Gel Combustion Route Research Articles

Enhancement of Bioactivity, Mechanical and Degradation Properties of the Diopside by Incorporation of Ba2+ Ion via Sol–gel Combustion Route

Enhancement of Bioactivity, Mechanical and Degradation Properties of the Diopside by Incorporation of Ba2+ Ion via Sol–gel Combustion Route

Nano triumphs bulk in red light emission from Eu3+ doped Y2Zr2O7: Gel combustion versus solid state synthesis

Red phosphors are integral element of a phosphor converted white light emitting diodes (pc-WLEDs) which significantly impacts the color rendering index (CRI) and correlated color temperature (CCT) and thus provides a white light suitable for indoor applications. Red Light emitting Eu doped Y2Zr2O7 (YZOE) has been synthesized by two different synthesis methods viz. gel combustion (GC) and solid-state route (SS) wherein the former yielded nanocrystalline and latter leads to bulk YZOE. By virtue of lower light scattering, better electron-hole overlap integral and lower symmetric surrounding, nano YZOE displayed better photoluminescence properties in terms of emission intensity, photoluminescence quantum yield (PLQY) and excited state lifetime compared to its bulkier counterpart.

Color tunable luminescence in ThO2:Er3+,Yb3+ nanocrystals: a promising new platform for upconversion.

Lanthanide-doped luminescent nanoparticles are an appealing system for many applications in the area of biomedical, solar cell, thermometry, anti-counterfeiting, etc. due to their sensitivity, reliability, high photochemical stability, and high optical transparency in the visible-NIR range. A color-tunable upconversion-luminescence (UCL) in a new low phonon energy ThO2 host based on modulating sensitizer concentration has been realized in this work and it may work as a potential candidate to replace corrosive and toxic fluoride based hosts in the future. Er3+-Yb3+ co-doped thoria nanoparticles were prepared using a gel combustion route and their structural and luminescence properties were determined as a function of the Yb3+ concentration. Phonon dispersion measurements have established the dynamic structural stability of the thoria nanoparticles. Density functional theory (DFT) was used to calculate the defect formation energy, highlighting the feasibility of dual ion (Er3+ and Yb3+) doping in thoria. The morphology and average size of the doped thoria was studied using high resolution transmission electron microscopy (HRTEM), and any defects evolving as a result of aliovalent doping were probed using positron annihilation lifetime spectroscopy (PALS). With 980 nm laser excitation, the nanothoria emits green and near-red light. A significant enhancement of the red-to-green intensity ratio of Er3+ ions in nanothoria was observed with an increase in Yb3+ concentration which resulted in beautiful color tunability from green to yellow light in going from lower (up to ∼5 mol%) to higher (10 and 15 mol%) Yb3+ concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two-photon upconversion processes for the green and red emissions.

Synthesis of hydroxyapatite via sol–gel combustion route: A comparative analysis of single and mixed fuels

Hydroxyapatite (HAp) is a highly biocompatible mineral source for bone and soft tissue repair, owing to its similarities to native bone. Researchers have adopted combustion synthesis by using various fuels for the synthesis of hydroxyapatite. This study sheds new light on the effects of glycine and succinic acid as single fuels as well as a mixed fuels for hydroxyapatite synthesis. A marked observation from the comparative analysis was that mixed fuels with an optimum ratio resulted in the formation of hydroxyapatite in a single phase with an average crystallite size of 21–23 nm. However, single fuels, such as glycine and succinic acid, produce hydroxyapatite with larger crystallite sizes of 25–28 nm and 38–41 nm. Additionally, the use of mixed fuels facilitated the product formation at a lower temperature of 500 °C, whereas single fuels produced hydroxyapatite at an elevated temperature of 900 °C.

Investigation of Praseodymium Ions Dopant on 9/65/35 PLZT Ceramics’ Behaviors, Prepared by the Gel-Combustion Route

In this work, were synthesized (Pb0.91La0.09)(Zr0.65Ti0.35)0.9775O3 ceramic materials with different concentrations of praseodymium (0, 0.1, 0.3, 0.5, 1 wt.%) via gel-combustion route and sintered by the hot uniaxial pressing method. Measurements were conducted on the obtained ceramics using X-ray powder diffraction (XRD), scanning electron microscope (SEM), EDS analysis, and examination of dielectric and ferroelectric optical properties. Results give us a detailed account of the influences of the praseodymium ions on the structural, microstructural, and dielectric properties. 3D fluorescence maps and excitation and emission spectra measurements show how a small admixture changes the ferroelectric relaxor behavior to an optically active ferroelectric luminophore.

