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A series of Z n 0.5 C o 0.25 C u 0.25 H o 0.037 F e 1.963 O 4 (ZCCHF)/Graphene nanoplatelets (GNPs) nanocomposites (where GNPs = 0 wt%, 1.25 wt%, 2.5 wt%, 3.75 wt%, 5 wt%) were prepared via sol-gel auto-combustion (SGAC) method followed by bath sonication and studied their structural, morphological, optical, dielectric, and magnetic properties. The structural analysis confirmed a single-phase crystal matrix of all the as-prepared nanocomposites. The optical analysis revealed that the energy bandgap (E g) lies within the range of 1.57 eV–1.62 eV. The dielectric analysis showed that the improvement in the dielectric constant (ε ′) and reduction in dielectric tangent loss (tan δ d) with increasing GNPs concentration from 0 wt% to 5 wt%. The real part of permeability (μ ′) was improved and magnetic tangent loss (tan δ M) was reduced with the addition of GNPs. Magnetic properties were studied at different temperatures (5 K, 300 K, and 400 K), and observed high saturation magnetization (M S), and coercivity (H C) at a low temperature (at 5 K). The low M S , and H C values were observed at high temperatures (300 K and 400 K). The combination of improved dielectric and tunable magnetic properties makes ZCCHF/GNPs nanocomposites promising candidates for applications in spintronics, high-frequency magnetic devices, and advanced electronic systems. [Display omitted] • The ZCCHF SFs and ZCCHF/GNPs nanocomposites were synthesized using a sol-gel auto-combustion (SGAC) method followed by bath sonication. • XRD analysis revealed a single-phase crystal structure and the tunable energy bandgap ranges from 1.57 eV to 1.62 eV. • The maximum dielectric constant and minimum dielectric tangent loss were found for ZCCHF/5 wt%GNPs nanocomposites. The nanocomposite with 5 wt%GNPs reveals the highest magnetic permeability around 0.995. The minimum magnetic tangent loss and skin depth was found for ZCCHF/5 wt%GNPs nanocomposites. • The saturation magnetization is lower across all temperatures with GNPs incorporation and the microwave operating frequency was 14.21 GHz at 300 K for ZCCHF/5 wt%GNPs nanocomposites. • The study highlights the multifunctional potential of ZCCHF/GNPs nanocomposites in promising candidates for a broad range of advanced technological applications. [ABSTRACT FROM AUTHOR]

Perovskites refer to ceramic materials with an ABO 3 structure. The optimization of synthesis parameters and material composition can enhance the catalytic efficiency in various chemical reactions, such as dry methane reforming. In order to highlight the differences in the catalytic properties, this study aims to compare three synthesis methods (citrate, auto-combustion and Pechini) for a same perovskite formulation namely SrZr 0·5 Ni 0·4 Fe 0·1 O 3. The crystal structure and reducibility profile are determined by XRD and TPR experiences respectively. Surface properties and composition are identified by chemisorption tests (allowing the study of basicity and nickel dispersion) and XPS analyses, respectively. Isothermal catalytic experiences from 600 to 750 °C, under atmospheric pressure and for a WHSV of 40 L / h. g together with stability tests for 25 h at 750 °C were conducted. The outcomes show the importance of properly choosing the perovskite preparation methods in order to achieve the desired surface, structural and reactivity properties. [Display omitted] • Comparison of synthesis methods for substituted perovskites SrZrO3 with Ni and Fe. • Utilisation of citrate, auto-combustion and Pechini methods. • Dry methane reforming considered as a test reaction. • Effect of the method on surface properties, crystal structure and reactivity. [ABSTRACT FROM AUTHOR]

Cobalt zinc chromium ferrites, which have been doped with chromium Co0.4Zn0.6-xCrxFe2O4 (x = 0.05, 0.10, 0.15, 0.20) (CZC) nanoferrites, are employed by the auto-combustion route. The magnetic and dielectric characteristics of Co–Zn nanoferrites were improved by Cr3+. Analysis using XRD, FTIR, and FESEM reveals the cubic spinel phase for CZC nanoferrites. SEM reveals a lot of clustering. The ferrite samples have cluster form with a spherical shape in the range 54.64–73.38 nm, as seen by the FESEM results. TEM studies show agglomeration. The Cr3+ concentration determines the magnetic properties of specimens. Ms declines from 62.38 emu/g to 42.59 emu/g by increasing Cr3+. For all samples, a frequency-dependent evaluation of the dielectric properties, including dielectric constant, dielectric loss, and ac conductivity, is performed. On the basis of Koop's theory, the Maxwell-Wagner polarization procedure, and the movement of electrons, the fluctuation of dielectric features at frequencies between 50 Hz and 108 Hz has been mentioned. The dielectric constant and dielectric loss tangent decreased with increasing frequency. The conduction of ferrite samples is influenced by the grain boundaries. Both recording media and high-frequency devices can benefit from using these nanoferrites. [ABSTRACT FROM AUTHOR]

