Single crystalline CaFe2O4 nanospheres were synthesized by solvothermal reflux method using high boiling point organic solvents mixture. Both X-ray diffraction and electron diffraction profiles were ...confirmed single phase nature of the compound. The sample shown spherical morphology with average particle size of 10 nm which is same as crystallite size determined from the XRD. A thin layer of surfactant oleic acid was adsorbed on the surface of the nanoparticles. The optical excitation spectra reveals that the compound has direct allowed energy bandgap of 1.26 eV. The temperature dependent dielectric constant (εr′) and dielectric loss (εr″) measurements show low values at room temperature and were nominally changes with enhance of temperature upto 650 K. Above which both εr′ and εr″ were steeply increased with small variation of temperature which could be assigned to enhanced electrical conductivity due to surface charge conduction and, partially, to on-set of decomposition of oleic acid present on the surface of the sample. The samples show variable electron hopping conductivity in the temperature range studied and was supported by both Arrhenius plots and electric modulus studies at different frequencies. The CaFe2O4 nanoparticles show superparamagnetic nature at room temperature with high saturation magnetization (48.54 emu/g). The magnetization is much higher than ferrimagnetic bulk magnetization. Langevin function fit to magnetization data give 8 nm magnetic domain diameter and 1 nm magnetically disordered thin shell on the surface of the nanoparticles. As CaFe2O4 nanoparticles were electrically resistive and low dielectric loss materials, they may find applications in microwave engineering. In addition, the CaFe2O4 superparamagnetic nanoparticles were biocompatible and have high saturation magnetization, they could be used in biomedical applications such as magnetic hyperthermia and directed drug delivery applications.
Variation of dielectric constant (εrI) with temperature and Nyquist plots of CaFe2O4 nanosphere pellet. Display omitted
•CaFe2O4 nanocrystals are prepared by “solvothermal reflux” technique.•The crystallite size found to be (10 nm) from powder X-ray diffraction.•The CaFe2O4 nanosphere pellet dielectric loss increased with increasing temperature.•At 300 K CaFe2O4 nanoparticles shows superparamagnetic nature. This kind of materials useful for biomedical applications.
Colloidal size, narrow size-distributed magnetite (Fe3O4) nanospheres of 12 nm diameter were synthesized by colloidal nanocrystal synthesis protocols. X-ray diffraction and transmission electron ...microscopy studies reveal that the as-synthesized magnetite particles were single grain, spherical shaped and well crysallined in cubic spinel structure. Lattice vibrational studies confirms the existence of metal-oxide nanospheres and organic functional group (oleic acid) present on the particles surface. The nanospheres exhibits slightly enhanced energy band gap compared to counterpart bulk. The sample shows space-charge type polarization under low electric field frequencies (0.1–3 MHz) in the high temperature range (305–790 K), with Curie temperature at 713 K. Hence the dielectric constant (ε') reduces with enhance of electric field frequency. Dielectric loss (ε″) also reduces with enhance of frequency and the loss is 0.015 upto 650 K under 3 MHz. Hence it may be suitable for low loss device applications. AC electrical conductivity (σac) enhances with frequency and polaron hopping is slower than the site relaxation. Temperature dependent impedance spectra analysis reveals that grain contribution is predominant than grain boundary contribution with Debye-type relaxation. The nanospheres exhibits typical superparamagnetic behaviour with reduced saturation magnetization (Ms) due to disordered spins on the nanospheres' surface. Langevin function fit gives 10.5 nm magnetic domain diameter in the nanospheres.
Display omitted
•Fe3O4 nanoparticles are synthesized by “colloidal nano-crystal synthesis” technique.•The particles size found to be (12 nm) from transmission electron micrographs.•Low dielectric loss of 0.015 is suitable for low noise device application.•The lowest Curie transition temperature (Tc) of 713 K is reported.•At room temperature Fe3O4 nanoparticles shows superparamagnetic nature.
•Site selective Cu2+ substitution is achieved in Fe1−xCuxFe2O4 single crystal nanoparticles.•Diffusion coefficient of metal cations were enhanced in low viscous boiling organic solvents.•Exothermic ...crystal lattice energies were removed by natural gas bubbles formed in the reflux solvents mixture.•The HRTEM micrographs show that single crystals are well crystallined up to the edge of the nanospheres.•Crystal structure, and magnetic studies confirms the selective octahedral site substitution of Cu2+ in Fe3O4.
