Low-temperature combustion synthesis of nanocrystalline HoFeO3 powders via a sol–gel method using glycin

Single phase nanocrystalline HoFeO₃ powders were successfully synthesized by the sol–gel self-propagation combustion method using glycin (C₂H₅NO₂) as the chelating reagent at a low combustion temperature. Four different mole ratios of glycin to metal nitrate (G/M) were used to prepare HoFeO₃ powders in the experiment. The XRD patterns indicate monophasic HoFeO₃ powders can be formed by further calcination, the SEM micrographs show that the nano-sized grains with distinguishable boundaries had been obtained. The M–H curves show HoFeO₃ powders had the characteristic of antiferromagnetism at 50 K, while the powders had the characteristic of paramagnetism as the ambient temperature reached 100 K or 300 K. The FC/ZFC magnetic measurement results demonstrate that there was a transition from antiferromagnetism to paramagnetism in HoFeO₃ nanopowders as the temperature was increased.     

Preparation of nanocrystalline SrTiO3 powder by sol–gel combustion method

In this research a sol–gel combustion route has been presented to synthesize strontium titanate (SrTiO₃:ST) nanocrystalline, using citric acid as fuel. The synthesis procedure was optimized by systematically varying the molar ratios of total metal nitrate to citric acid (MN:CA) from 1:1 to 1:3. The effect was investigated through XRD, SEM and TEM analysis. Analysis of XRD spectrum shows the complete of SrTiO₃ nanocrystalline, however, a minor phase of SrCO₃ impurity was found. Hence, an acid treatment process, with 1 mol/l HNO₃ solution and deionized water, was applied to remove the impurity. The results show that the appropriate condition to prepare the single phase nanocrystalline SrTiO₃ powders is MN:CA molar ratio of 1:3, coupled with an acid treatment process and at the lower calcination temperature of 500 °C. The particle size of powders was in nanometer ranges. The average crystallite size calculated from FWHM was about 23 nm. Morphology of powders was identified by SEM analysis. However, TEM estimated the average particle size about 7.5 nm after applying an acid treatment technique at 600 °C.     

Synthesis and characterization of nanocrystalline zinc aluminate spinel powder by sol–gel method

Single-phase nanocrystalline zinc aluminate (ZnAl₂O₄) spinel powder has been synthesized by the sol–gel method. Zinc aluminate nanoparticles were formed at 600 °C, which is at much lower temperature than by solid state reactions. Formation of ZnAl₂O₄ and their particle size depend on the calcination temperature. Calcination temperature also affects the specific surface area and pore volume. The nanocrystalline zinc aluminate was characterized by powder X-ray diffraction, FT-IR spectroscopy, thermal gravimetric analysis, diffuse reflectance spectroscopy, surface area measurements, field emission scanning electron microscopy coupled with energy dispersive X-ray analysis and transmission electron microscopy. Catalytic reactivity of nanocrystalline zinc aluminate was tested for the reduction of 4-nitrophenol to 4-aminophenol using NaBH₄.     

One-step synthesis of barium hexaferrite nano-powders via microwave-assisted sol–gel auto-combustion

Single phase barium hexaferrite nano-powders have been innovatively one-step synthesized via a microwave-assisted sol–gel auto-combustion in a specially designed quartz vessel using citric acid and ethylene diamine tetraacetic acid as composite chelating agents and freeze-drying technique to remove sols’ moisture. The auto-combustion product powder is characterized by fluffy particle aggregates with the crystallites ranging from 50 to 100 nm in diameter and containing single magnetic domains for each with a low apparent coercive field of 260 Oe and a high saturation magnetization of 64.1 emu/g. The direct formation of barium hexaferrite is believed to result from the effective improvement in the spatial distribution homogeneity of metal ions and oxidant in the gels. Moreover, the quartz vessel with barium hexaferrite ceramic pad on sample's support and film-strips on its interior wall can effectively build up a favorable temperature environment to promote the direct formation of barium hexaferrite with microwave assistance during the gel's uniform auto-combustion.     