Herein we report the effect of the Cr3+ content on the distinctive features of the first-ever auto-combustion-synthesis-produced Cr3+ doped ZnO nanoparticles utilizing leucine as the fuel. To assess the impact of fuel and Cr3+ content on the structural, optical, and luminescence characteristics, as-synthesized powders were systematically examined using powder XRD, UV–Visible, and Photoluminescence spectroscopy. Structural studies show that the exothermicity of the redox mixture containing oxidizer and fuel combination leads to the development of polycrystalline, single-phase, and nanosized particles. XRD analysis shows that, reduced crystallite size with Cr3+ content. In contrast, other characteristics like lattice parameters, unit cell volume, strain, and dislocation density, were shown to increase linearly with Cr3+ concentration up to 7 mol%. Additionally, it is seen that the predicted Urbach energy values rise as Cr3+ is added to the ZnO host matrix, indicating that the substitution of Cr3+ for Zn in the host ZnO lattice has increased structural disorder. In contrast to the other samples, the 5 mol% Cr3+ doped ZnO sample exhibits the emission near the white region according to the PL emission measurements. Furthermore, the photocatalytic activity of the as-prepared Cr3+ doped ZnO NPs was examined. It was found that the as-prepared samples exhibit outstanding photocatalytic activity in the visible wavelength region against Malachite Green (MG) dye. Among all, 9 mol% Cr3+ doped ZnO has shown the maximum 95.4% degradation against MG dye. All the investigated results conclude that the produced Cr3+ doped ZnO nanoparticles could be exploited in a variety of upcoming optoelectronic and photocatalytic applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fabrication of TmVO 4 nanocomposites by sonochemical approach. • Different solvents and content of TmVO 4 affect the purity, morphology, and size of products. • Investigation effect of tetra ethylene pentaamine as both capping and alkaline agent on size. • Utilization of TmVO 4 as a nanophotocatalyst for water treatment. • High ability of TmVO 4 for degradation of methyl violet dye (83%) in the visible area. The development of photocatalysts with adequate functions, particularly in the visible range, is one of the most significant issues facing scientists since they are essential compounds for the protection of the environment. A primary objective of this work was to simplify the preparation of thulium vanadate (TmVO 4) nanostructures in order to improve their photocatalytic efficiency. By using a facile auto-combustion route, this study presents a new method for fabricating TmVO 4 nanostructures. In order to achieve the desired size and homogeneity of the products, multiple factors were considered. As part of these parameters, several saccharides, such as glucose, fructose, lactose, maltose, and cellulose are analyzed for the first time, as well as the calcination temperature and the molar ratio. Various dye types and dye concentrations were studied to enhance catalyst performance. According to the catalyst activity, TmVO 4 was able to degrade 83.5% of the methyl violet (MV) after 90 min. TmVO 4 was found to be stable in the recycle test, with an efficiency reduction of 14.6% after five cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • The initial endeavors in employing Cr-doped CeO 2 , synthesized using the modified auto-combustion technique, for electrochemical applications. • Studied the effect of various percentages of Cr doping on CeO 2 matrix and its influence on structural, morphological, vibrational and optical properties of CeO 2. • The specific capacitance of pristine CeO 2 attained 30.42F/g and it further achieves to 73.56F/g for Ce 0.925 Cr 0.025 O 2 at 0.5 A/g. • C e 1 - x C r x O 2 x = 0 , 0.1 samples show no magnetic long-range ordering ensuring zero hysteresis loss. • C e 1 - x C r x O 2 x = 0 , 0.025 , 0.05 can be used as functional, and low-cost supercapacitors for energy storage applications and also in data storage applications. The emergence of cerium oxide (CeO 2) has garnered significant interest as an energy storage gadget owing to its inspiring electrochemical, electrical and mechanical properties. Current work, we have synthesized C e 1 - x C r x O 2 x = 0 , 0.025 , 0.05 , 0.1 via simple auto-combustion method. The structure–property relations were characterized by several physicochemical characterizations such as XRD, FESEM, EDAX, vibrational spectroscopy, XPS, BET and UV–visible spectroscopy. The suds-like CeO 2 morphology and oxygen defects were highly suitable for the electrolytic ion intercalation to the electrode. By employing the Trassati model, Power law establishment and Dunn's model, the innate charge storage mechanisms in the synthesized materials were revealed. The specific capacitance of pristine CeO 2 attained 30.42F/g and it enhances to 73.56F/g for Ce 0.925 Cr 0.025 O 2 at 0.5 A/g. Further Ce 0.925 Cr 0.025 O 2 possesses a capacitance retention of 108.85 % even after 1000 GCD cycles at a current density of 4 A/g. The electrochemical results suggest C e 1 - x C r x O 2 x = 0.025 as a good material for supercapacitor applications. The magnetic measurements on the doped and undoped samples show no long-range ordering indicating zero hysteresis loss. Further, magnetic studies suggests the suitability of C e 1 - x C r x O 2 x = 0.1 for supercapacitance applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Preparation of double perovskite La 2 CrMnO 6 nanoparticles by auto-combustion route. • Preparation of La 2 CrMnO 6 /g-C 3 N 4 nanocomposites by ultrasonic-assisted co-precipitation method. • Higher photodegradation yield due to synergistic effect between La 2 CrMnO 6 and g-C 3 N 4. • La 2 CrMnO 6 /g-C 3 N 4 (80:20) nanocomposites showed 80.98 % removal of methyl orange (MO). • Photocatalytic mechanism in nanocomposite system for MO degradation was proposed. Constructing semiconductor materials based on layered graphitic carbon nitride (g-C 3 N 4) and metal oxides can help in extending the lifetime of charge carriers and aid in resolving the low number of active sites on their surface for light-driven processes. Herein, we initially designed La 2 CrMnO 6 nanostructures through trimesic acid-assisted auto-combustion route and subsequently, La 2 CrMnO 6 /g-C 3 N 4 nanocomposites were prepared by ultrasonic-assisted co-precipitation method with improved UV-catalytic performance. The shape, size distribution and various properties of nano-sized products were measured via diverse description systems of microscopic and spectroscopic. The photocatalytic performances of the La 2 CrMnO 6 nanoparticles and La 2 CrMnO 6 /g-C 3 N 4 nanocomposites were compared by degradation of artificial dyes under the UV-light region. Besides, the impacts of dye type, diverse weight percentages of g-C 3 N 4 :La 2 CrMnO 6 in composite, scavenger kind and dye solution concentration were studied on modifying ability of nano-catalyst utility. The outcomes manifested La 2 CrMnO 6 /g-C 3 N 4 (80:20) nanocomposites have the greatest efficiency, where the highest MO decomposition of 80.98 % was achieved at 10 ppm within 90 min of irradiation. Moreover, the feasible mechanism of MO elimination by UV catalytic purpose was considered. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mn x Fe 2-x Mg 0.5 Ni 0.5 O 4 spinel ferrites were prepared utilizing a flash auto-combustion technique. • XRD confirmed formation of cubic phase spinel ferrite phase with space group Fd-3 m. • FTIR spectra validate the positions of the cations and their vibrational modes. • Optical band gaps Eg of investigated samples were found to decrease from 1.79 eV to1.24 eV. • The magnetic properties demonstrated soft ferrite nature with small hysteresis curve. Mn x Fe 2-x Mg 0.5 Ni 0.5 O 4 spinel ferrite nanoparticles (0.0 ≤ x ≤ 1) were prepared utilizing a flash auto-combustion technique. The as-prepared ferrite nanoparticles have been investigated and characterized using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and Fourier transform infrared analysis (FTIR). The dielectric, optical and magnetic characteristics of the synthesized spinel ferrite samples were investigated using broadband dielectric spectroscopy (BDS), diffuse reflectance spectroscopy (DRS) and vibration sample magnetometers (VSM). The cubic phase spinel ferrite with space group Fd-3m was identified through XRD. X-ray diffraction indicates that the lattice constant increases and the crystallite size declines with increasing Mn concentration. The positions of the cations and their vibrational modes in the crystal structure with oxygen ions are demonstrated through the FTIR spectra. The morphology was examined using HRTEM showed polycrystalline cubic spinel structure with faceted planes. The optical band gap Eg was determined using Kubelka–Munk model where, it decreased from 1.79 eV to1.24 eV as Mn content increases. The replacement of manganese significantly affects the dielectric characteristics of the synthesized spinel ferrites. The real (ε′), imaginary (ε″) parts of dielectric constant and ac conductivity exhibit an increase in their values as manganese substitution (x) increases from 0 to 0.25 mol %, and thereafter decreases. The presence of a relaxation phenomenon in all prepared samples except the undoped sample (Ni 0.5 Mg 0.5 Fe 2 O 4) is shown by the imaginary modulus's (M′′) dependence on frequency. The magnetic properties exhibited soft ferrite nature with small hysteresis curve for all spinel ferrites samples. The magnetic properties of Mn x Fe 2-x Mg 0.5 Ni 0.5 O 4 nanoparticles were measured and analysed, including saturation magnetization (Ms), remanence (Mr), coercivity (Hc), and squareness ratio. (Ms), and (Mr), exhibit an increase in their values as manganese substitution (x) increases from 0 to 0.25 mol %, and thereafter decreases while squareness ratio decreased. The magnetic parameters greatly affected by Mn substitution ratio. [ABSTRACT FROM AUTHOR]

In this article, MgO/Ca 2 Mn 3 O 8 nanocatalyst was used for the first time in the transesterification process for the production of green fuel from sunflower oil. Besides, the synthesis of layered nanostructured Ca 2 Mn 3 O 8 was done for first applied by combustion route as well. The effects of two heating sources including muffle furnace and microwave irradiation, and also various fuels including urea, glycine, and ethylene glycol were investigated on the characteristics of calcium-manganese oxide (Ca 2 Mn 3 O 8) as the support of the nanocatalysts loaded by MgO as active phase. The synthesized samples were characterized by different analyzes such as AFM, HRTEM, FESEM, FTIR, EDX, XRD, and BET-BJH. The nanocatalyst produced by the microwave irradiation combustion method and urea fuel scored the best performance. This nanocatalyst had the highest specific surface area (46.4 m2/g), and better pore size distribution, too. The roughness of this sample was reported at 5.1 nm in the range of 2 μm. It was found that the optimum sample has converted 96.7% of the oil extracted from sunflower seed to fatty acid esters that are gained by transesterification of fats with methanol. This sample exhibited better reusability in the same operating conditions in proportion to the sample synthesized with muffle furnace in twelve runs, which justified the positive influence of microwave irradiation on the catalytic properties. [ABSTRACT FROM AUTHOR]

LaFeO 3 was prepared via simple, economical and environmentally friendly auto-combustion methods using different fuels, including citrate, urea, sucrose, egg whites, gelatin and chitosan. The prepared ferrites were systematically characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, high resolution transmission electron microscopy (HRTEM), vibrating sample magnetometry (VSM) and electrical measurements to study the impact of the synthetic routes on the various properties. XRD showed the formation of a single orthorhombic phase, except for the samples prepared via egg white, gelatin and urea methods, which indicated a secondary La 2 O 2 CO 3 phase. The FT-IR and TEM studies confirmed the formation of the phase. Differential thermal analysis-thermogravimetry techniques (DTA-TG) were used to characterize the auto-combustion process up to ferrite formation. The obtained unsaturated magnetization for all of the samples suggested the presence of anti-ferromagnetic ordering in addition to weak ferromagnetic ordering. The egg white method showed higher magnetization (1.78 emu/g), while the urea and chitosan methods indicated lower magnetization (0.13 emu/g). The coercivity measurements confirmed the presence of ferromagnetic/anti-ferromagnetic interfaces with higher values than those reported in the literature. The AC-conductivity measurements indicated semiconducting characteristics and exhibited a change in the conduction mechanism from hopping to polaron conduction by increasing the temperature. LaFeO 3 prepared via the egg white method indicated an anti-ferromagnetic/paramagnetic transition at approximately 715 K. The dielectric measurements confirmed the AC-conductivity results and exhibited values higher than those reported in the literature. [ABSTRACT FROM AUTHOR]

