Influences of La^(3+) Substitution on Structure and Electromagnetic Properties of Nanocrystalline Nickel Ferrites

Nanocrystalline nickel ferrites with substitution of Fe3+ by rare-earth La3+, according to the formula NiLaxFe2-xO4 (with x=0, 0.05, 0.1 and 0.15), were prepared by polyacrylamide gel method. Influences of the amount of La3+ substitution on the structure and electromagnetic properties of NiLaxFe2-xO4 compounds were systematically investigated by DSC-TG, XRD, TEM and wave-guide method. XRD results indicated that the pure spinel-type crystal structure of the NiLaxFe2-xO4 (x=0 and 0.05) was obtained at 500 ℃. TEM results showed that the average particle sizes of NiFe2O4 and NiLa0.1Fe1.9O4 particles were about 10 and 15 nm, respectively. The complex permittivity and complex permeability was measured in the frequency range of 8.2～12.4 GHz. The results revealed that the nanocrystalline NiLaxFe2-xO4 had both dielectric loss and magnetic loss in the frequency range of 8.2～12.4 GHz. The tgδε and tgδm of NiLaxFe2-xO4 (with x=0 and 0.05) decreased with the increase of La3+ ions content, and some strong resonance peaks of the tgδε and tgδm of NiLaxFe2-xO4 (with x=0.1 and 0.15) appeared because of the secondary phases (LaFeO3) and more lattice defects.

Activated carbon induced oxygen vacancies-engineered nickel ferrite with enhanced conductivity for supercapacitor application

NiFe_(2)O_(4) is a kind of bimetallic oxide possessing excellent theoretical capacity and application prospect in the field of supercapacitors.Whereas,due to the inherent poor conductivity of metal oxides,the performance of NiFe_(2)O_(4) is not ideal in practice.Oxygen vacancies can not only enhance the conductivities of NiFe_(2)O_(4) but also provide better adsorption of OH,which is beneficial to the electrochemical performances.Hence,oxygen vacancies engineered NiFe_(2)O_(4)(NiFe_(2)O_(4)‒δ)is obtained through a two-step method,including a hydrothermal reaction and a further heat treatment in activated carbon bed.Results of electron paramagnetic resonance spectra indicate that more oxygen vacancies exist in the treated NiFe_(2)O_(4)‒δthan the original one.UV-Vis diffuse reflectance spectra prove that the treated NiFe_(2)O_(4)‒δowns better conductivity than the original NiFe_(2)O_(4).As for the electrochemical performances,the treated NiFe_(2)O_(4)‒δperforms a high specific capacitance of 808.02 F∙g^(‒1) at 1 A∙g^(‒1).Moreover,the asymmetric supercapacitor of NiFe_(2)O_(4)‒δ//active carbon displays a high energy density of 17.7 Wh∙kg^(‒1) at the power density of 375 W∙kg^(‒1).This work gives an effective way to improve the conductivity of metal oxides,which is beneficial to the application of metal oxides in supercapacitors.

Synthesis of Magnetic Nickel Ferrite Microspheres and Their Microwave Absorbing Properties

NiFe2O4 microspheres were synthesized using a solvothermal method. The morphologies and structures of NiFe2O4 micropheres were characterized via a field emission scanning electron microscope（FESEM）, a transmission electron microscope（TEM） and an X-ray diffractometer（XRD）. The NiFe2O4 microspheres were around 150--200 nm in diameter and assembled by nanoparticles. The magnetic and electromagnetic parameters were measured using a vibrating sample magnetometer and a vector network analyzer, respectively. The obtained products exhibited a saturation magnetization of 60.8 A.m2·kg-1 at room temperature. A minimum reflection loss（RL） of -27.8 dB was observed at 9.2 GHz with a thickness of 3.5 mm, and the effective absorption frequency（RL〈-10 dB） ranged from 8.2 GHz to 11.2 GHz, indicating the excellent microwave absorption performance of the NiFe2O4 microspheres in the X-band frequencies.

