aluminum oxide substrate. (A) core level Al 2p peak, (B) core level P 2p peak, (C) core level O 1s peak, and (D) core level C 1s peak.

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