PVA-assisted Sol-gel Research Articles

Mullite-type Bi2Mn4O10 thin films prepared by a PVA-assisted sol–gel method

Mullite-type Bi2Mn4O10 is an attractive material for several potential applications, such as energy conversion and storage, data storage, batteries and photoelectrochemical devices. Bi2Mn4O10 thin films were prepared by sol–gel from a simple and highly stable precursor solution, based on the corresponding metal nitrate salts, acetic acid and polyvinyl alcohol. The films were deposited by dip-coating onto FTO substrates and dried at 350 °C; the dipping-drying cycle was repeated six times and the films were finally sintered at 600 °C. The films were characterized using GIXRD, revealing an excellent match with the ICDD database and previous studies. The UV–Vis measurements showed a direct band gap of 1.78 eV for the films. Raman spectroscopy permitted the identification of the Ag, B1g and B2g vibrational modes. The electrical properties via Hall effect measurements showed that the Bi2Mn4O10 thin films exhibit an n-type semiconductor behavior. Finally, the FESEM micrographs and AFM images revealed homogeneous, nanostructured thin films. In summary, through this comprehensive characterization, it was observed that high quality, nanocrystalline semiconductor thin films of Bi2Mn4O10 can be produced using this simple sol–gel method.

Facile synthesis of nanoscale CuO and NiO via the PVA-assisted sol-gel method and their exploration in the catalytic epoxidation of styrene

The full-text of the article will be published in the English version of the journal "Catalysis in Industry" No. 4, 2024.Both nanoscale copper oxide and nickel oxides, with diameter 17 and 25 nm respectively, have been synthesized via an easy sol-gel method using polyvinyl alcohol. The method involves the simple dispersion of metal ions (M2+ = Cu or Ni) into the PVA gel and subsequent calcination of the dried gel at 400 °C for 3 h. The synthesized oxide materials are characterized by different physical tools like TGA, powder XRD, SEM, TEM and DRS UV-visible spectroscopic technique. The oxides are found to be very efficient catalysts in the epoxidation of styrene. CuO gives 87 % styrene conversion and 88 % SO selectivity while, NiO gives 69 % styrene conversion and 80 % with TBHP as an oxidant at the end of 6 h. Both the catalysts can suitably be reused for several successive runs without appreciable loss in activity and selectivity. The cost-effective synthesis, excellent catalytic performance and reusability make these oxides promising catalysts for the industrial use.

Tailoring the properties of Y2O3 via synthesis parameters varied during the PVA-assisted sol-gel route

Tailoring the properties of Y2O3 via synthesis parameters varied during the PVA-assisted sol-gel route

Temperature sensing with Er3+ doped Y2O3 nanoparticles operating within the 1st and 2nd biological window: The influence of particle size on the relative sensitivity of thermally decoupled levels

The luminescent properties of three nanocrystalline samples of Y2O3:Er3+ produced via PVA-assisted sol-gel route, with mean particle diameter of 21, 44 and 86 nm, were investigated aiming their application as optical temperature sensors within the first and second biological windows. Luminescence spectra were analyzed using three different wavelengths (532 nm, 660 nm and 800 nm) as excitation sources. The three samples exhibited up to four emission bands centered at 660 nm, 800 nm, 860 nm and 1000 nm, which were related to the 4F9/2 → 4I15/2, 4I9/2 → 4I15/2, 4S3/2 → 4I13/2 and 4I11/2 → 4I15/2 transitions of Er3+, respectively. Three luminescence intensity ratio (LIR) schemes associated with thermally decoupled levels were proposed and their dependence on ambient temperature was investigated, two for excitation at 660 nm and one for excitation at 800 nm. In all the three cases, excitation and emission wavelengths were within the first or second biological window. Relative sensitivities of up to 2.02 ± 0.06% K−1 were obtained, with good repeatability and reproducibility and with temperature uncertainties below 1 K. The influence of particle size on luminescence intensity and sensor sensitivity was also presented and discussed, considering the potential applications. The results showed that particle size can affect the sensitivity of each LIR differently depending on the phonon-assisted processes involved.

