Nanocrystalline ZnFe2O4 Research Articles

Nd <sup>3+</sup> Substituted Nanocrystalline Zinc Ferrite Sensors for Ethanol, LPG and Chlorine

Nd 3+ substituted zinc ferrites with chemical formula ZnNdxFe 2-x O4 (x = 0, 0.01, 0.02, and 0.03) were prepared by oxalate co-precipitation method and characterized by XRD, IR and SEM techniques. The gas sensing properties were studied for ethanol, LPG and chlorine. It was observed that nanocrystalline ZnFe2O4 shows maximum sensitivity to ethanol (~41%) followed by LPG (~22%) and less sensitivity to Cl2 (~10%) at an operating temperature of 327oC. The sensitivity of zinc ferrites increases with increase in Nd 3+ content. Response-recovery times of zinc ferrite decreases with increase in Nd3+ content.

Synthesis of a hydrogen producing nanocrystalline ZnFe2O4 visible light photocatalyst using a rapid microwave irradiation method

A rapid microwave solid-state synthesis method is systematically investigated to achieve a H2 producing visible light active spinel photocatalyst. ZnFe2O4 nanocrystallites were obtained by microwave irradiation of precursor compacts under optimized conditions. This investigation led to a uniform sized nanocrystalline photocatalyst that yielded a quantum-yield of H2 evolution ∼3.8 times higher than that of conventionally synthesized ZnFe2O4. The synthesis parameters – microwave power, synthesis temperature, and time, were found to control the physico-chemical properties viz phase formation kinetics, phase purity, crystallinity, specific surface area and photochemical efficiency, of the synthesized photocatalyst. The study reveals that the threshold microwave power of ≥3 kW was necessary to obtain a spinel phase structure, while lower power (<3 kW) could not induce the crystallization even after prolonged low-power irradiation of 180 min. At the threshold power, a minimum of 10 min. synthesis time was enough to obtain uniform sized nanocrystallites, indicating that the synthesis method is ∼24 times faster than the solid state reaction method, which needs nearly 4 h. The particle morphology evolution with irradiation time from 10–150 min. exhibited de-crystallization phenomena. Longer irradiation displayed a morphological crystallization probably induced due to the simultaneous area and volumetric heating effect. The possible “formation mechanism” of these uniform nanocrystallites has been presented here for qualitative understanding. Thus synthesized photocatalysts generated hydrogen from a water–methanol mixture even without the co-catalyst loading. The ferrite photocatalyst was found to decolorize methylene blue dye with a maximum decay constant of 0.232 h−1, thereby demonstrating its capability in the pollutant decomposition applications, all under visible light photons.

PHOTOCATALYTIC PROPERTIES OF NANOCRYSTALLINE ZnFe2O4 SYNTHESIZED AT LOW TEMPERATURE BY SOLVO-COMBUSTION METHOD

Facile, low temperature solvo-combustion synthesis route is used to prepare nanocrystalline ZnFe2O4 having spinel structure. Synthesized ZnFe2O4 has been analyzed using X-ray diffraction (XRD), TEM and UV-Visible spectrometry. XRD analysis indicates the single-phase of the material ZnFe2O4 , whose crystallite size was found to be 10 nm evaluated using Scherrer's equation and confirmed from TEM image. The visible-light-activated photocatalytic activity of the nanocrystalline ZnFe2O4 has been compared to P-25 degussa TiO2 reference catalyst, using a visible light for the degradation of phenol.

The preparation and EPR study of nanocrystalline ZnFe2O4

Nanocrystalline zinc oxide doped with different concentrations of Fe2O3(from 5 to 50 wt.%) has been prepared by means of coprecipitation and calcination processes. Depending on the chemical composition, phases of hexagonal ZnO, and/or cubic ZnFe2O4 were identified. The mean crystallite size of the latter phase, determined using the Scherrer's formula, varied from 8 to 12 nm. The EPR spectra for six different concentrations of Fe2O3 were recorded. A symmetrical, very intense and broad EPR resonance line has been obtained for the all the samples where the intensity strongly depended on the ratio of ZnO/Fe2O3 in the samples. The resonance field slightly shifted in the direction of lower magnetic field and the integrated intensities increased with increasing concentration of magnetic nanoparticles of ZnFe2O4, where the linewidth showed an extraordinary behaviour. The dipole-dipole interaction depended essentially on the concentration of magnetic nanoparticles.

Superparamagnetic Nanocrystalline ZnFe2O4 with a Very High Curie Temperature

Studies on the magnetic properties of nanocrystalline ZnFe2O4 synthesized by an autocombustion method are reported. Superparamagnetic behavior is observed for the nanocrystalline materials with particle sizes of 8 nm and 17 nm, with superparamagnetic blocking temperatures of 65 K and 75 K, respectively. Magnetic hysteresis with very large coercivities of 533 Oe and 325 Oe, respectively, are observed at 12 K. Studies on the temperature variation of the magnetization above room temperature indicate that the Curie temperature is as high as approximately 800 K when compared to the paramagnetic nature of bulk zinc ferrite at room temperature.

Generalized Preparation of Porous Nanocrystalline ZnFe2O4 Superstructures from Zinc Ferrioxalate Precursor and Its Superparamagnetic Property

In this paper, porous nanocrystalline ZnFe2O4 “timber-like” superstructures were synthesized through the thermal decomposition of zinc ferrioxalate precursor prepared from metal sulfates and sodium oxalate without adding any additives. The resulting ZnFe2O4 superstructures were systematically characterized by X-ray powder diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). We found that the porous nanocrystalline ZnFe2O4 superstructures exhibited superparamagnetic properties at room temperature. These porous nanocrystalline ZnFe2O4 superstructures may be applied in magnetic devices. Meanwhile, this general approach could be extended to synthesize porous nanocrystalline CoFe2O4 and NiFe2O4 “timber-like” superstructures.

