Modified Pechini Method Research Articles

Electrochemical Investigations on the Effect of Mg-Substitution in Li2MnO3 Cathode

The monoclinic Li2MnO3 is electrochemically inactive for lithium intercalation at voltages lower than 4.4 V vs. Li+/Li0. In order to activate Li2MnO3, magnesium has been incorporated in the lithium site of the structure which resulted in a mixture of active phases capable of cycling in the 2.8 to 4.8 V vs. Li+/Li0 voltage range. Li2MnO3, Li1.5Mg0.25MnO3, Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3 compositions were synthesized by the modified Pechini method and formulated based on the oxidation state of magnesium and lithium. The compounds were characterized using XRD, XPS, SEM, BET and tap density. The XRD patterns for Li1.5Mg0.25MnO3, Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3 indicated the presence of monoclinic/spinel phases. Li0.5Mg0.75MnO3 showed ideal values of tap density vs. surface area among all the Mg-substituted compounds. X-ray photoelectron spectroscopy of Mn 2p orbital showed a decrease in the oxidation state of manganese for Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3, while the change in binding energy for Li1.5Mg0.25MnO3 was not significant. The cyclic voltammetry and charge/discharge tests showed an increase in capacity and better stability for the Li1.0Mg0.50MnO3 (80 mAh g−1) and Li0.5Mg0.75MnO3 (112 mAh g−1) compositions.

Luminescence Characteristics of LaAlO<sub>3</sub>:Eu<sup>3+</sup> Obtained by Modified Pechini’s Method

The aim of the present work was to investigate the luminescent properties of europium-doped lanthanum aluminate (LaAlO3) powder prepared by Modified Pechini (MP) method. Samples were prepared at different Eu3+ concentrations and calcined at 1600°C. Structural and morphology characterizations were obtained by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). Luminescent properties were analyzed by photoluminescence (PL) and thermoluminescent phenomena. The XRD pattern shows pure lanthanum aluminate oxide LaAlO3 with a rhombohedral structure. Photoluminescence studies of the powders was related to 4f → 4f(5D0 → 7Fi) (i = 1, 2, 3, 4) transitions of Eu3+ ion, the most intense emission of Eu3+ in LaAlO3 was registered for the transition 5D0 → 7F1, for 5% of Eu3+. The recorded TL glow curves of excited samples showed a main TL peak, the main peak appeared its maximum as a function of excitation energy. The investigation demonstrates that polycrystalline LaAlO3:Eu3+ powders calcined at 1600°C have interesting luminescent characteristics.

Mo-doped Pr0.6Sr0.4Fe0.8Ni0.2O3-δ as potential electrodes for intermediate-temperature symmetrical solid oxide fuel cells

Mo-doped Pr0.6Sr0.4Fe0.8Ni0.2O3-δ (PSFNM) perovskites are synthesized by a modified Pechini method and evaluated as both anode and cathode for intermediate-temperature symmetrical solid oxide fuel cell (SSOFC). The influence of Mo-doping on structure, conductivity, thermal expansion coefficient and electrochemical performance of Pr0.6Sr0.4Fe0.8Ni0.2O3-δ (PSFN) electrode are investigated. The results indicate that PSFNM exhibits a cubic perovskite structure and shows a good reversibility. After heated at 800°C for 10h in humidified H2, some new phases of SrPrFeO4, Pr2O3, and Fe-Ni alloy in PSFNM are identified by powder X-ray diffraction analysis. Although the conductivity of Mo-doped sample is slightly decreased, the thermal expansion compatibility and hydrogen oxidation reaction (HOR) activity are gradually improved. The maximum power density of SSOFC increase from 435mW/cm2 to 500mW/cm2 at 800°C, and the corresponding polarization resistance decrease from 0.102Ω.cm2 to 0.070Ω.cm2, respectively. In addition, the SSOFC with PSFNM electrode shows a robust stability after operating at 700°C for 100h. These results demonstrate that PSFNM is a promising electrode for SSOFC at intermediate temperatures.

Modified Pechini method for the synthesis of weakly-agglomerated nanocrystalline yttrium aluminum garnet (YAG) powders

Modification of Pechini method for synthesis of weakly agglomerated yttrium aluminum garnet powder has been presented. Modified synthesis procedure is based on an additional calcination process in KCl melt at 1000 °C and allows obtaining weaker agglomeration of nanoparticles. Structure, morphology and particle size have been defined using scanning electron microscopy technique, X-ray diffraction, and static light scattering. Adsorption ability of powders has also been studied. Diffraction patterns of samples confirm existence of only one YAG phase; the average size of particles is about 200 nm. The size of coherent-scattering regions was determined to be 40–50 nm. Steady-state luminescence properties and lifetimes of nanocrystalline YAG:Eu3+ powders synthesized by standard and modified Pechini techniques were compared.

