NiFe2O4 Phase Research Articles

Hydrothermal synthesis of nickel iron oxide nano-composite and application as magnetically separable photocatalyst for degradation of Solar Blue G dye

In this research, nickel iron oxide nano-composite was effectively prepared via a simple hydrothermal route in an autoclave at 180 °C. The phase formation and opto-elctronic properties of nano-composite were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), UV–Vis diffuse reflectance spectra (UV–Vis DRS) and vibrating sample magnetometer (VSM) techniques. The VSM reults showed magnetization value of 38.25 emu/g. FTIR and XRD results confirmed the formation of cubic NiFe2O4 and rhombohedral Fe2O3 phases. The results of FESEM and EDAX studies indicate the formation of nickel iron oxide nano-composite with size of 7–10 nm. UV–Visible diffuse reflectance spectra experimental results showed transition energies of 1.66, 2.5 and 3.7 eV. Additionally, the prepared nickel iron oxide nano-composite were used as photocatalyst for for degradation Solar Blue G dye and the results showed good activity and recyclable by applying an appropriate magnetic field. The reuse of the prepared nickel iron oxide nano-composite for removal of Solar Blue G dye water pollutants was attained in five cycles with an average efficiency of 81%.

Low temperature preparation, characterization, magnetic measurements, thermal, optical, morphological and photo-catalytic properties of nano-size single phase nickel ferrite NiFe2O4

Low temperature preparation, characterization, magnetic measurements, thermal, optical, morphological and photo-catalytic properties of nano-size single phase NiFe2O4 are reported. The nano-size single phase NiFe2O4 powders were characterized by thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), UV–Vis diffuse reflectance spectra (UV–Vis DRS) and vibrating sample magnetometer (VSM) techniques. The XRD results of the powder samples showed that nano-size single phase nickel ferrite, NiFe2O4 were formed using the nitrate precursors and citric acid at relatively low annealing temperature of 600 °C. The TG–DTG results of the nitrate precursors showed that the major weight loss occurred below 400 °C. The crystallite size of nano-size single phase nickel ferrite, NiFe2O4 was 38 nm. FTIR results showed the iron–oxygen and titanium–oxygen vibration at 410 and 590 cm−1, respectively. The VSM results of the samples showed magnetization of Ms of 51.3 emu/g. Nano-size single phase nickel ferrite showed a wide absorbance in the visible light and therefore a photocatalytic activity for degradation of C.I. Direct Blue 71 as a triazo textile dye in water.

Controllable preparation of large-area arrays of Al-substituted CoCuNi ferrite rods with improvement of saturation magnetization and initial permeability

Co0.5Cu0.3Ni0.2Al x Fe2−x O4 (x = 0, 0.07, 0.14, and 0.21) rods of large-area arrays are synthesized by a solvothermal method, followed by calcination in air. The samples are characterized by powder X-ray diffraction, FT-IR spectra, scanning electron microscope, and vibrating sample magnetometer. The effect of diamagnetic Al3+ ion substitution and calcination temperature on the structure, morphology, and magnetic properties of Co0.5Cu0.3Ni0.2Al x Fe2−x O4 has been investigated. The results indicate that high-crystallized cubic Co0.5Cu0.3Ni0.2Al x Fe2−x O4 rods of large-area arrays are obtained when the precursors are calcined at 750 °C in air for 3 h. The crystallite size of Co0.5Cu0.3Ni0.2Al x Fe2−x O4 increases with the increase in Al3+ content, attributed to the decrease in lattice strain in Co0.5Cu0.3Ni0.2Al x Fe2−x O4 with the increase in Al3+ content. The lattice parameters of Co0.5Cu0.3Ni0.2Al x Fe2−x O4 slightly increase with the increase in Al3+ content. This is due to the transformation from cubic NiFe2O4 phase to cubic CoFe2O4 phase after doping Al3+ ion. Al3+ substitution can improve the magnetic properties of Co0.5Cu0.3Ni0.2Al x Fe2−x O4. Co0.5Cu0.3Ni0.2Al0.14Fe1.86O4, calcined at 950 °C, has the highest specific saturation magnetization (86.36 ± 2.25 emu/g) and magnetic moment (3.586 ± 0.093 μ B ). Co0.5Cu0.3Ni0.2Al0.21Fe1.79O4, calcined at 950 °C, has the highest initial permeability (17.216 ± 0.448). The results are explained by Neel’s two sublattices.