Catalytically Active and Carbon-Resistive Anode Catalyst for Solid-Oxide Fuel Cells Operated at Low Temperatures (500–600 °C)

The development of active catalysts is always challenging in the field of energy devices. In this work, Li-doped, Ni–Cu-based, and Ni-free nanocomposite anode catalysts are synthesized and studied for solid-oxide fuel cells (SOFCs) operated at a low temperature using hydrogen and biogas as fuels. The catalysts with compositions Ni0.6Li0.2Cu0.2-oxide/La0.2Ce0.8O2-δ (NLC622-LDC), Ni0.2Li0.2Cu0.6-oxide/La0.2Ce0.8O2-δ (NLC226-LDC), and Ni0.0Li0.2Cu0.8-oxide/La0.2Ce0.8O2-δ (NLC028-LDC) are synthesized using the glycerol-assisted gel combustion route (GGCR). The structural analysis revealed the cubic structure of metallic oxide materials such as NiO and CuO phases while the cubic fluorite structure of CeO2 as an ionic oxide phase. The optical band gaps (Eg’s) of anode catalysts NLC622-LDC, NLC226-LDC, and NLC028-LDC are found to be 2.08, 2.29, and 2.37 eV, respectively. Furthermore, the anode catalyst with a higher nickel concentration shows better electrical conductivity and a lower activation energy of 3.47 S cm–1 and 0.67 eV at 600 °C, respectively, as compared to those of a nickel-free anode catalyst with lower nickel content. The electrochemical behavior of nanocomposites is studied at 600 °C using Nyquist plots. Electrochemical impedance analysis is carried out to see the effect of hydrocarbon fuel like biogas at the anode side. Finally, the electrochemical performance of NiLiCu-LDC catalyst-based fuel cells is tested under hydrogen and biogas fuels. Overall, the fuel cell based on the NLC622-LDC anode catalyst has higher OCV and power density with both fuels, hydrogen and biogas. Therefore, NLC622-LDC is a highly catalytically active anode catalyst which demonstrated significantly better performance for SOFCs operated at a low temperature (500–600 °C) without any carbon resistance.

Synthesis and feasibility studies of doping U at Ti site of Y2Ti2O7 as a radioactive waste immobilization matrix.

In pursuit of clean and green nuclear energy one of the major challenges is to effectively immobilize the nuclear waste. In this context A2B2O7 type pyrochlore owing to its structural flexibility, ability to accommodate ions at both A/B-sites and high radiation tolerance has demonstrated excellent capability to store highly radioactive actinide ions. To fill the major gap area of actinide doping at the B site we have taken up the challenge of doping uranium ions at the Ti site of Y2Ti2O7 type pyrochlore. An yttria titanate (Y2Ti2-xUxO7; x = 0.05, 0.075, 0.1, 0.2, and 0.3) based matrix with uranium doped at the Ti site was synthesized using a simple gel combustion route under an air atmosphere. Rietveld refined X-ray diffraction (XRD) demonstrated that Y2Ti2O7 can accommodate U up to 5 mol% in the Ti site without any phase separation, which was further confirmed using Raman spectroscopy. Y2Ti2O7 based matrices are found to be radiation stable up to 1000 kGy and at the same time they are moderately thermally stable and on a par with the values reported for pyrochlores. Uranium in Y2Ti2O7 stabilizes in +6 oxidation state in the form of uranyl ion distributed near and far off from titanium vacancies with distinct excited state lifetime. This work could provide a smart and strategic way for selecting a suitable advanced ceramic matrix for immobilization of high level waste with additional and important information on solubility limit, actinide speciation, radiation/thermal stability, actinide concentration, etc.