Low temperature processed MnCo2O4 and MnCo1.8Fe0.2O4 as effective protective coatings for solid oxide fuel cell interconnects at 750 °C

Abstract In this study two materials, MnCo 2 O 4 and MnCo 1.8 Fe 0.2 O 4 are studied as potential protective coatings for Solid Oxide Fuel Cell interconnects working at 750 °C. First powder fabrication by a modified Pechini method is described followed by a description of the coating procedure. The protective action of the coating applied on Crofer 22 APU is evaluated by following the area specific resistance (ASR) of the scale/coating for 5500 h including several thermal cycles. The coating is prepared by brush painting and has a porous structure after deposition. Post mortem microstructural characterization performed on the coated samples shows good protection against chromium diffusion from the chromia scale ensured by a formation of a dense reaction layer. This study shows, that even without high temperature sintering and/or reactive sintering it is possible to fabricate protective coatings based on MnCo spinels.

A Synergistic Effect in a Composite Cathode Consisting of Spinel and Layered Structures To Increase the Electrochemical Performance for Li-Ion Batteries

In this work, a composite consisting of layered Li[Li0.2Ni0.12 Mn0.56Co0.12]O2 (LNMC) and spinel Li[Ni0.5Mn1.5]O4 (LNMO) was synthesized by a modified Pechini method. Extensive analysis was carried out to investigate the synergistic effect between the layered oxide and spinels in the composite by comparing its properties with baseline individual compounds, as well as a physical mixture of LMNC and LNMO. Comparing to the LNMC, the compsoite cathode exhibited a similar initial capacity of ∼250 mA·h/g at 0.1 C, but a much higher first-cycle effeciency, better cyclability and rate capability, attributed to the presence of spinel. The synertistic effect of integrated spinel on the microstructure, crystal strucutre, Mn oxidation states, and Li+/Ni2+ disordering of the composite was studied by X-ray absorption near edge structure (XANES), electron microscopy, and X-ray diffraction (XRD). The presence of a spinel component in the composite cathode is the origin for the improvement of cyclability and rate capabili...

Photodegradation of Phenol Red in a Compound of Type ZnO@Cr Core/Shell

urface properties core/shell nanoparticles have been investigated in recent years due to their promising reactivity in catalysis surface. In this work, the ZnO@Cr core/ shell nanoparticles were synthesized by Modified Pechini method and characterized by X-ray diffraction and scanning electron microscopy (SEM). The structural parameters were evaluated as a function of chromium coatings on the ZnO structure, using the Rietveld method. From the refinement of experimental diffractogram determined the crystallographic structure of the investigated system as being of the hexagonal type with space group P63mc. The coating of ZnO with chrome led to an increase of the structural parameters. Photocatalytic activity of ZnO@Cr nanoparticles was studied using a low power reactor and the phenol red dye in acid and basic medium. The nanoparticles showed level of degradation in acid medium 1.24 times higher than that in basic medium. The photodegradation follows a first order kinetics.

ChemInform Abstract: Anatase Mg0.05Ta0.95O1.15N0.85: A Novel Photocatalyst for Solar Hydrogen Production.

AbstractThe title catalyst is prepared in two steps involving the preparation of Mg0.05Ta0.95O2.425 via a modified Pechini method by combining solutions of MgCl2 and TaCl5 in EtOH and citric acid and subsequent addition of ethylene glycol (150 °C).

Evaluation of superparamagnetic and biocompatible properties of mesoporous silica coated cobalt ferrite nanoparticles synthesized via microwave modified Pechini method

Cobalt ferrite nano particles were synthesized by Pechini sol-gel method and calcined at 700°C in electrical and microwave furnace. The microwave calcined sample was coated with mesoporous silica by hydrothermal method. Characterization was performed by XRD, FESEM, TEM, VSM, BET and FTIR analysis. The cytotoxicity was evaluated by MTT assay with 3T3 fibroblast cells. The XRD and FTIR results confirmed spinal formation in both cases and verified the formation of silica coating on the nanoparticles. For microwave calcination, The XRD and SEM results demonstrated smaller and flat adhesion forms of nanoparticles with the average size of 15nm. The VSM results demonstrated nearly superparamagnetic nanoparticles with significant saturation magnetization equal to 64emu/g. By coating, saturation magnetization was decreased to 36emu/g. Moreover, the BET results confirmed the formation of mesoporous coating with the average pore diameters of 2.8nm and average pore volume of 0.82cm3g−1. Microwave calcined nanoparticles had the best structural and magnetic properties.