Competing magnetic interactions and superparamagnetism like behaviour in xNiFe2O4 - (1-x)BaTiO3 (x = 0.2 and 0.3) nano composites

We report on structural, spin glass behaviour and competing magnetic interactions in xNiFe2O4 - (1-x)BaTiO3 (x=0.2 and 0.3) nanocomposites prepared by sol-gel method. The structure and surface morphology of the NiFe2O4-BaTiO3 composites were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD measurements of composite materials show the presence of both NiFe2O4 and BaTiO3 phases. FESEM and energy dispersive X-ray (EDX) measurements indicate uniformly distributed nano size particles and presence of Ni, Fe, O, Ba and Ti elements respectively. Temperature variation Raman spectra indicates large structural disordering (Peak broadening and shift) around 395K due to the structural transformation of BaTiO3. Magnetization, zero field cooled (ZFC) and field cooled (FC) measurements were carried out from 2K to 320K for both composites. ZFC and FC measurements reveal the spin glass and Superparamagnetism like behaviour along with competing magnetic interaction in both composites. Saturation magnetization value is seen to increase from 6.7 to 10emu/g with increasing Ni ferrite composition from x=0.2 to x=0.3. Distribution function associated with magnetocrystalline anisotropy energy barrier exhibits broad peaks due to the random distribution of spins associated with different particle size in the x=0.3 composition.

Interaction of fatty acid chain length with NiFe2O4 nanoparticles

This work deals with the preparation of nickel ferrite (NiFe2O4) nanoparticles utilizing the co-precipitation technique and coating them with three different fatty acids viz. oleic acid, capric acid and myristic acid. Different synthesis parameters such as concentration ratio of precursor: fatty acids, reaction time and reaction temperature were considered to study their effect on the structural as well as magnetic properties of the synthesized nanoparticle. Bare nanoparticles and fatty acid coated nanoparticle thus prepared was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), vibrating sample magnetometer (VSM), transmission electron microscopes (TEM) and energy dispersive X-ray (EDX) analysis. The FTIR results suggested the intensity of the peaks decreased with an increase in length of fatty acid chain. TEM analysis revealed the spherical shape of the nanoparticles which was well dispersed after coating. The broad diffraction peaks during the XRD analysis corresponded to the Bragg reflections from (220), (222), (400), (511) and (333) planes and confirmed the formation of pure NiFe2O4 phase with cubic spinel structure. From SEM analysis it was observed that the size of the nanoparticles increased with fatty acid coating. Magnetic characterization was carried out at room temperature and M (H) loops were obtained with coercivity (Hc)=97.2Oe and magnetic saturation (Ms)=53.5 emu/g with the hysteresis loop confirming the prepared samples to be ferromagnetic in nature. The dispersion stability of both uncoated and coated nanoparticles was also studied. The uncoated nanoparticles remained dispersed for 4h, whereas the myristic acid coated nanoparticles showed highest dispersion stability till 144h.

The synthesis and characterization of nickel and cobalt ferrite nanopowders obtained by different methods

The ferrite materials, especially of nickel and cobalt, are popular due to their unique mechanical and magnetic properties. The single phase NiFe2O4 and CoFe2O4 ferrites were synthesized by three methods: the high frequency plasma chemical synthesis, the sol-gel self-combustion, and the co-precipitation technology combined with the hydrothermal synthesis method. Magnetic properties, crystallite size, the specific surface area of synthesized products are characterized. Nanopowders synthesized in the high frequency plasma have a specific surface area in the range of 28–30 m2/g (the average particle size 38–40 nm, crystallite size ~40 nm), but a wider particle size distribution is in the range of 10–100 nm with some particles of 200 nm. The ferrite nanopowders obtained by the sol-gel self-combustion and hydrothermal synthesis method have the specific surface area of 40 ± 3 and 60 ± 5 m2/g (average particle size 25–30 nm and 19–26 nm, crystallite size 10–20 nm and 12–20 nm), respectively. Cobalt ferrites after synthesis are characterized by the saturation magnetization MS of 75 emu/g (for plasma chemical synthesis), 53 emu/g (for the self-combustion method), and 57 emu/g (hydrothermal synthesis). The saturation magnetization for nickel ferrites is 44, 29 and 30 emu/g, respectively. After the thermal treatment up to 900 oC the particle size of all ferrites increases, but their magnetic properties are approaching those of monolithic ferrites.DOI: http://dx.doi.org/10.5755/j01.ct.67.1.15824

