Particulate sol–gel synthesis and optical and electrical properties of CeO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> nanocomposite

CeO₂/TiO₂ nanocomposite was synthesized by particulate sol–gel method. The X-ray diffractogram shows the presence of cubic CeO₂ and anatase TiO₂ in the composite. The high resolution scanning electron micrographs reveal the nanoparticulate nature of the prepared composite. The composite absorbs UV light and exhibits near-band gap emission corresponding to TiO₂ and deep level emission due to crystal defects. The Nyquist plot displays two semicircular arcs indicating the material heterogeneity. The physicochemical characteristics of the synthesized nanocomposite are in favour of its application as an ingredient of sunscreen formulations; under UV light the photocatalytic activity of CeO₂/TiO₂ composite, tested through the degradation of rhodamine B, is very much less than that by pristine anatase TiO₂. Reduced adsorption of moisture by the nanocomposite is a possible reason for the observed very low photocatalytic activity.     

Preparation of highly stable TiO<Subscript>2</Subscript> sols and nanocrystalline TiO<Subscript>2</Subscript> films via a low temperature sol–gel route

Highly stable TiO₂ sols were prepared by adjusting the water-to-titanium molar ratio to ~4 in the process of hydrolysis and condensation of titanium isopropoxide in ethanol with HNO₃. Particularly, long-term stable TiO₂ sols were prepared without adding any chemical additives. Anatase TiO₂ nanocrystallites with sizes of 3–5 nm in diameter were uniformly dispersed in the stable sol. Crystallized TiO₂ films were successfully deposited on Si (100) using the stable sol via a dip-coating process with low temperature curing at as low as 100 °C. The synthesized TiO₂ sols and films are promising for use in flexible or dye-sensitized solar cells.     

Preparation of LiCoPO<Subscript>4</Subscript> powders and films via sol–gel

Lithium intercalation materials are of special interest as cathodes in rechargeable batteries. An uncomplicated sol–gel process has been used for the synthesis of Li–Co phosphates powders and, for the first time, of LiCoPO₄ films. The powders were prepared from aqueous solutions, containing Li, Co and phosphate precursors to which acid citric and ethylene glycol was added, during the drying process at 75 °C. The X-ray diffraction patterns of the prepared powders confirmed the presence of LiCoPO₄ with an olivine-like structure as main phase. The morphological investigations of the powder showed a platelet-like structure with an average grain size of 0.75 μm. The films of LiCoPO₄ were deposited onto ITO glass substrates with the combination of the dip-coating process under the same conditions. Finally, the films were annealed in inert atmosphere at 300 °C. The morphological investigations reveal a smooth and homogeneous surface of the prepared Li–Co phosphate films. The preliminary electrical investigation on the prepared LiCoPO₄ films showed lithium ions electrochemical activity in the range 3.0–4.5 V.     

Preparation and characterization of TiO<Subscript>2</Subscript> hybrid sol for UV-curable high-refractive-index organic–inorganic hybrid thin films

In this study, UV-curable hybrid thin films were successfully prepared from TiO₂ and TiO₂ hybrid sols containing the acrylic monomer DPHA on PMMA substrates. The prepared TiO₂ and TiO₂ hybrid sols showed long-term storage stability and can provide operating control for the preparation of high-refractive-index hybrid thin films. The existence of interaction between the TiO₂ particle and the coupling agent was evidenced by FT-IR and UV–visible spectra. All hybrid thin films showed good adhesion to the PMMA substrate with refractive index falling over the range 1.64–1.77. These results suggested the potential application of present TiO₂ hybrid films in optical devices, such as anti-reflective coatings.     

