Many literature reports describe methods of producing silver nanoparticles of controllable size and shape, which leads to UV-Visible absorption peaks that are tunable throughout the visible region; however, there are only a few that report maxima above 800 nm, and these generally use a seeded synthetic approach.  Moreover, large, often polymeric, ligands are used as capping agents to sterically stabilize the IR-absorbing nanoparticles.  In this study, we further develop the method of producing silver nanoparticles via the reduction of silver ions by sodium borohydride in the presence of sodium citrate and hydrogen peroxide. Through careful variation of reactant concentrations, mixing rates, and other reaction conditions, the UV-Visible absorption peaks can be tuned well into the near-infrared region.  This approach is one-pot, seedless, and yields nanoparticles that not only possess reproducible optical properties but also are stabilized for at least one month at room temperature by the small, easily-displaced citrate anion. This latter property makes the nanoparticles very suitable for binding to substrates. Additional characterization of the nanoparticles was done by dynamic light scattering, transmission electron microscopy, and Raman spectroscopy. Extinction spectra simulated via the Discrete Dipole Approximation (DDA) for nanoparticle sizes and shapes observed in the transmission electron micrographs agree relatively well with the experimental spectra. The DDA simulations were done using conditions that resemble those of the experiments (dielectric constants of the environment, rotational averaging, etc.).

Seedless, one-pot synthesis and simulations of infrared-absorbing silver nanoparticles

2019 Fall National Meeting

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