Surfactant-Free Colloidal Syntheses of Gold-Based Nanomaterials in Alkaline Water and Mono-alcohol Mixtures

Abstract

Gold nanoparticles (Au NPs) and gold-based nanomaterials combine unique properties relevant for medicine, imaging, optics, sensing, catalysis, and energy conversion. While the Turkevich–Frens and Brust–Schiffrin methods remain the state-of-the-art colloidal syntheses of Au NPs, there is a need for more sustainable and tractable synthetic strategies leading to new model systems. In particular, stabilizers are almost systematically used in colloidal syntheses, but they can be detrimental for fundamental and applied studies. Here, a surfactant-free synthesis of size-controlled colloidal Au NPs stable for months is achieved by the simple reduction of HAuCl4 at room temperature in alkaline solutions of low-viscosity mono-alcohols such as ethanol or methanol and water, without the need for any other additives. Palladium (Pd) and bimetallic Au x Pd y NPs, nanocomposites and multimetallic samples, are also obtained and are readily active (electro)catalysts. The multiple benefits over the state-of-the-art syntheses that this simple synthesis bears for fundamental and applied research are highlighted.

Room Temperature Surfactant-Free Syntheses of Gold Nanoparticles in Alkaline Mixtures of Water and Alcohols: A Model System to Introduce Nanotechnology and Green Chemistry to Future Chemists and Engineers

“…Depending on the concept to illustrate, different variables can be investigated, and examples are given in Table . These results and trends essentially summarize the findings from previously published work. ,− The nanoparticles are typically in the size range of 10–30 nm.…”

“…Part II enables the students to (1) design their own experimental parametric study, (2) reflect on the importance of careful experimental design, (3) reflect on the importance of scientific watch, and (4) collaborate/data sharing for efficient resource management. Finally the students can reflect on what define an “optimal” synthesis, especially taking the Green Chemistry principles, practical limitations, and scaling into consideration. , Since the students have a limited number of resources (e.g., set amount of HAuCl 4 ), they are encouraged to pair with other groups and coordinate to produce complementary data sets to be combined.…”

Surfactant-Free Colloidal Syntheses of Precious Metal Nanoparticles for Improved Catalysts

“…Early on, it was shown than Ru NPs prepared by the polyol methods show up to six times more activity for the hydrogenation of o -chloronitrobenzene (CNB) than their counterpart NPs prepared using PVP . In general, the use of PVP is detrimental to catalytic activity, as also shown, for instance, with Au NPs for the EOR and the ethylene glycol oxidation reaction (EGOR) . The use of citrate has a less pronounced effect than PVP but also leads to lower activities. , This has been attributed, for instance, to the relatively more available surface as well as different metal–support interactions obtained for surfactant-free NPs in the case of the reduction of nitrophenol …”

“…267 While this monoalcohol approach is challenging for Au-and Pd-based nanomaterials, recent results show that a fine control over precursor and based concentration in water/alcohol mixtures could lead to the room temperature synthesis of stable surfactant-free NPs in a surprisingly simple manner. 268 The related nanomaterials are directly relevant for catalysis.…”

“…268 The use of citrate has a less pronounced effect than PVP but also leads to lower activities. 268,288 This has been attributed, for instance, to the relatively more available surface as well as different metal−support interactions obtained for surfactant-free NPs in the case of the reduction of nitrophenol. 288 The ability to compare surfactant-free NPs and NPs prepared with a surfactant also recently showed the impact of PVP in tuning the selectivity of Au catalysts for the electrochemical CO 2 RR.…”