Search Results (16)

Porous nanocrystalline lanthanum perovskite La-Fe-O (LaFeO₃) powders were synthesized by the sol–gel self-combustion method, using polyvinyl alcohol as the colloidal medium. The perovskite structure of the material, without secondary phases, was obtained at a calcination temperature of 900 °C for 40 min. The obtained powder was tested for catalytic activity at moderate temperatures (50–550 °C) for ethanol, methanol, acetone, benzene, and Pb-free gasoline vapors. Catalytic combustion begins at quite low temperatures (60–200 °C), compared to normal combustion, and this can be attributed to the nanometric crystallites, the large specific surface area, and the presence of iron cations with different valences, Fe³⁺/Fe²⁺, resulting from the method we used to obtain the material. The degree of conversion reaches values of over 99% for acetone and ethanol vapors at a temperature of 270 °C and 310 °C, respectively, and over 97% for methanol vapors at a temperature of 330 °C. The degree of conversion for Pb-free gasoline and benzene reaches somewhat lower values, over 88% at much higher temperatures, 470 °C and 550 °C, respectively. The lanthanum perovskite catalyst, LaFeO₃, obtained by the presented preparation method, can be recommended for the combustion of acetone, ethanol, and methanol vapors. The performance of this catalyst is remarkable and can be compared to that of a catalyst containing noble metals in its composition. Full article

Fly ash, a primary solid waste product of coal combustion, poses severe threats to human health and the environment due to its massive accumulation. Leveraging the modified porous structure and engineered adsorptive properties of fly ash, its integration with nano-photocatalytic materials can achieve dispersion and stabilization of the photocatalyst, significantly enhancing photocatalytic activity while enabling a synergistic effect between adsorption and photocatalysis. This paper focuses on the issue of agglomeration in semiconductor photocatalytic materials and briefly reviews the preparation methods and applications of modified fly ash-supported photocatalytic materials from both domestic and international perspectives in recent years. Initially, the properties and modification techniques of fly ash are analyzed, with a special emphasis on three methods for preparing fly ash-based photocatalytic composites: the sol-gel method, hydrothermal synthesis, and liquid-phase precipitation. A comparative analysis of the advantages and disadvantages of these three methods is conducted. Furthermore, the performance of the materials and the positive impacts of fly ash-composite photocatalysts are analyzed in terms of applications such as the degradation of pollutants in water, the degradation of NOx and VOCs gaseous pollutants, self-cleaning properties, and CO₂ reduction capabilities. These analyses indicate that fly ash primarily serves as an adsorbent and carrier in these applications. However, as a carrier, fly ash possesses a limited number of active sites, and its modification technology is not yet fully mature. Additionally, research in this area is still in the experimental stage and has not transitioned to engineered production. Therefore, there is a need for continuous improvement in fly ash modification techniques. Furthermore, additional research should be conducted on functional building materials loaded with fly ash-supported photocatalytic materials to enhance their practicality. Full article

A sol-gel matrix was generated from S– and P-based acids to prepare a fire-retardant solution system for coating natural cotton fibers. The physical properties, surface morphology, and elemental composition of the coated samples were assessed using optical scanning electron microscopy. The thermal behavior of the coated samples was documented using TGA and VFT tests, which confirmed higher thermal stability of the phosphate-based coatings. High char residue formation (~44.5%) and self-extinguishing properties were observed for the phosphate-based coating under non-curing conditions. The superior properties of phosphate-based coatings P5-4h could be ascribed to the collaborative effect of P–Si–N—i.e., the combined activity during the combustion process and pyrolysis of the coated sample. Full article

The paper shows the obtaining of nanocrystalline iron manganite (FeMnO₃) powders and their investigation in terms of catalytic properties for a series of volatile organic compounds. The catalyst properties were tested in the catalytic combustion of air-diluted vapors of ethanol, methanol, toluene and xylene at moderate temperatures (50–550 °C). Catalytic combustion of the alcohols starts at temperatures between 180 °C and 230 °C. In the case of ethanol vapors, the conversion starts at 230 °C and increases rapidly reaching a value of around 97% at 300 °C. For temperatures higher than 300 °C, the degree of conversion is kept at the same value. In the case of methanol vapors, the conversion starts at a slightly lower temperature (180 °C), and the degree of conversion reaches the value of 97% at a higher temperature (440 °C) than in the case of ethanol, and it also remains constant as the temperature increases. Catalytic combustion of the hydrocarbons starts at lower temperatures (around 50 °C), the degree of conversion is generally lower, and it increases proportionally with the temperature, with the exception of toluene, which shows an intermediate behavior, reaching values of over 97% at 430 °C. The studied iron manganite can be recommended to achieve catalysts that operate at moderate temperatures for the combustion of some alcohols and, especially, ethanol. The performance of this catalyst with regard to ethanol is close to that of a catalyst that uses noble metals in its composition. Full article

