Lanthanum Ferrite Research Articles

Illumination-enhanced oxygen reduction kinetics in hybrid lithium-oxygen battery with p-type semiconductor

Lithium-oxygen battery has attracted extensive attention for its high energy density. However, the lithium peroxide will accumulate at cathode during the discharge process, resulting in large charge–discharge overpotential. At present, the photo-assisted system reported in some work is an effective way to reduce charge overpotential. But the effect of photo-assisted process on the discharge potential is rarely studied. In this work, p-type semiconductor (lanthanum ferrite) was prepared and the photocurrent reaches 179.4 μA cm−2 at 0.7 V (vs RHE) in 0.1 M KOH. It was assembled in the lithium-oxygen battery which was self-designed based on aqueous electrolyte, and the discharge potential of this battery can be improved under illumination due to the enhancement of the oxygen reduction reaction. With light illumination, the LaFeO3 photocathode can promote discharge potential to 3.24 V compare with 2.81 V in dark and stably cycle for more than 400 h.

Structural, morphological, optical, magnetic and electrochemical behavior of solid state synthesized pure and Sr-doped LaFeO3 nanoparticles

Using the solid state reaction route, the present study compares the surface structural behaviour, electrochemical sensing, and magnetic properties of undoped and Sr-doped lanthanum ferrite (LaFeO3) products. Only an orthorhombic crystalline phase was found using the powder X-ray diffraction (XRD) studies for the undoped LaFeO3 and Sr-doped LaFeO3 materials, respectively. The Transmission Electron Microscopy (TEM) analysis confirms the polycrystalline nature of the doped nanoparticles with narrow sized distribution (particle size range of 10–15 nm). The Energy dispersive X-ray (EDX) analysis confirms the presence of the Sr element in the lanthanum ferrite. The vibrational group of the synthesized products is thoroughly discussed. Powder XRD, TEM, optical absorption spectra, vibrating sample magnetometer (VSM), and cyclic voltammetry (CV) reveal that Sr-doped LaFeO3 nanoparticles have a smaller size (10 nm), dispersed particles, a higher band gap (2.35 eV), coercivity (4275 Oe), and specific capacitance (256 at 2 mV/s) when compared to undoped LaFeO3 nanoparticles.

CO conversion over LaFeO3 perovskite during chemical looping processes: Influences of Ca-doping and oxygen species

As a critical intermediate substance or a target product, CO plays a vital role in the chemical looping processes. The control of CO conversion is significant since chemical looping processes with various target products have different requirements for CO content. In the present work, the CO oxidation behaviors with different oxygen species were investigated experimentally and theoretically with Ca-substituted lanthanum ferrite (LaFeO3) as the oxygen carrier to regulate the CO conversion. The results showed that the CO2 yield increased significantly when the adsorbed oxygen species was removed, suggesting that the lattice oxygen was the active oxygen species. It was consistent with the calculation result that the energy barrier of CO oxidation with lattice oxygen was lower than that with surface adsorbed oxygen. Moreover, the CO2 yield increased with the increase of Ca concentration, indicating that Ca doping was favorable for lattice oxygen migration and further promoted CO oxidation.

Preparation and characterization of Sr-doped LaFeO3

The present work is intended to increase orthorhombic distortion in lanthanum ferrite system by incorporating Sr as a dopant in lanthanum ferrite (La1-xSrxFeO3) [x = 0.02, 0.04, 0.06, 0.08, 0.10]. The systems are synthesized via Sol-gel combustion method. Structure is confirmed by X-ray diffraction (XRD). The Rietveld refined XRD data confirms the orthorhombic crystal structure of LFO and LSFO belongs to space group Pbnm. Impedance modulus and Nyquist plot were studied from Impedance spectroscopy data. To check its potential as a dielectric, frequency dependence dielectric behavior was studied. Frequency-dependent dielectric constant showed dispersive behavior at low frequencies with low loss.