Transition metal cations distribution among tetrahedral and octahedral sites in Fe3O4 has profound influence on it properties. The cations distribution among these sites were influenced by crystal field stabilization energy (CFSE) of a substituent ion. It was reported that Cu2+ substitutes both Fe3+ in tetrahedral and Fe2+ in octahedral sites of magnetite though it has high CFSE for octahedral sites. Thus it promotes mixed (normal & inverse) spinel structure and hence the properties deviate from the prediction. Here we show that selective octahedral site substitution of Fe2+ by Cu2+ in single crystal Fe3O4 nanoparticles was possible by solvothermal reflux method at moderate temperatures (≈300°C). It was attributed to reduced energy barrier for crystallization and high diffusion coefficient of the metal cations at moderate temperature in low viscous organic solvents mixture, at ambient pressure, compared to coprecipitation and solid state reaction protocols. In addition, effective removal of exothermic crystal lattice energy, released during nucleation and growth process, by natural gas bubbles formed in the reflux organic solvent mixture. This promotes effective diffusion of cations during the growth process and easy octahedral occupation by Cu2+ in Fe1−xCuxFe2O4 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5 & 0.6) single crystal nanospheres. The octahedral substitution was confirmed by reduction of crystal lattice parameter as well as ferromagnetic strength of octahedral sublattice with enhanced Cu2+ concentration. In addition, morphology, lattice vibrational frequency and electron excitation spectra of the nanospheres were studied. The Langevin function fit analysis reveals that superparamagnetic domain diameter were slightly less than the particle diameter obtained from TEM micrograph.
Biocompatible Mg1−xZnxFe2O4 (x=0.2, 0.4, 0.5, 0.6 & 0.8) nanoparticles were synthesized by solvothermal reflux method. All compounds were crystallized in cubic spinel structure with slightly enhance ...of lattice parameter with biocompatible substituent Zn2+ concentration. All compounds were shown spherical geometry with average particle diameter is around 12nm (colloidal size). The spinel structure formation was confirmed by X-ray diffraction,electron diffraction, infrared, Raman shift measurements. Infrared analysis shows oleic acid coating on the surface of nanoparticles and TGA analysis shows that oleic acid desorbs from nanoparticle by decomposition at around 400°C. UV-Vis-NIR spectra show all the compounds show energy band gap in the semiconductor range (≈ 1.9eV). All compounds show superparamagnetic characteristics at room temperature with enhanced saturated mass magnetization (Ms) with Zn2+ concentration up to x=0.5 and then reduces with further enhance of x up to 0.8. The Ms changes were ascribed to occupation of Zn2+ at tetrahedral sites and proportional enhance of Fe3+ at octahedral sites. The enhanced Fe3+ concentration at octahedral sublattice leads to formation Fe3+-O2−-Fe3+ networks which favor antiferromagnetic interactions due to superexchange phenomenon. Photocatalytic activity of all compounds were studied through methylene blue (MB) degradation analysis. All compounds show ≈ 96% degradation of MB upon 70min irradiation of light on photoreactor vessel. In addition, photocatalytic activity (degradation efficiency) enhances with Zn2+ concentration in MgFe2O4. The Zn2+ substitution enhances both Ms and photocatalytic activity biocompatible of MgFe2O4 nanoparticles.
Display omitted
•Mg1−xZnxFe2O4 (x=0.2, 0.4, 0.5, 0.6 and 0.8) nanoparticles are synthesized by “solvothermal reflux” method.•The particle sizes are found to be 11–12nm from transmission electron micrographs.•The lattice parameter (a) increases with an increase in Zn content and obeying Vegards law.•At room temperature Mg1−xZnxFe2O4 (x=0.2, 0.4, 0.5, 0.6 and 0.8) nanoparticles shows superparamagnetic nature.•The synthesized nanoparticles structure and crystallinity effect shows photocatalytic activity degradation of methylene blue.
