Spinel Ferrite Nanocrystals Research Articles

Sm3+-Doped CdFe2O4 Nanocrystals Prepared in Water-Soluble Polymeric Nanoreactors and Their Characterizations

The rare-earth ion doping in nanocrystals has the advantage on improving the interested properties. As one of rare-earths, the trivalent samarium ion (Sm[Formula: see text]) was used as a dopant. The precursor of Sm[Formula: see text]-doped cadmium ferrite (CdFe2O4) nanocrystals was reacted in water-soluble polymeric nanoreactors as a dispersed phase in miniemulsion, and then calcinated to form doped nanocrystals. The 1% Sm[Formula: see text]-doped nanocrystal in small size exhibited the smaller narrow gap energy and weak photoluminescent emission intensity; which attributed to the positive influences on the photocatalytic degradation. The selected Sm[Formula: see text]-doped spinel ferrite nanocrystals provide a unique catalyzer for organic compound photodegradation.

Surface Adsorption and Photoinduced Degradation: A Study of Spinel Ferrite Nanomaterials for Removal of a Model Organic Pollutant from Water.

Spinel oxide nanocrystals are attractive materials for photoinduced advanced oxidation processes that degrade organic pollutants in water due to their chemical stability and tunability, visible light absorption, and magnetic recoverability. However, a systematic understanding of the structural and chemical factors that control the reactivity of specific spinel oxide nanocrystal materials toward photoinduced degradation processes is lacking. This Perspective illustrates these knowledge gaps through an investigation into the impacts of surface chemistry and composition of spinel ferrite nanocrystals of formula MFe2O4 (M = Mg, Fe, Co, Ni, Cu, Zn) on their ability to remove a model organic pollutant (methyl orange (MO)) from water. We identify two mechanisms by which the nanocrystals remove MO from water: (i) surface adsorption and (ii) photoinduced degradation under visible light irradiation in the presence of hydrogen peroxide via the photo-Fenton reaction. Nanocrystals that do not contain any surface ligands are more effective at removing MO from water than nanocrystals that contain surface ligands, despite our observation that the ligand-less nanocrystals do not form stable colloidal dispersions in water, while ligand-coated nanocrystals are colloidally stable. For many of the spinel ferrite compositions studied here, the fraction of methyl orange removal via adsorption to the nanocrystal surface in the absence of photoexcitation is larger than the fraction removed under irradiation. Our data indicate that the composition-dependent surface charge of the nanocrystals controls the degree of surface adsorption of the charged MO molecule. Overall, these results demonstrate that careful consideration of the impacts of surface chemistry on the behavior of spinel ferrite nanocrystals is required to accurately assess and subsequently understand their activity toward the photoinduced degradation of organic molecules.

Structural, surface, magnetic, and dielectric properties of Ni0.3Cu0.3Zn0.4Fe1.4Cr0.6O4 spinel ferrite nanocrystals prepared by sol-gel auto combustion route

Structural, surface, magnetic, and dielectric properties of Ni0.3Cu0.3Zn0.4Fe1.4Cr0.6O4 spinel ferrite nanocrystals prepared by sol-gel auto combustion route

Toward a comprehensive understanding of effect of cation distribution and M2+ constituent in spinel ferrite nanocrystals MFe2O4 (M = Co, Mn, and Ni) on the electrochemical response in sensitive detection of chloramphenicol

This paper focuses on investigating the effect of the (M2+) cation constituent and the inverse degree within the lattice structure of MFe2O4 (M = Co, Mn, and Ni) nanocrystals on their electrochemical characteristics and sensing performance under the same experimental condition. Using Rietveld refinement of powder X-ray diffraction (XRD), Raman, and scanning electron microscopy (SEM), physical characterizations of CoFe2O4 (CFO), MnFe2O4 (MFO), and NiFe2O4 (NFO) are observed and analyzed. In particular, a detailed study on current response and kinetic parameters for the electron transfer reactions in the presence of K3/K4 probes and chloramphenicol (CAP) analyte is carried out, respectively, highlighting the positive influence of the electrode modification and comparing the electrochemical characteristics and sensing performance. The ordering of their electrochemical performance is listed as follows: CFO/SPE> NFO/SPE> MFO/SPE. The reason for their electrochemical performance difference is discussed in detail. Namely, the CFO sample possessing high crystallization and phase purity, uniform primary particle size, and especially wholly inversed spinel structure possessing multiple valence states (Co2+ and Co3+) on the octahedral sites offered many unique features, which are beneficial for electrical conductivity, charge transferability, surface area, and electrocatalytic active sites. Despite also being the inversed spinel structure, the NFO with the existence of impurity phases and larger grain size, as well as a lower degree of inversion than the CFO sample showed a lower enhancement in electrochemical response. However, its electrochemical signal response still is higher than that of the normal spinel MFO structure, further confirming the critical role of (M2+) cation constituent and the inverse degree to the electrochemical characteristics and sensing performance.

