(Invited) Nanosecond Electrical Discharges in Liquids: Applications in the Synthesis of Nanoparticles, Including Nanoalloys

Abstract

In recent decades, the field of nanotechnology has witnessed rapid growth, fueled by the exceptional physical, chemical, mechanical, and electrical properties of nanoscale materials. Nanomaterials have found applications across various domains, including catalysis, drug delivery, microelectronics, and more. Notably, plasma-based methods have emerged as promising avenues for nanomaterial synthesis, offering versatile approaches through both bottom-up and top-down techniques.One particularly innovative area of research is the plasma-liquid system, which has demonstrated remarkable efficiency in nanomaterial synthesis. This system involves the generation of plasma in a gas phase in contact with a liquid or directly within the liquid, sometimes aided by the introduction of bubbles. This communication has two goals: 1) present an overview of the physics of different discharge mechanisms, with a particular focus on the intriguing phenomena occurring at the interfaces, and 2) show different cases where nanomaterials of interest are produced. For instance, we will show that in-liquid spark discharges prouce nanoparticles through electrode erosion, and notably, the properties of these materials are highly sensitive to both the nature of the electrode and the composition of the liquid. In the second part, we introduce an innovative plasma-liquid system where a discharge can be produced at or close the interface of two immiscible liquids. In specific cases where the system is composed of a conductive solution (e.g. salty water) and a hydrocarbon liquid, spark discharges can be generated between a pin in liquid hydrocarbon and the surface of the conductive solution. This unique configuration facilitates therefore an interaction between a high-density plasma (generated in liquid) and a solution containing metal ions. At this stage, many reactions may occur and lead to the reduction of ions to produce nanomaterials. We found that the particles collected from hydrocarbon liquid are different from those collected from the solution, in terms of composition and size distribution. This finding suggests the triggering of different chemical reactions in each liquid, involving thus species with short- as well as long-lifetime species. Consequently, we adopted this approach to synthesize metal nanoparticles as well as binary and ternary nanoalloys, expanding the scope of possibilities in nanomaterial synthesis.