Why Citrate Shapes Tetrahedral and Octahedral Colloidal Platinum Nanoparticles in Water

Abstract

The performance of many advanced catalytic systems depends not only on the size and composition but also on the specific shape of the metal nanoparticles (NPs) from which they are assembled. In turn, the shape of colloidal NPs depends on the specific capping agent involved in their synthesis, though the mechanism is still poorly understood. Here, supported by electrochemical experiments, FTIR spectra and DFT calculations, on well-defined surfaces, we show how a specific capping agent determines the shape of colloidal NPs.Solvated citrate can become simultaneously adsorbed on the Pt(111) surface through three dehydrogenated carboxylic groups, each one of them in bidentate configuration. On the other basal planes, citrate is adsorbed through only two of them. For this reason, under the synthesis conditions, citrate is more favorably adsorbed on the Pt(111) than on the other two basal planes of platinum. This adsorption behavior explains why colloidal platinum NPs of tetrahedral and octahedral shape are produced when citrate is used as the capping agent in water. The mechanism for citrate would also operate determining the shape of other pure fcc metals and can inspire the engineering of future capping agents.

Citrate-Coated, Size-Tunable Octahedral Platinum Nanocrystals: A Novel Route for Advanced Electrocatalysts

“…14,36 In a recent report, it has clearly established through electrochemical experiments, Fourier Transform Infrared Spectra (FTIR) and Density Functional Theory (DFT) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 10 that citrate ions in aqueous solution can become simultaneously adsorbed on the Pt(111) surface through all three dehydrogenated carboxylic groups in bidentate configuration. 37 For this reason, citrate is more favorably adsorbed on the Pt(111) than on the other two basal planes of platinum, providing a stabilizing effect to this crystallographic facet.…”

“…S13), 32 is also included in (Fig S15, right panel). To obtain quantitative information of the {111} at the surface of the octahedral Pt nanocrystals, irreversible Bi adsorption experiments were performed as described in previous publications 37 , and tentatively characterized by STEM EDS (Figs. S16b-c).…”

Dispersion state phase diagram of citrate-coated metallic nanoparticles in saline solutions

“…So far, binding of citrate onto metals has been scrutinized for gold NPs. Specifically, recent studies have shed light on the binding mode and energetics of citrate molecules onto different gold facets 18 . These studies used a wide range of complementary techniques, including density functional theory (DFT) calculations 19 , scanning tunneling microscopy 20 , and X-ray photoelectron spectroscopy (XPS) 21 .…”

Ligand‐Guided Growth of Alloyed Shells on Intermetallic Seeds as a Route toward Multimetallic Nanocatalysts with Shape‐Control

“…Controlling the shape of multimetallic nanoparticles (NPs) through colloidal synthesis has attracted significant attention as shape‐control defines what facets are expressed and available to facilitate catalysis while multimetallic compositions provide unique and composition‐dependent surface electronics. In the synthesis of metal NPs, shape is often controlled by the use of capping agents, which are reagents ( e. g., small molecules, polymers, surfactants, and even ions) that adsorb onto the surfaces of the growing NPs and provide stability . Through the selection of capping agents with greater affinity for one surface‐type over another, controlled overgrowth is possible and enables selective facet expression and shape‐control .…”