Systematic Study on the Precursor Reduction Kinetics and Growth Pattern for Size-Tunable Palladium Nanocubes

Composition, Structure, and Thermal Properties of Potassium Acetate Hydrates

The crystal structure determines the properties of compounds and materials, although one can find simple yet industrially relevant compounds such as potassium acetate (KOAc) and its hydrates for which the properties and even the composition still remain misunderstood, owing to the lack of structural data. In this study, the crystal structures of KOAc polymorphs and hydrates were determined for the first time. The water content in the crystal hydrates was reliably determined revealing two new phases 3KOAc·2H2O and KOAc·xH2O (x = 0.38-0.44), instead of the "sesquihydrate" and "hemihydrate" that for a century were believed to be the main hydrated forms of KOAc at ambient temperature. The number and nature of phase transitions were clearly established, and the hydration-dehydration processes were studied in detail by variable-temperature X-ray diffraction and thermal analyses.

Temperature Dependent Growth Kinetics of Pd Nanocrystals: Insights from Liquid Cell Transmission Electron Microscopy

Quantifying the role of experimental parameters on the growth of metal nanocrystals is crucial when designing synthesis protocols that yield specific structures. Here, the effect of temperature on the growth kinetics of radiolytically-formed branched palladium (Pd) nanocrystals is investigated by tracking their evolution using liquid cell transmission electron microscopy (TEM) and applying a temperature-dependent radiolysis model. At early times, kinetics consistent with growth limited is measured by the surface reaction rate, and it is found that the growth rate increases with temperature. After a transition time, kinetics consistent with growth limited by Pd atom supply is measured, which depends on the diffusion rate of Pd ions and atoms and the formation rate of Pd atoms by reduction of Pd ions by hydrated electrons. Growth in this regime is not strongly temperature-dependent, which is attributed to a balance between changes in the reducing agent concentration and the Pd ion diffusion rate. The observations suggest that branched rough surfaces, generally attributed to diffusion-limited growth, can form under surface reaction-limited kinetics. It is further shown that the combination of liquid cell TEM and radiolysis calculations can help identify the processes that determine crystal growth, with prospects for strategies for control during the synthesis of complex nanocrystals.

Quantitative Study on the Influence of Bromide Ions toward the Reduction Kinetics for Size-Tunable Palladium Nanocubes

During the preparation of nanocrystals, regulating the dosage of key additives in the reaction system and the reaction temperature commonly affects the sizes and morphologies of the products. Despite the fact that bromide ions play a pivotal role in the synthesis of palladium nanocubes (Pd NCs), there is still a lack of quantitative and in-depth research on how the ions affect the reduction kinetics of Pd precursors and further on products. In this work, Pd NCs with different sizes have been prepared under various reaction conditions coupled to a systematic mechanism study. Quantitative measurements demonstrate that the reduction processes could be considered quasi-first-order reactions, and the corresponding kinetic parameters have been obtained. Furthermore, a linear relationship is discovered between k and the average size (d) of Pd NCs. The investigation on the growth patterns of four chosen systems reveals that given reaction conditions lead to certain results with unique growth patterns.