Atomistic understanding of cation exchange in PbS nanocrystals using simulations with pseudoligands

Abstract

Cation exchange is a powerful tool for the synthesis of nanostructures such as core–shell nanocrystals, however, the underlying mechanism is poorly understood. Interactions of cations with ligands and solvent molecules are systematically ignored in simulations. Here, we introduce the concept of pseudoligands to incorporate cation-ligand-solvent interactions in molecular dynamics. This leads to excellent agreement with experimental data on cation exchange of PbS nanocrystals, whereby Pb ions are partially replaced by Cd ions from solution. The temperature and the ligand-type control the exchange rate and equilibrium composition of cations in the nanocrystal. Our simulations reveal that Pb ions are kicked out by exchanged Cd interstitials and migrate through interstitial sites, aided by local relaxations at core–shell interfaces and point defects. We also predict that high-pressure conditions facilitate strongly enhanced cation exchange reactions at elevated temperatures. Our approach is easily extendable to other semiconductor compounds and to other families of nanocrystals.

Green solvent assisted synthesis of cesium bismuth halide perovskite nanocrystals and the influences of slow and fast anion exchange rates

“…44,45 These ion exchange reactions have a small activation energy as they are thought to proceed through a kick-out mechanism, and that the rate-determining step is not the rate of diffusion but instead the rate of the ion exchange. [44][45][46] These faster rates for the ion exchange reaction result in a signicant mass transport between the inner core and exterior of the particles, which could result in a dissolution or partial deterioration of their structure. 44 Powder X-ray diffraction (XRD) patterns were obtained for the as-synthesized Cs 3 Bi 2 I 9 NCs (Fig.…”

Thermally Induced Wurtzite to h‐BN Structural Transition

“…Similar fast ion solids with liquid‐like cations and solid‐like anions include Ag 2 S, Cu 2 Te, and AgI . Fast transportation of cations in anionic framework has also been observed in cation exchange reactions in colloidal nanocrystals …”

Ion exchange: an advanced synthetic method for complex nanoparticles

“…One of the most important factors for ion diffusion during a cation exchange reaction is defects such as vacancies and interstitial sites in a crystal structure [71, 77, 80–82]. When defects exist in the template NPs, the ion diffusion pathway having a low activation energy is formed, and the inter-diffusion of ions can be promoted along this pathway during cation exchange reaction.…”