In this work, compact and porous SiO
2
nanoparticles (NPs) were synthesized using the Stöber and the modified Stöber methods. Water-based nanofluids were characterized by dynamic light scattering, ...scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, and the porosity of the compact and porous SiO
2
samples was measured by N
2
adsorption–desorption isotherms. Thermal wave resonator cavity and inverse photopyroelectric configuration novel techniques were used for the first time to obtain the porous nanoparticles thermal diffusivity (
D
) and effusivity (
e
), respectively. Thermal conductivity (
k
) was obtained from the relationship between them
k
=
e
D
. An increase in the thermal conductivity of the porous SiO
2
NPs was obtained compared to the thermal conductivity of the compact NPs fluids with an enrichment of 14.7 %. Our results are supported by a theoretical model with a thermodynamic approach adapted for the thermal conductivity of porous SiO
2
governed by the parameters of the porosity and nanoparticle size.
A series of γ-LiAlO2-Ag cermets was studied to be integrated into a packed-bed membrane reactor with potential application in the selective separation of CO2 and O2; and simultaneous syngas ...production through the coupling of the oxidative CO2 reforming of methane process.
The γ-LiAlO2 was chemically synthesized and incorporated into an Ag matrix, in different amounts, by powder metallurgy using ball milling and uniaxial pressing techniques. The obtained cermets exhibit excellent wettability properties against molten carbonates, facilitating their infiltration and forming dense dual-phase membranes with the molten salts. Moreover, the cermet supports show corrosion resistance against the alkaline molten carbonates and superior thermal stability due to the γ-LiAlO2 suppresses the sintering of the metallic phase.
The membrane's performance was evaluated in the selective gas separation at high temperatures. The membranes exhibit simultaneous CO2 and O2 permeation with a flux of 0.78 and 0.43 ml·min-1·cm-2, at 850 °C, respectively. Besides, during the oxidative reforming process, the membrane reactor shows conversion of about 100 % of CO2 under the studied separation and reaction conditions. The syngas (H2+CO) production reaches values of 4.94 ml·min-1·cm-2 at 825 °C using a 10 % Ni/CeO2 catalyst.
A long-term permeation test was conducted for 225 h, during which the membrane exhibits excellent thermal and chemical stability properties under continuous reaction conditions of syngas production. This fact is attributed to its outstanding chemical inertness against carbonates as well as the observed sinterability properties of the used cermet support.
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•LiAlO2–Ag cermets exhibits remarkable wettability against molten carbonates.•The cermet phase shows chemical resistance to degradation induced by molten carbonates.•Concurrent and stable CO2 and O2 separation are achieved for the long-term test.•Stable behavior of the membrane reactor for the oxidative reforming of methane.
Li2CuO2 is synthesized via a solid-state reaction and its structure and microstructure is characterized using X-Ray Diffraction, Scanning Electron Microscopy and N2 adsorption–desorption isotherms. ...The capacity of cathode material is evaluated at different preparation conditions to determine the factors affecting charge retention, cyclability, and assuring reproducibility during electrode fabrication. Progressing from previous reports, a maximum capacity retention of 140mAhg−1 is attained in the potential window from 1.5 to 4.2V (Li/Li0) during ten cycles at C/15. The low capacity retention at extended cycling has been associated to the participation of irreversible oxygen redox process evaluated by theoretical calculations and cyclic voltammetry. These processes are minimized when the cycling potential window is confined from 2.0 to 3.8V (Li/Li0), thus, achieving a higher capacity retention up to 100mAhg−1 during 60cycles. Cycling at higher C/rates lowers the capacity down (60mAhg−1 at C/5), but the maximum capacity is restored when returning to C/15. Thus, making Li2CuO2 an attractive material either as active compound or additive in cathodes for Li-ion batteries, as a result of its intrinsic properties such as environmental benign, abundance, cost and straightforward preparation process.
