Please give me an explanation of the dependence of nanoparticle size on reaction temperature in solution phase synthesis such as polyol process?
Thank you for your comment.
Can you give some good references related to your comment
high temp leading to more nucleation of the nano clusters and more growth
The process of sol's coarsening (aging) takes place at the room temperature too, but heating accelerates this process. In the most cases, the nanoparticle size enlargement occurs by one of two mechanisms: Ostwald ripening (for more soluble materials) and oriented attachment (for less soluble crystals). In the first case, the growth of the larger particles is due to the dissolution of the smaller ones, in the second - by merging the smaller ones. Both processes depend on the temperature (at least through the diffusion via kT). Ostwald ripening occurs because larger particles are more energetically stable than smaller particles. Temperature influences Ostwald ripening due to its effect on the interfacial energy, growth rate coefficients, and solubility. Oriented attachment occurs because the aggregation decreases the interphase boundary and the total (surface) energy of the system. Some kinetics equations for prediction of the equivalent particle radii are in the attached links.
Article Crystal Growth by Oriented Attachment: Kinetic Models and Co...
Article Temperature effects during Ostwald ripening
Article Temperature effects on the transition from nucleation and gr...
Dear A. B. Shcherbakov,
So if we prepare nanoparticles (eg- silver nanoparticles) at the reaction temperatures such as 120, 130 and 140oC. We will get larger nanoparticles at 140oC. This is mainly due to enhanced Ostwald ripening process at higher temperature. Is this explanation correct?
Dear Shamjid Palappra,
The role of temperature in the growth of silver nanoparticles during synthesis depends on a lot of factors, such as synthesis protocols, the nature of precursors, reductants, stabilizers, solvent etc. It can be both direct (increasing of temperature leads to enlargement of particle size) and vice versa. According to my experience, the simple Turkevich’ method for nanogold leads to the small particles at high temperature and big at low ones. This effect appears through the slow reduction of gold ions and decreasing of the number of nucleation centers at low temperature.
However, if during the formation the re-crystallization takes place, the growth of particle size according to the temperature growth will appear. For example, even the “ideal” silver sol coarsens during storage; the increasing of temperature will result to the faster aging and the enlargement of particle size.
Dear A. B. Shcherbakov,
I know that it depends on the nature of precursors, reductants, stabilizers, solvent etc. My question is if we keep all these as constant and change the reaction temperature alone, why did we get large nanoparticles at higher temperature in a typical polyol process?
Dear Shamjid Palappra,
Probably, because the growth of Ag-nanoparticles in polyols is time-defined (kinetically limited), i.e. the size depends on duration of process (as for cadmium telluride QDs). Thus, the increase of temperature accelerates the diffusion rate and (from the point of view of mass transfer) is equal to increase of time of process. Possible, the increase of temperature accelerates the chemical process of silver reduction, according to Arrhenius rule and Van't Hoff equation. Or, perhaps there is the Ostwald re-crystallization too. However, this is a fact: see attached sample of the similar study.
Article Variable Frequency Microwave Synthesis of Silver Nanoparticles
Particle size increases along with an increase in annealing temperature.
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