Pure MnFe2O4 Research Articles

Sono-assisted rapid adsorption of anionic dye onto magnetic CaFe2O4/MnFe2O4 nanocomposite from aqua matrix

In this research the proficiency of a novel magnetic calcium ferrite and manganese ferrite nanocomposite (CF-MF-NC) was evaluated for adsorptive sequestration of Eriochrome black T (EBT) dye coupled with the ultrasonic irradiation. CF-MF-NC exhibits saturation magnetization of 38.17 emu/g, BET surface area of 47.67m2/g, and average pore diameter of 10.17 nm, which makes it a potential magnetic nano-scale adsorbent. The CF-MF-NC has shown superior adsorptive performance (~88%) towards EBT dye as compared to pure CaFe2O4 (~64%) and MnFe2O4 (~52%) and this may be due to the higher surface reactivity, and enhanced physicochemical properties of the composite. The pseudo-second order kinetic model could explain the sono-assisted adsorption of EBT dye onto CF-MF-NC and the involvement of ultrasound enhanced the diffusion rate. Performance evaluation study reveals that sono-assisted EBT dye adsorption onto CF-MF-NC was superior (~98% of EBT dye removal) to conventional adsorption process with batch stirring (78.33%) and shaker (84.34%).

MnFe2O4-coated carbon nanotubes with enhanced microwave absorption: Effect of CNT content and hydrothermal reaction time

Carbon nanotubes (CNT) coated with magnetic nanoparticles are promising microwave absorbing materials with high performance. Despite several previous investigations, the relationship between intrinsic composition and preparation conditions of this composite material to its microwave loss mechanisms and absorbing properties have not yet been fully understood. We present a convenient and cost-effective hydrothermal method to deposit crystalline manganese iron oxide (MnFe2O4) over CNT. Adjusting the hydrothermal reaction time and CNT content allows control over the microstructure of the resulting CNT-MnFe2O4 nanocomposite and its microwave absorbing properties, resulting in a better microwave absorber than pure MnFe2O4. Composites synthesized at 150 °C for 10 h with 10 wt% CNT reveal a reflection loss as high as −38 dB at 5.7 GHz for an absorber thickness of 5 mm and frequency bandwidth (RL < −10 dB) up to 3.59 GHz. As the hydrothermal reaction time is reduced to 1 h, the minimum reflection loss increases significantly to −41 dB at 11.8 GHz for a 2 mm coating thickness. Defects and functional groups on the surfaces of CNT act as nucleation sites for MnFe2O4 and help reduce agglomeration, which decreases overall particle size. Microwave absorbing mechanisms are also discussed. Coating CNTs with manganese iron oxide increases microwave dissipation by enhancing conduction loss, interface polarization, relaxation polarization, and magnetic loss, including the contributions of eddy current and natural resonance, which are all related to the reaction time and CNT content. Consequently, the synthesis-property relationship could potentially be used to design CNT-based nanomaterials that have more effective microwave absorption.

Facile Preparation of Iron-Manganese Oxide@Diatomite Composite for Effective Removal of Vanadium from Wastewater

Excess pentavalent vanadium(v) has severely degraded water quality and posed a huge threat to human health over the past several decades. Hence, it’s urgent and significant to explore a novel adsorbent which is low cost and efficient to treat vanadium pollution. In this work, a novel iron-manganese oxide@diatomite (MnFe2O4@DE) adsorbent with superior removal performance for simulated vanadium(v) wastewater was synthesised via a facile hydrothermal method. The as-prepared MnFe2O4@DE composite was characterised through different characterisation techniques. The results indicated that the MnFe2O4 nanoparticles were uniformly deposited on the surface of diatomite, resulting in a larger specific surface area and pore volume of the composite. In addition, the MnFe2O4@DE adsorbent exhibited the highest adsorption capacity for vanadium(v) (18.37mgg−1±0.5%), which was up to around 13.24 and 1.33 times as much as that of pure diatomite and MnFe2O4, respectively. This is mainly attributed to the enhanced specific surface area and pore volume. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis demonstrated vanadium(v) could be reduced to low valence vanadium with low toxicity by the MnFe2O4@DE composite which could exist as VO2+ and VO+ cations in solution. The adsorption process was better fitted with a pseudo-second-order kinetic model and Langmuir model, which is spontaneous and endothermic. Overall, the novel MnFe2O4@DE composite could be applied as a promising adsorbent in addressing vanadium pollution issues due to its properties of low cost, effectiveness, and environmental friendliness.

