Search

The photodegradation of oxytetracycline (OTC) antibiotic by Zn0.94M0.06O (M: Mn, Fe, Co, Ni, Cu and Zn) nanoparticles was investigated using a 100 W visible-light irradiation source. The creation of intrinsic defects, due to doping, reduced the electron–hole recombination and led to a photocatalytic efficiency of 81.65% for pure ZnO sample. The Ni and Cu doped nanoparticles showed the highest (87.50%) and lowest (39.76%) efficiency. The presence of inherent defects in the crystalline structure play an important role in the photocatalytic process, so that in Ni-doped sample, the interstitial zinc and nickel atoms, and oxygen vacancies enhance the degradation efficiency through electron–hole separation. Moreover, the presence of CuO phase eliminated the excitons and dramatically reduced the degradation efficiency in Cu doped sample. On the other hand, the NiO formed in the Ni@ZnO prevented electron–hole recombination and increased photocatalytic efficiency. Besides the doping, the morphology of the samples including surface area and particle size showed a noticeable contribution in the degradation process. The smaller particles showed higher efficiency, while by increasing the size, the degradation efficiency reduced dramatically. [ABSTRACT FROM AUTHOR]

Superparamagnetic manganese ferrite nanoparticles with mean size of = 6.5(±1.5) nm were synthesized through a solvothermal method using Tri-ethylene glycol as a solvent. The peak temperature of zero field cooled measurements of magnetization and AC magnetic susceptibility curves shifted toward higher temperatures by applying different pressures from 0 to 1 kbar and increasing the powders compaction. The frequency dependence of AC susceptibility measurements indicated the presence of weak dipole-dipole interactions between nanoparticles. By increasing the powders compaction and interactions strength, the coercive field (Hc) increased and squareness (Mr/Ms) decreased. The obtained effective anisotropy constant (Keff ), by susceptibility measurements, was from 1.72 x 106 to 2.36 x 106 ergs/cm³ for pressure of 0 to 1 kbar. These values are larger than those obtained from hysteresis loops at 5K (0.14 x 106 to 0.34 x 106 erg/cm³). Also, the Keff was two orders of magnitude greater than that of bulk MnFe2O4. Size, surface effects, and total energy barrier between equilibrium states were reported as the main causes of large anisotropy. Below 75 K, a signature of weak surface spin glass was observed. However, memory effect experiment indicated that there is no collective superspin glass state in the samples. This study suggests the role of powders compaction on properties of a magnetic nanoparticles system. Furthermore, the coercivity, the anisotropy constant, and the blocking temperature are affected by changing nanoparticles compaction. [ABSTRACT FROM AUTHOR]

A series of phase separated La0.5Ca0.5MnO3 manganite samples with different grain sizes were studied by ac susceptibility, direct magnetocaloric effect (ΔT), and heat capacity measurements. The ac susceptibility shows that fractions of ferromagnetic and antiferromagnetic phases and consequently the phase separated state can be controlled by means of sintering temperature. Lower sintering temperature leads to a ferromagnetic state, while higher sintering temperature increases antiferromagnetic phase fraction, resulting in a phase separated state. In the phase separated samples, ΔT shows a conventional positive peak near TC and an anomalous positive peak at lower temperature near TN. The anomalous positive peak appears at higher magnetic field and is accompanied with thermal hysteresis. It is suggested that the anomalous magnetocaloric behaviors result from phase separation and first order magnetostructural phase transition. This study shows that direct magnetocaloric effect is a useful technique for the study of manganites. [ABSTRACT FROM AUTHOR]