The undesirable inherent natural characteristics of wood, such as low mechanical strength, flammability, and hygroscopicity, limit its potential applications in the thermal insulation industry. Overcoming these disadvantages can greatly expand the application scope of wood. A new attempt at wood modification, the directional-freezing-assisted in situ sol–gel strategy, was used to obtain wood–silica composite aerogels with the unique multi-level ordered porous structure of wood. This method enables silica nanoparticles to successfully replace lignin and facilitates the formation of strong hydrogen bonds between the silica and cellulose molecules. This results in improved mechanical properties for the composite with a density similar to that of natural wood but a mechanical strength that can be up to five times greater. The thermal conductivity coefficient is also reduced to 0.032 W (m·K)⁻¹ compared to 0.066 W (m·K)⁻¹ for natural wood. This aerogel composite exhibits improved fire resistance and hygroscopicity, with a decomposition temperature increase of approximately 45 °C compared to natural wood. Additionally, the composite demonstrates self-extinguishing behavior, with the structure remaining intact after combustion, and thus enhanced fire resistance. Simultaneously, the enhanced aerogel composite hydrophobicity, with water contact angle of up to 120°, is beneficial to a prominent thermal insulation performance in a high-humidity environment. The successful synthesis of wood-based composite aerogels provides a new and innovative approach for the utilization of wood resources in the thermal insulation industry. Full article

Perovskite oxides were widely used as precursors for developing metal-support type catalysts. It is attractive to explore the catalytic properties of the oxides themselves for dry reforming of methane (DRM). We synthesized LaNi_xCr_1−xO₃ (x = 0.05–0.5) samples in powder form using the sol-gel self-combustion method. Ni atoms are successfully doped into the LaCrO₃ perovskite lattice. The perovskite grains are polycrystalline, and the crystallite size decreases with increasing Ni content. We demonstrated that the LaNi_xCr_1−xO₃ perovskites show intrinsically catalytic activity for DRM reactions. Reducing the Ni content is helpful to reduce carbon deposition resulting from the metal Ni nanoparticles that usually coexist with the highly active perovskite oxides. The CH₄ conversion over the LaNi_0.1Cr_0.9O₃ sample reaches approximately 84% at 750 °C, and the carbon deposition is negligible. Full article

In this research, we reported on the formation of highly porous foam SrTiO₃/NiFe₂O₄ (_100−xSTO/_xNFO) heterostructure by joint solid-state and sol-gel auto-combustion techniques. The colloidal assembly process is discussed based on the weight ratio x (x = 0, 25, 50, 75, and 100 wt %) of NiFe₂O₄ in the _100−xSTO/_xNFO system. We proposed a mechanism describing the highly porous framework formation involving the self-assembly of SrTiO₃ due to the gelation process of the nickel ferrite. We used a series of spectrophotometric techniques, including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N₂ adsorption isotherms method, UV-visible diffuse reflectance spectra (UV-Vis DRS), vibrating sample magnetometer (VSM), and dielectric measurements, to investigate the structural, morphological, optical, magnetic, and dielectric properties of the synthesized samples. As revealed by FE-SEM analysis and textural characteristics, SrTiO₃-NiFe₂O₄ nanocomposite self-assembled into a porous foam with an internally well-defined porous structure. HRTEM characterization certifies the distinctive crystalline phases obtained and reveals that SrTiO₃ and NiFe₂O₄ nanoparticles were closely connected. The specific magnetization, coercivity, and permittivity values are higher in the ₇₅STO/₂₅NFO heterostructure and do not decrease proportionally to the amount of non-magnetic SrTiO₃ present in the composition of samples. Full article

This paper presents the synthesis of gadolinium aluminate (GdAlO₃), an oxide compound with a perovskite structure, for applications as a capacitive and/or resistive humidity sensor. Gadolinium aluminate was synthesized by the sol-gel self-combustion method. This method allowed us to obtain a highly porous structure in which open pores prevail, a structure favorable to humidity sensors. Most of the materials studied as capacitive/resistive humidity sensors have significant sensitivities only with respect to one of these types of sensors. In the case of the studied gadolinium aluminate with p-type electric conductivity, the relative humidity of the air has a significant influence on both capacitive and resistive types of electric humidity sensors. The capacity increases about 10,000 times, and the resistance decreases about 8000 times as the relative humidity increases from 0 to 98%. The investigated gadolinium aluminate can be used successfully to obtain high-sensitivity capacitive and/or resistive humidity sensors. Full article

