Production of Pd Nanoparticles in Microemulsions. Effect of Reaction Rate on Particle Size.

SÁNCHEZ M, JHON F.; SANCHEZ, MIGUEL D; FALCONE, R. DARIO; RITACCO, HERNÁN ALEJANDRO

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2022 vol. 24 p. 1692 - 1701

1463-9076

In the synthesis of metallic nanoparticles in microemulsions, we hypothesized that particle size is controlled by the reaction rate not by microemulsion size. Thus, the changes observed on the particle sizes as reaction conditions, such as concentrations, temperature, type of surfactant used, etc., are varied should not be correlated directly to the modification of those conditions but indirectly to the changes they produce on the reaction rates.In this work, the microemulsions were formulated with benzene and water as continuous and dispersed phases respectively, using n-Dodecyltrimethylammonium bromide (DTAB) and n-octanol as surfactant and cosurfactant. Using time-resolved UV-vis spectroscopy, we measured the reaction rates in the production of Palladium (Pd) nanoparticles inside microemulsions at different reactant concentrations and temperatures, keeping all the other parameters constant. The measured reaction rates were then correlated with the particle sizes measured by transmission electron microscopy (TEM). We found that nanoparticle size increases linearly as the reaction rates increases, independently of the actual reactant concentrations or temperature. We proposed a simple model for the observed kinetics where the reaction rate is controlled mainly by the diffusion of the reducing agent. With this model, we predicted that particle size should depend indirectly, via the reaction kinetics, on the micelle radius, the water volume and the total microemulsion volume. Some of these predictions were indeed observed and reported in the literature.