Citrate Nitrate Auto Combustion Research Articles

Bi3+ doping-enhanced optical and photocatalytic activity with stability of cobalt nickel zinc ferrites for wastewater treatment applications

In this paper, the spinel ferrite nanoparticles Co0.5Ni0.25Zn0.25BixFe2−xO4 (CNZBF) were prepared by citrate-nitrate auto combustion method. Although the substitution process involves a large ion at the expense of a small one, the lattice constant didn't introduce a regular increment behavior with irregular shifts for the peak position at 34.62°, which is related to the (311) plane. Two hypotheses were introduced to justify this behavior. The crystallite size introduced a peculiar behavior in the span of 20.88–14.78 nm with increasing the Bi3+ content. Morphological study via FE-SEM manifested that the CNZBF nanoferrites have agglomerated spherical shapes. Kubelka-Munk function and Tauc's plot for direct allowed transitions were utilized to determine the band gap of all the CNZBF nanoferrites. The doping of Bi tuned the band gap (within 1.55 to 1.25 eV), boosted the light absorption, induced efficient e/h separation, and ensuing charge migration to the Co0.5Ni0.25Zn0.25BixFe2−xO4 surfaces. On account of the CNZBF advantages, a superb removal efficiency (∼96.41 %) of the sample Co0.5Ni0.25Zn0.25Bi0.08Fe1.92O4 via photocatalytic degradation was achieved. After five reusability cycles the nanocatalyst Co0.5Ni0.25Zn0.25Bi0.08Fe1.92O4 introduced 95.08% degradation which demonstrates a trivial efficiency decline of 1.33 % in the photocatalytic activities. These outcomes of excellent photocatalytic activity with the outstanding stability candidate the novel Co0.5Ni0.25Zn0.25Bi0.08Fe1.92O4 for wastewater treatment applications.

Correlation between structural phase transition and physical properties of Co2+/Gd3+ co-substituted copper ferrite

The doping of the spinel ferrites with selective cations usually improves the properties of the parent ferrite. The effect of Co2+/Gd3+ co-substitution on the microstructure, optical, and magnetic properties of Cu1–xCoxFe2–xGdxO4 prepared by the citrate-nitrate auto-combustion synthesis was investigated. Characterization of the samples was performed with powder X-ray diffraction (XRD), Raman and Fourier-transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy, X-ray energy-dispersive spectroscopy, UV-Vis spectroscopy, and a vibrating sample magnetometer. The results of XRD, Raman, and FTIR analysis show a gradual structural phase transition from a tetragonal (I41/amd) structure to a cubic (Fd3¯m) structure. The bandgap energy of the studied samples is in a range of 1.57–1.75 eV with a minimum in sample x = 0.06 and then increases. Magnetic investigations show that the presence of Co2+/Gd3+ cations in an octahedral site of the copper ferrite structure could increase saturation magnetization and coercive field from 567.9 Oe and 23.62 emu/g to 929.4 Oe and 28.27 emu/g, respectively.

The role of the A-site cation and crystal structure on the electrical conductivity of strontium-doped calcium and barium manganites

The influence of A-site cation doping, crystal structure and structural defects (oxygen nonstoichiometry) on the electrical conductivity of Sr-doped CaMnO3 (CSMO) and BaMnO3 (BSMO) was investigated. CSMO and BSMO were prepared by citrate-nitrate autocombustion and coprecipitation synthesis, pressed into pellets and sintered. Since the oxygen nonstoichiometry in CSMO was uniform, the increase in electrical conductivity was primarily caused by the increase in Sr content. On the other hand, the oxygen nonstoichiometry in BSMO was more pronounced and it decreased with Sr-doping. Therefore, the highest conductivities were obtained for the undoped BaMnO3 samples. The electrical conductivities of CSMO were similar to those of widely investigated rare-earth manganites and more than 104 times higher than those of BSMO. Therefore, CSMO has the potential to be a low-cost cathode material in solid oxide fuel cells.

