Modified Pechini Method Research Articles

Investigation of Sr-based perovskites for redox-type thermochemical energy storage media at medium-high temperature

Thermochemical heat storage system exhibits extraordinary properties compared with sensible or latent heat storage system. Owing to the versatility of perovskite, Sr-based perovskites were investigated for redox-type thermochemical energy storage at medium-high temperature. In this study, SrCoO3-δ, SrFeO3-δ and SrMnO3-δ were prepared via a modified Pechini method. The oxidation enthalpy of each sample was measured using a combination of tubular furnace and DSC. Composition analysis, redox and cyclability tests revealed that SrFeO3-δ possesses favorable behavior validating the design principles.

CO2-Tolerant Oxygen Permeation Membranes Containing Transition Metals as Sintering Aids with High Oxygen Permeability

Chemical doping of ceramic oxides may provide a possible route for realizing high-efficient oxygen transport membranes. Herein, we present a study of the previously unreported dual-phase mixed-conducting oxygen-permeable membranes with the compositions of 60 wt.% Ce0.85Pr0.1M0.05O2-δ-40 wt.%Pr0.6Sr0.4Fe0.8Al0.2O3-δ (M = Fe, Co, Ni, Cu) (CPM-PSFA) adding sintering aids, which is expected to not only improve the electronic conductivity of fluorite phase, but also reduce the sintering temperature and improve the sintering properties of the membranes. X-ray powder diffraction (XRD) results indicate that the CPM-PSFA contain only the fluorite and perovskite two phases, implying that they are successfully prepared with a modified Pechini method. Backscattered scanning electron microscopy (BSEM) results further confirm that two phases are evenly distributed, and the membranes are very dense after sintering at 1275 °C for 5 h, which is much lower than that (1450 °C, 5 h) of the composite 60 wt.%Ce0.9Pr0.1O2-δ-40 wt.%Pr0.6Sr0.4Fe0.8Al0.2O3-δ (CP-PSFA) without sintering aids. The results of oxygen permeability test demonstrate that the oxygen permeation flux through the CPCu-PSFA and CPCo-PSFA is higher than that of undoped CP-PSFA and can maintain stable oxygen permeability for a long time under pure CO2 operation condition. Our results imply that these composite membranes with high oxygen permeability and stability provide potential candidates for the application in oxygen separation, solid oxide fuel cell (SOFC), and oxy-fuel combustion based on carbon dioxide capture.

Magnetic properties of bulk nanocrystalline cobalt ferrite obtained by high-pressure field assisted sintering

We present here an investigation aimed at exploring the role of the microstructure on the magnetic properties of nanostructured cobalt ferrite. Bulk, almost fully dense, nanograined ferrites have been obtained starting from nanopowders prepared by a simple, inexpensive, water-based, modified Pechini method. This synthesis yielded largely aggregated, pure single-phase cobalt ferrite nanoparticles of ca. 35 nm average size, which have been then densified by high-pressure field-assisted sintering. Different sintering conditions (pressure up to 650 MPa and temperature up to 800 °C) and procedures have been used on both as-prepared and milled nanopowders in order to obtain materials with a spectrum of complex microstructures. In all cases, the sintering process did not produce any change in the phase composition. At the same time, using a high uniaxial pressure in combination with relatively low sintering temperatures and times, allowed for obtaining a high degree of densification while preserving the nanometric size of the crystallites. Moreover, we observed that in the densified materials the best magnetic properties are not necessarily associated with a more uniform microstructure, but rather arise from a delicate balance between moderate aggregation, grain size and high density.

X-ray powder diffraction data of LaNi0.5Ti0.45Co0.05O3, LaNi0.45Co0.05Ti0.5O3, and LaNi0.5Ti0.5O3 perovskites

In the present work, LaNi0.5Ti0.45Co0.05O3, LaNi0.45Co0.05Ti0.5O3, and LaNi0.5Ti0.5O3 perovskites were synthesized by the modified Pechini method. These materials were characterized using X-ray fluorescence, scanning electron microscopy, and powder X-ray diffraction coupled to the Rietveld method. The crystal structure of these materials is orthorhombic, with space group Pbnm (No 62). The unit-cell parameters are a = 5.535(5) Å, b = 5.527(3) Å, c = 7.819(7) Å, V = 239.2(3) Å3, for the LaNi0.5Ti0.45Co0.05O3, a = 5.538(6) Å, b = 5.528(4) Å, c = 7.825(10) Å, V = 239.5(4) Å3, for the LaNi0.45Co0.05Ti0.5O3, and a = 5.540(2) Å, b = 5.5334(15) Å, c = 7.834(3) Å, V = 240.2(1) Å3, for the LaNi0.5Ti0.5O3.

