One-step Sustainable Preparation of Superparamagnetic Iron Oxide Nanoparticles Supported on Mesoporous SiO2

•SPION/mesoporous SiO2 samples were prepared using Fe(NO3)3.9H2O dissolved in CO2+ EtOH.•γ-Fe2O3 NPs of average size 6−9 nm were homogeneously distributed on the supports.•EtOH helped to solubilize the salt in CO2 and favoured NP formation at 523 K.•Materials were superparamagnetic, with no MR that could lead to agglomeration.•The precursor is cheap, the T mild and the method simple and easy to scale-up.