•Preparation variables of Li2CuO2 electrode are examined and controlled.•Control of preparation variables leads to stable capacities, 140mAhg−1 for 10cycles.•Extended potential window generates irreversible structural changes.•The participation of oxygen redox processes leads to electrode degradation.•Restricted potential window increases the cyclability of Li2CuO2 electrodes achieving 100mAhg−1 and good rate performance.
In this work, solid solutions of general formula Ce1−x(Zr + Y)xO2−δ were chemically synthesized through the so-called citrate-EDTA complexing method, wherein the doping cations Zr and Y were ...substituted in the ceria lattice with an equimolar amount of 0.05 ≤ x ≤ = 0.25. The ternary oxides were heat-treated, and those that showed the best textural properties were superficially impregnated with Fe2O3 particles by the thermal decomposition method using a metalorganic precursor. The X-ray diffraction results suggest that co-doping with Zr4+ and Y3+ promotes a slight distortion of the CeO2 cubic cell. Nevertheless, the fluorite cubic structure of the oxides remains stable after being exposed to heat treatments. Furthermore, using scanning electron microscopy and Raman techniques, the presence of deposited Fe2O3 and the formation of extrinsic vacancies in the materials could be corroborated. Finally, the oxides’ catalytic evaluation in the soot oxidation reaction was carried out using the thermogravimetry technique. The ternary oxide with cerium molar content equal to 0.9 and impregnated with Fe2O3 presented excellent catalytic behavior for soot oxidation. T10, T50, and T90 temperatures were 310, 383, and 416 °C, respectively.
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► Barium sulfate/polyurethane nanocomposites were prepared by melt extrusion. ► Morphology of nanoparticles (spherical and fibers) modified the rheological behavior. ► Convenient ...levels of radio-opacity were found maintaining the mechanical properties. ► BaSO4 nanoparticles do not diminish the transparency of the polyurethane matrix.
Barium sulfate spherical agglomerates and fibers in the nanometric size range were used to prepare polyurethane (PU) nanocomposites (with 1wt.% concentration) via melt extrusion. A detailed analysis on the effect of the morphology of the barium sulfate phase upon the mechanical, rheological and optical properties was carried out. Results show that the inclusion of the dispersed phase (with various morphologies and sizes) in the polymer matrix does not decrease the polymer mechanical properties, as is observed when particles in the micrometric size range are included. Rheological studies show that the nanocomposite containing spherical particles presents a slightly higher shear viscosity than that of the polymer matrix, in contrast to the nano-fibers viscosity which presents lower values. This is reflected in the effect of the particle morphology on the processability of the material; in contrast, the morphology has no effect on the radio-opacity of the samples. The structure and dispersion of the particles were analyzed using scanning and transmission electron microscopy. The sample with 1wt.% nanofibers presents better processability than the system with spherical agglomerates maintaining the X-ray opacity properties.
Currently, perovskite structures have had an important impact in the development of gas sensors. In this work, perovskite LaCoO3 nanoparticles were synthesized by a simple, economic and reproducible ...processing by the solution method. The reactive precursors were nitrates of lanthanum and cobalt, using ethylenediamine as a chelating agent and distilled water as solvent. The gel formed by the solvent evaporation (through microwave radiation) was dried at 200 °C and later calcined at 300, 400, 500, 600, and 700 °C for 5 h. The samples were analyzed by X-ray diffraction, infrared spectroscopy, thermogravimetry, scanning, transmission, and atomic force microscopies, and nitrogen physisorption. These analyses confirmed the formation of LaCoO3 nanoparticles (size ~ 47 nm) at relatively low temperatures. The particles showed a continuous connectivity, generating a porous surface with a fibrous appearance. Starting with the synthesized powders, pellets were made and tested as gas sensors in carbon monoxide and propane atmospheres (at concentrations of 0–300 ppm) at different temperatures (25, 150, 250, and 350 °C). The nanoparticles presented high sensitivity, with a greater response in the propane atmosphere.
