Elucidating the mechanisms of noble metal nanoparticles formation in solid-state mechanochemical ball milling conditions using in situ techniques

Abstract

Noble metal nanoparticles have important applications in several areas, such as heterogeneous catalysis. Their efficiency toward the desired reaction are strongly dependent on structural features, shape, size, etc. Therefore, the control of such properties is of strong interest in the synthesis of these materials. Nevertheless, this faces several limitations related to reproducibility and scalability. Additionally, the solution-based protocols are strongly sensitive to the variations in the reaction media. In this context, mechanosynthesis is presented as an alternative to overcome some of the fundamental issues in the preparation of controlled metal nanostructures. Ball-milling mechanosynthesis has gained increasing attention in the last decades stimulated by the search of environmentally-friendly technologies to process matter. Currently, mechanochemistry covers the fields of minerals and metallurgy, organic chemistry, crystal engineering, sophisticated porous materials and, much less explored, the synthesis of noble metal nanostructures. Concerning the mechanosynthesis of nanoparticles, for a successful control of the morphologies, it is fundamental to understand the mechanisms of nanoparticle formation in real time directly in the solid-state. This would enable to guide the nanoparticle formation, and consequently a fine-tuning of the reaction process to obtain the specific architectures for the materials. To study the fundamentals of nanoparticles formation and to further develop the strategies to control it, the present project proposes the use of in situ techniques to monitor the formation of gold and palladium nanostructures. The materials will be synthesized in a ball milling device and XRD and Raman spectroscopy will be used to follow the reaction evolution, chemically and structurally. It is also intended to use SAXS and XANES during the solid-state reaction to acquire information concerning the size and morphology of the nanoparticles as well as in the oxidation state of the metal salt precursor. The structure-property relationships for applications in catalysis and plasmonics will be studied and the performance of the nanomaterials evaluated. We envision to obtain novel insights into the fundamentals of the synthesis of noble-metal nanoparticles with controlled and well-defined morphologies by mechanochemical approaches.