Role of the Deep Eutectic Solvent Reline in the Synthesis of Gold Nanoparticles

Abstract

This work presents a mechanistic understanding of the synthesis of small (<3 nm) gold nanoparticles in a nontoxic, eco-friendly, and biodegradable eutectic mixture of choline chloride and urea (reline) without the addition of external reducing or stabilization agents. Reline acts as a reducing agent by releasing ammonia (via urea hydrolysis), forming gold nanoparticles even at trace ammonia concentration levels. Reline also affects the speciation of the gold precursor forming gold chloro-complexes, stabilizing Au+ species, leading to an easier reduction and avoiding the otherwise fast disproportionation reaction. Such a capability is however lost in the presence of large amounts of water, where water replaces the chloride ligands in the precursor speciation. In addition, reline acts as a weak stabilizing agent, leading to small particles (<3 nm) and narrow distributions although agglomerates quickly form. Such properties are maintained in the presence of water, indicating that it is linked to the urea stabilization rather than the hydrogen-bonding network. This work has important implications in the field of green synthesis of nanoparticles with small sizes, especially for biomedical and health care applications, due to the nontoxic nature of the components of deep eutectic solvents in contrast to the conventional routes.

Synergistic Effect of Deep Eutectic Solvent and Zinc Oxide in Transesterification of Dimethyl Terephthalate for the Synthesis of Alkyl Terephthalate Esters

“…The initial degradation of the DES based on ChCl, starting at 85 °C, was already reported in the literature. − Due to this fact, the TGA, NMR, and Karl Fischer analyses of fresh DES–ZnO were performed. First, the temperature at which the weight loss of DES–ZnO begins on the TGA/DTG thermal curve was determined (Chart SI.1 80 °C).…”

Deep eutectic solvents as an emerging green platform for the synthesis of functional materials

“…Unfortunately, the specific mechanism for tuning of the various morphologies is yet to be fully understood. Datta et al 107 systematically investigated the role of ChClurea DES on the formation of small (<3 nm) Au nanoparticles. They found that the ChCl-urea DES played multiple roles in the formation of Au nanoparticles.…”

“…Datta et al 107 systematically investigated the role of ChCl–urea DES on the formation of small (<3 nm) Au nanoparticles. They found that the ChCl–urea DES played multiple roles in the formation of Au nanoparticles.…”

Deep eutectic solvents as green solvents for materials preparation

“…As the field advances, a critical focus will be on understanding the fundamental mechanisms underlying materials synthesis within DESs. 26,27 These mechanisms enable researchers to not only harness the current capabilities more effectively but also to design novel DESs tailored specifically for unique materials synthesis challenges. The marriage of green chemistry principles, meticulous engineering, and innovative materials design is poised to reshape industries and technologies in ways that are sustainable, efficient, and at the forefront of scientific innovation.…”