This work describes a green approach to the synthesis of iron nanoparticles supported in silica using tea extract of the South American plant yerba mate (Ilex paraguariensis). Catalysts with different iron contents were obtained according to the reaction conditions employed. Characterization by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) revealed the amorphous nature of the nanoparticles, tentatively ascribed to iron(II)/iron(III) oxide composites, as Fourier transform infrared (FTIR) and thermogravimetric analyses confirmed their functionalization by the tea polyphenolic compounds. For the sake of comparison, crystalline zero-valent iron nanoparticles were prepared by the classical method using NaBH 4 . Both materials were tested in the degradation of methyl orange and led to complete decolourization; the green nanoparticles were very active as heterogeneous Fenton-like catalysts in presence of hydrogen peroxide, while the nanoparticles prepared with NaBH 4 were efficient in the reductive degradation of the dye.