Effect of sintering temperature on thermal stability of Zn0.2Fe1.05NiMn0.75O4 ceramic materials by homogeneous co-precipitation method

The Zn0.2Fe1.05NiMn0.75O4 ceramic materials with different sintering temperatures are synthesized by homogeneous co-precipitation method. The effects of different sintering temperatures on the structure, electrical properties and stability of the ceramic materials are characterized by X-ray diffraction, scanning electron microscope, electrical measurement and impedance analysis. The results show the ceramic powders calcined at 800 °C can form a single cubic spinel structure NiFe2O4 phase, which exhibits great stability at sintering temperature from 1150 to 1300 °C. The values of B25/50 constant, ρ25 and Ea of Zn0.2Fe1.05NiMn0.75O4 ceramic samples at different sintering temperatures are in the range of 3786–3881 K, 84–134 KΩ cm and 0.327–0.335 eV, respectively. The values of relative resistance drift (ΔR/R0) are in the range of 0.58–0.78 % and have a minimum at 1300 °C after aging test at 125 °C for 600 h. The Zn0.2Fe1.05NiMn0.75O4 ceramic materials are desirable for high stability thermistor applications.

Relationship between the ferromagnetic phase and the magnetoelectric coupling in hot pressed Pb(Mg1/3Nb2/3)O3-PbTiO3 based particulate composites

ABSTRACTThe influence of ferromagnetic phase properties on the magnetoelectric response of hot pressed particulate composites formed by 80 mol% of 0.675[Pb(Mg1/3Nb2/3)O3]–0.325[PbTiO3] as piezoelectric matrix and 20 mol% of NiFe2O4, CoFe2O4 or BaFe12O19 phases was analyzed. The hot pressing sintering method was suitable for obtaining composites with apparent density higher than 94% and electric resistivity close to 109 Ω.m, independently of the ferromagnetic phases used. The magnitude of the magnetoelectric coupling seems to be governed by the piezoelectric properties of ferroelectric PMN-PT matrix, and the zero bias magnetoelectric coefficient values are determined by the ferromagnetic hardness of the magnetic phase.

Properties of NiFe2O4 ceramics from powders obtained by auto-combustion synthesis with different fuels

Nickel ferrite (NiFe2O4) powders derived by auto-combustion synthesis using three different fuels (citric acid, glycine and dl-alanine) have been characterized. The sintering behavior of ceramics using these powders has been compared. Oxygen balance (OB) setting for the chemical reaction is found to regulate the combustion reaction rate. A rapid reaction rate and a high flame temperature are achieved with dl alanine fuel yielding single phase NiFe2O4 powder in the as-burnt stage, whereas powders derived with citric acid and glycine fuels show poor crystallinity and necessitate post-annealing. The powder particles are largely agglomerated with a non-uniform distribution in shape and size, and the average particle size is estimated in the range ~ 54–71nm. Powders derived from dl-alanine fuel show better phase purity, smaller crystallite size, larger surface area and superior sintering behavior. Additional Raman modes discerned for dl-alanine derived powder support a 1:1 ordering of Ni2+ and Fe3+ at the octahedral sites relating to microscopic tetragonal P4122 symmetry expected theoretically for the formation of NiFe2O4 with inverse spinel structure. Microstructure of sintered ceramics depends on the precursor powders that are used and sintering at 1200°C is found to be optimum. Citric acid and glycine derived powders yield high saturation magnetization (Ms~47–49emu/g), but poor dielectric properties, whereas dl-alanine derived powders yield ceramics with high resistivity (~3.4×108Ωcm), low dielectric loss (tanδ~0.003 at 1MHz) and high magnetization (46emu/g). Dielectric dispersion and impedance analysis show good correlation with the changes in the ceramic microstructure.

Iron-nickel spinel oxide as an electrocatalyst for non-aqueous rechargeable lithium-oxygen batteries

A lithium-oxygen (Li–O2) battery requires effective catalyst to enable oxygen reduction and evolution. Herein, we report the synthesis of novel macroporous NiFe2O4 nanoparticles by a facile and cost-effective urea assisted co-precipitation process. Characterization of the catalysts by X-ray diffraction and transmission electron microscopy confirms the formation of a single phase NiFe2O4 structure. The use of macroporous NiFe2O4 particles as oxygen electrode catalyst in rechargeable Li–O2 batteries, exhibits a superior catalytic activity with high reversible capacity of 5940 mA h g−1. Additionally, catalytic activity results in low charge over potential and comparable discharge capacity and cycling stability, indicating its potential as a promising catalyst for Li–O2 batteries. The simple and cost effective chemical co-precipitation method can be explored for synthesis of another oxides based catalyst materials.