Eu3+-doped ratiometric optical thermometers: Experiment and Judd-Ofelt modelling

Rare earth-doped materials are successfully utilized as non-contact optical temperature sensors. Thermal sensing is usually based on the ratiometric technique between two separate emission lines originated from thermally-coupled levels. We study Gd 2 O 3 :Eu 3+ 1 at.% and YAG: Eu 3+ 4 at.% phosphors as luminescence thermometers in 298–473 K range using both conventional experimental and Judd-Ofelt based theoretical approaches. Thermometric performances of suggested sensors were quantified through absolute and relative thermal sensitivities and temperature resolution. Experiment and theoretical modelling gave similar results. This proves the theoretical model as a simple and fast method for estimation of the Eu 3+ -doped thermometer perspectives. • Eu 3+ -doped phosphors were synthesized via different modified Pechini methods. • Gd 2 O 3 :Eu 3+ and YAG:Eu 3+ nanopowders were used as contactless luminescence thermometers. • Thermometric performances were estimated through thermal sensitivities and temperature resolution. • Experimental approach and Judd-Ofelt based theoretical model give similar results.

Highly active and novel A-site deficient symmetric electrode material (Sr0.3La0.7)1−x (Fe0.7Ti0.3)0.9Ni0.1O3−δ and its effect on electrochemical performance of SOFCs

A-site deficient (Sr0.3La0.7)1-x (Fe0.7Ti0.3)0.9Ni0.1O3-δ ((SL)1-xFTN) symmetrical electrodes with compositions x = 0.1, 0.2 and 0.3 denoted as SLFTN-01, SLFTN-02, and SLFTN-03 respectively were synthesized via modified Pechini method. The as prepared samples were further coated on LGSM electrolyte through screen-printing technique. Electrochemical performance was significantly improved for A-site deficient (SL)1-xFTN due to increased concentration of oxygen vacancy. XRD patterns revealed better reversibility for (SL)1-xFTN with rhombohedral structure. Low polarization resistance (Rp) ~0.210, 0.195 and 0.165 Ωcm2 (in dry H2) and 0.069, 0.046 and 0.043 Ωcm2 (in air) was measured for SLFTN-01, SLFTN-02, and SLFTN-03 respectively at a temperature of 750 °C. Highest conductivities ~326, 338 and 342 Scm−1 were calculated in air and the conductivities obtained in dry H2 were ~0.64, 0.81 and 1.01 Scm−1 at 700 °C. It was observed that small polaron mechanism was responsible for the decreased conductivity with the increased temperature range. The fabricated symmetrical cell ((SL)1-xFTN/LDC|LSGM|LDC/(SL)1-xFTN), maintained good stability without any degradation during the test time ~500 h (in air) and 100 h (in dry H2). The detailed investigations categorized the fabricated cells well suited as anode and cathode with improved performance and excellent stability both in oxidizing and reducing atmospheres.

Structure and transport properties of the novel (Dy,Er,Gd,Ho,Y)3Fe5O12 and (Dy,Gd,Ho,Sm,Y)3Fe5O12 high entropy garnets

High-entropy, iron-containing, garnet-structured oxides with (Dy,Er,Gd,Ho,Y)3Fe5O12 and (Dy,Gd,Ho,Sm,Y)3Fe5O12 compositions are synthesized for the first time. A modified Pechini method followed by calcination at 700 °C and sintering at 1300 °C enables obtaining single-phase, homogenous materials of cubic structure with Ia-3d symmetry. High-temperature in-situ X-ray diffraction studies show excellent phase stability of the garnets, as well as moderate thermal expansion coefficient, ca. 11·10−6 K-1 in 25−1000 °C temperature range. Raman spectroscopy measurements indicate the presence of local distortion of structural polyhedra, likely associated with the high-entropy effect. The collected Mossbauer spectra confirm distorted character of the lattice. Influenced by the presence of Fe3+ in locally distorted octahedra and tetrahedra, the electrical conduction at low temperatures of both oxides remains much lower comparing to Y3Fe5O12 (yttrium iron garnet - YIG), as well as to other rare-earth garnets up to 600 °C, where it reaches value similar to YIG.

