Shape-Controlled Synthesis of Colloidal Metal Nanocrystals: Thermodynamic versus Kinetic Products

Abstract

This Perspective provides a contemporary understanding of the shape evolution of colloidal metal nanocrystals under thermodynamically and kinetically controlled conditions. It has been extremely challenging to investigate this subject in the setting of one-pot synthesis because both the type and number of seeds involved would be changed whenever the experimental conditions are altered, making it essentially impossible to draw conclusions when comparing the outcomes of two syntheses conducted under different conditions. Because of the uncertainty about seeds, most of the mechanistic insights reported in literature for one-pot syntheses of metal nanocrystals with different shapes are either incomplete or ambiguous, and some of them might be misleading or even wrong. Recently, with the use of well-defined seeds for such syntheses, it became possible to separate growth from nucleation and therefore investigate the explicit role(s) played by a specific thermodynamic or kinetic parameter in directing the evolution of colloidal metal nanocrystals into a specific shape. Starting from single-crystal seeds enclosed by a mix of {100}, {111}, and {110} facets, for example, one can obtain colloidal nanocrystals with diversified shapes by adjusting various thermodynamic or kinetic parameters. The mechanistic insights learnt from these studies can also be extended to account for the products of conventional one-pot syntheses that involve self-nucleation only. The knowledge can be further applied to many other types of seeds with twin defects or stacking faults, making it an exciting time to design and synthesize colloidal metal nanocrystals with the shapes sought for a variety of fundamental studies and technologically important applications.

Photoelectrochemically Active and Environmentally Stable CsPbBr3/TiO2 Core/Shell Nanocrystals

“…It should be noted that the size of NCs in the composite were almost unchanged but a rounding of the corners and edges was observed ( Figure S3b, Supporting Information). The resulting changes might be due to a trace amount of water on the CsPbBr 3 surface produced during the calcination, which could react with the corners and edges as they are the most active sites of the nanocubes, [17] therefore, partially dissolving the corners and edges during calcination.…”

“…[17] These surface reactions could generate surface defect and contribute to the decreased PL intensity.…”

Single-particle mapping of nonequilibrium nanocrystal transformations

“…1B and movies S1 and S4). In this scenario, the rate of etching is slow compared to the rate at which the particle is able to restructure and adopt a shape that is close to equilibrium (20). At high FeCl 3 concentrations, however, fast-reaction kinetics constantly drive the system out of equilibrium and the nanocrystal transiently adopts an ellipsoidal shape ( Fig.…”

“…Whereas in the near-equilibrium case, atoms at the tips have an opportunity to relax (e.g., via surface diffusion) (fig. S16 and movie S7) (20,23), the persistent oxidative environment reacts with these species selectively, accelerating the reaction and driving the transient stabilization of the ellipsoidal intermediate. Etching reactions conducted on rods with synthetically blunted tips follow the same reaction trajectory (ellipsoidal intermediate), albeit with slower initial kinetics corresponding to selective removal of the blunt features (Fig.…”

Nanostructured Inorganic Materials at Work in Electrochemical Sensing and Biofuel Cells

“…Su et al [93] combined the electrodeposition method and galvanic replacement reaction to design a controllable cobalt oxide/Au hierarchically nanostructured electrode that has glucose-sensing ability with a wide linear range from 0.2 µM to 20 mM and a low detection limit of 0.1 µM (S/N = 3). Typically, the galvanic replacement is a simple and well-established chemical way to fabricate metal (especially noble metal) nanostructures [94][95][96]. For instance, through a galvanic replacement reaction between a cobalt sacrificial template and gold ions, hollow gold nanostructures can be synthesized [97].…”