The lyophobic surface of monodisperse magnetic nanoparticles capped by oleic acid was made to be more lyophilic by ozonolysis to increase the stability of the suspension in polar solvents like ethanol. The ozone oxidatively cleaved the double bond of oleic acid to form carbonyl and carboxyl groups on the surface of the nanoparticles. Additionally, interfacial ligand exchange of the capping molecules was applied to make the hydrophobic particle surface more hydrophilic. The magnetic particles showed enhanced miscibility and short-term stability in water after interfacial ligand exchange. The structure changes of the capping molecules on the nanoparticle surfaces were investigated using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). From these spectroscopy studies, the cleavage of the oleic acid and the formations of the carboxyl and carbonyl groups on the particle surface were confirmed. The shape and the magnetic properties of the nanoparticles were maintained after the surface modification. Ozonolysis is an effective method in modifying the lyophobic surface of the magnetic nanoparticles.
Bibliographical noteFunding Information:
This work is supported by the U.S. Department of Energy (DEFG02-02-ER45975 and DEFG02-02-ER45976). The authors thank Dr. Gil Lee for the use of the UV-ozone cleaner and Dr. Albena Ivanisevic for the use of the FTIR and UV–vis spectrometers. We appreciate Dr. Sam Bader and Dr. Seok-Hwan Chung from Argonne National Laboratory for help with the PPMS and discussion. We thank Dr. Richard Haasch at UIUC for the XPS characterization and Mr. Bumsoo Kim for XRD analysis. The XPS experiments were carried out in the Center for Microanalysis of Materials, University of Illinois, which is partially supported by the U.S. Department of Energy under Grant DEFG02-91-ER45439.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films
- Colloid and Surface Chemistry