Polyvinyl pirrolidone-mediated phase transitions in metastable nanocrystalline cobalt

Osorio-Cantillo, C.; Perales-Pérez, Óscar; Guinel, Maxime J.-F.

doi:10.1063/1.3562450

Cited by 3 publications

(5 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The XRD pattern of the initial cobalt NPs is well-matched with the ε-Co phase (Figure a, pink bars). ε-Co has a metastable complex cubic structure and is the common phase for nanocrystals of cobalt. ,− The cobalt oxide phase is not detected from XRD patterns even though the oxide shell is observed in TEM, which is consistent with previous reports. , After the sample is oxidized for 5 min, the XRD pattern exhibits broad peaks corresponding to the CoO phase (Figure a, blue bars, JCPDS 48-1719) and has suppressed contributions from ε-Co, indicating that the first phase during the oxidation process of cobalt is CoO. According to the phase diagram of the Co–O system, the stable phase is Co 3 O 4 at 200 °C in air for both bulk and nanomaterials, but Co should transform to CoO before Co 3 O 4 since the transformation to Co 3 O 4 is much slower than that to CoO .…”

Section: Resultssupporting

confidence: 87%

The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co₃O₄: The Diffusion Mechanisms and Atomic Structural Transformations

et al. 2013

View full text Add to dashboard Cite

We report on the atomic structural changes and diffusion processes during the chemical transformation of ε-Co nanoparticles (NPs) through oxidation in air into hollow CoO NPs and then Co 3 O 4 NPs. Through XAS, XRD, TEM, and DFT calculations, the mechanisms of the transformation from ε-Co to CoO to Co 3 O 4 are investigated. Our DFT calculations and experimental results suggest that a two-step diffusion process is responsible for the Kirkendall hollowing of ε-Co into CoO NPs. The first step is O in-diffusion by an indirect exchange mechanism through interstitial O and vacancies of type I Co sites of the ε-Co phase. This indirect exchange mechanism of O has a lower energy barrier than a vacancy-mediated diffusion of O through type I sites. When the CoO phase is established, the Co then diffuses outward faster than the O diffuses inward, resulting in a hollow NP. The lattice orientations during the transformation show preferential orderings after the single-crystalline ε-Co NPs are transformed to polycrystalline CoO and Co 3 O 4 NPs. Our Co 3 O 4 NPs possess a high ratio of {110} surface planes, which are known to have favorable catalytic activity. The Co 3 O 4 NPs can be redispersed in an organic solvent by adding surfactants, thus rendering a method to create solution-processable colloidal, monodisperse Co 3 O 4 NPs.

show abstract

Section: Resultssupporting

confidence: 87%

The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co₃O₄: The Diffusion Mechanisms and Atomic Structural Transformations

et al. 2013

View full text Add to dashboard Cite

show abstract

“…sequence along the [0002] orientation of the hcp cobalt phase under fast growth. 36 Both factors dominate the formation of rods with hybrid hcp and fcc phases.…”

Section: Formation Mechanism Of Cobalt Materialsmentioning

confidence: 99%

Synthesis of shape-controllable cobalt nanoparticles and their shape-dependent performance in glycerol hydrogenolysis

et al. 2015

View full text Add to dashboard Cite

Cobalt nanorods were synthesized in polyol with using Ir as the nucleation agent and sodium stearate as the surfactant. The aspect ratio of rods can be facilely mediated by Ir/Co molar ratios. During rod growth, the solid cobalt alkoxide and stearate intermediates formed at initial stages and acted as the reservoir to control Co 2+ reduction, followed by further mediating the rod growth. Stearate played the critical role in controlling the formation of rods by its selective and covalent coating on {10-10} planes, which induces the anisotropic growth through [0002] direction. The cobalt rods presented hcp phase in the center part and fcc phase in the conical tips because of growth rate difference in stages, showing the hybrid crystallographic property. The slow growth can also induce the formation of fcc spheres by altering the alkali amount in polyol. In glycerol hydrogenolysis, the hcp rods with the mainly exposed {10-10} planes revealed much higher activity and 1,3-propanediol selectivity than the fcc spheres, demonstrating the facet-dependent performance as solid catalyst. To our knowledge, this is the first example for producing 1,3-propanediol by using facet effect of cobalt nanomaterials. Nano-metal materials with different sizes and shapes showed recently the significant applications in catalysis, selective sensing and optical performance. [1][2][3][4] Among those, cobalt nanomaterials with well defined geometries gained considerable attention owing to its applications in high density data storage [5] , magnetic separation [6] and heterogeneous catalysis [7,8] . Generally, these cobalt nanomaterials possess different crystallographic planes and relatively discrete energy band, both of which show the distinct ability to absorb/activate reactant molecule and mediate their catalytic performance. On the other hand, the shape of cobalt nanomaterials presents orientation effect along exotic magnetic field, thus altering the magnetic properties. Comparing to the spherical nanoparticles, the one-dimensional cobalt nanowires showed the significantly enhanced magnetic performance with larger coercivity and higher blocking temperature. [9] Interestingly, the cobalt nanoparticles with larger sizes possessed higher activity and C 5+ hydrocarbons selectivity in Fischer-Tropsch Synthesis. [10] Moreover, due to the mainly exposed {100} planes of cobalt nanocubes, the activity was comparable to the spherical cobalt which is mainly exposed {111} planes, but the selectivity for C 10+ hydrocarbons was much higher than the latter one, demonstrating the facet-dependent catalytic performance. [11,12] Large numbers of strategies were employed to synthesize cobalt nanomaterials with well defined geometries. By using ordered mesoporous SiO 2 , ZrO 2 , carbon nanotube, polystyrene as the hard templates, [13][14][15][16] and polyvinylpyrrolidone (PVP), cetyl trimethylammonium bromide (CTAB), sodium dodecyl sulfonate (SDS) as the soft templates, [17][18][19] cobalt nanowires, nanocubes and hollow spheres can be synthesized. In the pre...

