The effect of the calcination temperature of LaFeO3 precursors on the properties and catalytic activity of perovskite in methane oxidation

In the synthesis of perovskite-type LaFeO₃ oxides iron and lanthanum nitrates were used as a precursors. The nitrates were dissolved in water, evaporated, crushed and calcined in temperature range of 650–850?°C. The obtained perovskites were applied as an active layer on monolithic catalysts for the oxidation of methane. The increase in the calcination temperature of the perovskite precursors from 650° to 850°C results in a reduction in the surface area of the powders from 10.1 to 4.2?m²/g. XRD studies revealed that calcination at 800–850?°C caused the formation of an almost homogeneous LaFeO₃ perovskite phase. A decrease in the La/Fe surface ratio from 12 to 5.2 with the rise in calcination temperature from 650° to 800°C was detected by XPS. EDX results confirmed that at 750–850?°C, the La/Fe ratio in the perovskite layer is close to the stoichiometric and amount to 1.01–1.03. The highest activity in methane oxidation was achieved when the LaFeO₃ perovskite was calcined at 700?°C. A further slight increase in the activity was noticed after H₂ treatment. As the calcination temperature of the perovskites is increased, the catalyst activity decreases due to a reduction in the specific surface area, despite the more complete LaFeO₃ perovskite phase formation.     

Surface characterization of sulfated zirconia and its catalytic activity for epoxidation reaction of castor oil

The solid acid catalysts SO₄^2?/ZrO₂ were prepared by impregnation technique at different calcination temperatures. The surface characterizations were carried out by using scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), temperature programed desorption of NH₃ (NH₃-TPD), and N₂-BET. The SEM results showed that the size of the SO₄^2?/ZrO₂ was not uniform and varied from about 1 to 20?µm. The characteristic peaks in FTIR spectra were essentially the same within the calcination temperature range of 400–700?°C. The XRD results indicated that the transition temperature from amorphous to tetragonal phase was up to 500?°C. The strong acid and superacid sites of the samples could be observed by the NH₃-TPD results. The largest BET surface area was 140 m²/g, when the calcination temperature was at 500?°C, and all the pore size distributions belong to mesoporous range. The solid acid SO₄^2?/ZrO₂ was used for the epoxidation of castor oil. When the calcination temperature of SO₄^2?/ZrO₂ was 600?°C, reaction temperature 45?°C, and reaction time 8?h, the reaction effect was better with an iodine value of 33.0?±?1.6?g/100?g and an epoxy value of 2.45?±?0.11?mol/100?g.     

Low temperature densification by lithium co-doping and its effect on ionic conductivity of samarium doped ceria electrolyte

Low temperature densification and improving the ionic conductivity of doped ceria electrolyte is important for the realization of efficient intermediate temperature solid oxide fuel cell system. Herein, we report the effect of lithium co-doping (1, 3, 5 and 7?mol%) in 20?mol% samarium doped ceria on the low temperature sinterability and conductivity. The synthesized nanoparticles by citrate-nitrate combustion method showed a decrease in lattice parameter and increase in oxygen vacancy with lithium content after calcination due to the substitution of Li⁺ into CeO₂ lattice. Upon sintering at 900?°C, the density improved and reached a maximum value of 98.6% for 5% Li which exhibited a dense microstructure than at 7% Li. 5%Li co-doping exhibited the best conductivity of 3.65?×?10^?04–1.81?×?10^?3 S?cm^?1 in the operative temperature range of IT-SOFC (550–700?°C).Our results demonstrate the significance of lithium as co-dopant for efficient low temperature sintering as well as improving the electrolyte conductivity.     

Effect of precursors on the morphology and surface area of LaFeO3

Surface area and morphology of materials play an important role on their gas sensing performance because of the varying number and nature of adsorption sites. Current work reports a comparative study of LaFeO₃ synthesized by the facile hydrothermal method using two precursors; citric acid and KOH. The microstructure observed through FESEM and TEM showed different morphologies for the two precursors and calcination time (2?h & 6?h). Prior to calcination, higher surface area (50.54?m²/g) was obtained for LaFeO₃ prepared using KOH as compared to that for LaFeO₃ using citric acid (3.21?m²/g). Surface area increased from 3.21 to 7.06?m²/g for citric acid and decreased from 50.54 to 11.42?m²/g for KOH as calcination takes place for 6?h. Needle-shaped morphology of p-type LaFeO₃ with high surface area (50.54?m²/g) for KOH would provide large active sites which would enhance sensitivity towards gases. Hence, LaFeO₃ samples prepared using KOH with and without calcination are expected to give better performance for gas sensing than LaFeO₃ samples synthesized using citric acid.     