Abstract It is extremely desirable but challenging to develop a facile synthesis to directly prepare permanent magnet foam with high coercivity (H c) and low mass density to meet the requirements of advanced magnets in modern industry. In this work, we developed a facile strategy to synthesize cobalt ferrite foam by solution combustion method and subsequently annealing treatment. The structure and magnetic properties of the foams can be influenced by the ratios of glycine to nitrate (G/N), Co content and annealing treatment temperatures. The increase in the mean grain sizes within the single domain range gives rise to an enhancement in coercivities. The highest H c of ∼3 kOe with an ultra-low mass density of ∼45 mg/cm3 can be successfully obtained by controlling the preparation process. The work opens up a new way to prepare ultra-light Fe-based oxides for magnetic and catalytic applications. Highlights • Foam-like porous Co x Fe 3- x O 4 was prepared by facile auto-combustion method. • The effects of glycine to nitrate ratios and Co content were studied. • Ultra low mass density ∼45 mg/cm3 and large coercivity ∼3 kOe were obtained. [ABSTRACT FROM AUTHOR]

• Highly reactive ashes from bamboo leaves (BLA) were prepared by autocombustion. • BLA presented a high silica content (74.23%) most of it was amorphous silica. • Pozzolanic reactivity of BLA was characterized by different procedures. • Replacement of OPC by BLA (5–30%) was achieved, yielding good mechanical performance. • BLA is a suitable and sustainable alternative for partial OPC replacement. In the context of world concern with the environment, this study aims to characterize an auto-combustion produced bamboo leaf ash (BLA) by its pozzolanic behaviour, reactivity and its influence in the total porosity, pore size distribution, tortuosity and mechanical behaviour of cementitious matrices. The chemical and physical characterization of the BLA was carried using X-ray fluorescence, determination of amorphous silica content, X-ray diffraction, Fourier Transform Infrared Spectrophotometry (FTIR), laser granulometry and field emission scanning electron microscopy (FESEM). The assessed BLA is a siliceous material (74.23%) with an amorphous nature due to the amorphous silica content, which represents 92.33% of the total silica. The BLA was classified as highly reactive by assessing its pH and conductivity in a saturated calcium hydroxide (CH) medium for different proportions and temperatures. Frattini analysis, the study of CH:BLA pastes (Thermogravimetric analysis and FTIR) and Portland cement (OPC)/pozzolan pastes (Thermogravimetric analysis and FESEM) are in agreement with this classification. The replacement of OPC by BLA improved the mechanical behaviour of the cementitious matrices, as well their durability. All the mortars containing BLA presented very similar compressive strength to a control mortar (100% OPC) after only 3 days of curing and at the following tested curing ages: 7, 28 and 90 days. In the mercury intrusion porosimetry analysis, the pastes with 20 and 30% BLA content presented higher tortuosity or fewer connected pores than the control paste. Thus, the auto-combustion method proved to be successful and BLA is a suitable alternative for sustainable high-performance matrices. [ABSTRACT FROM AUTHOR]

• Nd-Fe-B wastes have been recycled by auto-combustion method assisted with microwave. • After recycling Nd-Fe-B/α-Fe composite magnetic powders are directly synthesized. • The coercivity of as-synthesized Nd 15 Fe 77 B 8 powders is higher than 400 kA/m. • The magnetic properties of products are comparable with those using pure reagents. The present work provides a facile and energy-saving approach to recycle Nd-Fe-B wastes. Employing the severely oxidized and contaminated sintered Nd-Fe-B scraps as the raw materials, sub-micro sized Nd-Fe-B/α-Fe composite magnetic powders were successfully synthesized by microwave assisted auto-combustion method followed by a reduction diffusion process. In details, the waste magnets were dissolved in HNO 3 solution and both the rare earth oxides and iron oxide were obtained by auto-combustion approach with the help of microwave heating. These oxides were then reduced to achieve Nd-Fe-B alloys with the reducing agent CaH 2. To modify the composition of the final product, Nd(NO 3) 3 ·6H 2 O and H 3 BO 3 were added during dissolving and consequently three compositions of the final products were obtained. TEM results demonstrate that the sizes of α-Fe and Nd 2 Fe 14 B grains are below 10 nm and 20 nm, respectively. The magnetic properties of the composite powders obtained from the wastes in this study are comparable to those obtained by other methods using pure reagents. The room temperature coercivity of as-synthesized Nd 15 Fe 77 B 8 is higher than 400 kA/m. In addition, an appropriate mass ratio of CaH 2 to Nd-Fe-B oxides is required in order to obtain good magnetic properties. [ABSTRACT FROM AUTHOR]

Highlights • Sol-gel auto-combustion method was exploited to prepare homogeneous nanocomposite. • Structural and microscopic analysis confirmed formation of two distinct phases. • Samples prepared by combustion method show single-step hysteresis loops. • Good exchange coupling between hard and soft phases confirmed by Henkel plots. • Increase in (BH) max was observed by overcoming exchange on dipolar interaction. Abstract Ferrite based hard-soft magnetic nanocomposites with the composition of (100 − x) SrFe 10 Al 2 O 19 /(x) Co 0.8 Ni 0.2 Fe 2 O 4 , where x = 10, 15, 20 and 30 wt%, were prepared by one-pot sol-gel auto-combustion method. The nanocomposites prepared by this method showed crystallographically two phase behavior, but magnetically a good single phase exchange spring-coupled behavior with high saturation as well as high coercivity. The nature of magnetic interactions in these nanocomposites and their magnetic properties were evaluated in detail using various characteristic methods including vibrating sample magnetometer measurements, Henkel plots measurements, magnetic force microscopy and magneto-optical Kerr effect microscopy. Microstructural evolution showed formation of soft phase below the critical size of exchange length in the vicinity of hard phase. The nanocomposite with 15 wt% of soft phase showed a 10.5% increase in the maximum energy product compared to pure hard phase and reaches as high as 29.5 kJ/m3 that is a high value of (BH) max for this type of materials. [ABSTRACT FROM AUTHOR]

The three-dimensional porous ceria (CeO 2) nanostructures and cobalt (Co) doped porous ceria with different cobalt contents (1 %, 2.5 %, 5 %, and 10 % wt%) were prepared by using the auto-combustion technique. Several characterization techniques, including ICP elemental analysis, XRD, DR UV-Vis, SEM, and TEM, were utilized to describe the fabricated products. The findings confirmed the incorporation of cobalt ions into the ceria framework. Furthermore, the light absorption property of cobalt-doped porous ceria samples was observed to be red-shifted, with the calculated bandgap decreasing from 3 to 2.1 eV for neat porous ceria and 10 % Co doped ceria, respectively. The photocatalytic efficiency of cobalt-doped porous CeO 2 was investigated in the decolourization of methyl green dye by utilizing visible light illumination. The photocatalytic data obtained revealed a remarkable increase in activity that is nearly three times greater than the un-doped ceria sample. Furthermore, the best performed cobalt-doped ceria sample was reusable until the fourth consecutive reaction without treatment. [ABSTRACT FROM AUTHOR]

• LSMO-AC and LSMO-PC crystallized in mixed phases with R-3c and Pbnm symmetries. • LSMO-AC and LSMO-PC samples are close to conventional universality class. • LSMO-PC, with porous surface, allows faster heat exchange. • LSMO-AC displays very high thermal stability of both ΔT M and ΔS M. In this work, La 0.8 Sr 0.2 MnO 3 (LSMO) nanopowders are synthesized using two different methods: Pechini (LSMO-PC) and auto-combustion (LSMO-AC). Nanoparticle sizes, structural, magnetic, and magnetocaloric properties were determined and compared. The X-ray diffraction confirms the coexistence of two phases; rhombohedral symmetry with space group R-3c and orthorhombic symmetry with space group Pbnm. The rhombohedral phase is dominant. The scanning electron microscope images show that LSMO-PC has larger nanoparticle sizes (∼495 nm) than LSMO-AC (∼195 nm). The samples exhibit ferromagnetic properties with distinct hysteresis loops and Curie temperatures of 340 K and 290 K for LSMO-PC and LSMO-AC, respectively. The variation of the magnetic entropy was measured indirectly using the Maxwell approach with increasing magnetic field. For LSMO-PC it reaches a maximum -ΔS M = 1.69 J/kg.K at 340 K and ΔH = 5 T. The associated adiabatic temperature change ΔT M is 1.04 K. While LSMO-PC demonstrates superior magnetic and magnetocaloric properties, LSMO-AC displays significant magnetocaloric thermal stability. The obtained values make LSMO-PC and LSMO-AC promising candidates for eco-friendly room-temperature magnetocaloric applications. [ABSTRACT FROM AUTHOR]

