# Co-precipitation of magnetite (Fe₃O₄) nanoparticles

> Ferrous and ferric salts in a 1 : 2 ratio are precipitated together by adding a base such as ammonia, under nitrogen so that Fe²⁺ is not oxidized. Black magnetite nanoparticles form at once; a magnet pulls them out of the liquid, and they are washed and can be coated with silica, polymers or small molecules. Small magnetite particles are superparamagnetic.

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- Updated: 2026-10-14
- Category: Nanomaterial synthesis
- Method: Co-precipitation, bottom-up
- Starting materials: Fe²⁺ and Fe³⁺ salts (e.g. FeCl₂ and FeCl₃) in water, and a base (NH₄OH or NaOH)
- Product: Magnetite (Fe₃O₄) nanoparticles, bare or coated
- Typical size: Nanoparticles small enough to be superparamagnetic; size set by pH, ionic strength, temperature and the Fe²⁺/Fe³⁺ ratio (Laurent et al.)
- Key result: Crystalline magnetite with a fairly broad size distribution; oxidizes slowly to maghemite in air
- Scalability: Very high: water, cheap salts, room-temperature or mild heating, minutes
- Figure: 1920 × 1080 px, 77 editable layers (13 generated objects with settings)

## Steps

1. **Iron salts**: Fe²⁺ and Fe³⁺ in water at a 1 : 2 molar ratio, deoxygenated and kept under N₂
2. **Precipitation**: Add the base with vigorous stirring: Fe²⁺ + 2Fe³⁺ + 8OH⁻ → Fe₃O₄ + 4H₂O; a black precipitate forms
3. **Magnetic separation**: A magnet holds the particles while the liquid is poured off
4. **Wash**: Wash with water (and ethanol) until neutral
5. **Coat (optional)**: Silica, polymers or small molecules stabilize the particles and add functional groups

## Strengths

- Simple, fast, cheap and scalable
- Water-dispersible particles
- Easy magnetic separation

## Limitations

- Broad size distribution compared with thermal decomposition
- Fe²⁺ oxidizes in air: needs N₂
- Bare particles aggregate; coating needed for stable colloids

## Uses

- MRI contrast agents
- Magnetic separation of cells and biomolecules
- Drug delivery and magnetic hyperthermia
- Ferrofluids

## References

1. Massart, “Preparation of aqueous magnetic liquids in alkaline and acidic media”, IEEE Trans. Magn. 1981. https://doi.org/10.1109/TMAG.1981.1061188 (method origin)
2. Laurent et al., “Magnetic iron oxide nanoparticles: synthesis, stabilization, vectorization, physicochemical characterizations, and biological applications”, Chem. Rev. 2008. https://doi.org/10.1021/cr068445e (review)

Credit: Redrawn and simplified after Massart, IEEE Trans. Magn. 1981 (doi:10.1109/TMAG.1981.1061188) and Laurent et al., Chem. Rev. 2008 (doi:10.1021/cr068445e).

## Questions

**What does the “Co-precipitation of magnetite (Fe₃O₄) nanoparticles” template show?** Ferrous and ferric salts in a 1 : 2 ratio are precipitated together by adding a base such as ammonia, under nitrogen so that Fe²⁺ is not oxidized. Black magnetite nanoparticles form at once; a magnet pulls them out of the liquid, and they are washed and can be coated with silica, polymers or small molecules. Small magnetite particles are superparamagnetic.

**What are the steps shown in “Co-precipitation of magnetite (Fe₃O₄) nanoparticles”?** 1. Iron salts: Fe²⁺ and Fe³⁺ in water at a 1 : 2 molar ratio, deoxygenated and kept under N₂. 2. Precipitation: Add the base with vigorous stirring: Fe²⁺ + 2Fe³⁺ + 8OH⁻ → Fe₃O₄ + 4H₂O; a black precipitate forms. 3. Magnetic separation: A magnet holds the particles while the liquid is poured off. 4. Wash: Wash with water (and ethanol) until neutral. 5. Coat (optional): Silica, polymers or small molecules stabilize the particles and add functional groups.

**What are the starting materials and the product?** Starting materials: Fe²⁺ and Fe³⁺ salts (e.g. FeCl₂ and FeCl₃) in water, and a base (NH₄OH or NaOH). Product: Magnetite (Fe₃O₄) nanoparticles, bare or coated.

**Which papers is “Co-precipitation of magnetite (Fe₃O₄) nanoparticles” based on?** Massart, “Preparation of aqueous magnetic liquids in alkaline and acidic media”, IEEE Trans. Magn. 1981 (doi:10.1109/TMAG.1981.1061188); Laurent et al., “Magnetic iron oxide nanoparticles: synthesis, stabilization, vectorization, physicochemical characterizations, and biological applications”, Chem. Rev. 2008 (doi:10.1021/cr068445e).

**Can I edit the “Co-precipitation of magnetite (Fe₃O₄) nanoparticles” template?** Yes. Open it in the LabCanvas editor: all 77 layers are editable, including 13 generated objects (structures, plots, equipment) with their own settings. Change the text, colours and layout, then export PNG, TIFF, SVG or PDF.

**Do I need an account to use this template?** Not to view it here. To open and edit it, sign in to LabCanvas or create a free account (the free plan keeps one design of each kind). Downloading the figure is part of LabCanvas Pro (US$19 a month or US$199 a year).