Spinel ferrites at nanoscale showed quite different properties rather than the bulk counterpart. Among all the ferrites, ZnFe
2
O
4
compound is chemically stable and showed very good properties at ...room temperature. In this investigation, we reported the synthesis and characterization of ZnFe
2
O
4
single-phase crystals of diameter 11 nm by solvothermal reflux method. Temperature-dependent dielectric constant, dielectric loss, and ac-electrical conductivity of the pellet were measured up to 450 °C under different alternating electric field frequencies from 1 kHz to 1 MHz. The obtained data revealed interfacial or space charge polarization mechanism. Furthermore, the sample showed superparamagnetic nature at room temperature. In addition, the magnetic hyperthermia value and specific heat generation rate (SHGR) of 128.76 J s
−1
g
−1
for ZnFe
2
O
4
compound at 1 mg mL
−1
concentration were evaluated. The data were interpreted by spin-relaxation mechanism. ZnFe
2
O
4
nanoparticles showed good photocatalytic activity under UV light irradiation. The data were interpreted by electron–hole pair and radical formation and degradation of Rhodamine B dye.
•Selective octahedral site substitution of Mg2+ is achieved in Fe1−xMgxFe2O4 (x=0, 0.1, 0.2, 0.3, 0.4 & 0.5) single crystal nanospheres of diameter ∼10nm.•Magnetic susceptibility enhances with Mg2+ ...concentration whereas saturation mass magnetization decrease with increase of Mg2+ content.•The HRTEM micrographs show that single crystals are well crystallined up to the edge of the nanospheres.•Magnetic hyperthermic power or specific heat generation rate of the magnetic material enhances with magnetic susceptibility as well as Mg2+ concentration. The Fe0.5Mg0.5Fe2O4 compound shows heat generation rate of 22.4W per gram compound.
Majority studies on magnetic hyperthermia properties were carried out by modifying the saturation mass magnetization (Ms) of the samples. Here efforts were made to enhance the specific heat generation rate (SHGR) of single domain superparamagnetic (SP) material by modifying its magnetic susceptibility. Well crystallined, inverse spinel structured and close to monosize Fe1−xMgxFe2O4 (x=0, 0.1, 0.2, 0.3, 0.4, & 0.5) compounds with nanosphere geometry (diameter 10nm) were synthesized by solvothermal reflux method at ≈300°C. In the literature it is reported that magnesium ferrites synthesized at high temperatures yield mixed (normal & inverse) spinel structures. The inverse spinel structure was confirmed by X-ray powder diffraction (XRPD), lattice vibrations and magnetic characteristics of the compounds. The Ms of the compounds decrease with increase of substituent Mg2+ concentration. Under high excitation energy the inter-valance charge transfer whereas under low excitation energy the intra-valance charge transfer process were predominant. The as-synthesized nanospheres were encapsulated by hydrophobic oleic acid and were exchanged by hydrophilic poly(acrylic acid) by chemical exchange process. Estimated magnetic hyperthermia power or SHGR of the x=0, 0.3 & 0.5 were 11, 11.4 & 22.4W per gram of respective compounds, respectively, under 63.4kAm−1 field amplitude and 126kHz frequency. The SHGR enhances with Mg2+ concentration though its Ms reduces and is attributed to reduced spin-orbital coupling in the compounds with enhanced Mg2+ concentration. This may pave a new way to develop magnetic hyperthermia material by modifying magnetic susceptibility of the compounds against to the reported Ms modification approach. The obtained high SHGR of the biocompatible compounds could be used in magnetic hyperthermia applications in biomedical field.
Biocompatible magnetic semiconductor Zn1−xMgxFe2O4 (x=0, 0.1, 0.3, 0.5 & 0.7) nanoparticles of around 10nm diameter were synthesized by solvothermal reflux method. The method produces well separated ...and narrow size distributed nanoparticles. Crystal structure, morphology, particles surface properties, surfactant quantity, colloidal stability, magnetic properties and photocatalytic properties of the synthesized nanoparticles were studied. Different characterizations confirmed that all compounds were single crystals and superparamagnetic at room temperature. Saturation mass magnetization (Ms=57.5emu/g) enhances with substituent Mg2+ concentration due to promotion of mixed spinel (normal and inverse) structure. Photocatalytic activity of all synthesized magnetic semiconductor nanoparticles were studied through methylene blue degradation. The degradation of 98% methylene blue was observed on 60 min irradiation of light. It is observed that photocatalytic activity slightly enhances with substituent Mg2+ concentration. The synthesized biocompatible magnetic semiconductor nanoparticles can be utilized as photocatalysts and could also be recycled and separated by applying an external magnetic field.
Display omitted
•Biocompatible Zn1−xMgxFe2O4 (x=0 to 0.7) nanoparticles are synthesized.•All samples show narrow size distribution with particle sizes around 10nm.•Saturation mass magnetization (Ms) enhances with enhancing of Mg content.•At 300K, Mg-doped ZnFe2O4 nanoparticles shows superparamagnetic nature.•All samples’ MB degradation efficiencies increase from 95% to 98% with Mg content.