Controlling Cation Distribution and Morphology in Colloidal Zinc Ferrite Nanocrystals.

This paper describes the first synthetic method to achieve independent control over both the cation distribution (quantified by the inversion parameter x) and size of colloidal ZnFe2O4 nanocrystals. Use of a heterobimetallic triangular complex of formula ZnFe2(μ3-O)(μ2-O2CCF3)6(H2O)3 as a single-source precursor, solvothermal reaction conditions, absence of hydroxyl groups from the reaction solvent, and the presence of oleylamine are required to achieve well-defined, crystalline, and monodisperse ZnFe2O4 nanoparticles. The size of the ZnFe2O4 nanocrystals increases as the ratio of oleic acid and oleylamine ligands to precursor increases. The inversion parameter increases with increasing solubility of the precursor in the reaction solvent, with the presence of oleic acid in the reaction mixture, and with decreasing reaction temperature. These results are consistent with a mechanism in which ligand exchange between oleic acid and carboxylate ligands bound to the precursor complex influences the degree to which the reaction produces a kinetically trapped or thermodynamically stable cation distribution. Importantly, these results indicate that preservation of the triangular Zn–O–Fe2 core structure of the precursor in the reactive monomer species is crucial to the production of a phase-pure ZnFe2O4 product and to the ability to tune the cation distribution. Overall, these results demonstrate the advantages of using a single-source precursor and solvothermal reaction conditions to achieve synthetic control over the structure of ternary spinel ferrite nanocrystals.

Toward a Comprehensive Understanding of Effect of Cation Distribution and M2+ Constituent in Spinel Ferrite Nanocrystals Mfe2o4 (M = Co, Mn, and Ni) on the Electrochemical Response in Sensitive Detection of Chloramphenicol

Toward a Comprehensive Understanding of Effect of Cation Distribution and M2+ Constituent in Spinel Ferrite Nanocrystals Mfe2o4 (M = Co, Mn, and Ni) on the Electrochemical Response in Sensitive Detection of Chloramphenicol

Cation Distribution in Spinel Ferrite Nanocrystals: Characterization, Impact on their Physical Properties, and Opportunities for Synthetic Control.

Metal oxide materials that adopt the spinel crystal structure, such as metal ferrites (MFe2O4), present tetrahedral (A) and octahedral [B] sublattice sites surrounded by oxygen anions that provide a relatively weak crystal-field splitting. The formula of a metal ferrite material is most precisely described as (M1-xFex)[MxFe2-x]O4, where the parentheses and square brackets denote the tetrahedral and octahedral sites, respectively, and x is the inversion parameter quantifying the distribution of M2+ and Fe3+ cations among these sites. The electronic, magnetic, and optical properties of spinel ferrites all depend on the magnitude of x, which, in turn, depends on the relative sizes of the cations, their charge, and the relative crystal-field stabilization afforded by tetrahedral or octahedral coordination. Compared to bulk spinel ferrites, the large surface-area-to-volume ratio of spinel ferrite nanocrystals provides additional structural degrees of freedom that enable access to a broader range of x values. Achieving synthetic control over the degree of inversion in addition to the size and shape is critical to tuning the properties of spinel ferrite nanocrystals. In this Forum Article, we review physical inorganic methods used to quantify x in spinel ferrite nanocrystals, describe how the electronic, magnetic, and optical properties of these nanocrystals depend on x, and discuss emerging strategies for achieving synthetic control over this parameter.

