Sol-gel Samples Research Articles

Effects of the Physical Properties of Thickener Sols on the Physical Properties and Sensory Characteristics of Sol-gel Mixed Samples

Effects of the Physical Properties of Thickener Sols on the Physical Properties and Sensory Characteristics of Sol-gel Mixed Samples

Pristine and coated LiNi1/3Mn1/3Co1/3O2 as positive electrode materials for li-ion batteries

Layered LiNi1/3Mn1/3Co1/3O2 (NMC) positive materials were synthesized by efficient, low cost and easy manageable methods such as oxalate co-precipitation and sol-gel processes. Preliminary electrochemical results show that sol-gel sample provide better results than co-precipitated samples. With the aim to improve the properties of the co-precipitated samples these were coated with carbon and alumina bearing in mind the co-precipitated method is suitable for large scale production. The subsequently performed local structure investigations revealed well crystallized layered cathode materials with α-NaFeO2-type structure (R-3m space group). Sample tests using both the scanning electron microscope (SEM) and the transmission electron microscope (TEM) showed submicron particles with a slight tendency to agglomerate and furthermore the existence of a thin film that encapsulates the oxide particles. 7Li magic angle spinning nuclear magnetic resonance (7LiMAS NMR) measurements were carried out for pristine and coated samples to compare the cation arrangement in the transition metal layers. Finally, electrochemical tests revealed a remarkable improvement in capacity retention of the coated oxides compared to the parent compounds.

Novel Nano-Zirconium Antimonate as Cation Exchange Material for Organic Dye Pollutants Purification

Nano-zirconium antimonate was successfully prepared using two different techniques of sol-gel and homogeneous precipitation. The different preparation parameters affecting onto the two preparation techniques such as HCl concentration, reactants molar ratio and effect reaction temperature were optimized to attain cation exchange material with high ion exchange capacity and produced in nano-size structure. The different prepared samples were screened based on their ion exchange capacities. The most proper prepared sample produced from the sol-gel technique poses higher ion exchange capacity value of 3.5meq/g compared with that produced from the homogeneous precipitation that recorded ion exchange capacity of 2.8meq/g. The physico-chemical properties of the two nano-zirconium antimonate samples produced from each technique were compared using various analytical techniques such as XRD, SEM and TEM. XRD results indicated that the sample produced from the homogeneous precipitation attains high crystallinity degree compared with the amorphous sol-gel prepared sample. The morphological structure investigation evident the nano-spherical morphology for the two prepared samples. The average nano-size of the homogeneous precipitation sample of 22nm is smaller than that of the sol-gel sample that recorded 34nm. The dye decontamination behavior of the two prepared nano-zirconium antimonate samples was compared for C.I basic blue 3dye. The sol-gel prepared sample recorded higher dye decolorization of 81.5% compared with 54% for the homogeneous precipitation sample.

Effect of the synthetic method on the catalytic activity of alumina: Epoxidation of cyclohexene

Al2O3 was prepared from different inorganic precursors via the Pechini method and compared with Al2O3 prepared by the sol–gel method. Structural characterization of these materials was carried out by FTIR, X-ray diffraction (XRD), N2 adsorption at −196°C and transmission electron microscopy (TEM). The solids were tested in the epoxidation of cyclohexene and a difference in their catalytic activities was observed. The characterization results indicate that the samples prepared by Pechini have a mixture of γ-alumina and boehmite, a condition favoring catalytic activity, whereas the sol–gel sample is less crystalline due to higher boehmite content. These results indicate that both the nature of the precursor and the method of synthesis strongly affect the catalytic activity of Al2O3.