Effect of fuel-to-oxidant ratio on phase constituents, microstructure and magnetic properties of NiFe2O4-based composite nanopowder synthesized by sol–gel auto-combustion method

In this research, NiFe2O4-based composite nanopowder with 0.8, 1, 1.35, 1.7 fuel-to-oxidant (F/O) ratios was synthesized by sol–gel auto-combustion method. Changes in phase constituents, microstructure and magnetic properties due to changes in F/O ratios were evaluated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM) techniques. XRD and Raman spectroscopy results show the presence of NiFe2O4, FeNi3, α-Fe2O3 and NiO phases. The amount of nickel ferrite was increased, while the amount of FeNi3 was decreased with increasing F/O ratio from 0.8 to 1.35. Mean crystallite sizes of the samples are in the range of 40–46 nm. FESEM studies depicted the formation of NiFe2O4 particles coexisting with FeNi3 phase. Changes in F/O ratios alter the saturation magnetization values from 37 to 60 emu/g as a result of changes in FeNi3 and NiFe2O4 amounts. Coercivity values are in the range of 135–177Oe. In this research nano-sized NiFe2O4 powders with 0.8, 1, 1.35, 1.7 Fuel to Oxidant (F/O) ratios were synthesized by sol–gel auto-combustion method. FESEM studies depicted the formation of NiFe2O4 particles coexisting with FeNi3 phase. Changes in F/O ratios alter the saturation magnetization values from 37 to 60emu/g as a result of changes in FeNi3 and NiFe2O4 amounts. Coercivity values are in the range of 135 to 177Oe.

Fabrication of 2 wt% NiFe<sub>2</sub>O<sub>4</sub>/HAp Composite Ceramic for Future Heavy Metal Removal Applications

In this study, 2 wt% NiFe2O4/HAp composite ceramic was fabricated by the solid state reaction method to form a composite with the future potentiality to remove heavy metals. HAp powders were synthesized by precipitation using Ca (NO3)2 as Ca source, (NH4)2HPO4 as the P source and ammonia as a pH adjuster. NiFe2O4 powders were prepared by mixing and milling NiO and Fe2O3 powders (using stoichiometry ratio) in ethanol and sequent dehydration and then calcination. 2 wt% of NiFe2O4 powders were milled with 98 wt% of HAp powders for 10 minutes before uniaxial pressing and sintering at 1200 °C for 3 hours to form 2 wt% NiFe2O4/HAp composite ceramic. The prepared ceramic was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). XRD result shown that 2 wt% NiFe2O4/HAp composite ceramic with only HAp and NiFe2O4 phases obtained. FT-IR results revealed vibration bands of standard HAp and indicated the interaction between ZnFe2O4 and HAp. For the SEM result, the morphology of the prepared ceramic revealed nanoand micro sized grains. These results could lead us to the development of a method for a NiFe2O4/HAp composite ceramic optimized for specific heavy metal removal applications.

One-Pot Synthesis of (NiFe2O4)x-(SrFe12O19)1-x Nanocomposites and Their Microwave Absorption Properties.

In this paper, we report a simple but novel aqueous solution based 'one-pot' method for preparation of (NiFe2O4)x-(SrFe12O19)1-x nanocomposites consist of hard ferrite-soft ferrite phases. A physical mixing method has also been employed to prepare nanocomposites having same compositions. The effects of synthetic methodologies on the microstructures of the nanocomposites as well as their magnetic and microwave absorption properties have been evaluated. Crystal structures and microstructures of these composites have been investigated by using X-ray diffraction, transmission electron microscope and scanning electron microscope. In the nanocomposites, prepared by both methods, presence of nanocrystalline NiFe2O4 and SrFe12O19 phases was detected. However, nanocomposites, prepared by one-pot method, possessed better homogeneous distribution of hard and soft ferrite phases than the nanocomposites, prepared by physical mixing method. Nanocomposites, prepared by one-pot method, demonstrated significant spring exchange coupling interaction between hard and soft ferrite phases and exhibited magnetically single phase behaviour. The spring exchange coupling interaction enhanced the magnetic properties (high saturation magnetization and coercivity) and microwave absorption properties of the nanocomposites, prepared by one-pot method, in comparison with the nanocomposites prepared by physical mixing method as well as pure NiFe2O4 and SrFe12O19 nanoparticles. Minimum reflection loss of the composite was ~ -17 dB (i.e., 98% absorption) at 8.2 GHz for an absorber thickness of 3.2 mm.

