Minimizing Formaldehyde Use in the Synthesis of Gold−Silver Core−Shell Nanoparticles

Abstract

Through a careful analysis of the role of formaldehyde in the preparation of silver nanomaterials, a previously unnoticed function of the reagent has been discovered. Formaldehyde reacts with ammonium hydroxide to form a polymer that changes how silver attaches to and coats a substrate. In the case of a gold nanoparticle substrate, this polymer is responsible for creating a nonconcentric core−shell nanoparticle with a near-infrared plasmon resonance at 700 nm. In contrast, when conditions do not favor synthesis of this polymer, concentric nanoparticles are formed that have a plasmon resonance between that of gold and silver at 498 nm. Understanding this second role of formaldehyde allowed us to decrease the amount used 100-fold compared to previous methods, providing a greener synthesis. In addition, it is shown that ascorbic acid can function as a partial substitute for formaldehyde in this synthesis. This strategy may be effective at minimizing or eliminating formaldehyde from the synthesis of other core−shell nanoparticles and nanoshells, facilitating their use in medical applications