Fabrication and magnetic properties of NiFe_2O_4 nanorods

NiFe2O4 nanorods have been successfully synthesized via thermal treatment of the rod-like precursor fabricated by Ni-doped （x-FeOOH, which was enwrapped by the complex of citric acid and Niz~. The morphology evolution during the calcination of the precursor nanorods was investigated with transmission electron microscopy （TEM）, and the phase and the magnetic properties of samples were analyzed through X-ray diffraction （XRD） and vibrating sample magnetometer （VSM）. The results indicated that the diameter of the NiFe204 nanorods obtained ranged between 30 and 50 nm, and the length ranged between 2 and 3 um. As the calcination temperature was up to 600℃, the coercivity, saturation magnetization, and remanent magnetization of the samples were 36.1 kA.m^-1, 27.2 A.m2.kg^-1, and 5.3 A.m2.kg^-1, respectively. The NiFe2O4 nanorods prepared have higher shape anisotropy and superior magnetic properties than those with irregular shapes.

EFFECT OF MnO_(2) ADDITIVE ON PERFORMANCES OF NiFe_(2)O_(4) SPINEL BASED INERT ANODE

The NiFe2O4 inert anode is synthesized by high-temperature solid-state reaction method using NiO and Fe2O3 as main raw materials and adding MnO2 powder as additive. Archimedes method using water immersion technique is used to measure the sintering performances of sampies. The static thermal corrosion rates of samples are measured by weight loss. SEM is employed for the observation of material microstructure, and phase structure of the sample surface after corrosion is determined by XRD. The experimental results indicate that a suitable MnO2 additive content is 2%, while the sintering performance is the best, and the static thermal corrosion rate is the lowest. Because of MnO2 dopant enriching at crystal boundary, the corrosion reaction of molten salt to crystal grain creates Mn2AlO4 phase, which is denser than NiFe2O4 phase, and prevents the cryolite molten salt to penetrate into the inert anode, thus reducing the corrosion.

Multiferroic behaviour of epitaxial NiFe_2O_4-BaTiO_3 heterostructures

Multiferroic NiFe2O4 （NFO）-BaTiO3 （BTO） bilayered thin films are epitaxially grown on （001） Nb-doped SrTiO3 （STO） substrates by pulsed-laser deposition （PLD）. Different growth sequences of NFO and BTO on the substrate yield two kinds of epitaxial heterostructures with （001）-orientation, i.e. （001）-NFO/（001）-BTO/substrate and （001）- BTO/（001）-NFO/substrate. Microstructure studies from x-ray diffraction （XRD） and electron microscopies show differences between these two heterostructures, which result in different multiferroic behaviours. The heterostructured composite films exhibit good coexistence of both ferroelectric and ferromagnetic properties, in particular, obvious magnetoelectric （ME） effect on coupling response.

Synthesis and Characterization of Magnetic TiO_2/SiO_2/NiFe_2O_4 Composite Photocatalysts

Magnetic TiO2/SiO2/NiFe204 composite photocatalytic particles with high crystalline TiO2 shell were synthesized via a mild solution route. The prepared composite particles were characterized with X-ray diffraction（XRD）, transmission electron microscopy（TEM）, high resolution transmission electron microscopy（HRTEM）, scanning electron microscopy（SEM）, ultraviolet-visible（UV-Vis） spectroscopy and vibrating sample magnetometer（VSM）. The results show that the obtained TiO2/SiO2/NiFe2O4 composite particles were composed of spherical nanoparticles, about 30 nm in diameter, with several NiFe/O4 fine particles about 20 nm in diameter as cores and silica as coatings and barrier layers between the magnetic cores and titania shells. The photocatalytic activity of the composite photocatalytic particles was also investigated for the degradation of Basic Violet 5BN（BV5） under UV irradiation. About 97% of original BV5 decomposed in 360 min in the presence of magnetic composite nanoparticles under UV light. The synthesized magnetic composite nanoparticles exhibited high photocatalytic efficiency that would find potential application to cleaning polluted water with the help of magnetic separation.

Evaluation of multi-cycle performance of chemical looping dry reforming using CO_2 as an oxidant with Fe–Ni bimetallic oxides

Chemical looping dry reforming（CLDR） is an innovative technology for CO2 utilization using the chemical looping principle.The CLDR process consists of three stages,i.e.CH4 reduction,CO2 reforming,and air oxidation.Spinel nickel ferrite（NiFe2O4） was prepared and its multi-cycle performance as an oxygen carrier for CLDR was experimentally investigated.X-ray diffraction（XRD） and Laser Raman spectroscopy showed that a pure spinel crystalline phase（NiFe2O4） was obtained by a parallel flow co-precipitating method.NiFe2O4was reduced into Fe-Ni alloy and wustite（FexO） during the CH4 reduction process.Subsequent oxidation of the reduced oxygen carrier was performed with CO2 as an oxidant to form an intermediate state：a mixture of spinel Ni（1-x）Fe（2＋x）O4,Fe（2＋y）O4 and metallic Ni.And CO was generated in parallel during this stage.Approximate 185 mL of CO was generated for 1 g spinel NiFe2O4 in a single cycle.The intermediate oxygen carrier was fully oxidized in the air oxidation stage to form a mixture of Ni（1＋x）Fe（2-x）O4 and Fe2O3.Although the original state of oxygen carrier（NiFe2O4） was not fully regenerated and agglomeration was observed,a good recyclability was shown in 10 successive redox cycles.