Electrochemical and optical properties of magnetic CuFe2O4 nanofibers grown by PVP and PVA-assisted sol–gel electrospinning

Electrochemical and optical properties of magnetic CuFe2O4 nanofibers grown by PVP and PVA-assisted sol–gel electrospinning

3D d-Ti3C2 xerogel framework decorated with core-shell SnO2@C for high-performance lithium-ion batteries

Three-dimensional (3D) delaminated-Ti3C2 (d-Ti3C2) xerogel framework decorated with core-shell SnO2@C nanoparticles is constructed via PVA-assisted sol-gel process, in which SnO2@C nanoparticles are synthesized by one-step hydrothermal route and then encapsulated into d-Ti3C2 framework. Remarkable improvement in the electrochemical performances as the lithium-ion batteries (LIBs) anode is achieved. Typically, the SnO2@C/d-Ti3C2 xerogel framework delivers a high initial capacity (1314 mA h g−1) and a reversible specific capacity up to 520 mA h g−1 after 1000 charge-discharge cycles at 1.0 A g−1. Furthermore, even at 10 A g−1, it still achieves a reversible specific capacity of 205.6 mA h g−1, with a discharge capacity of 169 mA h g−1 and a coulombic efficiency of 99.5% after 1000 cycles. Such excellent electrochemical performances are attributed to the synergistic effect between core-shell SnO2@C and 3D d-Ti3C2 conductive network: (i) the core-shell structure suppresses the pulverization of SnO2 during the Li insertion/extraction process, and (ii) the interconnected 3D MXene framework establishes a good conductive pathway for fast lithium ions diffusion and quick charge transfer.

Positron annihilation lifetime, cation distribution and magnetic features of Ni1−xZnxFe2−xCoxO4 ferrite nanoparticles

A series of Zn and Co-substituted nickel ferrite nanoparticles of nominal composition Ni1−xZnxFe2−xCoxO4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) have been synthesized by the PVA assisted sol–gel method.

Tailoring red-green-blue emission from Er3+, Eu3+ and Tb3+ doped Y2O3 nanocrystals produced via PVA-assisted sol-gel route

Y2O3 luminescent nanoparticles were synthesized via PVA-assisted sol-gel method and their structural and optical properties were investigated. Effects of rare earth (Er3+, Eu3+ and Tb3+) doping on luminescence properties of the produced nanophosphors have been investigated under NIR (800nm) and UV (240–300nm) excitation. Intense infrared to red and green emissions were observed and a weak blue upconverted luminescence was also detected. Moreover, it was observed that changing the doping ions, the color emitted by the samples could be modified and different combinations of UV excitation and doping produced effective white light emissions. The obtained results demonstrate that PVA-assisted sol-gel is an effective methodology for the synthesis of rare-earth doped Y2O3 nanophosphors.

Local atomic arrangement and scintillation properties of Eu- and Ce-doped NaYP2O7

Direct determination of rare earth location and local environment in NaYP2O7 are presented. Undoped and Ln-doped NaYP2O7 (Ln=Eu, Ce) were produced via PVA-assisted sol–gel method. Lattice parameters were determined from Rietveld refinement, showing monoclinic structure. XAS results suggested Eu3+ and Ce3+ are incorporated into NaYP2O7 host in substitution to Y3+ site, with first coordination shell formed by six oxygen ions. Measurements at Eu edge showed a single peak in R space for Eu–O distribution. In this case, uniform interatomic distances implied to absence of significant disorder. Analysis at Ce edge presented different behavior, with Ce–O distribution characterized by a split peak in R space. Nearest neighborhood was found to be distributed with Ce occupying an off-center position in Y site. Under X-ray excitation, 5D0→7FJ emission lines of Eu3+ were identified for NaYP2O7:Eu. NaYP2O7:Ce presented a broad emission formed by 5d→2FJ transitions of Ce3+, with the superposition attributed to the effect of distorted oxygen octahedra around the dopant ions.

Effect of carbon content and annealing atmosphere on phase purity and morphology of Li2MnSiO4 synthesized by a PVA assisted sol–gel method

Lithium transition metal orthosilicates of the general formula Li2MSiO4 have gained great interest as potential positive electrode material for Li-ion batteries. This study reports the dependence of phase purity and morphology on heat treatment atmosphere and the amount of corn-starch as carbonization agent during a PVA assisted sol–gel synthesis of nano-sized porous Li2MnSiO4/C composites. All samples were indexed to the orthorhombic Pmn21 polymorph, but samples with carbon contents less than 6% showed traces of the second orthorhombic polymorph Pmnb. Highest phase purities and a desired porous nano-sized morphology were obtained when heat treatments were carried out in 5% H2 and corn-starch amounts were ≥25wt.%. Powders with varying carbon amounts were produced and the electrochemical performance was determined by galvanostatic cycling at different current densities. Samples with a corn-starch amount of 25wt.% offered the highest initial discharge capacity of 155mAhg−1 at a current density of 3mAg−1.

