Designed to Heat and React: Fast Microwave-Engineered Iron Oxide Nanoflowers with Controlled Anisotropy for Magnetic...

Developing synthetic routes that are both scalable and structurally controlled is critical for translating functional nanomaterials into real-world technologies. Here, we demonstrate the microwave-assisted polyol synthesis of iron oxide nanoflowers (NFs), reducing reaction times from 16 (autoclave) to only 120 min while maintaining >90% reproducibility. Crystallographic alignment of the primary cores is achieved through a carefully optimized heating profile: slow ramp (0.2 °C s^-1) to 220 °C with a 20 min dwell, followed by microwave thermal sintering at 250 °C for 60 min to further enhance mesocrystal order. Magnetic anisotropy is tuned in situ by both sintering and cobalt incorporation, yielding improved magnetic performance and enhanced catalytic activity. electron paramagnetic resonance spectroscopy confirms reactive oxygen species generation with hydroperoxyl radicals (^•OOH) as the dominant species, while synchrotron X-ray absorption spectroscopy reveals changes in electronic state and local order that, together with the presence of specific redox-active sites, collectively enhance catalytic activity. The most ordered samples (NF5, NF7) display the highest ROS yields and benchmark magnetic hyperthermia performance, with specific absorption rate values up to 710 W g_NPs ^-1 (NF5) and 542 W g_NPs ^-1 (NF7) at 200 kHz/24 kA m^-1. Microwave-synthesized nanoflowers thus emerge as sustainable, reproducible, and multifunctional platforms coupling ROS generation with efficient magnetic heating.