Microstructural and nonlinear optical properties of Bi2ZnB2O7:RE3+ powders

For the first time an orthorhombic bismuth zinc borate (Bi2ZnB2O7, BZBO) with noncentrosymmetric structure was synthesized by means of modified Pechini method. This approach allowed to reduce both the duration and temperature of the procedure in comparison to conventional solid state synthesis of desirable compounds in form of polycrystalline powders. Selected RE3+ dopants were successfully introduced into BZBO matrix using this method. The obtained materials were studied and crystallographic calculations were performed in order to confirm the structure of as-prepared polycrystals. Morphology of obtained powders was investigated using Atomic Force Microscopy. Energy Dispersive X-Ray Spectroscopy measurements were done in order to proceed chemical microanalysis. Second Harmonic Generation measurements showed strong effect of incorporated RE3+ ions on the increasing second order nonlinear optical response of BZBO:RE3+ powders.

Photoluminescence properties of Pr3+ doped Bi2ZnOB2O6 microcrystals and PMMA-based composites

Photoluminescence properties of red-emitting Pr3+-doped Bi2ZnOB2O6 microcrystalline powder and PMMA-based composite materials were reported. Bi2ZnOB2O6:Pr3+ powders were synthesized by means of the modified Pechini method. The morphology and crystallographic structure of Bi2ZnOB2O6:Pr3+ microcrystals were investigated by XRD and HRTEM. The PMMA-based composite materials were prepared by embedding of Bi2ZnOB2O6:Pr3+ powder in the PMMA matrix. The vibrational properties of the powder and composite systems were investigated by μ-Raman spectroscopy. Emission spectra of the samples were measured under blue (451.6 nm) and UV (320 nm) excitation. Both, the powder and composite samples show enhancement of red emission (1D2 → 3H4) and quenching of greenish-blue luminescence from 3P0 level of Pr3+ ions after excitation in UV and VIS caused by the 3P0 ∼ 1D2 non-radiative relaxation of Pr3+ ion by low-lying charge transfer state and non-radiative de-excitation through Pr3+–Bi3+ energy transfer. The response of the powder and composite samples to pulsed excitation at 451.6 nm was measured by monitoring emission from the 1D2 level (595 nm/3P0 → 3H6 transition). The determined lifetimes τ1 and τ2 of the red emission at 595 nm (1D2 → 3H4 transition) of the composite are significantly longer in comparison to powder samples. Moreover, because of the good nonlinear optical properties of the Bi2ZnOB2O6 crystals and effective luminescence of the Pr3+-doped Bi2ZnOB2O6 powders and composites, they can be very useful as bi-functional materials in the new generation of optoelectronic devices.

Enhancement of multiferroic and magnetocapacitive properties in nanocrystalline Mg-doped GaFeO3

We have study the effect of Mg doping on structural, magnetic, electric and magnetocapacitive properties of nanocrystalline Ga1−xMgxFeO3 (GMFO, 0 ≤ x ≤ 0.10) prepared by a modified Pechini method. The presence of a single crystalline phase identified as the orthorhombic structure with Pc21n space in all the GMFO samples. Magnetization measurements reveal that with increasing Mg-content up to 0.10, the ferrimagnetic transition temperature (TC) increases from 302 to 325 K. It is also found that the Mg-doped GaFeO3 (GFO) samples exhibit the characteristics of ferroelectricity at room temperature. Furthermore, Mg substitution in GFO brings in the balance of structural distortion, cation distribution, and magnetic exchange interaction, which affects both ferrimagnetism and ferroelectricity. The simultaneous enhancement of magnetization, electric polarization and magnetocapacitance of Mg-doped GFO samples are prominent candidates for the applications of multiferroic devices.

Mesoporous carbon foam, synthesized via modified Pechini method, in a new dispersant of Salep as a novel substrate for electroanalytical determination of epinephrine in the presence of uric acid

Mesoporous carbon foam (MCF) with particular properties was prepared via a simplistic and template-free procedure. The synthesized MCF was characterized by transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction and BET surface area techniques. Porous MCF with pores diameters of 5 to 10nm provided a perfect substrate including extensive specific surface area to modify the electrodes surface. The obtained MCF was dispersed in Salep solution to prepare a stable suspension (S-MCF). The resultant composite was casted on the surface of glassy carbon electrode (GCE) to assemble the S-MCF modified GCE (S-MCF/GCE). Cyclic voltammetry (CV) was used to study the electrochemical behavior of epinephrine (Ep) and the determination of Ep was conducted by applying differential pulls voltammetry (DPV) in the presence of uric acid (UA). In the optimized conditions, the presented sensor is able to detect the concentration range of 0.1–12μM with a limit of detection of 40nM. The presented methodology possesses a reliable reproducibility, repeatability and stability in biological samples. These results proved that the S-MCF composite has a hopeful capacity in electrochemical sensors development.