LaFeO3 ceramics as selective oxygen sensors at mild temperature

In this study, an investigation about the oxygen sensing properties of lanthanum orthoferrite (LaFeO₃) ceramics is reported. LaFeO₃ nanoparticles were synthesized by using tartaric sol-gel route and annealed in air at different temperatures (500, 700 and 900 °C). The samples have been characterized by using thermal analysis (TA), BET surface area and porosity, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results of sensing tests indicate that LaFeO₃ nanoparticles exhibit good response to oxygen at mild temperatures (300–450 °C). The effect of annealing temperature on gas sensing performance was investigated, demonstrating that LaFeO₃ ceramics obtained after annealing at 500 °C display better characteristics with respect to others. The oxygen sensor developed shows also high stability in humid environment and excellent selectivity to oxygen over other interfering gases such as CO, NO₂, CO₂, H₂ and ethanol.     

A novel one-pot biosynthesis of pure alpha aluminum oxide nanoparticles using the macroalgae Sargassum ilicifolium: A green marine approach

A novel biological method is proposed for producing ceramic alpha aluminum oxide nanoparticles using an extract of the algae Sargassum ilicifolium. The algal extract functions as a bioreducing as well as a stabilizer agent. The presence of an absorption peak at 227?nm, confirmed the formation of the aluminum oxide nanoparticles using a UV–visible spectroscopy. FTIR analysis indicated that bioreduction of aluminum ions and nanoparticle stabilization probably occurred by interactions between aluminum and the biofunctional groups of algal extract. The XRD pattern revealed that after calcination at ~ 1200?°C, the Al₂O₃ nanoparticles were alpha crystalline in nature with a diameter of 35?nm and had a rhombohedral structure. TEM indicated that the alumina nanoparticles were well-dispersed and spherical in shape with an average size of 20?±?2.1?nm. EDX spectroscopy revealed that the sample contained only aluminum (46.31%) and oxygen (53.69%), confirming the high purity of the alumina nanopowder. The results demonstrated that alpha alumina NPs has an optical band gap of 5.46?eV.     

Factors influencing the PVA polymer-assisted freeze-drying synthesis of Al2O3 nanofibers

Three-dimensional (3D) nanofibrous structured Al₂O₃ was successfully synthesized using the poly (vinyl alcohol) (PVA) polymer-assisted freeze-drying method, and a series of factors that influence fiber performance were investigated in depth. PVA nanofibers were also investigated for the first time. The surface morphology, structure, and other properties of PVA nanofibers, precursor Al₂O₃/PVA nanofibers, and calcined Al₂O₃ nanofibers were characterized by scanning electron microscopy, X-ray diffraction, and nitrogen adsorption measurements. The results showed that Al₂O₃ nanofibers with good performances could be obtained at the optimum conditions where the precursor solution was prepared by boehmite nanoparticles (0.01 wt%) and PVA (0.1 wt%, DP = 500) with a mass ratio of 7: 3, followed by the use of the rapid freezing method at −196 °C under liquid nitrogen in the pre-frozen process; subsequently, calcination was performed at 500 °C for 5 h to form Al₂O₃ nanofibers. The increasing calcination temperature (500 °C–1300 °C) enabled the transformation of the Al₂O₃ crystalline phase from γ-Al₂O₃ to α-Al₂O₃. It also improved the specific surface area from 44.5 m² g⁻¹ for the precursor Al₂O₃/PVA nanofibers to 263.4 m² g⁻¹ for the Al₂O₃ nanofibers calcinated at 500 °C. However, an excessive calcination temperature at 1300 °C was detrimental to the specific surface area, presumably due to sintering or blocking by metal particles. This work provides optimum conditions that make Al₂O₃ nanofibers valuable for further development, and it has the potential for industrial applications.     

Freestanding hematite nanofiber membrane for visible-light-responsive photocatalyst

Freestanding mesoporous hematite (α-Fe₂O₃) nanofiber membranes were successfully fabricated by sol–gel electrospinning process using ferratrane precursor for use as a high-performance material for visible-light-responsive photocatalyst. Non-porous nanofiber membranes spun on the heated collector at 300 °C were crystalline α-Fe₂O₃ phase. Upon calcination, pure mesoporous nanofiber membranes were obtained even at a low temperature of 400 °C. The photocatalytic membrane calcined at 400 °C showed the highest efficiency for methylene blue (MB) degradation under visible-light irradiation. The synergetic effects of higher surface area, pore volume and pore diameter promoted the photocatalytic efficiency for MB degradation under visible light. The utilization of photocatalyst in the form of membrane could not only solve the problems of catalyst separation and recovery, but also produce high photodegradation efficiency for both systems without and with hydrogen peroxide even at a catalyst loading as low as 0.04 g/L. No appreciable loss in photocatalytic activity was observed and structural integrity was retained, even after five cycles of photodegradation, which predicted the stability and reusability of these nanofiber membranes for practical use in environmental applications.     