Effect of cobalt doping on structural parameters, cation distribution and magnetic properties of nickel ferrite nanocrystals

Here, thermal heat treatment method has been used for the synthesis of PVP capped nickel ferrite (NiFe2O4) and cobalt doped nickel (Ni0.5Co0.5Fe2O4) spinel ferrite nanocrystals with the aim of investigating the effect of Co doping on the structural and magnetic properties of NiFe2O4 nanocrystals. XRD analysis confirms the formation of a pure form of FCC nanocrystals of spinel ferrite type, where the average crystallite size has been found to be approximately 17 nm and 19 nm respectively for nickel ferrite (NF) and cobalt doped nickel ferrite (CNF) from XRD. Again, HRTEM study gives the average size for NF and CNF as 20 nm and 25 nm respectively. Further, SAED pattern indicates the polycrystallinity of both the sample, whereas EDX analysis confirms the presence of expected elements in the sample. From XRD data analysis different structural parameters such as lattice spacing, lattice constant, tetrahedral and octahedral ionic radii, oxygen position parameter, average cation radius per molecule, ionic packing coefficients (Pa, Pb), the degree of ionic packing (α), vacancy parameter (β), hopping lengths, and bond lengths etc. have been calculated for both nickel and cobalt doped nickel ferrite nanocrystals. Further, obtained cation distribution for NF and CNF nanocrystals from their XRD pattern analysis shows huge change in the distribution as a result of doping. In addition, FTIR spectral analysis also confirms the phase purity of both the samples. Magnetic characterization shows the improvement of different magnetic parameters due to cobalt doping on nickel, thereby making CNF nanocrystals suitable for different application purposes.

Gamma radiation shielding characteristics of various spinel ferrite nanocrystals: a combined experimental and theoretical investigation.

This work presents the facile synthesis of Ni, Mn, Zn, Cu and Co spinel ferrite nanocrystals via sol–gel auto-ignition and the investigation of their structural and gamma ray shielding characteristics. Experimentally, gamma ray shielding parameters are determined with different gamma ray sources and NaI(Tl) scintillation detector and theoretically via Monte-Carlo simulation (Geant4) as well as NIST-XCOM database. X-ray diffractograms elucidate the cubic spinel structure without any contaminating phases for all synthesized nano-ferrites. TEM results evidence the formation of ultrafine crystallites in nano-regime dimensions. Nanocrystalline spinel ferrites in pellet form have been exposed to gamma radiation from diverse sources by changing the radiation dose intensity. The comparative study of the linear attenuation coefficient, mass attenuation coefficient, total atomic cross section, total electronic cross section, effective atomic number, effective electron density and half value layer for manufactured spinel ferrites is carried out using NIST-XCOM and Geant4 at 122–1330 keV. Gamma ray energy absorption buildup factor (EABF) is investigated for five selected ferrites at 100 keV to 1500 keV incident photon energy and penetration depth from 1 to 40 mfp using geometric progression (G-P) fitting technique. EABF is found to be maximum at an intermediate region, mainly attributed to the Compton scattering process. Zinc ferrite exhibits a higher value of EABF among other ferrites, which mainly depends on the chemical composition of the material and crystallite size effect. The EABF is investigated as a function of penetration depth and is found to be maximum for a penetration depth of 40 mfp. Experimental and theoretical simulation results are found to be in good agreement. The Monte-Carlo simulation of radiation interaction with materials has evidenced to be an excellent approximation tool in exploring spinel ferrite performance in radiation atmosphere.

Tuning of physical properties of multifunctional Mg-Zn spinel ferrite nanocrystals: a comparative investigations manufactured via conventional ceramic versus green approach sol-gel combustion route

