Sol–gel synthesis and characterization of mesoporous manganese oxide

Mesoporous manganese oxide (MPMO) from reduction of KMnO₄ with maleic acid, was obtained and characterized in detail. The characterization of the material was confirmed by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffractometry (XRD) and N₂ sorptometry. The results showed that MPMO is a pseudo-crystalline material with complex network pore structure, of which BET specific surface area is 297 m²/g and pore size distribution is approximately in the range of 0.7–6.0 nm. The MPMO material turns to cryptomelane when the calcinating temperature rises to 400 °C. The optimum sol–gel reaction conditions are KMnO₄/C₄H₄O₄ molar ratio=3, pH=7 and gelation time>6 h.     

Sol–gel auto-combustion synthesis of spinel-type ferrite nanomaterials

Recent developments and trends of sol–gel auto-combustion method for spinel ferrite nanomaterial synthesis are briefly discussed and critically analyzed. The analysis of various parameters of reaction which could be used for better understanding of synthesis process and control of microstructure and property of spinel ferrite nanopowder products was the main objective of this review article. Special attention was paid to variety of particle size and phase purity. For these purposes the correlation between complexant, oxygen balance and combustion process chemical additives, as well as heating mechanism and atmosphere, was established. These results are relevant from standpoints of both application and processing of ferrites.     

Sol–gel synthesis and spectrometric structural evaluation of strontium substituted hydroxyapatite

Investigations of the electronic structures of substituted strontium apatites were carried out by using X-ray photo electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction technique (XRD) has been used to determine the structural parameters. Electron microprobe microanalysis technique was used to estimate the elemental concentrations in each substituted apatite material. The present work aims at studying the changes in the electronic structure of Sr₅(PO₄)₃OH (Sr-HAP) upon isomorphic substitution by F and Cl at the OH site of apatite and Sr by Na at trans Sr-HAP. The ion exchange between Na⁺ in sodium alginate and aqueous Ca²⁺ was important for the preparation of calcium hydroxyapatite. In contrast, the reaction of sodium alginate with the mixture of Na₄P₂O₇ and aqueous Sr²⁺ afforded strontium hydroxyapatite at the specific ratio. The structure of calcium and strontium phosphates prepared from the sol–gel process evidently depended on the amount of sodium alginate introduced into the mixture of Na₄P₂O₇ and the corresponding divalent cations. The findings have ensured that substitution of Sr-HAP by Na enhances the binding energy of O and Sr core levels. It was also noticed that the same substitution decreases the binding energy of P 2s-level. These observations point out to a decrease in the electron density at P and an increase in the electron density at O in Sr atoms.     

Sol–gel autocombustion synthesis of Co–Ni alloy powder

Sol–gel autocombustion is confirmed to be an efficient method in the synthesis of Co–Ni alloy powder. Addition of adequate amount of ethanol can make the reduction reaction thorough and increase the purity of the samples. X-ray diffraction measurement indicates that the obtained samples consist of a single phase with bcc structure. Transmission electron microscopy study shows the grain size is about 10 nm. The magnetic measurements show that the samples are a soft magnetic material with the coercive field smaller than 100 Oe and the saturation magnetization about 95% of the theoretical value.     

Sol–gel synthesis and characterization of mesoporous yttria-stabilized zirconia membranes with graded pore structure

Mesoporous yttria-stabilized zirconia (YSZ) membranes can be used for liquid phase applications in harsh environments and as supports for ultra-thin dense ceramic, carbonate, or metallic membranes. This article reports on the synthesis and characterization of three-layer mesoporous ceramic membranes consisting of a mesoporous YSZ layer, a macroporous YSZ intermediate layer, and macroporous α-alumina support. The macroporous YSZ intermediate layer was coated on the alumina support using a suspension of submicron-sized YSZ powders, and the mesoporous YSZ layer was obtained by dip-coating with diluted zirconia sol doped with yttrium nitrate. The mesoporous YSZ layer has desired cubic phase structure. Crack-free mesoporous YSZ membranes could be obtained by multiple dip-coating, drying, and calcination using a dilute YSZ sol at a concentration of 0.014 M with the help of using a drying control chemical additive. The 5 times dip-coated mesoporous YSZ membranes were about 1 μm in thickness with an average pore diameter of 3 nm. The mesoporous YSZ membranes exhibited Knudsen separation factor. The characteristics of the dip-coating process for the mesoporous YSZ membranes on the macroporous YSZ support are similar to those on the macroporous alumina support.     