Synthesis and characterization of mesoporous ZnTiO3 rods via a polyvinylpyrrolidone assisted sol–gel method

Mesoporous ZnTiO₃ rods were fabricated via a polyvinylpyrrolidone assisted sol–gel method. In this method, the control of nanostructure growth was achieved by the cooperative assembly among precursors and polyvinylpyrrolidone, through which well-designed one-dimensional morphology and mesoporosity could be obtained. The regularity of rod-like morphologies was sensitive to cooperative assembly temperature. Furthermore, the mesoporous ZnTiO₃ rods were used for photodegradation of organic dyes and proved to be useful photocatalysts with excellent reusability thanks to the well-designed nanostructure and one-dimensional structure. Hence mesoporous ZnTiO₃ rods with good photocatalytic activity and low cost could offer broad opportunities for environmental remediation.     

Synthesis and electrochemical properties of LiV3O8 via an improved sol–gel process

LiV₃O₈ cathode material was synthesized via a hydrothermal improved sol–gel process using LiOH, NH₄VO₃ and oxalic acid as raw materials. The thermal decomposition process of the as-prepared LiV₃O₈ precursor was investigated by thermogravimetric (TG) and differential scanning calorimetry (DSC). The structure, morphology and electrochemical performance of the as-synthesized LiV₃O₈ samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM) and the galvanostatic charge–discharge test. The effects of synthesis conditions on phases, structure and electrochemical performance of the LiV₃O₈ samples were particularly discussed. Result shows that pure LiV₃O₈ sample can be obtained at 300 °C, which is much lower than that of normal citric assisted sol–gel method. The sample synthesized at 350 °C exhibits the best electrochemical performance, which can present an initial discharge capacity of 301.1 mAh/g at a current density of 50 mA/g and maintain 271.6 mA/g (about 90.2% of its initial value) after 10 cycles.     

Synthesis of monodisperse nanocrystalline 8 mol-% yttria doped ceria powder by oleate complex route

Abstract

Preparation of monodisperse nanocrystalline yttria doped ceria powder by the oleate complex route has been reported. Y(III) and Ce(III) oleate complexes have been prepared by the reaction between YCl₃, Ce(NO₃)₃ and sodium oleate at the interface of hexane rich and water rich conjugate layers of water-ethanol-hexane ternary liquid system. Cubic yttria doped ceria crystallises when the waxy solid containing Y(III) oleate and Ce(III) oleate complexes was heat treated at 400°C. The powder after planetary ball milling contains monodisperse near spherical particles of 0·2?μm. These particles contain monodisperse nanocrystallites of size <10?nm. The yttria doped ceria powder pellets were sintered to >98% theoretical density at 1450°C. The sintered ceramic showed an ionic conductivity of 0·0623?S?cm^?1 at 800°C and activation energy of 1·0?eV.     

Ultrafast sol–gel synthesis of graphene aerogel materials

Graphene aerogels derived from graphene-oxide (GO) starting materials recently have been shown to exhibit a combination of high electrical conductivity, chemical stability, and low cost that has enabled a range of electrochemical applications. Standard synthesis protocols for manufacturing graphene aerogels require the use of sol–gel chemical reactions that are maintained at high temperatures for long periods of time ranging from 12 h to several days. Here we report an ultrafast, acid-catalyzed sol–gel formation process in acetonitrile in which wet GO-loaded gels are realized within 2 h at temperatures below 45 °C. Spectroscopic and electrochemical analysis following supercritical drying and pyrolysis confirms the reduction of the GO in the aerogels to sp² carbon crystallites with no residual carbon–nitrogen bonds from the acetonitrile or its derivatives. This rapid synthesis enhances the prospects for large-scale manufacturing of graphene aerogels for use in numerous applications including sorbents for environmental toxins, support materials for electrocatalysis, and high-performance electrodes for electrochemical capacitors and solar cells.     

