Quantitative Analysis of the Multiple Roles Played by Halide Ions in Controlling the Growth Patterns of Palladium Nanocrystals

Abstract

Despite the pivotal roles played by halide ions (e. g., Cl− and Br−) in directing the evolution of seeds into metal nanocrystals with diverse shapes, it is still unclear how halides affect the reduction kinetics of a salt precursor and thus the outcome of a synthesis. Here we report a quantitative analysis of the multiple roles played by halides in controlling the growth behaviors of Pd seeds with cubic and octahedral shapes, respectively. Our quantitative measurements clearly indicate the existence of a transition point around 10−3 mM min−1 for the reduction rate, which separates the reduction into two distinctive pathways (solution versus surface) for the formation of completely different products. More significantly, we demonstrate that the speciation, reduction kinetics, and reduction pathway of a Pd(II) precursor can all be manipulated by varying the type and/or amount of halides introduced into a synthesis for the deterministic formation of a specific product. This work represents a critical step forward in achieving a quantitative understanding of the multiple roles of halides involved in the shape‐controlled synthesis of Pd nanocrystals, with the knowledge potentially extendible to other noble metals and their alloys.

One‐Step Preparation of Biocompatible Gold Nanoplates with Controlled Thickness and Adjustable Optical Properties for Plasmon‐Based Applications

“…In the second regime when the FeBr 3 concentration is increased from 1.42 to 3.78 mm, AR increases sharply from 26.5 to well over 100 and shows a much larger CV of edge length (≈29%). The introduction of increasing levels of bromide ions can considerably slow down the reduction process generating Au atoms (reduction potential: AuBr 4 − /Au 0 : +0.854 V, NHE; AuCl 4 − /Au 0 : +1.002 V, [48] NHE; NHE, normal hydrogen electrode), inducing an autocatalytic surface reduction, [49] which may contribute to the drastic increase of AR and CV of edge length in this regime.…”

Synthesis of Citrate-Coated Penta-twinned Palladium Nanorods and Ultrathin Nanowires with a Tunable Aspect Ratio

“…Indeed, it has been proven in the literature that the specific surface atomic structure of the seeds controls the final shape of nanomaterials. 21 …”

“… 1 − 14 For palladium (Pd) nanocrystals, the shape and size play a key role as they regulate their catalytic and enzymatic activity 10 , 15 − 18 as the surface structure greatly influences the catalytic properties. 19 − 21 …”

“…These features greatly enhance the performance of nanorods and nanowires in catalysis and electrocatalysis by strongly reducing Ostwald ripening, sintering, and detachment from the support and providing improved resistance against dissolution. 21 …”

“… 1 , 28 For these methods, it has been clearly established that oxidative etching provoked by the coupling of O 2 and halides and the seed morphology are two crucial parameters to be strictly controlled to favor anisotropic growth. 21 In a colloidal solution of Pd particles, halides (Br – , I – , and Cl – ) can chemisorb on the Pd surfaces. The chemisorption efficiency of halides on the Pd surface decreases in the order I – > Br – > Cl – .…”