Sol–gel synthesis and spark plasma sintering of Ba0.5Sr0.5TiO3

Ultrafine Ba_0.5Sr_0.5TiO₃ powders were prepared by using barium nitrate, strontium nitrate, tetrabutyl titanate, and ammonia via citrate–nitrate combustion process at low temperature (500 °C), along with the X-ray diffraction (XRD), differential scanning calorimetry (DSC)/thermogravimetry analysis (TGA) and scanning electron microscopy (SEM) analytic reports. Spark plasma sintering was carried out to obtain the ultrafine crystalline BST and to improve the dielectric properity. It was found that the sintered BST showed ultrafine crystalline microstructure. At 25 °C, the dielectric constant and dissipation factor of the sintered sample were 1533 and 0.0063 at 10 kHz.     

Sol–gel assisted hydrothermal synthesis of ZnO microstructures: Morphology control and photocatalytic activity

ZnO microstructures of different morphologies were synthesized by the sol–gel assisted hydrothermal method using Zn(NO₃)₂, citric acid and NaOH as raw materials. Twining-hexagonal prism, twining-hexagonal disk, sphere and flower-like ZnO microstructures could be synthesized only through controlling the pH of the hydrothermal reaction mixture at 11, 12, 13 and 14, respectively. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM). Optical properties were examined by UV–Vis absorption/diffuse reflectance spectroscopy and room-temperature photoluminescence measurements (PL). Photocatalytic activities of the samples were evaluated by degradation of Reactive Blue 14 (KGL). The results indicated that the flower-like ZnO composed of nanosheets possessed superior photocatalytic activity to other ZnO microstructures and commercial ZnO, which could be attributed to the morphology, surface defects, band gap and surface area. The formation mechanisms of different ZnO morphologies were also investigated based on the experimental results.     

Sol–gel template synthesis and characterization of aligned anatase-TiO2 nanorod arrays with different diameter

Template-based growth has been demonstrated as an attractive method for the synthesis of oxide nanorod arrays. In this paper, TiO₂ nanorod arrays in anodic alumina membranes have successfully been synthesized by an improved sol–gel template method. TiO₂ nanorods were obtained to injection of prepared TiO₂-sol from the sol–gel process and then the samples were immediately immersed into boiling TiO₂-sol solutions. Aligned TiO₂ nanorod arrays were polycrystalline anatase-phase after annealing at 400 °C for 2 h with diameters about 160–250, 80–130 and 40–70. A lateral shrinkage approximately 15–20% was found in TiO₂ nanorods with respect to the template pore diameter. This size difference is likely due to the volume shrinkage caused by removing residual materials and densification during annealing.     

Sol–gel synthesis, characterization, and in vitro compatibility of iron nanoparticle-encapsulating silica microspheres for hyperthermia in cancer therapy

We prepared iron nanoparticle-encapsulating silica (FeSi) microspheres and tested their suitability as thermal seeds for hyperthermia in cancer therapy. These microspheres were prepared by introducing a ferric ion (Fe³⁺) into microspheres of a SiO₂ gel matrix derived from the hydrolysis of tetramethoxysilane in a water-in-oil emulsion that was then heat-treated at 850?°C in an argon atmosphere. The particles obtained were 5–30?μm in size and had a saturation magnetization up to 21?emu?g^?1 and a coercive force of 86–133?Oe. Heat generation in an alternating current magnetic field of 300?Oe at 100?kHz was estimated to be 7.7–28.9?W?g^?1. The in vitro cell biocompatibility of the microspheres was assessed by culturing rat fibroblast Rat-1 cells in medium supplemented with microspheres containing 6.7?% of iron nanoparticles. At microsphere concentrations of <7.5?g?L^?1 proliferation of Rat-1 cells was not significantly inhibited.     

Sol–gel synthesis of TiO2–SiO2 photocatalyst for β-naphthol photodegradation

Silica gel supported titanium dioxide particles (TiO₂–SiO₂) prepared by sol–gel method was as photocatalyst in the degradation of β-naphthol in water under UV-illumination. The prepared sample has been characterized by powder X-ray diffraction (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The supported catalyst had large surface area and good sedimentation ability. The photodegradation rate of β-naphthol under UV-irradiation depended strongly on adsorption capacity of the catalyst, and the photoactivity of the supported catalyst was much higher than that of the pure titanium dioxides. The experiments were measured by high performance liquid chromatography (HPLC). The photodegradation rate of β-naphthol using 60% TiO₂–SiO₂ particles was faster than that using TiO₂ “Degussa P-25”, TiO₂ “PC-50” and TiO₂ “Aldrich” as photocatalyst by 2.7, 4 and 7.8 times, respectively. The kinetics of photocatalytic β-naphthol degradation was found to follow a pseudo-first-order rate law. The effect of the TiO₂ loading on the photoactivity of TiO₂–SiO₂ particles was also discussed. With good photocatalytic activity under UV-irradiation and the ability to be readily separated from the reaction system, this novel kind of catalyst exhibited the potential effective in the treatment of organic pollutants in aqueous systems.     