Influence of DL-Alanine Fuel Concentrationon Structural and Magnetic Properties ofNickel Ferrite Nanoparticles

Nano sized NiFe2O4 has been prepared through Sol-gel auto combustion route by using DL-Alanine as fuel. The phase formation of NiFe2O4 is investigated by XRD and Raman techniques.In the case of higher fuel content two molar (2M) in the mixture, it is noted that the as-prepared powders were highly crystalline, and exhibited the typical XRD peaks corresponding to the formation of the NiFe2O4.According to the XRD spectra, the sample prepared with 2M of fuel has better crystallinity than those prepared with one molar (1M) of fuel. Therefore, 2M of fuel is preferable to prepare single phase NiFe2O4 nanoparticles with better crystallinity. Nickel ferrite powders (NFO) were further investigated using Raman spectroscopy in order to differentiate the NFO from other phases like Fe3O4 and gamma Fe2O3, which have the similar structures and therefore similar XRD patterns. The Raman spectra for all the samples resemble to the inverse spinel structure of NiFe2O4. It is observed that sample NiFe2O4 powders that were prepared with different molar concentration (1M and 2M) of the fuel DL-Alanine added to the solution mixture have different magnetization. Sample added with 2M DL-Alanine fuel shows higher magnetization as compared to the sample added with 1M DL-Alanine fuel due to better crystallinity. The room temperature VSM studies show that the nano NiFe2O4 particles exhibit soft ferromagnetic nature with high saturation magnetization of 34.993 emu/g for 2 M fuel amount.

The effect of microstructure on the gas properties of NiFe2O4 sensors: Nanotube and nanoparticle

To explore the effect of structure on gas properties of sensor, hollow nanotubes with the length of 1μm and the diameter of 100nm and nanoparticles of nickel ferrite had been synthesized by an effective anodic aluminum oxide (AAO) templates method and hydrothermal method, respectively. Phase composition, structural, morphology characters and specific surface area were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption–desorption isotherm analysis. The results indicated that the nanotubes and nanoparticles were consisted of pure NiFe2O4 phase with homogenous size. The ammonia gas sensing properties of NiFe2O4 nanotubes and nanoparticles based sensors were measured. Based on the results, nanotube gas sensors showed more favorable response than those of nanoparticle ones. And the nanotube gas sensor showed the best response in 100ppm ammonia gas at 150°C and favorable repeatability which was related to the higher specific surface area of special porous structure.

Chemical‐Looping Reforming of Methane Using Iron Based Oxygen Carrier Modified with Low Content Nickel

AbstractFe2O3/Al2O3 and Fe2O3/Al2O3 modified by low content of Ni (below 2% in weight) oxygen carriers were prepared by mechanical mixing and impregnation method. The synthesized oxygen carriers were characterized by means of X‐ray diffraction (XRD), X‐ray fluorescence (XRF), scanning electron microscopy (SEM), BET‐surface area and temperature programmed reduction (TPR). Besides, redox cyclic reactivity and the performance of chemical looping reforming of methane of the oxygen carriers were studied in a thermal gravimetrical analysis (TGA) and fixed bed at 850°C. It was observed that the redox reactivity of the oxygen carriers is improved by Ni addition because synergic effect may occur between NiO and Fe2O3/Al2O3 to form NiFe2O4 and NiAl2O4 spinel phases. However, the improvement was not apparent as Ni addition reached 1 wt% or more because more nickel loaded resulted in methane decomposition into H2 and carbon leading to carbon deposition. The SEM and BET analysis showed that NiFe2O4 and NiAl2O4 particles dispersed into the pores of the Fe2O3/Al2O3 particles in the course of preparation. In addition, the resistance to sintering of the modified samples increased with the Ni addition increasing. The results of successive redox cycles showed that the Ni modified Fe2O3/Al2O3 oxygen carriers have good regenerability. With integration of reactivity and carbon deposition, the content 1.04 wt% of nickel doping was an optimal amount in the three modified samples.

