Experimental Evaluation of Kinetic and Thermodynamic Reaction Parameters of Colloidal Nanocrystals

Abstract

The unique properties of colloidal semiconductor nanocrystals, or quantum dots, have attracted enormous interest in a wide range of applications, including energy, lighting, and biomedical fields. However, widespread implementation is hampered by the difficulty of developing large-scale and inexpensive synthesis routes, mainly due to our limited knowledge of formation reaction parameters. We report here a simple yet powerful method to experimentally determine critically important reaction parameters such as rate constants, activation barriers, equilibrium constants and reaction enthalpies. This method was applied to wurtzite cadmium selenide nanocrystals, yielding activation energies for growth and dissolution of 14 ± 6 kJ mol–1 and 27 ± 8 kJ mol–1, respectively, and a reaction enthalpy for nanocrystal growth of −15 ± 7 kJ mol–1. Moreover, the Gibbs free energy for growth was found to be negative at low temperatures, whereas dissolution becomes the spontaneous process above 150 °C.

The role of nanoparticle size and ligand coverage in size focusing of colloidal metal nanoparticles

“…CdSe), the extracted activation energy for growth was found to be in the range of $20-50 kJ mol À1 . 47,93 The ligand coverage on the nanoparticle surface and its effect on the evolution of the size distribution for the case of ligand coverage-dependent growth rate constant is shown in Fig. 8.…”

Ligand-Mediated Nanocrystal Growth

“…Distinguishing among different ligands would require additional fitting parameters, but these could be estimated separately from ligand binding experiments using nongrowing QDs. 40 More information on the ligand binding kinetics could also help unveil the role of ligands in reversible nucleation and reversible growth. In the present model, ligands are hypothesized to mediate both the addition and the dissociation of monomers, only accounting for the number of available sites.…”

“…Knowing the competitive ligand adsorption kinetics could guide model improvement, especially if experimental insights into how ligand densities change with QDs’ sizes were available. Distinguishing among different ligands would require additional fitting parameters, but these could be estimated separately from ligand binding experiments using nongrowing QDs . More information on the ligand binding kinetics could also help unveil the role of ligands in reversible nucleation and reversible growth.…”

Modeling of Nucleation and Growth in the Synthesis of PbS Colloidal Quantum Dots Under Variable Temperatures

“…However, these efforts based on Rempel’s model predict too high rates to produce bigger particles, which leads to monomer source quickly depleted. To find formation parameters of the nanocrystal, in situ dissolution studies were made to experimentally determine the corresponding parameters, such as activation energies, equilibrium constants, and reaction enthalpies . Mazzotti et al named the type of Rempel’s model as the kinetic rate equation (KRE) model and compared it with the population balance equation (PBE) model in terms of different parameter sets.…”

“…To find formation parameters of the nanocrystal, in situ dissolution studies were made to experimentally determine the corresponding parameters, such as activation energies, equilibrium constants, and reaction enthalpies. 26 Mazzotti et al 27 The PBE model is widely applied to describe the crystallization process in the literatures; 28,29 proposed a PBE-type model to simulate the formation kinetics and size distribution of CdSe CQDs and further improved this model to describe ligand-mediated nanocrystal growth in a microfluidic reactor. 30,31 Though very powerful, the PBE model cannot model nucleation and OR growth simultaneously.…”