Modified Sol Gel Route Research Articles

Tuning of structural and optical properties by sintering of multiferroic GdMnO3 precursor

ABSTRACTMultiferroic GdMnO3 was synthesized by the modified sol-gel route. The GdMnO3 precursor were sintered for 2 hours at different temperatures ranging from 300 (GMO300) to 800°C (GMO800). X-ray diffraction pattern shows that the crystallinity improves with sintering temperatures. The Raman data and Fourier transform infrared analysis also support the X-ray diffraction data. UV-Visible spectrum of the sample GMO300 shows absorption peak at 2.39 eV whereas the completely crystallized sample sintered at 800°C (GMO800) shows two absorption bands at 2.25 and 2.56 eV. These bands are attributed to the Mn (d-d) transitions. Higher energy bands at (3.27 and 4.94 eV) of GMO700 and (3.26, 4.40, 4.74 and 5.08 eV) of GMO800 are attributed to the charge transfer transitions from O(2p) to Mn(3d) state. Moreover, the completely crystallized sample (GMO800) exhibits the signature of magneto-dielectric coupling.

Size and strain dependent anatase to rutile phase transition in TiO2 due to Si incorporation

Powders with compositions Ti(1−x)SixO2 (where 0 ≤ x ≤ 0.25) were prepared to systematically study the effects of Si doping on anatase to rutile phase transformation. Samples were synthesized using a modified sol–gel route and were heat treated at various temperature in 450–950 °C range. XRD, Raman Spectroscopy, UV–vis spectroscopy, SEM, TEM were used to study the effects of dopant concentration and heat-treatments on the crystal structure, crystallite size and particle size. Rutile phase was found to occur only above a critical crystallite size. Si doping was found to delay the onset of anatase to rutile phase transformation from 500 °C (for composition x = 0) to 800 °C (for x = 0.25) through the lattice strain and crystallize size modification. Interplay between the average crystallite sizes, lattice strain, annealing temperature, and their effect on phase transition are discussed in terms of Si incorporation in lattice.

Active MgO-SiO2 hybrid material for organic dye removal: A mechanism and interaction study of the adsorption of C.I. Acid Blue 29 and C.I. Basic Blue 9

A comparative analysis was performed concerning the removal of two different organic dyes from model aqueous solution using an inorganic oxide adsorbent. The key element of the study concerns evaluation of the influence of the dyes’ structure and their acid-base character on the efficiency of the adsorption process. The selection of sorbent material for this research – an MgO-SiO2 oxide system synthesized via a modified sol-gel route – is also not without significance. The relatively high porous structure parameters of this material (ABET = 642 m2/g, Vp = 1.11 mL and Sp = 9.8 nm) are a result of the proposed methodology for its synthesis. Both organic dyes (C.I. Acid Blue 29 and C.I. Basic Blue 9) were subjected to typical batch adsorption tests, including investigation of such process parameters as time, initial adsorbate concentration, adsorbent dose, pH and temperature. An attempt was also made to estimate the sorption capacity of the oxide material with respect to the analyzed organic dyes. To achieve the objectives of the research – determine the efficiency of adsorption – it was important to perform a thorough physicochemical analysis of the adsorbents (e.g. FTIR, elemental analysis and porous structure parameters). The results confirmed the significantly higher affinity of the basic dye to the oxide adsorbents compared with the acidic dye. The regeneration tests, which indirectly determine the nature of the adsorbent/adsorbate interactions, provide further evidence for this finding. On this basis, a probable mechanism of dyes adsorption on the MgO-SiO2 oxide adsorbent was proposed.

Effect of gelatin on structural properties of lead-free piezoelectric (K0.5Na0.5) NbO3 nanopowders synthesized by a modified sol-gel route in gelatin media

Effect of gelatin on structural properties of lead-free piezoelectric (K0.5Na0.5) NbO3 nanopowders synthesized by a modified sol-gel route in gelatin media

Laser induced white emission generated by infrared excitation from Eu3+:Sr2CeO4 nanocrystals.