In recent decades, manganese oxide (MnO2) has been an attractive catalyst for organic pollutants removal from wastewater by ozonation. However, the effect of the MnO2 crystalline phase on Bisphenol A ...ozonation in water has never been investigated. In the present study, three crystalline phases of MnO2 were synthesized by hydrothermal method, including α-, γ-, and δ-MnO2, the last generating three different kinds. The as-prepared MnO2 were evaluated in the ozonation of Bisphenol A (BPA) and correlated with their physicochemical properties obtained by different characterization techniques. The activity of MnO2 polymorphs for TOC removal followed the order of γ-MnO2 > δ3-MnO2 > δ1-MnO2 > α-MnO2 > δ2-MnO2. The catalytic activity of MnO2 strongly depended on the presence of active sites such as density of the surface oxygen vacancy, Mn+3/Mn+4 ratio, and OH-groups on the catalyst surface. The catalysts with the highest amount of oxygen vacancies (but the minor density of the surface oxygen vacancy) and OH-groups were δ3-MnO2 and γ-MnO2, respectively, demonstrating excellent catalytic activity on BPA removal. The effect of stabilities of δ3-MnO2 and γ-MnO2 was also investigated in this research. Furthermore, the toxicity bioassay based on Lactuca sativa seeds demonstrated that by-products generated during conventional and catalytic ozonation were non-toxic. The elimination of the model mixture of emergent compounds in four types water were also tested with δ3-MnO2 and γ-MnO2, obtaining mineralization values around 47–59 % and 40–55 %, respectively, at 120 min compared with 18–23 % of conventional ozonation.
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•Thermal characterization of centrifuged aromatic citrus oils was studied.•Thermal lens (TL) and open photoacoustic cell (OPC) were used for characterization.•Thermal diffusivity, thermal effusivity ...and thermal conductivity were obtained.•Thermal effusivity and conductivity of green mandarin oil is first time reported.•Absorption coefficients and chemical structure of the citrus oils were determined.
In this work, thermal characterization of centrifuged aromatic citrus oils was studied using thermal lens (TL) and open photoacoustic cell (OPC). The thermal diffusivity (D) was obtained by TL, fitting the critical time parameter of the experimental curves to the theoretical values. An experimental arrangement of non-matched mode lasers with a probe and an excitation lasers was used. On the other hand, the thermal effusivity (e) of the samples was obtained by using OPC. The thermal conductivity (k) was calculated from the relationship between D and e. The thermal parameters obtained were compared with theoretical values in the literature. UV–vis spectroscopy, Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) and 1H Nuclear Magnetic Resonance (NMR) were used to determine the absorption coefficients and chemical structure of the citrus oils. The importance of this research work was the determination of the thermal parameters of essential oils as an alternative technique for quality control application.
•Nanocrystalline Li2SiO3 powders were synthesized via microwave-assisted hydrothermal method.•Pure Li2SiO3 phase was obtained using short reaction time at low temperature.•Li2SiO3 particles exhibited ...hollow sphere morphologies and high specific surface area.•Water vapor and CO2 capture properties were evaluated by thermogravimetric analysis.•Exhibited properties suggested potential applications of Li2SiO3 as catalyst and CO2 sorbents.
A series of lithium metasilicate (Li2SiO3) powder materials has been successfully synthesized by the microwave-assisted hydrothermal route using lithium hydroxide and tetraethyl-orthosilicate-derived sol precursors. Ceramic powders were obtained under hydrothermal conditions of autogenous pressure in the presence of a nonionic surfactant. The production of pure and well-crystallized Li2SiO3 using very short reaction times at low temperatures was shown by X-ray diffraction, scanning electron microscopy, and N2 adsorption-desorption analyses. Synthesized Li2SiO3 particles were nanocrystalline and exhibited different morphologies and specific surface areas depending on the synthesis conditions. Additionally, the capability of selected Li2SiO3 samples to absorb H2O and CO2 was evaluated via thermogravimetric analyses by varying the temperature, carrier gas, and water vapor concentration. Li2SiO3 particles exhibited interesting textural and morphological characteristics that make them suitable for use as a CO2 absorbent and which suggest that they also have the potential to be used in other applications.
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