Hematite and iron carbonate precipitation-coexistence at the iron–montmorillonite–salt solution–CO2 interfaces under high gas pressure at 150 °C

The hydrothermal reactivity of swelling clays has relevant implications on the geological storage of radioactive waste and greenhouse gases because the clay geo-materials have been proposed as engineered or natural barriers due to their low permeability in confined systems and their high capacity to sequester ions. In the present study, the iron–montmorillonite–salt solution–CO₂ interactions were investigated under high gas pressure (200 bar) at 150 °C.Various chemical processes were characterized at the solid–fluid interfaces such as the dissolution of montmorillonite fine particles and oxidative-dissolution of elemental iron. The ionic supersaturation of solution and possibly the surface complexation in the system produced the precipitation of hematite nanoparticles (< 200 nm) after 15 days of solid–fluid contact. The hematite nanoparticles dispersed and/or coagulated on the clay matrix caused a stable red coloration of the montmorillonite composite. We assume that initial dissolved oxygen was progressively consumed in this closed-stirred system favouring the presence of divalent iron (in-situ change of redox conditions) and then leading the surface precipitation of iron carbonate nanocrystals (< 500 nm) after 60 days of solid–fluid contact. Thus, an atypical mineral coexistence of hematite–iron carbonate was observed in our system. A qualitative comparison with the blank experiment, i.e. at the same P–T conditions, but without CO₂ injection, suggested that the carbon dioxide increased the hydrothermal reactivity of montmorillonite because the hematite and iron carbonate formation were not observed after the same reaction time.     

Narrowing size distribution widths of small α-Al2O3 nanoparticles by addition of large nanoparticles in coagulation separation

α-Al₂O₃ nanoparticles separated by fractionated coagulation still have broad size distributions which limit their wider applications. By adding 20-time mass of large α-Al₂O₃ (40.5 nm) into α-Al₂O₃ nanoparticles to be separated in coagulation separation, the average size of separated α-Al₂O₃ nanoparticles decrease from 6.6 nm without addition of large α-Al₂O₃ NPs to 4.4 nm, and the size distribution changes from 3–10 nm without addition of large α-Al₂O₃ NPs to 3–6 nm. With increasing amount of large α-Al₂O₃ NPs added, separated α-Al₂O₃ NPs exhibit smaller average sizes and narrower size distribution widths at the same separation concentrations. This approach may be applied to narrow size distribution widths in large-scale size-selective separations of other nanoparticles.     

Nanodispersed Au/Al2O3 catalysts for low-temperature CO oxidation: Results of research activity at the Boreskov Institute of Catalysis

This paper presents some important results of the studies on preparation and catalytic properties of nanodispersed Au/Al₂O₃ catalysts for low-temperature CO oxidation, which are carried out at the Boreskov Institute of Catalysis (BIC) starting from 2001. The catalysts with a gold loading of 1–2 wt.% were prepared via deposition of Au complexes onto different aluminas by means of various techniques (“deposition-precipitation” (DP), incipient wetness, “chemical liquid-phase grafting” (CLPG), chemical vapor deposition (CVD)). These catalysts have been characterized comparatively by a number of physical methods (XRD, TEM, diffuse reflectance UV/vis and XPS) and catalytically tested for combustion of CO impurity (1%) in wet air stream at near-ambient temperature. Using the hydroxide or chloride gold complexes capable of chemical interaction with the surface groups of alumina as the catalyst precursors (DP and incipient wetness techniques, respectively) produces the catalysts that contain metallic Au particles mainly of 2–4 nm in diameter, uniformly distributed between the external and internal surfaces of the support granules together with the surface “ionic” Au oxide species. Application of organogold precursors gives the supported Au catalysts of egg shell type which are either close by mean Au particle size to what we obtain by DP and incipient wetness techniques (CVD of (CH₃)₂Au(acac) vapor on highly dehydrated Al₂O₃ in a rotating reactor under static conditions) or contain Au crystallites of no less than 7 nm in size (CLPG method). Regardless of deposition technique, only the Cl-free Au/Al₂O₃ catalysts containing the small Au particles (d_i ≤ 5 nm) reveal the high catalytic activity toward CO oxidation under near-ambient conditions, the catalyst stability being provided by adding the water vapor into the reaction feed. The results of testing of the nanodispersed Au/Al₂O₃ catalysts under conditions which simulate in part removal of CO from ambient air or diesel exhaust are discussed in comparison with the data obtained for the commercial Pd and Pt catalysts under the same conditions.     