Microstructural analysis of highly active cathode material La0.7Sr0.3Ti0.15Fe0.65Ni0.2O3-δ (LSTFN) by optimizing different processing parameters

The modified Pechini method was applied to prepare a highly active and novel cathode material La0.7Sr0.3Ti0.15Fe0.65Ni0.2O3-δ (LSTFN). This material was coated on the LGSM electrolyte through a screen-printing technique with variable thicknesses of 28 ± 8, 41 ± 8, and 62 ± 8 μm, respectively. Different fabrication parameters, including sintering temperature, time, coating thickness, and variations in ball-milling, which affect the electrochemical performance of the cathode material, were investigated. X-ray diffraction analysis of the cathode material suggested that it exhibits a cubic crystal structure with a LSTFN single phase. The morphological studies were conducted using scanning electron microscopy (SEM), which confirmed that the electrode material had a highly porous structure. Meanwhile, the electrochemical properties of the material were studied by electrochemical impedance spectroscopy (EIS), which revealed that by varying different parameters, the electrochemical performance of the electrode material was enhanced. The coated cathode materials with variable thicknesses were analyzed at different sintering temperatures and times. Experimental results suggest that the optimum sintering temperature and time were 950 °C and 3 h, respectively, at which LSTFN exhibits the minimum polarization resistance (RP) of 0.046 Ωcm2 when sintered at 800 °C for 3 h.

Promoting Electrocatalytic Activity and Stability via Er0.4Bi1.6O3-δ In Situ Decorated La0.8Sr0.2MnO3-δ Oxygen Electrode in Reversible Solid Oxide Cell.

Weak electrocatalytic activity of the La0.8Sr0.2MnO3-δ (LSM) oxygen electrode at medium and low temperatures leads to decreasing performance both in the solid oxide fuel cell (SOFC) mode and the solid oxide electrolysis cell (SOEC) mode. Herein, we design an Er0.4Bi1.6O3-δ (ESB) functionalized La0.8Sr0.2MnO3-δ (labeled as LSM/ESB) oxygen electrode via a one-step co-synthesis modified Pechini method. The unique LSM/ESB with polarization resistance of only 0.029 Ω·cm2 at 750 °C enables a highly enhanced rate of oxygen reduction and evolution reaction. The single cell with the LSM/ESB electrode achieves a maximum power density of 1.747 W cm-2 at 750 °C, 2.6 times higher than that of the mechanically mixed LSM-ESB electrode (0.667 W cm-2). In the SOEC mode, it also shows the improved performance of the LSM/ESB electrode. Furthermore, the cell exhibits admirable durability of 90 h in the fuel cell mode and excellent reversibility. The better performance can be concluded as a better surface-active state and a tighter connection between the LSM and ESB particles of LSM/ESB via a co-synthesis process. This work proposes a novel strategy to advance the application of the one-step modified Pechini technology for an efficient and stable oxygen electrode.

Comparative Study of Zn2Ti3O8 and ZnTiO3 Photocatalytic Properties for Hydrogen Production

In the present work, zinc titanates (ZTO) as photocatalysts were synthesized, characterized, and evaluated aiming to study their photocatalytic properties for hydrogen production under visible-light irradiation and employing MeOH (methanol) and TEOA (Triethanolamine) as sacrificial agents. ZTO were synthesized by modified Pechini method. Characterization of materials consisted in TGA, XRD, TEM, EELS, BET, and UV–Vis. Surface interaction studies consisted of FT-IR spectroscopy and determination of MeOH and TEOA adsorption–desorption capacities on the ZTO by TGA. Zinc titanates were evaluated as photocatalyst for H2 production using an artificial visible light and monitored by GC. TGA results led to establish calcination temperatures of 550 °C (Zn2Ti3O8) and 700 °C (ZnTiO3) to reach their crystalline phases. XRD analysis of sample cds-ZTO found cubic Zn2Ti3O8 and traces of the ZnO crystalline phase, while p-ZTO exhibited a mixture of cubic and hexagonal ZnTiO3 crystalline phases. Surface area for cds-ZTO was 88 m2/g, while ZnTiO3 had 13 m2/g. Photocatalytic H2 production for cds-ZTO and p-ZTO using TEOA as sacrificial agent showed the highest photocatalytic activities generating 548 and 441 µmolH2/h.gcat. TEOA adsorption–desorption capacity was found superior on cds-ZTO and p-ZTO than that for MeOH on both samples.