Biodiesel was produced in laboratory in two consecutive steps i.e. esterification followed by transesterification using a novel heterogeneous base catalyst and Madhuca indica (Mahua) oil as a feedstock. Barium lanthanum oxide, a novel catalyst was synthesized by four different methods i.e., co-precipitation (BLOC), solid state (BLOS) and the citrate route or auto-combustion method (BLOA1 and BLOA2). The catalyst was characterized and the catalytic activity was measured by quantifying the FAME content of the biodiesel. It has been observed that BLOA1, BLOA2, and BLOC resemble with each other as they have the same phase with an identical structural formula of Ba 2 La 2 O 5 . This observed structural formula constituted the mixture of the perovskite and metal oxides. The BLOS sample had the structural formula of Ba 10 La 2 O 13 which proved the extensive formation of individual metal oxides. Out of the samples, BLOA2 synthesized by citrate route was efficient in biodiesel production. The citrate route synthesis performed at pH 2.31 enriched the catalyst mixed metal oxide surface with free OH − groups, which ultimately avoided the formation of the carbonate species, produced biodiesel with 97.5% FAME conversion. Hence, Barium Lanthanum Mixed metal oxide prepared by citrate route in acidic medium is a potential catalyst for biodiesel production. The reaction mechanism followed first-order kinetics. The activation energy (E A ) was 34.44 kJ mol −1 and the frequency factor (A) was 7.94 min −1 . The physicochemical properties of the synthesized Mahua oil methyl ester (MOME) were measured according to ASTM D 6751 and were found to be within the permissible range. [ABSTRACT FROM AUTHOR]

The effect of Ni 2+ doping on the magnetic and magnetocaloric properties of La 0.7 Ca 0.3 MnO 3 manganites synthesized via the auto-combustion method is reported. The aim of studying Ni 2+ -substituted La 0.7 Ca 0.3 Mn 1 − x Ni x O 3 ( x = 0 , 0.02 , 0.07 , and 0.1) manganites was to explore the possibility of increasing the operating temperature range for the magnetocaloric effect through tuning of the magnetic transition temperature. X-ray diffraction analysis confirmed the phase purity of the synthesized samples. The substitution of Mn 3+ ions by Ni 2+ ions in the La 0.7 Ca 0.3 MnO 3 lattice was also corroborated through this technique. The dependence of the magnetization on the temperature reveals that all the compositions exhibit a well-defined ferromagnetic to paramagnetic transition near the Curie temperature. A systematic decrease in the values of the Curie temperature is clearly observed upon Ni 2+ doping. Probably the replacement of Mn 3+ by Ni 2+ ions in the La 0.7 Ca 0.3 MnO 3 lattice weakens the Mn 3+ –O–Mn 4+ double exchange interaction, which leads to a decrease in the transition temperature and the magnetic moment in the samples. By using Arrott plots, it was found that the phase transition from ferromagnetic to paramagnetic is second order. The maximum magnetic entropy changes observed for the x = 0 , 0.02 , 0.07 , and 0.1 composites was 0.85, 0.77, 0.63, and 0.59 J/kg K, respectively, under a magnetic field of 1.5 T. In general, it was verified that the magnetic entropy change achieved for La 0.7 Ca 0.3 Mn 1 − x Ni x O 3 manganites synthesized via the auto-combustion method is higher than those reported for other manganites with comparable Ni 2+ -doping levels synthesized via standard solid state reaction. The addition of Ni 2+ increases the value of the relative cooling power as compared to that of the parent compound. The highest value of this parameter (∼60 J/kg) is found for a Ni-doping level of 2% around 230 K in a field of 1.5 T. [ABSTRACT FROM AUTHOR]

Di-phase ceramic composites, with general formula xNi 0.7 Zn 0.3 Fe 2 O 4 – (1-x)BaTiO 3 (x = 0.9, 0.7, 0.5, 0.3, 0.1), were prepared by a mixing method. X-ray analysis, for powder and ceramics, indicated the formation of ferrite and barium titanate phases without the presence of the impurities. SEM analysis indicated that the composite morphology contained two types of grains, polygonal and rounded. Homogeneous microstructure and the smallest grain size were obtained in ceramics with 70% of barium titanate. The electrical properties of these materials were investigated using impedance spectroscopy, dielectric and ferroelectric measurements. The NZF-BT(30-70) composite has shown better electrical properties in comparison to other investigated ceramics, confirmed by dielectric and ferroelectric data analysis. Saturation magnetization and coercive field decreased with the increase of the content of ferroelectric phase. [ABSTRACT FROM AUTHOR]

A series of solids was synthesized by the incorporation of Ni and Mo active species on delaminated clay with novel acidic properties, by impregnation and auto-combustion. The resulting solids were characterized by X-ray fluorescence, X-ray diffraction (XRD), textural analysis by N 2 physisorption, temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and, in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). Decane hydroconversion was used to evaluate the potential of the materials as hydrocracking catalysts for vacuum bottoms. XRD was used to confirm modification of the material and good active phase dispersion. TPR revealed an important decrease in the reduction temperatures with auto-combustion method. Low-temperature reducible species play a key role in the catalytic performance for decane hydroconversion. [ABSTRACT FROM AUTHOR]

A novel compound Gd 3+ -substituted Li 0.35 Zn 0.3 Gd x Fe 2.35− x O 4 ( x = 0.1) spinel ferrite was successfully synthesized via citrate-gel combustion. XRD patterns confirm formation of single phase compound (with average 15 nm crystallites) after annealing an as-prepared powder at 400 °C for 2 h in air. This sample shows a lower lattice parameter 0.8440 nm as compared to 0.8443 nm in parent compound Li 0.35 Zn 0.3 Fe 2.35 O 4 . Substitution by a paramagnetic ion Gd 3+ → Fe 3+ weakens magnetic super-exchange interactions. Large saturation magnetization M s = 75.56 emu/g (with coercivity H c = 11.55 Oe) in the parent sample is reduced to 51.41 emu/g (with a higher H c = 61.43 Oe) on substitution. Dielectric constant ε r of 535 (with a loss tan δ of 2.48) in Li 0.35 Zn 0.3 Fe 2.35 O 4 has dropped to ∼118 (with tan δ = 0.62) in the Li 0.35 Zn 0.3 Gd 0.1 Fe 2.25 O 4 at 1 kHz. Dielectric properties can be explained from polarization effect. [ABSTRACT FROM AUTHOR]

In this study, CoFe 2 O 4 nanoparticles were synthesized using simple, economic and environmentally friend auto-combustion methods including citrate sol-gel, urea, sucrose, Egg-white, gelatin and chitosan methods. Differential thermal analysis-thermogravimetry-differential scanning calorimetry (DTA-TG-DSC) techniques were used to characterize auto-combustion reactions and followed ferrites formation. Structural, morphological, magnetic and electrical properties were studied using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and conductivity as well as dielectric measurements. XRD showed single-phase ferrites with sizes ranging between 30 and 62 nm depending on the utilized method. TEM showed spherical agglomerated particles with some irregularity in shape with sizes agreed well with those estimated through XRD. FT-IR spectra showed the two characteristic ferrite bands attributed to the stretching frequency of the octahedral and tetrahedral sites. The broadening of the tetrahedral band in case of urea and gelatin methods can be attributed to the low crystallinity. VSM exhibited ferromagnetic characteristics with high remanences and coercivities. The highest magnetization was obtained via sucrose method (67.6 emu/g) while the lowest one was obtained for egg-white route (44 emu/g). The obvious variation in the saturation magnetization with different methods can was possibly attributed to the change in sizes as well as the entire cation distribution. The high coercivities obtained suggested their using as permanent magnets or as magnetic recording media. ac-conductivity as a function of temperature indicating semi-conducting behavior with conductivity increases with decreasing size. The changes in the real ( ε ‵) and imaginary ( ε ‵‵) parts of dielectric constant as a function of both frequency and temperature indicated, in accordance with the ac-conductivity study, magnetic transition from ferro- to paramagnetic characteristics for all the samples except for those prepared via sucrose and citrate method. This behavior was discussed in view of the obtained magnetization values. [ABSTRACT FROM AUTHOR]

In this work, for the first time, W-type barium ferrite nanostructures (BaFe 18 O 27 ) were synthesized by sol–gel auto combustion method. The role of the calcination temperature and the type of sugar were investigated on the basis of their morphology and the size of the particles. The obtained products were characterized by Electron microscopy (EM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and energy dispersive spectrometry (EDS) and vibrating sample magnetometer (VSM). Adsorptive desulfurization (ADS) is one of the most promising complementary and alternative methods. To evaluate the ADS reactivity over the W-ferrite, a series of ADS experiments with a model gasoline feedstock were performed using a fixed-bed reactor. The results of catalytic tests reveals that BaFe 18 O 27 nanoparticles have the potential to be used as a new absorptive for desulfurization of liquid fuels. 0.5 g BaFe 18 O 27 exhibited the highest ADS properties. This ferrite was successfully regenerated after calcining at 500 °C in air. [ABSTRACT FROM AUTHOR]

