Argentous Deep Eutectic Solvent Approach for Scaling Up the Production of Colloidal Silver Nanocrystals

Abstract

Conventional colloidal nanocrystal synthesis is conducted in batch formats which produce materials on a scale far below what is required for industrial applications. As a practical solution to this challenge, we show herein that a task-specific argentous deep eutectic solvent (DES) comprising a 1:4 mixture of silver triflate with acetamide can be used as a fluidic metal precursor to push the production of silver nanocrystals to large quantities. This approach employs oleylamine as cosolvent, reductant, and colloid capping agent and is shown to quickly produce large amounts of high-quality monodispersed silver nanocrystals (AgNCs) in a simple microwave-mediated reduction (2 min reaction at 200 °C). The large initial silver concentration ([Ag]0) of the DES-based reaction medium in turn allows a high colloidal concentration of AgNCs to be accomplished. For an [Ag]0 of 0.50 M, the highest silver concentration which gave uniform AgNCs a colloidal concentration of 54 mg mL–1 was attained, equivalent to the production of ∼58 g of AgNCs per kilogram of DES reaction medium. Interestingly, although low concentrations of metal have been historically preferred in order to suppress uncontrolled nanocrystal growth, aggregation, and fusion, a “size-focusing” effect is evident in the highly concentrated regime. Indeed, for an [Ag]0 of 0.30 M, the reaction yielded 15.7 ± 2.1 nm AgNCs (13% relative standard deviation), which were more uniform than AgNCs made in the [Ag]0 = 0.02–0.26 M range. Notably, little loss in nanocrystal quality occurred under more intensified process conditions (i.e., higher silver concentration) until 0.63 M [Ag]0 was reached. This work highlights the promise of metallic DESs for the purpose of high-volume colloidal nanocrystal production by novel yet rational synthetic strategies in future nanomanufacturing efforts.