Sol-gel Combustion Synthesis Research Articles

Effect of structural promoters on calcium based sorbents from waste derived sources

Calcium looping process is an important technology for high temperature CO2 scrubbing. Calcium based sorbent decays rapidly after cyclic reactions, hence enhanced cyclic stability of the sorbent should be developed. We studied three different refractories including Al, Mg and La based supports which were synthesized using the dry mixing, wet-mixing method and Sol Gel Combustion Synthesis (SGCS) methods, through which the dopants are completely mixed into CaO/CaCO3 particles. The sorbents were characterized by SEM/EDS and XRD. The carbonation conversion and cyclic stability of sorbents were tested by Thermo-Gravimetric Analyser (TGA) under similar conditions. TGA results demonstrated that marble-dust doped sorbents are able to achieve higher conversion than eggshell sorbents. Hence, further analysis was focused on marble-dust sorbents. SGCS exhibit much superior cyclic performance as compared to wet and dry method, however, wet method is effective due to the low cost less time consumption and scale up issues. This analysis demonstrated that marble-dust sorbents doped with Al i.e CaO:Al (90:10) maintained the best conversion (91 %) and stability over 20 reaction cycles in comparison with dopant ratio CaO: Al (80:20) i.e., 73 %. Similarly, Mg and La dopants showed best conversion and cyclic strength at the doping ratio of 90:10. Hence, conversion rate and cyclic stability is maximum for all the dopants Al, Mg and La with dopant ratio of 90:10 in comparison with ratios 80:20 and 70:30. Furthermore, among all the dopants, Al dopant gives highest conversion rate and cyclic stability.

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.

Study of Green and Chemical Methods for Synthesis of Nano Spinel MgFe2O4 and its Study on Degradation of Rose Bengal Dye

MgFe2O4 nanoferrites were synthesized by sol-gel and solution combustion synthesis (SCS) methods through green and chemical methods. Green and chemical methods for sol-gel were processed with use of lemon extract and citric acid, respectively. A green and chemical method for solution combustion synthesis was followed by using Phyllanthus acidus leaf extract and urea, respectively. The influence of synthesis approach on the behaviour of prepared nanoferrites were studied using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and UV visible spectroscopy, vast variation in particle size, crystallinity, electrochemical and photocatalytic activity of the nanoferrites synthesized by various methods were witnessed. Powder X-ray diffraction (PXRD) result of prepared nanoferrites acquired by green and chemical approaches clarified phase structure as spinel and the crystalline size found to be around 11-24 nm. The spinel surface morphology was witnessed for the synthesized nanoferrites. The tetrahedral and octahedral sites of the prepared nanoferrites were confirmed by FTIR spectra. MgFe2O4 nanoferrites synthesized by green sol-gel approach exposed superior electrochemical activity by possessing very less charge transfer resistance. The results of EIS were correlated with the photocatalytic degradation of Rose Bengal dye. Photocatalytic property of the prepared nanoferrites was examined for photodegradation of Rose Bengal dye under UV-light.

Application of Mn–Fe Composite Oxides Loaded on Alumina as Oxygen Carrier for Chemical Looping Gasification

The reactivity of oxygen carriers is curial for biomass chemical looping gasification (CLG) process. In this work, Mn–Fe composite oxides were loaded on Al2O3 through sol–gel combustion synthesis to improve their reactivity. The feasibility of these composite oxygen carriers for straw CLG process was proved in a thermogravimetric analyzer and better recyclability was found from oxygen carriers with Al2O3. Fixed-bed tests showed that the addition of Al2O3 could enhance the stability at relatively high temperature but decrease the oxygen transfer ability when temperature was low. Mn–Fe composite oxide with 60 wt% Al2O3 was chosen as the ideal oxygen carrier and the optimum condition was temperature at 850 °C, steam flow of 0.0432 g/min and OC/C mole ratio of 0.2. Under these parameters, gasification efficiency and carbon conversion efficiency reached 92.93% and 94.52% respectively. Moreover, cyclic experiments indicated that Al2O3 enhanced the stability of Mn–Fe composite oxides and gasification efficiency was decreased by 1.96% after 10 cycles. It was contributed to the porous structure supported by Al2O3, which could improve the sintering resistance and lattice oxygen transmission ability.

Spectroscopic investigation of red Eu3+ doped ceria nanophosphors and promising color rendition for warm white LEDs

Europium-ion doped CeO2 phosphors with different Eu3+ concentrations were synthesized via sol-gel combustion synthesis. X-ray diffraction patterns revealed the formation of pure cubic structure of CeO2 even after the incorporation of 35 mol% Eu3+. The excitation spectra of CeO2:Eu3+ displayed a broad band (330–370 nm) and several sharp peaks (393–532 nm) owing to the charge transfer (CT) from O2− to Ce4+ ions and f-f transitions of Eu3+ ions respectively. The evaluation of CT band was explained on the basis of environmental factors. The phosphors were illuminated with blue light and showed the characteristic red luminescence corresponding to the 5D0→ 7FJ transitions of Eu3+ as confirmed from XPS. The emission was observed to increase with the increase in the Eu3+ concentration up to 35 mol% without any quenching. Judd-Ofelt parameters were evaluated using the emission spectroscopy to explain the variation in ligand environment and enhancement of red color purity to 80%. The thermal stability of present phosphors was measured by estimating activation energy and TG-DSC analysis. Robust blue-excitation and sharp red-emission with high color-purity and promising thermal stability in fabricated WLEDs indicated the suitability of CeO2:Eu3+ phosphors for white light emitting diodes with quantum yield efficiency up to 84.6%.

Morphology and Structural Stability of Bismuth-Gadolinium Co-Doped Ceria Electrolyte Nanopowders

The reduction of the sintering temperature of doped ceria ceramics remains an open challenge for their real exploitation as electrolytes for intermediate temperature solid oxide fuel cell (IT-SOFCs) at the industrial level. In this work, we have used Bi (0.5 and 2 mol %) as the sintering aid for Gd (20 mol %)-doped ceria. Nano-sized powders of Bi/Gd co-doped ceria were easily synthesized via a simple and cheap sol-gel combustion synthesis. The obtained powders showed high sinterability and very good electrochemical properties. More importantly, even after prolonged annealing at 700 °C, both of the powders and of the sintered pellets, no trace of structural modifications, phase instabilities, or Bi segregation appeared. Therefore, the use of a small amount of Bi can be taken into account for preparing ceria-based ceramic electrolytes at low sintering temperatures.

Controllable growth of LiMn2O4 by carbohydrate-assisted combustion synthesis for high performance Li-ion batteries

LiMn2O4 (LMO) spinels with diverse achievable morphologies are realized using solution processing techniques including sol-gel and cofuel-assisted combustion synthesis (CS). These LMOs are utilized as cathode materials in lithium ion batteries (LiBs), with LMO produced here by low-temperature, sorbitol-assisted combustion synthesis (SA-CS) yielding superior performance metrics. Morphological analysis by combined X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy demonstrates that these SA-CS LMO powders have optimum LiB grain (<500 nm) and crystallite (~30 nm) dimensions as well as spinel phase purity. Cathode mixtures having micron-scale, uniformly distributed LMO, conductive carbon, and a polymer binder provide effective electron and Li transport as assessed by electrochemical impedance spectroscopy and fabricated battery performance, showing high capacity (~120 mA h/g), good cycling stability (~95% capacity retention after 100 charge/discharge cycles), and high charge/discharge rates (up to 86 mA h/g at 10 C). SA-CS provides a simple, efficient, lower temperature, and scalable process for producing morphology-controlled high-performance LiB cathode oxides.

Characteristics and Photocatalytic Activity of Sm Doped ZnO Nanoparticles

Sm2O3/ZnO nanoparticles were prepared via microwave-assisted hydrothermal and sol-gel combustion synthesis. Characteristics of obtained samples were compared in dependence of Sm2O3 content and calcination temperature. Prepared nanostructures were characterized with scanning electron microscopy and X-ray diffraction. Nanoparticles prepared via microwave-assisted hydrothermal and sol-gel method have flower-like and spherical shape respectively. The photocatalytic activity of samples under solar light simulated illumination was found to be affected by content of Sm2O3, calcination temperature and preparation method. The first-order rate constant of MB solution degradation of samples prepared via microwave-assisted hydrothermal method approximately three times exceeds that of sol-gel samples.

Optimized lithium-doped ceramic electrolytes and their use in fabrication of an electrolyte-supported solid oxide fuel cell

Lithium-gadolinium-doped ceria electrolytes (2–5 mol% of lithium) are prepared by fast and reliable one-pot sol gel combustion synthesis and sintered at low temperature. The aim is to improve the microstructure, electrochemical and power generation of electrolyte-supported intermediate temperature solid oxide fuel cells. Time-of-flight coupled secondary ions mass spectroscopy and transmission electron microscopy reveal the uniform distribution of lithium and the structural modification and surface change induced by the doping. Lithium addition reduces the sintering temperature to 950 °C, and the electrochemical properties compared to the pure gadolinium doped ceria are highly superior. A maximum of 3.59·10−2–1.41·10−1 S·cm−1 for total conductivity are achieved for 3 mol.% of lithium addition at intermediate operative temperature range. An electrolyte-supported solid oxide fuel cell is then fabricated and tested in different gas conditions and operative temperatures. The maximum power density is 359 mW·cm−2 at 668 mA·cm−2 (750 °C). The results demonstrate the reliability, the short time-to-product and the feasibility of both synthesis cycle and electrolyte production for industrial application to develop a cost-effective and marketable fuel cell technology.

Structure and surface characteristics of Fe-promoted Ni/Al2O3 catalysts for hydrogenation of 1,4-butynediol to 1,4-butenediol in a slurry-bed reactor

Nanostructured Ni–xFe/Al2O3 catalysts prepared by sol–gel combustion synthesis (SGC) display superior activity in hydrogenation of 1,4-butynediol to 1,4-butenediol. The Fe addition promoted the Ni reducibility and stabilized the Al2O3 structure.

Structural, Morphological and Methanol Sensing Properties of Jet Nebulizer Spray Pyrolysis Effect of TiO2 Doped SnO2 Thin Film for Removal of Heavy Metal Ions

Lead (Pb) and mercury (Hg) are two highly toxic heavy metals which must be removed completely or reduced to very low levels in drinking water supplies. TiO2:SnO2 nanoparticles and thin films were exploited for this purpose. TiO2:SnO2 nanoparticles were prepared by using the sol–gel combustion synthesis technique. The synthesized particles obtained were used in the analysis of the heavy metals of (Pb and Hg). The same material was used to deposit TiO2:SnO2 thin films by employing the Jet Nebulizer Technique (JNT). The films were subsequently characterized and used as adsorbents in the removal of heavy metal residues from contaminated water samples. The developed TiO2:SnO2 absorbents were characterized by transmission electron microscopy. The crystallite size of the prepared samples varied from 27 nm to 33 nm. The shape of the response curve for a given temperature variation depends on the well agreement with previously reported values ranging from zero for clean air to high positive values for strong interaction with reducing gas molecules. The application of these materials in many water filters may be helping to filter the sediments and economically feasible technology to filter microorganisms biological zone to purify the water.

Design of ultrasensitive Ag-LaFeO3 methanol gas sensor based on quasi molecular imprinting technology

An ultrasensitive methanol gas sensing device based on the quasi-molecular imprinting technology (quasi-MIT) is studied in this work. We applied the sol-gel method (ALS denotes Ag-LaFeO3 prepared by the sol-gel method) and combustion synthesis (ALC denotes Ag-LaFeO3 prepared by combustion synthesis) to prepare Ag-LaFeO3 based sensors. The morphologies and structures of the Ag-LaFeO3 materials were examined via various detection techniques. The ALSM and ALCM sensor (ALSM and ALCM denotes the devices prepared by coating the ALS and ALC materials with methanol, respectively) fabricated using the sol-gel method and combustion synthesis combined with quasi-MIT exhibit good gas sensing properties to methanol, in contrast with the two devices (ALSW and ALCW denote the devices prepared for coating the ALS and ALC materials with water, respectively) without the use of quasi-MIT. The results show that quasi-MIT introduced the target gas in the fabrication process of the device, playing an important role in the design of the ultrasensitive methanol gas sensor. The sensing response and the optimum working temperature of ALSM and ALCM gas sensor are 52.29 and 155 °C and 34.89 and 155 °C, respectively, for 5 ppm methanol, and the highest response to other gases is 8. The ALSM and ALCM gas sensors reveal good selectivity and response for methanol.

Characteristics and Sinterability of Ceria Stabilized Zirconia Nanoparticles Prepared by Chemical Methods

Microwave assisted and molten salts synthesis were extended for preparation of ceria (10 mol%; 15 mol%) stabilized zirconia and their parameters and sinterability were compared with that of particles prepared by the sol-gel combustion method. As-prepared powders by using microwave assisted and sol-gel combustion synthesis contained single tetragonal ZrO2 phase but powders prepared by molten salts combustion method contained two ceria-stabilized tetragonal phases with different content of ceria. The crystallite size of the as-prepared zirconia phases was in the range of 3.2 – 9.4 nm and the average particles size is in the range of 7.6 – 24.6 nm depending on the synthesis method. Additional calcination of the powders up to 1000 °C led to increase of crystallite size in the range of 19 – 25 nm and decrease of specific surface area in the range of 18 – 21 m2/g and partial formation of monoclinic phase of ZrO2. Bulk materials with fine-grained microstructure (0.8 – 1.6 µm) and density in the range of 95.2 – 97.2 % were obtained by spark plasma sintering at 1280 – 1310 °C during 3 min. Nanoparticles prepared by microwave assisted synthesis showed better sinterability and higher density.DOI: http://dx.doi.org/10.5755/j01.ms.24.3.18288

Direct addition of lithium and cobalt precursors to Ce0.8Gd0.2O1.95 electrolytes to improve microstructural and electrochemical properties in IT-SOFC at lower sintering temperature

To improve the microstructural and electrochemical properties of gadolinium-doped ceria (GDC) electrolytes, materials co-doped with 0.5–2 mol% of lithium and cobalt oxides were successfully prepared in a one-step sol gel combustion synthesis route. Vegard's slope theory was used to predict the dopant solubility and the sintering behaviour. The charge and size of the added dopant influence the atom flux near the grain boundary with a change in the lattice parameter. In fact, compared to traditional multi grinding steps, sol gel combustion facilitates molecular mixing of the precursors and substitution of the dopant cations into the fluorite structure, considerably reducing the sintering temperature. Adding precursors of lithium and cobalt, as dopant, increases the GDC densification and reduces its traditional sintering temperature down to 1000–1100 °C, with an improvement of electrochemical properties. Impedance analysis showed that the addition of 2 mol% of lithium or 0.5 mol% of cobalt enhances the conductivity with a consequent improvement of cell performances. High total conductivities of 1.26·10−1 S cm−1 and 8.72·10−2 S cm−1 at 800 °C were achieved after sintering at 1000 °C and 1100 °C for 2LiGDC and 0.5CoGDC, respectively.

Solution-Plasma-Mediated Synthesis of Si Nanoparticles for Anode Material of Lithium-Ion Batteries.

Silicon anodes have attracted considerable attention for their use in lithium-ion batteries because of their extremely high theoretical capacity; however, they are prone to extensive volume expansion during lithiation, which causes disintegration and poor cycling stability. In this article, we use two approaches to address this issue, by reducing the size of the Si particles to nanoscale and incorporating them into a carbon composite to help modulate the volume expansion problems. We improve our previous work on the solution-plasma-mediated synthesis of Si nanoparticles (NPs) by adjusting the electrolyte medium to mild buffer solutions rather than strong acids, successfully generating Si-NPs with <10 nm diameters. We then combined these Si-NPs with carbon using MgO-template-assisted sol-gel combustion synthesis, which afforded porous carbon composite materials. Among the preparations, the composite material obtained from the LiCl 0.2 M + H3BO3 0.15 M solution-based Si-NPs exhibited a high reversible capacity of 537 mAh/g after 30 discharge/charge cycles at a current rate of 0.5 A/g. We attribute this increased reversible capacity to the decreased particle size of the Si-NPs. These results clearly show the applicability of this facile and environmentally friendly solution-plasma technique for producing Si-NPs as an anode material for lithium-ion batteries.

Sol-gel combustion synthesis of high-quality chromium-doped mixed-metal garnets Y3Ga5O12 and Gd3Sc2Ga3O12

In this study the chromium-doped (0–20 mol% of Cr3+) garnet structure materials Y3Ga5O12 (YGG) and Gd3Sc2Ga3O12 (GSGG) were synthesized via aqueous sol-gel combustion (SGC) method. The synthesis process was investigated by thermogravimetric (TG) analysis and infrared (IR) spectroscopy. The phase formation at the following synthesis steps was characterized by powder X-ray diffraction (XRD) analysis. Scanning electron microscopy (SEM) was used for the characterization of surface morphology of the end products. Luminescence properties were examined by photoluminescence (PL) spectroscopy and decay time measurements (DT).

Chemical Looping Combustion of a Typical Lignite with a CaSO4–CuO Mixed Oxygen Carrier

Calcium sulfate (CaSO4) has attracted a great amount of attention as a potential oxygen carrier (OC) to be applied in chemical looping combustion (CLC) due to its high oxygen transfer capacity, wide distribution, and easy accessibility, but its low reactivity and sulfur emission from side reactions of CaSO4 should be well resolved. In this research, the CaSO4–CuO mixed OC was prepared using the template method combined with the sol–gel combustion synthesis (SGCS). Its reaction characteristics with a selected lignite (designated as YN) were investigated and the greatly enhanced reactivity of this mixed OC was confirmed relative to the single CaSO4 and CuO. Meanwhile, the comprehensive heat effect showed the desired exothermic characteristics for this mixed OC reaction with YN when the mass ratio of CaSO4 to CuO was fixed as 6:4. Furthermore, morphological analysis indicated that the solid products from YN reaction with the CaSO4–CuO mixed OC were porous without discernible sintering, mainly because the CaS...

Chemical looping gasification of biomass: Part I. screening Cu-Fe metal oxides as oxygen carrier and optimizing experimental conditions

Fe2O3 and CuO are commonly used as oxygen carrier (OC) for chemical looping gasification (CLG) of biomass. However, Fe2O3 shows relatively low reactivity even though it is cheap, whilst CuO presents too high reactivity to react with the produced syngas and suffers from sintering problem at high temperatures. This paper is the first part of a two-part series work, where synthetic OCs of bimetallic Cu-Fe oxides prepared by the sol-gel combustion synthesis (SGCS) method were proposed for the biomass-derived CLG process. The reforming reactivity of Cu-Fe OCs with sawdust was first investigated in a thermogravimetric analyzer (TGA). The result indicated that Cu-Fe OCs with higher Cu loading ratio demonstrated better reactivity towards sawdust. Subsequently, the performances of five kinds of Cu-Fe OCs in biomass-derived CLG process were evaluated in a batch fluidized-bed reactor. By comparing the product gas components, gas yield, tar yield and carbon conversion, Cu5Fe5 OC (50 mol.% CuO + 50 mol.% Fe2O3) was found to demonstrate the best comprehensive CLG performance. The effects of steam to biomass ratio (S/B), temperature and oxygen carrier to biomass ratio (O/B) on the performance of Cu5Fe5 were further investigated. The optimum operation state can be attained when the S/B was 0.75, the temperature was 800 °C and the O/B was 0.2. The results of XRD and ESEM characterization showed that the addition of Fe2O3 into CuO-based OC significantly improved the sintering resistance, and the existence of CuO component in Fe2O3 was conductive to improving the porous structure of OC.

Sol-gel combustion synthesis of Ag doped CaSiO3: in vitro bioactivity, antibacterial activity and cytocompatibility studies for biomedical applications

CaSiO3 is one of the bioactive calcium silicate materials and known as wollastonite. Herewith, for the first time, we have employed sol–gel combustion method to synthesize Ag-doped CaSiO3 using glycine as a fuel. The sintered powders were characterized by ATR-FTIR, XRD and SEM analysis which proved the existence of characteristic functional groups, pure phase formation and flakes, dense morphology with agglomeration, respectively. TEM-SAED analysis confirms that particles are in nano regime with crystalline nature. SBF immersion reveals that pure and Ag-doped CaSiO3 exhibit the good apatite layer formation for 7 and 14 days. Pure and Ag-doped CaSiO3 were evaluated for their antibacterial behaviour against E. coli and S. aureus which reflects the excellent inhibition of microorganisms. MTT assay proves that the prepared 5 wt-% of Ag-doped CaSiO3 exhibits the excellent cellular metabolic activity with MG-63 cells at different concentrations (50–250 μg ml−1) for 24–48 h.

Investigation of distribution of metals in Cr3+-doped Y3Ga5O12 and Gd3Sc2Ga3O12 using ICP-OES and EDX

In this study the series of Cr3+-doped Y3Ga5O12 (YGG) and Gd3Sc2Ga3O12 (GSGG) garnets were investigated. The garnet samples doped with a different amount of Cr3+ were synthesized using an aqueous sol–gel combustion synthesis method. The phase purity and morphology of the obtained garnets were characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The chemical composition of differently Cr3+-doped garnet structure compounds was analysed and compared with the nominal one. The content of elements in all samples was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) after dissolving these garnets in diluted nitric acid and by energy-dispersive X-ray spectroscopy (EDX) coupled with SEM. The empirical formula were calculated for both garnet series and compared with the theoretical formula.