Efficiency LaFeO3 and BiOI heterojunction for the enhanced photo-Fenton degradation of tetracycline hydrochloride

Long-term exposure to antibiotic may have adverse effects on human health including carcinogenesis or teratogenicity and the emergence of antibiotic resistance. Developing effective catalysts to degrade antibiotic pollution is an urgent demand. Herein, a heterogeneous photo-Fenton catalyst with enhanced tetracycline hydrochloride (TCH) degradation activity was developed by hydrothermally synthesizing lanthanum ferrite (LaFeO3) and bismuth iodide oxide (BiOI). LaFeO3/BiOI showed excellent repeatability and stability, and still maintained an extremely high degradation efficiency of 80.6% after three cycles. The LaFeO3/BiOI with 35 wt% LaFeO3 showed significantly enhanced degradation rate (93.6%) of TCH within 40 mins in the photo-Fenton system, compared with single photocatalytic degradation (41.2%) and Fenton degradation (83.1%). The parameter characterization and quenching experiments were carried out on the heterojunction. The possible degradation mechanisms of TCH were proposed. The results indicated that the existence of the built-in electric field in the heterojunction effectively promote the separation of photogenerated electrons and hole pairs. The photoelectrons activate H2O2 to generate OH and accelerate FeIII/FeII conversion. This work has developed a promising heterogeneous photo-Fenton catalysts, and stipulated some new insights for the removal of antibiotic pollutants.

Crystal Structure Refinement, Magnetic and Mössbauer Analysis of LaFeO3 Perovskite Synthesized by SOL-GEL method

In this present study, LaFeO3 nanoparticles have been successfully synthesized by sol-gel method and annealed the produced sample at 600 °C, 800 °C, 1000 °C, 1200 °C. The influence of annealing temperature on the structural, morphological and magnetic properties of the developed nanoparticles has been investigated systematically. The XRD patterns confirmed the absence of impurity or secondary phase in the spectra. Orthorhombic crystal system of pbnm space group was successfully determined by Rietveld refinement. Scherrer method was used to calculate crystallite size. An increasing trend in crystallite size and improving crystallinity were obtained with increasing annealing temperature. Scanning Electron Microscopy (SEM) images showed a homogeneous distribution of increasing average particle sizes ranging from 35 nm to 450 nm. Magnetic hysteresis (M-H) loop was recorded at room temperature revealed weak ferromagnetism in nanocrystalline lanthanum ferrite. The maximum magnetization was found to be 1.82 emu/g at 600 °C, and it was sharply decreased to 0.33 emu/g at 1200 °C annealing temperature. Interactions between the antiferromagnetic and ferromagnetic exchange coupling are influenced by the uncompensated spin canting causes to accomplish the ordering of weak ferromagnetism in LaFeO3. Moreover, the bond length of Fe-O and the bond angle of Fe-O-Fe were decreased with decreasing annealing temperature. As a result, Fe ions, come closer to each other, enhancing the ferromagnetic exchange interaction between iron ions via oxygen ions made significant contributions to the magnetic properties of LaFeO3 nanoparticles. Mössbauer spectroscopy was used to find the nature of interactions for the observed magnetic behavior depending on different site environments with varying annealing temperatures. Bangladesh Journal of Physics, 27(2), 27-37, December 2020

Modified Catalysts and Their Fractal Properties

Obtaining high-area catalysts is in demand in heterogeneous catalysis as it influences the ratio between the number of active surface sites and the number of total surface sites of the catalysts. From this point of view, fractal theory seems to be a suitable instrument to characterize catalysts’ surfaces. Moreover, catalysts with higher fractal dimensions will perform better in catalytic reactions. Modifying catalysts to increase their fractal dimension is a constant concern in heterogeneous catalysis. In this paper, scientific results related to oxide catalysts, such as lanthanum cobaltites and ferrites with perovskite structure, and nanoparticle catalysts (such as Pt, Rh, Pt-Cu, etc.) will be reviewed, emphasizing their fractal properties and the influence of their modification on both fractal and catalytic properties. Some of the methods used to compute the fractal dimension of the catalysts (micrograph fractal analysis and the adsorption isotherm method) and the computed fractal dimensions will be presented and discussed.