In this study, the manganese-doped manganese–cobalt–iron spinel was prepared by the sol–gel self-combustion method, and its physical and chemical properties were analyzed by XRD (X-ray diffraction analysis), SEM (scanning electron microscope), and VSM (vibrating sample magnetometer). The mercury removal performance of simulated flue gas was tested on a fixed bed experimental device, and the effects of Mn doping amount, fuel addition amount, reaction temperature, and flue gas composition on its mercury removal capacity were studied. The results showed that the best synthesized product was when the doping amount of Mn was the molar ratio of 0.5, and the average mercury removal efficiency was 87.5% within 120 min. Among the fuel rich, stoichiometric ratio, and fuel lean systems, the stoichiometric ratio system is most conductive to product synthesis, and the mercury removal performance of the obtained product was the best. Moreover, the removal ability of Hg⁰ was enhanced with the increase in temperature in the test temperature range, and both physical and chemical adsorption play key roles in the spinel adsorption of Hg⁰ in the medium temperature range. The addition of O₂ can promote the removal of Hg⁰ by adsorbent, but the continuous increase after the volume fraction reached 10% had little effect on the removal efficiency of Hg⁰. While SO₂ inhibited the removal of mercury by adsorbent, the higher the volume fraction, the more obvious the inhibition. In addition, in an oxygen-free environment, the addition of a small amount of HCl can promote the removal of mercury by adsorbent, but the addition of more HCl does not have a better promotion effect. Compared with other reported adsorbents, the adsorbent has better mercury removal performance and magnetic properties, and has a strong recycling performance. The removal efficiency of mercury can always be maintained above 85% in five cycles. Full article

The mixed ionic-electronic conducting (MIEC) oxygen transport membrane (OTM) can completely selectively penetrate oxygen theoretically and can be widely used in gas separation and oxygen-enriched combustion industries. In this paper, dual-phase MIEC OTMs doped with Bi are successfully prepared by a sol-gel method with high-temperature sintering, whose chemical formulas are 60wt.%Ce_0.9Pr_0.1O_2−δ-40wt.%Pr_0.6Sr_0.4Fe_1−xBi_xO_3−δ (60CPO-40PSF_1−xB_xO, x = 0.01, 0.025, 0.05, 0.10, 0.15, 0.20). The dual-phase structure, element content, surface morphology, oxygen permeability, and stability are studied by XRD, EDXS, SEM, and self-built devices, respectively. The optimal Bi-doped component is 60wt.%Ce_0.9Pr_0.1O_2−δ-40wt.%Pr_0.6Sr_0.4Fe_0.99Bi_0.01O_3−δ, which can maintain 0.71 and 0.62 mL·min⁻¹·cm⁻² over 50 h under He and CO₂ atmospheres, respectively. The oxygen permeation flux through these Bi-doped OTMs under air/CO₂ gradient is 12.7% less than that under air/He gradient, which indicates that the Bi-doped OTMs have comparable oxygen permeability and excellent CO₂ tolerance. Full article

This paper presents the results of an investigation on the magnetic and dielectric properties of Mg_0.5Zn_0.5Fe₂O₄ spinel ferrite with a 1% weight percentage of Li⁺ and K⁺ added cations. The addition of metal ions plays an important role in increasing the porosity and favors the formation of ferrite at low temperatures. The goal of this new research is to demonstrate that by selecting the type of metallic cations for addition or choosing an optimal sintering temperature, it may be possible to improve the magnetic and electrical properties of Mg-Zn ferrite. The samples were prepared using sol-gel self-combustion techniques and annealed at 1000 °C, 1100 °C, and 1200 °C. Scanning electron microscopy revealed the shape and grain size of the samples, and the phase composition was analyzed using the X-ray diffraction technique. The magnetic information, such as remanent magnetization M_R, saturation magnetization M_S, and coercivity H_C, were extracted from the hysteresis loops of the samples. The electrical investigation was focused on the low- and high-frequency dependence of dielectric constant and dielectric losses. The results are discussed in terms of microstructural changes induced by the additions of Li⁺ and K⁺ metallic cations. Conclusions are drawn concerning the optimization of magnetic and electrical properties for the development of Mg-Zn ferrite with possible applications in the field of magnetic materials or electronics. Full article

