Monodispersity and Reproducibility of Au and Ag Nanoparticle Syntheses

Monodispersity and Reproducibility of Au and Ag Nanoparticle Syntheses

 

James R. Brenner*, Kristen Brenner, James Barr, Martha Perez-Linares,

Robert Andringa and Debra Kowalczyk

Florida Institute of Technology, Nanotechnology Minor Program, 150 West University Blvd., 256 Olin Engineering Bldg., Melbourne, FL 32901

Phone: 321-749-3437, FAX: 321-674-7565, E-mail: jbrenner@fit.edu

This project is the preliminary work as part of a larger effort to make stable, yet electrically conducting, metallic nanoparticles that can later be used in 3D printing and/or rocket propellant applications. To make metallic nanoparticles stable, it is customary to reduce the metal, occasionally attach Raman-active dyes, and then always put surfactant capping ligands around the metal nanoparticles. Metallic nanoparticles typically are not conducting; the ligands stabilize the nanoparticles by putting a charge on the metal. The main scientific goal of this work was to prepare metallic nanoparticles capped with ligands containing extended conjugation such as carotenoids and tannins to sufficiently delocalize electrons from the metal such that the entire nanoparticles would conduct electricity.

A comprehensive literature search yielded several dozen articles in which metallic nanoparticles had been coated with carotenoids or tannic acid derivatives. Most of these used tannic acid in an effort toward green chemistry because of tannic acid's dual purpose as both a capping agent and a weak reducing agent. All the carotenoids and tannic acid should serve as reductants, but in some of the articles, other reductants (most commonly, sodium borohydride) were used as well. The articles were further screened and ranked in terms of NP monodispersity, zeta potential, electron and scanning probe microscopic data, and evidence for shifting of Raman-active peaks for either the metal or a dye, if present. Most of the syntheses with the best monodispersities were layer-by-layer syntheses involving polydimethyldiallylammonium chloride, polyallylamine hydrochloride, or polyethyleneimine as positively charge polyelectrolytes and/or sodium polystyrenesulfonate or polyvinylpyrrolidone as negatively charged polyelectrolytes.

This poster shows the log mean diameters and geometric standard deviations of the fifteen synthesis method candidates being evaluated for use in the aforementioned applications, as assessed by electron and scanning probe microscopies, capillary hydrodynamic fractionation, and electroacoustic analysis. The electroacoustic analyzer was also used to determine the NPs' zeta potential as a function of pH. Finally, where applicable, Raman features indicating a strong coupling between the metal nanoparticles and dyes were identified.

Keywords: zeta potential, gold nanoparticles, silver nanoparticles, layer-by-layer synthesis