Synthesis and characterization of nanocrystalline zirconia powder by simple sol–gel method with glucose and fructose as organic additives

The present study has devised the sol–gel method using glucose and fructose as two organic additives so as to synthesize zirconia nanoparticles. The presence of these organic additives has produced some positive effect on the phase transition from tetragonal to monoclinic and played an important role in the morphology and crystallite size of the nanoparticles. Fourier transform infrared (FT-IR) spectra have shown Zr–O–Zr bond. Crystal phase and crystallite size have been determined by X-ray Diffraction (XRD) analysis. Besides, the morphology of the samples has been investigated by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The optical properties of the samples have been analyzed using photoluminescence (PL) spectroscopy, too. All the analyses consistently have shown fairly uniform nanoparticles with small size, containing both tetragonal and monoclinic phases with crystallite size between 10 and 30 nm.     

Effect of sol–gel combustion temperature on the luminescent properties of trivalent Dy doped SrAl2O4

Trivalent dysprosium doped strontium aluminates (SrA1₂O₄:Dy³⁺) were synthesized by firing the sol–gel at 600, 700 and 800 °C. The morphology, crystal structure, photoluminescence and long afterglow of the synthesized SrAl₂O₄:Dy³⁺ phosphors were characterized with scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and photoluminescence spectroscopy, respectively. It is found that SrA1₂O₄:Dy³⁺ phosphors exhibit broadband afterglows with its peak at about 510 nm. As the sol–gel synthesis temperature increases from 600 to 800 °C, the green afterglow of the SrA1₂O₄:Dy³⁺ phosphors becomes weaker in intensity and shorter in lifetime. The results are discussed in terms of thermally generated point defects in the host material.     

Effect of synthesis methods and aging on synthesis of uvarovite garnet by ceramic and sol–gel processes

Abstract

The uvarovite garnet (CaO)₃ (Cr₂O₃ )(SiO₂ )₃ has been synthesised (mineralised with borax to facilitate diffusion of precursors) by several sol–gel methods. Two routes for uvarovite formation have been observed: where CaCrO₄ forms as an intermediate phase; and where metastable pseudowollastonite (α-CaSiO₃ ) forms as an intermediate phase. Synthesis via CaCrO₄ appears to be more reactive in unaged samples. The reactivity of samples can be directly related to the chemical homogeneity of raw powders, and two methods of synthesis, Pechini and alkoxide, were found to stand out for their reactivity. Aging of raw powders for 6 months inhibits nucleation. Consequently, samples without nucleating agents (i.e. chlorides), such as gels from alkoxides, lead to the stabilisation of amorphous material or metastable phases (α-CaSiO₃ ) and, as a result, hinder uvarovite formation. In contrast, aged samples involving heterogeneous nucleation agents, as in the Pechini method with CaCl₂ as precursor, enhance reactivity.     

Conductivity of Co and Ni doped lanthanum-gallate synthesized by citrate sol–gel method

Solid solutions of Sr and Mg doped lanthanum-gallate (LSGM) with addition of 3 and 5 at% of cobalt and nickel at the B-site in ABO₃ perovskite structure were obtained using citrate sol–gel method. The synthesized powders were calcined at 900 °C and then finally sintered at 1450 °C for only 2 h, which resulted in approximately 95% density. Impedance spectroscopy was utilized for electrical characterization in the temperature range 200–600 °C. The activation energies calculated from impedance spectra for bulk and grain boundary conductivities were decreased by the addition of transition metals (Co and Ni) and subsequently the conductivity was increased. Two different regions were clearly distinguished in the plots ln(σT) vs. 10,000/T for grain boundary conductivities, indicating changes in the mechanism of charge transport with the temperature. It is concluded that addition of cobalt above 5 at% in the LSGM prepared by citrate sol–gel method does not enhance the electrolytic properties of LSGM. XRD results suggested possible coexistence of two perovskite crystalline phases in nickel doped samples. However, it is still more favorable for use in IT-SOFC applications than cobalt since it has less influence on the electrolytic domain of LSGM.     