Novel magnetic MnO2/MnFe2O4 nanocomposite as a heterogeneous catalyst for activation of peroxymonosulfate (PMS) toward oxidation of organic pollutants

Novel magnetic MnO2/MnFe2O4 nanocomposite was successfully fabricated by hydrothermal method. Subsequently, this nanocomposite was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microcopy (TEM), X-ray photoelectron spectra (XPS), vibrating sample magnetometer (VSM) and Brunauer-Emmett-Teller (BET) measurements. Then the material was applied to activate PMS for Rhodamine B (Rh B) degradation. The results displayed that the decomposition efficiency of the MnO2/MnFe2O4 nanocomposite with a mole ratio of 7:1 was 90% for Rh B within 5 min in the presence of PMS, higher than other MnO2/MnFe2O4 ratio, homogeneous catalysts (Fe3+ and Mn2+), pure MnO2 and pure MnFe2O4. In addition, influences of pivotal factors (PMS concentration, catalyst dosage and initial pH value), performance of different processes and reusability of MnO2/MnFe2O4 nanocomposite were also evaluated. Radical scavenging experiments were conducted and SO4− was indicated as the primary radical. What’s more, the MnO2/MnFe2O4 nanocomposite could be convenient to recycle in practical application benefited from its magnetism. Finally, according to the results and previous studies, the believable mechanism of activating PMS by MnO2/MnFe2O4 nanocomposite was put forward, which could occupy an important position as a fast treatment option in sewage disposal.

Synthesis of magnetic CuO/MnFe2O4 nanocompisite and its high activity for degradation of levofloxacin by activation of persulfate

Magnetic CuO/MnFe2O4 nanocomposite were synthesized and characterized as a heterogeneous catalyst. Subsequently, it was used to activate persulfate (PS) for levofloxacin (LVF) removal with the operating parameters optimized. Results reveled that the sample of CuO/MnFe2O4-9% showed higher catalytic performance than pure CuO, pure MnFe2O4 and other fabricated CuO/MnFe2O4 nanocomposites. And under the optimized conditions of 1 g·L−1 CuO/MnFe2O4-9% and PS at pH 9 and 25 °C, 91.3% of LVF could be decomposed within 120 min. Besides, the underlying mechanism of CuO/MnFe2O4 nanocomposite activating PS was proposed by free radical quenching experiment and XPS results. Eventually, several degradation intermediates of LVF were identified and three decomposition pathways were proposed. Especially, the CuO/MnFe2O4 nanocomposite exhibited superparamagnetic property and good stability, which favored the catalyst to be efficiently recovered through the applied magnetic field and reused from aquatic environment. Thus, the as-prepared CuO/MnFe2O4 nanocomposite might be applied to the removal of refractory organics in environmental remediation.