Generation and characterization of catalytic nanocomposite materials of highly isolated iron nanoparticles dispersed in clays

Nanostructured metallic iron particles in montmorillonite matrix have been prepared at ambient temperature through iron intercalation followed by reduction of resulting iron pillared montmorillonite with potassium borohydride. The resulting nanocomposites have been characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), UV–VIS-diffuse reflectance spectrometer (UV–VIS). The catalytic performances of resulting nanocomposites have been evaluated by probe phenol oxidation reaction with hydrogen peroxide. The results reveal that the nanosized iron polyoxocations intercalated clays can be successfully obtained by conventional synthesis of pillared clays, and after reduction of pillars, the highly dispersed zero-valent iron nanoparticles in clay matrix with diameter in the range of 3–10 nm can be successfully yielded. Over the nanocomposites catalyst prepared at a molar ratio of [CO ₃ ²⁻ ]/[Fe³⁺] = 0.5, the catalytic conversion of phenol oxidation is 49.5% with a 67.4% of selectivity to carbon dioxide and tar. The iron species dispersed in clay matrix may provide the catalytic active sites and the size of iron species has an effect on selectivity. More highly isolated iron nanoparticles dispersed in clays could lead to higher catalytic deep oxidation.     

Low-temperature synthesis of redispersible iron oxide nanoparticles under atmospheric pressure and ultradense reagent concentration

Highly dispersed α-Fe₂O₃ nanoparticles ca. 3 to 8 nm in diameter were prepared at atmospheric pressure, low temperature, and at an ultradense reagent concentration by titrating an aqueous ammonia solution into a dense iron oleate/toluene mixture. A transparent suspension was obtained by redispersing the prepared particles in nonpolar solvents since they were redispersible to primary particles without aggregate formations. The prepared particles were characterized by TEM, XRD, and FT-IR, and their dispersion stability in organic solvents was determined by dynamic light scattering (DLS) and viscosity measurements. In order to analyze the formation process of the highly dispersed α-Fe₂O₃ nanoparticles, time-course measurements of DLS and viscosity during the nanoparticle synthesis in toluene were carried out. A significant increase in the suspension viscosity and the formation of an aggregated structure were observed as soon as the titration of the aqueous ammonia solution. The suspension viscosity and aggregated particle size gradually reduced with continuous vigorous stirring; finally, α-Fe₂O₃ nanoparticles that were completely redispersible in nonpolar solvents were obtained after ca. 24 h. The particle size could be controlled by the synthesis temperature, and such redispersible α-Fe₂O₃ nanoparticles were obtained even when the reagent concentration was increased to 2.8 mol/L.     

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Nanocrystalline manganese ferrites (MnFe₂O₄) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H₂O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe₂O₄ nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe₂O₄ is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe₂O₄ sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.     

Correlation between microstructure parameters and anti-cancer activity of the [Mn0.5Zn0.5](EuxNdxFe2-2x)O4 nanoferrites produced by modified sol-gel and ultrasonic methods

[Mn_0.5Zn_0.5](Eu_xNd_xFe_2-2x)O₄ ferrite nanoparticles (FNP) were obtained by ultrasonic (USM) and sol-gel (SGM) methods. It was observed that SGM allows us to produce nanoparticles with the average crystal size of 10–40 nm and the specific surface area of 5–7.5 × 10⁴ m²/g with a strong correlation between the chemical composition (x) and the crystal size distribution. At the same time using USM, we obtained nanoparticles with the average crystal size of 3–15 nm and the specific surface area of 1.5–1.7 × 10⁵ m²/g without a strong correlation between Eu/Nd concentration and the crystal size distribution. The specific surface area and average crystal size are the main factors determining the antiproliferative activity of FNP. The anti-cancer activity of FNP was investigated both on cancerous cells, human adenocarcinoma cells and human colorectal carcinoma cells. It was established that samples obtained using USM were more effective in producing cytotoxic effects on cancer cells. Thus, we confirm a strong correlation between the main microstructure parameters for [Mn_0.5Zn_0.5](Eu_xNd_xFe_2-2x)O₄ ferrite nanoparticles.     