Efficient removal of Pb (II) from water solution using CaFe2−x−yGdxSmyO4 ferrite nanoparticles

Rare-earth doped calcium nano ferrites (CaFe2−x−yGdxSmyO4; x = y = 0.0; x = 0.025, y = 0.05) are synthesized by citrate nitrate auto combustion method. The prepared samples are characterized using X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), high-resolution transmission electron microscope (HRTEM), and vibrating sample magnetometer (VSM) analyses. After that, the samples were examined for Pb (II) ions removal from the water solution. The orthorhombic structure with space group Pnma is ratified from XRD. The average crystallite size of the synthesized powders is estimated from the broadening of the XRD lines in the range of 18–21 nm. FTIR confirms the molecular signature of the samples. The magnetic property is discussed based on super exchange interactions. The hysteresis loop shows two different magnetic behaviors of the investigated sample as well as increasing the coercivity from 14 to 240 G due to the doping. The electrical parameters are discussed in the basic hopping charge model, while the conduction mechanism of the samples will be discussed based on de-Boer and Verwey. The experimental results are subjected to kinetic and isotherm analyses. The Langmuir and Freundlich isotherms describe the adsorption of heavy metal ions as designated by the high correlation coefficient (R2). The use only 4 mg of the doped sample with low price ferrite nanoparticles has been utilized for 99.31% removal of Pb (II) from wastewater at a contact time of 10 min at room temperature.

The effect of synthesis method on oxygen nonstoichiometry and electrical conductivity of Sr-doped lanthanum manganites

The strontium-doped lanthanum manganites (La1-xSrxMnO3, LSMO) have potential use in devices for energy conversion and storage due to their chemical stability and high electrical conductivity. In this study, LSMO (x = 0, 0.1, 0.2, 0.3) were prepared by the citrate-nitrate autocombustion (CNA) and coprecipitation synthesis. The formation of the LSMO phase was confirmed by X-ray diffraction and the lattice parameters were determined by Rietveld refinement analysis. The oxygen nonstoichiometry in samples was determined by permanganate titration. The results of electrical conductivity measurement have shown semiconductor behaviuor in all samples, with conductivity rising with temperature and Sr-amount. Furthermore, it was observed that LSMO samples prepared by the coprecipitation method possess higher conductivity than samples prepared with the CNA method due to the higher oxygen nonstoichiometry. Electrical conductivities of all LSMO samples were in 10−2–0.45 Ω−1 cm−1 range, which is comparable to the conductivity of Si.

Simultaneous oxidation of aromatic compounds using Sr‐doped lanthanum manganites as catalysts

Strontium-doped lanthanum manganites, La1-xSrxMnO3 (LSMO), are promising and affordable catalysts for oxidative degradation of volatile organic compounds. LSMO catalysts (x = 0, .1, .2, and .3) were prepared by the citrate-nitrate autocombustion (CNA) and coprecipitation synthesis. The phase composition was confirmed by X-ray diffraction and Rietveld refinement analysis, while the oxygen content was determined by Mohr's salt permanganate titration. Morphology and porosity of prepared catalysts was correlated to catalytic oxidation of benzene, toluene, ethylbenzene and o-xylene. It was observed that both synthesis methods yielded catalysts of similar average pore size diameter and specific surface area, but the pore size distribution differed: CNA-prepared catalysts had a multimodal pore size distribution, while the coprecipitated ones had a single maximum at 4 nm. Catalysts prepared by the CNA method have shown a higher catalytic activity in the temperature range 373–723 K, as the presence of Mn3+/Mn4+ mixed valences increased their reducibility.