This work focused on the impact of synthesis routes on the structural, microstructural, magnetic, electrical and dielectric characteristics of Mg1−x Zn x Fe2O4 (x = 0.00, 0.25, 0.50, 0.75, and 1.00) nanocrystals manufactured via the ceramic and green approach sol–gel route. The powder X-ray diffraction (XRD) analysis reveals that the entire synthesized ferrite solids crystallize in single phase spinel structure. The XRD outcomes highlight the impact of the synthesis routes and Zn2+ replacement on the morphology, crystallite size and structural parameters of magnesium nano-ferrites. The transmission electron microscopy (TEM) images illustrate that the process of synthesis causes extensive lessening of grain and crystallite sizes. The magnetic study reveals that the magnetic properties of magnesium ferrite can be tuned by zinc substitution. The saturation magnetization (Ms), retentivity (Mr), coercive force (Hc) and magneton number diminutions meaningfully with the replacement of diamagnetic Zn2+ ions in Mg-ferrite for both the synthesized systems. The deterioration of magnetic parameters with Zn2+ substitution can be clarified on the base of the random spin canting model. Likewise, the magnetic parameters, enhanced meaningfully for sol-gel derived samples this can be attributed due to decline of crystallite size effect. The DC electric resistivity displays NTCR behaviour like ideal semiconducting materials for all the produced samples. The DC resistivity values of sol-gel produced samples were found to be little bit higher than that of ceramic derived samples. The experimental dielectric constant as a function of frequency behaviour can be elucidated with the support of the heterogeneous model of the polycrystalline structure of ferrites. The dielectric constant and loss tangent decreases with Zn2+ content for both the systems. The dielectric constant enhances for sol-gel derived samples; however, lower values of loss tangent were found. The obtained outcomes can be suitable for multifunctional applications in electronics devices and biomedical field.

Sol–gel auto-ignition fabrication of Gd3+ incorporated Ni0.5Co0.5Fe2O4 multifunctional spinel ferrite nanocrystals and its impact on structural, optical and magnetic properties

Monophasic nanocrystals of rare earth gadolinium (Gd3+) ion doped nickel–cobalt ferrite, Ni0.5Co0.5GdyFe2−yO4 (y = 0.00, 0.025, 0.050, 0.075, 0.100 and 0.125) have been synthesized by l-ascorbic acid assisted sol–gel auto-ignition process. Thermogravimetric and differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) with selected area electron diffraction (SAED) patterns, ultraviolet–visible spectrophotometry and vibrating sample magnetometer were employed to characterize the microstructure, optical and magnetic properties. Structural investigations verified the presence of cubic spinel phase short of any contamination peak. The average crystallite size was seen in nano-regime dimensions and well confirmed by TEM results. SAED patterns showed bright and intense ring of (311) plane revealed the establishment of spinel ferrite nanocrystals. Lattice constant (a) increases steadily with the rise in Gd3+ content following the Vegard’s law. FTIR spectra confirmed the creation of spinel ferrite structural geometry. Saturation magnetization (Ms) and a remanence magnetization (Mr) decreased from 29.77 to 20.78 emu/g and 21.62 to 15.79 emu/g, respectively, with increasing the Gd3+ content. However, coercivity (Hc) is significantly increased. The highest value of Hc = 1132 Oe was found for y = 0.075 sample. The reduction in Ms values can be justified owing to the replacement of Fe3+ existing at the octahedral [B]-sites by the Gd3+ ions which is paramagnetic at room temperature. The elucidation of magnetic parameters with Gd3+ doping was attributed to the discrepancy of anisotropy constant, the paramagnetic nature of Gd3+ and crystallite size effect.

La3+ doped LiCo0.25Zn0.25Fe2O4 spinel ferrite nanocrystals: Insights on structural, optical and magnetic properties

This paper addresses the manipulation of structural, morphology, optical and magnetic properties of LiCo0.25Zn0.25Fe2O4 ferrite via incorporation of different proportions of La3+ at the expense of iron ions using a sol-gel method. The samples were characterized using the X-ray diffraction technique (XRD), Fourier transform infrared (FT-IR) spectroscopy, the energy dispersive X-ray spectra (EDX), inductively coupled plasma optical emission spectroscopy (ICP-OES), high resolution scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, ultraviolet-diffuse reflectance spectroscopy (UV-DRS), and vibrating sample magnetometer (VSM) technique. The Rietveld refinements of the samples indicate that at higher concentrations of La3+, nanostructures with dual phase, i.e. cubic spinel and orthorhombic LaFeO3 perovskite with space group (Pbnm) appear. Optical studies show that the energy band gap (Eg) of the bare LiCo0.25Zn0.25Fe2O4 ferrite sample (2.18 eV) reaches up to 2.47 eV at x = 0.06 and above this concentration, it drops sharply to 2.00 eV. Although the saturation magnetization and the coercivity of LiCo0.25Zn0.25LaxFe2–xO4 are lower than that of LiCo0.25Zn0.25Fe2O4 NPs. Overall, the superparamagnetic nature and low values of saturation magnetization and coercivity of LiCo0.25Zn0.25LaxFe2-xO4 NPs are suitable to be applied in transformers core.

