Microstructure Evolution and Applications of Electrospun Metal Oxide Nanostructures

Abstract

Metal oxide nanostructures are of great technological interest due to their wide range of engineering applications. For their fabrication, ‘electrospinning’ has recently turned out to be an economic and facile process. The current work uncovers the hidden potential of this process and shows how the simple ways, such as the variation in solution composition and the heat-treatment procedures, can drastically affect the morphological and microstructural characteristics of the electrospun metal oxide nanostructures. In addition, the potential of this process for producing other structural forms of metal oxides, such as nanoparticles and crystals, is shown. The study includes copper oxide and nickel oxide as model materials which were synthesized via electrospinning in different nanostructural forms with varying morphological and microstructural characteristics. The electrospun copper oxide nanofibers were found to be fast infrared photodetectors. These nanofibers were developed further into individual nanoparticles which were found to be efficient heterogeneous catalysts. In addition, copper oxide nanoparticles having lower crystallinity were found to be better photocatalysts when compared to their highly crystalline counterparts. In case of electrospun nickel oxide nanofibers, the most significant finding is their unique microstructure consisting of both the crystalline and the amorphous part along with their non-stoichiometric surface. By varying the solution composition and heat treatment routes, control over the relative crystalline and amorphous content, the surface stoichiometry as well as their morphology can be achieved. These microstructural, compositional and morphological differences were strongly reflected in the performance when these different nickel oxide nanostructures were employed in different applications. As a gas sensor, the nickel oxide nanofibers with intermediate roughness and crystallinity were found to possess highest sensitivity to the reducing gases. However, as compared to their fully crystalline counterparts, their recovery rate was much lower. When tested as lithium-ion battery anodes, the specific capacity was found to be nearly twice in case of semi-crystalline nickel oxide nanofibers; however, the nickel oxide crystals displayed superior cyclability during charge-discharge process. Thus, the present work demonstrates the ability of the electrospinning process for fabricating metal oxides nanostructures with controlled morphological and microstructural characteristics and links these characteristics to their performance in various engineering applications.

Date of Award	May 2016
Original language	American English
Supervisor	Raed Hashaikeh (Supervisor)