Influence of annealing process on conductive properties of Nb-doped TiO2 polycrystalline films prepared by sol-gel method

Nb-doped TiO₂ (TNO) thin films were prepared by sol-gel dip-coating method with Nb content in a wide range of 0-20 at.%. The prepared films were preheated at 400 °C and then undertaken by two different post-annealing processes: (a) three times vacuum annealing and (b) multi-round annealing. The designed multi-round annealing was shown to be an effective way to improve the conductive properties of the films, compared to the traditional vacuum annealing process. The minimum resistivity reached approximately 0.5 Ω cm with Nb doping concentration around 12 at.%, and the carrier density increased with Nb-doping concentration until the critical point of 12 at.%, which might be the optimal doping content for our TNO films prepared by sol-gel method.     

Correlation between microstructure and optical properties of nano-crystalline TiO2 thin films prepared by sol-gel dip coating

Titanium dioxide thin films have been prepared from tetrabutyl-orthotitanate solution and methanol as a solvent by sol-gel dip coating technique. TiO₂ thin films prepared using a sol-gel process have been analyzed for different annealing temperatures. Structural properties in terms of crystal structure were investigated by Raman spectroscopy. The surface morphology and composition of the films were investigated by atomic force microscopy (AFM). The optical transmittance and reflectance spectra of TiO₂ thin films deposited on silicon substrate were also determined. Spectroscopic ellipsometry study was used to determine the annealing temperature effect on the optical properties and the optical gap of the TiO₂ thin films. The results show that the TiO₂ thin films crystallize in anatase phase between 400 and 800 °C, and into the anatase-rutile phase at 1000 °C, and further into the rutile phase at 1200 °C. We have found that the films consist of titanium dioxide nano-crystals. The AFM surface morphology results indicate that the particle size increases from 5 to 41 nm by increasing the annealing temperature. The TiO₂ thin films have high transparency in the visible range. For annealing temperatures between 1000 and 1400 °C, the transmittance of the films was reduced significantly in the wavelength range of 300-800 nm due to the change of crystallite phase and composition in the films. We have demonstrated as well the decrease of the optical band gap with the increase of the annealing temperature.     

Annealing temperature effect on the properties of mercury-doped TiO2 films prepared by sol-gel dip-coating technique

This work presents the annealing temperature effect on the properties of mercury (Hg)-doped titanium dioxide (TiO₂). Thin films and polycrystalline powders have been prepared by sol-gel process. The structure, surface morphology and optical properties, as a function of the annealing temperature, have been studied by atomic force microscopy (AFM), Raman, reflectance and ellipsometric spectroscopies. In order to determine the transformation points, we have analyzed the xerogel-obtained powder by differential scanning calorimetry (DSC). Raman spectroscopy shows the crystalline anatase and rutile phases for the films annealed at 400 °C and 1000 °C respectively. The AFM surface morphology results indicate that the particle size increases from 14 to 57 nm by increasing the annealing temperature. The complex index and the optical band gap (E_g) of the films were determined by the spectroscopic ellipsometry analysis. We have found that the optical band gap decreases by increasing the annealing temperature.     

Morphology and natural wettability properties of sol-gel derived TiO2-SiO2 composite thin films

Previous studies suggest that granular interfaces induce a natural and persistent super-hydrophilicity in TiO₂-SiO₂ composite thin films deposited by sol-gel route. This effect enables to consider self-cleaning applications that do not require a permanent UV exposure, whereas such a permanent exposure is necessary for pure TiO₂ films. In this study, TiO₂-SiO₂ composite thin films have been deposited from a TiO₂ anatase crystalline suspension and different SiO₂ polymeric sols. Wettability studies show that a suitable control of the TiO₂-SiO₂ mixed sol formulations noticeably enhances persistence of the natural super-hydrophilicity in composite films. It is shown that, beside granular interface effects, modifications in the composite film morphologies can noticeably influence wettability properties.     

Preparation of continuous TiO2 fibers by sol-gel method and its photocatalytic degradation on formaldehyde

The continuous TiO₂ fibers were prepared by sol-gel method using the tetrabutyl orthotitanate as the precursor. The sol-formation process is studied by FT-IR spectroscopy. The synthesized continuous TiO₂ fibers were characterized using SEM, HRTEM and XRD. Results demonstrate that the titanate sol has good spinnability when R ≤ 2 (R = H₂O:Ti(OC₄H₉)₄, molar ratio). The fibers have the length of several meters and the diameter of about 30 μm. The fibers are a radial close-packed product of nano-particles with high crystallinity. The continuous TiO₂ fibers are co-crystal including anatase phase and rutile phase. The formaldehyde degradation ratio of continuous TiO₂ fiber was 98.6%.     