Study of the optical properties of Zn doped Mn spinel ferrite nanocrystals shows multiple emission peaks in the visible range –a promising soft ferrite nanomaterial for deep blue LED

Here, in this report, chemical co-precipitation method has been used for the synthesis of zinc doped manganese spinel ferrite nanocrystals, having the chemical formula of Mn0.5Zn0.5Fe2O4. The structural and morphological analysis have been carried out using X-ray diffraction (XRD) analysis and High Resolution Transmission Microscope (HRTEM). XRD analysis has revealed the formation of pure phase face centred cubic (FCC) spinel ferrite nanocrystals with the average size of 28 nm approximately. Electron Microscopic images show the spherical morphology of the prepared ferrite nanocrystals and the average size obtained from these observation matches well with that from XRD result. Further, Selected Area Diffraction Pattern (SAED) of the prepared nanocrystals gives the combined pattern of concentric rings and sharp bright spots over the rings, which indicates the polycrystalline nature of the sample. Again, elemental analysis of the nanocrystals has been studied by Energy dispersive X-ray spectroscopy (EDX). Ultraviolet–Visible (UV–Vis) spectroscopy measurement shows an absorption peak in the visible range at around 346 nm. From the absorption data, the optical band gap energy has been calculated using Tauc’s plot, which is found to be approximately 3.47 eV. Similarly, UV–Vis diffuse reflectance spectra (DRS) also provide almost the same band gap, following Kubelka–Munk function. Luminescence spectra gives three sharp emission peaks in the visible range at 409 nm, 430 nm and 460 nm of wavelength, on exciting the samples with 350 nm and the intensity of the peaks has been found to decrease on exciting again the sample with 380 nm and 400 nm respectively. In addition, Commission Internationale de L’Eclairage (CIE) diagram shows that this sample can act as a blue light emitting diode (LED). Vibrating Sample Magnetometer (VSM) shows the superparamagnetic nature of the prepared sample and hence, Mn0.5Zn0.5Fe2O4 nanocrystals can be used as a soft ferrite substance and it’s interesting optical properties make it a more technologically applicable nanocrystals.

X-ray diffraction analysis for the determination of elastic properties of zinc-doped manganese spinel ferrite nanocrystals (Mn0.75Zn0.25Fe2O4), along with the determination of ionic radii, bond lengths, and hopping lengths

Zinc-doped manganese spinel ferrite nanocrystals with chemical formula Mn0.75Zn0.25Fe2O4 were synthesized by the chemical co-precipitation method. The structural properties of the synthesized nanoparticles were studied by X-ray diffraction analysis (XRD), whereas morphological analysis was performed by high-resolution transmission electron microscopy (HR-TEM) and scanning electron microscopy. The XRD study confirmed the formation of single-phase spinel face-centered cubic nanocrystals with an average size of approximately 19 nm. HR-TEM analysis gave an average particle size of approximately 15 nm, with the nanocrystals being almost spherical. The selected-area electron diffraction pattern obtained in the HR-TEM study clearly indicated the polycrystalline nature of the nanocrystals. The Fourier transform infrared spectrum confirmed the formation of a pure spinel ferrite structure. Williamson-Hall plot analysis, using the XRD data, was used to obtain information on the different elastic properties, such as residual strain, stress, and energy density, considering the uniform deformation model, the uniform stress deformation model, and the uniform deformation energy density model. The results were compared with the results obtained by the size-strain plot method. The XRD data were used to determine the lattice parameter, which was found to be 0.81 nm. With use of the calculated lattice parameter, the ionic radii, bond lengths of the tetrahedral and octahedral sites, and hopping lengths of the spinel ferrite nanocrystals were calculated. Finally, a magnetic study using a vibrating-sample magnetometer showed that the nanocrystal sample is superparamagnetic.

