Calixarene-mediated synthesis of cobalt nanoparticles: An accretion model for separate control over nucleation and growth

Zhenguo Chen, Jie Liu, Andrew J. Evans, Laura Alberch, Alexander Wei

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

The nucleation and growth of crystalline cobalt nanoparticles (Co NPs) under solvothermal conditions can be separated into distinct stages by using (i) polynuclear clusters with multivalent capping ligands to initiate nucleation, and (ii) thermolabile organometallic complexes with low autonucleation potential to promote crystalline growth. Both nucleation and growth take place within an amorphous accretion, formed in the presence of polyvalent surfactants. At the prenucleation stage, a calixarene complex with multiple Co2-alkyne ligands (Co16-calixarene 1) undergoes thermal decomposition above 130 C to form "capped cluster" intermediates that coalesce into well-defined Co nanoclusters, but are resistant to further aggregation. At the postnucleation stage, a monomer (pentyne-Co4(CO)10, or PTC) with a low thermal activation threshold but a high barrier to autonucleation is introduced, yielding ε-Co NPs with a linear relationship between particle volume and the Co mole ratio ([Cofinal]/[Co seed]). Co nanocrystals can be produced up to 40 nm with a 10-12% size dispersity within the accretion, but their growth rate depends on the activity of the supporting surfactant, with an octapropargyl calixarene derivative (OP-C11R) providing the most efficient transport of reactive Co species through the amorphous matrix. Postgrowth digestion with oleic acid releases the Co NPs from the residual accretion, which can then self-assemble by magnetic dipolar interactions into flux-closure rings when stabilized by calixarene-based surfactants. These studies demonstrate that organometallic complexes can be designed to establish rational control over the nucleation and growth of crystalline NPs within an intermediate accretion phase.

Original languageEnglish (US)
Pages (from-to)941-950
Number of pages10
JournalChemistry of Materials
Volume26
Issue number2
DOIs
Publication statusPublished - Jan 28 2014

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Keywords

  • cobalt
  • growth
  • magnetic properties
  • nucleation
  • organometallic

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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