Densification of zirconia doped yttria transparent ceramics using co-precipitated powders

Ho:Y₂O₃ ceramics were prepared using co-precipitated powders, with ammonium sulfate as dispersant. Y³⁺ was co-precipitated together with Ho³⁺ and Zr⁴⁺ to produce precursors, which were calcined at 1100–1400 °C to produce yttria-based powders. At calcination temperatures of ≤1300 °C, agglomeration of powders was not observed. When the temperature was increased to 1400 °C, severe agglomeration was detected. Densification was closely related to the calcination temperature: a lower calcination temperature resulted in a faster densification of ceramics to the relative density of 99.7%. The ultimate densification to ~100% was also closely related to powders' impurity level and agglomeration. Grain growth was mainly determined by sintering temperature, but not by the initial crystallite size of powders. The optimal calcination temperature was 1300 °C, at which the obtained Ho:Y₂O₃ powder was free from agglomeration. Using this powder, the resultant Ho:Y₂O₃ ceramics showed pore-free microstructure and good optical transparency.     

Iron, and Manganese Doped SO4 2−/ZrO2–TiO2 Mixed Oxide Catalysts: Studies on Acidity and Benzene Isopropylation Activity

Sulfated zirconia–titania and its transition metal doped compositions with 1.5 wt% iron, and 0.5 wt% manganese were prepared and characterized for surface acidity, and activity towards benzene alkylation. Acidity measurement of the 600 °C calcined samples showed that upon doping with Mn, the protonic acid strength of the material increased, whereas iron doping decreased the strength of surface protons and followed the order Mn-SO₄ ^2?/ZrO₂–TiO₂ > SO₄ ^2?/ZrO₂–TiO₂ > Fe-SO₄ ^2?/ZrO₂–TiO₂. Samples calcined at 110 and 600 °C were XRD amorphous. However, on calcination at 800 °C these samples showed crystalline phases characteristic of ZrTiO₄. The Mn doped catalyst also showed highest activity and improved catalyst stability towards isopropylation of benzene. A good correlation between surface acidity and isopropylation activity was obtained. Increase in acidity in case of Mn doped sample was attributed to the increased stability of the surface sulfate groups.     

New La3+ doped TiO2 nanofibers for photocatalytic degradation of organic pollutants: Effects of thermal treatment and doping loadings

The pure TiO₂ and lanthanum (La³⁺)-doped titanium dioxide (TiO₂) nanofibers were synthesized by electrospinning method followed via calcination at different temperatures (from 400 °C to 700 °C). Structures of the nanofibers were characterized by X-ray diffraction, scanning electron microscopy, TEM images and diffuse reflectance spectroscopy. The size of the nanofiber diameters was determined to be 129 and 101 nm, for pure TiO₂ and (0.1%)La³⁺:TiO₂ materials, respectively. The prepared nanofibers possess a crystalline structure, and wide distribution of the band-gaps, in the 2.867–3.210 eV range. Effects of La³⁺-dopant content, calcination temperature, and different doses of photocatalysts on the photodegradation efficiency were studied. The optimal level of La³⁺ and the optimal temperature of calcination were 0.1% La³⁺ and 600 °C, respectively. The photocatalytic degradation of methylene blue (91%, with a rate constant of 2.179 × 10^?2 min^?1) and ciprofloxacin (CIP) (99.5%, with a rate constant of 1.981 × 10^?2 min^?1) pollutants was highest on the (0.1%)La³⁺:TiO₂ annealed at 600 °C, after 300 min irradiation under visible light. This photocatalyst displayed sustainable efficiency for CIP degradation up to five consecutive uses.     