Manganese ferrite, MnFe 2 O 4 nanoparticles with average size of ∼6.5 nm were synthesized by using a thermal decomposition method. The nanoparticles were aggregated which was confirmed by FESEM and TEM images. The aggregates with a diameter of ∼50 nm showed interacting superspin glass (SSG) behavior. The powders were dispersed in the molten paraffin wax by using ultrasonic bath. Samples with different paraffin/ferrite weight ratios of P / F = 0, 1, 5, 10 and 20 were prepared. M – H curves of the samples revealed presence of superparamagnetic state at 300 K. Saturation magnetization ( M s ) decreased from 26.6 to 1.3 emu/g by increasing the P / F value from 0 to 20, respectively. Furthermore, the VSM measurements showed a decrease in surface spin disorder of paraffin-embedded nanoparticles in comparison with bare particles. The AC magnetic susceptibility peak temperature, T P increased from 230 to >300 K with increasing the paraffin content in the samples. The present study showed that by dispersing the particles in a non-magnetic matrix, the blocking temperature could be increased. [ABSTRACT FROM AUTHOR]

The effect of dipole-dipole and exchange interactions on dynamics of superspins in a system of MnFeAgO (where x = 0, 0.1, 0.2, 0.3, and 0.6) nanoparticles has been studied by Ac magnetic susceptibility measurements. Average crystallite size of samples was estimated to be ~7 to ~4 nm, with respect to the doping level of x = 0-0.6. It was found that the nanoparticles are superparamagnetic at room temperature with almost zero coercivity. Saturation magnetization of samples showed a remarkable reduction by increasing non-magnetic Ag doping level. By decreasing the temperature, a transition to frustrated superspin glass state was observed in all samples. Freezing temperatures of superspins were decreased by increasing the Ag content, as a result of decreasing size of crystallites, magnetization of nanoparticles, and consequently weakening of dipole-dipole interactions. The estimated values of zυ, τ, and T, using critical slowing down model, justify the observed variation of freezing temperatures. Furthermore it was realized that sensitivity of samples to the variation of applied frequency, an important parameter in hyperthermia based therapy, is affected by magnetic interactions between nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we report structural and magnetic properties of Fe3O4 nanoparticles synthesized by thermal decomposition of ball milled iron nitrate and citric acid in N2 and air ambient. The XRD pattern of samples which are prepared in air shows some impurity phases, while the samples synthesized in the N2 atmosphere are almost pure Fe3O4 phase. The result shows that by increasing the particle size, the magnetization of the samples increases. The increase of magnetization by increasing the particle size could be attributed to the lower surface spin canting and surface spin disorder of the larger magnetic nanoparticles. The results of ac magnetic susceptibility measurements show that the susceptibility data are not in accordance with the Néel -Brown model for superparamagnetic relaxation, but fit well with conventional critical slowing down model which indicates that the dipole-dipole interactions are strong enough to cause superspin-glass like phase in these samples. [Copyright &y& Elsevier]

Abstract: Nanosized MnFe2O4 ferrites were synthesized by a simple method, which is based on the solid state ball-milling and calcinations of nitrate precursors and citric acid. The samples were characterized by using different methods. The results indicate that the products mainly consist of MnFe2O4 nanoparticles. The effect of different annealing temperatures on particle sizes and crystallinity of the samples was also studied. By increasing the particle size, the coercivity and magnetization of the samples increase. The increase of magnetization by increasing the crystallite size could be attributed to the lower surface spin canting and surface spin disorder of the larger magnetic nanoparticles. Our analysis of ac susceptibility measurements shows that the interparticle magnetic interaction leads to the superspin glass-like behavior in these nanoparticle samples. [Copyright &y& Elsevier]

Abstract: In this study, the effect of Ti substitution on structural, electrical and magnetic properties of La0.8Sr0.2Mn1−x Ti x O3 () are investigated by XRD, electrical resistivity and ac susceptibility measurements. The XRD refinement result indicates that the lattice parameters and volumes increase by an increase of the Ti doping level. The resistivity measurement results show that by increasing the Ti doping level, the metal insulator transition temperatures decrease and system becomes an insulator. The paramagnet–ferromagnet transition temperature, also decreases as the Ti content increases. The reentrant spin glass (RSG) state exists in the and 0.075 samples. The RSG behavior is mainly ascribed to an increase of disorder in the FM matrix induced by the random Ti impurity substitution. [Copyright &y& Elsevier]