Synthesis and electrochemical investigation of Z-type barium hexaferrite nanoplatelets

This work reports the supercapacitor performance of Z-type barium hexaferrite (Ba3Co2Fe24O41) nanoplatelets prepared by citrate-nitrate auto combustion approach. The single-phase Z-Type hexagonal structure was confirmed through structural investigation using XRD results. Metal oxygen stretching bands in various environments such as tetragonal and octahedral coordinates has been confirmed using FTIR spectra. Hexagonal plate-like shaped grains were clearly seen from the morphological studies. The magnetic characteristics of Ba3Co2Fe24O41 sample were calibrated with VSM instrument at room temperature. The maximum saturation magnetization of 52.72 emu/g, retentivity of 29.88 emu/g and a coercivity of 124.97 Oe were obtained for Ba3Co2Fe24O41 nanoplatelets. The electrochemical (EC) performance of the Ba3Co2Fe24O41 nanoplatelets was studied for the first time with CV, GCD and EIS analysis. There is no report in the literature on studying the electrochemical performance of such important Ba3Co2Fe24O41 hexaferrites. The electrochemical GCD studies exhibited non-symmetrical discharge curves and a significant specific capacitance of 126 F g−1 was attained at constant discharge current density (0.5 A g−1). The cyclic stability observation exposed 93% of capacitance retention after 1000 cycles, recommending the potential utilization of Ba3Co2Fe24O41 hexaferrites in energy-storable devices.

Tuning the Microstructure, Magnetostatic and Magnetodynamic Properties of Highly Al-Substituted M-Type Sr/Ca Hexaferrites Prepared by Citrate-Nitrate Auto-Combustion Method

Tuning the Microstructure, Magnetostatic and Magnetodynamic Properties of Highly Al-Substituted M-Type Sr/Ca Hexaferrites Prepared by Citrate-Nitrate Auto-Combustion Method

Tuning the morphology and magnetic properties of single-domain SrFe8Al4O19 particles prepared by a citrate auto-combustion method

Single-domain particles of SrFe8Al4O19 were prepared by thermal treatment of porous products of citrate–nitrate autocombustion at 1200 °C, and the effect of synthesis time on the particle morphology and magnetic properties was estimated. The procedure allows one to obtain SrFe8Al4O19 particles with mean diameters of 100–460 nm and coercivity ranges from 14.5 to 18.4 kOe, while ferromagnetic resonance frequencies vary from 149 to 164 GHz.

Permanganometric determination of oxygen nonstoichiometry in manganites

Strontium and lanthanum manganites are nowadays the subject of extensive research because of their promising electrical and magnetic properties. Strontium manganite, SrMnO3, was successfully prepared by citrate-nitrate autocombustion (CNA) and by the coprecipitation method. These methods were then applied to synthesis of strontium doped lanthanum manganites, La1-xSrxMnO3 (x ​= ​0, 0.1, 0.2 and 0.3). The optimal phase formation conditions were determined by thermogravimetry and differential scanning calorimetry. Crystallization of precursors and calcined powders was studied by X-ray diffraction. Powders, in which pure manganite phase was obtained, were also analyzed by permanganate titration with Mohr’s salt in order to determine oxygen nonstoichiometry. Oxygen stoichiometry was achieved in SrMnO3 powders obtained by the CNA method and calcined at 1000 ​°C as well as in powders obtained by the coprecipitation method and calcined at 1200 ​°C. La1-xSrxMnO3 phase was oxygen stoichiometric for x ​= ​0.3 while decreasing of x resulted in cation deficiency, i.e. oxygen excess. Oxygen deficit was achieved for x ​= ​0.09 upon calcination at 1200 ​°C. The obtained results were confirmed by thermogravimetry and the Rietveld refinement analysis.