A further investigation on the MnO2-Fe2O3 system roasted under CO-CO2 atmosphere

Investigations on the MnO2-Fe2O3 system roasted in air has been reported in our previous work. This study further investigated the MnO2-Fe2O3 system roasted under CO-CO2 atmosphere. Extensive investigations were concentrated on the reduction of simplex iron oxides or manganese oxides, and little attention were paid on the reduction of MnO2-Fe2O3 system regarding to interactive reactions between them. In this work, it was found that spinel-type MnxFe3−xO4 with high magnetism formed easily under CO-CO2 atmosphere. The reduction and thermodynamic analyses of pure MnFe2O4 were also researched to better understand the reduction behaviors of MnO2-Fe2O3 system. Phase study showed that a series of Mn-Fe composite oxides, including MnxFe3−xO4 and (MnO)y(FeO)1−y, generated during the reduction of MnO2-Fe2O3 system. MnxFe3−xO4 was readily generated under CO content of 2.5–25 vol% at 1000 °C. With further increase of CO content, MnxFe3−xO4 was reduced to (MnO)y(FeO)1−y and then to MnO and metallic iron. Reduction of manganese oxides, iron oxides and manganese ferrites happened concurrently during the reduction of MnO2-Fe2O3 system. And the reduction of MnO2, Fe2O3, Fe3O4 and MnFe2O4 were compared by TG and thermodynamic analyses. In addition, the morphology evolution and magnetism change of the MnO2-Fe2O3 system reduced under different CO contents were also studied.

Synthesis and Enhanced Photocatalysis of Magnetic Reduced Graphene Oxide-MnFe2O4 Nanohybrids

Background: The hybrid photocatalysts constructed with various semiconductor and graphene can show dramatically enhanced photocatalytic activities. The separability of a photocatalyst from degraded pollutant aqueous solution is very important in some cases. Objective: The magnetic MnFe2O4 nanoparticles and reduced graphene oxide were used to construct magnetically separable (rGO)-MnFe2O4 hybrids with high photo- catalytic properties. Method: The pure MnFe2O4 nanoparticles and rGO/MnFe2O4 hybrid photocatalysts were synthesized with a facile hydrothermal process. Results: The nanoparticles showed great sunlight-excited photocatalytic and Fenton- like photocatalytic activities in the photodegradation of dye solution. Introducing rGO resulted in further enhancement of the activity compared to the nanoparticles. The effect of initial dye solution pH and H2O2 on the activities were also studied. The greater activities of the hybrids are ascribed to good interface charge transfer that was verified by the estimation of optical conductivity and band energy level. The hybrids also showed an magnetically separable performance from degraded pollutant solution. Conclusion: This work suggested a facile method to synthesize the magnetic MnFe2O4 nanoparticles and rGO/MnFe2O4 hybrids. The hybrids are an promising photocatalytic materials for environmental applications.

MWCNT decorated MnFe2O4 nanoparticles as an efficient photo-catalyst for phenol degradation

A MWCNT/MnFe2O4 nanocomposite was successfully synthesized by the hydrothermal method and its structural, optical, morphological and magnetic characterizations were done by XRD, FT-IR, TEM, SEM and VSM techniques. The nanocomposites have inverse spinel structure with a particle size of about 27–30 nm. Magnetic measurements reveal that all the MWCNTs/MnFe2O4 nanocomposites display ferromagnetic behavior at room temperature. The nanocomposites exhibit superior photo catalytic activity of phenol degradation compared to pure MnFe2O4, owing to the reduction of photo-induced electron–hole pair recombination induced by the introduction of MWCNTs.

Influence of Sm3+ ions on structural, optical and solar light driven photocatalytic activity of spinel MnFe2O4 nanoparticles

In this article, co-precipitation method was used to produce a series of samarium substituted manganese ferrite nanoparticles, MnFe2−xSmxO4 (x = 0.0, 0.5, 1.0, 1.5, 2.0) with oleic acid as surfactant. The effect of Sm3+ substitution and calcination temperature on the MnFe2O4 was explored. The MnFe2−xSmxO4 sample calcinated at 973K induced an enhanced optical behaviour. The influence of Sm3+ ions on cationic distribution and optical properties of MnFe2O4 were probed by various physicochemical techniques. The presence of secondary orthorhombic (SmFeO3) phase with initial cubic phase was confirmed by doublet peak in the X-ray diffraction pattern. The particle size distribution of MnFe0.5Sm1.5O4 sample was about 40nm from HRTEM. The visible light absorption ability extended as Sm content was increased up to x = 1.5 in MnFe2O4. At an optimum concentration of Sm as x = 1.5 in MnFe2O4, photocatalyst exhibited decrease in energy band gap (1.64eV); as a result effective visible light driven photocatalytic activity was achieved than the pure MnFe2O4. The MnSm1.5Fe0.5O4 sample exhibits pronounced photodegradation towards Rose Bengal with in 50min under direct sunlight illumination as energy input. The broad emission band is observed in the entire photoluminescence (PL) spectrum. Current study provides an excellent competency of rare earth substituted ferrite as a new class of photocatalyst and they found to be a beneficial in the field of environmental cleaning application.