• Vacuum and air sintered Bi-doped YIG have been prepared along with pure YIG using the sol–gel auto-combustion method. • The dielectric properties have enriched, and tangent loss has decreased for vacuum sintered Bi-doped YIG compared to YIG and air sintered Bi-doped YIG ceramics. • It also shows the better dielectric response with applied magnetic field so that it can be used for field sensing applications along with passive microwave devices. • We have observed large magneto-electric effect at the room temperature for all the ceramic samples and YBIG-V ceramic is maximum among them. • We have correlated the enhanced dielectric characteristics to the magnetic properties obtained through VSM measurements and attribute to the reduction in deficit oxygen states or Fe2+ concentration due to the vacuum sintering process which has also been confirmed through XPS studies. Yttrium iron garnet (YIG; Y 3 Fe 5 O 12) is an important material in the field of electronics because of its unique magnetic properties. This makes it ideal for use in devices such as microwave filters, amplifiers, sensors, and even magnetic storage devices. It is also used in spintronics, which is the study of the spin of electrons and how it can be manipulated for storage and computation. Additionally, it is highly stable and has low losses when exposed to electromagnetic fields, making it useful in applications such as controlling electric properties with magnetic fields or vice-versa, and magnetic resonance imaging (MRI). Herein, we have prepared YIG and Bi-doped YIG (Bi: YIG: Y 2 Bi 1 Fe 5 O 12) nanoparticles (NPs) using the sol–gel auto-combustion method. The obtained garnet powders were sintered at 950 °C both in an air and vacuum environment. We have explored the structural, electrical, optical, magnetic, and magneto-electric (ME) properties of Bi-doped YIG sintered in a vacuum (YBIG-V) and compared it with YIG and Bi-doped YIG sintered in the air (YBIG-A). We found the enhancement in dielectric response, magnetic properties, and the reduction in leakage current for the YBIG-V ceramics than for YBIG-A, YIG ceramics. We have studied the magneto-electric (ME) coupling at room temperature and found that YBIG-V ceramics show the better coupling strength with a maximum coupling coefficient, α ME of 354.3 mV/cm-Oe. The dielectric response of these samples significantly varies with the applied magnetic field, which will be positive in Bi-doped YIG ceramics and negative in pure YIG ceramics. Compared to YBIG-A, YBIG-V samples have better variation in dielectric response with the magnetic field, due to which they may be utilized for magnetic field sensing applications. We also observed that the resonance frequency varies with the applied magnetic field, which may be another parameter for field sensing applications. We attribute the enhancement of these properties in YBIG-V sample to the reduction in the average oxygen valency which is 1.63 for YBIG-A and 1.58 for YBIG-V. These values have been determined with the help of X-ray photoelectron emission spectroscopy data. [ABSTRACT FROM AUTHOR]

The Cu 2+ doped Ni 0.5− x Cu x Zn 0.5 Fe 2 O 4 (with x =0, 0.1, 0.2 and 0.3) ferrites of nanorods morphology was synthesized by glycine–nitrate auto-combustion method. The samples presents the diffraction peaks of cubic spinel crystal structure with Fd 3 ̅ m space group. An average crystallite size of 47 nm is obtained for undoped Ni 0.5 Zn 0.5 Fe 2 O 4 . The Cu ( x =0.1) doping is increased the crystallite size to 50 nm, thereafter, it is decreased to 42 and 38 nm at x =0.2 and 0.3 respectively. The lattice parameter is found to increase from 8.354 Å to 8.408 Å with increasing the Cu 2+ content. The formation of ferrite phase is further confirmed by obtaining the active Raman mode peaks of A 1g + E g +3 T 2g bands in all samples. The bands are linked with the symmetric and asymmetric stretching as well as the symmetric bending. The Cu ( x =0.1) doping showed 20% enhancement in coercivity, i.e. 105 Oe and 16% enhancement in saturation magnetization 87.16 emu/g compared to 87 Oe and 73.13 emu/g at x =0. The dielectric constant of 450 for the Cu ( x =0) and 50 for Cu ( x =0.1) is obtained at a constant frequency of 100 Hz. The dielectric loss as low as 0.05 is measured for Cu ( x =0.1) at 1 MHz. [ABSTRACT FROM AUTHOR]

The aim of this paper is to assess the pozzolanic reactivity of sugar cane straw ash (SCSA) obtained through an auto-combustion process and the mechanical properties of SCSA-containing systems. Characterization of SCSA (X-ray diffraction, chemical composition, particle size, and microscopy) and reactivity studies on hydrated lime/SCSA and Portland cement/SCSA pastes through infrared spectroscopy, thermogravimetric analysis, and microscopy demonstrated the high pozzolanic activity. This reactivity made it possible to achieve good mechanical properties in mortars in which 15–30% of the cement was replaced by SCSA. After 90 days of curing, the SCSA fixed 100% of the lime present in lime/SCSA pastes, and the compressive strength of mortars containing SCSA reached 44 MPa, a value similar to those found for control mortars after the same number of curing days. The results for the microstructural and mechanical properties showed that SCSA is a good pozzolanic material. [ABSTRACT FROM AUTHOR]

In this paper, barium hexaferrite nanostructures have been successfully synthesized via sol–gel auto combustion method based on the reaction between Ba(NO 3 ) 2 and Fe(NO 3 ) 3 ·9H 2 O in water, in the presence of carbohydrate sugar as fuel, reducing and capping agent. The products were characterized by X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy analysis. To investigate the effects of calcination temperature, the Ba 2+ molar ratio to Fe 3+ and the type of sugar on the morphology of products and finding optimal condition, several experiments were carried out. It was found that the phase and morphology of products could be influenced by these parameters. Vibrating sample magnetometer (VSM) was used to study the magnetic properties of BaFe 12 O 19 samples. The uniform nanoparticles are produced when the maltose is used as the reduction and the molar ratio of Fe 3+ to Ba 2+ reaches 12. The resulted product has the properties of the hard magnetic material, so, it has got the specific saturation magnetization and coercivity 48 emu/g and 5000 Oe, respectively. [ABSTRACT FROM AUTHOR]

In the present work we have illustrated the physics of the electrical characteristics of nanocrystalline La 1− x Pb x FeO 3, (0 ⩽ x ⩽ 0.2) powder prepared using auto-combustion synthesis. The effect of lead doping on the dielectric, impedance and ac conductivity characteristics of lanthanum ferrite has systematically been investigated. The synthesized powders were phase pure and crystallized into centro-symmetric Pnma space group. As compared to pure LaFeO 3 ceramics (dielectric constant ∼ 14,000), the dielectric constant is grossly increased (∼30,000) in Pb doped LaFeO 3 . The temperature dependence of dielectric constant of 10.0 at.% Pb doped LaFeO 3 exhibits dielectric maxima similar to that observed in ferroelectric ceramics with non-centrosymmetric point group. For La 0.8 Pb 0.2 FeO 3 ceramics, the frequency dependence of the dielectric constant and loss tangent at various temperatures (300–450 K) exhibit typical colossal dielectric constant (CDC) like behavior. From the impedance spectroscopy we have estimated the grain and grain boundary resistance and capacitance of Pb doped LaFeO 3 that follow a small polaron hopping conduction model. Long range movement of the charge carriers govern the CDC behavior. [ABSTRACT FROM AUTHOR]

A series of Y and Fe co-doped Ca 3− x Y x Co 4− y Fe y O 9+ δ (0 ⩽ x ⩽ 0.3, 0 ⩽ y ⩽ 0.1) samples synthesized by auto-combustion reaction and followed by a spark plasma sintering (SPS) processing with the effects of Fe and Y doping on the high temperature (RT to 800 °C) thermoelectric properties were systematically investigated. For the Fe-doped system ( x = 0, y ⩽ 0.1), the electrical resistivity ( ρ ) decreased over the whole measured temperature range, while the Seebeck coefficient ( S ) remained almost the same. For the co-doped system, at any fixed Fe doping content, both ρ and S tended to increase with increasing Y dopants, however, the effect is more substantial on ρ than on S , particularly in the low temperature regime. In contrast to ρ and S, the in-plane thermal conductivity ( κ ) is only slightly influenced by Y and Fe substitutions. Among all the investigated samples, the co-doped sample with x = 0.1 and y = 0.03 showed a decrease of ρ , enhanced power factor over the measured temperature range, and improved ZT at 800 °C as compared to un-doped Ca 3 Co 4 O 9+ δ . [ABSTRACT FROM AUTHOR]