Synergistic Effect on Photocatalytic Activity of Co-Doped NiTiO3/g-C3N4 Composites under Visible Light Irradiation

Co-doped NiTiO3/g-C3N4 composite photocatalysts were prepared by a modified Pechini method to improve their photocatalytic activity toward methylene blue photodegradation under visible light irradiation. The combination of Co-doped NiTiO3 and g-C3N4 and Co-doping into the NiTiO3 lattice synergistically enhanced the photocatalytic performance of the composite photocatalysts. X-ray photoelectron spectroscopy results for the Co-doped NiTiO3/g-C3N4 composite photocatalysts confirmed Ti-N linkages between the Co-doped NiTiO3 and g-C3N4. In addition, characteristic X-ray diffraction peaks for the NiTiO3 lattice structure clearly indicated substitution of Co into the NiTiO3 lattice structure. The composite structure and Co-doping of the C-x composite photocatalysts (x wt % Co-doped NiTiO3/g-C3N4) not only decreased the emission intensity of the photoluminescence spectra but also the semicircle radius of the Nyquist plot in electrochemical impedance spectroscopy, giving the highest kapp value (7.15 × 10−3 min−1) for the C-1 composite photocatalyst.

An A- and B-Site Substitutional Study of SrFeO3-δ Perovskites for Solar Thermochemical Air Separation.

An A‑ and B‑site substitutional study of SrFeO3−δ perovskites (A’xA1−xB’yB1−yO3−δ, where A = Sr and B = Fe) was performed for a two‑step solar thermochemical air separation cycle. The cycle steps encompass (1) the thermal reduction of A’xSr1−xB’yFe1−yO3−δ driven by concentrated solar irradiation and (2) the oxidation of A’xSr1−xB’yFe1−yO3−δ in air to remove O2, leaving N2. The oxidized A’xSr1−xB’yFe1−yO3−δ is recycled back to the first step to complete the cycle, resulting in the separation of N2 from air and concentrated solar irradiation. A-site substitution fractions between 0 ≤ x ≤ 0.2 were examined for A’ = Ba, Ca, and La. B-site substitution fractions between 0 ≤ y ≤ 0.2 were examined for B’ = Cr, Cu, Co, and Mn. Samples were prepared with a modified Pechini method and characterized with X-ray diffractometry. The mass changes and deviations from stoichiometry were evaluated with thermogravimetry in three screenings with temperature- and O2 pressure-swings between 573 and 1473 K and 20% O2/Ar and 100% Ar at 1 bar, respectively. A’ = Ba or La and B’ = Co resulted in the most improved redox capacities amongst temperature- and O2 pressure-swing experiments.

Structural and Magnetic Characterisations of Pb-Doped MgO Nanoparticles by a Modified Pechini Method

Doping magnesium oxide nanoparticles (MgO-NPs) forms a good material for magnetisation applications. The Room Temperature Ferromagnetic (RTFM) of Pb2+-doped ions MgO-NPs synthesised by a modified Pechini method are discussed in the present paper. The structural, morphological and magnetic properties of the samples were characterised by X-ray diffraction (XRD), Field Emission scanning electron microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS) and vibrating sample magnetometer (VSM).The XRD results showed that the synthesised materials have a single set of peaks in the XRD patterns, corresponding to the cubic phase of MgO-NPs. As the Pb content increased in the host MgO-NPs leading to an increase in the lattice parameter, the interplanar spacing and the crystallite size; however, the intensity decreased.Small spherical nanoparticles (22.87–29.05nm) were observed in the Pb2+-doped ions MgO samples by (FE-SEM). The purity of the samples was confirmed using EDS spectroscopy.The pure MgO and doped samples exhibiting RTFM may be attributed to vacancy defects, which caused local magnetisation. The saturation magnetism (Ms) was found to be varied as a function of doping concentration. The maximum (Ms) was found at x=0.015 of Mg0.985Pb0.015O sample. The obtained results suggest that both Pb doping and oxygen vacancies play an important role in the development of room-temperature ferromagnetism.