show abstract

“…25 Please do not adjust margins Please do not adjust margins The coercivity at 300 K (~ 60 Oe) is significantly less than would be expected for 30 nm metallic cobalt particles, which would be expected to have relatively high coercivity > 500 Oe. However the higher symmetry of the e-Co phase means that this phase is considered relatively soft 23,29 despite only a marginally lower magnetocrystalline anisotropy than the hcp cobalt phase. 29 In addition, the 30 nm particles are not single crystal but polycrystalline and hence consist of randomly orientated smaller crystallites.…”

Section: Resultsmentioning

confidence: 99%

“…We have explored methods based on changes to the heating regime and diffusion of reactants rather than altering the surfactant system. Our synthetic procedure is different to the other reported methods for producing cobalt nanoparticles of this size and shape, 16,22,23 in that only oleic acid and trioctylphosphine oxide are used as surfactants. The particle morphology is controlled by modification of the temperature, rate of agitation and surfactant concentration.…”

Section: Introductionmentioning

confidence: 94%

“…20,21 A number of larger cubic cobalt nanoparticles with sizes > 20 nm have been produced with the use of additional surfactants to the thermal decomposition. 16,22,23 Large cobalt particle systems have been developed for a number of magnetic applications including those based on exchange bias. Cobalt nanoparticles readily undergo surface oxidation on exposure to air.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A simple procedure for the production of large ferromagnetic cobalt nanoparticles

et al. 2016

View full text Add to dashboard Cite

Epsilon cobalt (ε-Co) nanoparticles in a number of octahedral morphologies have been synthesised. The particles are polycrystalline, with sizes in the order of 30 nm. Magnetic studies reveal the particles are ferromagnetic, with a room temperature saturation magnetisation of 131 emu g(-1). Unlike other large cubic ε-Co syntheses, we have not added an additional co-surfactant. Instead, we have modified the heating regime and reaction agitation. This alternative method highlights the complex chemistry associated with the formation of cobalt nanoparticles by thermal decomposition.

show abstract

Polyvinyl pirrolidone-mediated phase transitions in metastable nanocrystalline cobalt

Abstract: Articles you may be interested inFacile synthesis of single-phase spherical α″-Fe16N2/Al2O3 core-shell nanoparticles via a gas-phase method

Cited by 3 publications

References 16 publications

The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co₃O₄: The Diffusion Mechanisms and Atomic Structural Transformations

The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co₃O₄: The Diffusion Mechanisms and Atomic Structural Transformations

Synthesis of shape-controllable cobalt nanoparticles and their shape-dependent performance in glycerol hydrogenolysis

A simple procedure for the production of large ferromagnetic cobalt nanoparticles

Contact Info

Product

Resources

About

Polyvinyl pirrolidone-mediated phase transitions in metastable nanocrystalline cobalt

Abstract: Articles you may be interested inFacile synthesis of single-phase spherical α″-Fe16N2/Al2O3 core-shell nanoparticles via a gas-phase method

Cited by 3 publications

References 16 publications

The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co3O4: The Diffusion Mechanisms and Atomic Structural Transformations

The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co3O4: The Diffusion Mechanisms and Atomic Structural Transformations

Synthesis of shape-controllable cobalt nanoparticles and their shape-dependent performance in glycerol hydrogenolysis

A simple procedure for the production of large ferromagnetic cobalt nanoparticles

Contact Info

Product

Resources

About

The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co₃O₄: The Diffusion Mechanisms and Atomic Structural Transformations

The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co₃O₄: The Diffusion Mechanisms and Atomic Structural Transformations