Nanosized powders of compositions, Bi 0.8 Er 0.2 O 1.5 (ESB) and Ce 0.85 La 0.15 O 1.925 (CLO) have been prepared using citrate–nitrate auto combustion method. ESB added CLO (ECLO) samples have been prepared by mixing nanosized CLO powder with 0.5, 1, 2 and 3 wt.% of ESB. X-ray diffraction patterns confirm that all the samples are single phase having cubic fluorite structure similar to CeO 2 . Density of Ce 0.85 La 0.15 O 1.925 increases with increasing ESB content. All the samples have been sintered at 1350 °C. All the ECLO samples have density more than 97% of the theoretical value. Field emission scanning electron microscope images show dense microstructure with distinct grains and grain boundaries. Impedance measurements have been made in the temperature range 200–700 °C in air. Addition of ESB increases the conductivity of the bulk as well as of grain boundaries. Ce 0.85 La 0.15 O 1.925 with 0.5 wt.% of ESB exhibits the maximum conductivity 1.41 × 10 −2 S cm −1 at 600 °C of all the compositions. This value is one order of magnitude higher than the conductivity of Ce 0.85 La 0.15 O 1.925 (1.99 × 10 −3 S cm −1 ). [ABSTRACT FROM AUTHOR]

Long afterglow SrAl 2 O 4 :Eu 2+ ,Dy 3+ nanophosphors were synthesized via a facile but effectual auto-combustion technique followed by post-annealing treatment at elevated temperatures. The influence of various fuels during synthesis and thereafter improvement in the luminescence decay characteristics under various illuminant irradiations of long afterglow nanophosphors have been reported. Extensive studies on structural, morphological and luminescent properties of the as-synthesized afterglow nanophosphors have been presented. Powder X-ray diffraction studies confirm the presence of high-purity, single-phase monoclinic nanophosphors. HRTEM investigations confirm the formation of nanophosphors of particle size less than 50 nm. Photoluminescence emission is attributed to the characteristic d–f transition (4f 6 5d 1 →4f 7 ) of Eu 2+ ions and was positioned at 512 nm. As-synthesized nanophosphors exhibit considerable confinement effects resulting into blue shift in emission maxima as compared to their bulk counterparts. The mechanism underlined for long afterglow has been discussed using trapping–detrapping model. The nanophosphor being multifunctional finds many interesting applications including dark-vision display, energy storage, fingerprint detection, in vivo and in vitro biological staining, etc. [ABSTRACT FROM AUTHOR]

MnMgAlO x mixed oxides were prepared by means of the auto-combustion methodology using glycine/nitrate ratios of 1.0, 0.56 and 0.2; and M 2+ /M 3+ = 3.0 and Mn 2+ /Mg 2+ = 1.0 ratios. Additionally, MnMgAlO x oxide was obtained from the hydrotalcite-type precursor by the traditional co-precipitation method. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (H 2 -TPR), temperature programmed desorption (O 2 -TPD), textural analysis, scanning electron microscopy (SEM) and their catalytic performances were evaluated in the total oxidation of two volatile organic compounds (VOCs) representative of aromatic compounds (toluene) and of esters (ethyl acetate). The manganese mixed oxides resulting from the auto-combustion exhibited a chemical composition similar to that of the oxide obtained by thermal decomposition of the hydrotalcite with ∼36% of manganese loading. The mixed oxides obtained by both methodologies were active in the VOC oxidation. However, the mixed oxides synthesized by the auto-combustion methodology with stoichiometric and rich fuel conditions, showed better performance in the oxidation of toluene and ethyl acetate. The fuel/oxidizer ratio determined the redox properties, specific area and the catalytic performance of the materials in the oxidation of VOCs. Using the auto-combustion method was possible to obtain mixed oxides with a high manganese load which showed lower size particle (4–7 nm) and better structural stability than the mixed oxide obtained by the co-precipitation method (34 nm). The auto-combustion allowed for the obtaining of mixed oxides in very short synthesis times (∼5 h) with equal or superior catalytic properties as the oxide obtained by the co-precipitation method probably due to the maximization of the properties of the materials, where the decrease of the particle sizes and the improvement of the active phase distribution and oxidation-reduction properties are favorable for the improvement of catalytic performances. [ABSTRACT FROM AUTHOR]

Mixed oxides of manganese, cobalt and their mixture were synthesized by auto-combustion and co-precipitation methodology maintaining a constant M 2+ /Al 3+ ratio of 3.0, which is characteristic of the oxides obtained from the thermal decomposition of hydrotalcite-type precursors (in manganese oxides M 2+ = Mg + Mn, in cobalt oxides M 2+ = Mg + Co and in manganese-cobalt oxides M 2+ = Mg + Mn + Co). The catalysts were characterized by the following techniques: X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), N 2 adsorption, temperature-programmed reduction (H 2 -TPR), temperature programmed desorption of oxygen (O 2 -TPD) and 18 O isotope exchange. All of the materials were evaluated for the catalytic oxidation of two organic compounds of different reactivities: toluene and 2-propanol. It was observed that the joint participation of the absorbed oxygen species on the surface and the lattice oxygen atoms are responsible for the catalytic activity of the materials. However, the redox properties and the oxygen mobility play a determining role in the oxidation of the two volatile organic compounds (VOCs), with the oxygen mobility playing a more significant role in the cobalt oxides, whereas the redox properties are fundamental in the manganese oxides and in the Co and Mn mixture. The existence of a cooperative effect between the Co and Mn oxides is demonstrated when the co-precipitation method is used for the synthesis of the mixed oxide. This effect is not observed when auto-combustion is used for the synthesis; therefore, the autocombustion manganese oxide is the most active catalyst in the oxidation of the two VOCs by this methodology. [ABSTRACT FROM AUTHOR]

The covalent binding of yeast alcohol dehydrogenase (YADH) enzyme complex in a series of magnetic crystalline Ni-Co nanoferrites, synthesized via sol-gel auto combustion technique was investigated. The structural analysis, morphology and magnetic properties of Ni-Co nanoferrites were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), vibrating-sample magnetometer (VSM), high resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). The comparative analysis of the HRTEM micrographs of bare magnetic nanoferrite particles and particles immobilized with enzyme revealed an uniform distribution of the particles in both the cases without undergoing change in the size which was found to be in the range 20–30 nm. The binding of YADH to Ni-Co nanoferrites and the possible binding mechanism have been suggested by comparing the FTIR results. The binding properties of the immobilized YADH enzyme were also studied by kinetic parameters, optimum operational pH, temperature, thermal stability and reusability. The immobilized YADH exhibits enhanced thermal stability as compared to the free enzyme over a wide range of temperature and pH, and showed good durability after recovery by magnetic separation for repeated use. [ABSTRACT FROM AUTHOR]

Undoped and Ba and Ag-doped SrTiO 3 -based nanopowders (NPs) were successfully grown by a modified auto-combustion method. An optimum ratio of citric acid and nitric acid was used as the polymerization agent and fuel. The X-ray diffraction (XRD) results revealed that the products were crystalline with cubic and tetragonal structures. The particle aggregation state, nanoparticles size distribution, morphology and electrical properties were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), atomic force microscopy (AFM) and ultraviolet–visible (UV–vis) were studied, respectively. Using the X-ray peak broadening and size–strain plot (SSP) method the crystallite sizes and lattice strain of the samples were investigated. The UV–vis absorption spectra revealed that the band gap of the STO-based has a strong absorption peak which lies in the UV region. [ABSTRACT FROM AUTHOR]

• This work studies the structural and photoluminescence properties of europium doped barium carbonate. • Barium carbonate materials have been prepared with high purity. • Our compound has high color purity. • Based on the optical results and CIE chromaticity diagram, the Eu3+ doped BaCO 3 phosphor material can be considered as good candidate for red luminescence applications. Nanostructured powders of undoped and europium (Eu3+) doped barium carbonate (BaCO 3) were prepared by the autocombustion method. We investigated the influence of Eu3+ doping on the optical properties of barium carbonate. The samples nanostructures were characterized by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA) and differential thermal analysis (DTA) and photoluminescence (PL). The results obtained by XRD revealed that the samples consist of the BaCO 3 phase with orthorhombic structure having the space group Pmcn, retaining this crystalline phase after doping with Eu3+. These products were found for undoped and BaCO 3 : Eu3+ nanoparticles with 56–71 nm and 49–60 nm ranges, respectively. SEM reveals that the barium carbonate nanoparticles had a spherical morphology. Symmetric stretches, asymmetric stretches, and in plane bending vibrations, and out of plane of CO 3 2− complexes have detected. The photoluminescence of the obtained BaCO 3 :Eu3+ were studied. The CIE co-ordinates for the Eu3+ doped BaCO 3 were x = 0.580 and y = 0.330. From the CIE chromaticity diagram for the emissions of Eu3+ doped BaCO 3. The material has such color purity and reaches 76%. Thus, having color tenability and has been considerate as a candidate of the laser emission. [ABSTRACT FROM AUTHOR]

Highlights: [•] La5/3Sr1/3NiO4–YSZ composite powders have been synthesized by a simple method. [•] The effect of YSZ addition on the electrode microstructure and performance was investigated. [•] The effect of sintering temperature on the electrode microstructure and performance was investigated. [Copyright &y& Elsevier]