Synthesis and characterization of cerium doped lanthanum ferrites

In this work, Lanthanum ferrites doped with cerium concentration of 1% at, 3% at, and 5% at were synthesized by sol-gel method, considering calcination temperatures of 700 °C, 800 °C and 900 °C. Conventional X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry techniques were used to study the cerium effect and calcination temperature on structural, morphological, and magnetic properties of powder samples. The identified phase for samples corresponds to an orthorhombic perovskite structure with Pbnm (#62) space group without the presence of impurity phases. Crystallite size increases with calcination temperature, which is associated with crystallinity of the samples, however a decrease in the crystallite size of the doped samples can be evidenced with respect to the pure sample. A weak ferromagnetic behavior coexisting with a paramagnetic behavior is evidenced for the samples with calcination temperatures of 700 °C and 800 °C. The samples calcined at 900 °C, reflect a predominant paramagnetic behavior.

Conventional synthesis of perovskite structured LaTixFe1-xO3: A comprehensive evaluation on phase formation, opto-magnetic, and dielectric properties

Abstract Perovskite structured LaTixFe1-xO3 (x = 0, 0.05, 0.15, 0.25) lanthanum ferrites were synthesized by conventional solid-state reaction. The structural Rietveld refinement and Raman analysis were conducted and confirmed that single-phase orthorhombic phase with Pbnm symmetry formed. The positions of the ions and their bonds of these ferrites were investigated. The spherical shaped morphology of these ferrites was examined. The quantitative chemical composition and distribution of these ferrites were confirmed. The excitonic absorption edge was observed at 590 nm; ascribed to the electronic transition from O2p→Fe3d and optical band gap values increased from 1.85– 2.02 eV as Ti concentration increased. The dielectric and magnetic behavior of these ferrites was studied. It is suggested that synthesized LaTixFe1xO3 powders with different properties could be tailored for different requirements.

Preparation of Crystalline LaFeO3 Nanoparticles at Low Calcination Temperature: Precursor and Synthesis Parameter Effects.

Substantial effort has been devoted to fabricating nanocrystalline lanthanum ferrite (LaFeO3), and calcination is the crucial process of crystallization in both high-temperature strategies and wet chemical methods. Lowering the calcination temperature gives the ability to resist the growth and agglomeration of nanoparticles, therefore contributing to preserve their unique nanostructures and properties. In this work, we prepared crystalline LaFeO3 nanoparticles with a calcination process at 500 °C, lower than the calcination temperature required in most wet chemistry methods. Correspondingly, the experimental conditions, including stoichiometric ratios, pH values, precipitants, complexant regent, and the calcination temperatures, were investigated. We found that the crystalline LaFeO3 was formed with crystalline NaFeO2 after calcination at 500 °C. Furthermore, the structure of FeO6 octahedra that formed in coprecipitation was associated with the process of crystallization, which was predominantly determined by calcination temperature. Moreover, an illusion of pure-phase LaFeO3 was observed when investigated by X-ray diffraction spectroscopy, which involves amorphous sodium ferrite or potassium ferrite, respectively. These findings can help prepare nanostructured perovskite oxides at low calcination temperatures.

Assessment of the Arsenic Removal From Water Using Lanthanum Ferrite.

The catalytic performance of a perovskite‐type lanthanum ferrite LaFeO3 to remove arsenic from water has been investigates for the first time. LaFeO3 was prepared by citrate auto‐combustion of dry gel obtained from a solution of the corresponding nitrates poured into citric acid solution. Kinetic studies were performed in the dark with As(V) and in the dark and under UV‐C irradiation at pH 6–7 with As(III) (both 1 mg L−1), and As : Fe molar ratios (MR) of 1 : 10 and 1 : 100 using the LaFeO3 catalyst. As(V) was removed from solution after 60 min in the dark in 7 % and in 47 % for MR=1 : 10 and MR=1 : 100, respectively, indicating the importance of the amount of the iron material on the removal. Oxidation of As(III) in the dark was negligible after 60 min in contact with the solid sample, but complete removal of As(III) was observed within 60 min of irradiation at 254 nm, due to As(III) photooxidation to As(V) and to As(III) sorption to a minor extent. Morphological and microstructural studies of the catalyst complement the catalytic testing. This work demonstrates that LaFeO3 can be used for the removal of As(III) from highly arsenic contaminated water.