Syngas production via dry reforming of CH4 over Co- and Cu-promoted Ni/Al2O3–ZrO2 nanocatalysts synthesized via sequential impregnation and sol–gel methods

In this study, the effect of synthesis method (impregnation and so-gel) as well as Co and Cu addition on the catalytic and physicochemical properties of Ni/Al2O3–ZrO2 nanocatalyst was evaluated in dry reforming of methane. The XRD, FESEM, PSD, BET and FTIR analysis were used to characterize the nanocatalysts. Highly dispersed Ni and Zr species and no spinel production in the sol–gel synthesized samples were confirmed by XRD results. The FESEM images showed small and uniform nanoparticles in the sol–gel synthesized catalyst. Also, after Cu added to Ni/Al2O3–ZrO2, the particles were more compact than others. Moreover, the promoters addition especially Co to Ni/Al2O3–ZrO2 nanocatalyst improved the particles size uniformity. Particle size distribution of sol–gel synthesized Ni–Co/Al2O3–ZrO2 nanocatalyst represented that the majority of the particles (nearly 95%) lies between 10 and 40 nm with an average size of 27.4 nm. BET analysis showed higher surface area in the sol–gel samples, especially when it was coupled with Co and Cu addition. The results indicated the remarkable synergetic effect of sol–gel method and Co addition on the surface morphology and elemental dispersion. Activity of nanocatalysts were evaluated as a function of temperature from 550 to 850 °C at GHSV = 24 l/g h, P = 1 atm and CH4/CO2 = 1. The sol–gel synthesized nanocatalyst showed better catalytic performance. Moreover, it was observed that, Cu and Co addition improved feed conversion, products yield and better syngas ratio. The comparison between promoters revealed that activity of Co was better than Cu. During the 1440 min time on stream test at 850 °C, the sol–gel synthesized Ni–Co/Al2O3–ZrO2 nanocatalyst exhibited the best activity compared to the other samples and produced syngas with approximately stoichiometry ratio.

The magnetic and neutron diffraction studies of La1−xSrxMnO3 nanoparticles prepared via molten salt synthesis

Series of single-phase La1−xSrxMnO3 nanoparticles (x=0.25−0.47) with the size of about 50nm was prepared in molten NaNO2. TEM evidenced well dispersed particles that are not interconnected by sintering bridges in contrast to traditional products. Interestingly, some reduction of the perovskite cell volume, particularly at higher Sr-contents, was detected by XRD. Moreover, reduced magnetization and decreased Curie temperature in comparison to sol–gel samples were observed. Neutron diffraction analysis of the as-prepared nanoparticles and several comparative samples with x=0.37 indicated that the anomalous behavior of studied particles probably originate in the overdoped outer shell. The overdoping might result from both the surface oxygen chemisorption and from an increased Sr concentration in the shell. By all means, the overdoping would lead to compressive surface stress, driving the x=0.37 ground state toward a mixture of FM and A-type AFM ordering as observed by neutron diffraction.

Dielectric, Ferroelectric and Piezoelectric Properties of Sr0.8Na0.1Nd0.1Bi4Ti4O15 Prepared by Sol Gel and Solid State Technique

Effect of lower ionic radii (Na and Nd) substitution in A-site on the structure, dielectric, ferroelectric and piezoelectric properties of SrBi4Ti4O15 (SBT) is investigated in this paper. The samples are prepared by solid state double sintering method and sol gel method based on pechini process. Substitution of smaller ions reduced the dielectric constant and remanent polarization values. But sol gel samples showed good dielectric and ferroelectric properties. A-site substitution has resulted in improved Curie temperature and piezoelectric properties. As a result, Na and Nd modified SBT ceramics are found to be excellent high temperature piezoelectric materials.

Enhanced CO2absorption kinetics in lithium silicate platelets synthesized by a sol–gel approach

Platelet-shaped lithium orthosilicate particles synthesized by a sol–gel approach employing the precursors lithium nitrate and colloidal silica displayed enhanced absorption kinetics for CO2 compared to the powders prepared by a solid-state reaction process involving Li2CO3 and silica. The sol–gel samples showed a CO2 absorption capacity of 350 mg g−1 at an absorption rate of 22.5 mg g−1 min−1, a value 70% higher than the rate of 13.2 mg g−1 min−1 measured with the solid-state samples under similar conditions. The higher sorption kinetics of CO2 by the sol–gel derived lithium orthosilicate could be attributed to the unique platelet morphology of the particles, which have a very small thickness. A porous carbon mesh coated with the sol–gel based particles exhibited CO2 absorption capacity of 150 mg g−1 at an absorption rate of 37.5 mg g−1 min−1. This supported absorbent also showed stable absorption and desorption performance for the 8 cycles examined in this study. The excellent absorption characteristics of the sol–gel prepared powders, more specifically the coated strips, provide a successful pathway for the commercialisation of these materials.

