水溶液プロセスによるフェライトナノ粒子の生成機構に関する電気化学的研究

抄録

Aqueous growth mechanism of ferrite (intermediate between Fe₃O₄ and γ-Fe₂O₃) nanoparticles via the precipitation and oxidation of green rust was studied by monitoring pH and ORP of the reaction solution. While Fe₃O₄ was growing, both pH and ORP reached plateaus of pH=6 ∼ 7 and ORP=−400 ∼ −300 mV. The pH was kept constant because the formation of Fe₃O₄ from green rust is expressed by the formula [Fe^II₂Fe^III₁(OH)₆]⁺ · [Cl₁ · mH₂O]⁻+NO₃⁻→Fe₃O₄+(3+m)H₂O+Cl⁻+NO₂↑ where H⁺ is not released. The observed value of ORP was ascribed to the interfacial potential between Fe₃O₄ and FeOH⁺, a dissolved species from the green rust. After ending the growth by exhausting the green rust, the surface of Fe₃O₄ was oxidized to γ-Fe₂O₃, which gave the final values of pH=4 ∼ 5 and ORP ≈ 0 mV. Adding sucrose, a disaccharide, to the reaction solution decreased the growth rate of the ferrite particles. This supported our proposal that a disaccharide suppresses the growth of each crystal plane and thus enables the particles to grow spherical in shape.