Synthesis and properties of titanomagnetite (Fe3-xTixO4) nanoparticles: A tunable solid-state Fe(II/III) redox system

JOURNAL OF COLLOID AND INTERFACE SCIENCE

卷:387

Article

Pearce, C. I.¹  Qafoku, O.¹  Liu, J.¹  Arenholz, E.²  Heald, S. M.³  Kukkadapu, R. K.¹  Gorski, C. A.⁴  Henderson, C. M. B.⁵  Rosso, K. M.¹ 

[1] Pacific NW Natl Lab, Richland, WA 99352 USA

[2] Univ Calif Berkeley, Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA 94720 USA

[3] Argonne Natl Lab, Argonne, IL 60439 USA

[4] Eawag, Swiss Fed Inst Aquat Sci & Technol, CH-8600 Dubendorf, Switzerland

[5] SERC, Daresbury Lab, Sci & Technol Facil Council, Warrington WA4 4AD, Cheshire, England

关键词: Magnetite;    Ulvospinel;    Site occupancy;    Dissolution;    Electron transfer;    X-ray magnetic circular dichroism;    Master Curve;   

DOI  :  10.1016/j.jcis.2012.06.092

来源: Elsevier

【 摘 要 】

Titanomagnetite (Fe3-xTixO4) nanoparticles were synthesized by room temperature aqueous precipitation, in which Ti(IV) replaces Fe(III) and is charge compensated by conversion of Fe(III) to Fe(II) in the unit cell. A comprehensive suite of tools was used to probe composition, structure, and magnetic properties down to site-occupancy level, emphasizing distribution and accessibility of Fe(II) as a function of x. Synthesis of nanoparticles in the range 0 <= x <= 0.6 was attempted; Ti, total Fe and Fe(II) content were verified by chemical analysis. TEM indicated homogeneous spherical 9-12 nm particles. mu-XRD and Mossbauer spectroscopy on anoxic aqueous suspensions verified the inverse spinel structure and Ti(IV) incorporation in the unit cell up to x <= 0.38, based on Fe(II)/Fe(III) ratio deduced from the unit cell edge and Mossbauer spectra. Nanoparticles with a higher value of x possessed a minor amorphous secondary Fe(II)/Ti(IV) phase. XANES/EXAFS indicated Ti(IV) incorporation in the octahedral sublattice (B-site) and proportional increases in Fe(II)/Fe(III) ratio. XA/XMCD indicated that increases arise from increasing B-site Fe(II), and that these charge-balancing equivalents segregate to those B-sites near particle surfaces. Dissolution studies showed that this segregation persists after release of Fe(II) into solution, in amounts systematically proportional to x and thus the Fe(II)/Fe(III) ratio. A mechanistic reaction model was developed entailing mobile B-site Fe(II) supplying a highly interactive surface phase that undergoes interfacial electron transfer with oxidants in solution, sustained by outward Fe(II) migration from particle interiors and concurrent inward migration of charge-balancing cationic vacancies in a ratio of 3:1. (C) 2012 Elsevier Inc. All rights reserved.

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