Structural analysis, optical and dielectric function of [Ba0.9Ca0.1](Ti0.9Zr0.1)O3 nanocrystals

This work presents the identification of inter-band transitions in the imaginary part of the dielectric function (ε2) derived from the Kramers–Kronig analysis for [Ba0.9Ca0.1](Ti0.9Zr0.1)O3 (BCZT) nanocrystals synthesized by the modified Pechini method. The analysis started with the chemical identification of the atoms that conform BCZT in the valence loss energy region of a high energy-resolution of electron energy loss spectroscopy. The indirect band energy (Eg) was determined in the dielectric response function. This result is in agreement with the UV-Vis technique, and it obtained an optical band gap of 3.16 eV. The surface and volume plasmon peaks were observed at 13.1 eV and 26.2 eV, respectively. The X-ray diffraction pattern and the Rietveld refinement data of powders heat treated at 700 °C for 1 h suggest a tetragonal structure with a space group (P4 mm) with the average crystal size of 35 nm. The average particle size was determined by transmission electron microscopy.

Methane reforming over Ni-based pyrochlore catalyst: deactivation studies for different reactions

A 1 wt% Ni-based La2Zr2O7 pyrochlore catalyst was synthesized using the modified Pechini method. The catalyst was characterized by H2-TPR, and pre- and post-reaction XRD, and tested for its methane-reforming activity under three different reaction conditions: (a) dry-reforming (CH4 + CO2), (b) oxy-CO2 reforming (CH4 + CO2 + O2), and (c) bi-reforming (CH4 + CO2 + H2O). The TPR results show that NiO in the fresh, calcined catalyst is completely reversible to Ni0. The XRD results show that the crystalline pyrochlore structure is stable under all three reaction conditions. Under dry-reforming conditions, the catalyst deactivated rapidly. In oxy-reforming, the catalyst activity also decreased, but far less rapidly than under dry-reforming conditions. However, under bi-reforming conditions, no deactivation was observed at comparable times-on-stream. TPO of the spent catalysts showed greatest carbon deposition for the dry-reforming, a significant portion of which was graphitic and difficult to remove. For oxy-reforming, there was much less carbon deposition as compared to the dry-reforming, and a major part of which was the amorphous, atomic carbon, which is relatively easy to remove. Unlike under bi-reforming, no significant carbon deposition was observed at the conditions tested here. This indicates that the presence of steam resists carbon deposition compared to dry-reforming or oxy-reforming.

A clear effect of charge compensation through Na+ co-doping on luminescent properties of new CaGa4O7:Nd3+

Two series of new calcium gallates: Ca1−xNdxGa4O7 and Ca1−2xNdxNaxGa4O7 (x = 0.001, 0.01, 0.03, 0.05, 0.1) were synthesized by a modified Pechini method and their optical properties at 298 K and 77 K were investigated. Relatively intense characteristic Nd3+ luminescence in IR region with maximum located at around 1075 nm was observed in all samples on direct excitation into f-f transitions. The effects of activator concentration and Na+ co-doping on morphology, luminescence and absorption spectra as well as decay kinetics were studied in details. The results show that both, the Nd3+ concentration and the alkali metal co-doping affected the optical properties but had no influence on the powders morphology. The studies of luminescence spectra (298 and 77 K) in a function of activator concentration showed an increasing distortion of the local symmetry of Nd3+ with raising activator content due to certain defects created in the crystal lattice. On the other hand co-doping with Na+ ions led to smaller disturbance of Nd3+ ions local symmetries and significantly enhanced luminescence. Analysis of decay kinetics of both series of compounds showed smaller concentration quenching in charge compensated with Na+ ions powders due to smaller clustering of Nd3+ ions in CaGa4O7 lattice.

Synthesis, luminescence and photocatalyst properties of zirconia nanosheets by modified Pechini method

Pure tetragonal zirconia nanosheets and semi-spherical nanoparticles were successfully prepared by modified Pechini method. In this approach, ZrOCl2·6H2O, triethanolamine (TEA) and citric acid (CA) were used as the source of Zr4+, the chelating and polymerization agent, respectively. The effects of heat treatment and TEA:CA:Zr4+mole ratios on the structure, morphology and zirconia particle size were investigated.The microstructure of the products was characterized by X-ray diffractometry (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FT-IR) analysis. The zirconia nanosheets exhibit photoluminescence at room temperature with a broad emission in the blue region of the visible spectrum. Finally, the effect of calcination temperature on the photocatalyst properties of nanosheets was investigated.

