Low-Field Magnetic Separation of Monodisperse Fe3O4 Nanocrystals
Cafer T. Yavuz,1
J. T. Mayo,1
William W. Yu,1
Arjun Prakash,2
Joshua C. Falkner,1
Sujin Yean,3
Lili Cong,3
Heather J. Shipley,3
Amy Kan,3
Mason Tomson,3
Douglas Natelson,4
Vicki L. Colvin1*
Magnetic separations at very low magnetic field gradients (<100
tesla per meter) can now be applied to diverse problems, such
as point-of-use water purification and the simultaneous separation
of complex mixtures. High–surface area and monodisperse
magnetite (Fe
3O
4) nanocrystals (NCs) were shown to respond to
low fields in a size-dependent fashion. The particles apparently
do not act independently in the separation but rather reversibly
aggregate through the resulting high-field gradients present
at their surfaces. Using the high specific surface area of Fe
3O
4 NCs that were 12 nanometers in diameter, we reduced the mass
of waste associated with arsenic removal from water by orders
of magnitude. Additionally, the size dependence of magnetic
separation permitted mixtures of 4- and 12-nanometer–sized
Fe
3O
4 NCs to be separated by the application of different magnetic
fields.
2 Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main Street, Houston, TX 77005, USA.
3 Department of Civil and Environmental Engineering, Rice University, 6100 Main Street, Houston, TX 77005, USA.
4 Department of Physics and Astronomy, Rice University, 6100 Main Street, Houston, TX 77005, USA.
* To whom correspondence should be addressed. E-mail: colvin{at}rice.edu