Structural and Magnetic Studies of SrFe12O19 by Sol-gel Method

Strontium hexaferrite (SrFe12O19) particles were prepared by sol gel method at two different calcination temperatures, namely, at 800°C and 1000°C. It was found that SrFe12O19 prepared, at 800°C showed a mixture of Fe2O3 co-existed while at a higher temperature of 1000°C, no other oxide impurities was detected. Superconducting quantum interference device (SQUID) was performed on both the sol-gel prepared samples. The coercivity for the low temperature prepared SrFe12O19 showed a much higher value of 6250Oe compared with the high temperature prepared SrFe12O19 which was only 4500Oe. In addition to the calcination temperature, the presence of Fe2O3 also affected the coercivity of the hexaferrite particles. Thermogravimetric analysis (TGA) was performed at 950°C on both the sol-gel samples and it was noted that the low temperature prepared SrFe12O19 has a higher weight loss about 3.2% compared to the high temperature sample which has a much smaller weight loss of only 0.6%. The high weight loss was attributed by the breakdown of Fe2O3.

Alteration of the Cytochrome C Folding Pathway in Solution and Within Sol-Gel Glasses by Addition of Hofmeister Salts

The ferric cytochrome c (un)folding mechanism in the presence of steric constraints and salts is examined. Unfolding was initiated both thermally and with chemical denaturants. Sol-gel encapsulation was used to constrain the protein to a volume close to the “molten globule state.” Hofmeister salts were added singly and in pairs to alter protein stability. UV/VIS absorption spectroscopy and a basis spectra fitting analysis were used to determine the populations of each protein conformation along the folding pathway. These species can be differentiated by their axial heme ligands. Four species exist in solution: the native HM state (His18/Met80), the partially folded HW (His18/water) and HH (His18/His33) intermediates, and the 5C (water) unfolded state. An additional unfolded state found only within the sol-gel contains an unligated four-coordinate heme sequestered from aqueous solution. Solution results indicate that the thermal and chemical denaturization pathways are not the same, but that both involve significant backbone rearrangement. Further, while every species observed in solution is also observed in the sol-gel, their relative populations are different, indicating that backbone motions are hindered by encapsulation within the sol-gel matrix. The ranking of salts in the Hofmeister series (from stabilizing to destabilizing protein structure) was found to persist in the sol-gel samples, and in some cases a larger effect on protein stability was found in the sol-gels. Additionally, it was found that addition of multiple salts changed the protein's stability in an additive manner. Both the (un)folding kinetics and the accessible conformations were found to depend on the identity of ions present. These results are discussed in terms of the hydrophobic effect and an altered water structure within the confines of the gel pores.

Effects of the Physical Properties of Gels on the Physical Properties and Sensory Characteristics of Sol-gel Mixed Samples

Effects of the Physical Properties of Gels on the Physical Properties and Sensory Characteristics of Sol-gel Mixed Samples

Light absorption in Ge nanoclusters embedded in SiO2: comparison between magnetron sputtering and sol–gel synthesis