3D aligned-carbon-nanotubes@Li2FeSiO4 arrays as high rate capability cathodes for Li-ion batteries

3D aligned-carbon-nanotubes (ACNTs)@Li2FeSiO4 nanocomposite arrays on Al foil were developed as cathode materials for Li-ion batteries. The ACNTs were grown directly on an Al foil by a chemical vapor deposition method to achieve a 3D current collector structure for direct charge transport. Li2FeSiO4 nanoparticles were deposited on the surface of the ACNTs by a polyvinylalcohol (PVA)-assisted sol–gel method. The 3D samples showed a high degree of alignment of nanotubes with a favorable pore morphology before and after cycling. According to electrochemical measurements, the 3D sample with optimized mass ratio of ACNTs and Li2FeSiO4 (2:1) showed excellent rate capability and capacity retention, delivering a discharge specific capacity of 142 mAh g−1 at a rate of 0.5 C (C = 160 mAg−1) and maintaining 99% of the initial discharge capacity after 50 cycles at 24 ° C. Up to 20 C, the delivered charge/discharge capacity was 94 mAh g−1 after 172 cycles, which is 54% of the value obtained at C/20 (175 mAh g−1). In comparison, carbon coated nanoporous Li2FeSiO4 obtained under analogous conditions by a PVA-assisted sol–gel method can only deliver a capacity of 80 mAh g−1 and showed poor rate capability. In addition, despite amorphization, dissolution and chemical composition changes occurring in the 3D samples upon extended cycling, the 3D samples showed good long-term cycling stability at a high current density (5 C), maintaining ∼80% of the initial discharge capacity after 1000 cycles and ∼70% after 2000 cycles.

Comparative study of structural and optical properties of ZnO nanostructures prepared by three different aqueous solution methods

In the present work, zinc oxide (ZnO) nanoparticles with different morphologies and sizes were successfully synthesized via three different aqueous solution routes named proteic sol–gel, PVA-assisted sol–gel and microwave-assisted hydrothermal method. Sol–gel samples were crystallized into hexagonal structure after calcination at 350 °C, presenting uniform growth and predominantly spherical particles. On the other hand, the sample produced via hydrothermal method assumed nanorod morphology, probably due to the adsorption of ammonium on the surface of ZnO nuclei, which affect the growth orientation of the crystals. All the samples exhibited a sharp UV emission peak, related to excitonic recombination, and a broad emission band in the visible region, attributed to internal transitions in color centers. Sol–gel samples calcined at the lowest temperatures presented an UV emission intensity that was 44 and 89 times higher than the visible emission, which can be related to the passivation of the defects by hydrogen ions. As-prepared hydrothermal sample presented a broad emission band centered at approximately 596 nm, which is possibly related to OH groups adsorbed on the particle surfaces. Nevertheless, the emission band of samples calcined above 800 °C was shifted to 540 nm, which is probably related to oxygen vacancy according to the results from chemical analysis.

High capacity nanostructured Li2FexSiO4/C with Fe hyperstoichiometry for Li-ion batteries

Li2FeSiO4-based materials have attracted a great deal of interest as cathodes for lithium ion batteries for its excellent thermal stability and good cycling ability. Nanoporous Li2FeSiO4/C composites with varying Fe stoichiometry were synthesized by a PVA-assisted sol–gel method. Different gel formation processes were used to control morphology and pore size distribution. The pore size distribution was controlled by adjusting the parameters of the gel ageing process, the carbon content and phase purity was controlled by adjusting the starch content, and the amount of secondary phases was controlled by adjusting the Fe stoichiometry. The electrochemical properties of the Li2FeSiO4/C composite were assessed using coin cells at 24 °C, and the optimized material showed an initial discharge capacity of 163 mAh g−1 at a discharge rate of C/16 (C = 160 mA g−1) and a high capacity retention of 96% after 200 cycles at a discharge rate of 1 C.

Synthesis of CoFe2O4 powder via PVA assisted sol–gel process

CoFe2O4 ferrites were synthesized by sol–gel method, having metal nitrates as precursors and PVA as surfactant, followed by a heat treatment at 960 °C for 2 h. The ultrafine ferrite powders obtained have been characterized by X-ray diffraction, thermal gravimetry, differential scanning calorimetry and room temperature magnetic measurement studies. The morphology of the powder was identified by high resolution-scanning electron microscopy. X-ray diffraction results indicate that the resultant CoFe2O4 crystallites consist of spinel phase. Significant differences in magnetic properties of CoFe2O4 samples synthesized with various concentrations of PVA were observed. The magnetisation measurements show that when the PVA concentration increased, coercivity initially decreased and then increased where as retentivity and magnetisation decreased. The optimum concentration of PVA for the synthesis of CoFe2O4 ferrites is obtained from this investigation. Obviously this material can be used as an efficient candidate for practical recording purpose.