The influence of Ca substitution on LaFeO3 nanoparticles in terms of structural, optical and catalytic properties

Nanoparticles of Lanthanum ferrite (LaFeO3) and calcium doped lanthanum ferrite (La1-xCaxFeO3, x= 0.1–0.3) with perovskite structure are synthesized by solution combustion method using polyethylene glycol as fuel. The prepared samples are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–Vis diffuse reflectance spectroscopy, and UV- Vis absorption spectroscopy. The photocatalytic activity was examined with Methylene blue (MB) dye degradation. The results revealed that as the dopant concentration increases, the band gap decreases tremendously but the photocatalytic degradation efficiency decreases. This may be due to the fact that the dopant acts as a site for electron-hole pair recombination which decreases the degradation efficiency.

Magnetic behavior, photocatalytic activity and gas-sensing performance of porous lanthanum ferrites powders

Porous perovskite lanthanum ferrites (LaFeO3) powders were synthesized under the different pH value by sol-gel technique and self-propagating combustion method. After the characterization with XRD, SEM, VSM, nitrogen adsorption-desorption isotherm and UV–Vis spectroscopy, the magnetic properties, photocatalytic activity and gas-sensing performance are discussed in detail. All LaFeO3 samples exhibit ferromagnetism for the spin mismatch due to oxygen vacancies. LaFeO3 powders present the good photocatalytic performance to MB and could be easily separated by magnetic separation technique after photocatalysis. Furthermore, the LaFeO3 gas sensors exhibited the considerable sensitivity to ethanol gas. Among all samples, LF-1 (LaFeO3 powders prepared at pH = 1) present the highest removal rate of MB (68%), the largest saturation magnetization (4.57 emu/g) and the best gas response to ethanol. The highest response for LF-1 sensor reaches (263.4) at the optimized operating temperature of 250 °C to 100 ppm ethanol gas, which should be attributed to the higher oxygen vacancies.

The enhanced water splitting activity of a ZnO-based photoanode by modification with self-doped lanthanum ferrite.

The difficult separation and transfer of photoexcited charge carriers in composite photoelectrodes is a decisive factor limiting the efficiencies of semiconductor-based photoelectrochemical water splitting systems. Herein, to further enhance the photoelectrochemical properties of ZnO-based photoanodes, we constructed composite ZnO nanoarray photoanodes with Fe-self-doped lanthanum ferrite (denoted as La1-xFe1+xO3/ZnO NRs), which had the effect of killing two birds with one stone. This improvement strategy differs from the previously popular multi-step modification process, and integrates the dual benefits of a heterojunction and cocatalyst using the same material, the doped LaFeO3, which bypasses the shortcomings of multi-step charge transfer. Gratifyingly, benefitting from the suitable energy bands and excellent electrocatalytic oxygen evolution activity of La0.9Fe1.1O3, the photoanode exhibits outstanding bulk charge separation and surface charge utilization efficiencies, as well as achieving a photocurrent density that is over three times higher than that of pristine ZnO NRs, with a small onset potential (0.33 V vs. RHE). This electrode modification concept provides guidance for the development of other highly active photoelectrodes.

Tailoring of properties in the preparation level of nano crystalline Ce0.8Sm0.2O1.9-δ(SDC) for the use of SOFC electrolyte

