The Role of Supercritical Carbon Dioxide and Water in the Synthesis of Metal and Metal Oxide Nanoparticles: Current State of the Art, Further Perspectives and Needs

Abstract

Design, development and synthesis of nanostructured materials, such as supported metal nanoparticles (NPs), are of particular interest for both scientific and industrial communities. NPs are characterised by unique properties, such as high specific surface area, leading to an enhanced energetic state and thus a higher reactivity. At this scale, optical, magnetic and electrical properties are dramatically sensitive to particle size and shape. A promising alternative to classical particle preparation methods is the application of supercritical fluids (SCFs) to design nanostructured materials. Particle formation processes are one of the most important areas of application of SCFs, such as supercritical (sc)CO2 or scH2O. In this chapter, a short introduction into the supercritical fluid reactive deposition (SFRD) and the continuous hydrothermal synthesis (CHTS) technologies and their underlying basic processes is given. Based on this, typical results obtained from SFRD and CHTS experiments are presented and discussed. At the end of the chapter, the main conclusions and further perspectives are summarised. Based on a critical analysis and evaluation of the current status, the focus is on discussion of recent research results, as well as on critical analysis of the advantages and disadvantages of the different preparation methods. Thereafter, selected examples for successful applications of NPs prepared by these particle synthesis processes are given. Finally, a brief overview of future work is provided.