Pechini Sol-gel Process Research Articles

Reversible multielectron redox activity of the anti-NASICON-type phosphate LiNbV(PO4)3 towards lithium and sodium intercalation.

The LiNbV(PO4)3 phosphate with the anti-NASICON structure (a = 12.126(1) Å, b = 8.6158(4) Å, c = 8.6959(6) Å, V = 908.5(1) Å3, S.G. Pbcn) has been synthesized using a Pechini sol-gel process. It exhibits reversible multielectron transitions versus Li and Na anodes. In a Li half-cell, it supports a 4e- transfer due to the activation of the Nb5+/Nb3+ and V4+/V2+ redox couples, being the first example of 4d metal redox transitions within the anti-NASICON framework confirmed by XANES measurements. X-ray diffraction performed in ex situ and operando regimes disclosed a single-phase mechanism of lithium (de)intercalation. In a Na half-cell, the material demonstrates reversible uptake of 2.77 Na+ ions. Density functional theory calculations revealed percolation barriers of ∼0.5-0.7 eV for Na+ hopping, thus supporting the activation of Na+ ion diffusion in the NbV(PO4)3 framework. This study introduces a new approach to improve anti-NASICON-structured electrode materials by utilizing redox transitions of 4d elements for energy storage.

Improved pechini sol-gel fabrication of Li2B4O7/NiO/Ni3(BO3)2 nanocomposites to advanced photocatalytic performance

In current research, nano-scaled Li 2 B 4 O 7 /NiO/Ni 3 (BO 3 ) 2 (LiBNi) composites were fabricated through improved pechini sol–gel method for advanced photocatalytic applications to remove dye contaminations of drinking water under UV/Visible irradiation. To optimize LiBNi nanocomposites properties, different complexing agents including ethylenediaminetetraacetic acid (EDTA), citric acid, tannic acid, tartaric acid and phthalic acid were utilized in pechini sol–gel process. Various sizes and morphologies of Li 2 B 4 O 7 /NiO/Ni 3 (BO 3 ) 2 nanocomposites obtained that were characterized by SEM and TEM techniques. Also, to confirm crystalline and structural features of nano-sized LiBNi samples, analyses of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and energy dispersive X-ray (EDX) were performed. By consideration of UV–Vis data, band-gap of LiBNi nanocomposites premeditated is 3.35 eV. Moreover, photocatalytic degradation of Li 2 B 4 O 7 /NiO/Ni 3 (BO 3 ) 2 nanocomposites was examined via UV/visible waves in aqueous solution for degradation acid red 88 pollutant after 90 min. Some operative factors such as nanocatalyst concentration and irradiation type for optimized LiBNi nanocomposites were assessed for removal of drinking water contaminant.

A comparative study of the properties of yttrium and lanthanum aluminates obtained by Pechini sol–gel process

The optical and photocatalytic properties of yttrium and lanthanum aluminates obtained by Pechini sol-gel process were studied by comparison. The aluminates were characterized by XRD, TEM, SEM, DRS, FTIR and PL spectroscopy. The photocatalytic properties were investigated in the removing of both cationic and anionic dyes from aqueous solutions. A higher photocatalytic activity was identified for yttrium aluminate (90% - 97% after 90 min), with the maximum value for methylene blue solution (97.15%), and a photocatalytic activity of 46.88% was determined for lanthanum aluminate in the degradation of methylene blue. The photocatalytic activity was in a good correlation with the aluminates optical behavior.

Study on Ce and Y co-doped BaFeO3-δ cubic perovskite as free-cobalt cathode for proton-conducting solid oxide fuel cells

The use of triple-conducting (electron, proton, oxide ion) cathodes is an effective strategy for significantly decreasing cathode polarization of proton-conducting SOFCs. In this study, a new triple-conducting BaFe0.8Ce0.1Y0.1O3-δ (BFCY) perovskite cathode is prepared by Pechini sol-gel process and its properties are evaluated comprehensively. High-temperature XRD measurement demonstrates that the codoping of Ce and Y can stabilize the cubic perovskite of BFCY in investigated temperature range from room temperature to 900 °C. BFCY material exhibits a moderate average thermal expansion coefficient of 22.08 × 10−6 K−1 smaller than cobalt-based cathode and good chemical compatibility with BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte after the calcining treatment at 1000 °C. XPS analysis indicates the existence of Ce3+/4+ and Fe3+/4+ ions and abundant oxygen vacancies in BFCY powder surface. Thermal gravimetric analysis reveals that a larger number of oxygen deficiencies -are generated at elevated temperatures, which favors the catalytic activity on oxygen reduction. The maximum value of BFCY electrical conductivity remains at 1.55 S cm−1 at 600 °C in humidified air. BCFY (BaCe0.8Fe0.1Y0.1O3-δ) material is introduced in order to construct BFCY-BCFY composite cathode with the good cathode/electrolyte interface adhesion. For the single cell with BFCY-BCFY composite cathode, the polarization resistance as low as 0.05 Ω cm2 and peak power density as high as 750 mW cm−2 are reached at 700 °C, respectively, demonstrating the great potential of BFCY oxides as proton-conducting SOFC cathode.