Synthesis of Substituted Barium Ferrites and Hexaferrites and Their Electrochemical Characterization

Magnetic nanoparticle has been an attractive area of research in view of their unique physical and chemical properties. [1] In the field of electrochemistry, particularly electroanalysis, they are extensively used as functional materials due to their high surface area, mass transport, catalytic effect, and control over the local environment. Barium based ferrites have emerged as attractive materials of interest due to their interesting physical, chemical, magnetic and electrical properties. [2] Hexaferrite and ferrites such as barium ferrite are very important group of magnetic oxides and these are used in different technologies including sensors because of their specific properties such as low cost, corrosion resistance chemical stability and large magneto crystalline anisotropy. [3] However, the investigation of the effect by various other elements on the structure of hexaferrite and ferrite particles and its electrochemical properties remains the subject of popular research. In this work, mixed metallic oxides hexaferrite and ferrite were synthesized by sol–gel combustion route using glycerin as an adjuvant. [4] Their structure was confirmed by means of X-ray powder diffraction. Scanning electron microscopy were used to investigate the morphology of the sample and the vibrations of the functional groups were determined by Raman and IR-ATR spectroscopy. The electrochemical behavior of substituted hexaferrite and ferrite were determined by cyclic voltammetry using an Ag/AgCl electrode, platinum wire and a glass carbon electrode (GCE), as reference electrode, counter electrode and working electrode, respectively. The GCE was modified with mixed metal oxides obtained to analyze their electrochemical behavior.Bibliographic Xueli X, Wei S 2019 Materials Technology, 1-5Kefeni, K.K.; Msagati, T.A.; Mamba, B.B. 2017, Sci. Eng. B. 215, 37–55Valenzuela R, Magnetic Ceramics, Chemistry of Solid State Materials 4 serie. Cambridge (Great Britain): Cambridge University Press, 1994, p. 50Sandra F. Basante-Delgado, Dalliver González-Vidal, Jimmy A. MoralesMorales, William A. Aperador-Chaparro, Jairo A. Gómez-Cuaspud, 2020 Phys.: Conf. Ser. 1541 012013

Electrochemical Characterization in Neutral Electrolyte of Mixed Metal Oxide

The mixed metal oxides, have been used in different environmental and chemical applications in view of their physical and chemical properties. In the field of electrochemistry, particularly electroanalysis, they are extensively used as functional materials due to their high surface area, mass transport, catalytic effect, and control over the local environment. [1] Mixed metal oxides providing a material with different physicochemical and morphological properties, such as, greater surface area, high dispersion, thermal stability, acid/base properties, making its application in various fields of chemistry, mainly as catalysts in various organic reactions. [2]In this work, mixed metal oxides of CuO-Fe2O3 and CoFe2O4 ferrite were synthesized by sol–gel combustion route using glycerin as an adjuvant. [3-4] The mixed metal oxides CuO-Fe2O3 and CoFe2O4 ferrites structure was confirmed by means of X-ray powder diffraction. Scanning electron microscopy were used to investigate the morphology of the sample and the vibrations of the functional groups were determined by Raman and IR-ATR spectroscopy. [3-4]The electrochemical behavior of mixed metal oxides CuO-Fe2O3 and CoFe2O4 ferrite were determined by cyclic voltammetry using an Ag/AgCl electrode, platinum wire and a glass carbon electrode (GCE), as reference electrode, counter electrode and working electrode, respectively. It was used a solution of KNO3 (0,1 mol L-1) as electrolytic medium. The GCE was modified with mixed metal oxides obtained to analyze their electrochemical behavior.Bibliographic Kefeni, K.K.; Msagati, T.A.; Mamba, B.B. 2017, Sci. Eng. B. 215, 37–55Veisi, S.S.; Yousefi, M.; Amini, M.M.; Shakeri, A.R.; Bagherzadeh, M. 2019, Alloy. Compd. 773, 1187–1194Basante-Delgado, S.F.; González-Vidal, D.; Morales-Morales, J.A.; Aperador-Chaparro, W.A.; Gómez-Cuaspud, J.A. 2020 Phys. Conf. Ser. 1541, 012013Granja-Banguera CP, Silgado-Cortázar DG, Morales-Morales JA. 2022, Molecules. 2022, 27, 1550.

Structural spectral, dielectric, and magnetic properties of Mg substituted Ba3CoFe24O41 Z-type hexaferrites

The Ba3Co2-xMgxFe24O41 hexaferrites were prepared by the sol–gel combustion route. The materials were annealed at 1350 °C and displayed the single-phase characteristics. X-ray density (Dx) decreases owing to increasing Mg-concentration. Crystallite size was calculated with the help of Debye Scherrer's formula and found within the 17–18 nm range. Fourier transform infrared spectroscopy was used to determine the specific absorption peaks of hexagonal ferrites. It was executed in the region of 420–700 cm−1—the occupancy of Mg2+ ions at the octahedral site at delayed alternation of Fe3+ ions. As a result, the dielectric permittivity decreased. The grain boundary contribution was clearly seen in synthesized ferrites' cole plots. The cole – cole plots show a single semi-circle which reveals that grain boundaries play a significant role in the conduction process. Magnetic measurement indicated the ferrimagnetic behavior of all samples.

Antibacterial wollastonite supported excellent proliferation and osteogenic differentiation of human bone marrow derived mesenchymal stromal cells

Biocompatibility and bacterial infections are the primary concerns associated with the current bone graft substitutes. The application of wollastonite-based scaffolds for bone tissue engineering becomes a novel subject of interest. In the present study, a single phasic wollastonite scaffold was synthesised using citric acid-based sol–gel combustion route. Its physicochemical characteristics, antibacterial properties as well as its biocompatibility and osteogenic induction effect on human bone marrow derived stromal cells (hBMSCs) are yet to be explored. The TGA/DTA, XRD and SEM/EDX confirmed the characteristics of wollastonite. The antibacterial test indicated wollastonite inhibition of 47.81% and 45.54% for gram-positive, Staphylococcus aureus and Staphylococcus epidermidis and 47.04% and 46.07% for gram-negative, Escherichia coli and Pseudomonas aeruginosa bacterial strains, respectively. The SEM micrographs demonstrated an excellent attachment of hBMSCs on wollastonite and comparable to commercial hydroxyapatite (cHA) scaffold. The alamar blue cell proliferation assay confirmed 1.7- and 1.8-fold significant increase in hBMSCs seeded on wollastonite and cHA scaffold, respectively, on day 14 as compared with day 1. The immunohistochemistry analysis on Type-I collagen (Col1) and Bone morphogenetic protein-2 (BMP2) expression on day 14 confirmed the osteogenic differentiation of hBMSCs seeded on wollastonite and comparable with cHA scaffold. In conclusion, wollastonite scaffold has a greater potential to substitute bone grafts in orthopaedic applications.

PZT 50/50 nanocrystalline powders with tetragonal structure prepared via gel combustion route: Effect of heat treatment on phase and chemical compositions

Comparative structural and thermal investigations of a process of formation of nanocrystalline lead zirconate titanate Pb(Zr0.50Ti0.50)O3 (PZT 50/50) powders, with a tetragonal structure, prepared via a gel combustion route under different thermal treatment conditions, were conducted. The thermal behaviour of a gel and an as-formed combustion product (powdered precursor) was studied using TGA/DTA techniques. The XRD study of the powdered precursor calcined at various temperatures, in combination with the TGA/DTA data, resulted in the establishment of the optimal temperature mode for obtaining a single-phase PZT 50/50 nanopowder. A possible mechanism for the formation of the PZT 50/50 phase during gel combustion has been proposed.Formation of a single-phase PZT powder with a given molar ratio of Pb/Zr/Ti = 1/0.5/0.5 was verified by XRD, μ-XRF and EDS methods. The results of XRD and FTIR spectroscopy indicated the tetragonal crystal structure of the PZT powder. The nanocrystalline nature of PZT 50/50 was confirmed by both XRD and SEM data. SEM studies revealed that the prepared nanopowders had a homogeneous, porous, coral-like microstructure with an average grain size in the range of 90–100 nm. According to the simultaneous thermal analysis (TGA/DSC) results, thermal stability of the PZT 50/50 nanopowder was observed up to 1000 °C. Local capacitance and the distribution of its values were measured on the surface of the PZT 50/50 coating, formed on Pt/Al2O3/Pt substrate using the screen printing technique, using scanning capacitance microscopy (SCM).