Processamento e caracterizações estruturais, microestruturais e ferroelétricas do composto magnetoelétrico BiFeO3-PbTiO3 obtido pelo método de Pechini

Resumo Neste trabalho uma rota alternativa de síntese, o método de Pechini modificado, foi utilizada para obter nanopartículas do composto BiFeO3-PbTiO3 (BFPT). As imagens obtidas por microscopia eletrônica de varredura revelaram tamanhos de partículas inferiores a 120 nm. Análises estruturais apontaram a organização estrutural do composto (formação de estruturas com simetria tetragonal) como função da temperatura de síntese. Cálculos da polarização espontânea indicaram a intensidade alcançada no composto BFPT. As análises de densidade eletrônica obtidas pelo método da máxima entropia indicaram a configuração das ligações químicas presentes no composto.

Experimental assessment of oxygen exchange capacity and thermochemical redox cycle behavior of Ba and Sr series perovskites for solar energy storage

Thermochemical redox processes involving novel oxygen ion conducting materials with perovskites structure are studied to evaluate their application potential for solar energy storage in concentrated solar power plants. A series of Ba and Sr containing perovskites was synthesized via modified Pechini method and their crystal structure was characterized by XRD. The thermochemical reduction–oxidation steps of the redox cycle and oxygen exchange capacity of the perovskites were investigated by thermogravimetric (TG) analysis. The results revealed that Co-based perovskites are the most promising candidates for solar thermochemical energy storage application. The O2 release/absorption of Co-based perovskites is completed in a reversible way when reaching a given temperature. BaCoO3 reduction occurs promptly when the temperature reaches 900°C in Ar atmosphere (pO2=10−6atm), and the oxidation proceeds completely as soon as the gas is switched from Ar to 20% O2 at 600°C. In these conditions, the amount of monatomic oxygen released/captured reaches 0.47/0.49mol per mol BaCoO3. Part substitution in A-site improves the O2 exchange capacity of Ba0.5Sr0.5FeO3−δ but not Ba0.5Sr0.5CoO3−δ, while part substitution in B-site improves the O2 exchange capacity of SrCo0.8Fe0.2O3−δ and SrCo0.2Fe0.8O3−δ. Part substitution together in A-site and B-site of perovskites does not improve the O2 exchange capacity of Ba0.5Sr0.5Co0.8Fe0.2O3−δ and Ba0.5Sr0.5Co0.2Fe0.8O3−δ. The Fe-based perovskites generally exhibit continuous non-stoichiometry changes according to the temperature change suggesting continuous topotactic evolution, while the non-stoichiometry of Mn-based systems is almost not changed at the considered temperatures. Ba containing systems (BaCoO3, BaFeO3 and Ba0.5Sr0.5CoO3) show the largest oxygen release ability under inert (pO2=10−6atm) or oxidizing atmosphere (pO2=0.2atm) up to 1050°C, while only BaCoO3 can be fully re-oxidized at 600°C in a 20% O2 atmosphere, with an energy storage capacity of 292J/g.

Structural and Physical Properties of Mixed‐Layer Aurivillius‐Type Multiferroics

Different from the homogeneous layer structure of famous Bin+1Fen−3Ti3O3n+3 compounds with integer n values, the mixed‐layer structure of the compounds with fractional n values and their related physics have been rarely reported in recent years. In this work, the mixed‐layer compound Bi11Fe3Ti6O33 (n = 4.5) was synthesized by the modified Pechini method, and its structure was characterized as an inhomogeneous phase generating from the disordered intergrowths of the n = 4 and 5 perovskite slabs. Multiferroic properties of this compound were discussed in detail, compared with two adjacent homologous Aurivillius phases Bi5FeTi3O15 (n = 4) and Bi6Fe2Ti3O18 (n = 5). Significantly, the ferroelectric polarization of the mixed‐layer sample at room temperature is higher than that of the adjacent homologous phases with integer n, mainly arising from the intrinsic mixed‐layer structure. The ferroelectric Curie temperature (~992 K) and a magnetic transition temperature (~7 K) of the 4.5‐layer phase of Bi11Fe3Ti6O33 fall in between those of the homogeneous 4‐ and 5‐layer phases, conforming to the change trends of such oxides with integer n. These results provide important contributions to understand the Aurivillius‐type materials and open up a new avenue to enhance multiferroic properties in single‐phase multiferroics.