Structure and photoluminescence properties of Er3+-doped TiO2-SiO2 powders prepared by sol-gel method

Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions.     

Synthesis of fluorinated TiO2 hollow microspheres and their photocatalytic activity under visible light

Fluorinated TiO₂ hollow microspheres with three-dimensional hierarchical architecture were prepared by solvothermally treatment using solid microspheres as precursor. The obtained solid and hollow TiO₂ microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectrum (DRS) and photoluminescence (PL) spectra. The photocatalytic activity of as-prepared solid and hollow TiO₂ microspheres was determined by degradation of methyl orange (MO) under visible light irradiation. The results showed that the surface fluorination, the existence of accessible mesopores channels, and the increased light harvesting abilities could remarkably improve the photocatalytic activity of TiO₂ hollow microspheres.     

Comparison of photocatalytic performance of anatase TiO2 prepared by low and high temperature route

Anatase TiO₂ was prepared by a facile sol-gel method at low temperature through tailoring the pH of sol-gel without calcination. As a control, anatase TiO₂ was also synthesized by the conventional sol-gel process, in which calcination at 500 °C was required to transform the amorphous oxide into highly crystalline anatase. As-prepared samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). Their photocatalytic activities were evaluated by degradation of methyl orange under UV light irradiation. On the basis of experiment results, it could be concluded that TiO₂ prepared by low temperature route showed more advantages in small particle size, highly dispersion nature, abundance of surface hydroxyl groups, strong PL signal, and high photocatalytic activity over TiO₂ obtained by the conventional sol-gel process. Furthermore, the reason of the former possessing higher photocatalytic activity was discussed.     

Structural study of sol-gel Au/TiO2 films from nanopowders

TiO₂ represents one of the most important sol-gel materials, due to its photocatalytic properties, in the case of both powders and coatings. Nanostructured titania has been reported to be used in many applications in different fields ranging from optics to gas sensor via solar energy. Recent researches point out the existence of new procedures used in order to enhance the efficiency of the photocatalytic process. The metal ion doping is such an example. Two types of 2 wt.% Au containing TiO₂ powders have been embedded in sol-gel vitreous TiO₂ matrices. Au-doped TiO₂ films have been prepared from these sols, by dipping procedure using quartz microscopic slides, as substrates. The relationship between the synthesis conditions and the properties of titania nanosized materials, such as thermal stability, phase composition, crystallinity, and the influence of dopant was investigated. The hydrophilic properties of the films were correlated with their structure, composition and surface morphology.     

Influence of the OH groups on the photocatalytic activity and photoinduced hydrophilicity of microwave assisted sol-gel TiO2 film

In the present work the influence of the OH groups on the photocatalytic activity and the photoinduced hydrophilicity of microwave assisted sol-gel TiO₂ films was investigated. The prepared TiO₂ films were characterized using XRD and AFM. Furthermore, the surface of the TiO₂ films was examined by help of XPS in order to determine the amount of OH groups before and after UV irradiation at different humidities. The activity of the TiO₂ films was determined using stearic acid as a model compound and the photoinduced superhydrophilicity was investigated through contact angle measurements.The results of this investigation showed that the microwave assisted sol-gel technique produces highly homogeneous and efficient TiO₂ films without the need for heat treatment for crystallization. Based on the conducted experiments it is suggested that the amount of OH groups on the TiO₂ surface highly influence the photocatalytic activity and the photoinduced superhydrophilicity and that the two mechanisms may be closely related. It is suggested that the superhydrophilicity is obtained through a combination of photocatalytic degradation of organic contaminants and surface structural changes in form of an increased amount of OH-groups.     

