Synthesis of Magnetite Particles by Oxidation of Hydroxyl-chloride Green Rust Suspension under Controlled Conditions

Abstract

Magnetite (Fe3O4) particles were synthesized by oxidation of a hydroxyl chloride green rust (GR(Cl -)) suspension at room temperature. The formation process of Fe3O4 particles was characterized by X-ray diffraction, magnetization and electrochemical measurements. The results showed that a small amount of fine Fe3O4 particles were nucleated when the supernatant solution of the as-synthesized GR(Cl -) suspension was replaced by deaerated water. By controlling the injection of oxygen gas at room temperature, Fe3O4 particles of about 70 nm in diameter formed from such GR(Cl -) suspension, while goethite (α-FeOOH) particles were mainly obtained from the as-synthesized GR(Cl -) suspension under the same oxidation conditions. Hence, the saturation magnetization of final oxidation products obtained from the GR(Cl -) suspension in which the supernatant solution was replaced was about 60 emu/g, which was six times larger than that obtained from the as-synthesized GR(Cl -) suspension. In the early stage of the oxidation process, the oxidation-reduction potential (ORP) in the GR(Cl -) suspension in which supernatant solution was replaced was lower than that in the as-synthesized GR(Cl -) suspension. In addition, the value of pH of the former suspension was higher than that of the latter suspension. It is concluded that the formation of Fe3O4 particles is enhanced in solution with relatively low ORP and high pH.

Solid-State Schikorr Reaction from Ferrous Chloride to Magnetite with Hydrogen Evolution as the Kinetic Bottleneck

“…Historically, Fe 3 O 4 was first homogeneously prepared by the thermolysis of Fe(OH) 2 under an inert atmosphere, the so-called Schikorr reaction. 36,37 Later, improved methods including sol−gel, 38,39 co-precipitation, 40 hydrothermal, 41,42 high-temperature organic phase decomposition, 27,43,44 and γ-radiolysis 45,46 methods were developed to selectively form Fe 3 O 4 . Controlled nanostructures have also been achieved under homogeneous conditions.…”

“…The question here is how to prepare and regenerate Fe 3 O 4 from accessible iron sources efficiently. Historically, Fe 3 O 4 was first homogeneously prepared by the thermolysis of Fe­(OH) 2 under an inert atmosphere, the so-called Schikorr reaction. , Later, improved methods including sol–gel, , co-precipitation, hydrothermal, , high-temperature organic phase decomposition, ,, and γ-radiolysis , methods were developed to selectively form Fe 3 O 4 . Controlled nanostructures have also been achieved under homogeneous conditions. ,− Nevertheless, preparation by solid-state reaction may be more suitable for large-scale and continuous operation .…”