Synthesis of NiFe_2O_4 Powders Well Defined in Size and Morphologies

The uniform NiFe2O4 powders with different particle size and morphologies (octahedral, cubic and spherical) have been prepared from different precursors via hydrothermal process. The nanocrystallines derived from precursor B in the weak alkali solution (pH≤10) are superparamagnetic.

The performance of activated carbon/NiFe_(2)O_(4) magnetic composite to retain heavy metal ions from aqueous solution

A novel magnetic activated carbon composite(AC/NiF) was synthesized by a precipitation method and applied in retention of Cu(Ⅱ),and Zn(Ⅱ) ions from aqueous solutions.The impact of different sorption parameters such as:equilibration time,solution pH value,competing cations and ionic strength on the amount sorbed of Cu(Ⅱ),and Zn(Ⅱ) was clarified.Results illustrated that the magnetic composite had retention ability towards both metal ions significantly higher than that of activated carbon(AC).The magnetic composite exhibited an affinity to adsorb Cu(Ⅱ) higher than Zn(Ⅱ) ions.The maximum sorption capacities(Q_(max)) of the applied magnetic composite(AC/NiF)towards Cu(Ⅱ) and Zn(Ⅱ) were 105.8 and 75.1 mg·g^(-1),respectively.Retention of Cu(Ⅱ) and Zn(Ⅱ) was proposed to be achieved though an ion exchange and surface adsorption in neutral conditions,while precipitation was believed to be the relevant mechanism in their removal from basic solutions.The kinetic studies showed that sorption process followed the kinetics of pseudo-second-order reactions with rate constant of 3 × 10^(-3) and 2 × 10^(-3) min^(-1)for sorption of Cu(Ⅱ) and Zn(Ⅱ) onto AC/NiF composite.Removal of Cu(Ⅱ) slightly decreased with increasing the ionic strength of aqueous solution,using NaCl as a background electrolyte.In contrast,presence of Mn(Ⅱ),Mg(Ⅱ)and Co(Ⅱ) in reaction solutions highly depressed the sorption of Cu(Ⅱ) and Zn(Ⅱ) with a competing efficiency followed the order:Mg(Ⅱ)> Mn(Ⅱ)> Co(Ⅱ).The magnetic composite was rapidly recovered from aqueous solution by an external magnetic field,and effectively regenerated using 0.1 mol L^(-1) HCl and 0.1 mol L^(-1) FeCl_(3) as eluents.Sorption of Cu(Ⅱ) and Zn(Ⅱ) onto the surface of AC/NiF composite occurred via a spontaneous reaction.And thermodynamically favorable process had ΔH~o values of 30.9 kJ·mol^(-1) and 19.7 kJ·mol^(-1),respectively.The results confirm that the magnetic composite can be viewed as a promising novel composite opens new opportunities for the attainment of required adsorption and operative magnetic separation.

Structural & Magnetic Characterizations of NiLiZn Nanoferrites Synthesized by Co-precipitation Method

Synthesis of Ni0.sLixZn（0.5-x）Fe204 nanoparticles with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5 were realized via coprecipitation method. X-ray diffraction （XRD） and vibrating sample magnetometer （VSM） measurements were performed on the samples to determine the characteristics of the crystal structures and the magnetic properties of the samples, respectively. The spinel phase structures of the samples were confirmed by XRD analysis. Patterns of decreased lattice parameter and increased crystallite size values were observed by increasing the Li concentration at longer synthesis reaction periods. Similarly, for the magnetic properties, both the saturation magnetization （Ms） and coercivity （Hc） were found to vary with increasing patterns at higher Li doping levels and longer synthesis reaction periods. The results and mechanisms concerned were discussed.