The laser induced white emission (LIWE) was observed from Eu3+:Sr2CeO4 nanocrystals. The samples were obtained in form of powders by the modified sol-gel route. The structure and morphology of the phosphors were investigated by powder X-ray diffraction and transmission electron microscope techniques. The intense LIWE occurred under reduced pressure and focused beam of near infrared laser excitation. The power and pressure dependencies exhibit evident threshold character typical for the avalanche effect. The photoconductivity of the Eu3+:Sr2CeO4 nanocrystals measured as a function of different powers of excitation source was analyzed.

Low-temperature synthesis of mesoporous nanocrystalline magnesium aluminate (MgAl2O4) spinel with high surface area using a novel modified sol-gel method

A simple, template-free and scalable modified sol-gel route was developed for the synthesis of mesoporous flake-like magnesium aluminate spinel (MgAl2O4) at low temperature (700°C) with high surface area (281m2g−1). The obtained spinel materials were characterized by means of physicochemical techniques including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and N2 adsorption-desorption analysis. The propylene oxide was used as gelation and pore forming agent in the sol-gel process. Different morphologies and sizes of flake were generated by the varied synthesis conditions. The result materials reveal that the textural properties of the MgAl2O4 product are strongly associated with the nature and amount of addictive solvent and calcination temperatures. It shows that the BET surface area decrease as the increase of calcination temperature and the optimal temperature of 700°C result in the pure phase of MgAl2O4 spinel. This synthesis strategy offers a feasible approach for scalable fabrication of mixed metal oxides for various catalytic reactions or catalyst supports due to the large surface area.

Photocatalytic Degradation of Organics by Using Nanocrystalline Titania

Titanium dioxide nanoparticles were prepared by a modified sol-gel route. Titanium butoxide was used as precursor and nebulizer was used for a fine spray of particles. The prepared powders were characterized by FT-IR, SEM, XRD, and TGA-DTA methods. The results indicated that nanoparticles with small size and high surface area were synthesized. XRD result indicated that TiO2nanoparticles were obtained in pure anatase crystalline form with a crystallite size of 40 nm. The catalytic activity of as-synthesized nanoparticles was tested for the degradation of formic acid and toluene.

Synthesizing nanostructured crack-free thick films of Fe-doped lead zirconate titanate by sol–gel dip coating method

Lead zirconate titanate is one of the most well-known ferroelectric oxides and has been widely used in nano/micro-electromechanical systems and piezoelectric industries. Doping the lead zirconate titanate thick films by Fe3+ as an acceptor dopant leads to hard lead zirconate titanate piezoelectrics for specific applications including high frequency transducers. In this article, Fe-doped lead zirconate titanate thick films with the thickness of 27 µm are synthesized by using a modified acetic acid/alcoholic based sol–gel method and applying diethanolamine as a complexing agent. Crystallographic measurements are performed considering lattice constants and lattice distortion of the films by means of X-ray diffraction. Pure perovskite phase is obtained by adding the dopant up to 5 at. % Fe. The tetragonal lattice distortion and lattice parameters decrease by adding Fe and reach to its minimum level of c t = 4.024 A and a t = 3.966 A at 3 at. % Fe. The surface morphology and grain size are surveyed using field emission scanning electron microscopy, which shows the reduction in grain size by adding the dopant. Polarization-voltage loops and dielectric constants of the films are calculated by electrical measurement and illustrate reduction in the polarization by increasing Fe dopant. The highest value of coercive voltage is achieved at 3 at. % Fe. Moreover, the lowest dielectric constant of 318 is obtained at 5 at. % Fe. Nanostructured crack-free Fe-doped PZT thick films are successfully prepared by using modified sol–gel route with different Fe dopant percentages (a) surface morphology of PF(3 %)ZT, (b) cross section of PZT thick film.

Novel and facile synthesis of transparent-monolithic TiO2 gels by sol-gel method based on an esterification reaction

AbstractTransparent TiO2 monoliths were obtained through a modified sol-gel route from titanium isopropoxide as a precursor. By controlling the hydrolysis of this precursor through the intermediate of esterification reaction between acetic acid and isopropanol at 40 °C, transparent TiO2 xerogel monoliths were obtained. The monoliths prepared by this method were transparent in the wavelengths between 400 nm and 700 nm. Fourier transform infrared (FT-IR) spectroscopy suggested that the acetic acid played also an active role as a chelating agent, forming Ti[(OH)y(OOCCH3)x] less reactive species. Powder X-ray diffraction confirmed the amorphous-to-anatase phase transformation with the formation of unknown Ti-containing complex at 90 °C. Only anatase TiO2 could be observed in the samples calcined at 250 °C and 450 °C. Optical aspects of the gel (transparent-transluscent transformation of monolithic gel) and gelation time were controlled by changing the amount of external water.

Biomimetic growth of hydroxylapatite on SiO2–PMMA hybrid coatings

A PMMA-SiO2–hybrid material was produced through a modified sol–gel route by using as precursors tetraethyl orthosilicate (TEOS), Methyl methacrylate (MMA) and 3-(Trimethoxysilyl)propyl methacrylate (TMSPM) as the coupling agent. The hybrid films were deposited by dip coating onto 316L stainless steel plates and then these substrates were immersed in a Simulated Body Fluid (SBF) at 5, 10, 15, 20 y 25 days at a constant temperature of 37°C and pH=7.4. The resulting hydroxylapatite (HAp) overgrown coatings were characterized by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. After 5 days of immersion in SBF the substrate is partially covered with HAp spherulites and after 15 days the surface is entirely and uniformly coated.

Improved performance of Ag-doped TiO2 synthesized by modified sol–gel method as photoanode of dye-sensitized solar cell

Ag-doped TiO2 with Ag content ranging from 1 to 7 mol% was synthesized by a modified sol–gel route, and its performance as the photoanode of dye-sensitized solar cells (DSSCs) was compared with undoped TiO2 photoanode. Titanium(IV)isopropoxide was used as precursor and hexamethylenetetramine as the capping agent. XRD results show the formation of TiO2 nanoparticles with an average crystallite size of 5 nm (1 % Ag-doped TiO2) and 9 nm (undoped TiO2), respectively. The TiO2 nanopowder was used to prepare its thin film photoelectrode using doctor’s blade method. Significant improvement in light-to-energy conversion efficiency was achieved when thin films of 1 % Ag-doped TiO2 were applied as photoanode in DSSC taking N719 as the sensitizer dye. As evidenced by EIS measurements, the electron lifetime of DSSC with Ag-doped TiO2 increased from 1.33 (for undoped TiO2) to 2.05 ms. The short-circuit current density (J sc), open-circuit voltage (V oc), fill factor (FF) and the overall energy conversion efficiency (η) were 1.07 mA cm−2, 0.72 V, 0.73 and 0.40 %, respectively, with the use of 1 % Ag-doped TiO2 photoanode, whereas with undoped TiO2 under similar conditions, J sc = 0.63 mA cm−2, V oc = 0.70 V, fill factor 0.45 and conversion efficiency 0.14 % could be obtained. Therefore, compared with the reference DSSC containing an undoped TiO2 photoanode, the power conversion efficiency of the cell based on Ag-doped TiO2 has been remarkably enhanced by ~70 %. The substantial improvement in the device performance is attributed to the reduced band-gap energy, retarded charge recombination and greater surface coverage of the sensitizing dye over Ag-doped TiO2, which ultimately resulted in improved IPCE, J SC and η values.

Sol–gel synthesis and in vitro bioactivity of glass–ceramics in SiO2–CaO–Na2O–P2O5 system

Bioactive glass–ceramic powder in SiO2–CaO–Na2O–P2O5 system was successfully synthesised through a modified sol–gel route. The gel was prepared using tetraethyl orthosilicate, calcium nitrate, sodium nitrate and triethyl phosphate raw materials. The gel was calcined in the temperature range 700–1050 °C to get the glass–ceramic powder. Dissolution of the glass–ceramic powder was studied by in vitro immersion in Tris buffer solution for various period of time. The biodegraded powder was analyzed using XRD. The sintered glass–ceramic was characterized for in vitro bioactivity in simulated body fluid, and the incubated pellet was then analyzed for phase identification by XRD, surface morphology using SEM and elemental analysis using energy-dispersive X-ray analysis. The biocompatibility of the glass–ceramics was evaluated through MTT assay using MG-63 cells.

Microwave dielectric properties of sol-gel derived CoTiNb2O8 ceramics

CoTiNb2O8 microwave dielectric ceramics were synthesized via a modified sol-gel route. The thermal decomposition behavior of the as-prepared precursor was characterized by differential thermal analysis (DTA)/thermogravimetry (TG). Highly reactive CoTiNb2O8 nano-powders with average particle size of 34 nm were achieved by the reaction between TiO2 and intermediate phase CoNb2O6 at 800 °C. The microwave dielectric properties of ceramics were sensitive to processing condition and crystal structure. For the CoTiNb2O8 compounds, the variations of εr and Q × f value agreed well with that of the relative density. The τf was explained in terms of oxygen octahedral distortion and B-site bond valence. At 1000°C/4h, CoTiNb2O8 ceramic possessed optimal microwave dielectric properties with an εr of 64.19, a high Q × f of 16,800 GHz (at 6.4 GHz) and a τf of 66.17 ppm/°C.

Synthesis of mesoporous TiO2 and its role as a photocatalyst in degradation of indigo carmine dye

A modified sol–gel route without the use of acid or base was used to synthesize mesoporous TiO2 catalyst which was characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force spectroscopy, optical absorption spectroscopy and Brunauer–Emmett–Teller adsorption isotherm technique. The synthesized mesoporous TiO2 is highly crystalline, pure and consisting of very high porosity and surface area 226.25 m2 g−1. The catalyst showed an excellent photocatalytic activity against the degradation of indigo carmine in the presence of visible light. It was found that 50 mL dye solution of 4 × 10−5 M concentration has been completely degraded and decolorized with optimum catalyst dose of 1.5 g/L in 180 min, acidic pH and at 25 ± 1 °C reaction temperature. The reaction kinetic was studied, and it was found that the indigo carmine dye photocatalytic degradation followed pseudo first-order reaction kinetics with rate constant, k of 0.007 min−1. Degradation of dye was confirmed by chemical oxygen demand analysis and UV–Vis spectrophotometry.

Gas sensing properties of Al-doped ZnO for UV-activated CO detection

Al-doped ZnO (AZO) samples were prepared using a modified sol–gel route and charaterized by means of trasmission electron microscopy, x-ray diffraction and photoluminescence analysis. Resistive planar devices based on thick films of AZO deposited on interdigitated alumina substrates were fabricated and investigated as UV light activated CO sensors. CO sensing tests were performed in both dark and illumination condition by exposing the samples to UV radiation (λ = 400 nm).Under UV light, Al-doped ZnO gas sensors operated at lower temperature than in dark. Furthermore, by photoactivation we also promoted CO sensitivity and made signal recovery of AZO sensors faster. Results demonstrate that Al-doped ZnO might be a promising sensing material for the detection of CO under UV illumination.

Synthesis of Zinc Oxide Thin Films by Modified Sol-Gel Route for Solar Water Splitting

Zinc oxide (ZnO) is one of the promising candidates for solar water splitting application. Due to immerging of nanotechnology, ZnO nanostructures have been extensively studied and the properties are still under debate. Vertically aligned ZnO nanorods (NRs) offer higher surface-to-volume ration compared to other shapes and become the most seeked by researches ever since. The facile growth of vertically aligned ZnO NRs thin films out of two different zinc salt, namely , zinc acetate and zinc nitrate using the modified sol-gel route were performed with the assistant of ultrasonic rinse. Sonication of ZnO NRs thin films has significant improvement on the structural and optical properties. Several sonication periods have been employed to synthesize these ZnO NRs thin films. Deposited ZnO NRs films were characterized under FE-SEM, AFM, XRD and UV-Vis. Comparative investigation performed on acetate and nitrate precursor materials showed a preferable (0 0 2) with homogeneous surface formation single crystal growth, high quality transparent thin film of 3.23 eV in acetate precursor material at 30 seconds sonication were reported in this paper.

Solar photocatalytic purification of water with Ce-doped TiO2/clay heterostructures

This work investigates the photocatalytic purification of water upon solar light over novel Ce-doped TiO2/clay heterostructures. These novel nanomaterials were prepared by a modified sol–gel route that allows, in a unique step, the formation of Ce-doped anatase nanoparticles and their assembling over an exfoliated clay material. Several synthesis parameters were optimized, including the anatase/clay ratio and the percentage of doping Ce incorporated. Remarkably enhanced activities toward the photodecomposition of several organic compounds were observed depending on the Ce and TiO2 contents. A synergistic effect has been observed among the textural properties, the amount of anatase formed and that of Ce doping.

CO sensing properties under UV radiation of Ga-doped ZnO nanopowders

In this study, the effect of Ga-doping and UV radiation on CO sensing of ZnO nano-powders has been investigated. GZO nanoparticles with different Ga loadings were prepared using a modified sol–gel route and charaterized by means of trasmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL) analysis. Electrical and CO-sensing tests were performed on resistive planar devices consisting of thick films of GZO deposited on interdigitated alumina substrates in both dark and illumination condition by exposing the samples to UV radiation (λ=400nm). The baseline resistance in dark decreases strongly with the increase of Ga loading. This effect is reinforced by using UV radiation at low temperature in samples containing up to 3at.% of Ga, which suggests also an effect of the microstructure of GZO on UV light promoting mechanism. The combined effect of Ga doping and UV irradiation allowed to monitor CO in air at low concentration with high sensitivity and lower operating temperature than on unpromoted ZnO sensor.

Permittivity of citrate sol–gel derived Bi2Ti4O11 dielectric ceramics

Bi2Ti4O11 microwave dielectric ceramics were synthesized by a modified sol–gel route. The thermal decomposition behavior of the as-prepared precursors was characterized by differential thermal analysis (DTA)/thermogravimetry (TG). Based on the XRD results, it could be concluded that Bi2Ti4O11 began to form at around 678°C by the reaction of TiO2 with intermediate phase Bi2Ti2O7. Bi2Ti4O11 particles with uniform spherical shape were obtained by calcining the xerogel at 750°C. XRD patterns of the ceramics sintered at various temperatures confirmed the formation of single Bi2Ti4O11 phase with monoclinic structure. The microwave dielectric properties of Bi2Ti4O11 ceramics were considerably affected by bulk density, ionic polarizability and microstructure. The Bi2Ti4O11 samples sintered at 1050°C reached the maximum relative density of 97.39% and possessed excellent microwave dielectric property with εr of 52.35, a high Q×f of 4850GHz, and a τf of −350ppm/°C, making them promising for applications in military microwave radar, dielectric resonator and mobile communication base station.

Enhanced photocatalytic activity of silver-doped nanoparticulate TiO2 thin films with respect to the method of doping

A nanoparticle photocatalysts based on silver-doped titanium dioxide were synthesized using a modified sol–gel route and also a dip-and-pull step photochemical method. The catalysts were characterized by UV/Vis absorption spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, electron microprobe analysis, and Raman spectroscopy. The effects of the experimental parameters on the photoreactivity of the catalysts were evaluated for the decolorization of Rhodamine B in water and by photoelectrochemistry. The activity results show that silver doping significantly promotes the photoreactivity of the titanium dioxide catalyst with some phase transformation from anatase to brookite. The enhanced photoactivity of new nanoparticulate photocatalysts is predominantly attributable to an improvement in crystallinity, band gap lowering, the nature of precursor materials used, and also the method of doping.