Novel Mo/Bi2MoO6/Bi3ClO4 heterojunction photocatalyst for ultra-deep desulfurization of thiophene under simulated sunlight irradiation

In the present work, a visible-light-driven Mo/Bi2MoO6/Bi3ClO4 heterojunction photocatalyst was fabricated via the Pechini sol–gel process. The type and amount of gelling agent, chelating agent and mole ratio of chelating agent to total metals were balanced to generate ultrafine nanoparticles. The Mo/Bi2MoO6/Bi3ClO4 nanocomposite as a novel photocatalyst not only exhibited an excellent visible-light photocatalytic desulfurization performance of thiophene (~97%), but also had better photodesulfurization efficiency than Mo/Bi2MoO6 and Bi3ClO4 nanostructures. The ultra-deep photocatalytic desulfurization performance of the Mo/Bi2MoO6/Bi3ClO4 nanocomposite can be attributed to the strong visible-light absorption, unique nanostructures, high separation and low recombination of electron–hole pairs due to the as-formed heterojunctions. Furthermore, a photocatalytic desulfurization mechanism was elucidated via radical trapping experiments, which revealed that the •O2− and •OH radicals play a key role in the photocatalytic desulfurization process.

Evaluation of kinetic data for crystallization of Mn–Fe co-doped ZnO nanoparticles synthesized via sol–gel process

Crystallization kinetics of metal oxides is an exciting subject because it directly relates to the structure and property of the metal oxides. Recently, doping ZnO by transition metals shown advantageous in the modification of the morphology of ZnO in photocatalytic applications as well as other specific applications. In the current research, Mn–Fe co-doped ZnO nano-powders synthesized via the Pechini sol–gel process. Through differential scanning calorimetry (DSC), X-ray diffraction (XRD), High-Resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy (FE-SEM), and selected area electron diffraction (SAED) the crystallization kinetics, growth mechanism; morphological as well as the structural characteristics of the Mn–Fe co-doped ZnO dry gels studied, respectively. The XRD and SAED results revealed that the dry gels calcined at 800 °C for 2 h have a wurtzite symmetry. By a non-isothermal DSC technique, the crystallization activation energy for wurtzite Mn–Fe co-doped ZnO calculated ~308.19 kJ/mol. Bulk nucleation was dominant in the wurtzite Mn–Fe co-doped ZnO crystallization; since the crystallization growth mechanism index (m) and morphology parameter (n) were close to 3.0. Wurtzite Mn–Fe co-doped ZnO powders had a semispherical morphology with a primary particle size from 20 to 30 nm using the electron microscopy examination.

Synthesis and scintillation properties of cerium-doped Gd2SiO5 nanopowders under alpha radiation and the importance of selecting the appropriate calcination temperature

In this study, single phase cerium-doped Gd2SiO5 (GSO:Ce) nanopowders were successfully synthesized by a Pechini sol-gel process, and the effect of calcination temperature on the crystallinity and purity of GSO phase was investigated by XRD and FTIR analyses. The suitable temperature for calcination of nanopowders and the formation of single phase GSO is estimated to be about 1250 °C. The morphology of samples, elemental composition, and nanoparticle size distribution of the single phase sample were examined by using FESEM, EDX, and DLS analyses. In addition to crystallite size and crystal lattice strain, the crystal lattice parameters of this sample were obtained using a series of equations, the results of which are very close to those obtained from the Rietveld refinement method. Studies show that unlike undoped GSO single crystal, the optical absorption spectra of synthesized GSO nanopowders are continuous and doping with 2 mol% cerium causes the highest photoluminescence intensity at 435 nm under excitation at 345 nm. The scintillation pulse height spectra of these samples were also investigated under alpha radiation. Finally, the importance of selecting the appropriate calcination temperature and its effect on the size of the nanoparticles, photoluminescence intensity, and scintillation pulse height spectrum has been studied.

