Synthesis of hcp-Co Nanodisks

Puntes, Víctor; Zanchet, Daniela; Erdonmez, Can K.; Alivisatos, A. Paul

doi:10.1021/ja027262g

Cited by 655 publications

(562 citation statements)

References 18 publications

Supporting

Mentioning

532

Contrasting

Unclassified

Order By: Relevance

“…to investigate size-and shape-dependent confinement effects. Spheres [5], cubes [6], rods [7], disks [8], wires [9] and other non-trivial shapes like tetrapods [10] or arrows [11] can be prepared from a wide variety of materials. Of these, nanorods of the direct band-gap II-VI semiconductor CdSe are especially interesting.…”

Section: Introductionmentioning

confidence: 99%

Optical phonons in colloidal CdSe nanorods

Lange

Mohr

Artemyev

et al. 2010

Physica Status Solidi (b)

View full text Add to dashboard Cite

Colloidal CdSe nanorods are nanoparticles synthesized in solution. The synthesis allows the growth of CdSe nanorods with well defined diameters and aspect ratios. They have many potential applications in the field of optoelectronics and biotechnology. The nanorods can be epitaxially covered with a graded CdS/ZnS shell of a few monolayers in thickness. The shell leads to an increased quantum efficiency and improved photostability of the nanorods. However, the lattice mismatch between the nanorod core material and the shell material introduces strain into the core lattice. In this work Raman spectroscopy, accompanied by ab-initio calculations, is used to determine the amount of this strain, the exciton-phonon coupling strength in the nanorods and to investigate confinement effects. The longitudinal optical phonons in a nanorod are confined to the nanorod volume. The confinement of a phonon wavefunction leads to a neutralization of the q = 0 rule and the phonon frequency is found to depend on the nanorod diameter. The coupling strength between longitudinal optical phonons and excitons is investigated. It also depends on the nanorod diameter. The total coupling strength is much lower than in bulk material due to a decrease of the influence of the Coulomb interaction in nanoparticles. However, the coupling strength is found to rise for decreasing diameters. This is due to the increasing contributions of higher frequency phonons for smaller nanoparticle sizes. A radial breathing mode with a diameter dependent frequency is deduced from ab-initio calculations and its existence in nanorods is verified experimentally. The diameter-dependence of the modes' frequency can be used to estimate the nanorod diameter from a Raman measurement. In core-shell structures, the coverage of a CdSe nanorod with a ZnS shell leads to a compressive strain of the CdSe core due to the smaller lattice parameter of ZnS compared to CdSe. Ab-initio calculations show that all bonds of the CdSe core are shortened. The bonds in the lateral direction are much more strongly compressed than the bonds parallel to the c-axis. The amount of strain is estimated from the Raman spectra. The compressive nature of the shell decreases for thicker nanorods. The exciton wave function changes with the modified boundary from air to ZnS. This is reflected in a altered exciton-phonon coupling strength and can be monitored in the Raman spectra. ZusammenfassungCdSe Nanorods sind Nanopartikel, die in einer kolloidalen Lösung synthetisiert werden. Für diese existieren viele mögliche Anwendungen im Bereich der Optoelektronik und der Biotechnologie. Der Durchmesser und die Länge der Nanorods lässt sich durch die Syntheseparameter festlegen. Die Nanorods können in eine epitaktische Hülle aus einem Halbleitermaterial mit einer größeren Bandlücke, ZnS, eingebettet werden. Diese Hülle verbessert die optischen Eigenschaften und ermöglicht eine weitere Funktionalisierung der Oberfläche. Der Unterschied der Gitterparameter zwischen ZnS und CdSe führt jedoch zu Verspannung...

show abstract

Section: Introductionmentioning

confidence: 99%

Optical phonons in colloidal CdSe nanorods

Lange

Mohr

Artemyev

et al. 2010

Physica Status Solidi (b)

View full text Add to dashboard Cite

show abstract

“…For example, silver nanocubes, 1 cobalt nanodiscs, 2,3 and iron nanorods 4 have been synthesized. It is believed that a surfactant or polymer plays an important role in the metallic nanoparticles synthesis and, particularly, in their shape control.…”

Section: Introductionmentioning

confidence: 99%

Controlled Crystalline Structure and Surface Stability of Cobalt Nanocrystals

et al. 2005

View full text Add to dashboard Cite

The synthesis of monodispersed 10 nm cobalt nanocrystals with controlled crystal morphology and investigation of the surface stability of these nanocrystals are described. Depending on the surfactants used, single crystalline or multiple grain nanocrystals can be reproducibly produced. The relative surface stability of these nanocrystals is analyzed using the temperature dependences of the dc magnetic susceptibility. The novel method, which allows sensitive monitoring of the surface stability, is based on the observation that, with particle oxidation, an anomalous peak appears at 8 K in zero-field-cooled magnetization measurements. It is found that the surfactant protective layer is more important for long-term stability at room temperature, while the hightemperature oxidation rate is controlled by the crystal morphology of the nanoparticles.