Enhanced photocatalytic activity of TiO2 nano-structured thin film with a silver hierarchical configuration

TiO₂ sol-gels with various Ag/TiO₂ molar ratios from 0 to 0.9% were used to fabricate silver-modified nano-structured TiO₂ thin films using a layer-by-layer dip-coating (LLDC) technique. This technique allows obtaining TiO₂ nano-structured thin films with a silver hierarchical configuration. The coating of pure TiO₂ sol-gel and Ag-modified sol-gel was marked as T and A, respectively. According to the coating order and the nature of the TiO₂ sol-gel, four types of the TiO₂ thin films were constructed, and marked as AT (bottom layer was Ag modified, surface layer was pure TiO₂), TA (bottom layer was pure TiO₂, surface layer was Ag modified), TT (pure TiO₂ thin film) and AA (TiO₂ thin film was uniformly Ag modified). These thin films were characterized by means of linear sweep voltammetry (LSV), X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy and transient photocurrent (I_ph). LSV confirmed the existence of Ag⁰ state in the TiO₂ thin film. SEM and XRD experiments indicated that the sizes of the TiO₂ nanoparticles of the resulting films were in the order of TT > AT > TA > AA, suggesting the gradient Ag distribution in the films. The SEM and XRD results also confirmed that Ag had an inhibition effect on the size growth of anatase nanoparticles. Photocatalytic activities of the resulting thin films were also evaluated in the photocatalytic degradation process of methyl orange. The preliminary results demonstrated the sequence of the photocatalytic activity of the resulting films was AT > TA > AA > TT. This suggested that the silver hierarchical configuration can be used to improve the photocatalytic activity of TiO₂ thin film.     

Photocatalysis and wave-absorbing properties of polyaniline/TiO2 microbelts composite by in situ polymerization method

Polyaniline (PANI)/TiO₂ composite is prepared by in situ polymerization of polyaniline on the surface of TiO₂ template obtained by the sol-gel process via cotton template. The TiO₂ microbelts are prepared by sol-gel method using the absorbent cotton as template for the first time. Then the TiO₂ microtubules are used as template for the preparation of polyaniline/TiO₂ composites. The structure, morphology and properties of the composites are characterized with scanning electron microscope (SEM), IR, Net-wok Analyzer. A possible formation mechanism of TiO₂ microtubules and polyaniline/TiO₂ composites has been proposed. The effect of the mol ratio of polyaniline/TiO₂ on the microwave loss properties and photocatalysis properties of the composites is investigated.     

Effect of TiO2/Al2O3 film coated diamond abrasive particles by sol-gel technique

The diamond abrasive particles were coated with the TiO₂/Al₂O₃ film by the sol-gel technique. Compared with the uncoated diamonds, the TiO₂/Al₂O₃ film was excellent material for the protection of the diamonds. The results showed that the incipient oxidation temperature of the TiO₂/Al₂O₃ film coated diamonds in air atmosphere was 775 °C, which was higher 175 °C than that of the uncoated diamonds. And the coated diamonds also had better the diamond's single particle compressive strength and the impact toughness than that of uncoated diamonds after sintering at 750 °C. For the vitrified bond grinding wheels, replacing the uncoated diamonds with the TiO₂/Al₂O₃ film coated diamonds, the volume expansion of the grinding wheels decreased from 6.2% to 3.4%, the porosity decreased from 35.7% to 25.7%, the hardness increased from 61.2H_RC to 66.5H_RC and the grinding ratio of the vitrified bond grinding wheels to carbide alloy (YG8) increased from 11.5 to 19.1.     

溶胶-凝胶法制备MgO/(Ba0.8Sr0.2)TiO3多层薄膜及其介电和漏电特性研究

采用改进的溶胶-凝胶方法在LaNiO₃/Si(100)衬底上制备了MgO/(Ba_{0.8Sr0.2)TiO3多层薄膜.实验结果表明，MgO层的引入改变了(Ba0.8}Sr_0.2)TiO₃的介电特性和漏电流行为，使薄膜的漏电 流降低了3个数量级，但介电常数也有相应降低.漏电流的显著降低是由MgO子层的高阻特性 以及微量Mg向(Ba_0.8关键词： 0.8Sr_0.2)TiO₃多层薄膜')" href="#">MgO/(Ba_0.8Sr_0.2)TiO₃多层薄膜 漏电流 介电常 数     

Oblique angle deposition of TiO2 thin films prepared by electron-beam evaporation

Optical, structural and photocatalytic properties of TiO₂ thin films obliquely deposited on quartz glass substrate using an electron-beam evaporation method were investigated. The photocatalytic activity of the films was evaluated by photodecomposition of methylene blue. An increase in incident deposition angle increased the porosity and surface roughness of the TiO₂ films. As a result, the photocatalytic activity was enhanced with incident deposition angle up to 60°. However, a further increase in incident deposition angle to 75° reduced the photocatalytic activity due to a lack of the crystalline phase.     