Synthesis, characterization, and luminescence properties of BiVO4:Eu3+ embedded Fe3O4@mSiO2 nanoparticles

Magnetic Fe3O4 nanospheres with high dispersion, high saturation magnetization and narrow particle size distribution were synthesized by a CaF2 mediated solvothermal method. Next, a nonporous silica layer and a mesoporous silica (mSiO2) layer were uniformly coated on the surface of the magnetic nanospheres sequentially to form Fe3O4@mSiO2 nanoparticles. It was shown that the pore size and thickness of the mSiO2 shell could be fine-tuned by adjusting the composition of the double-template micelle system consisting of a partially fluorinated short-chain anionic fluorocarbon surfactant and cetyltrimethylammonium bromide. Finally, Eu3+ in the BiVO4 host was embedded on the surface of Fe3O4@mSiO2 nanoparticles with the Pechini sol-gel process, thus to form magnetic fluorescent nanoparticles. It was found that the fluorescence of the inorganic nanoparticles can be further enhanced by the complexation of 2-thenoyltrifluoroaceate (TTA) to the Eu3+ on the surface of the nanoparticles. The as-prepared nanoparticles were well characterized and the preparation process was optimized in order to establish a robust preparation method for the multiple functionalized luminescent nanoparticles.

Sol-gel synthesis of red phosphor GdPO4-Gd3PO7:Eu3+: luminescence and morphology

A down-conversion luminescent material GdPO4-Gd3PO7:Eu3+ has been synthesized by Pechini sol-gel process. The XRD patterns indicated that the obtained powders have a mixed crystalline phase. An intense luminescent red emission was obtained upon excitation 275 nm. The influence of different synthesis conditions on morphology and the PL emission ratio I(5D0 → 7F2)/I(5D0 → 7F1) was established.

Synthesis of Cr-doped Al2O3 by Pechini sol-gel method and its application for reversible thermochromic sensors

Abstract Aluminum oxide doped with a small amount of chromium is known as “ruby” or “ruby solution” and can be used as a thermochromic material. The Pechini sol-gel process is applied to synthesize this advanced material. The crystal structure, chemical composition, and morphology of the synthesized materials are analyzed using X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, and Fourier transform infrared (FT-IR) spectroscopy. The color performance of the synthesized material is analyzed using UV-VIS spectrometry. Finally, the thermochromism exhibited by the pigment powders at high temperatures is investigated. The pigment exhibits exceptional thermochromic properties, transitioning from pink to gray in a temperature range of 25–600 °C. The change in color is reversible and is dependent on the temperature and chromium concentration; however, it is independent of the exposure time. This novel property of Cr-doped Al2O3 can be potentially employed in reversible thermochromic sensors that could be used not only for warning users of damage due to overheating when the environmental temperature exceeds certain limits, but also for detecting and monitoring the temperature of various devices, such as aeronautical engine components, hotplates, and furnaces.

Pechini sol-gel synthesis of La2CaB8O16:Eu3+ red phosphor and its photoluminescence spectral properties

Powder material fabricated by solid-state reaction process has the characteristics of large particulate size, wide size-distribution and being subject to agglomeration. To circumvent these issues, Pechini sol-gel method has firstly been utilized to synthesize the red phosphor La2CaB8O16:Eu3+. Phase identification, morphology observation and photoluminescence spectra measurement have been carried out on La2CaB8O16:Eu3+ samples. The results show that a narrow size-distribution, good dispersibility phosphor with high emission intensity can be obtained by exploiting Pechini sol-gel process. The suitable process parameters are the calcination temperature T = 900 °C, the molar ratio of citric acid to metal ion N = 1.0, and pH = 7–8 with addition of a small amount of polyethylene glycol.

Fabrication of nanocomposite photocatalyst CuBi2O4/Bi3ClO4 for removal of acid brown 14 as water pollutant under visible light irradiation.