Abstract: A rapid method for the synthesis of Ca3Co4O9+δ powder is introduced. The procedure is a modification of the conventional citric-nitrate sol–gel method where an auto-combustion process is initiated by a controlled thermal oxidation–reduction reaction. The resulting powders inherit the advantages of a wet chemical synthesis, such as morphological and compositional homogeneity, and fine, well-defined particle sizes coming from the controlled nature of the auto-combustion. Optimized spark plasma sintering (SPS) processing conditions were determined and used to fabricate dense and highly c-axis oriented samples. The microstructure and thermoelectric transport properties were determined both parallel (||) and perpendicular (⊥) to the SPS pressure axis in order to investigate any possible anisotropy variations in the transport properties. At 800°C, power factors of 506μW/mK2 (⊥) and 147μW/mK2 (||), thermal conductivities values of 2.53W/mK (⊥) and 1.25W/mK (||), and resulting figures-of-merit, ZT, of 0.21 (⊥) and 0.13 (||) were observed. [Copyright &y& Elsevier]

• Auto-combustion route was optimized to obtain pure BiFeO 3 powder without calcination. • Magnetization of powders and composites originate from Fe 3 O 4 nanoparticles. • Auto-combustion synthesis of BiFeO 3 with glycine fuel forms Fe 3 O 4 as a by-product. • Dopants influence the properties in a more complex way than only by charge and size. • Y3+ and Zr4+ as dopants led to best improvement in electrical properties. Bismuth ferrite (BiFeO 3) powders were synthesized by auto-combustion method using glycine as a fuel. Doping ions of different valence were used to study the influence on electrical conductivity and ferroelectric properties. Powders were mixed and hot-pressed with α-PVDF to form flexible composite samples. Composites endured significantly higher electrical fields with lower leakage and retained the weak ferromagnetism present in powders. Dielectric properties were improved by doping with Zr4+, Y3+ and Ca2+ as well as the electrical resistivity. Flexible composites exhibited improved electrical resistivity and modified conduction mechanism. Relatively high magnetization of powders completely originates from magnetite particles formed during the combustion, while sintered samples exhibited typical antiferromagnetic behaviour. [ABSTRACT FROM AUTHOR]

The color-tunable GdCaAl 3 O 7 : RE3+ (RE = Eu, Tb, Eu@Tb) phosphors were synthesized via an ultrafast sol-gel auto-combustion synthesis method. The X-ray diffraction patterns confirmed the forming of GdCaAl 3 O 7 tetragonal phase, and the scanning electron microscopy images indicated that the obtained products presented honeycomb-like structure due to the gas releasing during the auto-combustion process. The luminescent properties, concentration quenching mechanism, energy transfer mechanism, luminescent dynamics, thermal stability and product practicability of GdCaAl 3 O 7 : RE3+ (RE = Tb, Eu, Eu@Tb) phosphors were investigated systematically. All the GdCaAl 3 O 7 : RE3+ products presented the characteristic emission of doped RE3+. Using GdCaAl 3 O 7 : 50% Tb3+@3.0% Eu3+ as yellow-emitting phosphors in combination with commercial BAM: Eu2+ blue-emitting phosphors and a NUV chip can successfully package a warm white LED device with high color rendering index (CRI, 86.3) and low correlated color temperature (CCT, 3348 K) that was very suitable for near-ultraviolet light-triggered indoor illumination. • Color-tunable phosphors were prepared by an ultrafast auto-combustion method. • Luminescent properties, dynamics and product practicability were investigated. • Energy transfer mechanism and concentration quenching effects were discussed. • Glaring warm white light with high CRI and low CCT was obtained. • Products were very suitable for near-ultraviolet light-triggered indoor illumination. [ABSTRACT FROM AUTHOR]

In this study, pure phase BiFeO 3 was prepared via a facile sol-gel auto-ignition route using water as a solvent. The influence of citric acid to metal nitrates molar ratio on physicochemical properties of BiFeO 3 was also investigated through FTIR, XRD, PL, UV, SEM, and BET analysis. The XRD of the prepared samples revealed the rhombohedral perovskite structures belong to space group R3c. In addition, the BFO2:1 sample showed the smallest crystallite size (42 nm) with the highest purity and recombination rate; while the BFO1:2 sample showed the lowest purity and electron charge recombination rate. The surface areas of the BFO1:1, BFO1:2, and BFO2:1 samples were 1.63, 2.13, and 1.84 m2/g, respectively. Moreover, the bandgaps were found to be 2.17, 2.11, and 2.21 eV for the prepared BFO1:1, BFO1:2, and BFO2:1, respectively. In addition, the appearance of a near-IR band around 814 cm−1 confirms the presence of Bi 2 Fe 4 O 9 byproduct in the BFO1:2 sample. Finally, SEM revealed that BFO2:1 sample was well-distributed and exhibited uniform morphology, referring to citric acid's ability to stabilize and disperse bismuth ferrite NPs. Furthermore, BFO1:2 sample showed enhanced photocatalytic activity in CR dye degradation than BFO1:1 and BFO2:1 samples, attributed by the increase in the surface area and minimized electron-hole recombination. This strategy eliminates the use of conventional organic solvents and provides an effortless and efficient way to prepare pure BiFeO 3 and BiFeO 3 /Bi 2 Fe 4 O 9 heterojunction nanocomposite that are potentially applicable for photocatalyst and in solar cell production. • Synthesis of pure phase BiFeO 3 and heterojunction nanocomposite BiFeO 3 /Bi 2 Fe 4 O 9 by sol-gel auto combustion route. • Citric acid is used as a fuel and stabilizer, and water is used as a solvent instead of an organic solvent. • Study the effect of citric acid to metal nitrates molar ratio on physicochemical properties of the synthesized samples. • The formation of nanocomposite between bismuth ferrite phases enhanced the photocatalytic degradation of CR. • The enhanced performance is associated with improved surface area and charge separation. [ABSTRACT FROM AUTHOR]

Highlights: [•] A series of Al2O3 and YBCO powders are simultaneously prepared by citrate–nitrate auto-combustion reaction. [•] The Al2O3 nanoparticles have successfully been yield and well distribute inter grain sample. [•] The samples electrically superconducting at comparable temperature as pure YBCO at around 90K. [ABSTRACT FROM AUTHOR]

Abstract: A CoFe2O4/cetyl trimethylammonium bromide (CTAB) nanocomposite has been fabricated by a sol–gel auto-combustion method. Characterization of the material revealed the composition of the crystalline phase as CoFe2O4 while FT-IR confirmed the presence of CTAB on the nanoparticles. From X-ray line profile fitting, average crystallite size was estimated to be 22±6nm. SEM analysis showed a porous sheet-like morphology with internal nanosize grains of about 30nm. The room temperature coercive field (H c ) of the CoFe2O4/CTAB nanocomposite was found to be 1045Oe which is close to the previously reported room temperature values for bulk CoFe2O4. The H c was observed to decrease almost linearly with the square root of the temperature (√T) according to Kneller's law. From the linear fit of H c versus √T, the zero-temperature coercivity (H c0) and superparamagnetic blocking temperature (T B ) of the CoFe2O4/CTAB nanocomposite were found to be ∼9.1kOe and ∼425K, respectively. The remanence magnetization (M r ), the reduced remanent magnetization (M r /M s ), and the effective magnetic anisotropy (K eff ) decrease with increasing temperature. The M r /M s value of 0.6 at 10K higher than the theoretical value of 0.5 for non-interacting single domain particles with the easy axis randomly oriented suggests the CoFe2O4/CTAB nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. [Copyright &y& Elsevier]

Abstract: In this experiment, nanocrystalline Y3Ba5Cu8O18 superconductor powder was prepared by citrate–nitrate auto-combustion reaction. A series of Y3Ba5Cu8O18 precursor gels with different citrate–nitrate ratio ranged from 0.3 to 1.0 have been prepared by varying the amount of citric acid added. The auto-combustion reaction during drying process transformed the precursor gels into ashes powder that upon calcinations at 900°C yield Y3Ba5Cu8O18 nanocrystalline powders. The TG/DTA analysis reveals that the precursor gels with 0.3⩽ c/n <1.0 decomposed in a single-step reaction combusted at temperature of around 230°C. Established from XRD and SEM characterization, the Y3Ba5Cu8O18 calcined powder prepared from c/n =0.7 precursor gels has got the orthorhombic structure with smallest particle size (∼10nm) compared to the rest of the batches. Samples with c/n =0.5 and 0.7 appeared in this work to be electrically superconducting at temperature above 100K as measured using standard four-probe technique. This emphasized on maintaining a stoichiometric or near stoichiometric reaction for the analysis. [Copyright &y& Elsevier]