Vanadium pentoxide: Synthesis and characterization of nanorod and nanoparticle V2O5 using CTAB micelle solution

Using a surfactant-mediated method (surfactant based on cetyltrimethyl ammonium bromide, CTAB) V₂O₅ nanorod and nanoparticles have been successfully prepared. Morphologies of V₂O₅ nanostructures can be controlled by applying different precursors and by varying reaction conditions within the CTAB soft template. With ammonium metavanadate and sulfuric acid as precursors, nanoparticles are synthesized in the size range of 45–160 nm. Precursors of vanadyl sulfate hydrate and sodium hydroxide yield vanadium pentoxide nanorods with diameters of 30–90 nm and lengths of 260–600 nm. The resulting products are characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), variable pressure scanning electron microscopy (VPSEM) and X-ray photoelectron spectroscopy (XPS). Temperature programmed reduction (TPR) is included to test catalytic performance. The results show that V₂O₅ nanoparticles and nanorods achieve better catalytic performance compared to bulk V₂O₅, i.e. lower onset temperature, workability at lower temperatures, and higher H₂ consumption (μmol/g).     

Alumina nanocrystalline ceramic by centrifugal casting

Centrifugal casting is an established molding method to prepare ceramics with high strength and high reliability and it has been well demonstrated in Al₂O₃. However, it has not yet been applied to Al₂O₃ nanocrystalline ceramic with < 100 nm grain size, primarily due to the unavailability of high-quality α-Al₂O₃ nanoparticles. In addition, ultrafine nanoparticles may be difficult to cast from the solution unless high-speed ultracentrifuge (e. g., >60,000 rpm) is used. Here we addressed these two challenges by home-made dispersed α-Al₂O₃ nanoparticles with 10 nm average particle size and HCl-assisted casting under a “normal” centrifuge condition and report the first attempt to produce Al₂O₃ nanocrystalline ceramic by centrifuge casting and pressureless sintering. The sintering kinetics and microstructure were analyzed, which assists the design of optimal two-step sintering schedule. We showed that dense Al₂O₃ nanocrystalline ceramic with 65 nm average grain size and ultra-uniform microstructure (the standard deviation of the grain size distribution to the average grain size is 0.358) can be obtained by two-step sintering at 1175 °C without holding followed by holding at 1025 °C for 20 h. The ultra-uniform microstructure may result from the denser and more uniform packing of particles in the green bodies produced by centrifugal casting. The two-step sintered Al₂O₃ nanocrystalline ceramic has a microhardness of 19.9 GPa. The microhardness indicates potential softening (inverse Hall-Petch relationship) of Al₂O₃ nanocrystalline ceramic at such a grain size.     

Mechanochemical Synthesis and Electrochemical Characterization of Nano Crystalline Calcium Ferrite

Abstract  

The studies on the mechanochemical synthesis and electrochemical characterization of orthorhombic calcium ferrite (CaFe₂O₄) are reported in this paper. Stoichiometric mixtures of α-Fe₂O₃ and granulated Ca metal were used as the starting materials for the synthesis process. The synthesized calcium ferrite was characterized by room-temperature M?ssbauer spectra, XRD and TEM. The electrochemical characterisation was carried out using cyclic voltammetry studies. M?ssbauer spectra provide the yield of the reaction, information on the charge status, the local symmetry and the magnetic state of the iron ions in the mechanosynthesized ferrite material. XRD analysis of the CaFe₂O₄ compound reveals the orthorhombic crystal structure with an average crystalline size of about 28 nm. TEM micrographs reveal the nanoparticles with irregular crystal morphology ranging from 8 to 30 nm. The electrochemical studies clearly show that the calcium ferrite compound can act as an electrocatalyst for Oxygen Evolution Reaction (OER).     

