Aqueous Superparamagnetic Magnetite Dispersions with Ultrahigh Initial Magnetic Susceptibilities

Abstract

Superparamagnetic nanoparticles with a high initial magnetic susceptibility χ 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 χ 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 (FeO) with a χ 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 χ 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.

Agglomeration Dynamics of Magnetite Nanoparticles at Low Magnetic Field Gradient

“…The M sat of the bulk magnetite, M sat (bulk) is reported as 4.79 x 10 5 A/m . The M sat of the magnetite nanoparticle, M sat (NP) varies in a wide range depending on the size and the capping materials . The Langevin functions of Figure are simulated for the nanoparticles with different diameters, 8, 11, and 14 nm.…”

Mobility of Sub-50 nm Iron Oxide Nanoparticles with Ultrahigh Initial Magnetic Susceptibility in Intact Berea Sandstone at High Salinity

“…The synthesis of IONPs reported in our earlier work is briefly summarized here. 25 The reagent, Fe(II) acetate (5 g) was dissolved with 50 mL of triethylene glycol in a 250 mL 3-neck round-bottom flask with a reflux column. The reaction time was 2 h at 210 °C with vigorous stirring.…”

“…20,23 However, there are two major challenges that impede nanoparticle development of this application. First, (a) the synthesis of IONPs with higher initial susceptibilities is required to generate sufficient signals in low magnetic fields, 24,25 and second, (b) the stability as well as mobility of nanoparticles through the porous reservoir at high salinities and temperatures must be improved. 7,8,10,26−32 Numerous techniques have been developed to synthesize IONPs with high initial susceptibility including coprecipitation, 33,34 ultrasound irradiation methods, 35 organic colloid methods, 36 and hydrothermal methods.…”

“…Herein, we report a new class of polymer-grafted IONPs <50 nm in size and with ultrahigh initial susceptibility (∼3.3) synthesized via decomposition of an organometallic precursor in organic solvent at high temperature. 25 Controllable particle size and morphology, narrow size distribution, high magnetic susceptibility, and excellent colloidal stability in water and concentrated brine are achieved through this simple synthesis approach. In addition, this process has the potential to be expanded to large-scale production.…”

“…This “illumination of the reservoir” would potentially improve the depth of investigation beyond what is possible with conventional techniques. , However, there are two major challenges that impede nanoparticle development of this application. First, (a) the synthesis of IONPs with higher initial susceptibilities is required to generate sufficient signals in low magnetic fields, , and second, (b) the stability as well as mobility of nanoparticles through the porous reservoir at high salinities and temperatures must be improved. ,,,− …”