Physical properties of Al-doped cobalt nanoferrite prepared by citrate–nitrate auto combustion method

Cobalt aluminum ferrites have been synthesized by citrate–nitrate auto combustion method. To obtain different crystallite sizes, the prepared powder was heated at different temperatures. X-ray diffraction (XRD) measurements showed that all the prepared samples were crystalized in single phase cubic spinel structure. Different heat treatments lead to different particle sizes which was confirmed by transmission electron microscopy (TEM) micrograph. The crystallite size (D) of the prepared samples ranges from 5 to 37 nm. The structure and elastic properties were investigated using Fourier-transform infrared (FTIR) spectroscopy. The elastic moduli and Debye temperature were calculated out of the FTIR results. The magnetic properties were studied using vibrating sample magnetometer (VSM) and the magnetic parameters; saturation magnetization ( $$M_{\text {S}}$$ ) and coercitvity ( $$H_{\text {c}}$$ ) were determined. The $$M_{\text {S}}$$ and $$H_{\text {c}}$$ size dependence of CoFeAlO $$_{4}$$ nanoparticles introduce a distinctive behaviour; from a structure with multi magnetic domains ( $$D> 9$$ nm) to that without magnetic domains (single domain structure) below $$D= 9$$ nm. Interestingly, the signature of the change from multi-domain to a single magnetic domain is reflected in the size dependence of the elastic moduli and Debye temperature obtained from FTIR results.

Dependence of structural/morphological and magnetic properties of LaCoO3 nanoparticles prepared by citrate nitrate auto combustion

Perovskite LaCoO3 nanopowders were synthesized via solution auto-combustion chemical route, using lanthanum and cobalt nitrates as oxidants and citric acid as fuel. Qualitative and Quantitative phase analysis performed by Rietveld refinements indicated the presence of pure single LaCoO3 phase. From fit parameters, goodness of fit “S” parameter (close to 1) and the difference between the experimental and theoretical XRD patterns. FTIR spectra showed two characteristics bands at 408 and 589 cm−1 characteristics of metal oxygen bands vibration, thus confirming the formation of LaCoO3 phase, whereas the strong absorption band at 589 cm−1 was assigned to Co–O stretching vibration and O–Co–O deformation modes of LaCoO3 compound. SEM micrographs clearly revealed quite spherical particles with a mean size in the range 139–178 nm and high tendency to clustering, meanwhile EDAX analysis confirmed the corresponding chemical composition with homogeneous distribution of the constituent elements. A weak paramagnetic order is observed irrespective of F/O ratio, with slight increase of the effective magnetic moment with F/O ratio; 2.72–2.93 μB, due to the presence of more high spin states.

Optical And Electrical Properties of PVA/A-Al2O3 Nanocomposite Films

In the present study, a-Al2O3 nanoparticles were synthesized using the citrate-nitrate auto combustion method. Nanocomposites of PVA/a-Al2O3 were intended by solution casting technique. The micrograph of samples were analysed by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and UV-visible spectroscopy analysis. UV-visible results showed that the direct optical band gap decreased with the increase of a-Al2O3 content. The refractive index has been dissected using Wemple and DiDomenico model. Hopping of charge carriers besides interfacial polarization could expound the demeanor of dielectric constant (E'), dielectric loss (E'') and ac electrical conductivity (0-ac) with the frequency and temperatures.

Influence of Lanthanum Doping on Structural and Electrical/Electrochemical Properties of Double Perovskite Sr2CoMoO6 as Anode Materials for Intermediate-Temperature Solid Oxide Fuel Cells.

Lanthanum (La3+)-doped double perovskites Sr2CoMoO6 (Sr2-xLaxCoMoO6, 0.00 ≤ x ≤ 0.03) were synthesized via the citrate-nitrate autocombustion route. The Reitveld refinement analysis of X-ray diffraction reveals the tetragonal symmetry as the main phase with space group I4/m and also confirms the presence of some peaks corresponding to extra phase SrMoO4. The SEM micrograph images reflect that grains are in irregular shape and sizes for all samples. Average grain size gradually decreases with the increase of the SrMoO4 phase. The X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of mixed valence states of Mo5+/Mo6+, Co2+/Co3+, and O-lattice/O-chemisorbed/O-physisorbed species. Coefficient of thermal expansion (CTE) analysis shows that the particular composition Sr1.97La0.03CoMoO6 has the lowest CTE value among the compositions studied. The electrical conductivity of Sr2CoMoO6 is enhanced effectively by doping La at Sr sites. The measured area-specific resistance (ASR) for the composition Sr1.97La0.03CoMoO6 (SLCM03) is found to be appreciably low, ∼0.053 Ohm cm-2 at 800 °C. The obtained highest electrical conductivity with the lowest activation energy and low ASR value for the composition Sr1.97La0.03CoMoO6 encompasses it as a promising candidate for anode material in the intermediate-temperature solid oxide fuel cell (IT-SOFC) application.