Effect of annealing temperature on persistent luminescence of Y3Al2Ga3O12:Cr3+ co-doped with Ce3+ and Pr3+

Abstract Y3(Al,Ga)5O12 (YAGG) materials doped with Ce3+, Cr3+ and Pr3+ were synthesized by using a modified Pechini method and subsequently annealed in air at selected temperatures between 900 and 1500 °C. According to X-ray powder diffraction (XRPD) and transmission electron microscopy (TEM) analyses, the particles and size distributions become large and broad, respectively, due to sintering and agglomeration at high annealing temperatures. Based on infrared (FTIR) spectra and calculation of multi-phonon de-excitation probabilities, the high energy O–H vibrations are not causing significant multi-phonon de-excitation of the emitting 5d level of Ce3+ if the annealing temperature is above 900 °C. The analysis of the photoluminescence excitation (PLE), photoluminescence (PL) and persistent luminescence (PersL) spectra as well as the luminescence decay curves revealed that both the energy transfer efficiency and luminescence intensity increase with increasing annealing temperatures. The charge carrier trapping-detrapping model was applied to explain the PersL mechanism of the YAGG materials studied.

Sol-gel synthesis and characterization of Co3O4/CeO2 nanocomposites and its application for photocatalytic discoloration of organic dye from aqueous solutions.

Herein, Co3O4/CeO2 nanocomposite was synthesized by the modified Pechini method. Citric, maleic, succinic, and trimsic acids were used as a stabilizer, and the variation affected the morphology and size of the synthesized nanocomposites. Subsequently, the formation of Co3O4/CeO2 nanocomposites was confirmed by various analyses. Furthermore, the particles were considered for size and morphology by SEM and HRTEM analyses, and the sample that used trimsic acid as the stabilizer was designated as the goal sample to continue the route. The optimum sample was used to investigate the photocatalytic properties of the synthesized nanocomposite. The UV-light photocatalyst test was performed in neutral, alkaline, and acidic states against two aqueous solutions containing color contamination of methylene blue and erythrosine B dyes. The results showed decolorization at 85% for methylene blue and 90% for erythrosine B over 120 min test time.

The structure and electrical properties of lithium doped pyrochlore Gd2Zr2O7

The lithium-doped phases Gd1.7Li0.3Zr2O6.7 and Gd2Zr1.7Li0.3O6.55 with a pyrochlore structure were prepared by the modified Pechini method using citric acid and glycerol. Monitoring of the lithium content by using a nuclear microanalysis showed that a significant loss of lithium occurred after heat treatment above 1200 °C. Dense ceramics with a stoichiometric lithium content can be prepared by a low temperature microwave sintering (1100 °C). The introduction of lithium in the Gd-sublattice was accompanied by a decrease in the unit cell parameter (a = 10.5208 (1) Å vs 10.5346 (2) Å for Gd2Zr2O7) and during doping at the Zr-sites with lithium, the cell parameter increased (10.5720 (1) Å). The doping in both cases led to an increase in the free cell volume. The impedance spectroscopy results showed that the bulk conductivity can be enhanced by the Li+-doping at the Gd3+-site by almost an order of magnitude. The sample Gd2Zr1.7Li0.3O6.55 had a conductivity lower than that of Gd1.7Li0.3Zr2O6.7 due to the possible trapping of oxygen vacancies by a high-charged acceptor defect LiZrʹʹʹ. The conductivity−pO2 measurements showed that the Li-containing phase was a pure oxide-ion conductor at T < 800 °C.