Effect of sintering temperature on the thermal expansion behavior of ZrMgMo3O12p/2024Al composite

A 2024Al metal matrix composite with 10?vol% negative expansion ceramic ZrMgMo₃O₁₂ was fabricated by vacuum hot pressing, and the influence of sintering temperature on the microstructure and thermal expansion coefficient (CTE) of alloys was investigated. Experimental results showed that all ZrMgMo₃O_12p/2024Al composites sintered at 500–530?°C had a similar reticular structure and exhibited different linear expansion coefficients at 40–150?°C and 150–300?°C. The addition of 10?vol% ZrMgMo₃O₁₂ decreased the CTEs of 2024Al by ~ 16% at 40–150?°C and by ~ 7% at 150–300?°C. This addition also increased the hardness of 2024Al by ~ 23%. The density of the composites and the content of Al₂Cu in ZrMgMo₃O_12p/2024Al increased as the sintering temperature increased. The CTEs of the composites decreased, whereas hardness increased. Thermal cycling from 40?°C to 300?°C caused the CTEs of the composites to decrease gradually and reach a stable value after seven cycles. The lowest CTEs of 15.4?×?10^?6 °C^?1 at 40–150?°C and 20.1?×?10^?6 °C^?1 at 150–300?°C were obtained after 10 thermal cycles and were reduced by ~ 32% and ~ 17%, respectively, compared with the CTE of the 2024Al. Among the current reinforcements, ZrMgMo₃O₁₂ negative expansion ceramics showed the highest efficiency to decrease the CTE of Al matrix composites.     

Fast Response NO2 Gas Sensor Based on In2O3 Nanoparticles

In this research, hydrothermal‐calcination route was applied to synthesize In₂O₃ nanoparticles for gas sensor application. Hydrothermal synthesis with duration of 5 h at 180°C resulted in In(OH)₃ nanorods. Then, in the calcination step, considering controlled rate of heating and temperature, In₂O₃ nanoparticles with rough surfaces were obtained. In the next step, these nanoparticles were deposited by low frequency AC electrophoretic deposition between the interdigitated electrodes to fabricate gas sensor. Deposition in the frequency of 10 kHz resulted in the chained nanoparticles in the interelectrode space. At the end, gas sensitivity measurements were conducted at 150°C–300°C and revealed that fabricated sensor had fast response and recovery times to NO₂ gas.     

Mechanical properties of LaFeO3 ceramics

The fracture strength, fracture toughness and apparent Young’s modulus of LaFeO₃ ceramics in the temperature region 25–800 °C are reported. The fracture strength of the material was observed to increase from 202 ± 18 MPa at room temperature to 235 ± 38 MPa at 800 °C. The room temperature fracture toughness was 2.5 ± 0.1 MPa m^1/2. The fracture toughness decreased to 2.1 ± 0.1 MPa m^1/2 at 600 °C, followed by an increase to 3.1 ± 0.3 MPa m^1/2 at 800 °C. The temperature dependence of the fracture toughness correlates well with the crystallographic strain, |(a−c)|/(a+c), and ferroelastic toughening of LaFeO₃ materials is inferred. Non-elastic stress–strain behaviour of the LaFeO₃ materials due to ferroelasticity was confirmed by cyclic compression experiments, and residual strain was observed in the material after unloading.     

Catalytic-assisted synthesis, characterization and low frequency AC conduction of nanostructured conducting polyaniline

Polymerizations of aniline at the reaction temperatures of 25 and 50 °C have been performed in the presence of iron catalyst. The prepared conducting polyaniline at different reaction periods was investigated for physicochemical and electrical properties, through X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR) and frequency-dependent electrical conductivity measurements, respectively. XRD studies established the improved nanostructured crystalline nature for the polymer prepared at 50 °C. Size of the particles ranging from 10 to 20 nm was calculated for the prepared polyaniline. SEM analysis shows the cauliflower-like morphology for optimized reaction temperature. The study further establishes the attainment of uniform distribution of polyaniline at the reaction temperature of 50 °C. The charge transitions between benzenoid (B-band) and quinonoid (Q-band) bands were witnessed by UV–Vis spectrum analysis. The band gap analysis revealed the narrow band gap direct transition semiconducting nature of the conducting polymer. Quinonoid and phenylene rings were identified through vibrational bands between 1570 and 827 cm^?1 via FTIR spectroscopy analysis. The AC conductivity of the sample synthesized at 50 °C showed 1.50 × 10^?1 S cm^?1. Enhancement in conductivity with increasing temperature represented the improved crystalline nature of the polyaniline prepared at 50 °C.     

Effect of Cu and Zr Co-doped SiO<Subscript>2</Subscript> Nanoparticles on the Stability of Phases (Quartz-Tridymite-Cristobalite) and Degradation of Methyl Orange at High Temperature

SiO₂ nanoparticles doped by 10 mol% Zr and 10 mol% Cu were prepared via the sol-gel method in a controled process. The effects of doping and calcination temperature on the structural and photo-catalytic properties of SiO₂ nanopowders were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis absorption spectroscopy. The phases of cristobalite, quartz and tridymite were found at a calcinations temperature range of 800 to 1000 ^°C and only cristobalite phase was formed at a temperature of 1200 ^°C. The degradation of methyl orange was examined under visible light radiation indicating that the effect of doped elements (Zr, Cu) on SiO₂ reduces the band gap effectively.     

