Gas-Phase Flame Synthesis and Characterization of Iron Oxide Nanoparticles for Use in a Health Effects Study

Abstract

Iron oxide nanoparticles, to be used in a health effects study, were synthesized in a H₂/air diffusion flame and characterized by transmission electron microscopy, X-ray diffraction, surface area measurement, inductively coupled plasma mass spectrometry, and a spectrophotometric speciation method. The nanoparticles exhibited the maghemite (γ -Fe₂O₃) crystal structure and contained only trivalent iron. There were two size modes in the particles. The large size mode contained crystalline, non-agglomerated particles with a median diameter of approximately 45 nm; the small size mode contained particles that were in the size range of 3–8 nm and were mostly amorphous. Depending on the value taken for the small particle size, the small mode accounted for 73–82% of the particle surface area. The particles in the small size mode were likely formed from the vapor of FeO and Fe.

Acknowledgments

Recieved 14 March 2007; accepted 31 July 2007. The authors thank Dr. Alexandra Navrotsky, Mr. John M. Neil, and Dr. Sergey Ushakov of UC Davis for the XRD and BET analyses, Drs. Valerie Leppert and Jacek Jasinski of UC Merced for part of the TEM analysis, and Dr. Ryoji Shiraki of UC Davis for the ICP-MS analysis. The Microscopy and Imaging Center of Texas A&M University is acknowledged for the use of the JEOL2010 microscope. The authors thank two anonymous reviewers for useful suggestions. The authors acknowledge the support of the Superfund Basic Research Program with Grant 5P42ES04699 from the National Institute of Environmental Health Sciences, NIH. Financial support was also received from the Texas Engineering Experiment Station and Texas A&M University.