Nanocomposite Fe2O3–SiO2 inclusion pigments from post-functionalized mesoporous silicas

High-surface mesoporous silicas with different pore sizes were employed for the first time as silicon precursors in the synthesis of reddish Fe₂O₃–SiO₂ inclusion pigments. Interestingly, the size of included Fe₂O₃ nanoparticles was partially controlled through confinement effects into silica mesopores. Notably, impregnated samples showed a more homogeneous and efficient encapsulation of smaller and monodisperse hematite nanoparticles (sizes around 10–35 nm). Moreover, they resulted in an improved reddish color at 1000 °C within a ceramic glaze. The best red shade (a* ≈ 18) was associated to nanocomposite with smaller hematite nanoparticles (around 5 nm). These promising results suggest the possibility to improve the reddish coloration and thermostability of Fe₂O₃–SiO₂ ceramic pigments through and adequate control of confinement effects into sintered mesoporous silicas.     

Visible light active Cu-doped iron oxide for photocatalytic treatment of methylene blue

In recent work, pure α-Fe₂O₃ (F-1) and series of 5% Cu doped Fe₂O₃ (CF-5) , 10% Cu doped Fe₂O₃ (CF-10) and 15% Cu doped Fe₂O₃ (CF-15) nanoparticles by facile chemical coprecipitation method were synthesized to study the effect of concentration of doping for photocatalytic activity. As prepared F-1, CF-5, CF-10, CF-15 nanoparticles were subjected to X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) techniques to analyse the structural and functional groups features. These characterization techniques confirmed the successful doping of Cu ²⁺ ions in α-Fe₂O₃. The crystallite size of synthesized samples was calculated by Scherrer formula. Gradually decline in crystallite size from 18 to 15 nm was observed for undoped to doped samples. Scanning electron microscopic (SEM) analysis expressed that doping of Cu reduced the aggregation of particles and enhanced the surface area of nanoparticles. UV–Visible spectroscopic analysis of synthesized samples was used to calculate the bandgap energy of F-1, CF-5, CF-10, CF-15 nanoparticles i.e., 2.0, 1.7, 1.5, 1.4eV respectively. Narrowing bandgap energy of doped hematite supported to perform excellent photocatalytic activity. Maximum degradation of methylene blue was recorded via CF-10 within 140 min. Higher degradation rate of methylene blue by optimal concentration of CF-10 is due to effective electron trapping ability of photocatalyst.     

Catalytic activity of supported metal particles for sulfuric acid decomposition reaction

Production of hydrogen by splitting of water in the thermochemical sulfur-based cycles that employs the catalytic decomposition of sulfuric acid into SO₂ and O₂ is of considerable interest. However, all of the known catalytic systems studied to date that consist of metal particles on oxide substrates deactivate with time on stream. To develop an understanding of the factors that are responsible for catalyst activity, we investigate the fresh activity of several platinum group metals (PGM) catalysts, including Pd, Pt, Rh, Ir, and Ru supported on titania at 850 °C and perform an extensive theoretical study (density-functional-theory-based first-principles calculations and computer simulations) of the activity of the PGM nanoparticles of different size and shape positioned on TiO₂ (rutile and anatase) and Al₂O₃ (γ- and η-alumina) surfaces. The activity and deactivation of the catalytic systems are defined by (i) the energy barrier for the detachment of O atoms from the SO_n (n = 1, 2, 3) species, and (ii) the removal rate of the products of the sulfuric acid decomposition (atomic O, S, and the SO_n species) from metal nanoparticles. We show that these two nanoscale features collectively result in the observed experimental behavior. The removal rate of the reaction products is always lower than the SO_n decomposition rates. The relation between these two rates explains why the “softer” PGM nanoparticles (Pd and Pt) exhibit the highest initial catalytic activity.     