In this investigation, the effect of Lanthanum vacancy on the structural, electrical and magnetic properties of La1-xMnO3+δ manganite (x=0, 0.05) was studied. Decreasing La3+ amount in samples led to creation of some Mn4+ cations. By increasing the Mn4+ content in atomic structure of samples, double exchange interaction was strengthened. Results of Ac magnetic susceptibility measurements indicated that both samples (x=0, 0.05) have spin glass-like behavior at low temperatures. Electrical transport measurements showed a decrease in resistivity of samples, which can be attributed to variation in Mn3+ to Mn4+ ratio and different kinds of magnetic interactions in the samples. Furthermore, it was shown that fast cooling (FC) is an appropriate method in controlling the oxygen of samples. The samples prepared by FC method showed similar properties with stoichiometric La1-xMnO3. [ABSTRACT FROM AUTHOR]

Abstract: Structural, magnetic, and electrical properties of the La0.8− x Sm x Sr0.2MnO3 (0⩽ x ⩽0.45) manganites prepared by a solid-state reaction technique was studied systematically. It was found that with increase in the Sm content, the crystal structure transformed from rhombohedral (x <0.3 samples) to orthorhombic (x >0.3 samples). The ac magnetic susceptibility measurements show that all samples undergo a transition from paramagnetic (PM) to ferromagnetic (FM) phase at the Curie temperature, TC , which decreases from 296K down to 165K with increase in the Sm doping level from x =0 to x =0.45. In addition, the glassy state exists in the x =0.15–0.45 samples, which is stronger in higher doped compounds (x =0.30 and x =0.45). This behavior indicates that the substitution of Sm weakens the double exchange (DE) process. The field dependence of magnetization for the samples shows a soft FM nature with a small hysteresis loop and a low coercive field, Hc , for the doped samples. The irreversibility in the magnetization for increasing and decreasing the applied field is due to the glassy behavior observed in highly doped samples. The temperature dependence of resistivity, ρ(T), measurement indicates that by increasing the Sm doping level, the metal–insulator transition temperature decreases, and the heavily doped samples become insulators. The metallic region of the ρ(T) curve for the x =0–0.10 samples was fitted with the model of electron–electron and electron–magnon scattering, while the insulating region was fitted with the small polaron hopping (SPH) at T > θD /2 (θD , Debye temperature) and the variable range hopping (VRH) models at T < θD /2. [Copyright &y& Elsevier]

A magnetic perovskite-spinel oxide nanocomposite synthesized through a sol-gel self-combustion process is used for the first time as an adsorbent to remove toxic heavy metals (i.e., Pb 2+ ). The synthesized LaFeO 3 :CoFe 2 O 4 ((LFO) 1 :(CFO) x ) (x = 0.11-0.87) nanocomposites possess good stability, abundant oxygenated active binding sites, and unique structural features, making them suitable for removing divalent Pb 2+ ions. Scanning electron microscopy, X-ray diffraction, BET surface area, magnetization measurements, zeta-potential analyses, and X-ray photoelectron spectroscopy were used to analyze the nanocomposites, and their structural changes after Pb 2+ ions adsorption. Batch tests confirmed that (LFO) 1 :(CFO) x efficiently removes Pb 2+ from water with a maximum adsorption capacity of 105.96 mg/g. The detailed quantitative study indicates that the interaction of hydroxyl groups with Pb 2+ ions occurs through electrostatic interactions and complex formation. We also demonstrate a new ring-magnetic separator system that allows magnetic separation of the toxic ions at a higher speed compared to traditional block magnets. The unique structure, high porosity, large specific surface area, and oxygenated functional groups of (LFO) 1 :(CFO) x nanocomposites make them promising materials for removal of heavy metal ions and possibly other environmental pollutants. This study provides a new approach to preparing nanocomposites of magnetic spinel ferrites with perovskite oxides for environmental applications., (© 2024. The Author(s).)

