Research Spotlight: Metal oxide nanoparticle formation using γ-radiation
Transition metal oxide nanoparticles find application in many areas including cancer treatment, environmental cleanup, catalysis, and gas sensors. Traditional methods used for the synthesis of these nanoparticles include hydrothermal synthesis, sol–gel technique, laser-induced pyrolysis, sonochemical method, and spray pyrolysis. For many of these methods the mechanisms of particle formation are poorly understood, and the final particle size and distribution are not well controlled. As the properties of nanoparticles can be strongly size-dependent, better control of the size distribution is desrirable.
Radiolysis is a promising alternative technique for generating nanoparticles with a narrow size distribution due to differential control of the particle nucleation and growth processes. This can help mitigate the drawbacks of traditional solution phase methods which include large particle size distribution, agglomeration of the particles or the need for chemical additives to control the final size of the particles
Gamma-radiation decomposes water molecules to a number of species including some very powerful reducing (·e-aq, ·H) and oxidizing species (·OH, H2O2) which can be used to carry out solution redox reactions. These redox active species consist only of H and O atoms. The reactive products (such as ·OH and ·e-aq) recombine to reform water upon termination of irradiation and hence leave no unwanted chemical wastes. The chemical environments created by γ-radiolysis are therefore ideal for nanoparticle syntheses which require a chemically pure product.
An example of this is the formation of magnetite (Fe3O4) nanoparticles from dissolved Fe(II) using γ-radiation. The mechanism summarized in the diagram below was determined by measuring the change over time in concentration of Fe(II) and Fe(III) in solution and characterizing the nanoparticles formed using electron microscopy and various spectroscopic techniques. Note that this method makes use of both the oxidizing and reducing power of water radiolysis products, whereas most gamma-induced nanoparticle synthesis uses only one or the other.
Our publication on this work can be found here:
We have also used γ-radiation to produce chromium and cobalt oxide nanoparticles:
L.M. Alrehaily, J.M. Joseph, J.C. Wren, Radiation-Induced Formation of Co3O4 Nanoparticles from Co2+(aq): probing the kinetics using radical scavengers, Phys. Chem. Chem. Phys. 17 (2015) 24138 - 24150.
L.M. Alrehaily, J.M. Joseph, J.C. Wren, Radiation-Induced Formation of Chromium Oxide Nanoparticles: Role of Radical Scavengers on the Redox Kinetics and Particle Size, J. Phys. Chem. C, 119 (2015) 16321-16330.