Magnetic iron oxide nanoparticles with tunable size and free surface obtained via a "green" approach based on laser irradiation in water

Crystalline structure, size and surface coating are the relevant parameters influencing the catalytic and magnetic properties of iron oxide nanoparticles (FeOxNPs). The development of a "green" method for the synthesis of FeOxNPs with good crystallinity, controlled size and uncontaminated surface all at the same time is challenging. Here we show that laser ablation in water can be combined with laser irradiation at 355 nm to obtain FeOxNPs with average size tunable in the 10-30 nm range and a percentage of ferrimagnetic phase up to the 94% of crystalline phases, while maintaining the particles surface free from stabilizers or other chemical by-products and without using harmful or toxic reagents. The final FeOxNPs show good magnetization values and have the typical magnetic behaviour of exchange bias systems, due to their highly polycrystalline structure and small (ca. 3 nm) crystalline domains. The one-step coating with phosphonate ligands conferred long time stability in physiological medium to FeOxNPs.