Iodine Ions Mediated Formation of Monomorphic Single-Crystalline Platinum Nanoflowers

Abstract

Well-defined and strikingly monomorphic single-crystalline Pt nanoflowers were successfully synthesized through the addition of a large amount of iodine ions into polyol process (5 mM H 2 PtCl 6 , 30 mM KI, and 50 mM PVP in ethylene glycol solution at 160°C). The detailed structures of the Pt nanoflowers were studied with high-resolution TEM, indicating that high-quality production of the Pt nanoflowers could be obtained when the KI concentration was increased to six times of H 2 PtCl 6 . The size of Pt nanoflowers could be tuned by changing the concentration of H 2 PtCl 6 with the constant Pt/I ratio (1:6). The formation process of the nanoflowers was investigated by the UV−vis and EXAFS spectroscopic studies, demonstrating that the iodine ions played a key role in inducing the formation of the single-crystalline Pt nanoflowers. After the addition of iodine ions into the polyol synthesis, the Pt−I complex was formed and reduced by different kinetics compared with that of H 2 PtCl 6 to induce the overgrowth of Pt nanocrystals. Additionally, a small portion of iodine element was found to be strongly adsorbed on the surfaces of Pt nanoflowers, which probably also favored the anisotropic overgrowth of Pt nanocrystals resulting in the single-crystalline Pt nanoflowers. A comprehensive set of systematic studies on the synthesis factors (the concentrations of Pt precursor, iodine ions and PVP, reaction temperature, different kinds of Pt precursors and reaction atmosphere) was also reported.

Shape‐directed platinum nanoparticle synthesis: nanoscale design of novel catalysts

“…A high precursor‐to‐seed ratio leads to larger particles, as will be discussed with size control, but it can also change the morphologies of the final particles. Such a ratio results in overgrowth conditions where metal cations are reduced to zero‐valent metal atoms at the corners and edges of the nanocrystal, forming branched and dendritic structures . Growth occurs through a diffusion‐limited process where the platinum precursor surrounding the particle is depleted as the particle grows, resulting in a concentration gradient directly around the growing particle.…”

“…This process is still commonly used industrially due to its ease of scalability; however, the resulting nanoparticles suffer from a lack of size monodispersity since the method has limited parameters for directing shape . Electrochemical reduction is also common due to the exact control of the reduction potential and current waveform, both of which can direct shape and size, as well as the ease of deposition directly onto a support of choice . However, scalability via electrochemical reduction remains a challenge.…”

“…A general mechanism for the control of size and shape of the nanoparticles has not been established, but it is generally accepted that kinetics is the primary driving force. Control of reaction conditions causes a change in kinetics, thereby altering the rate of reduction or the growth along a specific facet . Controllable reaction conditions include the addition of organic or inorganic ligands which bind to the surfaces of the growing nanoparticles and direct the growth of specific shapes by altering nucleation or growth kinetics .…”

“…Although there is not as much control over the reduction potential as with electrochemical methods, varying temperatures, solvents and reducing agents can yield a large diversity of sizes and shapes. The primary advantage of this method is that there is a high degree of size monodispersity for the nanocrystals and many parameters, such as the addition of foreign ions, can be altered to control the size and shape of the particles …”

One-Pot Synthesis of Platinum Nanodendrites with Enhanced Catalytic Performance for Methanol Oxidation Reaction

“…22 Yin et al demonstrated that monomorphic single-crystalline Pt nano°owers could be synthesized by a facile iodine ion-mediated polyol process. 23 In this work, we developed a simple one-pot hydrothermal method to prepare well-dispersed 3D Pt nanodendritic structures. Fructose not only acts as a reducing agent, but also forms a hydrothermal carbon (HTC), which, as a capping agent, is absorbed on the surface of nanocrystals and induces the anisotropic growth of the Pt nanodendrites.…”