Synthesis of Highly Uniform Nickel Multipods with Tunable Aspect Ratio by Microwave Power Control

Abstract

As the importance of anisotropic nanostructures and the role of surfaces continues to rise in applications including catalysis, magneto-optics, and electromagnetic interference shielding, there is a need for efficient and economical synthesis routes for such nanostructures. The article describes the application of cycled microwave power for the rapid synthesis of highly branched pure-phase face-centered cubic crystalline nickel multipod nanostructures with >99% multipod population. By controlling the power delivery to the reaction mixture through cycling, superior control is achieved over the growth kinetics of the metallic nanostructures, allowing formation of multipods consisting of arms with different aspect ratios. The multipod structures are formed under ambient conditions in a simple reaction system composed of nickel acetylacetonate (Ni(acac)), oleylamine (OAm), and oleic acid (OAc) in a matter of minutes by selective heating at the (111) overgrowth corners on Ni nanoseeds. The selective heating at the corners leads to accelerated autocatalytic growth along the ⟨111⟩ direction through a "lightning rod" effect. The length is proprtional to the length and number of microwave (MW)-on cycles, whereas the core size is controlled by continuous MW power delivery. The roles of heating mode (cycling versus variable power versus convective heating) during synthesis of the materials is explored, allowing a mechanism into how cycled microwave energy may allow fast multipod evolution to be proposed.

Oleic acid/oleylamine ligand pair: a versatile combination in the synthesis of colloidal nanoparticles

“…The authors studied the role of the heating mode, concluding that the particle length is proportional to the duration and number of microwave cycles, whereas the core size is controlled by the continuous MW power delivery. 291 Sun et al synthesized monodisperse Ni NPs via the reduction of Ni(acac) 2 with borane–tributylamine (BTB) complex in a mixture of OAm/OAc. The ligand pair also acted as the solvent medium, while OAc assisted especially the stabilization of the Ni NPs.…”

“…High aspect ratio multipod structures will form under cycled conditions, as depicted in (f). Reprinted with permission from ref 291…”

Sulfur-Mediated Synthesis of Spherical Nickel Nanoparticles in a Chemical Vapor Reactor

“…Therefore, we attempted to synthesize spherical particles by adding the nonpreferentialadsorption type of impurity to the surface of Ni, which could destabilize the nanocrystal facet and strategically tune the shape of the Ni-NPs. 21,22 It is necessary to manipulate selective impurities that can alter the adsorption properties such as the surface energy and surface anisotropy of Ni. We chose sulfur among the various elements that are adsorbed nonpreferentially on the Ni surface and cause a sintering delay effect that can eliminate the defects in MLCCs.…”

“…However, the process window is narrow, which inevitably acts as a constraint during the scale-up. Therefore, we attempted to synthesize spherical particles by adding the nonpreferential-adsorption type of impurity to the surface of Ni, which could destabilize the nanocrystal facet and strategically tune the shape of the Ni-NPs. , …”

Introducing Stacking Faults into Three-Dimensional Branched Nickel Nanoparticles for Improved Catalytic Activity

“…Successfully tuning the type and number of stacking faults was first achieved by inducing changes between cubic and hexagonal crystal phases in semiconductor systems, such as InAs, ZnSe, and ZnS nanowires. Because Ni is able to adopt both face-centered cubic ( fcc ) and hexagonal close packed ( hcp ) crystal structures, Ni nanoparticles can have stacking faults. − We recently demonstrated that 3D branched Ni nanoparticles made from a mixture of fcc and hcp Ni showed a high activity for the electrocatalytic oxidation of biomass due to high surface area and controlled surface facets . Controlling the amount of hcp – fcc transitions in these 3D branched Ni nanoparticles provides an opportunity to control stacking fault density in a catalytically active metal to enhance catalytic performance.…”