Catalytic ozonation treatment of papermaking wastewater by Ag-doped NiFe2O4 : Performance and mechanism

The catalytic ozonation treatment of secondary biochemical effluent for papermaking wastewater by Ag-doped nickel ferrite was investigated.Ag-doped catalysts prepared by sol-gel method were characterized,illustrating that Ag entirely entered the crystalline of Ni Fe2O4 and changed the surface properties.The addition of catalyst enhanced the removal efficiency of chemical oxygen demand and total organic carbon.The results of gas chromatography-mass spectrometer,ultraviolet light absorbance at 254 nm and threedimensional fluorescence excitation-emission matrix suggested that aromatic compounds were efficiently degraded and toxic substances,such as dibutyl phthalate.In addition,the radical scavenging experiments confirmed the hydroxyl radicals acted as the main reactive oxygen species and the surface properties of catalysts played an important role in the reaction.Overall,this work validated potential applications of Ag-doped Ni Fe2O4 catalyzed ozonation process of biologically recalcitrant wastewater.

Enhanced solar-light-driven photocatalytic properties of novel Z-scheme binary BiPO_(4)nanorods anchored onto NiFe_(2)O_(4)nanoplates:Efficient removal of toxic organic pollutants

Global environmental problems have been increasing with the growth of the world economy and have become a crucial issue.To replace fossil fuels,sustainable and eco-friendly catalysts are required for the removal of organic pollutants.In this study,nickel ferrite(NiFe_(2)O_(4))was prepared using a simple wet-chemical synthesis,followed by calcination;bismuth phosphate(BiPO_(4))was also prepared using a hydrothermal method.Further,NiFe_(2)O_(4)/BiPO_(4)nanocomposites were prepared using a hydrothermal technique.Numerous characterization studies,such as structural,morphology,surface area,optical,photoluminescence,and photoelectrochemical investigations,were used to analyze NiFe_(2)O_(4)/BiPO_(4)nanocomposites.The morphology analysis indicated a successful decoration of BiPO_(4)nanorods on the surface of Ni Fe_(2)O_(4)nanoplate.Further,the bandgap of the NiFe_(2)O_(4)/BiPO_(4)nanocomposites was modified owing to the formation of a heterostructure.The as-prepared NiFe_(2)O_(4)/BiPO_(4)nanocomposite exhibited promising properties to be used as a novel heterostructure for tetracycline(TC)and Rhodamine B(Rh B)removal.The NiFe_(2)O_(4)/BiPO_(4)nanocomposite degrades TC(98%)and Rh B(99%)pollutants upon solar-light irradiation within 100 and 60 min,respectively.Moreover,the trapping experiments confirmed the Z-scheme approach of the prepared nanocomposites.The efficient separation and transfer of photogenerated electron-hole pairs rendered by the heterostructure were confirmed by utilizing electrochemical impedance spectroscopy,photocurrent experiments,and photoluminescence.Mott–Schottky measurements were used determine the positions of the conduction and valence bands of the samples,and the detailed mechanism of photocatalytic degradation of toxic pollutants was projected and discussed.

Synthesis and Characterization of NiFe_2O_4 Magnetic Nanoparticles by Combustion Method

Magnetic nanoparticles of nickel ferrite （NiFe204） have been successfully synthesized by microwave-assisted combustion method using stable ferric and nickel salts as precursors and glycine as fuel. The as-synthesized samples were characterized by Fourier transform infrared spectroscopy （FT-IR）, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, vibrating sample magnetometer （VSM） and field emission scanning electron microscopy （FESEM）. The effect of different dose of glycine on the structural parameters and magnetic properties of the prepared NiFe204 nanoparticles was also investigated. This study revealed that it was possible to produce larger size of nanoparticles with lower saturation magnetization by using higher dose of fuel.

Facile Synthesis of NiFe_2O_4/Reduced Graphene Oxide Hybrid with Enhanced Electrochemical Lithium Storage Performance

In this work, a facile, one-pot route has been applied to synthesize nanohybrids based on mixed oxide NiFe2O4 and reduced graphene oxide （rGO）. The hybrid is constructed by nanosized NiFe2O4 crystals confined by few- layered rGO sheets. The formation mechanism and microstructure of the hybrids have been clarified by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical tests show that the performance of NiFe2O4 can be considerably improved by rGO incorporation. The performance improvement can be attributed to the two-dimensional conductive channels and the unique hybrid structure rGO constructed. The easy synthesis and good electrochemical performance of NiFe2O4/rGO hybrid make it a promising anode material for Li-ion batteries.