Composition dependent structural and morphological modifications in nanocrystalline Mn-Zn ferrites induced by high energy γ-irradiation

We report the high energy γ-irradiation induced structural transformations in nanocrystalline Mn1-xZnxFe2O4 (x = 0, 0.25, 0.5, 0.75 and 1) samples synthesized by solution combustion method using a mixture of fuels. All samples were exposed to a gamma radiation dose of 50 kGy. The γ-irradiation decomposes the single phase cubic spinel (Fd-3m) structure of the samples into new stable phases. The pure MnFe2O4 sample transformed to Mn2O3 and Fe1-xO phases whereas the pure ZnFe2O4 sample retained its phase. For the samples with intermediate Zn-content γ-irradiation facilitates the formation of stable α-Fe2O3 and ZnFe2O4 phases, along with amorphous MnO phase. The scanning electron micrographs demonstrate the complete change of the sample morphology with fusion of the particles after γ-irradiation. Our results are important for the understanding of the stability and performance of the devices used in various technological applications near intense high energy radiation sources.

Activation of persulfate by magnetic MnFe2O4-bentonite for catalytic degradation of 2,4-dichlorophenol in aqueous solutions

Magnetic MnFe2O4-bentonite was synthesized by chemical co-precipitation method(CCM) and applied as catalyst in heterogeneous activation of persulfate(PS) to oxidize a target pollutant, 2,4-dichlorophenol(2,4-DCP), in aqueous solutions. The surface morphology and structure of MnFe2O4-bentonite were characterized by X-ray diffraction( XRD), scanning electron microscope(SEM), energy dispersive X-ray(EDX) and X-ray photoelectron spectroscopy(XPS) analyses.The catalytic activity of MnFe2O4-bentonite for 2,4-DCP degradation was evaluated considering the effects of various process parameters, such as mass ratio of MnFe2O4 to bentonite, concentration of catalyst, PS concentration, and pH. The MnFe2O4-bentonite hybrid exhibited higher catalytic activity than pure MnFe2O4. Treatment with 5 g/L MnFe2O4-bentonite at 30 °C for 240 min oxidized 92% of 100 mg/L 2,4-DCP(70.2% mineralization), whereas treatment with pure MnFe2O4 under the same condition oxidized only 70% of the pollutant. This result indicate the enhanced performance of the activated PS. Moreover, MnFe2O4-bentonite exhibits stable performance with minimal loss in activity after five successive runs. Thus, MnFe2O4-bentonite could be a promising catalyst in oxidative degradation of 2,4-DCP.

Facile hydrothermal synthesis of cubic spinel AB2O4 type MnFe2O4 nanocrystallites and their electrochemical performance

Cubic spinel MnFe2O4 nanoparticles were synthesized using a simple hydrothermal method followed by post-annealing. The effects of the reaction temperature on the crystallinity, morphology, and electrochemical performance were studied. The reaction temperature played an important role in the synthesis of highly crystalline MnFe2O4 nanoparticles. At low reaction temperatures (<160°C), the synthesized product contained a secondary inactive Fe2O3 phase as well as MnFe2O4 nanoparticles. In contrast, pure MnFe2O4 nanoparticles were obtained at temperatures above 180°C. Furthermore, the crystallinity of the MnFe2O4 nanoparticles was enhanced significantly by increasing the reaction temperature to 200°C. The cubic spinel MnFe2O4 nanoparticles synthesized at 200°C delivered a maximum specific capacitance of 282.4Fg−1 at a current density of 0.5Ag−1 in a 2M aqueous KOH solution, and exhibited long-term cyclic stability of 85.8% capacitance retention after 2000 cycles. This was attributed to the cubic spinel ferrite nanocrystallite particles not only providing the more active sites for OH− ion diffusion but also reducing the path lengths for OH− ion diffusion. These results show that the synthesized MnFe2O4 nanoparticles are promising candidates for pseudocapacitors and other electrochemical applications.