SiGeO films have been produced by a sol–gel derived approach and by magnetron sputtering deposition. Post-thermal annealing of SiGeO films in forming gas or nitrogen atmosphere between 600 and 900 °C ensured the phase separation of the SiGeO films and synthesis and growth of Ge nanoclusters (NCs) embedded in SiO2. Rutherford backscattering spectrometry analysis evidenced a similar Ge concentration (~12 %), but a different Ge out-diffusion after annealing between the two types of techniques with the formation of a pure SiO2 surface layer (~30 nm thick) in sol–gel samples. The thermal evolution of Ge NCs has been followed by transmission electron microscopy and Raman analysis. In both samples, Ge NCs form with similar size increase (from ~3 up to ~7 nm) and with a concomitant amorphous to crystalline transition in the 600–800 °C temperature range. Despite a similar Ge concentration, a significant lower NCs density is observed in sol–gel samples attributed to an incomplete precipitation of Ge, which probably remains still dispersed in the matrix. The optical absorption of Ge NCs has been measured by spectrophotometry analyses. Ge NCs produced by the sol–gel method evidence an optical band gap of around 2 eV, larger than that of NCs produced by sputtering (~1.5 eV). These data are presented and discussed also considering the promising implications of a low-cost sol–gel based technique towards the fabrication of light harvesting devices based on Ge nanostructures.

Up-conversion fluorescence characteristics and mechanism of Er3+-doped TiO2 thin films

Er3+-doped TiO2 thin films were prepared by RF magnetron sputtering. The effects of Er3+ concentration and annealing conditions upon up-conversion fluorescence were studied. The result shows that 490 nm green emission and 670 nm red emission can be obtained from Er3+-doped TiO2 thin films excited by 980 nm lasers. TiO2 thin films with 1.0 mol% Er3+ manifested the best up-conversion property when the annealing temperature reached 900 °C. Under such conditions, we observed intense 490 nm green emission that has not been observed in powder or sol–gel samples and the mechanism of up-conversion fluorescence were studied. We also confirmed the up-conversion properties are closely related to the formation of Er2Ti2O7 in thin films, which is proved to reduce state densities of phonons and therefore inhibit nonradiative transition in an up-conversion process.

A comparative study of Cu2ZnSnS4 thin films growth by successive ionic layer adsorption–reaction and sol-gel methods

Owing to the high natural abundance and non-toxicity of all the constituents, the copper–zinc–tin–sulfide compound has been attracting attention in recent years for the production of cheap solar absorber materials. Solution-based low-cost approaches are being developed for the deposition of this compound. In this comparative study, we have investigated Cu2ZnSnS4 thin films prepared by using successive ionic layer adsorption–reaction and sol-gel methods. X-ray diffraction studies indicated the polycrystalline nature of the films. No secondary phases were observed. The sol-gel grown Cu2ZnSnS4 film was found to have smaller crystallite size and higher micro-strain and dislocation density values. Phase purity and good crystalline quality of the studied films were proved through the Raman studies. From the scanning electron microscopy images, sol-gel grown Cu2ZnSnS4 film was found to have more homogenous and smooth morphology. Possible chemical formula of the films was determined. The optical absorption of the sol-gel grown film covered a wider wavelength range by means of absorbing more visible photons. The optical band gap values were estimated to be 1.45 and 1.40eV for the successive ionic layer adsorption–reaction and sol-gel grown samples, respectively. It was concluded that both methods are effective and can be used to produce high-quality Cu2ZnSnS4 thin films for cheap and green solar cell applications.

High capacity Li[Ni0.8Co0.1Mn0.1]O2 synthesized by sol–gel and co-precipitation methods as cathode materials for lithium-ion batteries

Abstract Layered Li[Ni0.8Co0.1Mn0.1]O2 cathode materials have been prepared by sol–gel and co-precipitation methods. The structural, morphological and electrochemical properties of the materials were compared. The XRD patterns show that both the sol–gel and the co-precipitation method formed single phase materials with good layered characteristics. Rietveld refinement reveals some differences in cation disorder between the two materials, where the sample synthesized by the sol–gel method shows lower Li/Ni cation disorder. SEM and BET measurements show that the sol–gel sample consists of relatively less aggregated particles giving larger BET surface area compared to the co-precipitation sample. Electrochemical tests indicate that the material prepared by the sol–gel method has slightly better electrochemical properties, with an initial discharge capacity of 200 mAh·g− 1 and capacity retention of 82.2% after 50 cycles at a cycling rate of 0.5 C, as well as better capability at 5 C. The improved performances of the sol–gel synthesized material may be attributed to the low Li/Ni disorder combined with high surface area, the latter increasing the interfacial contact area between the electrolyte and the active material. Effects of calcination conditions on the structure and electrochemical performance of the materials were also investigated. The electrochemical performance was improved by either increasing the O2 concentration in the calcination atmosphere, or by increasing the flow rate of air, showing the potential of developing low-cost synthesis routes for high-quality cathode materials.