Investigation of Transport Properties of Pr Doped Cerium Oxide Nanoparticles as a Solid Electrolyte for IT-SOFC Applications

Pure and Pr doped CeO2 nanoparticles were synthesized by citrate–nitrate auto combustion method. The XRD patterns of the prepared nanoparticles were found to be polycrystalline nature having cubic fluorite CeO2 structure. SEM images depicted all the samples exhibited flaky and porous structure with few large aggregates. FT-Raman studies showed the suppression of F2g peak in Pr doped CeO2 nanoparticles which indicated the increased oxygen vacancy concentration. UV-DRS spectra revealed the red shifting of absorption edge on Pr doping. The vibrational band assignment of pure and Pr doped CeO2 nanoparticles were analyzed by FT-IR spectroscopy. PL intensities of doped CeO2 nanoparticles decreased compared with pure CeO2 nanoparticles due to the evolution of non-radioactive oxygen vacancies in the structure. The variation of ionic conductivity as a function of temperature was studied using impedance spectroscopy for pure and Pr doped CeO2 nanoparticles. It was observed that the ionic conductivity of Pr doped CeO2 nanoparticles increased compared to pure CeO2 nanoparticles at the intermediate temperature.

Structural, optical and magnetic properties of Pr doped CeO2 nanoparticles synthesized by citrate–nitrate auto combustion method

In the present work, pure and Pr doped CeO2 nanoparticles in the form of Ce1−xPrxO2 (x = 0, 0.05, 0.10, 0.15 and 0.20) were synthesized by citrate–nitrate auto combustion method. The combustion derived products were annealed at 700 °C and characterized by X-ray diffraction (XRD) studies, scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-diffuse reflectance spectroscopy (UV-DRS), Fourier transform-infrared spectroscopy (FT-IR), Fourier Transform-Raman Spectroscopy (FT-Raman), photoluminescence analysis (PL) and vibrating sample magnetometer (VSM) studies. XRD studies revealed that all the samples exhibited single phase cubic fluorite structure. SEM images displayed that pure and Pr doped CeO2 nanoparticles had irregular flaky shape with few agglomerations. TEM results show the proper formation of cubic fluorite structure of nanoparticles. UV-DRS spectroscopy results showed the red shifting in the absorption band edge with increased Pr concentration. The vibrational band assignment of pure and Pr doped CeO2 nanoparticles were analyzed by FT-IR spectroscopy. FT-Raman studies revealed increased defect concentration for the doped samples compared with pure CeO2. PL intensities of doped CeO2 nanoparticles decrease compared with pure CeO2 nanoparticles due to the evolution of non-radioactive oxygen vacancies in the structure. VSM results depicted the suppression of ferromagnetic behavior on Pr doping.

Rare Earth Yb3+ Doped Gd2O3 Single Phase Nanophosphors: Structural, Morphological and Photoluminescence Studies

In this paper, a report has been acclaimed on the structural, morphological and photoluminescence properties of the pure and Yb3+ (2, 5 and 10 wt %) doped gadolinium oxide nanophosphor, synthesized by the citrate-nitrate auto combustion method. The influence of doping concentration on the properties of the prepared phosphor was studied using different characterization techniques. Structural studies carried out using XRD revealed crystalline cubic phase for both the pure and doped Gd2O3 nanoparticles. The phase formation and purity were further confirmed from the FTIR spectra. Surface morphology was found using SEM analysis showed the clusters of tiny particles. Optical absorption measurements were recorded in the UV-Vis-NIR wavelength region and the optical band gap variations with dopant concentration were discussed. The probable mechanism for the visible PL emissions by Yb3+ doped Gd2O3 phosphors are explained by different transition phenomenon. Fluorescence lifetime along with energy transfer efficiency from Gd3+ to Yb3+ was determined.

