Iron oxide nanoparticles (IONPs) were synthesized by combining garlic and onion peel extracts with iron (III) chloride salt (FeCl 3) in a simple chemical method to develop an environmentally green treatment for toxic dyes. Onion and garlic peels act as reducing, stabilizing, and anti-caking agents to rapidly transform FeCl 3 salt into IONPs. A change in the color of the resulting solutions indicates the formation of IONPs. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), UV–visible (UV–vis), and Fourier-transform infrared (FTIR) spectroscopy were used to characterize the structural and optical properties of IONPs. The FeO NPs were constructed using a garlic peel extract. They were 34–70 nm in size with a cubic structure, while the Fe 2 O 3 NPs synthesized using an onion peel extract were 37–66 nm in size with a hexagonal structure. FE-SEM images showed the biosynthesized FeO NPs had a nanosheet-like structure with a particle size of 24–44 nm, and biosynthesized Fe 2 O 3 NPs demonstrated a nanofiber-like structure with a particle size of 29–32 nm. UV–vis measurements indicated a blue shift for the energy gap value from 3.1 eV for biosynthesized FeO NPs to 4.1 eV for biosynthesized Fe 2 O 3 NPs. The strong FT-IR absorption peaks at 650 and 660 cm−1represented an Fe–O vibration band for the biosynthesized FeO and Fe 2 O 3 NPs, respectively. Methylene blue (MB) degradation was rapid using biosynthesized Fe 2 O 3 and FeO NPs, reaching 97% at 30 min and 90% at 35 min. These degradation rates indicate the effectiveness of the application of IONPs in the removal of MB dye through the adsorbent process. Green synthesis of iron oxide nanoparticles (IONPs) were prepared by combining (garlic and onion) peels extract with iron chloride (III) salt (feCl 3) through a simple chemical method at 200 °C for 2 h. The main objective of this research is the environment treatment of toxic dyes. The (onion and garlic) peels acts as a reducing, stabilizing, and anti-caking agent to transform FeCl 3 salt to IONPs in a short period of time. It is observed that a change in the color of the resulting solutions indicates the formation of IONPs. By using different physical techniques such as X-ray Diffraction (XRD), Field Emission-Scanning Electron Microscopy (FE-SEM), UV–Visible (UV–Vis), Fourier Transform Infrared (FT-IR), the structural and optical properties of IONPs were characterized. The crystallite size of FeO NPs using the garlic peel extract ranged from (34–70) nm with a cubic structure, while the crystallite size increased from (37–66) nm for Fe 2 O 3 NPs synthesized using the onion peel extract with a hexagonal structure. FE-SEM images showed a nanosheet-like structure with a particle size of (24–44) nm for FeO NPs synthesized using the garlic peel extract. The morphology of Fe 2 O 3 NPs synthesized using the onion peel extract revealed a nanofiber-like structure with a smaller particle size of (29–32) nm. UV–vis measurements indicated a blue shift for the energy gap value from 3.1 eV for FeO NPs using the garlic peel extract to 4.1 eV for Fe 2 O 3 NPs using the onion peel extract. The peak of strong absorption at 650 and 660 cm−1 indicated that an Fe–O vibration band reported on the FT-IR spectrum belongs to FeO and Fe 2 O 3 NPs using the garlic and onion peel extract, respectively. This experiment indicates successful removal of methylene blue (MB) by application of IONPs through the adsorbent process. The results of quick degradation efficiency of MB dye by Fe 2 O 3 NPs prepared using the onion peel extract reached 97% at 30 min, with high photocatalytic activity than that observed with FeO NPs prepared using the garlic peelextract, for which the degradation efficiency was 90% at 35 min. • First, the synthesis bioactive materials of eco-friendly IONPs (FeO and Fe2O3) by a simple chemical method using new plant peels extract. • Secondly, the first time (garlic and onion) peels were used to prepared bioactive, and safe materials of IONPs. • Third, bioactive materials of IONPs were used in environmental treatment for remove the toxic blue methylene dye under room normal light irradiation. • Finally, Because of the effectiveness of IONPs have demonstrated their ability to quick remove dyes without catalysts and other external factors in very short time because have high active. [ABSTRACT FROM AUTHOR]