A comparative study of the synthesis of nanocrystalline Yttrium Aluminium Garnet using sol-gel and co-precipitation methods

Nanocrystalline yttrium aluminium garnet (nYAG) powder has been synthesized via sol-gel and co-precipitation methods using nitrate precursors. Thermal evolution and crystallisation kinetics of both the methods were investigated. The optimised calcination condition for the formation of nYAG was also examined. It was found that a complete transformation to nYAG was observed at 925°C/2h and 1000°C/1h for the coprecipitation and sol-gel samples respectively. An intermediate YAlO3 phase was formed at 900°C in all powders regardless of the synthesis methods. The powder morphologies obtained from TEM revealed very similar particle sizes for the two routes (20–30nm); whilst the extent of agglomeration was higher for the sol-gel method. It was also observed that by controlling the pH in a narrow range, maintaining the precipitate processing temperature and dehydrating excess OH- ions in the precipitates using n-butanol treatment, the extent of agglomeration was further reduced in the co-precipitated nYAG powder.

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.

Effects of Synthesis and Spark Plasma Sintering Conditions on the Thermoelectric Properties of Ca3Co4O9+δ

Ca3Co4O9+δ samples were synthesized by solid-state (SS) and sol–gel (SG) reactions, followed by spark plasma sintering under different processing conditions. The synthesis process was optimized and the resulting materials characterized with respect to their microstructure, bulk density, and thermoelectric transport properties. High power factors of about 400 μW/m·K2 and 465 μW/m·K2 (at 800°C) were measured for SS and SG samples, respectively. The improved thermoelectric performance of the SG sample is believed to originate from the smaller particle sizes and better grain alignment. The SG method is suggested to be a beneficial means of obtaining high-performance thermoelectric materials of Ca3Co4O9+δ type.

Influence of synthesis methods and calcination temperature on electrical properties of La1−xCaxMnO3 (x=0.33 and 0.28) ceramics

Abstract La 1− x Ca x MnO 3 ( x =0.33 and 0.28) powders were prepared by both coprecipitation and sol–gel methods. Circular pellets with different radial shrinking ratios (RSR) were obtained by changing the calcination temperature of the powders. The influence of the powder synthesis process and the shrinking ratio of the sample on the structural, morphological and electrical properties of the ceramics were investigated. It has been found that sol–gel method is more efficient and stable to obtain ceramic samples with good electrical properties. The radial shrinking ratio of the ceramic increases with the decreasing calcination temperature. The experimental results show that RSR significantly affects the electrical properties of the ceramics prepared by coprecipitation method and has negligible influence on the samples made by sol–gel method. The coprecipitation samples with larger RSR have higher insulator to metal transition temperature T p which is comparable to that of the sol–gel samples.

Influence of the chemical synthesis on the physicochemical properties of N-TiO2 nanoparticles

Nitrogen doped TiO2 materials were successfully prepared following three different preparation routes (sol–gel, hydrothermal and pyrolysis) and characterized by various spectroscopic techniques. All samples absorbed radiation in the visible range and were active in the photocatalytic degradation of cyanotoxin microcystin-LR under visible light and in acidic conditions. The different preparation routes led to the formation of various impurities into the solids. In the case of hydrothermal and sol–gel samples, these impurities were weakly bound at the surface whereas the materials prepared by pyrolysis, the impurities showed a relevant stability and could not be removed even at high temperature. These species can affect the photocatalytic performance in different ways depending on their bulk or surface nature. On the basis of the photocatalytic data illustrated in this paper, the presence of such species at the surface was not detrimental for the photocatalytic activity of nitrogen doped TiO2 but actually contributed to a higher interaction with the target cyanotoxin; leading to a higher photocatalytic activity than that observed for samples prepared via the classic sol–gel method.