Size-Selective Synthesis of Cubooctahedral Palladium Particles Mediated by Metallomicelles

Abstract

The reduction of [PdCl4]2- by hydrazine in the postmicellar region of even-numbered alkyltrimethylammonium bromides C n TABr (with n = 8 to 16) yielded fairly monodisperse Pd particles with mean diameters in the range 1.6−6.8 nm. Transmission electron microscopy (TEM) measurements indicated that the particle size decreases with increasing length of the alkyl chain, decreasing precursor concentration, and decreasing surfactant concentration. Kinetic measurements demonstrated that the nucleation is a fast process and well separated from the growth. TEM and high-resolution TEM micrographs of the particles suggested that the dominant morphology is cubooctahedral. Composition analysis (1H NMR, total organic carbon, and inductively coupled plasma atomic emission spectroscopy), titration microcalorimetry, and spectroscopic methods (IR, Raman, and UV−vis) revealed that [PdCl4]2- is not the real precursor species in the reduction process. In the presence of a large excess of Br-, [PdCl4]2- transforms to [PdBr4]2-. The ligand-exchange reaction is accompanied by the formation of stoichiometric complex−surfactant aggregates [C n TA]2[PdBr4], and followed by a slow, higher-order aggregation to microcrystals. The organic salt precipitates below the critical micelle concentration but undergoes solubilization above it, leading to the formation of palladate−surfactant metallomicelles. In the postmicellar region, the close proximity of the surfactant molecules to the reduction centers ensures rapid adsorption of the amphiphiles on the surface of the nascent particles, and a protective bilayer is formed, ultimately leading to long-term stability of the Pd hydrosols.

Comparative study of size-quantized Pd-montmorillonite catalysts in liquid-phase semihydrogenations of alkynes

“…It may therefore be concluded that the amount of organic residues on the surface of the Pd particles was insignificant. The above synthesis method afforded organophilic Pd-M samples with the same Pd content, differing only in the mean crystallite diameter and the size distribution of the Pd particles [20,21]. The Pd contents of the samples Pd-M1, Pd-M2 and Pd-M3, which were subjected to further investigations, were 0.15 ± 0.01%, as confirmed by ICP-AES measurements (Jobin Yvon 24 spectrometer, λ = 229.7 and 324.3 nm).…”

A review of plasma–liquid interactions for nanomaterial synthesis

“…Thereby, the liquid chemistry such as pH value will be changed by the plasma irradiation, which can influence the rate and probability of chemical reactions in liquid, that we must pay attention if we want to elaborately control the synthesis. Interestingly, hydrazine (N2H4) has been observed after an exposure of N2 and CO2 [96] or Ar/ammonia [97] plasma on water, and Pd [98] Anodic dissolution has been used for electrochemical synthesis of Pd [100] and Ag [101] NPs, and gold nanorods [102], anodic dissolution can also take place in the PLIs since the plasma-liquid system is actually a modified electrochemical cell [15,103]. While just a few studies considered the effect of anodic dissolution in the NP synthesis from the PLIs [46,69].…”

Ethylenediamine tetramethylene phosphonic acid assisted synthesis of palladium nanocubes and their electrocatalysis of formic acid oxidation

“…Pd nanocrystals with diverse morphologies have been synthesized, including wires [13], spheres [14], tubes [15], cubes [16], plates [17], rods [18][19][20], tetrahexahedra [21], cubooctahedra [22], octahedra [23], tetrahedra [24], and concave tetrahedra [25]. Among various shapes, {100}-enclosed Pd nanocubes are of particular interest in relation to formic acid oxidation because the {100} facet of Pd shows the highest catalytic activity among the three lowindex facets (Pd{100} > Pd{111} > Pd{110}) [26].…”