Preparation and characterization zirconium and samarium co-doped ceria solid electrolytes for IT-SOFC applications

Zirconium and Samarium co-doped ceria solid electrolyte materials Ce0.8–xSm0.2ZrxO2-δ (x=0, 0.05, 0.10, 0.15 and 0.20) for intermediate temperature-solid oxide fuel cells were synthesized by citrate-nitrate auto combustion synthesis technique. Powder x-ray diffraction results reveal that all the synthesized samples show a single-phase with cubic fluorite structure. The lattice parameter values were calculated from the powder x-ray diffraction data. Samples with high density were obtained by sintering the samples at 1300°C for 4h. The average crystallite sizes were calculated from the Scherer formula. Surface morphologies of all the samples were obtained by using the scanning electron microscope. The total ionic conductivity of all the samples was carried out from impedance analysis in the temperature range RT – 500°C. The highest total ionic-conductivity with lowest activation energy values were observed for Ce0.65Sm0.2Zr0.15O2-δ at 500°C makes it as a useful solid electrolyte material for intermediate temperature-solid oxide fuel cells (IT-SOFCs) applications.

Structural and electrical characterizations of cerium (Ce3+)-doped double perovskite system Sr2NiMoO6−δ

The double perovskite system Sr2−xCexNiMoO6−δ (SCNM) with 0.01 ≤ x ≤ 0.05 was synthesized by the citrate–nitrate auto-combustion synthesis route. Thermal studies were carried out by simultaneous differential scanning calorimetry and thermal gravimetry. Phase constitution was analyzed by powder X-ray diffraction (XRD). Rietveld refinement showed that the major phase exists in tetragonal form with space group I4/m. Microstructural investigations revealed the formation of uniform grains. The electrical conductivity studied by impedance spectroscopy in the temperature range 300–600 °C was found to follow a thermally activated process. The sample with x = 0.01 showed the highest conductivity with lowest activation energy. The electrical conductivity of the system was discussed in terms of identified impurity phases and charge density \(\left[{{\text{Mo}}_{{{\text{Mo}}^{6 +}}}^{5 +} {}^{\prime}} \right]\). The variation of electrical conductivity with composition was explained on the basis of X-ray photoelectron spectroscopy and XRD studies.

Synthesis, characterization and thermal expansion of Ce0.8–xSm0.2ZrxO2-δ Solid electrolytes for IT-SOFC applications

The solid electrolyte materials Ce0.8–xSm0.2ZrxO2- (CSZ) (x=0, 0.05, 0.10 and 0.15) for intermediate temperature-solid oxide fuel cells (IT-SOFCs) are prepared by citrate-nitrate auto combustion (CNAC) method. The x-ray diffraction studies of the prepared samples confirm the presence of single phase-cubic fluorite structure with the space group Fm QUOTE m. The calculated average crystallite sizes are found to be in the range of 14 nm to 19 nm. The lattice parameter values are calculated from the XRD patterns. Microstructure analysis and elemental distributions of the composition of the sintered samples are obtained by using the scanning electron microscope (SEM) and energy dispersive spectrum (EDS). The measurements of coefficients of thermal expansion (TECs) are determined from thermal expansion of the CSZ system. The observed TEC values are found to increase with the increase of the doping content of Zr4+. It is found that the thermal expansion coefficients of Zr4+ and Sm3+ co-doped ceria samples match with commonly used electrode materials for IT-SOFCs.