The peculiarities of reduction of iron (III) oxides deposited on expanded graphite
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Olga Shornikova and Alexander Dunaev Chemistry Department, Lomonosov Moscow State University, Moscow 119991, Russia; and Institute of New Carbon Materials and Technologies (JSC), Moscow 119991, Russia
Dmitry Filimonov, Alina Schur, and Makhsud Saidaminov Chemistry Department, Lomonosov Moscow State University, Moscow 119991, Russia
Natalya Sorokina and Viktor Avdeev Chemistry Department, Lomonosov Moscow State University, Moscow 119991, Russia; and Institute of New Carbon Materials and Technologies (JSC), Moscow 119991, Russia (Received 24 May 2013; accepted 10 December 2013)
A reduction of iron (III) oxides deposited on expanded graphite (EG) matrixes of three types in hydrogen flow was studied in dynamic and static regimes. In the dynamic regime, the EG matrix was shown not to influence the temperature range of the iron (III) oxide reduction. However, the C/O atomic ratios, varying depending on the type of EG matrixes, affect the completeness of reduction of these oxides to metallic iron. The reduction kinetics of iron (III) oxides deposited on EG and of bulk oxides were found to be similar and could be described by the combination of expanded Prout–Tompkins autocatalysis and n-dimensional growth of nuclei models. The prolonged hydrogen treatment at 600 °C of the samples in the static regime results in quantitative reduction of iron (III) oxide to a-Fe independent of the type of EG matrix used. The obtained samples demonstrate the relatively high values of saturation magnetization of 35 emu/g together with a high sorption capacity for crude oil of 93 g/g.
I. INTRODUCTION
Magnetic sorbents are very promising materials for wastewater purification or oil spill removal applications because they make it possible to use electromagnetic collection of the sorbents after sorption.1–3 Expanded graphite (EG) decorated with magnetic iron compounds is considered as one of the most advanced magnetic sorbent, which demonstrates the high sorption capacity of liquid hydrocarbons3–5 and can be produced from inexpensive components. The higher the magnetic saturation of the sorbents, the lower the power of electromagnets that is required, reducing the energy consumption. Among the various iron compounds, metallic iron possesses the highest saturation magnetization value (Ms 5 220 emu/g),6 making the expanded graphite decorated with metallic iron (EG/Fe) of particular interest. One of the possible ways to produce the EG/Fe materials is to reduce the precursor materials of EG with iron oxides. The reduction can be carried out either by solid chemical reducers, viz., KBH4, etc., or by gaseous reducers, i.e., hydrogen.3,5,7–10 The main drawbacks of a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.384 252
J. Mater. Res., Vol. 29, No. 2, Jan 28, 2014
http://journals.cambridge.org
Downloaded: 14 Mar 2015
solid reducers are the necessity of using solvents and decreasing the bulk density of EGs,11 which results in the sorption capacity decrease.4 The reduction of EG/Fe2O3 by gaseous redu
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