Optical and hydrophilic properties of Cr doped TiO2-SiO2 nanostructure thin film

Cr doped TiO₂-SiO₂ nanostructure thin film on glass substrates was prepared by a sol-gel dip coating process. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the structural and chemical properties of the films. A UV-vis spectrophotometer was used to measure the transmittance spectra of the thin film. The hydrophilicity of the thin film during irradiation and storage in a dark place was measured by a contact angle analyzer. The results indicated that Cr doping has a significant effect on the transmittance and super-hydrophilicity of TiO₂-SiO₂ thin film.     

Visible-light photocatalytic activity of nitrogen-doped TiO2 thin film prepared by pulsed laser deposition

Nitrogen-doped titanium dioxide (TiO_2−xN_x) thin films have been prepared by pulse laser deposition on quartz glass substrates by ablated titanium dioxide (rutile) target in nitrogen atmosphere. The x value (nitrogen concentration) is 0.567 as determined by X-ray photoelectron spectroscopy measurements. UV-vis spectroscopy measurements revealed two characteristic deep levels located at 1.0 and 2.5 eV below the conduction band. The 1.0 eV level is attributable to the O vacancy state and the 2.5 eV level is introduced by N doping, which contributes to narrowing the band-gap by mixing with the O2p valence band. The enhanced degradation efficiency in a broad visible-light range was observed from the degradation of methylene blue and methylene orange by the TiO_2−xN_x film.     

Enhancement of the photocatalytic activity of TiO2 nanoparticles by surface-capping DBS groups

TiO₂ nanoparticles capped with sodium dodecylbenzenesulfonate (DBS) are synthesized by a sol-hydrothermal process using tetrabutyl titanate and DBS as raw materials. The effects of surface-capping DBS on the surface photovoltage spectroscopy (SPS), photoluminescence (PL) and photocatalytic performance of TiO₂ nanoparticles are principally investigated together with their relationships. The results show that the surface of TiO₂ nanoparticles can be well capped by DBS groups while the pH value and added DBS amount are controlled at 5.0 and 2% of TiO₂ mass weight, respectively, and the linkage between DBS groups and TiO₂ surfaces is mainly by means of quasi-sulphonate bond. The intensities of SPS and PL spectra of TiO₂ obviously decrease after DBS-capping, while the activity can greatly increase during the photocatalytic degradation of Rhodamine B (RhB) solution, which are mainly attributed to the electron-withdrawing character of the DBS groups. Moreover, the enhancement of photocatalytic activity of DBS-capped TiO₂ is also related to the increase in the capability for adsorbing RhB.     

Microstructural, optical and photocatalytic properties of CdS doped TiO2 thin films

CdS doped TiO₂ thin films (with CdS content=0, 3, 6, 9 and 12 at%) were grown on glass substrates. The X-ray diffraction analysis revealed that the films are polycrystalline of monoclinic TiO₂ structure. The microstructure parameters of the films such as crystallite size (D_ν) and microstrain (e) are calculated. Both the crystallites size and the microstrain are decreased with increasing CdS content. The optical constants have been determined in terms of Murmann's exact equations. The refractive index and extinction coefficient are increased with increasing CdS content. The optical band gap is calculated in the strong absorption region. The possible optical transition in these films is found to be an allowed direct transition. The values of E_g^opt are found to decrease as the CdS content increased. The films with 3 at% CdS content have better decomposition efficiency than undoped TiO₂. The films with 6 at% and 9 at% CdS content have decomposition efficiency comparable to that of undoped TiO₂, although they have lower band gap. The CdS doped TiO₂ could have a better impact on the decomposing of organic wastes.     

Microstructures and magnetic properties of CoPt-TiO2 nanocomposite films prepared by annealing CoPt/TiO2 multilayers

CoPt-TiO₂ nanocomposite films were synthesized by rapid thermal annealing of CoPt/TiO₂ multilayers. The effects of annealing temperature, annealing time, Ag addition and TiO₂ volume fraction on the microstructures and magnetic properties of the CoPt-TiO₂ nanocomposite films were studied. Results showed that the ordering degree of CoPt and coercivity of CoPt-TiO₂ nanocomposites increased with annealing temperature. Increasing annealing time and Ag addition were able to increase the ordering degree and coercivity of CoPt. However, complete L1₀-ordering of CoPt at 550 °C annealing was not realized by increasing annealing time up to 30 min and Ag addition up to 30 vol.%. Increasing TiO₂ volume fraction at 700 °C annealing did not lead to the change of ordering of CoPt. However, the grain structure of the films changed slightly when TiO₂ volume fraction was larger than 56%. The coercivity of the film decreased slightly with the addition of TiO₂.