Radiolytic synthesis of magnetic iron oxide nanoparticles: A study on the importance of controlling precursor concentration, pH, polymer concentration and polymer molecular mass

In this study parameters influencing the radiolytic synthesis of iron oxides, namely the effect of precursor concentration, pH, polymer type, concentration, and molecular weight on generation of Fe²⁺ during gamma-irradiation of Fe(III) precursor suspensions were investigated. Results indicated that decreasing Fe³⁺ concentration enhanced the degree of reduction, with 100 % Fe³⁺ conversion achievable at doses as low as 10 kGy. Polymer concentration and molecular weight significantly influenced the Fe(III) precursor stabilization, degree of reduction, and phase composition and morphology of synthesized nanoparticles. At low polymer concentrations (<0.185 %) the precursor particles were not stabilized, resulting in large aggregates, while high polymer concentrations (10 %) impeded the interaction of reducing species with precursor particles; in both cases the degree of reduction was lower than with intermediate polymer concentration (1.85 %). Higher molecular weight dextrans (40,000 and 500,000 Da) yielded better stabilization, while low molecular weight polymer (6000 Da) could not stabilize precursor nanoparticles, confirming that precursor nanoparticles are sterically stabilized. The role of radiolytically generated polymer radicals in the reduction was found to be minor, in comparison to the role of electrons and isopropanol radicals. This work highlights the importance of precise control of synthesis parameters in order to obtain well-defined iron oxide nanoparticles by the radiolytic method.