Rapid synthesis of the low thermal expansion phase of Al2Mo3O12 via a sol–gel method using polyvinyl alcohol

Aluminum molybdate was successfully synthesized using a simplified PVA assisted sol–gel method resulting in highly crystalline, monophasic (monoclinic P21/a) samples. These materials could readily be obtained at temperatures of 600 and 700 °C after calcining for as little as 15–20 min. Scanning electron microscopy and X-ray powder diffraction indicated that even the sample calcined at 600 °C for 20 min was free of impurities and composed of submicron sized particles (~300 nm). Transmission electron microscopy was used to confirm the monophasic character and submicron dimensions of the as-prepared powders. In addition to producing high quality samples, it was also observed that the metal to PVA ratio used during this simplified synthesis, could be used as a control parameter for tailoring the particle sizes of the final product.

Carbon coated Li 3V 2(PO 4) 3 cathode material prepared by a PVA assisted sol–gel method

Carbon coated Li 3V 2(PO 4) 3 cathode material was prepared by a poly(vinyl alcohol) (PVA) assisted sol–gel method. PVA was used both as the gelating agent and the carbon source. XRD analysis showed that the material was well crystallized. The particle size of the material was ranged between 200 and 500 nm. HRTEM revealed that the material was covered by a uniform surface carbon layer with a thickness of 80 Å. The existence of surface carbon layer was further confirmed by Raman scattering. The electrochemical properties of the material were investigated by charge–discharge cycling, CV and EIS techniques. The material showed good cycling performance, which had a reversible discharge capacity of 100 mAh g −1 when cycled at 1 C rate. The apparent Li + diffusion coefficients of the material ranged between 9.5 × 10 −10 and 0.9 × 10 −10 cm 2 s −1, which were larger than those of olivine LiFePO 4. The large lithium diffusion coefficient of Li 3V 2(PO 4) 3 has been attributed to its special NASICON-type structure.

A new candidate cathode material as (Co/Mg)-coated Ni powder for molten carbonate fuel cell

Co/Mg solid solution coated Ni powder, where Mg-doped LiCoO 2 is coated on NiO in molten carbonate, has been used as a new cathode material to reduce the solubility of NiO and to maintain the advantages of NiO cathode. The (Co/Mg)-coated NiO cathode was prepared by a coating Co/Mg solid solution on the surface of the Ni powder using a PVA assisted sol–gel method. The phase changes of the (Co/Mg)-coated Ni powder after immersed into Li/K eutectic carbonate mixtures at 550 °C ∼ 850 °C for 48 h was performed by XRD and Raman. SEM was used to study the particle morphologies. Co/Mg solid solution was coated on the surface of the Ni powder and Li(NiCoMg)O 2 is formed on NiO in molten carbonate. It is expected that the Li(NiCoMg)O 2 phase will reduce the solubility of NiO cathode in molten carbonate.

Properties of a new type of cathode for molten carbonate fuel cells

Abstract The solubility of a nickel oxide cathode in molten carbonate fuel cell (MCFC) electrolyte is one of the major technical obstacles to the commercialization of such fuel cells. Lithium cobalt oxide, LiCoO 2 , has been selected as a candidate material for MCFC cathodes because its solubility is small and the rate of dissolution into the melt is slower than that for nickel oxide. On the other hand, the electrical conductivity of LiCoO 2 is lower than that of nickel oxide. Thus, nickel oxide has been coated with stable LiCoO 2 in carbonate by a PVA-assisted sol–gel method to give a LiCoO 2 -coated NiO (LC-NiO) cathode. Raman spectra show that the structure of LC-NiO is different from that of nickel oxide, and that a LiCo 1− y Ni y O 2 phase is formed during heat-treatment of the LC-NiO cathode. The coating of LiCoO 2 on NiO electrode increases with increase in the dipping and heating times. The performance of unit cells show that the mean voltage of the cells is 0.80 V using a NiO cathode and 0.85 V with a LC-NiO cathode at a current density of 150 mA cm −2 . The solubility of the LC-NiO cathode in molten carbonate electrolyte is half that of NiO cathode after 300 h at 650°C.