In the present study, CuBi2O4/Bi3ClO4 nanocomposites have been fabricated via an improved Pechini sol-gel process using the mixtures of various gelling agents and polybasic acids. This work shows that by controlling the reaction conditions such as kind of polybasic acids, gelling agents, pH and mole ratio of polybasic acid to total metals, the CuBi2O4/Bi3ClO4 nanocomposites with ultrafine sphere-like, irregular polyhedral-like, plate-like and cubic-like morphologies were prepared. The phase, elemental composition, morphology and optical characteristics of as-synthesized CuBi2O4/Bi3ClO4 nanostructures were analyzed utilizing UV-Vis, FESEM, TEM, HRTEM, FT-IR, XRD, TOC and EDS techniques. Furthermore, the CuBi2O4/Bi3ClO4 nanocomposites exhibited excellent TOC removal (75%) and photocatalytic activity (92%) to photodegradation of acid brown 14 azo dye as water pollutants under visible light irradiation. The excellent degradation activity of CuBi2O4/Bi3ClO4 photocatalyst can be attributed to the strong visible light absorption, high charge separation efficiency, fine particle size distribution and proper band gap of the nanocomposite. In addition, the reliable photocatalytic mechanism was discussed on the basis of the radical trapping study, which revealed the h+ and O2- radicals were the prevailing active species in the photocatalytic process.

Sol-gel synthesis and up-conversion luminescence of GdPO4–Gd3PO7:Yb3+, Ln3+ (Ln = Er, Ho, Tm) phosphor

This work reports the structural, morphological and luminescent properties of GdPO4–Gd3PO7:Yb3+, Ln3+ (Ln = Er, Ho, Tm) phosphors which have been synthesized by Pechini sol-gel process. The XRD patterns indicated that all the samples are crystalline and have a mixture of monoclinic monazite and monoclinic phases. Some samples were synthesized with ammonium hydroxide (NH4OH) and had better crystallinity than these synthesized without NH4OH. The up-conversion emissions were obtained under excitation at 967 nm. According to our results, the color emission was tuned from red to green by increasing the Yb3+ concentration from 5 mol% to 20 mol%. Moreover, the use of NH4OH to synthesize the samples doped with 20 mol% of Yb3+ enhanced their green emission band ≈3 times. The results reveal that doping the GdPO4–Gd3PO7 particles with rare earths produce an up-conversion emission which can be useful for the fabrication of luminescent coatings or lighting devices.

Substitutional Ta-doping in Y2O3 semiconductor by sol-gel synthesis: experimental and theoretical studies

The Pechini sol-gel method has been employed for the synthesis of pure and (181Hf→)181Ta-doped Y2O3 nanopowders. We performed a structural characterization from the micro to the subnanoscopic scale by means of scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and time-differential perturbed γ–γ angular correlation (PAC) spectroscopy. The results show the formation of the cubic bixbyite structure after a thermal treatment at 1473 K. For the synthesized 181Ta-doped Y2O3, the PAC experiments demonstrate that the impurities are mainly located at both substitutional cationic sites of the bixbyite structure. The experimental investigation was complemented by performing first-principles electronic structure calculations for Ta atoms localized at the two cationic sites of the Y2O3 semiconductor structure, which allow the study of the structural and electronic modifications induced in the host system when the impurities are introduced. These calculations confirm that the measured electric-field gradients for the synthesized 181Ta-doped Y2O3 correspond to double-ionized impurities located at substitutional defect-free cationic sites of the bixbyite host structure and indicate the site occupancy preference for 181Hf(→181Ta) doping. The behaviour of the site preference of 181Ta impurities with temperature is also discussed. In addition to an extensive structural and electronic characterization of pure and Ta-doped Y2O3 semiconductor, our results demonstrate that the Pechini sol-gel process is an affordable and effective way to successfully synthesize these PAC substitutional doped samples.

Bifunctional ferromagnetic Eu-Gd-Bi-codoped hybrid organo-silica red emitting phosphors synthesized by a modified Pechini sol-gel method

Red phosphor, composed of Eu-Gd-Bi-codoped hybrid organo-silica glass, has been synthesized via a modified Pechini sol-gel process. The synthesized hybrid glass was analyzed with powder X-ray diffraction (XRD), differential thermal analysis coupled with thermogravimetry (DTA-TG) and Fourier transform infrared (FTIR) spectroscopy. XRD and DTA-TG confirmed its amorphous structure up to 1000 °C. Magnetic behavior of the produced phosphor was investigated using vibrating specimen magnetometer (VSM) and the obtained results revealed its unsaturated ferromagnetic behavior. Photoluminescence (PL) properties of the obtained phosphor have been investigated under near-UV excitation at 395 nm. The influence of calcination temperature on the PL intensity and its decay behavior as well as on the ferromagnetic characteristics has been studied to determine the optimal reaction temperature of the phosphor. The PL emission spectra show the characteristic emission bands of Eu3+ ions in the wavelength range from 580 to 700 nm. These emission spectra have been dominated by the electric dipole 5D0→7F2 transition of the Eu3+ peaked at 610–620 nm producing the red light emission of the phosphors. It was found that the phosphor performance, expressed by its PL intensity and life time, could be significantly improved by increasing of the heat treatment temperature up to 900 °C. Also, calcination at 900 °C for 6 h greatly increased both of the magnetization and retentivity, while decreased the coercivity value. The organic phenomenon of metal citrate-ethylene glycol chelation and its degradation by calcination were well followed by FTIR spectroscopy. The obtained results are promising and could afford a basis for designing of efficient red phosphors for displays, lighting and bifunctional biosensors for biomedical applications.