Assembly and photochemical properties of mesoporous networks of spinel ferrite nanoparticles for environmental photocatalytic remediation

Spinel ferrite materials have an electronic band structure that is well suited for visible light-induced catalysis, however, their photocatalytic activity remains low due to the daunting charge-carrier separation process. In this article, we report that high-surface-area mesoscopic architectures composed of tightly connected ultrasmall spinel ferrite nanocrystals can efficiently suppress electron-hole recombination, manifesting an exceptional activity and magnetic recyclability in photocatalytic reduction of aqueous Cr(VI). Revealed by electron microscopy, N2 physisorption, and X-ray scattering studies, the resulting materials, which were obtained through a block copolymer-assisted cross-linking aggregation of colloidal nanoparticles, show a 3D interconnected nanoporous structure with a large internal surface area (up to 159 m2 g−1) and exhibit small grain composition (ca. 6–8 nm in size). Through a systematic synthesis of various structural analogues to the spinel ferrite family and optical absorption and electrochemical impedance spectroscopy analyses, we demonstrate that the electronic band structure fits the electronic requirements for both Cr(VI) reduction and water oxidation under UV–vis light irradiation. Among spinel ferrites, ZnFe2O4 presents the highest activity, readily operating without additional sacrificial reagents in photocatalytic detoxification of aqueous Cr(VI), which together with transient gas analysis and fluorescence spectroscopy results suggest a competitive formation of oxygen and hydroxyl radicals at the catalyst surface. These findings provide an essential tool for the delineation of the electronic structure-catalytic property relationship in spinel ferrite nanostructures offering intriguing possibilities for designing new photocatalytic systems for efficient environmental pollution purification and energy conversion.

Synthesis and Size-Selective Precipitation of Monodisperse Nonstoichiometric MxFe3–xO4 (M = Mn, Co) Nanocrystals and Their DC and AC Magnetic Properties

Spinel ferrite nanocrystals (NCs) have shown great promise for a wide variety of electromagnetic and medical applications. In this work, the AC magnetic properties of nonstoichiometric manganese and cobalt ferrites (MxFe3–xO4, M = Mn, Co) NCs are systematically studied as a function of composition. Samples of very similar average size and shape, but different Mn to Fe and Co to Fe ratios are prepared to study the effect of composition. Conventional syntheses are combined with a size-selective precipitation method using oleic acid as an antisolvent yielding nearly monodisperse samples. DC and AC magnetic measurements shows that introducing Co to the ferrite crystal increases the blocking temperatures and magnetic anisotropies of the nanocrystals with corresponding shifts in AC magnetic susceptibilities, while manganese ferrites are relatively insensitive to the variation in compositions as size and shape dominate over crystal anisotropy. The systematic AC-magnetic characterizations of superparamagnetic Mnx...

Synthesis of magnetically recyclable spinel ferrite (MFe2O4, M = Zn, Co, Mn) nanocrystals engineered by sol gel-hydrothermal technology: High catalytic performances for nitroarenes reduction

Highly stable and magnetically recoverable MFe2O4 (M=Zn, Co, Mn) spinel ferrite nanoparticles; synthesized using sol gel-hydrothermal technology via utilizing polyvinyl alcohol surfactant, were proposed as heterogeneous catalysts for the reduction of nitroarenes. The morphological characteristics, structural exploration, surface, optical, vibrational and magnetic properties were performed using powder X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray, N2 sorptiometry, diffused UV–vis reflectance spectroscopy, FTIR, point of zero charge, vibrating sample magnetometer (VSM) and thermokinetic analysis via TGA technique. The results showed that MnFe2O4 exhibited the best performance in the reduction of 4-nitrophenol (4-NP), 2,4,6 tri-nitrophenol (2,4,6-NP) and 4-nitroaniline (4-NA) and revealed 100% conversion into the corresponding amino derivatives in 270sec with rate constant equal 0.01061s−1, 0.01134s−1 and 0.01355s−1, respectively. The superiority of the catalytic reduction of MnFe2O4 was due to increasing the pore radius and pore volume (6.75nm, 0.227cm3/g) values compared to other nanoferrites. The synthesized nanoferrites indicate independence of the activity on crystallite sizes due to the insignificant margin of change (from 6 to10nm). Conversely, decreasing the activity of ZnFe2O4 was due to increasing the Zn2+ ions size that induces an increase in lattice parameter values and thus increases the long-range electron transfer between Fe2+–Fe3+ ions. The MnFe2O4 catalyst that presented the highest saturation magnetization (135emu/g) indicated the highest reduction potential for 4-NA comparatively in the presence of NaBH4 and the reduction reaction followed pseudo first-order kinetics. Increasing the reduction performance of 4-NA compared to other nitroaromatics on MnFe2O4 was explained based on the formed intermediates, their reactivities, hydrophobicity and to point of zero charges. It has been explored that the reduction efficacy of 4-NP was enhanced on MnFe2O4 with the addition of ammonium oxalate and benzoquinone where it was inferior following the addition of tertiary-butyl alcohol. More important correlations concerning the effect of octahedral sites, residual organics, heat of activation (Ea) and activation free energy (ΔG*) values; determined while the removal of citrate/PVA moieties, on nitroarenes reduction rates were well scrutinized and discussed.