Abstract: This study presents an original approach to the improvement of advanced oxidation process (AOP) efficiencies through the design of highly active catalysts. Then, removal of phenol was obtained under mild conditions by catalytic wet peroxide oxidation (CWPO) process over silica supported micropore and/or mesopore confined copper oxide nanoparticles. The materials, i.e. y wt.% CuO (y ranging from 4 to 10) on SBA-15 exhibiting different pore structure properties, were entirely characterized. In this study, we took advantage from the evolution of the micropore fraction in the mesoporous silica with the autoclaving temperature of synthesis. While only mesopore nanocasted copper oxide nanoparticle formed when the support exhibits only mesoporosity, micropore silica confined nanoparticles other formed the two supports exhibiting both micropores and mesopores. In this case, mesopore nanocasted nanoparticles can be only observed when copper oxide loading reaches 10wt.%. As a consequence, the copper active surface is suggested to be higher when copper incorporates interconnected micropores, without limited pore plugging issued from mesopore confined nanoparticle formation. For the phenol removal reaction, all the materials are exhibiting interesting activity, with a complete conversion of phenol and almost 60–80% of mineralization obtained in less than 2h at 60°C. Nevertheless, the results showed that the increase in copper loading up to high values is not needed to achieve high mineralization degree, due to the typical morphology of the materials, i.e. confinement of nanoparticles inside micropores or mesopores. In addition, the prepared materials allow a continuous use in reaction with leaching of active phase (≤4.4mgL−1) which also results in no water post-purification for cation removal as in the case of the classical homogeneous Fenton process. [Copyright &y& Elsevier]

Abstract: A series of the as-burnt and the burnt Cu/ZnO catalysts were prepared by a sol–gel auto-combustion method using metal nitrates with the mole ratio of Cu/Zn=1/1 (noted as M, M=Cu+Zn) and citric acid (noted as CA). When the xerogels were burnt in the argon atmosphere, H2 and CH4 which were came from the decomposition of the citric acid, were the reducing agents and were used in the redox process for synthesizing metallic Cu from Cu2+ in the chelated compound. The XRD patterns revealed that all the as-burnt catalysts with different M/CA molar ratios were converted into pure Cu and ZnO species. TPR analysis of the as-burnt catalyst illustrated that almost no hydrogen was consumed. It proved that Cu2+ in the chelated compound was absolutely reduced to metallic Cu in the as-burnt catalyst. The effects of M/CA molar ratio on the properties of catalysts were studied by TG-DTA, FT-IR, Raman spectrum, XRD, SEM-EDS, BET, and N2O chemisorption techniques. The activity of the as-burnt catalysts without reduction was investigated for low-temperature methanol synthesis from syngas containing CO2 using ethanol as a promoter at 443K and 5.0MPa for 12h. The total carbon conversion increased with increasing the content of citric acid and reached a maximum for the as-burnt Cu/ZnO catalyst C0.8 with M/CA=1/0.8, and then decreased. The variation trend was in accordance with that of the copper (Cu0) surface area. Comparing with the burnt catalyst C0.8-air after reduction, the methanol selectivity of the as-burnt Cu/ZnO catalyst was much lower owing to lower hydrogenation activity of the ethyl formate. The as-burnt catalyst C0.8 was also used in continuous low-temperature methanol synthesis at 443K and 5.0MPa for 40h. The total carbon conversion was stable after 15h and no obvious deactivation during 40h reaction, but the methanol selectivity was still not high. [Copyright &y& Elsevier]

Abstract: Using spent alkaline Zn–Mn batteries as raw material, Mn–Zn soft magnetic ferrite nanoparticles are prepared by multi-step processes including acid leaching, chemical treatment of battery iron shells and citrate-nitrate precursor auto-combustion. Acid leaching and chemical treatment mechanisms are investigated. Dried gels thermal decomposition process, auto-combustion, phase composition, morphological and magnetic properties of as-prepared Mn–Zn ferrite nanoparticles are characterized by thermogravimetric and differential thermal analysis, X-ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer. Synthesized Mn–Zn ferrite nanoparticles (Mn0.5Zn0.5Fe2O4) have pure ferrite phase, larger saturation magnetization (M s =60.62emug−1) and lower coercivity (H c =30Oe) compared with the same composition ferrites prepared by other techniques due to better crystallinity. Mn–Zn ferrite nanoparticles synthesis method presents a viable alternative for alkaline Zn–Mn batteries recycling. [Copyright &y& Elsevier]

Abstract: Quasi-single magnetic domain M-type barium hexaferrite powders have been synthesized via sol–gel auto-combustion route, followed by secondary heating treatment at 800°C for 4h, using barium nitrate, ferrite nitrate, ammonium nitrate, citric acid, and ammonia solution as the starting materials. The auto-combustion producing powders were γ-Fe2O3 and BaCO3 with aid of additional ammonium nitrate to increase the combustion temperature. The influences of the citric acid to metal ions (CA/M) and pH values on the gel auto-combustion, the phase compositions of the synthesized powders and their magnetic properties have been studied. The results showed that the chelation of barium and ferrite ions were important for the phase formation of barium hexaferrite: the phase compositions of the synthesized powders changed from a multi-phased mixture to a single phase of M-BaFe12O19 for the gradually complete complexing of barium and iron ions with citrate as the pH values and CA/M increased. The resulting powders demonstrated that various magnetic properties mainly depended on the variation in phase composition, sintering adhesion between grains and grown-up of crystalline sizes. With CA/M=1.5, pH 7, the synthesized powders had a particle size distribution in the range of 100–200nm and a saturation magnetization of 58.0emu/g at 12kOe. [Copyright &y& Elsevier]

• Ce 1− x La x O 2−δ (x = 0 − 0.1) solid solutions showed linear increase in ionic conductivity with La3+ • Ea is 1.49, 0.94, 0.87 and 0.70 eV for x = 0, 0.01, 0.03, 0.05 and 0.1 composition. • LDC showed highest ionic conductivity of 1.01 × 10−2 S cm−1 at 750 °C. • Electronic and ionic transference numbers are 0.20 and 0.80 at 700 °C for x = 0.1. • 0.05 LDC showed the OCV of 0.81 V and max. power density of 41 mWcm−2. [Display omitted] La-doped CeO 2 nanoparticles of composition Ce 1− x La x O 2−δ (0 ≤ x ≤ 0.1) have been studied here as prospective electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFCs). They were synthesized by auto-combustion method and the powder samples were calcined at 700 °C to get ultrafine nanocrystalline particles. They were characterized by XRD, Raman, FTIR, XPS, DRS, FESEM/EDX, particle size analyzer and ac-impedance techniques. Ionic conductivity was measured from 350 − 750 °C. The Ce 0.90 La 0.1 O 2−δ (0.1 LDC) and Ce 0.95 La 0.05 O 2−δ (0.05 LDC) showed a maximum conductivity of 8.89 × 10−3 and 8.32 × 10−3 S cm−1 at 700 °C, respectively. The σ t of 0.1 LDC = 1.01 × 10−2 S cm−1 at 750 °C. The activation energy of 0.1 LDC and 0.05 LDC was found to be 0.70 eV and 0.87 eV, respectively. These values are higher than those reported for La-doped CeO 2 in literature. The SOFC performance with 0.05 LDC as electrolyte showed open circuit voltage of 0.81 V and maximum power density of 41 mW cm−2 at 650 °C using hydrogen as fuel. [ABSTRACT FROM AUTHOR]

Jarosite and other metal sulphates are common on Mars and are interpreted to have formed in an extreme acidic saline aqueous environment, similar to modern Earth analogues where jarosite precipitates. We examined an alternative Earth analogue, at the Smoking Hills (known as Ingniryuat by Inuvialuit), Northwest Territories, Arctic Canada. The Smoking Hills are characterised by auto-combusting pyritic mudstones of the Smoking Hills Formation in a polar desert. The Smoking Hills Formation was deposited in an outer shelf to slope marine environment, during a Late Cretaceous Ocean Anoxic Event. Oxidative weathering of this unit creates extensive jarosite-rich deposits, and banded jarosite- and phyllosilicate-rich mudstones, similar to those observed on Mars. Slumping of these mudstones exposes large masses to atmospheric oxygen leading to generation of high temperatures (sufficient to produce paralavas) through pyrite oxidation, and the subsequent formation of a diverse suite of hydrated metal-sulphate minerals. Weathered combustion sites are characterised by a simpler jarosite-rich mineralogy along with thermally-altered mudstone. Away from sites of auto-combustion (bocannes), pyrite-rich layers within the mudstone oxidise to jarosite, creating a yellow-banded appearance in outcrops. These jarosite-rich layers, similar to those observed interbedded in mudstones on Mars, reflect post depositional oxidation processes - not acidic conditions during the time of deposition. As such, this could reflect a more habitable environment than is commonly interpreted for Mars. [ABSTRACT FROM AUTHOR]