Fe-doping effects on the structural, vibrational, magnetic, and electronic properties of ceria nanoparticles

Abstract

In this work, we report on a single-pot synthesis route based on a polymeric precursor method used for successfully producing undoped and iron-doped CeO2 nanoparticles with iron contents up to 10.0 mol. %. The formation of high-crystalline nanoparticles with a cubic fluorite structure is determined for all the studied samples. Meanwhile, the magnetic measurements of the undoped ceria nanoparticles revealed the occurrence of ferromagnetism of bound magnetic polarons of a fraction of Ce3+ at room temperature, and only a paramagnetic behavior of Fe3+ ions was determined for Fe-doped ceria nanoparticles. A monotonous reduction of the effective magnetic moment of the Fe3+ ions was determined. It suggests a change from a high-spin to low-spin state of Fe ions as the Fe content is increased. The 3+ valence state of the iron ions has been confirmed by the Fe K-edge X-ray absorption near-edge structure (XANES) and Mössbauer spectroscopy measurements. X-ray photoelectron spectroscopy data analysis evidenced a coexistence of Ce3+ and Ce4+ ions and a decreasing tendency of the relative fraction of Ce3+ ions in the surface region of the particles as the iron content is increased. Although the coexistence of Ce3+ and Ce4+ is confirmed by results obtained via Ce L3-edge XANES measurements, any clear dependence of the relative relation of Ce3+ ions on the iron content is determined, suggesting a homogeneous distribution of Ce3+ and Ce4+-ions in the whole volume of the particles. Ce L3-edge extended X-ray absorption fine structure revealed that the Ce-O bond distance shows a monotonous decrease as the Fe content is increased, which is in good agreement with the shrinking of the unit cell volume with the iron content determined from XRD data analysis, reinforcing the substitutional solution of Ce and Fe ions in the CeO2 matrix.

Design Aspects of Doped CeO2 for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach

“…The low activity exhibited by these two specific mixed metal oxides is due to the low reducibility of the respective surface metal cations at low temperatures (H 2 -TPR, Figure C), which is strongly related to the low mobility of lattice oxygen at relatively low temperatures. This can be attributed to the following reasons: In the case of the Zn heteroatom, according to the XRD studies, ZnO phase impurity was identified, introducing ZnO/Zn–Ce–O phase (grain) boundaries for oxygen diffusion. A low tendency of the valence state of Zn 2+ species to be reduced in the presence of CO, thus leading to low oxygen mobility in the ceria lattice. In the case of the Fe heteroatom, not all Fe added participated in the formation of substitutional solid solution, resulting in Fe at interstitial sites, according to the present Raman results. , High temperatures are thereby necessary to engage the diffusion of bulk oxygen onto the surface of zinc- and iron-doped ceria for CO oxidation. Thus, at a temperature of 250 °C at which the oxygen mobility was studied (see Section ), O lattice participation was found to a small extent only in the case of Zn–Ce–O. CO 2 -TPD traces for Zn–Ce–O and Fe–Ce–O (Figure S8C–E) showed that CO 2 is released at temperatures as high as their T 50 .…”

“…In the case of the Fe heteroatom, not all Fe added participated in the formation of substitutional solid solution, resulting in Fe at interstitial sites, according to the present Raman results. , High temperatures are thereby necessary to engage the diffusion of bulk oxygen onto the surface of zinc- and iron-doped ceria for CO oxidation. Thus, at a temperature of 250 °C at which the oxygen mobility was studied (see Section ), O lattice participation was found to a small extent only in the case of Zn–Ce–O.…”

Comparison of Enhanced Photocatalytic Degradation Efficiency and Toxicity Evaluations of CeO2 Nanoparticles Synthesized Through Double-Modulation

“…Figure 1 b shows the Raman spectra of CeO 2 , Cr@CeO x , and Fe@CeO x NPs. All samples were characterized by a prominent band at ∼464 cm −1 , which corresponds to the F 2g Raman active mode in the cubic fluorite structure of CeO 2 [ 35 , 36 ]. The main F 2g band shifted to a slightly lower wavenumber (~5 cm –1 ) in the Cr@CeO x and Fe@CeO x NPs when compared to that of the CeO 2 NPs.…”

“…This shift was caused by the incorporation of Cr and Fe ions in the fluorite lattice (during the doping process). Additionally, the Raman spectrum of Fe@CeO x was characterized by a weak band at 412 cm −1 (blue mark), which can be assigned to hematite (α-Fe 2 O 3 ) [ 35 ]. This result suggests that α-Fe 2 O 3 was formed on the surface as a secondary phase.…”

Tuning the magnetic properties of Sn1−x−yCe4+xCe3+yO2 nanoparticles: an experimental and theoretical approach

“…In order to study the valence state of the cerium ions all spectra were compared with the spectra obtained for the standard compounds Ce(C 2 H 3 O 2 ) 3 ·H 2 O and CeO 2 , for more details see the previous work. 41 …”