In this study, Fe 3 O 4 /activated carbon nanocomposite was successfully synthesized for removal of Chromium from aqueous solutions. The Fe 3 O 4 nanoparticles were decorated on vine shoots-derived activated carbon using co-precipitation method. The atomic absorption spectrometer was used to evaluate the removal of Chromium ions by the prepared adsorbent. The effect of various parameters such as adsorbent dose, pH, contact time, reusability, electric field, and initial Chromium concentration were examined to find the optimum conditions. According to the results, the synthesized nanocomposite showed a high ability to remove Chromium at an optimized pH of 3. At optimum conditions, a high removal efficiency of 90% and an excellent adsorption capacity of 305.30 mg/g was obtained. In addition, adsorption isotherms and adsorption kinetics were studied in this research. The results showed that the data are well fitted with the Freundlich isotherm and the adsorption process is spontaneous and follows the pseudo-second-order model., (© 2023. The Author(s).)

Developing ultrabroad radar-infrared compatible stealth materials has turned into a research hotspot, which is still a problem to be solved. Herein, the copper sulfide wrapped by reduced graphene oxide to obtain three-dimensional (3D) porous network composite aerogels (CuS@rGO) were synthesized via thermal reduction ways (hydrothermal, ascorbic acid reduction) and freeze-drying strategy. It was discovered that the phase components (rGO and CuS phases) and micro/nano structure (microporous and nanosheet) were well-modified by modulating the additive amounts of CuS and changing the reduction ways, which resulted in the variation of the pore structure, defects, complex permittivity, microwave absorption, radar cross section (RCS) reduction value and infrared (IR) emissivity. Notably, the obtained CuS@rGO aerogels with a single dielectric loss type can achieve an ultrabroad bandwidth of 8.44 GHz at 2.8 mm with the low filler content of 6 wt% by a hydrothermal method. Besides, the composite aerogel via the ascorbic acid reduction realizes the minimum reflection loss (RL min ) of - 60.3 dB with the lower filler content of 2 wt%. The RCS reduction value can reach 53.3 dB m 2 , which effectively reduces the probability of the target being detected by the radar detector. Furthermore, the laminated porous architecture and multicomponent endowed composite aerogels with thermal insulation and IR stealth versatility. Thus, this work offers a facile method to design and develop porous rGO-based composite aerogel absorbers with radar-IR compatible stealth., (© 2022. The Author(s).)

Recent advances in the field of magnetic materials emphasize that the development of new and useful magnetic nanoparticles (NPs) requires an accurate and fundamental understanding of their collective magnetic behavior. Studies show that the magnetic properties are strongly affected by the magnetic anisotropy of NPs and by interparticle interactions that are the result of the collective magnetic behavior of NPs. Here we study these effects in more detail. For this purpose, we prepared Co x Fe 3- x O 4 NPs, with x = 0-1 in steps of 0.2, from soft magnetic (Fe 3 O 4 ) to hard magnetic (CoFe 2 O 4 ) ferrite, with a significant variation of the magnetic anisotropy. The phase purity and the formation of crystalline NPs with a spinel structure were confirmed through Rietveld refinement. The effect of Co doping on structure, morphology and magnetic properties of Co x Fe 3- x O 4 samples was investigated. In particular, we examined the interparticle interactions in the samples by δ m graphs and Henkel plots that have not been reported before in literature. Finally, we studied the hyperthermia properties and observed that the heat efficiency of soft Fe 3 O 4 is about 4 times larger than that of hard CoFe 2 O 4 ferrite, which was attributed to the high coercive field of samples compared with the external field amplitude.

The effect of cobalt doping on the magnetic properties of Mn 1- x Co x Fe 2 O 4 nanoparticles was investigated. All samples consist of ensembles of nanoparticles with a spherical shape and average diameter of about 10 nm, showing small structural changes due to the substitution. Besides having the same morpho-structural properties, the effect of the chemical composition, i.e., the amount of Co doping, produces marked differences on the magnetic properties, especially on the magnetic anisotropy, with evident large changes in the coercive field. Moreover, Co substitution has a profound effect on the interparticle interactions, too. A dipolar-based interaction regime is detected for all samples; in addition, the intensity of the interactions shows a possible relation with the single particle anisotropy. Finally, the sample with the strongest interaction regime shows a superspin glass state confirmed by memory effect dynamics.