Structural,magnetic, and textural properties of iron oxide-reduced graphene oxide hybrids and their use for the electrochemical detection of chromium

Superparamagnetic Fe₃O₄ nanoparticles were anchored on reduced graphene oxide (RGO) nanosheets by co-precipitation of iron salts in the presence of different amounts of graphene oxide (GO). A pH dependent zeta potential and good aqueous dispersions were observed for the three hybrids of Fe₃O₄ and RGO. The structure, morphology and microstructure of the hybrids were examined by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, Raman and X-ray photoelectron spectroscopy. TEM images reveal lattice fringes (d₃₁₁ = 0.26 nm) of Fe₃O₄ nanoparticles with clear stacked layers of RGO nanosheets. The textural properties including the pore size distribution and loading of Fe₃O₄ nanoparticles to form Fe₃O₄–RGO hybrids have been controlled by changing the concentration of GO. An observed maximum (～10 nm) in pore size distribution for the sample with 0.25 mg ml^?1 of GO is different from that prepared using 1.0 mg ml^?1 GO. The superparamagnetic behavior is also lost in the latter and it exhibits a ferrimagnetic nature. The electrochemical behavior of the hybrids towards chromium ion was assessed and a novel electrode system using cyclic voltammetry for the preparation of an electrochemical sensor platform is proposed. The textural properties seem to influence the electrochemical and magnetic behavior of the hybrids.     

Efficient visible light magnetic modified iron oxide photocatalysts

Magnetite iron oxide (Fe₃O₄) nanoparticles were synthesized via simple co-precipitation method using ferrous and ferric ions salts. Fe₃O₄ nanoparticles were modified by silica and titania. Pure and modified nanoparticles were employed for dye degradation under visible light. X-ray diffraction analysis indicated inverse spinel structure of Fe₃O₄ nanoparticles. The particle size of magnetite nanoparticles is decreased due to coating of silica and titania. Scanning and transmission electron microscopy indicated the spherical morphology for all samples. The synthesized Fe₃O₄ nanoparticles were ferromagnetic in nature with highest saturation magnetization value of 1.1034 emu as compared to silica and titania coated samples. Fourier transform infra-red spectra confirmed the incorporation of magnetite nanoparticles with silica and titania. Titania modified magnetite sample showed the highest photocatalytic activity as compared to silica modified magnetite nanoparticles and bare iron oxide under visible light irradiations.     

Cytotoxic effect of functionalized superparamagnetic samarium doped iron oxide nanoparticles for hyperthermia application

Magnetic Fluid Hyperthermia (MFH) is an emerging and safe technique for cancer treatment. Radiotherapy and Chemotherapy are widely adopted techniques for treating cancer but cause damage to the nearby healthy tissue. This paves the way for hyperthermia treatment for cancer. Since healthy cells are more heat-tolerant than malignant cells, magnetic nanoparticles with superparamagnetic properties were used in hyperthermia treatment. Surface modified magnetite (Fe₃O₄) iron oxide nanoparticles with enhanced stability, solubility, bio-compatibility and magnetic property were employed in hyperthermia treatment. In the present study, Superparamagnetic Samarium doped magnetite (Fe₃O₄:Sm) nanoparticles were functionalized with Oleylamine (OAm) and polyvinyl alcohol (PVA) by the sol-gel process. The obtained nanoparticles were characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Transmission Electron Microscopy (TEM), and UV–Visible diffuse reflectance spectroscopy (UV-DRS), Thermogravimetric analysis (TGA) and Vibrating Sample Magnetometer (VSM). From XRD data, the crystallite size of oleylamine coated samarium doped magnetite (OAm–Fe₃O₄:Sm) and PVA-coated samarium doped Fe₃O₄ (PVA- Fe₃O₄:Sm) were found to be 9.5 nm and 10.9 nm, respectively. TEM images of the functionalized nanoparticles were visualized as a spherical structure with reduced agglomeration. UV-DRS gives the bandgap value of OAm–Fe₃O₄:Sm and PVA- Fe₃O₄:Sm coated samarium doped magnetite to be 2.3 eV and 2 eV respectively. VSM measurement of OAm-Fe₃O₄:Sm and PVA- Fe₃O₄:Sm coated, showed superparamagnetic behaviour. The cytotoxicity study on the L929 cell line shows that both oleylamine and PVA-coated samarium doped magnetite were less toxic and biocompatible compared to the uncoated Fe₃O₄:Sm. The hyperthermia study reveals a rise in temperature within a few seconds with a high Specific Absorption Rate (SAR) value, confirming that the functionalized Samarium doped Fe₃O₄ was an effective nanomaterial for hyperthermia application.     