Conventional sol-gel solutions have received significant attention in thin-film transistor (TFT) manufacturing because of their advantages such as simple processing, large-scale applicability, and low cost. However, conventional sol-gel processed zinc tin oxide (ZTO) TFTs have a thermal limitation in that they require high annealing temperatures of more than 500 °C, which are incompatible with most flexible plastic substrates. In this study, to overcome the thermal limitation of conventional sol-gel processed ZTO TFTs, we demonstrated a ZTO TFT that was fabricated at low annealing temperatures of 350 °C using self-combustion. The optimized device exhibited satisfactory performance, with μ_sat of 4.72 cm²/V∙s, V_th of −1.28 V, SS of 0.86 V/decade, and I_ON/_OFF of 1.70 × 10⁶ at a low annealing temperature of 350 °C for one hour. To compare a conventional sol-gel processed ZTO TFT with the optimized device, thermogravimetric and differential thermal analyses (TG-DTA) and X-ray photoelectron spectroscopy (XPS) were implemented. Full article

Sol-gel spread self-combustion is the burning of the complexing agent in dried gel and the oxidant. Meanwhile, high temperature takes place during the combustion process, which is harmful to the pore structure of the catalyst. The nitrate from metal nitrate precursors as an oxidant could participate in the spread of the self-combustion process. Therefore, the influence of nitrate from metal nitrate on the spread self-combustion of an iron–cerium–tungsten citric acid gel and its catalytic performance of NO_x reduction were investigated by removing nitrate via the dissolution of washing co-precipitation with citric acid and re-introducing nitric acid into the former solution. It was found that the removal of nitrate contributes to enhancing the NH₃–SCR activity of the magnetic mixed oxide catalyst. The NO_x reduction efficiency was close to 100% for Fe₈₅Ce₁₀W₅–CP–CA at 250 °C while the highest was only 80% for the others. The results of thermal analysis demonstrate that the spread self-combustion process of citric acid dried gel is enhanced by re-introducing nitric acid into the citric acid dissolved solution when compared with the removal of nitrate. In addition, the removal of nitrate helps in the formation of γ-Fe₂O₃ crystallite in the catalyst, refining the particle size of the catalyst and increasing its pore volume. The removal of nitrate also contributes to the formation of Lewis acid sites and Brønsted acid sites on the surface of the catalyst compared with the re-introduction of nitric acid. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrates that both Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanisms exist over Fe₈₅Ce₁₀W₅–CP–CA at 250 °C with E–R as its main mechanism. Full article

New hybrid sol–gel coatings based on tetraethoxysilane (TEOS) and phytic acid (PA) were designed and applied to cotton; the flame-retardant properties of the treated fabrics were thoroughly investigated by means of flame-spread and forced-combustion tests. The first goal was to identify the TEOS:PA weight ratio that allowed the achievement of the best flame-retardant properties, with the lowest final dry add-on on the fabrics. Therefore, different TEOS:PA sols were prepared and applied to cotton, and the resulting coated fabrics were thoroughly investigated. In particular, solid-state NMR spectroscopy was exploited for assessing the condensation degree during the sol–gel process, even for evaluating the occurrence of possible reactions between phytic acid and the cellulosic substrate or the alkoxy precursor. It was found that a total dry add-on of 16 wt % together with 70:30 TEOS:PA weight ratio provided cotton with self-extinction, as clearly indicated by flame-spread tests. This formulation was further investigated in forced-combustion tests: a significant reduction of heat release rate (HRR), of the peak of HRR, and of total heat release (THR) was found, together with a remarkable increase of the residues after the test. Unfortunately, the treated fabrics were not resistant to washing cycles, as they significantly lost their flame-retardant properties, consequently to the partial removal of the deposited hybrid coatings. Full article

Spinel copper ferrite (CuFe₂O₄) and zinc ferrite (ZnFe₂O₄) nanoparticles were synthesized using a sol-gel self-combustion technique. The structural, functional, morphological and magnetic properties of the samples were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). XRD patterns conform to the copper ferrite and zinc ferrite formation, and the average particle sizes were calculated by using a transmission electron microscope, the measured particle sizes being 56 nm for CuFe₂O₄ and 68 nm for ZnFe₂O_4. Both spinel ferrite nanoparticles exhibit ferromagnetic behavior with saturation magnetization of 31 emug⁻¹ for copper ferrite (50.63 Am²/Kg) and 28.8 Am²/Kg for zinc ferrite. Both synthesized ferrite nanoparticles were equally effective in scavenging 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) free radicals. ZnFe₂O₄ and CuFe₂O₄ nanoparticles showed 30.57% ± 1.0% and 28.69% ± 1.14% scavenging activity at 125 µg/mL concentrations. In vitro cytotoxicity study revealed higher concentrations (>125 µg/mL) of ZnFe₂O₄ and CuFe₂O₄ with increased toxicity against MCF-7 cells, but were found to be non-toxic at lower concentrations suggesting their biocompatibility. Full article