Tuning sizes, morphologies, and magnetic properties of mono- vs. multi-core iron oxide nanoparticles through control of added water in the polyol synthesis

TL;DR

This study explores how water addition during polyol synthesis influences the size, shape, and magnetic properties of iron oxide nanoparticles, enabling tailored nanostructures for biomedical applications.

Contribution

It reveals the crucial role of water in controlling nanoparticle morphology and magnetic properties, introducing a method to tune these features via water amount and injection temperature.

Findings

Nanoparticle sizes ranged from 4 nm to 37 nm.

Distinct morphologies including smooth spheres and nanoflowers were achieved.

Magnetic properties suited for hyperthermia and MRI contrast were demonstrated.

Abstract

The polyol route is a versatile and up-scalable method to produce large batches of iron oxide nanoparticles with well-defined structure and magnetic properties. Controlling parameters such as temperature and duration of reaction, heating profile, nature of polyol solvent or of organometallic precursors were reported in previous studies of literature, but none of them described yet the crucial role of water in the forced hydrolysis pathway, whose presence is mandatory for nanoparticle production. This communication investigates the influence of the water amount and temperature at which it is injected in the reflux system for either pure polyol or mixture with a poly(hydroxy) amine. Distinct morphologies of nanoparticles were thereby obtained, from ultra-ultra-small smooth spheres down to 4 nm in diameter to large ones up to 37 nm in diameter. Nanoflowers were also synthesized, which are well-defined multi-core assemblies with narrow grain size dispersity. A diverse and large library of samples was obtained by playing on the nature of solvents and amount of water traces while keeping all the other parameters fixed. The varied morphologies lead to magnetic nanoparticles well-fitting to required applications among magnetic hyperthermia and MRI contrast agent, or both.