Controlling metal oxide nanoparticle size and shape with supercritical fluid synthesis
Metal oxide nanoparticles are emerging as important contributors in a variety of applications including water treatment, catalytic transformations, and energy generation and storage, among others. Controlling size and shape is of significant interest in the nanotechnology community as these are critical in determining nanoparticle performance, impacting properties such as reactivity, conductivity, and magnetic behavior. In addition to employing green solvents, supercritical fluid nanoparticle synthesis is a robust and facile method to meet the need to control size and shape for a variety of metal oxide nanoparticles. Supercritical water, supercritical ethanol, and supercritical carbon dioxide solvent systems offer tunable properties that allow for control of nanoparticle size and shape. This review investigates the synthesis routes, the mechanisms for size and shape control, and unique characteristics particular to each green solvent. Finally, a decision tree is developed to facilitate synthetic route design for the intended nano metal oxide composition, size, and shape that highlights the need for consideration of energy and life cycle impacts.