Bandgap modification of TiO<Subscript>2</Subscript> sol–gel films by Fe and Ni doping

Nickle and iron doped TiO₂ thin films were prepared on glass substrates by sol–gel dip coating process. Indirect and direct optical energy gaps were calculated with the incorporation of different concentrations of both the ions. Indirect bandgap was found to be a strong function of the dopant concentration, whereas direct energy gap has negligible dependence on the nature of dopant and its concentration. Direct energy gap has always been found to retain a value higher than the indirect energy gap. Variation of observed energy gap properties shows a trend similar to that reported on the basis of numerical calculations or the samples obtained by other techniques. Increase in refractive index and corresponding density of the film sample does not support the change in turn over frequency. The influence of crystalline phase change is also ruled out by XRD investigations. It is concluded that red shift of band edge absorption takes place by incorporation of dopant and sol–gel dip coating technique offers an effective low cost route to the production of these coatings.     

Preparation and characterization of In<Subscript>2</Subscript>S<Subscript>3</Subscript> semiconductor thin films using the sol–gel method

This study describes the In₂S₃ semiconductor thin film coating on glass substrate by sol–gel method. The In₂S₃ thin film samples were prepared and examined by the X-ray diffraction (XRD), the UV–visible optical absorption and transmission study, and the Scanning Electron Microscope (SEM) image analyses. The XRD analysis results show that the In₂S₃ semiconductor thin films prepared by sol–gel method is formed at T~360–520 °C temperature interval. Band gap energy and optical absorption spectrum analysis of the In₂S₃ thin films reveal that Eg~2.51 eV for the In₂S₃ thin films. According to the EDX result the film was In-rich with the In/S = 1.42 ratio. The thickness of prepared In₂S₃ layer is about 400 nm.     

Characterization of TiO<Subscript>2</Subscript> powders and thin films prepared by non-aqueous sol–gel techniques

Stable TiO₂ sols were prepared using two non-aqueous sol–gel processes with titanium n-butoxide and titanium isopropoxide, respectively. Crystallization and phase transitions of powders and thin films were studied by ex situ and in situ X-ray diffraction. For both methods, TiO₂ began to crystallize around 320 °C in air. Using helium instead of air during heat treatment slowed down the crystallization and substoichiometric powders were formed. TiO₂ thin films were obtained by spin coating. The morphology of the films was evaluated using scanning electron microscopy. The films were homogeneous and transparent in the visible range. The effect of the heating atmosphere and the type of substrate was investigated.     

Oxalic acid sensors based on sol–gel nanostructured TiO<Subscript>2</Subscript> films

Titanium (IV) oxide semiconducting layers were prepared by means of the templated sol–gel method and deposited on conductive ITO substrates. The films were described by a series of techniques involving X-ray diffraction (XRD), Raman spectroscopy, X-ray reflectivity (XRR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and ultraviolet–visible spectroscopy (UV–Vis). The photo-excitation properties of the films were characterized by electrochemical tests and evaluated from the obtained polarization curves. The generated photocurrents were measured in the presence of the hole-scavengers—oxalic acid and formic acid in the electrolyte. It was shown that especially in the case of oxalic acid the developed system can be used as an efficient and simpler concentration sensor. The relationship between values of the generated photocurrent and the layers’ thicknesses was also investigated.     

Preparation of Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin films by sol–gel technique

In this study we describe the preparation of Ga₂Se₃ semiconductor compound thin films by sol–gel method for different crystal formation temperatures. The films were characterized by X-ray diffraction analyses (XRD), UV–visible spectrometer, and scanning electron microscope (SEM). The XRD spectrum showed that the formation of Ga₂Se₃ crystals were between 743 and 823 K. The thin film crystals that were formed at 773 K corresponded to the β phase and the preferred crystal structure was monoclinic. The value of band gap from optical absorption spectra for the Ga₂Se₃ thin films was estimated to be about E _g ~ 2.56 eV. The thickness of the one-coat Ga₂Se₃ thin films, which was measured by a Spectroscopic Ellipsometer, was about ~200 nm. The average grain sizes of scattered particles were within the limits between 200 and 500 nm.     