Nontemplate sol–gel synthesis of catalytically active mesoporous titanosilicates

A method for the nontemplate sol–gel synthesis of micro-mesoporous and mesoporous titanosilicates is developed using commercially available raw materials (a mixture of oligomer esters of orthosilicic acid (Ethylsilicate-40) and a water–alcohol solution of titanium(IV) ethoxide). The effect of the pH values of the reaction mixture on sol–gel synthesis is studied using the characteristics of the porous structure of titanosilicates. Samples of amorphous structure with different textural characteristics are obtained by varying the pH in the range of 3–10: specific surface area, 320–740 m²/g; micropore volume, 0.04–0.15 cm³/g; and mesopore volume, 0–0.92 cm³/g. It is shown that a sample of mesoporous titanosilicate obtained with alternating pH values has maximum catalytic activity in the oxidation reaction of 4-tert-butylphenol (TBP) in aqueous solutions of hydrogen peroxide. (Conversion of 4-tert-butylphenol, 45 wt %; selectivity of the formation of 4-tert-butylcatechol, 66 wt %. Conditions: 10 wt % of titanosilicate; TBP/H₂O₂ = 1/2; 75°C; 1 h).     

Ionic–gelation synthesis of gadolinium doped ceria (Ce0.8Gd0.2O1.90) nanocomposite powder using sodium-alginate

Nanocomposite powders of gadolinium-doped ceria (GDC, Ce_0.8Gd_0.2O_1.9) were synthesized via thermal treatment of the gel formed by contacting ionic solutions of sodium alginate as the jelling template and metal (gadolinium/cerium) nitrates as the starting material. The influence of calcination temperature and sodium alginate loading fraction on the properties of the synthesized GDC nanocomposite powders was investigated. Characterization was performed by energy dispersive X-ray spectroscopy, powder X-ray diffraction, thermogravimetric analysis, Field Emission Scanning Electron Microscopy, Fourier transformed infrared spectroscopy and nitrogen adsorption/desorption analysis. It was observed that the particle size and the surface area of the produced GDC nanocomposite powders are dominantly controlled by the calcination temperature, while the effect of sodium alginate loading fraction is limited by the range of the calcination temperature. In this study, the smallest mesoporous GDC nanocomposite powder with cubic fluorite structure (8 nm crystallite size and 3.05±0.005 m²/g surface area) was synthesized using 2 wt% of sodium alginate at a calcination temperature of 550 °C (for 4 h). The results of this study could help to perceive the influence of the basic processing variables on the particle size and the other physiochemical properties of GDC nanocomposite powders produced by the ionic-gelation method.     

Optimization of process parameters using D-optimal design for synthesis of ZnO nanoparticles via sol–gel technique

The experimental conditions for the synthesis of ZnO nanoparticles to produce minimal size were optimized using the D-optimal design. The influence of process parameters involves molar ratio of the starting materials, pH and the calcination temperature on the particle size were evaluated using the polynomial regression. The optimum conditions revealed by the model for obtaining a minimum particle size of ZnO were predicted to have a molar ratio of 1.76, pH of 1.50 and calcination at 402.2 °C. The obtainable particle size upon applying the model is 22.9 nm in compare to experimental result of 18 ± 2 nm was obtained.     

Synthesis and characterization of boehmitic alumina coated graphite by sol–gel method

Non-wettability property makes graphite a good protecting material against the molten metal and/or slag. Properties like high oxidation potential between 600 and 1200 °C and non-wettability with water at room temperatures limits the usage of graphite in castable refractory applications. In this study, sol–gel method, which is a relatively cheaper process, was used. Boehmitic sol was obtained by hydrolyzing and peptiziting the alkoxide AIP (aluminum isopropoxide) used as alumina source. Then natural flake graphite was mixed with the boehmitic solution for coating of graphite. At 120 °C boehmitic sol coated graphite was dried and gelled. Then heat threaded at 550 °C for γ-Al₂O₃ transformation of boehmite. Products that obtained from the studies were characterized with FTIR and XRD tests. Alumina coated graphite samples were made by repeating the same steps and TG analysis were made to investigate the oxidation behaviour of the samples. Finally, SEM–EDS analyses were carried out to investigate the microscopic properties of the alumina coated graphite powders.     