Microstructure and magnetic properties of MFe2O4 (M = Co, Ni, and Mn) ferrite nanocrystals prepared using colloid mill and hydrothermal method

Three kinds of spinel ferrite nanocrystals, MFe2O4 (M = Co, Ni, and Mn), are synthesized using colloid mill and hydrothermal method. During the synthesis process, a rapid mixing and reduction of cations with sodium borohydride (NaBH4) take place in a colloid mill then through a hydrothermal reaction, a slow oxidation and structural transformation of the spinel ferrite nanocrystals occur. The phase purity and crystal lattice parameters are estimated by X-ray diffraction studies. Scanning electron microscopy and transmission electron microscopy images show the morphology and particle size of the as-synthesized ferrite nanocrystals. Raman spectrum reveals active phonon modes at room temperature, and a shifting of the modes implies cation redistribution in the tetrahedral and octahedral sites. Magnetic measurements show that all the obtained samples exhibit higher saturation magnetization (Ms). Meanwhile, experiments demonstrate that the hydrothermal reaction time has significant effects on microstructure, morphologies, and magnetic properties of the as-synthesized ferrite nanocrystals.

Catalytic Activity of the Spinel Ferrite Nanocrystals on the Growth of Carbon Nanotubes

We prepared three ferrite nanocatalysts: (i) copper ferrite (CuFe2O4) (ii) ferrite where cobalt was substituted by nickel (NixCo1−xFe2O4, with x=0, 0.2, 0.4, 0.6), and (iii) ferrite where nickel was substituted by zinc (ZnyNi1−yFe2O4 with y=1, 0.7, 0.5, 0.3), by the sol-gel method. The X-ray diffraction patterns show that the ferrite samples have been crystallized in the cubic spinel structural phase. We obtained the size of grains by field emission scanning electron microscopy images and their magnetic properties by vibrating sample magnetometer. Next, carbon nanotubes were grown on these nanocatalysts by the catalytic chemical vapor deposition method. We show that the catalytic activity of these nanocrystals on the carbon nanotube growth depend on cation distributions in the octahedral and tetrahedral sites, structural isotropy, and catalytic activity due to cations. Our study may have applications in finding a suitable candidate of doped ferrite nanocrystals as catalysts for carbon nanotube growth. More interestingly, the yield of fabrication of carbon nanotubes can be considered as an indirect tool to study catalytic activity of ferrites.

Adsorption capability for Congo red on nanocrystalline MFe2O4 (M = Mn, Fe, Co, Ni) spinel ferrites

In this contribution, we compare the adsorption capacity of different MFe2O4 (M=Mn, Fe, Co, Ni) ferrite nanocrystals synthesized by hydrothermal method for Congo red (CR). It is the first time to give a comprehensive comparison and analysis of the adsorption capacity of ferrite nanocrystals with spinel structure for CR. Research indicates that the cations distribution of MFe2O4 ferrites is the most important factor to decide their adsorption capacity. Electrostatic absorption was conceived as the main adsorption mechanism. Meanwhile, the MFe2O4 nanoparticles exhibited a clearly ferromagnetic behavior under applied magnetic field, which allowed their high-efficient magnetic separation from wastewater. Furthermore, acetone is an effective desorption agent for desorption of MFe2O4 nanoparticles loaded by CR. All of the spinel ferrite nanocrystals possess good soft-magnetism, especially, CoFe2O4 nanocrystals exhibit a higher saturation magnetization of 86.1emug−1 as well as the outstanding adsorption capacity for CR. By the calculation of Langmuir isotherm model, the maximum adsorption capacity of CoFe2O4 for CR is 244.5mgg−1.