Preparation and characterisation of NdAlO<Subscript>3</Subscript> nanocrystals by modified sol–gel method

Nanocrystalline single-phase neodymium monoaluminate (NdAlO₃) has been prepared from neodymium oxide and aluminium nitrate by modified Pechini’s method. Malic acid has been used for the first time as a new complexing agent in the sol–gel process. It has facilitated, without adding 1,2-ethanediol, a low-temperature synthesis at 1,050 °C compared to the temperature of 1,630 °C needed for the solid-state preparation. The characterisation of the nanoparticles has been carried out by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy in the range 75–4,000 cm⁻¹. The smallest particles have size of 30 nm and are anisometric; agglomerates of particles have been also observed. The material has pyknometric density of 3.956 g/cm³ at T = 293.15 K and specific surface area 5.2 m²/g. The binding energies of O 1s, Al 2p, Nd 3d, and Nd 4d electrons have been found chemically shifted in NdAlO₃ compared to the values for the respective elements.     

Synthesis and characterization of spinel-type CuAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystalline by modified sol–gel method

Nanocrystalline Copper aluminate (CuAl₂O₄) was prepared by sol–gel technique using aluminum nitrate, copper nitrate, diethylene glycol monoethyl ether and citric acid were used as precursor materials. This method starts from of the precursor complex, and involves formation of homogeneous solid intermediates, reducing atomic diffusion processes during thermal treatment. The formation of pure crystallized CuAl₂O₄ nanocrystals occurred when the precursor was heat-treated at 600 °C in air for 2 h. The stages of the formation of CuAl₂O₄, as well as the characterization of the resulting compounds were done using thermo–gravimetric analysis, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The products were analyzed by transmission electron microscopy and ultraviolet–visible (UV–Vis) spectroscopy to be round, about 17–26 nm in size and E _g = 2.10 eV.     

Synthesis and characterization of novel InVO<Subscript>4</Subscript>–TiO<Subscript>2</Subscript> thin films using the low temperature sol

The InVO₄ sol was obtained by a mild hydrothermal treatment (the precursor precipitation solution at 423 K, for 4 h). Novel visible-light activated photocatalytic InVO₄–TiO₂ thin films were synthesized through a sol–gel dipping method from the composite sol, which was obtained by mixing the low temperature InVO₄ sol and TiO₂ sol. The photocatalytic activities of the new InVO₄–TiO₂ thin films under visible light irradiation were investigated by the photocatalytic discoloration of methyl orange aqueous solution. The thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–Vis absorption spectroscopy (UV–Vis). The results revealed that the InVO₄ doped thin films enhanced the methyl orange degradation rate under visible light irradiation, 3.0 wt% InVO₄–TiO₂ thin films reaching 80.1% after irradiated for 15 h.     

Structural and optical characterization of Zn doped TiO<Subscript>2</Subscript> nanoparticles prepared by sol–gel method

Undoped and zinc-doped TiO₂ nanoparticles (Ti_1−xZn_xO₂ where x = 0.00–0.10) were synthesized by a sol–gel method. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV–VIS spectrometer. XRD pattern confirmed the tetragonal structure of synthesized samples. Average grain size was determined from X-ray line broadening using the Debye–Scherrer relation. The crystallite size was varied from 10 to 40 nm as the calcination temperature was increased from 350 to 800 °C. The incorporation of 3–5 mol% Zn²⁺ in place of the Ti⁴⁺ provoked a slight decrease in the size of nanocrystals as compared to undoped TiO₂. The SEM and TEM micrographs revealed the agglomerated spherical-like morphology with a diameter of about 10–30 nm and length of several nanometers, which is in agreement with XRD results. Optical absorption measurements indicated a blue shift in the absorption band edge upon 3–5 mol% zinc doping. Direct allowed band gap of undoped and Zn-doped TiO₂ nanoparticles measured by UV–VIS spectrometer were 2.95 and 3.00 eV at 550 °C, respectively.     

Simple sol–gel route to synthesis of mesoporous TiO<Subscript>2</Subscript>

Mesoporous TiO₂ with a high specific surface area was prepared from titanium sulfate solution in a simple sol–gel route, where formamide was used as pH adjusting agent. TiO₂ had a high resistance to phase transformation, and maintained monophasic anatase after calcinating at 600 °C. The highest specific surface area achieved on the prepared samples is 231.90 m² g⁻¹ after calcinating at 450 °C.     

