Amorphous to crystalline phase transition in iron oxide nanoparticles prepared by Aloe vera assisted green synthesis

• Iron oxide nanoparticles were synthesized through a simple green method. • Aloe-vera leaf extract was used as a natural reducing agent. • The effect of post-synthesis thermal treatment was investigated. • The transition from the amorphous phase to a mixed hematite-maghemite phase was detected via TEM and Raman analyses. Iron oxide nanostructures synthesized through green methods have gained significant attention due to their eco-friendly nature, low cost and the possibility to avoid toxic reagents. In this work, we present the green synthesis of Fe 2 O 3 nanoparticles (NPs) using Aloe-vera leaf extract as a natural reducing and stabilizing agent. The as-prepared nanostructures exhibit an amorphous nature, which evolves into a crystalline structure upon thermal annealing. The detailed structural and spectroscopic analyses reveal the coexistence of two iron oxide phases, maghemite (γ-Fe 2 O 3 ) and hematite (α-Fe 2 O 3 ), providing valuable insights for the development of strategies to tune the properties of iron oxide nanomaterials for targeted applications. In particular, the crystalline NPs were evaluated as photothermal agents for potential use in light-driven therapeutic applications.