Microwave-assisted sol–gel synthesis of alpha alumina nanopowder and study of the rheological behavior

In the present work, alpha alumina nanopowder was synthesized via a sol–gel route. After preparation of bohemite (AlOOH) sol, carbon black was added and the resultant sol was dried and calcined in microwave furnace for 10 min. XRD results showed that alpha alumina was the only crystalline phase with specific surface area, mean diameter and crystallite size of 51 m² g^?1, 100 and 25 nm, respectively. Rheological measurements revealed that the optimal content of Tiron at pH=10 is 1 and 0.1 g per 100 g nano- and micron-alumina (1.5 m² g^?1), respectively. Furthermore, the optimum solid content of the slips was determined as 35–45 and 70 wt.% for nano- and micron-alumina, respectively.     

Fabrication of durable superhydrophobic and superoleophilic cotton fabric with fluorinated silica sol via sol–gel process

Superhydrophobic and superoleophilic cotton fabric was successfully prepared with fluorinated silica sol via a facile sol–gel method. A fluorinated polymeric sol–gel precursor (PHFBMA-MTS) was synthesized via free-radical polymerization by using hexafluorobutyl methacrylate (HFBMA) in the presence of (3-mercaptopropyl)trimethoxysilane (MTS) as the chain transfer agent, which led to the formation of fluoropolymer with alkoxysilane end groups. Then the fluorinated silica sol was prepared by introducing PHFBMA-MTS as the co-precursor of tetraethylorthosilicate (TEOS) in the sol–gel process with ammonium hydroxide as the catalyst, which was then used to fabricate superhydrophobic and superoleophilic fabric coatings through a simple dip-coating method. The coated fabrics showed superhydrophobic property with a high water contact angle of 154.1° and superoleophilic property with an oil contact angle of 0°. Moreover, the coated fabrics still kept superhydrophobicity even after ultrasonic treatment, as well as for organic solutions, acidic solutions. Thus, the coated fabrics were successfully applied to separate oil–water mixture with separation efficiency up to 99.8%. More importantly, the separation efficiency had no significant change after 20 cycles of oil–water separation. These present a simple, low-cost, and durable approach to achieve industrialized application of coated fabrics in oil–water separation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47005.     

In-situ sol–gel synthesis of zirconia networks in flexible and conductive composite films

The conductive and stretchable films with improved hardness are suitable for the fabrication of flexible electronic devices. This study describes the sol–gel technique to prepare a novel conductive and flexible film consisting of epoxidized natural rubber (ENR), doped polyaniline (PD) and zirconia. The zirconia networks were directly synthesized in-situ in ENR/PD solution and flexible conductive composite film with improved hardness was obtained. The morphology study revealed the size of PD decreased significantly from 77.89 ± 43.95 nm to 4.32 ± 1.13 nm and highest electrical conductivity of 1.9 × 10⁻³ S/cm was achieved with 10 wt.% percolation threshold of zirconia precursor. The binding energy of Zr3d_5/2 and Zr3d_3/2 decreased, suggesting that zirconia was converted to the lower oxidation state. Furthermore, the shape of PD changed from spherical to rod-like structure with root mean square value of 2 nm, while the hardness and reduced modulus improved to 1.72 MPa and 36.7 MPa, respectively.     

Green gelatine-assisted sol–gel synthesis of ultrasmall nickel oxide nanoparticles

Nickel oxide nanoparticles (NiO NPs) were synthesised using a sol–gel method in a gelatinous medium. Gelatine was used as a size-limiting polymerisation agent for the growth of NiO NPs. X-ray diffraction (XRD) analysis revealed that increasing the calcination temperature increased the crystallite size and decreased the size of the lattice constant. The size-strain plot method (SSP) was used to measure the individual contribution of grain sizes and micro strain on the peak broadening of NiO NPs. Transmission electron microscopy (TEM) showed the ultrasmall size of the NiO NPs with a narrow size distribution(10±0.2 nm). The band gap value of NiO NPs was calculated using ultraviolet–visible (UV–Vis) spectroscopy and decreased with increased calcination temperature.