Solid-phase interaction in ZrO2-Fe2O3 nanocrystalline system

Superparamagnetic iron oxide γ-Fe 2 O 3 (maghemite) nanoparticles (SPION) encapsulated into water-soluble microspheres of rock salt were synthesized via a new aerosol spray pyrolysis procedure. Humic acids (HA) were employed to stabilize the aqueous suspensions of γ-Fe 2 O 3 nanoparticles released upon dissolution of the NaCl matrix. The effect of HA on the surface charge of maghemite-based colloids was studied in pH range of 3 -10. Humic polyanions compensate positive charges on a hydrated γ-Fe 2 O 3 surface resulting in strongly negative ζ-potential (< −40 mV) of colloid even in acidic environment. In neutral and alkaline environment, ζ-potential of maghemite-based colloid drops below −55 mV; thus, HA should effectively stabilize the nanoparticle colloid over the whole pH range studied. Meanwhile, bare maghemite SPION at pH 3 -6 have ζ-potential in the +20 mV to −20 mV range (isoelectric point at pH 4.35), which is insufficient for electrostatic stabilization of the suspensions. The absence of embryotoxicity of HA-stabilized nanoparticles was demonstrated.

Section: Resultssupporting

confidence: 63%

Humic acid-stabilized superparamagnetic maghemite nanoparticles: surface charge and embryotoxicity evaluation

Goldt¹,

Polyakov²,

Sorkina³

et al. 2019

“…As shown by the analysis of the data given in Table 1, the fraction of iron required for substitution of nickel and manganese in octahedral sites of double perovskite is less than the total iron content of the sample. This can be associated with both the non-stoichiometry of double perovskite, the possibility of which it was noted in [23], and with the localization of a part of iron-containing component in the non-autonomous (intergranular) phase, which occurs especially frequently in nanocrystalline materials [70][71][72][73][74].…”

Section: Findings and Discussionmentioning

confidence: 99%

Formation of nanocrystalline particles on the basis of La2(Ni,Mn,Fe)2O6 variable composition phases having a structure of double perovskite under conditions of solution combustion

Averkiev¹,

Larina²,

Shevaleevskiy³

et al. 2022

Nanocrystalline particles on the basis of La 2 (Ni,Mn,Fe) 2 O 6 variable composition phases of a double perovskite structure have been produced by glycine-nitrate combustion. The size of crystallites grows from 5 to 45 nm with an increase in iron content of synthesized particles. It is demonstrated that iron unevenly builds into octahedral sites of nickel and manganese ions substituting mainly manganese ions. At the same time, the dependence of double perovskite unit cell volume on the iron ions concentration is well described by Retgers' law. KEYWORDS double perovskite, nanocrystals, solution combustion, photovoltaics. ACKNOWLEDGEMENTS The authors express their gratitude to V. V. Gusarov for the attention he paid to the work. X-ray diffraction and SEM was performed using the equipment of the Engineering Center of Saint Petersburg State Institute of Technology. This study was financially supported by the Russian Science Foundation (project no. 20-63-47016). FOR CITATION Averkiev D.D., Larina L.L., Shevaleevskiy O.I., Almjasheva O.V. Formation of nanocrystalline particles on the basis of La 2 (Ni,Mn,Fe) 2 O 6 variable composition phases having a structure of double perovskite under conditions of solution combustion.

“…An increase in the hydrothermal fluid pH, according to the data on phase equilibria in the Fe 2 O 3 -H 2 O system [32], will lead to an increase in the FeOOH→ α-Fe 2 O 3 transition temperature, which must be taken into account when studying the BFWO -α-Fe 2 O 3 phase equilibrium region. It should be noted that the hematite phase may turn out to be nanocrystalline in the obtained samples, and a part of iron (III) may also be present in the amorphous phase located, for example, along the BFWO grain boundaries [33,34]. In both described cases, X-ray diffraction does not make it possible to identify the iron-containing impurity phase in the presence of a complex oxide, in which the main scattering centers are "heavy" bismuth and tungsten atoms.…”

Section: Xrd Analysismentioning

confidence: 99%

Pyrochlore phase in the Bi2O3-Fe2O3-WO3-(H2O) system: its formation by hydrothermal synthesis in the low-temperature region of the phase diagram

Lomakin¹,

Проскурина²,

Гусаров³

2023

The present paper investigates features of a (Bi, Fe, ) 2 (Fe, W) 2 O 6 O δ cubic pyrochlore-structured phase (hereinafter BFWO) formation in the Bi 2 O 3 -Fe 2 O 3 -WO 3 -(H 2 O) system under the hydrothermal synthesis conditions at T < 200 • C and in the range of pH < 1. It was found that the BFWO phase is formed even when the amorphous precursor suspension is less than 100 • C. The BFWO phase particles have a conditionally spherical morphology and are polycrystalline. The dependency of the average particle size on the synthesis temperature correlates well with the dependency of the average crystallite size on this parameter: both values increase abruptly with an increase in the amorphous precursor suspension treatment temperature from 90 to 110 • C (from ∼140 and 70 nm to ∼180 and 90 nm, respectively), and with a further increase in the hydrothermal treatment temperature to 190 • C, they increase more smoothly (up to ∼210 and 110 nm, respectively). It was found that the average number of crystallites in a particle is ∼9 units regardless of the synthesis temperature, i.e. an increase in the BFWO phase particle size with the increasing temperature (in the considered temperature range) occurs mainly due to an increase in the size of their constituent crystallites. KEYWORDS pyrochlore-structured phase, hydrothermal synthesis, phase formation, nanocrystals.ACKNOWLEDGEMENTS The authors are grateful to D.P. Danilovich for assistance in performing the synthetic part of the work. XRD studies, SEM and EDXMA of samples were performed employing the equipment of the