Synthesis and characterization of an iron oxide poly(styrene-co-carboxybutylmaleimide) ferrimagnetic composite

In situ precipitation of iron oxide nanoparticles within the cross-linked styrene-(N-4-carboxybutylmaleimide) copolymer was carried out by an ion-exchange method. The resulting composite was studied by X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopies. FTIR analysis showed the evolution of iron oxide deposition and the formation of sodium carboxylate due to the deposition treatment. In addition, XPS analysis indicated the complete oxidation of iron(II) to iron(III) by the presence of the representative peaks of iron oxide and iron oxyhydroxide. X-ray diffraction analysis was used to identify the inorganic phases. The results showed the formation of maghemite (γ-Fe₂O₃), and after several deposition cycles, goethite (α-FeOOH). The morphology and spatial distribution of iron oxide particles within the copolymer matrix were determined by transmission electron microscopy. The mean particle size of the iron oxide was of 14 nm as determined from wide-angle X-ray diffraction using the Scherrer equation. The evolution of magnetic properties with the number of deposition cycles was investigated by magnetometry at room temperature. The poly(styrene-co-N-4-carboxybutylmaleimide)/γ-Fe₂O₃/α-FeOOH/composite showed a soft ferrimagnetic behavior and, after the third deposition cycle, showed a saturation magnetization of 8.04 emu/g at 12 kOe and coercivity field of 51 Oe.     

Natural fuel assisted synthesis of Mg–Cu ferrite nanoparticles: Evaluation of structural,dielectric, magnetic and humidity sensing properties

The effects of lemon juice and annealing treatment on phase composition, vibrational modes, microstructural and dielectric behavior of Mg doped copper ferrite nanoparticles have been synthesized and analyzed in detail in this present work. The various characterization techniques are used to examine the phase, microstructural, vibrational and dielectric nature of the samples at different annealing temperatures (600 °C and 900 °C). The phase and microstructure of Mg substituted CuFe₂O₄ nanoparticles have been analyzed by XRD, SEM and TEM. The secondary phase peaks free XRD spectra revealed that the as burst and the annealed Mg–CuFe₂O₄ nanoparticles have single phase cubic spinel structure. The average crystallite size of the as burnt, annealed 600 °C and annealed 900 °C of as prepared nanoparticles are calculated as 8.9 nm, 12.8 nm and 31.6 nm respectively. Another verification of the spherical shaped particle's size was confirmed by TEM analysis and it found as average size of 28.7 nm, this result is well matched with XRD analysis. The effect of size with impact of annealing treatment on magnetic and dielectric properties also analyzed. The size-dependent Mg–CuFe₂O₄ nanostructures exhibit promising sensing properties which ensure them as a potential candidate for humidity sensor applications. The as-burnt and annealed samples both show a humidity response over the humid range of 10–95 %RH. The sample annealed at 900 °C has the highest average sensor response (6.02 MΩ/%RH) among the as-burnt sample (6.38 MΩ/%RH) and annealed sample at 600 °C (7.11 MΩ/%RH).     

Impact of rare earth europium (RE-Eu3+) ions substitution on microstructural,optical and magnetic properties of CoFe2−xEuxO4 nanosystems

In this study, pure cobalt ferrite (CoFe₂O₄) nanoparticles and europium doped CoFe₂O₄ (CoFe_2−xEu_xO₄; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe³⁺) ions by trivalent rare earth europium (RE-Eu³⁺) ions on the microstructure, optical and magnetic properties of the produced CoFe₂O₄ nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu₂O₃ phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ₁ and υ₂) and tetrahedral A-site (υ₃) around 415 cm⁻¹, 470 cm⁻¹ and 600 cm⁻¹ respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu³⁺ ions within CoFe₂O₄ host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu³⁺ added to CoFe₂O₄ in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe_2−xEu_xO₄, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe₂O₄ have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu³⁺ in CoFe₂O₄ lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe₂O₄ samples. Substitution of Fe³⁺ ions in CoFe₂O₄ nanoparticles with RE-Eu³⁺ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications.