Modified Sol Gel Route Research Articles

Effect of annealing temperature on the crystallization and oxygen sensing property of strontium titanate ferrite sol–gel thin films

SrTi0.6Fe0.4O3−δ (STF40) gas sensors were deposited using a novel modified sol–gel route. The influences of thermal annealing (400–750°C) on the crystallization and oxygen sensing performance were investigated. As revealed by XRD, TEM and XPS studies, the deposited sol–gel thin films had amorphous structure and the formation of cubic perovskite phase started at 450°C. The crystallization of the films improved with annealing temperature and completed at around 650°C. The oxygen sensing characterization of the film sensors were carried out using a custom-designed gas sensing characterization system. Abnormal n-type oxygen sensing response was observed for the sensors annealed at 400 and 450°C, which was found attributed by the n-type amorphous phases that remained in the sol–gel films. On the other hand, good and repeatable p-type oxygen sensing response was obtained for sensors annealed at 500°C and above.

Synthesis, characterization and photocatalytic evaluation of visible light activated C-doped TiO2 nanoparticles

We have demonstrated heterogeneous photocatalytic degradation of microcystin-LR (MC-LR) by visible light activated carbon doped TiO2 (C–TiO2) nanoparticles, synthesized by a modified sol–gel route based on the self-assembly technique exploiting oleic acid as a pore directing agent and carbon source. The C–TiO2 nanoparticles crystallize in anatase phase despite the low calcination temperature of 350 °C and exhibit a highly porous structure that can be optimized by tuning the concentration of the oleic acid surfactant. The carbon modified nanomaterials exhibited enhanced absorption in the broad visible light region together with an apparent red shift in the optical absorption edge by 0.5 eV (2.69 eV), compared to the 3.18 eV of reference anatase TiO2. Carbon species were identified by x-ray photoelectron spectroscopy analysis through the formation of both Ti–C and C–O bonds, indicative of substitution of carbon for oxygen atoms and the formation of carbonates, respectively. Electron paramagnetic resonance spectroscopy revealed the formation of two carbon related paramagnetic centers in C–TiO2, whose intensity was markedly enhanced under visible light illumination, pointing to the formation of localized states within the anatase band gap, following carbon doping. The photocatalytic activity of C–TiO2 nanomaterials was evaluated for the degradation of MC-LR at pH 3.0 under visible light (λ > 420 nm) irradiation. The doped materials showed a higher MC-LR degradation rate than reference TiO2, behavior that is attributed to the incorporation of carbon into the titania lattice.

Effect of Ni doping on the microstructure and high Curie temperature ferromagnetism in sol–gel derived titania powders

Undoped, 0.05 and 0.5mol% Ni-doped TiO2 powders were prepared by a modified sol–gel route. The doping effects on the microstructure and magnetism for the powdered samples have been systematically investigated. Doping of Ni in TiO2 inhibited rutile crystal growth. The probable reason for this is discussed on the basis of band calculation based analysis of electronic structures of 3d transition metal-doped TiO2 and the energetic, transformation kinetics and phase stability of anatase over rutile as the function of particle size. Room temperature ferromagnetism (RTFM) with the saturation magnetization of 12memug−1 and Curie temperature as high as 820K is observed only in case of 0.05mol% Ni:TiO2 powdered sample, whereas undoped TiO2 was diamagnetic and 0.5mol% Ni:TiO2 was paramagnetic in nature. The role of any magnetic impurity or any Ni metal in the origin of the RTFM has been ruled out by energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) analysis, whereas magnetic force microscopy (MFM) established the presence of magnetic domains, supporting the intrinsic diluted magnetic semiconductor behavior. The observed ferromagnetism has been attributed to the spin ordering through exchange interaction between holes trapped in oxygen orbitals adjacent to Ni substitutional sites.

Photocatalytic Degradation of Azo Dyes Using Au:TiO2, γ-Fe2O3:TiO2 Functional Nanosystems

We report photocatalytic degradation studies on Navy Blue HE2R (NB) dye on significant details as a representative from the class of azo dyes using functional nanosystems specifically designed to allow a strong photocatalytic activity. A modified sol-gel route was employed to synthesize Au and gamma-Fe2O3 modified TiO2 nanoparticles (NPs) at low temperature. The attachment strategy is better because it allows clear surface of TiO2 to remain open for photo-catalysis. X-ray diffraction, Raman and UV-VIS spectroscopy studies showed the presence of gold and iron oxide phases along-with the anatase TiO2 phase. TEM studies showed TiO2 nanocomposite particles of size approximately 10-12 nm. A detailed investigation on heterogeneous photocatalytic performance for Navy Blue HE2R dye was done using the as-synthesized catalysts Au:TiO2 and gamma-Fe2O3:TiO2 in aqueous suspension under 8 W low-pressure mercury vapour lamp irradiation. Also, the photocatalytic degradation of Amranth and Orange G azo dyes were studied. The surface modified TiO2 NPs showed significantly improved photocatalytic activity as compared to pure TiO2. Exposure of the dye to the UV light in the presence of pure and gold NPs attached TiO2 catalysts caused dye degradation of about approximately 20% and approximately 80%, respectively, in the first couple of hours. In the presence of gamma-Fe2O3 NPs attached TiO2, a remarkable approximately 95% degradation of the azo dye was observed only in the first 15 min of UV exposure. The process parameters for the optimum catalytic activity are established which lead to a complete decoloration and substantial dye degradation, supported by the values of the Chemical Oxygen Demand (COD) approximately 93% and Total Organic Carbon (TOC) approximately 65% of the treated dye solution after 5 hours on the employment of the UV/Au:TiO2/H2O2 photocatalytic process.

Preparation and Characterization of Pb(Zr,Ti)O3 films prepared by a modified sol-gel route

ABSTRACTPb(Zr0.53Ti0.47)O3 (PZT) films have been fabricated on stainless steel substrates by a Polyvinylpirrolidone (PVP) modified sol-gel route. The single layer of about 0.26 μm was achieved by using the PVP-modified PZT sol, and Crack-free PZT films with thickness of up to 2.37 μm were fabricated by repeating the deposition process. The variations in crystallite orientation, microstructure, dielectric and ferroelectric properties of PZT films were investigated as a function of film thickness. Our results indicate that PZT films prepared on stainless steel substrates maintain good dielectric and ferroelectric properties.

Phosphotungstic Acid Nanoclusters Grafted onto High Surface Area Hydrous Zirconia as Efficient Heterogeneous Catalyst for Synthesis of Octahydroquinazolinones and β-Acetamido Ketones

Phostungstic acid (PWA) nanoclusters grafted onto high surface area polycrystalline hydrous zirconia powder (PWA/ZrO2) was prepared by wet impregnation method. The zirconia particles were synthesized using a modified sol–gel route. The obtained material was characterized by X-ray diffraction (XRD), UV–Vis–diffuse reflectance spectroscopy (UV–Vis–NIR–DRS), infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and sorptometric techniques. XRD study revealed the presence of tetragonal phase of zirconia in the synthesized sample. TEM study indicates presence of small PWA clusters with size in the range of 5–15 nm well dispersed on the surface of the ZrO2 particles. The characteristic UV and IR absorption feature of the PWA was retained in the PWA/ZrO2 material. The PWA/ZrO2 material was used as an efficient catalyst for the preparation of octahydroquinazolinones and β-acetamido ketones. The octahydroquinazolinones were synthesized by the multicomponent condensation of dimedones, urea and aryl aldehydes in ethanol. Similarly, β-acetamido ketones were synthesized with high yield and purity by four component condensation of aryl aldehydes, enolizable ketones, and acetyl chlorides in acetonitrile. The protocols developed in this investigation using the PWA/ZrO2 catalyst is advantageous in terms of simple experimentation, high yield and purity of the products and recovery and reutilization of the heterogeneous catalyst.

High surface area BaZrO 3 photocatalyst prepared by base-hot-water treatment

Barium zirconate (BaZrO 3) nanoparticles have been prepared by modified sol–gel route. Low temperature process of base-hot-water treatment (BHWT) was conducted to obtain high surface area BaZrO 3. The treatments were carried out at 90 °C and at pH 14 with various concentrations of NaOH solution. Single phase nanocrystalline perovskite structure of BaZrO 3 powders was successfully obtained by immersing the BaZrO 3 precursor into hot-basic condition of 1 M NaOH solution for 1 h and consecutively calcined at 1000 °C for 2 h. BaZrO 3 powders with BHWT showed surface area of 18.4 m 2/g which is nearly 8 times larger than those of the powders without BHWT. Photocatalytic activities of BaZrO 3 powders upon bleaching of methylene blue in an aqueous solution under UV light irradiation were enhanced by the increment of their surface area.

PMMA-SiO2 organic–inorganic hybrid films: determination of dielectric characteristics

Organic–inorganic hybrid thin films have been prepared by a modified sol–gel route using tetraethyl orthosilicate as the inorganic (silica) source, methyl methacrylate (MMA) as the organic source, and 3-trimetoxysilylpropyl methacrylate as the coupling agent. The films were prepared by spin coating on Si (100) p-type substrates and subsequently heat-treated at 90 °C. Fourier transform infrared results reveal a set of absorption bands associated with the formation of both PMMA and SiO2 phases in the hybrid films. Capacitance–voltage (C–V) characterization was carried out on metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures, with the hybrid films as the insulator layer to evaluate the electrical properties. We present a detailed comparative analysis of the dielectric constant obtained from C–V characterization in the frequency range of 1 kHz–1 MHz. For the PMMA-SiO2 hybrid material the dielectric constant values obtained were around 9.5 at 1 MHz which is superior to the values reported for thermally grown SiO2 and pure PMMA materials. The interface state density for PMMA-SiO2 on Si was approximately 1010 cm−2, which is comparable to the standard SiO2/Si structures. Due to the electrical behavior and low processing temperatures this hybrid dielectric is a very promising candidate for flexible electronic devices and its subsequent implementation does not require complex equipment.

Photoluminescence properties of sesquioxide doped ceria synthesized by modified sol–gel route

Highly crystalline and porous sesquioxide (Sm 2O 3, La 2O 3) doped ceria with different molar ratio is successfully synthesized by a simple modified sol–gel route. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) are used to investigate their phase, microstructure and composition. XRD analysis confirmed the formation of highly crystalline cubic fluorite phase in all samples. The Raman spectroscopy revealed a single triple degenerated F 2g mode as the attestation of the oxygen vacancy in the doped and undoped samples. Strong photoluminescence lines due to interconfigurational transition and vacancy mediated transition were observed in doped CeO 2. The oxygen vacancy induced luminescence of CeO 2 was strongly enhanced due to La doping. The effect of rare earth dopant on the photoluminescence properties has been studied in details.

Thermal induced changes of lead zirconium titanate films and their consequences for liquid crystal devices applications

Thin films of lead zirconate titanate (PZT) were obtained by a modified sol–gel route on float glass and indium tin oxide (ITO)-covered float glass substrates. Different thermal treatments were performed on the deposited films in the temperature range 100–700°C. Spectroscopic ellipsometry was used to investigate the optical properties of the deposited films, and the changing optical absorption spectra were interpreted in terms of the growth of two different crystal phases, pyrochlore and ferroelectric perovskite, as a function of annealing temperature. Moreover, a specific resonance at 1.9 nm was detected when thin PZT films are deposited on ITO substrates and was attributed to a particular charge distribution at the interface. Finally, the performance in rectifying the electro-optical response of asymmetric nematic liquid crystal cells was tested for some of the films undergoing different thermal treatments.

N-doped ZrO2/TiO2 bimetallic materials synthesized in supercritical CO2: Morphology and photocatalytic activity

A series of N- and N/Zr-doped titanium nanomaterials were synthesized via an acetic acid modified sol–gel route using supercritical carbon dioxide (scCO2) as both the synthesis and drying medium. Titanium isopropoxide (TIP), and triethylamine (TEA) w/wo zirconium propoxide precursors were reacted with acetic acid in a polycondensation reaction in scCO2. The effects of N and N/Zr doping on the morphology, phase structure, mean crystallite size, textural properties, thermal and crystallization behavior, and photocatalytic degradation of methylene blue was investigated. SEM and TEM analysis showed that pure titania formed nanofibers from TIP and acetic acid whereas the doped samples gave a flake-like structure. The SEM and TEM images showed that a porous material consisting of ca. 10–15nm crystals were formed. XPS spectra indicated that the N1s peak for both N-doped titania and Ti–Zr binary metal oxide were centered at 400eV, indicating effective doping of nitrogen in the TiO2 matrix. From the XRD analysis, it was observed that a small amount of nitrogen and zirconia inhibited the crystal growth, resulting in smaller crystallite materials. The BET analysis of the N2 isotherm data revealed that small amount of zirconia and nitrogen (0.4at%) increased the surface area. All synthesized doped samples gave superior photocatalytic degradation of methylene blue compared to P25. These results show that scCO2 is a new promising route to provide N- and N/Zr-doped advanced photocatalytic nanomaterials.

Synthesis, characterization and electrocatalytical behavior of Nb–TiO 2/Pt nanocatalyst for oxygen reduction reaction

In order to point out the effect of the support to the catalyst for oxygen reduction reaction nano-crystalline Nb-doped TiO 2 was synthesized through a modified sol–gel route procedure. The specific surface area of the support, S BET, and pore size distribution, were calculated from the adsorption isotherms using the gravimetric McBain method. The support was characterized by X-ray diffraction (XRD) technique. The borohydride reduction method was used to prepare Nb–TiO 2 supported Pt (20 wt.%) catalyst. The synthesized catalyst was analyzed by TEM technique. Finally, the catalytic activity of this new catalyst for oxygen reduction reaction was investigated in acid solution, in the absence and the presence of methanol, and its activity was compared towards the results on C/Pt catalysts. Kinetic analysis reveals that the oxygen reduction reaction on Nb–TiO 2/Pt catalyst follows four-electron process leading to water, as in the case of C/Pt electrode, but the Tafel plots normalized to the electrochemically active surface area show very remarkable enhancement in activity of Nb–TiO 2/Pt expressed through the value of the current density at the constant potential. Moreover, Nb–TiO 2/Pt catalyst exhibits higher methanol tolerance during the oxygen reduction reaction than the C/Pt catalyst. The enhancement in the activity of Nb–TiO 2/Pt is consequence of both: the interactions of Pt nanoparticles with the support and the energy shift of the surface d-states with respect to the Fermi level what changes the surface reactivity.

Electrophoretic Codeposition of La0.6Sr0.4Co0.8Fe0.2O3−δ and Carbon Nanotubes for Developing Composite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

Carbon nanotubes (CNTs)/La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF) composite films have been fabricated by electrophoretic codeposition on Ce0.9Gd0.1O1.95 (CGO) substrates. CNTs are used as a sacrificial phase to produce ordered porous LSCF cathodes for intermediate temperature solid oxide fuel cells. The synthesis of LSCF powder by a modified sol–gel route is presented. The possible mechanism of formation of CNT/LSCF composite nanoparticles in suspension is discussed. Moreover the optimal suspension composition and the conditions for achieving successful electrophoretic deposition (EPD) of CNTs/LSCF composite nanoparticles were evaluated. Experimental results showed that the CNTs were homogeneously distributed and mixed with LSCF nanoparticles forming a mesh‐like structure, which resulted in a highly porous LSCF film when the CNTs were burned out during heat treatment in air at 800°C for 2 h. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) techniques were employed to characterize the microstructure of the precursors and of the composite films.

Low-Temperature Anode-Supported SOFC with Ultra-Thin Ceria-Based Electrolytes Prepared by Modified Sol-Gel Route

The utilization of anode-supported electrolytes is a very promising strategy to improve the electrical performance in solid oxide fuel cells (SOFCs) application, because it is possible to decrease considerably the electrolytes thickness. In this paper, ultra-thin ceria-based electrolyte films were successfully prepared on porous NiO/GDC anode support. The electrolyte films with thickness of 0.5-1 µm were deposited by a novel citrate sol-gel route combined with a suspension spray coating technique. The characterization and microstructure of the ultra-thin films were investigated by DTA/TGA, XRD and FE-SEM. The results showed that ceria-based films prepared were pure fluorite type nanocrystalline, homogenous and almost fully dense. Electrochemical performance of single cells based on the ultra-thin electrolyte films was also tested. The single cell with electrolyte thickness of 1 µm provided an OCV of 0.832 V at 500 °C which was close to that of the reported single cell with thicker ceria-based electrolyte film of 10 µm, and maximum power densities of 59.6, 121.9 and 133.8 mW/cm2 at 500, 600, and 700 °C, respectively. These ultra-thin electrolyte films showed good combination with the porous NiO/GDC anode supports, and good insulating ability for inactive electron migration at temperatures less than 600 °C.

Fabrication of Highly-Ordered TiO2 Nanotube Arrays and Their Use in Dye-Sensitized Solar Cells

Highly ordered TiO(2) nanotubes were successfully fabricated using a nanoporous alumina templating method. A modified sol-gel route was used to infiltrate the alumina pores with Ti(OC(3)H(7))(4) which was subsequently converted into TiO(2) nanotubes. The average external diameter, tube lengths, and wall thickness achieved were 295 nm, 6-15 microm, and 21-42 nm, respectively. Diffraction data reveals that the nanotubes consist solely of the anatase phase. Dye-sensitized solar cells using TiO(2) nanotube arrays as the working electrode yielded power conversion efficiencies as high as 3.5% with a maximum incident photon-to-current conversion efficiency of 20% at 520 nm.

Electrocaloric effect in antiferroelectric PbZrO3 thin films

AbstractAntiferroelectric PbZrO3 thin films have been deposited on Pt(111)/Ti/SiO2/Si substrate by polymer modified sol–gel route. Temperature dependent P –E hysteresis loops have been measured at 51 MV/m within a temperature range of 40 °C to 330 °C. The maximum electrocaloric effect ∼0.224 × 10–6 K mV–1 has been observed near the dielectric phase transition temperature (235 °C) of the thin films. The electrocaloric effect and its strong temperature dependence have been attributed to nearly first‐order phase transition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation and electrochemical study of a new magnesium intercalation material Mg 1.03Mn 0.97SiO 4

Orthorhombic magnesium manganese silicate (Mg 1.03Mn 0.97SiO 4) was prepared and evaluated as a new cathode material for rechargeable magnesium batteries. Although the electrochemical activity of the Mg 1.03Mn 0.97SiO 4 synthesized by high-temperature solid-state reaction is low, the magnesium storage capacity of nanosized Mg 1.03Mn 0.97SiO 4 prepared by modified sol–gel route and in situ carbon coating reaches 244 mAh g −1. The capacity increase mechanism during charge/discharge cycling was also preliminary studied.

Fast synthesis of monodisperse TiO 2 submicrospheres via a modified sol-gel approach

Monodisperse titania glycolate submicrospheres were synthesized by a modified sol-gel route, in which ultrasonic treatment was introduced to improve the reaction efficiency. The as-prepared products were characterized by means of Fourier transform infrared spectrum (FT-IR), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that the as-prepared products are titania glycolate submicrospheres with diameters of 230–330 nm. The average particle diameter is estimated to be about 280 nm. Ultrasonic treatment has an important influence on the morphology of the produced titania glycolates. After calcination at 450°C for 2 h, these titania glycolates were completely converted into anatase TiO 2. The morphology of TiO 2 particles was well reserved during the calcination process except for a reduction of 18% in the average particle size.

Synthesis and Characterization of (Zn,Cd)TiO3 by a Modified Sol–Gel Method

Ilmenite‐type (Zn1−xCdx)TiO3 (0≤x≤0.15 and 0.8≤x≤1.0) was synthesized by a modified sol–gel route including the Pechini process via two‐step heat treatments. The thermal stability of (Zn1−xCdx)TiO3 depended on the amount of cadmium content. The as‐synthesized (Zn1−xCdx)TiO3 (0≤x≤0.15 and 0.8≤x≤1.0) showed higher thermal stability than that of ZnTiO3. The variation of the dielectric constant of all synthesized (Zn1−xCdx)TiO3 samples for all measurement frequencies showed a similar tendency. The dielectric constant of each (Zn1−xCdx)TiO3 sample decreased first with increasing frequencies and then increased slightly when the frequency was up to 107 Hz. Moreover, the dielectric loss tangent of all synthesized (Zn1−xCdx)TiO3 samples for all measurement frequencies also changed in similar patterns. The dielectric loss tangent decreased with increasing measurement frequencies. The microwave dielectric properties of (Zn1−xCdx)TiO3 were changed with the cadmium doping content in the range of microwave frequency.

Reaction Pathway to the Synthesis of Anatase via the Chemical Modification of Titanium Isopropoxide with Acetic Acid

Anatase nanoparticles were obtained through a modified sol–gel route from titanium isopropoxide modified with acetic acid in order to control hydrolysis and condensation reactions. The modification of Ti(OiPr)4 with acetic acid reduces the availability of groups that hydrolyze and condense easily through the formation of a stable complex whose structure was determined to be Ti(OCOCH3)(OiPr)2 by means of FTIR and 13C NMR. The presence of this complex was confirmed with FTIR in the early stages of the process. A doublet in 1542 and 1440 cm−1 stands for the asymmetric and symmetric stretching vibrations of the carboxylic group coordinated to Ti as a bidentate ligand. The gap of 102 cm−1 between these signals suggests that acetate acts preferentially as a bidentate rather than as a bridging ligand between two titanium atoms. The use of acetic acid as modifier allows the control of both the degree of condensation and oligomerization of the precursor and leads to the preferential crystallization of TiO2 in the ...