Enhanced near room temperature magnetocaloric effect in La0.6Ca0.4MnO3 for magnetic refrigeration application

Perovskite manganite La0.6Ca0.4MnO3 (LCMO) nanomaterials were synthesized by a modified Pechini sol–gel process followed by high temperature sintering.

Modification of Pechini sol–gel process for the synthesis of MgO-Y2O3 composite nanopowder using sucrose-mediated technique

This study aims to modify Pechini sol-gel process for synthesizing MgO-Y2O3 composite nanopowder by adding sucrose to precursors as a mediation. The precursor solution for synthesis of MgO-Y2O3 composite nanopowder contained magnesium acetate tetrahydrate, yttrium(III) nitrate hexahydrate, ethylene glycol, citric acid, and sucrose. The effect of the mole ratio of citric acid to the whole precursors on the particle size as well as the effect of calcination temperature on the specific surface area were investigated. The optimized sample was synthesized using a mixture of citric acid: sucrose: transition metal (in the molar ratio of 1:4:1), which had the average particle size of 18.3nm and specific surface area of 69.2m2/g. The specific surface area increased from 69.2 to 105.2m2/g with decreasing the calcination temperature from 800 to 600°C. The sucrose addition increased the specific surface area, but decreased the particle size. Moreover, the FESEM observations showed that MgO and Y2O3 phases had a uniform phase distribution in MgO-Y2O3 composite.

Up-Conversion Y2O3:Yb(3+),Er(3+) Hollow Spherical Drug Carrier with Improved Degradability for Cancer Treatment.

The rare earth hollow spheres with up-conversion luminescence properties have shown potential applications in drug delivery and bioimaging fields. However, there have been few reports for the degradation properties of rare earth oxide drug carriers. Herein, uniform and well-dispersed Y2O3:Yb(3+),Er(3+) hollow spheres (YOHSs) have been fabricated by a general Pechini sol-gel process with melamine formaldehyde colloidal spheres as template. The novel YOHSs with up-conversion luminescence has good drug loading amount and drug-release efficiency; moreover, it exhibits pH-responsive release patterns. In particular, the YOHSs sample exhibits low cytotoxicity and excellent degradable properties in acid buffer. After the sample was loaded with anticancer drug doxorubicin (DOX), the antitumor result in vitro indicates that YOHS-DOX might be effective in cancer treatment. The animal imaging test also reveals that the YOHSs drug carrier can be used as an outstanding luminescent probe for bioimaging in vivo application prospects. The results suggest that the degradable drug carrier with up-conversion luminescence may enhance the delivery efficiency of drugs and improve the cancer therapy in clinical applications.

Preparation of chromatic composite hollow nanoparticles containing mixed metal oxides for full-color electrophoretic displays

The green and blue hollow nanospheres were prepared via emulsifier-free emulsion polymerization and the Pechini sol–gel process. They exhibit bright color and hollow structures with uniform size and shape, which also present excellent performance and quick response of electrophoretic display.

Substitution-driven enhanced magnetic and ferroelectric properties of BiFeO3 nanoparticles

Multiferroic BiFeO3 (BFO) nanoparticles along with co-substitution of Gd, a rare-earth element, and Co, a transition metal, were synthesized through modified Pechini sol–gel process. A compositional-driven structural change in the rhombohedral phase (R3c) due to the inclusion of Gd and Co was identified with the help of X-ray diffraction analysis. Dense oblate nanospheres with average grain sizes less than the spin periodicity of BFO were observed through field emission scanning electron microscopy studies, where the grain sizes were found to decrease with increasing concentration of substituent ions. The co-substitution modified the BFO's original magnetic structure, which eventually led to the enhancement of spontaneous magnetization as evident from their M−H hysteresis loops. Large difference between ZFC and FC curves indicates some glassiness in the co-substituted samples. In addition to the observed distortion in crystal structure, a considerable reduction of Fe2+ ions confirmed by XPS has favored enhancement of polarization.