Optical, Electrochemical and Photocatalytic Properties of Sunlight Driven Cu Doped Manganese Ferrite Synthesized By Solution Combustion Synthesis

A series of well crystallized copper substituted MnFe2O4 (1,3 & 5 mol%) nanoparticles have been synthesized by solution combustion synthesis using Oxalyl Dihydrazide (ODH) as fuel. The synthesized samples were characterized by Powder X-ray Diffraction (PXRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS) and electrochemical impedance studies (EIS). The PXRD analysis showed that pure single phases of cubic ferrites for all the synthesized samples. The energy band gap of copper doped MnFe2O4 was found to be less compared to pure MnFe2O4. The morphology for synthesized samples indicates the formation of spinel structure. The copper doped MnFe2O4 nanoparticles exhibits enhanced photocatalytic activity of 90% for malachite green dye under Sunlight compared to pure MnFe2O4.

Enhanced performance of SnO2-Mn(1−X)Cu(X)Fe2O4 gas sensors towards carbon dioxide and oxygen

Mn(1−X)Cu(X)Fe2O4 nanoparticles with different ‘X’ values (X = 0, 0.5, 1.0) are synthesized initially by the chemical co-precipitation method and followed by equal (1:1) weight percentages of Cu/MnFe2O4 are combined with SnO2. XRD parameters of all the materials are well agreed with the standard JCPDS files and confirm the presence of polycrystalline cubic spinel structure for ferrite materials and tetragonal phase for SnO2. The addition of SnO2 on copper substituted manganese ferrite increases the crystalline size and decreases the strain values. Morphological analysis for ferrite material depicts the average particle size is linearly decreased with the decrease in Mn2+ concentration. Moreover, the addition of SnO2 on ferrite materials increases the particle size. VSM analysis exhibits superparamagnetic behaviour for all the samples except SnO2 and MnFe2O4. The observed Ms values are diluted with the addition of SnO2 on ferrite materials. Pure SnO2 shows a weak paramagnetic behaviour and MnFe2O4 shows a ferromagnetic nature with the MR = 0.318 emu/g and Hc = 0.0019 T. EDAX spectrum for SnO2, MnFe2O4, CuFe2O4 and Mn0.5Cu0.5Fe2O4 shows the observed stoichiometric ratios for all the samples are in accordance with chemical formulas. The gas sensing properties of MnFe2O4, Mn0.5Cu0.5Fe2O4, CuFe2O4 and SnO2 added Cu/Mn ferrite materials are studied for O2 and CO2. SnO2-MnFe2O4 and SnO2-Mn0.5Cu0.5Fe2O4 samples under gas sensor test shows better response than pure MnFe2O4 and Mn0.5Cu0.5Fe2O4 for both O2 and CO2. After gas reduction, the material shows almost a pristine behaviour confirms these materials are suitable for gas sensor application. However, in the case of SnO2-CuFe2O4 shows a decrease in trend of gas response when compared to pure copper ferrite.