Ce0.8Sm0.2O1.9-δ (SDC) has been a potential candidate for SOFC electrolyte for its compatibility with other cell components such as with Lanthanum ferrite based electrodes. Crystalline Ce0.8Sm0.2O1.9-δ (SDC) has been synthesized by a novel combustion route. A fuel rich configuration of the precursors favours the formation of agglomerate free fine particles. The XRD pattern of the powder has been observed as a function of calcination temperature. As synthesis powder has been observed phase pure except with traces of residual carbon impurities as has been observed from the FTIR pattern. The purity of the as synthesized powder has been attributed to the optimized value of elemental stoichiometric coefficient, which in turn has been attributed to the supplement of optimized thermal energy to the precursor gel. The crystallite size has been calculated and compared for the different calcination temperatures which as expected, has enhanced with the calcinations temperature. The chemical reactivity with LSCF cathode material tested under XRD reveals no reactive phase formed in the operating temperature range. The FESEM image of the powder reveals the fineness of the powder and its homogeneity. Circular discs have been pressed and sintered for densification. Density above 96% was observed from the measurement. The SEM of the sintered pellet has been checked for phase purity and pure crystalline XRD peaks confirmed the crystalline character. The sintering temperature 1450 °C has been observed to be one of the lowest of the reported values. It was attributed to the fine powder with high surface area.The study facilitates a combustion synthesis of ceramic oxide powder in general and of SDC in particular at comparatively low temperatures such as those 550 °C or even lower.

Micro-emulsion synthesis of La1 − xCrxFeO3 nanoparticles: effect of Cr doping on ferroelectric, dielectric and photocatalytic properties

AbstractIn the present study, La1 − xCrxFeO3(x = 0.0, 0.3, 0.6, 0.9, 1.0) was synthesized by micro-emulsion route and characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Scanning electron microscope (SEM), Energy-dispersive X-ray (EDX) techniques. The dielectric, ferroelectric and photocatalytic properties were investigated and compared with un-doped material. The XRD analysis revealed orthorhombic geometry of La1 − xCrxFeO3(x = 0.0, 0.3, 0.6, 0.9, 1.0), Cr was doped successfully into the lattice structure of LaFeO3and particles were spherical and in agglomerated form. The grain sizes were recorded to be 15, 16.9, 17.1, 17.65 and 18.3 (nm) for La1 − xCrxFeO3(x = 0.0, 0.3, 0.6, 0.9, 1.0), respectively. EDX analysis confirmed the purity of LaCrFeO3samples. The lattice parameters, bulk density, X-ray density, crystalline size and porosity were determined were also determined of all the La1 − xCrxFeO3samples. The dielectric constant and dielectric loss values decreased at higher frequency and Cr concentration affected the dielectric properties. The photocatalytic activity (PCA) was evaluated by degrading Congo Red (CR) dye under solar light irradiation and up to 85.43% dye degradation was achieved within 45 min of irradiation. Phyto-toxicity analysis before and after dye degradation was performed, which revealed the toxicity reduction in response of dye degradation. Results revealed that lanthanum ferrite (perovskite) doping with Cr could possibly be employed to enhance the ferroelectric, dielectric and photocatalytic properties.

High-performance composite cathode for electrolysis of CO2 in tubular solid oxide electrolysis cells: A pathway for efficient CO2 utilization

High temperature solid oxide electrolysis cells (SOECs) have a tremendous potential to provide a practical pathway for onsite on demand production of high purity CO by recycling waste CO2 at industry relevant production scale. CO is an important feedstock for production of numerous chemicals required for the pharmaceutical, food and plastics industry. Recently, SOECs are also being developed to produce renewable fuels and energy carriers to allow transport and storage of renewable energy. Despite promising pre-commercial demonstrations, some key technical challenges need to be addressed to make this technology economically feasible. These include lowering capital costs with low cost materials and cell designs, and improvements in the electrode performance and lifetime, the cathode. The conventional Nickel-YSZ cathode is found to be promising in terms of performance during initial operation; however, a continuous supply of valuable reducing gas is needed to prevent oxidation of Ni to NiO, and accelerated degradation has been observed due to Ni migration and deactivation. In the present study we have evaluated the performance of A-site deficient doped lanthanum ferrites ((La0.60Sr0.40)0.95Co0.20Fe0.80O3-x) - Gd0.20Ce0.80O1.95) dual phase mixed ionic and electronic conducting cathode for CO2 electrolysis in a symmetrical tubular cell without the addition of reductant or protective gas during the cell operation. A polarization resistance as low as 0.36 ohm-cm2 was observed at 1.2 V after 350 h of CO2 electrolysis at 800 °C. The electrochemical performance of the electrode is also compared with state-of-the-art Ni-YSZ cathode using similar cells and experimental conditions.

