Investigation of the transformations of metal oxides induced by milling

Abstract

Metal oxides have many technological applications. For example, due to the thermal and mechanical stability compared to other structures, they can act as active catalysts or as passive support for active metals in the industry. As supporting materials, the oxides can also interact with the active metal and improve the respective activity towards a reaction. The deposition of the catalytic metal nanoparticles over the supports is commonly carried out by impregnation methods, followed by several washing steps and thermal treatments to clean the surface of metal nanoparticles, which is essential for the catalyst to perform appropriately. These steps can, many times, induce modification on the nanostructures, leading to a respective loss of activity. More recently, mechanochemical means such as manual grinding and ball milling have been employed as an alternative and greener route for the preparation of metal nanoparticles directly over the solid supports, including oxides. The procedures have enabled generating active and stable materials, without the use of additional surface agents, in sample preparation steps. With increasing interest in mechanochemical routes in the preparation of advanced materials, it is necessary to understand the effects of milling in the final structures. Mechanochemically induced transformations are known to occur in metal oxides. In addition to comminution, phase transitions and surface changes can take place during milling procedures. Therefore, if one aims to use metal oxides as supporting materials via mechanochemistry, it is of paramount importance to first investigate the behavior of such material under mechanochemical stress. In this context, in this undergraduate student research project, the effect of milling on the structures of different metal oxides will be studied. ZnO and Al2O3 will be investigated based on their industrial relevance. Potentially optically active oxides MoO3 and WO3 will also be studied. The influence of the role of the mechanical input represented by the type of milling device employed in the mechanochemical treatments and the intensity of milling on the structure of the oxide will be evaluated. This project, integrated into WP2, will pave the way for further studies on the use of oxides as supports for nanomaterials obtained by milling. (AU)