Probing the effects of redox conditions and dissolved Fe²⁺ on nanomagnetite stoichiometry by wet chemistry, XRD, XAS and XMCD

Abstract

Magnetite nanoparticles, commonly found in subsurface environments, are extensively used in various applications such as environmental remediation, catalysis, electronics and medicine. However, the oxidative transformation of magnetite (mixed-valent Fe-oxide) into...

Prediction of nanomagnetite stoichiometry (Fe(ii)/Fe(iii)) under contrasting pH and redox conditions

“…The initial Fe(II)/Fe(II) ratios (R ini ) of these (non)-stoichiometric magnetites were determined by acid digestion in 0.6 M HCl for 3 days, followed by spectrophotometric determination of dissolved [Fe(II)] and total [Fe] (= [Fe(III)] + [Fe(II)]) using the 1,10 phenanthroline colorimetric method, 30 as well as by X-ray magnetic circular dichroism (XMCD). 27 The results were in excellent agreement with the expected values from the amount of H 2 O 2 added, as expected from previous studies. 15,27,31 Acid digestion followed by spectrophotometry was repeated three times for R0.5 and each non-stoichiometric magnetite, which led to an error of ±0.01 on the determination of R ini .…”

“…27 The results were in excellent agreement with the expected values from the amount of H 2 O 2 added, as expected from previous studies. 15,27,31 Acid digestion followed by spectrophotometry was repeated three times for R0.5 and each non-stoichiometric magnetite, which led to an error of ±0.01 on the determination of R ini . This error is consistent with previous work.…”

“…Magnetite nanoparticle (10 nm) preparation was described previously. 27 The samples used in the present study come from the same batch. The synthesis procedure is repeated for clarity.…”

“…The procedure involves a room temperature aqueous precipitation process. 27,28 Briefly, a 0.5 M HCl solution (40 mL) containing 0.5 M FeCl 2 and 1 M FeCl 3 (1 : 2 molar ratio) was added dropwise into a 0.5 M NaOH solution (250 mL) with continuous stirring, leading to instantaneous precipitation of magnetite particles. After the synthesis, the pH of the suspension was adjusted to 8.5.…”

“…Known amounts of H 2 O 2 were added to R0.5 to produce defined non-stoichiometric magnetite (R0.1, R0.2, R0.3, R0.4) sets. 15,27 Then, mother solutions were replaced with ultrapure water (at pH = 8.5) in order to remove residual H 2 O 2 . The initial Fe(II)/Fe(II) ratios (R ini ) of these (non)-stoichiometric magnetites were determined by acid digestion in 0.6 M HCl for 3 days, followed by spectrophotometric determination of dissolved [Fe(II)] and total [Fe] (= [Fe(III)] + [Fe(II)]) using the 1,10 phenanthroline colorimetric method, 30 as well as by X-ray magnetic circular dichroism (XMCD).…”