Aqueous Superparamagnetic Magnetite Dispersions with Ultrahigh Initial Magnetic Susceptibilities

Yunping Fei, Muhammad Iqbal, Seong D. Kong, Zheng Xue, Charles P. McFadden, Jesse L. Guillet, Linda H. Doerrer, Esen E. Alp, Wenli Bi, Yi Lu, Chola B. Dandamudi, Prashant J. Ranganath, Kevin J. Javier, Mohsen Ahmadian, Christopher J. Ellison, Keith P. Johnston

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Superparamagnetic nanoparticles with a high initial magnetic susceptibility χo are of great interest in a wide variety of chemical, biomedical, electronic, and subsurface energy applications. In order to achieve the theoretically predicted increase in χo with the cube of the magnetic diameter, new synthetic techniques are needed to control the crystal structure, particularly for magnetite nanoparticles larger than 10 nm. Aqueous magnetite dispersions (Fe3O4) with a χo of 3.3 (dimensionless SI units) at 1.9 vol %, over 3- to 5-fold greater than those reported previously, were produced in a one-pot synthesis at 210 °C and ambient pressure via thermal decomposition of Fe(II) acetate in triethylene glycol (TEG). The rapid nucleation and focused growth with an unusually high precursor-to-solvent molar ratio of 1:12 led to primary particles with a volume average diameter of 16 nm and low polydispersity according to TEM. The morphology was a mixture of stoichiometric and substoichiometric magnetite according to X-ray diffraction (XRD) and Mössbauer spectroscopy. The increase in χo with the cube of magnetic diameter as well as a saturation magnetization approaching the theoretical limit may be attributed to the highly crystalline structure and very small nonmagnetic layer (∼1 nm) with disordered spin orientation on the surface.

Original languageEnglish (US)
Pages (from-to)622-629
Number of pages8
JournalLangmuir
Volume34
Issue number2
DOIs
StatePublished - Jan 16 2018

Bibliographical note

Funding Information:
This work was supported by the Advanced Energy Consortium: http://www.beg.utexas.edu/aec/. Member companies include BHP Billiton, ExxonMobil, Repsol, Sandia National Laboratories, Shell, Total, and US Department of Energy. It was also supported by the Department of Energy (DOE) Center for Subsurface Energy Security and the Welch Foundation (F-1319). We thank Karalee Jarvis, at Texas Materials Institute (TMI), for assistance with HRTEM and STEM-EDX.

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