Adsorption and photodegradation of methylene blue on TiO2-halloysite adsorbents

TiO₂-halloysite (TiO₂-HNT) composites were fabricated by depositing anatase TiO₂ on the halloysite (HNT) surfaces with calcination treatment at 100, 200, 300 and 500 °C. The obtained composites were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-Ray diffraction (XRD). HNT was attached with TiO₂ particles or clusters in sizes of 10–30 nm. With the increasing of calcination temperature, the crystalline of anatase became more perfect, but the structure of HNT could be destroyed at 500 °C. The adsorption and photodegradation of methylene blue (MB) by TiO₂-HNTs were investigated. The kinetic adsorption fit the pseudo second-order, and the isotherm data followed the Langmuir model. The maximum adsorption capacities of MB were in the range of 38.57 to 54.29 mg/g. TiO₂-HNTs exhibited an efficient photocatalytic activity in the decomposition of MB. For TiO₂-HNT calcined at 300 °C, 81.6% MB were degraded after 4 h treatment of UV irradiation.     

Effect of Calcination Conditions on Crystalline Structure and Pore Size Distribution for a Mesoporous Alumina

In this article, a mesoporous commercial alumina was calcined in the temperature range of 600°C–1200°C. The effect of several parameters such as calcination temperature, calcination time, heating rate, and calcination steps on phase transformation and crystal size was experimentally investigated. The characterization of the commercial mesoporous alumina and samples calcined at 1000°C, 1040°C, 1070°C, 1100°C, and 1200°C by single-step and multi-step calcination was performed using XRD and N₂ adsorption/desorption techniques. For the commercial mesoporous alumina, TG/DTA analysis was also performed. Experimental results showed that mostly pure α-Al₂O₃ was obtained at 1100°C.     

Temperature-controlled synthesis of spinel lithium nickel manganese oxide cathode materials for lithium-ion batteries

In this work, we successfully synthesized series of LiNi_0.5Mn_1.5O₄ (LNMO) cathode materials with spinel structure by using a facile sol-gel method and then calcined at various temperature ranging from 600 to 1000 °C. The application of different calcination temperatures significantly influenced the surface morphology, stoichiometry and crystalline nature of the as-synthesized LNMO material. According to the results of physical characterizations, the LNMO materials calcined at various temperatures mainly revealed the stoichiometric disordered Fd-3m structure with a small amount of well-ordered P4₃32 phase. The structural analysis also exhibited that the control of the calcination temperature contributed to the higher crystalline nature. Moreover, the morphological investigations indicated that the increasing calcination temperatures caused the formation of large micron-sized LNMO material. In turn, the electrochemical evaluations revealed the impact of the calcination temperatures on enhancing the electrochemical performances of the LNMO electrode materials up to 900 °C. The LNMO electrode calcined at 900 °C exhibited an impressive initial discharge specific capacity of ca. 142 mAh g⁻¹ between 3.5 and 4.9 V vs. Li/Li⁺, and remarkably improved capacity retention of 97% over 50 cycles. Those excellent electrochemical properties were associated with the presence of the dominant Fd-3m phase over the P4₃32 phase. Additionally, the results of the corrosion and dissolution tests which were performed for all calcined LNMO materials in order to estimate the amount of manganese and nickel ions leached from them, proved that the micro-sized LNMO calcined at 900 °C was the most stable.     

LaFeO3 porous hollow micro-spindles for NO2 sensing

LaFeO₃ micro-spindles with intriguing structural characteristics were synthesized using cyano-bridged coordination polymers as sacrificial templates. Within a longitudinal dimension of less than 5?µm, each micro-spindle features a hollow center contained in a mesoporous shell with hexagonal cross section. Conductometric gas sensors developed from these micro-spindles demonstrate a comprehensively improved NO₂-sensing performance over other-reported LaFeO₃ devices, including lower operating temperature (155?°C), higher sensitivity (response of 81.4% under 5?ppm) and expedited response and recovery (40?s/329?s). Such performance is enabled by a semiconducting mechanism governed by the formation and catalytic dissociation of nitrite species during NO₂ adsorption on LaFeO₃, facilitated by the special hierarchical structure of the micro-spindle.