Molten-Salt Synthesis of Metal Oxide Nanoparticles

Abstract

The search for synthesis methods which are simple, green, reliable, scalable and generalizable for functional metal oxide nanoparticles has been an area of interest for many researchers in recent years. Because of its meritorious features including environmental friendliness, low cost, simple to operate, easy to scale-up, etc., molten-salt synthesis (MSS) method becomes an excellent bottom-up synthesis technique of nanomaterials with various chemical compositions and morphologies. In this talk, I will start with the status, potential and challenges of MSS for the synthesis of nanomaterials to give a concise flavor on the importance of synthesis on the properties and application of nanomaterials. I will discuss different aspects of MSS such as the role of used molten salt, the choice of desirable molten salt, the effect of various synthesis parameters, typical oxosalts and their electrochemical aspects. More importantly, I will cover the recent progress of MSS for inorganic metal oxide nanoparticles. Other than the nanomaterials of a few binary oxides synthesized by the MSS, I will highlight how the MSS method has been successful in synthesizing complex metal oxide nanoparticles, such as AMO2 delafossites, AMO3 perovskites, AM2O4 spinels, and A2M2O7 pyrochlores. Specifically, in the past few years, we have focused on the studies of lanthanide and actinide doped pyrochlore AIII 2MIV 2O7 nanoparticles (where A = trivalent rare earth ions, and M = Zr4+, Hf4+, etc.) useful for solid-state lighting, X-ray scintillators, thermometry, bioimaging, and radioactive waste containment. We have achieved substantial tunability of their particle size, crystal phase, and more importantly, luminescence properties. We have gained a clear understanding of the influences of synthesis conditions, particle morphology and composition on their photoluminescence and radioluminescence. Therefore, MSS opens a new avenue for making size and shape tunable nanomaterials for various catalytic, optoelectronic, magnetic and electrical applications.