In this study, NiFe
2
O
4
nanocrystals were prepared by solvothermal reflux method. The average crystallite size was found to be 9 nm by X-ray powder diffraction analysis. Selected area electron ...diffraction profile confirms the crystallinity behavior of the compound. Nanocrystals’ surface of the metal oxide and organic functional groups confirm the lattice vibrational studies. Temperature-dependent dielectric constant (
ε
′) and dielectric loss (
ε
″) analyses show small values at low temperature and high values at high temperature at different frequencies. Nyquist plot shows non-Debye type of relaxation up to 350 °C, and above 360 °C the plot reveals a Debye type of relaxation. The saturation magnetization of the obtained powder sample is 46.86 emu/g which is lower than that of bulk NiFe
2
O
4
. Specific absorption rates (SAR) of sample at two different concentrations were estimated using commercial induction heating system at a field of 235.2 Å and frequency of 316 kHz.
The development of monosize superparamagnetic nanoparticles (NPs) with high saturation mass magnetization (M
s
) and colloidal stability are required for advanced biomedical as well as electronic ...applications. Here we report synthesis, phase formation, morphology, magnetic and colloidal stability studies of monodisperse, single crystallined Zn
1−x
Co
x
Fe
2
O
4
(x = 0, 0.1, 0.3, 0.5 and 0.7) superparamagnetic NPs. Monodisperse NPs were synthesized by solvothermal reflux method through homogeneous nucleation and self focused growth protocols using quickly decomposable organic metal complex precursors and organic surfactant. All synthesized compounds show cubic mixed spinel structure with monodisperse spherical morphology. X-ray diffraction, electron diffraction, FTIR and Raman spectra analysis reveals that the ferrites are single phase compounds. However, the cubic lattice parameter reduces with enhance of Co
2+
concentration due to small ionic radius compared to Zn
2+
. The Zeta potential studies shows that NPs form a stable dispersion in a nonpolar solvent at room temperature. The M
s
enhances from 50.4 to 61.2 emu/g with substituent Co
2+
concentration x = 0 to x = 0.7 in compounds. Enhanced magnetic properties may be useful in the fabrication of self assembled 2D layered electronic devices and biomedical applications such as drug delivery, magnetic contrast agents, magnetic hyperthermia materials.
Spinel ferrite nanoparticles are widely studied to evaluate their suitability in many applications. Magnetic, electrical, optical, and catalytic properties of spinel ferrites nanoparticles depend on: ...i) intrinsic property such as cation distribution among tetrahedral (A-site) and octahedral ligand (B-site) sublattices in spinel structure and ii) extrinsic properties such as specific surface area and particle size distribution of nanoparticles. To enhance the above properties by modifying both the intrinsic and extrinsic parameters, narrow size distributed Mg 0.7 Zn 0.3 Fe 2 O 4 mixed spinel ferrite nanoparticles are synthesized by the solvothermal reflux method using high boiling point reflux solvents. The particles are crystallized in a cubic spinel structure and are single crystallites with an average particle diameter of 12 nm, measured from an electron micrograph. The temperature-dependent dielectric constant <inline-formula> <tex-math notation="LaTeX">(\varepsilon^{\prime}) </tex-math></inline-formula> and dielectric loss <inline-formula> <tex-math notation="LaTeX">(\varepsilon^{\prime \prime}) </tex-math></inline-formula> of the sample show no change below 290 °C and increase with temperature up to 450 °C. Both <inline-formula> <tex-math notation="LaTeX">\varepsilon^{\prime} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">\varepsilon^{\prime} </tex-math></inline-formula> decrease with the increase of electric field frequency and shows dominant space charge polarization at grain boundaries. The DC conductivity estimated from impedance spectra (Cole-Cole plot) shows the Arrhenius model electron hopping conductivity mechanism above 390 °C. Nanoparticles show high Ms (57.41 emu/g) than that synthesized by other methods. The sample shows the magnetic hyperthermia value of 189 W/g at 1 mg/mL concentration. The sample degraded 95% of rhodamine B dye in water in 320 min under UV light illumination. Some of these properties are superior to Mg 0.7 Zn 0.3 Fe 2 O 4 nanoparticles synthesized by other wet chemical and/or ball milling methods.