Synthesis, Characterization and sintering of nanocrystalline (U1-yCey)O2±x

Nanocrystalline solid solutions of (U1-yCey)O2±x [y = 0.15, 0.22, 0.28, 0.35] have been synthesized by citrate gel-combustion route with a fuel to oxidant ratio of 1. The “as prepared” powders were calcined at 873 K in air for 6 h and were consolidated into pellets at 220 MPa. These green pellets were reduced at 1073 K under flowing hydrogen for 8 h and were sintered at 1873 K under flowing Ar+8% H2 for 6 h. All these powders were characterized for their X-ray crystallite size (XCS), specific surface area (SSA), particle size distribution (PSD), porosity, bulk density (BD) and residual carbon (RC). The morphology and microstructures of these powders were studied by using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM), respectively. The Hall–Williamson analysis of the X-ray diffraction (XRD) data revealed that the “as-prepared” powders consist of nano grains with a size of about 10 to 20 nm and the results have been substantiated by bright field HRTEM image analysis of these samples. These sintered pellets were characterized for their phase composition, density and microstructure. Presence of a single phase fluorite solid solution was confirmed by XRD. A sintered density of 95.88±0.62% of theoretical density (TD) could be achieved. A systematic study on the gel-combustion synthesis of nanocrystalline (U1-yCey)O2±x [y = 0.15, 0.22, 0.28, 0.35] powders is being reported for the first time.

A preliminary study of oxides of Fe doped with Ba, Co, Cu and synthetized by the citrate sol–gel combustion route

In the present work we report the synthesis of mixed ferrites doped with Co2+, Cu2+ and Ba2+ cations, using citrate sol–gel combustion route in air atmosphere, at 950 °C for 3 hours, produced substituted M-type barium ferrites powders particles with crystallite sizes varying between 145 and 155 nm. The percentages of yield obtained were on average 42%. The synthesized ferrites were characterized by techniques such as powder X-ray diffraction, evidencing the formation of M-type barium hexaferrite and copper and cobalt substituted M-type barium ferrite with hematite in smaller proportion. The possible growth of M-type barium ferrite with copper and cobalt may be due to a larger size of the cobalt atom with respect to copper and that a higher proportion of cobalt salt was used in the synthesis route. Increase in the metal ion substituted content leads to a decrease in the lattice strain and may be responsible for an increase in the crystallite size because greater tensile strain leads to elongation of the particles. The particle size of the synthesized ferrites differs significantly when they are doped, with Ferrite doped with copper having the smallest particle size compared to Ferrite doped with cobalt. We also performed spectroscopic analyses, RAMAN that showed, the substitution of cooper or cobalt in the M-type barium ferrite powders particle leads to a minor intensity of resonance band when compared with the parent compound and the differences between Fe3+, Cu2+ and Co2+ ions in a tetrahedral coordination is their ionic radii. The increase in the ionic radii causes a local distortion and vibrational bands of distorted polyhedra in substituted M-type barium ferrites. The chemical composition of this sample was determined as Ba1.0Fe11.83O19.22, Ba1.0Co1.02Fe11.01O18.35 and Ba1.02Cu0.56Fe11.35O18.26 using an AAS device. Both are very close to the theoretical formula. The influence of the synthesized ferrite samples was explored in the ozonation of a dye of unknown chemical structure. The effect was evidenced by visible ultraviolet spectroscopy technique. The results obtained show that the ink could be decolorized by applying oxidation by ozonation, however, when substituted M-type barium ferrite is added, the discoloration increases when this is doped with copper and cobalt, being higher using this last ferrite. The degradation process by ozonation presented in this work, carried out in the presence of copper and cobalt substituted M-type barium ferrites, would constitute an example of technology for the environment.

