A New Catalytically Active Colloidal Platinum Nanocatalyst:  The Multiarmed Nanostar Single Crystal

Abstract

Nanocatalysis has attracted great attention in the past two decades, both in heterogeneous solution-phase colloidal reactions [1][2][3] and in heterogeneous supported nanoparticle gas-phase reactions. 3,4 Our group published a Science report early on showing that platinum nanoparticles can be synthesized in a variety of shapes 5 (tetrahedral, cubic, and truncated octahedral). In that report, it was suggested that catalysis could be shape-dependent, and since that time the field has developed extremely rapidly. 6-9 Narayanan and El-Sayed 6 later showed that, indeed, the activation energy of the nanocatalyzed electron-transfer reaction between thiosulfate and hexacyanoferrate III is shape-dependent in colloidal nanocatalysis in which nanocatalysts that have more atoms on edges or corners (i.e., more valency unsaturated atoms) possess more catalytic activity. More recently, shape-dependence was also found to occur in heterogeneous gas-phase nanocatalysis. 7,8 Furthermore, we found that the catalytically active nanoparticles undergo shape changes to the less active nanospheres, causing them to lose some of their activity. [10][11][12] The possible mechanism for shape change and particle growth was recently discussed where the high-resolution TEM images were reported. 13 Previously, 14 tetrahedral platinum nanoparticles have been prepared by the hydrogen reduction technique, and different sizes were synthesized by changing the ratio of the preprepared platinum seed concentration to the Pt +2 concentration. Very recently in a Science report, 3 tetrahexahedral platinum nanocrystals with high index facets, i.e., rich in active valency unsaturated atoms, have been synthesized electrochemically. The authors showed that they are also catalytically very active. These particles were prepared and studied on the surface of an electrode and were not transferable to colloidal solutions.In the present work, tetrahedral platinum nanocrystals (TPNs) were used as seeds for the preparation of a new shape of a colloidal platinum nanostar, without the need for organic solvents, templates, ion replacements, or substrates. The TPNs used were themselves synthesized in large yields by a simple new technique. The lowand high-resolution TEM of the nanostar particles are determined, and the number of arms on each nanostar is found to vary from particle to particle, ranging from a few to over 30. More interesting is that even the largest nanostars are found to form single crystals. This strongly suggests a mechanism of formation involving seeded growth rather than an aggregation or an assembly process of the seed particles. The catalytic activity for these multiarmed nanostar platinum single crystals is examined for the reaction between hexacyanoferrate III (HCFIII) and thiosulfate and found to be higher than the platinum TPN, which are known to be the most active shape of this metal in colloidal solutions.To prepare the tetrahedral platinum nanocrystals (TPNs), 0.0667 g of PVP (MW 360 000) was dissolved in 33 mL of deionized water, 4 drops of...

Shape‐Controlled Synthesis of Pd Nanocrystals in Aqueous Solutions

“…This so-called seeded growth approach offers an alternative way for synthesizing uniform nanocrystals by taking advantage of the absence of homogenous nucleation during the growth step. Although seeded growth has been proven to be www.afm-journal.de extremely powerful in Au, Ag, and Pt systems, [66][67][68][69][70] little attention has been paid to the seeded growth of Pd nanocrystals. Here we demonstrate that Pd nanocrystals can be completely converted from cubes to truncated and regular octahedrons via seeded growth.…”

Tailored Nanoparticles for Clean Technology–Achieving Size and Shape Control

“…Changes in the morphology of tetrahedral and cubic particles have been explained by dissolution of reactive corner and edge atoms, and it is found that they correlate with changes in the observed activation energy over longer period of time. Synthesis of the branched 11.2 ± 2.7 nm ''multiarmed nanostar'' nanoparticles and their catalytic activity in a model electron transfer reaction between hexacyanoferrate(III) and thiosulfate were reported in the follow-up paper [243]. In this case, more than 90% of the catalyst contained branched particles with (Reprinted with permission from [242].…”

Noble Metal-Based Nanocomposites for Fuel Cells

“…Thus, numerous shape-controlled synthetic strategies are established in colloidal reaction system, such as facet-selective capping (CO [38,39], halide anions [40], amines [9], formaldehyde [30,41], etc. ), seed growth [42,43] and oxidative etching [44].…”