Synthesis of Aqueous Ferrofluid

Procedure modified by Jonathan Breitzer and George Lisensky from "Preparation and Properties of an Aqueous Ferrofluid" by Patricia Berger, Nicholas B. Adelman, Katie J. Beckman, Dean J. Campbell, Arthur B. Ellis, and George C. Lisensky, J. Chem. Educ., 76, 943-948 (1999).

Ferrofluids are colloidal suspensions of magnetic nanoparticles. Ferrofluids respond to an external magnetic field enabling the solution's location to be controlled through the application of a magnetic field. Fe3O4 magnetite nanoparticles can be produced by mixing Fe(II) and Fe(III) salts together in a basic solution. The particles must remain small and separated from one another in order to remain suspended in the liquid medium. Surfactants are used to prevent the nanoparticles from approaching one another too closely. Once prepared, ferrofluids have the captivating property of exhibiting "spikes" when placed in the proximity of a strong magnet.

Procedure
Wear eye protection
Chemical gloves recommended
Ferrofluids can be messy. The particular ferrofluid you will prepare will permanently stain almost any fabric.

Check that the iron solutions are good since Fe(II) slowly reacts with O2 to become Fe(III). Verify the solution colors!
1 M FeCl3 in 2 M HCl (shown at left)
2 M FeCl2 in 2 M HCl (shown at right)

Add 4.0 mL of 1M FeCl3 and 1.0 mL of 2M FeCl2 solution to a 100 or 150 mL beaker.

Continue stirring throughout the addition of 50 mL 1.0 M aqueous NH3 solution over a period of about 5 minutes, adding approximately 1 mL every 10 seconds. Avoid addition that is faster than the solution can be mixed, but also avoid addition that is so slow that the particles grow large. CAUTION: Although 1 M NH3 is fairly dilute, NH3 is a strong base.

If a magnetic stir bar was used instead of stirring manually with a glass rod, turn off the stirrer and immediately use a strong magnet to work the stir bar up and down the walls of the beaker in order to detach product from the stir bar. Remove the stir bar with tongs or a gloved hand before it touches the magnet.

Let the magnetite settle. You can speed the settling process by putting a magnet under the container.

Decant (pour off) and discard the clear liquid without losing a substantial amount of solid. This works best if you keep a magnet under the container.

Transfer the solid to a weighing boat with the aid of a few squirts from a wash bottle.

Use a strong magnet to attract the ferrofluid to the bottom of the weighing boat.

Pour off and discard as much clear liquid as possible, again keeping the magnet under the weighing boat. Rinse with water from a wash bottle and decant the rinse as before (not shown).

Add 1-2 mL of 25% tetramethylammonium hydroxide. Gently stir with a glass rod for at least a minute to suspend the solid in the liquid. Use a strong magnet to attract the ferrofluid to the bottom of the weighing boat. Pour off and discard the dark liquid. Move the strong magnet around and again pour off any liquid. If the ferrofluid does not spike, continue to move the strong magnet around, pouring off any liquid.

What happens when you move a magnet under the ferrofluid? If you are using a very strong magnet you might get more interesting results by varying the distance of the magnet below the boat.

Materials


Good Fe(II)

Bad Fe(II)


Exploring the Nanoworld   |   MRSEC Nanostructured Interfaces
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This page created by George Lisensky, Beloit College.  Last modified April 4, 2011 .