Synthesis and characterization of high aspect ratio NiFe2O4 nanowire

Highly ordered nickel ferrite nanowires were successfully grown via a sol–gel chemical route using an anodic aluminum oxide (AAO) template. The thermal decomposition of the gel and phase evolution were investigated to determine the appropriate calcination temperature. The X-ray diffraction and Fourier transform infrared spectroscopy results showed the single phase NiFe2O4 nanowires can be achieved after calcination at 600°C. Furthermore, the defect free NiFe2O4 nanowires with the high aspect ratio of about 600 exhibited shape magnetic anisotropy.

Magnetic and Structural Study of FeNi3 Nanoparticles: Effect of Calcination Temperature

Bimetallic Fe–Ni alloy nanoparticles (NPs) with molar ratio of Fe to Ni 1:3 were synthesized via chemical reduction using hydrazine in aqueous solution and then calcined at different temperatures. The prepared NPs have been characterized utilizing X-ray diffraction (XRD), energy-dispersive X-ray (EDS) spectroscopy, and vibrating sample magnetometer (VSM). XRD results show that FeNi3 NPs with face-centered cubic (FCC) crystalline structure were formed. FeNi3 phase completely disappeared and pure NiO and NiFe2O4 phases observed on further heating at 550° C. VSM results reveal a superparamagnetic characteristic for the synthesized NPs when calcined at 50° C. An increased coercivity and decreased saturation magnetization has been observed with increasing calcination temperature up to 550° C.

Ni–Fe and Co–Fe binary oxides derived from layered double hydroxides and their catalytic evaluation for hydrogen production

Binary oxides based on Co–Fe and Ni–Fe were synthesized thermal treatment of layered double hydroxides (LDH) having distinct Ni/Fe and Co/Ni ratios. The solids were characterized through X-ray diffraction (XRD), Raman and Mössbauer spectroscopy, nitrogen adsorption–desorption isotherms, thermoprogrammed reduction (TPR) and thermoprogrammed desorption of CO2 (TPD-CO2), scanning electron microscopy (SEM) and evaluated in dry reforming of methane. XRD results revealed the spinel oxides such as NiFe2O4 and CoFe2O4 coexisting with γ-Fe2O3, α-Fe2O3, Co3O4 and NiO monoxides. These phases were confirmed by Raman and Mössbauer spectroscopy. Nitrogen adsorption–desorption isotherms showed a porosity within micro-to-meso pores range, with some samples displaying macropores. Catalytic evaluation in the dry reforming of methane by varying the temperature in the 650 and 750°C range suggested in situ Co°/CoFe2O4 and Ni°/NiFe2O4 phases formation, which gives best results with the temperature increment, resulting in H2/CO ratios close to 1. The elevated resistance to coking showed by Co–Fe series is particularly remarkable, however, sintering effects were observed over these solids.

Preparation and characterization of porous fly ash/NiFe2O4 composite: Promising adsorbent for the removal of Congo red dye from aqueous solution

A series of fly ash/NiFe2O4 composites were prepared using fly ash and aqueous solutions of Ni, Fe nitrate salts and NaOH by co-precipitation followed by calcination method. The % mass ratio of fly ash: NiFe2O4 was varied in the range of 0:100 to 100:0. Samples were characterized by powder XRD, SEM, FTIR and N2 adsorption–desorption measurements. These samples were further evaluated for their adsorptive performance in removal of Congo red (CR) dye from an aqueous solution. In all the composites, spinel nickel ferrite phase was found to be capable to get anchored with the fly ash surface and exhibited more crystalline nature as compared to pure NiFe2O4 phase. The BET surface area and porous character of the composite were found to increase with the decrease in the contribution of the fly ash, reach to maximum and then decreases on further decrease in fly ash. The composite having % mass ratio of fly ash: NiFe2O4 = 50:50 exhibited maximum CR adsorption from the aqueous solution on account of the higher BET surface area, more porous character, favorable condition for diffusion of dye molecules and combined effect of chemisorption and physisorption. Under optimum conditions, it has shown the recyclability with adsorption capacity of the magnitude 23.33 mg g−1, which is much higher than individual fly ash, NiFe2O4 and other composites. The sorption data provided good fit with pseudo-second order kinetic model. The analyses of the adsorption data indicated that, the Langmuir model provides better correlation with the experimental data.