Nonaqueous synthesis, assembly and formation mechanisms of metal oxide nanocrystals
by Markus Niederberger, Georg Garnweitner, Jianhua Ba, Julien Polleux, Nicola Pinna
International Journal of Nanotechnology (IJNT), Vol. 4, No. 3, 2007

Abstract: Nonaqueous solution routes to metal oxide nanoparticles are a valuable alternative to the well-known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and avoidance of surfactants in order to control the crystal growth. In the first part of this paper we give an overview of the various solution routes to metal oxides in organic solvents, with a strong focus on surfactant-free processes developed in our group. In most of these synthesis approaches, the organic solvent plays the role of the reactant that provides the oxygen for the metal oxide, controls the crystal growth, influences particle shape and, in some cases, also determines the assembly behaviour. In general, these routes involve the reaction of metal oxide precursors such as metal halides, alkoxides, or acetylacetonates with benzyl alcohol, benzylamine or carbonyl compounds like ketones and aldehydes. Whereas the reaction between metal halides and benzyl alcohol enables the direct synthesis of crystalline nanoparticles via simple beaker chemistry, the other reaction systems require a solvothermal treatment at temperatures between 200°C and 250°C. The metal halide–benzyl alcohol system additionally allows for an insitu functionalisation process, where the surface of the nanoparticles can be modified during nanoparticle synthesis in order to tailor the solubility as well as the assembly behaviour. This is an important step towards the use of metal oxides as nanobuilding blocks for the fabrication of structures like nanowires or mesoporous materials. In the second part, various reaction pathways to nanoparticle formation are discussed. Solvothermal processes are not easy to monitor insitu. In order to elucidate possible formation mechanisms, we analyse the reaction solution obtained after synthesis of the nanoparticles as well as after reference experiments with altered reaction conditions. The organic species found in the mixtures allow us to propose possible formation mechanisms. As an important example, we will discuss the formation mechanism of ceria nanoparticles synthesised from cerium(III) isopropoxide and benzyl alcohol, involving a C-C bond formation between the isopropoxy ligand and benzyl alcohol. This reaction pathway was also found to lead to the formation of BaTiO3 nanoparticles. The last part of this paper deals with possible applications of metal oxide nanoparticles, especially with regard to gas sensing devices.

Online publication date: Tue, 01-May-2007

The full text of this article is only available to individual subscribers or to users at subscribing institutions.

Existing subscribers:
Go to Inderscience Online Journals to access the Full Text of this article.

Pay per view:
If you are not a subscriber and you just want to read the full contents of this article, buy online access here.

Complimentary Subscribers, Editors or Members of the Editorial Board of the International Journal of Nanotechnology (IJNT):
Login with your Inderscience username and password:

    Username:        Password:         

Forgotten your password?

Want to subscribe?
A subscription gives you complete access to all articles in the current issue, as well as to all articles in the previous three years (where applicable). See our Orders page to subscribe.

If you still need assistance, please email