Synthesis of mixed oxide Ti/Fe2O3 as solar light-induced photocatalyst for heterogeneous photo-Fenton like process

Ti/Fe2O3 (Ti/Fe mass ratio ∼ 0.22) magnetic catalysts were prepared by a modified Pechini method and evaluated for heterogeneous photo-Fenton-like process for degradation of Reactive Black 5 (RB5) textile dye under artificial solar light irradiation. Catalysts were calcined at temperatures of 500–700 °C, and were characterized by TGA, XRD, N2 adsorption/desorption, FTIR, SEM, EDX and UV/Vis DRS analyses. The photo-Fenton experiments were conducted at pH 2.5, H2O2 initial concentration of 12 mmol L−1 and 0.40 g L−1 of catalyst. Results showed that catalyst calcined at 500 °C (TiFeO-500) achieved 100 % degradation of textile dye, the highest photoactivity, when compared with the materials calcined at either 600 or 700 °C and to the pure oxides α−Fe2O3 or TiO2, under the same conditions. Kinetic data related to RB5 dye degradation with TiFeO-500 catalyst was well fitted to the pseudo-first order model with initial reaction rate of 0.28 mg L−1 min−1. The high catalytic activity of this material was favored by its multiple bandgap from UV to visible range, as well as to its nanometric particle size and low agglomeration. Photoreduction efficiency of the Fe3+ to Fe2+ was favored by the synergy with Ti4+ and possible amorphous Fe and Ti oxysulfate species in the photo-Fenton like process for the production of hydroxyl radical (•OH) and dye degradation.

Effect of carbon shell on stabilization of single-phase lanthanum and praseodymium hexaaluminates prepared by a modified Pechini method

A modified Pechini method involving the formation of carbon shell was proposed and used for the synthesis of the unsubstituted lanthanum and praseodymium hexaaluminates with the magnetoplumbite structure. The peculiarities of the LaAlO3 and LaAl11O18 phases' formation were studied in a wide temperature range starting from their appearance at 700 °C and finishing at 1300 °C when the complete phase formation occurs. It was found that the size of the formed hexaaluminate's crystallites is a crucial factor affecting the phase purity of the final product. The critical size of the thermodynamic stability of the LaAlO3 phase is supposed to be 10 nm, which corresponds to the specific surface area of 90 m2/g. The use of a carbon template approach leading to the formation of a core-shell structure during the synthesis procedure allows stabilizing the oxide particles in size and preventing their agglomeration at high temperatures. Depending on the carbon template nature, the carbon content in the samples was found to be 13 wt% (low-carbon-shelled samples) and 40 wt% (high-carbon-shelled samples). In the case of high carbon content, the resulting LaAl11O18 and PrAl11O18 hexaaluminates possess the surface areas as high as 160 m2/g.

Performance evaluation of highly active and novel La0.7Sr0.3Ti0.1Fe0.6Ni0.3O3-δ material both as cathode and anode for intermediate-temperature symmetrical solid oxide fuel cell

In comparison to various power generating devices/energy conversion systems, solid oxide fuel cell (SOFC) has received much attention due to its remarkable efficiency, reliability and low pollution. Modified pechini method is used to synthesize La0.7Sr0.3Ti0.1Fe0.6Ni0.3O3-δ (LSTFN) perovskite material and is utilized as cathode and anode for intermediate-temperature symmetrical solid oxide fuel cell (IT-SSOFC). The X-ray diffractometer (XRD) patterns reveals perovskite cubic structure with single phase for LSTFN. The maximum conductivity ~318 Scm−1 is obtained for LSTFN in air at a temperature of 700 °C, but is decreased with further increase in temperature due to small polaron mechanism. However, the conductivity is enhanced up to ~1.1 Scm−1 at the same temperature in the presence of dry H2, being capable to be utilized both as anode and cathode. Low polarization resistance (Rp) ~0.047 (with air) and 0.201Ωcm2 (with dry H2) is exhibited by as prepared perovskite material at a temperature of 800 °C. The fabricated symmetrical cell maintains good stability with no apparent degradation during the tested hours ~300 in air and ~100 with dry H2.

Infrared Reflection and Transmission Spectra of MgAl2O4 Ceramic Spinel

IR spectra of magnesium aluminate spinel (MAS, MgAl2O4) ceramic are recorded in the wide ranges 50–1000 cm–1 (reflection) and 1000–5000 cm–1 (transmission). In addition, the IR reflection spectrum of crystalline α-Al2O3 is recorded in the range of structural bands. A comparative analysis allows the origin of a series of spectral bands appearing as a combination of vibrations localized on AlO6 octahedral and MgO4 and AlO4 tetrahedral cells to be clarified. Spectra of ceramics synthesized by both the hydrolysis of double Mg–Al isopropylate and a modified Pechini method are compared.