show abstract

“…15 After aging for a matter of minutes these were spherical structures, which grow from nanodisks formed in the initial fast nucleation stage of the reaction. 16 The role of the TOPO was believed to be in enabling size focusing by stabilizing the process of transferring Co monomers from one nanoparticle to another, 16 and it was reported that in the absence of TOPO when only oleic acid is used as a stabilizing agent, a wide size distribution results. 15 Here we exploit this approach for producing model Co nanoparticle catalysts and show that it is possible to control size effectively below 10 nm using temperature as the controlling variable and also excluding TOPO, which we identify as a serious catalytic poison for CO 2 hydrogenation.…”

mentioning

confidence: 99%

Size-Controlled Model Co Nanoparticle Catalysts for CO₂ Hydrogenation: Synthesis, Characterization, and Catalytic Reactions

et al. 2012

Self Cite

View full text Add to dashboard Cite

Model cobalt catalysts for CO 2 hydrogenation were prepared using colloidal chemistry. The turnover frequency at 6 bar and at 200−300°C increased with cobalt nanoparticle size from 3 to 10 nm. It was demonstrated that near monodisperse nanoparticles in the size range of 3−10 nm could be generated without using trioctylphosphine oxide, a capping ligand that we demonstrate results in phosphorus being present on the metal surface and poisoning catalyst activity in our application.KEYWORDS: Cobalt nanoparticles, CO 2 hydrogenation, heterogeneous catalysis, catalytic poisoning C obalt-catalyzed processes and specifically the conversion of synthesis gas to hydrocarbons using cobalt (Co), Fischer−Tropsch synthesis, although long established, 1 have recently become a topic of renewed interest. This results from increased demand and declining fossil fuel reserves making both gas-to-liquid and biomass-to-liquid attractive routes to transportation fuels. 2 Especially when derived from biomass, the synthesis gas typically contains a significant fraction of CO 2 , however studies on CO 2 hydrogenation and its catalytic mechanism on Co are much less well developed than the analogous reaction with CO. 3,4 Because of its environmental impact through the greenhouse effect, fixation of CO 2 by reaction (rather than simply capture and storage) also makes studying the possibility of Co-catalyzed CO 2 hydrogenation a topic of considerable interest. 4 Additionally, there is an important technical precedent in terms of producing desirable oxygenated products by incorporation of CO 2 in such reactions (important in producing synthetic fuels). In the case of classical Cu/ZnO catalyzed methanol production, Chinchen et al. demonstrated using isotopic labeling studies that it is CO 2 , rather than CO, that is incorporated in the methanol produced. 5 Few kinetic studies of the chemistry of Co-catalyzed CO 2 hydrogenation exist. In our laboratory the conversion of CO 2 to CH 4 was explored at atmospheric pressure in a batch reactor over high-purity Co foil, 6 subsequently Welder and co-workers also studied the hydrogenation of CO 2 over Co foils in a flow reactor. 7,8 Wetherbee and Bartholomew however have reported on the use of a Co/SiO 2 catalyst prepared by incipient wetness impregnation to obtain various kinetic parameters, 9 although this does not contain information at the atomic scale about the nature of the Co catalyst particles, and it is this problem that we now address.In our laboratory size-and morphology-controlled nanoparticles, which are synthesized using colloidal techniques, have allowed the production of model catalysts via deposition within mesoporous silica supports. This is important because selectivity in multipath reactions has been found to vary with catalyst particle size and shape. In combination with powerful characterization techniques that provide atomic-and molecularlevel information, these model nanoparticle catalysts have been employed in studying fundamental mechanistic questions in many key chemica...

show abstract

Synthesis of hcp-Co Nanodisks

Cited by 655 publications

References 18 publications

Optical phonons in colloidal CdSe nanorods

Optical phonons in colloidal CdSe nanorods

Controlled Crystalline Structure and Surface Stability of Cobalt Nanocrystals

Size-Controlled Model Co Nanoparticle Catalysts for CO₂ Hydrogenation: Synthesis, Characterization, and Catalytic Reactions

Contact Info

Product

Resources

About

Synthesis of hcp-Co Nanodisks

Cited by 655 publications

References 18 publications

Optical phonons in colloidal CdSe nanorods

Optical phonons in colloidal CdSe nanorods

Controlled Crystalline Structure and Surface Stability of Cobalt Nanocrystals

Size-Controlled Model Co Nanoparticle Catalysts for CO2 Hydrogenation: Synthesis, Characterization, and Catalytic Reactions

Contact Info

Product

Resources

About

Size-Controlled Model Co Nanoparticle Catalysts for CO₂ Hydrogenation: Synthesis, Characterization, and Catalytic Reactions