Preparation and Characterization of Spinel-Type Nanocrystalline ZnFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; by Radiation Method

A new electron beam radiation method was developed to prepare spinel-type nanocrystalline ZnFe2O4 at room temperature and ambient pressure, without any kind of catalysts. The structure, morphology and size were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), infrared spectroscopy (IR). The obtained Nanocrystalline ZnFe2O4 particles have Spinel structure, spherical shape morphology and a mean particle size distribution of 20 and 40 nm.

Origin of ferromagnetism in Fe- and Cu-codoped ZnO

Fe- and Cu-codoped ZnO was previously reported as a room-temperature dilute magnetic semiconductor. We have investigated the origin of the ferromagnetism in Zn0.95−xFe0.05CuxO using the zero-field Fe57 nuclear magnetic resonance and neutron diffraction. These measurements reveal that some Fe ions of Zn0.95−xFe0.05CuxO form a secondary phase, ZnFe2O4. Detailed comparison of nuclear magnetic resonance spectra of Zn0.95−xFe0.05CuxO, bulk ZnFe2O4 with normal spinel structure, and nanocrystalline ZnFe2O4 with inverted spinel structure shows that the secondary phase possesses an inverted spinel structure and is ferrimagnetic at room temperature, while normal zinc ferrite is nonmagnetic. The ferromagnetism in Fe- and Cu-codoped ZnO stems from the secondary phase, while the majority of Fe ions substituted into the ZnO lattice appears to remain magnetically inert.

Preparation of zinc ferrite by high-energy ball-milling and microstructure characterization by Rietveld’s analysis

Nanocrystalline zinc ferrite is synthesized at room temperature by high-energy ball-milling the stiochiometric (1:1mol%) mixture of ZnO–α-Fe2O3. Nucleation of nanocrystalline Zn-ferrite particle takes place by solid-state diffusion between nanocrystalline ZnO and α-Fe2O3 particles. Both the particle size and collision temperature favors the formation mechanism. The process of mechanosynthesis of zinc ferrite at room temperature led to the formation of metastable inverse spinel structure. The formation of normal and inverse spinel structures is noticed after 30min and 2.5h ball-milling, respectively, and the degree of inversion increased with increasing milling time. The structural and microstructural evolution of ZnFe2O4 caused by milling is investigated by X-ray powder diffraction. The relative phase abundances of different phases, particle size, rms strain, lattice parameter change, etc. have been estimated from Rietveld powder structure refinement analysis of XRD data. A significant amount (wt.%) of nanocrystalline ZnFe2O4 is formed within 2.5h ball-milling with a very compressed lattice parameter. However, lattice parameter of 10h-milled sample annealed at 1273K for 1h agreed well the literature value and surprisingly, inverse spinel structure is completely absent in the annealed material. This leads to the conclusion that inverse spinel structure is a metastable one, formed under high-energy impact with a very small particle size (∼6nm) and high temperature annealing even for a shorter time is sufficient to reduce the disorderness in occupancy of tetrahedral and octahedral sites by Zn2+ and Fe3+ cations.

Ferrimagnetic ordering in nanostructured zinc ferrite

Recent investigations of nanocrystalline ZnFe2O4 have suggested that the cation distribution in this material is partially inverted and this gives rise to scope for potential technological applications [1. T. Sato, K. Haneda, M. Seki and T. Iijima. Appl. Phys. A. 50 (1990), p. 13. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (96)1]. In view of this a considerable amount of research has been done to investigate the effect of grain size on the cation distribution and magnetic properties of nanocrystalline ZnFe2O4. All these studies agree in one aspect that ZnFe2O4 is magnetically ordered with high ordering temperature and large magnetic moment. But they differ in predicting the type of magnetic ordering [2, 3, 4, 5 and 6]. In order to confirm the type of magnetic ordering and to study the effect of grain boundary and surface spins on the magnetic properties of nanostructured ZnFe2O4, we have carried out Mossbauer and magnetisation studies on nanostructured ZnFe2O4 with various grain sizes prepared by ball milling technique.

Nanocrystalline oxide zinc materials studied by the Mössbauer effect, μSR and neutron diffraction

ZnO and ZnFe2O4 were investigated in nanocrystalline form using various hyperfine techniques in conjunction with neutron diffraction and bulk magnetic measurements. For the zinc oxide, the main interest was the influence of the nanocrystalline state on lattice dynamics and on the local symmetry of the Zn atom as reflected in its quadrupolar coupling, employing the high-resolution Mossbauer resonance of 67Zn. Measurements were carried out on nanocrystalline materials with particle sizes between 4 and 25 nm. It was found that the asymmetry parameter increases drastically from η=0 in ZnO single crystals to η≈0.5 in nanostructured material, indicating an off-axis displacement of either Zn or O atoms in finite size grains. The dependences of the Lamb-Mossbauer factor on grain size and temperature are well described by a two-component model in which small crystallites are surrounded by a network of grain boundaries. For the zinc ferrite the question of changes in the magnetic properties stood in the foreground. Using the combination of techniques mentioned, the magnetic behavior of nanocrystalline ZnFe2O4, which had an average particle size of about 9 nm was compared to differently prepared crystalline samples. It was seen that the role of cation-site occupation, which changes substantially with nanocrystallinity, plays a decisive role for the magnetic properties.