Structural, electrical, and weak ferromagnetic-to-antiferromagnetic nature of Ni and La co-doped BaTiO3 by sol–gel combustion route

We report on structural, electrical, and weak ferromagnetic-to-antiferromagnetic possessions of Ba(1−x)LaxNi0.01Ti0.99O3 (BLNT) samples with x = 0.00, 0.25, 0.50, and 0.75%. The X-ray diffraction (XRD) and Raman spectra show that the sol–gel combustion route synthesized samples are successfully incorporated with La3+ ions into BaNi0.01Ti0.99O3 (BNT) lattice. The EPR signals at g = 1.967 and g = 2.003 are attributed to the V(Ba) and V(Ti) defects, respectively. For x = 0.75%, V(Ba) signal disappears due to the subtle charge-compensation mechanism present in the BLNT sample. The BNT ceramics exhibit a weak ferromagnetic nature; upon La ion doping, the weak ferromagnetic (WFM) tends to exhibit strong antiferromagnetic (AFM) nature in BLNT. This magnetic phase transition can be described in the stipulation of the change in the oxidation state. Escalating in the dielectric constant and ac conductivity was due to the higher doping concentration of La3+ ion in BNT ceramics. BLNT clearly shows that as La3+ ion-doping concentration increases, the diameter of the impedance semicircle decreases due to the increased conducting nature of the samples. The ferroelectric property was deliberately investigated by a P–E hysteresis loop and its saturation polarization was found to decrease with increasing concentrations of La3+ ion doping, and the observed results are discussed.

One-step synthesis of pure γ-FeNi alloy by reaсtive sol–gel combustion route: mechanism and properties

A pure crystalline γ-FeNi alloy powder was fabricated through the one-step process of sol–gel combustion. An experiment was conducted in inert atmosphere with the hexamethylenetetramine (HMTA) used as an oxygen-free fuel and metal nitrites as oxidizers. It was demonstrated that fuel-to-oxidizer ratio is a critical parameter to produce pure γ-FeNi alloy. A concentration of the fuel necessary for the alloy synthesis is three times higher (φ = 3) than at the stochiometric molar ratio. The ~1100 K maximum temperature, 830 K/s heating and 170 K/s cooling rates and the total reaction time of ~3 s are characteristics of the optimized sol–gel combustion synthesis of the γ-FeNi alloy powder. A mechanism of the alloy formation through the coordination metals—HMTA complex was proposed and experimentally verified. Microstructural and magnetic properties of the synthesized material are also investigated and discussed.

Influence of nano-copper oxide concentration on bactericidal properties of silver–copper oxide nanocomposite

The study investigated influence of copper oxide nanoparticle (CuO NP) concentrations on the bactericidal properties of silver-copper oxide (Ag/CuO) nanocomposite against Escherichia coli PTCC 1329, Klebsiella pneumoniae PTCC 1290 and Staphylococcus aureus PTCC 1189. Silver–copper oxide nanocomposite with varying concentrations of CuO was synthesized using a facile sol–gel combustion route. Formation of Ag/CuO crystalline structure and particle size were characterized by X-ray diffraction, Transmission Electron Microscopy and Field Emission Scanning Electron Microscopy. Elemental analyses were performed by energy dispersive X-ray. Morphologies of CuO NPs showed that Ag/CuO nanocomposite consisted of interconnected nanoparticles with a porous channel. Ag/CuO nanocomposite with higher CuO NPs content exhibited superior bactericidal effects. Bacterial growth profile also confirmed superior bactericidal effects of the nanocomposite at higher CuO NPs concentrations. A facile sol–gel technique with enhanced bactericidal effects at higher concentration of CuO NPs is promising for the development of cost-effective and efficacy-enhanced nanomaterials.

Process dynamic investigations and emission analyses of biodiesel produced using Sr–Ce mixed metal oxide heterogeneous catalyst