Tribological performance of fluoroalkylsilane modification of sol–gel TiO<Subscript>2</Subscript> coating

This paper explores the possibility of making coatings with super friction-reducing and wear protection properties by using both sol–gel and self-assembling techniques. The thin film of TiO₂ was firstly prepared on glass substrates via a sol–gel method, followed by sintering at 480°C. The self-assembled monolayer of Fluoroalkylsilane (FAS) were then prepared on TiO₂ thin film to obtain TiO₂–FAS dual-layer film. The contact angle measurement and X-ray photoelectron spectroscopy were used to determine the wetting behavior and chemical structure of films, respectively. The friction behavior of films sliding against a steel ball was examined on a macro friction and wear tester. It is shown that FAS is strongly adsorbed on sol–gel derived TiO₂ thin film, making it strongly hydrophobic. Good friction-reducing and wear protection behavior is observed for the glass substrate after duplex surface-modification with sol–gel TiO₂ and top layer of FAS.     

Preparation of nanocrystalline CuAlO<Subscript>2</Subscript> through sol–gel route

Nanocrystalline powders of CuAlO₂ were synthesized through sol–gel method using nitrate-citrate route and also through solid state reaction method. We used a new set of precursor materials for the synthesis of CuAlO₂ through sol–gel route which were not reported in the past. A little lowering of the synthesis temperature (1,000 °C) was observed in case of sol–gel process compared to the solid state reaction method (1,100 °C) and also at shorter time duration. The particle size of the synthesized powders was determined through small angle X-ray scattering. It has been observed that the particle size prepared by nitrate-citrate technique is less than the particle size prepared by the solid-state reaction method. Chemical states of the atomic species were determined by X-ray photoelectron spectroscopy. The formation of phase pure CuAlO₂ were also confirmed by Fourier transformed infrared spectroscopy. A number of solvents were also used for finding the best possible combinations for obtaining phase pure CuAlO₂ at 1,000 °C and it was observed that only the combination of nitrate salts, citric acid and ethanol resulted phase pure CuAlO₂.     

Structural and optical characterization of sol–gel derived boron doped Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanostructured films

Pure and boron (B) doped iron oxide (Fe₂O₃) nanostructured thin films were prepared by sol–gel spin coating method. The effects of B (0.1, 0.2, 0.5 and 1 %) content on the crystallinity and morphological properties of Fe₂O₃ films were investigated by X-ray diffractometer and atomic force microscopy. X-ray diffraction patterns revealed that the Fe₂O₃ films have a rhombohedral crystalline phase of α-Fe₂O₃ phase (hematite) with nanostructure and their crystallite size (D) is changed from 27 ± 2 to 45 ± 5 nm with B dopant content. The minimum crystallite size value of 27 ± 2 nm was obtained for 0.2 % B doped Fe₂O₃ film. Carrying out UV–VIS absorption study for both doped and undoped films at room temperature, it was realized that allowed optical transitions may be direct or indirect transitions. The direct and indirect energy gap values for pure Fe₂O₃ were obtained to be 2.07 and 1.95 eV, respectively. The optical band gap value of the films was changed with 0.1 % B doping to reach 1.86 eV for direct band gap and 1.66 eV in case of indirect band gap.     

Sol–gel synthesis and characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> nanocrystalline powder

Al₂O₃–TiO₂ nanocrystalline powders were synthesized by sol–gel process. Aluminum sec-butoxide and titanium isopropoxide chemicals were used as precursors and ethyl acetoacetate was used as chelating agent. Thermal and crystallization behaviors of the precursor powders were investigated by thermal gravimetric-differential thermal analysis, Fourier-transform infrared spectrum and X-ray diffraction. The average crystalline size of heat treated Al₂O₃–TiO₂ powders at 1,100 °C is ~100 nm.