Sol–gel preparation and characterization of non-substituted and Sr-substituted gadolinium cobaltates

An aqueous sol–gel chemistry approach for the preparation of Sr-substituted perovskite gadolinium cobaltates Gd_1−xSr_xCoO_3−δ (x = 0.0, 0.25, 0.5 and 0.75) has been applied. The metal ions, generated by dissolving starting materials in diluted acetic acid were complexed by EDTA to obtain the precursors for non-substituted and Sr-substituted GdCoO₃. However, only two single-phase cobaltate samples with x = 0.0 and 0.25 have been obtained by the suggested sol–gel method. The influences of synthesis temperature and the amount of substituent on the phase purity of Gd_1−xSr_xCoO_3−δ were investigated. The evolution of the gels during heating, composition and micro-structural features in the polycrystalline samples was studied by thermal analysis (TG/DSC), infrared spectroscopy (IR), powder X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM).     

Sol–gel synthesis of tantalum oxide and phosphonic acid-modified carbon nanotubes composite coatings on titanium surfaces

Carbon nanotubes used as fillers in composite materials are more and more appreciated for the outstanding range of accessible properties and functionalities they generate in numerous domains of nanotechnologies. In the framework of biological and medical sciences, and particularly for orthopedic applications and devices (prostheses, implants, surgical instruments, …), titanium substrates covered by tantalum oxide/carbon nanotube composite coatings have proved to constitute interesting and successful platforms for the conception of solid and biocompatible biomaterials inducing the osseous regeneration processes (hydroxyapatite growth, osteoblasts attachment). This paper describes an original strategy for the conception of resistant and homogeneous tantalum oxide/carbon nanotubes layers on titanium through the introduction of carbon nanotubes functionalized by phosphonic acid moieties (P(O)(OH)₂). Strong covalent CP bonds are specifically inserted on their external sidewalls with a ratio of two phosphonic groups per anchoring point. Experimental results highlight the stronger “tantalum capture agent” effect of phosphonic-modified nanotubes during the sol–gel formation process of the deposits compared to nanotubes bearing oxidized functions (OH, CO, C(O)OH). Particular attention is also paid to the relative impact of the rate of functionalization and the dispersion degree of the carbon nanotubes in the coatings, as well as their wrapping level by the tantalum oxide matrix material. The resulting effect on the in vitro growth of hydroxyapatite is also evaluated to confirm the primary osseous bioactivity of those materials. Chemical, structural and morphological features of the different composite deposits described herein are assessed by X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopies, energy dispersive X-rays analysis (EDX) and peeling tests.     

Sol–gel synthesis, structure and bioactivity of Polycaprolactone/CaO • SiO2 hybrid material

A method has been developed to cast novel organic/inorganic polymer hybrids from multicomponent solutions containing tetramethyl orthosilicate, calcium nitrate tetrahydrate, polycaprolactone, water, and methylethyketone via sol-gel process. The existence of the hydrogen bonds between organic and inorganic components of the hybrid and hydroxyapatite formation on the surface was proved by Fourier transform infrared analysis. The morphology of the hybrid material was studied by scanning electron microscopy. The structure of a molecular level dispersion was disclosed by atomic force microscopy, pore size distribution, and surface measurements. The infrared spectra of the hybrid relative to sample soaked in a fluid simulating the composition of human blood plasma suggests that polycaprolactone/CaO * SiO(2) hybrid material synthesised via sol-gel process is bioactive as well as the CaO * SiO(2) gel glass.     

Sol–gel auto-combustion synthesis of PVP/CoFe2O4 nanocomposite and its magnetic characterization

Poly(vinyl pyrrolidone)/CoFe₂O₄ nanocomposite has been fabricated by a sol–gel auto-combustion method. Poly(vinyl pyrrolidone) was used as a reducing agent as well as a surface capping agent to prevent particle aggregation and stabilize the particles. The average crystallite size estimated from X-ray line profile fitting was found to be 20 ± 7 nm. The high field irreversibility and unsaturated magnetization behaviours indicate the presence of the core–shell structure in the sample. The exchange bias effect observed at 10 K suggests the existence of the magnetically aligned core surrounded by spin-disordered surface layer. The reduced remanent magnetization value of 0.6 at 10 K (higher than the theoretical value of 0.5) shows the PVP/CoFe₂O₄ nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model.