The present study explores the feasibility of Sr–Ce based mixed metal oxides for its performance in transesterification reaction of waste cooking oil. The catalyst synthesis was carried out through gel combustion route and was characterized through several techniques including thermal analysis (TGA-DTA), X-ray diffraction (XRD), attenuated total reflectance based Fourier transform infrared spectroscopy (ATR-FTIR), high resolution scanning electron microscopy (HR-SEM) assisted with EDX, BET specific surface area and Hammett indicator basicity. The enhanced activity of the catalyst was investigated at pH 7.0 with Sr–Ce atomic ratio of 3:1 at 900 °C of calcination temperature. Influences of various process parameters on transesterification efficiency were carefully investigated. The experimental results demonstrated that maximum transesterification efficacy of 99.5% was achieved under optimized reaction conditions with catalyst dose of 2.0 wt %, oil-to-methanol ratio 1:14, reaction time 120 min, reaction temperature 65 °C and stirring speed of 700 rpm. For better interpretation of the process, the reaction rate was computed by employing pseudo-first and pseudo-second order kinetics model at varying reaction temperature (50 °C–75 °C). The transesterification data agreed well with pseudo-first order model with highest rate constant value of 2.5 × 10−3 min−1 was evaluated at 65 °C. Activation energy and frequency of the reaction was quantified from the Arrhenius expression as 17.04 kJ/mol and 9.92 min−1, respectively. Thermodynamic analysis of the reaction system suggests that the transesterification of the waste cooking oil followed endergonic reaction pathway. Synthesis of biodiesel was ascertained from the H1-NMR and FTIR analysis of the transesterified product, further, the physicochemical properties of the biodiesel were also compared with that of diesel fuel and the resultant values were found to be within ASTM limits. Reusability study was also conducted and it indicated that the catalyst can be easily regenerated and could be effectively reused up to four runs.

Citrate-nitrate gel combustion synthesis of micro/nanostructured SiOx/C composite as high-performance lithium-ion battery anode

A facile and low-cost citrate-nitrate gel combustion route was conceived to synthesize micro/nanostructured SiOx/C composite. Auto combustion process generated ultrafine and chemically active SiO2 nanopowders with a loose and porous structure. A simple carbon coating process was continuously adopted to carbothermally reduce the O/Si atomic ratio of the combustion synthesized SiO2 precursor, and simultaneously create a carbon outer layer on secondary particles. The obtained SiOx/C composite has a micro-sized loose particle structure, composing of a great deal of primary nanoparticles. The micro/nanostructured SiOx/C composite exhibits a high and stable reversible capacity of ca. 740 mAh g−1, and excellent good rate capability. The low O/Si atomic ratio, unique micro/nanostructure and sufficient carbon component ensure the excellent electrochemical performance of the combustion synthesized micro/nanostructured SiOx/C.

Tailorable nano MgO.xAl2O3 spinel compositions along line of homogeneity via gel combustion route: Influence on phase evolution

Very fine sized (∼5–15 nm) magnesium aluminate spinel (MgO.xAl2O3) powder of different degree of solid solubility (x = 1, 1.25, 1.50, 1.75, and 2) have been attempted for synthesis following a gel combustion method to meet its high demand in the fields of refractory, photo catalysis, sensor and strategic applications, etc. Nitrates of magnesium and aluminum were used as oxidants for exothermic reactions fuelled by urea added with formaldehyde solution acting as reductant. Thermal decomposition reactions of polymer gels resulting in phases containing varied cationic ratio (Mg2+:Al3+) were investigated through DTA-TGA studies. Phase identification of synthesized powders derived from varying mole ratio of metal nitrates was performed by X-ray diffractometry (XRD) through Rietveld refinement using HighScore Plus software and was reconfirmed by Fourier Transform Infrared Spectroscopy (FTIR). Particle morphology was examined under Field Emission Scanning Electron Microscope (FESEM) & Transmission Electron Microscope (TEM). XRD pattern revealed the as-synthesized stoichiometric magnesium aluminate spinel (MgAl2O4) powder to be in amorphous state. In contrast, increasing trends in the extent of crystallinity in the as-synthesized form was obvious for alumina richer compositions. Dependence of development of crystallinity was explained in the light of thermal stability of polymer containing varied valent cations. Unlike crystallinity, a reverse trend is observed in case of cell parameter of the as-synthesized different non-stoichiometric spinel varieties where lattice parameter decreased with increasing alumina concentrations following Vegard's law. Variation in cell dimension against alumina concentration is caused by the insertion of smaller substituting Al3+ ions (0.054 nm) for Mg2+ ions (0.072 nm) in the unit cell. TEM observation reveals that the synthesized powder is aggregate of fine nano crystals. Crystallites were larger with increasing alumina concentration. An initial sintering behavior of the powder synthesized at 1400 °C has also been reported. Initial sintering trials were attempted under spark plasma sintering process.