Lanthanum Ferrites-Based Exsolved Perovskites as Fuel-Flexible Anode for Solid Oxide Fuel Cells.

Exsolved perovskites can be obtained from lanthanum ferrites, such as La0.6Sr0.4Fe0.8Co0.2O3, as result of Ni doping and thermal treatments. Ni can be simply added to the perovskite by an incipient wetness method. Thermal treatments that favor the exsolution process include calcination in air (e.g., 500 °C) and subsequent reduction in diluted H2 at 800 °C. These processes allow producing a two-phase material consisting of a Ruddlesden–Popper-type structure and a solid oxide solution e.g., α-Fe100-y-zCoyNizOx oxide. The formed electrocatalyst shows sufficient electronic conductivity under reducing environment at the Solid Oxide Fuel Cell (SOFC) anode. Outstanding catalytic properties are observed for the direct oxidation of dry fuels in SOFCs, including H2, methane, syngas, methanol, glycerol, and propane. This anode electrocatalyst can be combined with a full density electrolyte based on Gadolinia-doped ceria or with La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) or BaCe0.9Y0.1O3-δ (BYCO) to form a complete perovskite structure-based cell. Moreover, the exsolved perovskite can be used as a coating layer or catalytic pre-layer of a conventional Ni-YSZ anode. Beside the excellent catalytic activity, this material also shows proper durability and tolerance to sulfur poisoning. Research challenges and future directions are discussed. A new approach combining an exsolved perovskite and an NiCu alloy to further enhance the fuel flexibility of the composite catalyst is also considered. In this review, the preparation methods, physicochemical characteristics, and surface properties of exsoluted fine nanoparticles encapsulated on the metal-depleted perovskite, electrochemical properties for the direct oxidation of dry fuels, and related electrooxidation mechanisms are examined and discussed.

Lanthanum Ferrite Ceramic Powders: Synthesis, Characterization and Electrochemical Detection Application.

The perovskite-type lanthanum ferrite, LaFeO3, has been prepared by thermal decomposition of in situ obtained lanthanum ferrioxalate compound precursor, LaFe(C2O4)3·3H2O. The oxalate precursor was synthesized through the redox reaction between 1,2-ethanediol and nitrate ion and characterized by chemical analysis, infrared spectroscopy, and thermal analysis. LaFeO3 obtained after the calcination of the precursor for at least 550–800 °C/1 h have been investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). A boron-doped diamond electrode (BDD) modified with LaFeO3 ceramic powders at 550 °C (LaFeO3/BDD) by simple immersion was characterized by cyclic voltammetry and tested for the voltammetric and amperometric detection of capecitabine (CCB), which is a cytostatic drug considered as an emerging pollutant in water. The modified electrode exhibited a complex electrochemical behaviour by several redox systems in direct relation to the electrode potential range. The results obtained by cyclic voltammetry (CV), differential-pulsed voltammetry (DPV), and multiple-pulsed amperometry proved the electrocatalytic effect to capecitabine oxidation and reduction and allowed its electrochemical detection in alkaline aqueous solution.

Influence of secondary oxide phases in enhancing the photocatalytic properties of alkaline earth elements doped LaFeO3 nanocomposites

An improvement in the photocatalytic activity of lanthanum ferrite was attempted by doping individual alkaline earth elements (Ba, Ca and Sr) in its La site and Mg in Fe site to get the desired energy band characteristics. All doped compositions of LaFeO3 were synthesised by sol-gel method. Structural studies show the formation of secondary oxide phases when calcined at 800 °C and phase pure compounds when calcined at 1100 °C. Optical studies reveal the capability of these perovskites to be visible light active and indicate that the bandgaps become narrower after doping alkaline earth elements. Photocatalytic activity was tested through Congo Red (CR) dye degradation studies and hydrogen evolution through water splitting. The results indicate that Mg doped LaFeO3 composite which was obtained after the calcination at 800 °C shows higher hydrogen evolution rate and the highest rate of Congo red (CR) dye degradation among all synthesised compositions of undoped and doped LaFeO3 under natural Xenon lamp irradiation. The possible mechanism of the photocatalytic activity is also proposed in this study.