Is the Anion the Major Parameter in the Shape Control of Nanocrystals?

Abstract

In this paper, copper nanocrystals are produced by using Cu(AOT)2−isooctane−water solution as a template. Even if the template does not change with various salt additions, the nanocrystal growth markedly depends on the salt used. It is demonstrated that chloride ions enable the growth of nanorods with an aspect ratio varying with chloride concentration. Conversely, only a slight amount of bromide ion is needed to increase the nanorod aspect ratio from 3 to 5 without any changes when increasing the bromide ion concentration. A rather large number of cubes are produced. Formations of nanorods and cubes are explained in terms of anion adsorption on (111) and (100) faces, respectively. By replacing chloride by other ions, the morphology of copper nanocrystals drastically changes. In all cases, the nanocrystals formed are fcc single crystals with a polyhedral shape or crystals composed of fcc tetrahedra (deformed or not) bounded by (111) faces. Some cylinders are formed by the connection of 2 different crystals with different 5-fold axes and/or with additional planes. This gives rise to various particle shapes.

Recent advances in nanoparticle synthesis with reversed micelles

“…4,14 Investigations have shown that the identity of anion species added as electrolyte are important for generating different shapes of copper nanocrystals. 56 The tendency is to follow the Hoffmeister series. 57 However, the initial micellar shape is shown to be largely unaffected by these additives.…”

New Trends on the Synthesis of Inorganic Nanoparticles Using Microemulsions as Confined Reaction Media

“…Electrolytes: Some studies reveal the possible dependence of nanoparticle shape with electrolyte addition (Filankembo et al, 2003). Pileni (Pileni, 2003) has postulated that the selective ion or molecule adsorption over nanocrystal layers can affect their growth in certain directions, which could explain the apparent preference on certain particle shape.…”

Short Gold Nanorod Growth Revisited: The Critical Role of the Bromide Counterion

“…[30] It has also been found that addition of electrolytes has a great impact in controlling the nanocrystal shapes. [13,31] Indeed, halide ions interact with gold surfaces and the interaction strength follows the increasing order of F À < Cl À < Br À < I À . [31,32] Among the halides, F À ions nonspecifically adsorb to gold surface; Cl À ions also bind to gold through a weak interaction, whereas I À ions bind too strongly to gold surfaces and tend to destroy gold nanoparticles.…”