Crystallographic and Magnetic Properties of Co, Zn, Ni-Zn Substituted Nano-size Manganese Ferrites Synthesized by Sol-gel Method

Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, MnFe₂O₄, Mn 0.8 Co 0.2 Fe₂O₄, Mn 0.8 Zn 0.2 Fe₂O₄ and Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄, were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently studied. The MnFe₂O₄ ferrite powder annealed at temperatures above 523 K exhibited a spinel structure, and the particle size increased as the annealing temperature increased. All ferrites annealed at 773 K showed a single spinel structure, and the lattice constants and particle size decreased with the substitution of Co, Zn, and Ni-Zn. The Mossbauer spectrum of the MnFe₂O₄ ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the Mossbauer spectra of the MnFe₂O₄, Mn 0.8 Co 0.2 Fe₂O₄, and Mn 0.8 Zn 0.2 Fe₂O₄ ferrite powders annealed at 773 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe 3+ ions. However, the Mossbauer spectrum of the Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄ ferrite powder annealed at 773 K consisted of two Zeeman sextets and one quadrupole doublet due to its ferrimagnetic and paramagnetic behavior. The area ratio of the Mossbauer spectra could be used to determine the cation distribution equation, and we also explained the variation in the Mossbauer parameters by using this cation distribution equation, the superexchange interaction and the particle size. Relative to pure MnFe₂O₄, the saturation magnetizations and coercivities were larger in Mn 0.8 Co 0.2 Fe₂O₄ and smaller in Mn 0.8 Zn 0.2 Fe₂O₄, and Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄. These variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.

Magnetically recyclable MnFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;/polyaniline composite with enhanced visible light photocatalytic activity for rhodamine B degradation

The magnetically recyclable MnFe2O4/Polyaniline (PANI) composite was successfully synthesized by a combination of a salt-assisted solution combustion method and an in situ oxidative polymerization method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (DRS) were employed to characterize the physical and chemical properties of the samples. The results showed that MnFe2O4/PANI composite exhibited higher photocatalytic activity and stability than pure PANI and MnFe2O4 nanoparticles toward the degradation of rhodamine B (RhB) under visible light irradiation, suggesting the existence of a synergic effect between PANI and MnFe2O4. The excited state electrons in the lowest unoccupied molecular orbital (LUMO) of PANI can readily migrate into conduction band (CB) of MnFe2O4, while the holes in the valence band (VB) of MnFe2O4 migrate to the π-orbital of PANI because of the enjoined electric fields of the two materials, which can further improve the separation of the photoinduced electron–hole pairs.

Microwave Based Synthesis; Structural, Optical and Magnetic Measurements of Co²⁺ Doped MnFe₂O4.

CO²⁺ doped manganese ferrite (Mn₁₋xCoxFe₂O₄, x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) samples were synthesized by a microwave combustion method. Nitrates of the constituent elements and urea were respectively used as the oxidizer and fuel to drive the reaction. On an average a yield of 80% were obtained for all the compositions. Light-absorbing properties from UV-Vis diffuse reflection spectrum were studied and the results infer that the band gap energy (Eg) of the pure MnFe2O4 is 1.76 eV and with increase in C02+ ion concentration, it increases to 2.25 eV. The phase purity and crystal lattice symmetry were estimated from X-ray diffraction (XRD) and was identified as the spinel cubic crystal structure. The lattice parameter is found to decrease with an increase in Co content. The crystallite size was in the range of 19-25 nm. The purity and the composition of the elements were further confirmed by energy dispersive X-ray (EDX) results. Microstructural features obtained by scanning electron microscope (SEM) demonstrate that the nanocrystals were formed with a decrease in average grain size with C02+ content. Room temperature magnetic measurement for stoichiometric samples is discussed with the help of vibrating sample magnetometer (VSM). The saturation magnetization (M), remanant magnetization (Mr) and coercivity (H.) are measured from the respective hysteresis plots.

Magnetic epoxy nanocomposites with superparamagnetic MnFe2O4 nanoparticles

Manganese iron oxide (MnFe2O4) nanoparticles successfully served as nanofillers for obtaining magnetic epoxy nanocomposites. The viscosities of MnFe2O4/epoxy resin liquid suspensions increased with increasing the nanoparticles loading except the suspension with 5.0 and 1.0 wt% loading, whose viscosities were lower than that of pure epoxy. The introduction of MnFe2O4 nanoparticles showed a lower onset decomposition temperature and glass transition temperature (Tg), which decreased with increasing the nanoparticles loading. The storage modulus and tensile strength of 1.0 wt% MnFe2O4/epoxy were a little higher than that of pure epoxy. The coercivity of MnFe2O4/epoxy nanocomposites with 5.0 wt% (44.7 Oe) and 10.0 wt% (43.9 Oe) displayed much higher than that of pure MnFe2O4 nanoparticles (14.94 Oe). The magnetic moment (m) of nanocomposites (1.354 μB for 10 wt% MnFe2O4/epoxy) are higher than that of pure MnFe2O4 nanoparticles (1.244 μB). The increased real permittivity observed in the nanocomposites was attributed to the interfacial polarization. The intrinsic permittivity of the MnFe2O4 nanoparticles was also calculated.

One-pot hydrothermal synthesis, characterization, and electrochemical properties of rGO/MnFe2O4 nanocomposites

In this work, a simple facile route for preparing an rGO/MnFe2O4 nanocomposite through a one-pot hydrothermal approach was demonstrated. Graphite oxide (GO) was prepared from graphite powder by a modified Hummers method. Fe(NO3)2 ∙ 9H2O and Mn(NO3)2 ∙ H2O were used as the precursors for the preparation of the rGO/MnFe2O4 nanocomposite. The formation of the rGO/MnFe2O4 nanocomposite was confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and Rama spectroscopy (Raman). The specific surface area of the prepared composite obtained by Brunauer–Emmett–Teller (BET) analysis was lower than that of pure rGO but higher than that of pure MnFe2O4. Consequently, the electrochemical performance was investigated by using a three-electrode cell system in 6.0 M KOH. The results show that the specific capacitance was determined to be 190.3, 276.9, and 144.5 F/g at a scan rate of 10 mV/s, and 194.9, 274.6, and 134.4 F/g at a current density of 5.0 A/g for rGO, rGO/(5 mmol) MnFe2O4, and rGO/(10 mmol) MnFe2O4, respectively. These results suggest that the composite of MnFe2O4 nanoparticles on an rGO nanosheet can improve the capacitive behavior of the fabricated electrode, but the electrochemical properties are reduced when the MnFe2O4 concentration ratio is high.

A Novel Synthesis, Structural, Morphological, and Opto-magnetic Characterizations of Magnetically Separable Spinel Co x Mn1−x Fe2O4 (0 ≤ x ≤ 1) Nano-catalysts

Spinel CoxMn1−xFe2O4 (0≤x≤1) nano- crystals were successfully synthesized by a simple microwave-assisted combustion method. High-resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (HR-TEM) analysis was used to study the morphological variations and found the particle-like nanocrystal morphologies. Energy dispersive X-ray (EDX) results showed that the composition of the elements were relevant as expected from the combustion synthesis. Powder X-ray diffraction (XRD) analysis showed that all composition was found to have cubic spinel-type structure. Average crystallite size of the samples was found to be in the range of 10.36–21.16 nm. The lattice parameter decreased from 8.478 to 8.432 A with increasing Co2+ content. Fourier transform infrared (FT-IR) spectra showed two strong absorption peaks observed at lower frequency (∼435 to ∼800 cm−1), which can be assigned to the M–O (Mn, Co, and Fe) bonds. UV-Visible diffuse reflectance spectroscopy (DRS) shows that the energy band gap of pure MnFe2O4 is 1.78 eV and with increase in the Co2+ ion, it increases from 1.87 to 2.33 eV. Addition of Co2+ in MnFe2O4 reduces the particle size, which can be confirmed by the blue shift in the photoluminescence (PL) spectra. Vibrating sample magnetometer (VSM) results that confirmed a weak ferromagnetic behavior for all composition with saturation magnetization values in the range of 50.05 ±04 to 67.09 °03 emu/g. All composition of spinel CoxMn1−xFe2O4 nano-crystals were successfully tested as catalyst for the oxidation of benzyl alcohol to benzaldehyde, which has resulted 87.32 and 94.28 % conversion efficiency of MnFe2O4 and Co0.6Mn0.4Fe2O4, respectively.