Nm For Anatase Research Articles

Strongly Bound Frenkel Excitons on TiO2 Nanoparticles: An Evolutionary and DFT Approach

An evolutionary algorithm was employed to locate the global minimum of TiO2n nanoparticles with n=2–20. More than 61,000 structures were calculated with a semiempirical method and reoptimized using density functional theory. The exciton binding energy of TiO2 nanoparticles was determined through the fundamental and optical band gap. Frenkel exciton energy scales as EB eV=8.07/n0.85, resulting in strongly bound excitons of 0.132–1.2 eV for about 1.4 nm nanoparticles. Although the exciton energy decreases with the system size, these tightly bound Frenkel excitons inhibit the separation of photogenerated charge carriers, making their application in photocatalysis and photovoltaic devices difficult, and imposing a minimum particle size. In contrast, the exciton binding energy of rutile is 4 meV, where the Wannier exciton energy scales as EB eV=13.61 μ/ε2. Moreover, the Wannier excitons in bulk TiO2 are delocalized according to the Bohr radii: 3.9 nm for anatase and 7.7 nm for rutile.

Effect of Temperature Sintering on Grain Growth and Optical Properties of TiO2 Nanoparticles

Titanium dioxide (TiO2) nanoparticles were prepared by the sol–gel method and the structural, morphological, and optical properties were investigated at different sintering temperatures of 500, 600, 700, 800, and 900°C. A tetragonal structure of anatase, mixed (anatase–rutile), and rutile phases are observed in the X-ray diffraction (XRD) analysis. Pure anatase phase formation occurred at 500°C, whereas anatase-to-rutile phase transformation began at 600°C, and reaching complete conversion to rutile at 800°C. The average crystallite size increased from 23 to 34 nm for anatase and 38 to 62 nm for the rutile when sintering temperature increased from 500 to 900°C. The scanning electron microscope (SEM) result presented the increase of grain size (25–100 nm) with increasing the sintering temperature. The Fourier transform infrared (FTIR) spectra demonstrated the presence of TiO2 vibrational bonds in all samples. The optical bandgaps of the sintered TiO2 nanoparticles decreased with rising sintering temperature. Photoluminescence spectra exhibited three characteristic peaks centered at 380, 450, and 550 nm. The emission intensity increased with increasing the sintering temperature. The Mie analysis was also studied to calculate scattering cross-section, forward scattering, and asymmetry for different grain sizes. The results showed that by increasing the nanoparticle diameters, the peaks of all spectra are redshifted for larger grain sizes and cross-section peaks shift to high values. In this study, the sintering temperature is observed to have a strong influence on crystalline phase transformation, microstructure, and optical properties of TiO2 nanoparticles. The TiO2 sample sintered at 900°C shows the best result to be used as luminescent material due to the low optical bandgap energy.

Heat-assisted sol–gel synthesis of tio2 nanoparticles structural, morphological and optical analysis for self-cleaning application

This study synthesized TiO2 nanoparticles using the sol–gel method assisted by heat from Titanium (IV) Isopropoxide. Samples were calcined at 400, 600, and 800 °C, and studied for self-cleaning application. The nanoparticles were characterized using X-ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and UV–vis spectroscopy. A self-cleaning application test was also performed using methylene blue dye as a form of contaminant. The TiO2 nanoparticles showed improved crystallinity with increased calcination temperature and experienced a phase transformation from anatase to rutile after 800 °C calcination. Crystallite size ranged from 5.11 to 24.97 nm for anatase and 15.85 to 24.72 nm for the rutile from the XRD result. Raman spectra showed increased peak intensities with an increase in calcination temperature. The grain size distribution from TEM analysis revealed the particle size with the uniform count at 400 °C and 800 °C than at 600 °C. The bandgap for direct transition was evaluated to be 3.07 eV. The self-cleaning test confirmed that the TiO2 nanoparticles would be effective in self-cleaning applications. The sample that was calcined at 600 °C displayed the highest self-cleaning ability.

Facile synthesis and comparative study for the optical performance of different TiO2 phases doped PVA nanocomposite films

TiO2/PVA nanocomposites film was assembled using a solution casting technique, whereas the synthesis of TiO2 nanoparticles was achieved by the Sol-gel method. The control in TiO2 phases nanoparticle from Anatase, mix, and Rutile was taken place only by controlling the time and temperature of the calcination process, which belief as a new technique for that purpose. TiO2 nanoparticles with different phases employed as a filler and PVA as a host matrix. The established of TiO2 with different phases were examined by X-ray diffraction (XRD). At the same time, the shape and the approximate crystal size carried out by Transmission electron microscope (TEM), the XRD reveals the existence of anatase, rutile and mixed TiO2 phases with average crystallites size (D) of 7 nm 78 nm and 42 nm for anatase, rutile, and mix phases, respectively. TEM of TiO2 nanoparticles indicates the spherical shape of the rutile phase, and the tetragonal shape appears clearly in anatase, and the impact of the calcination process on crystal size was considerable. The grain size noted in the TEM image has a good agreement with the XRD results estimated by applying Scherrer's equation. The optical properties of TiO2/PVA composite films have been examined. The red-shifted of the direct optical band gap is achieved from 3.25 to 2.63 eV for phase transformation from anatase to rutile. The refractive index (n) dispersion was analyzed by applied the Wemple– Didomenico single oscillator model, and the dispersion parameters (Eo and Ed) were determined. Besides the photo-stability investigation of TiO2/PVA nanocomposite with the anatase phase of TiO2, which considers the characteristic phase.

Stable inks for inkjet printing of TiO2 thin films

In recent years, inkjet printing has been found to be a very promising and useful method for material deposition, and even semiconductor films can be deposited directly from a colloidal dispersion (ink) onto a large variety of substrates. The ink properties, such as solvodynamic particle size, zeta potential, isoelectric point, jetting performance, wetting and adhesion on substrates, should be optimized in order to achieve uniform deposition. In this work, the preparation of very stable colloidal dispersions based on TiO2 in three different crystal phases is presented. TiO2 has received a lot of attention because of its potential application in electronic devices. TiO2 inks were characterized by dynamic light scattering (DLS) measurements and the results show that the average solvodynamic particle size is around 25, 32 and 28 nm for anatase, rutile and brookite, respectively. The films obtained by inkjet printing were characterized by X-ray diffraction analysis, scanning electron microscopy, and UV–Vis spectrophotometry. The results show that the inkjet printed films were uniform, with thicknesses of 70, 140 and 130 nm for anatase, rutile and brookite, respectively. The current-voltage characteristics of conducting oxide-TiO2-Ag devices show diode behavior, confirming the semiconductor nature of the TiO2 films prepared by the inkjet printing technique. The ink preparation procedure reported in this work allows for the deposition of homogeneous and uniform films of all three phases of TiO2, and their potential for application in electronic devices.

Raman Spectroscopy and XRD investigation on TiO2 sol-gel dip coating thin films synthesizes with and without solvents

TiO2 coating films were prepared by sol-gel dip coating method using TTiP precursors with and without ethanol as a medium to hydrolyze the HCl catalyst. The prepared samples of titanium dioxide (TiO2) coating were dried at 110°C for 30 minutes then heated at 500°C and 600°C for 1h and 3h respectively to study effect of annealing temperature and soaking time. The crystallinity of the TiO2 coating were identified by using X-ray Diffraction technique and crystallite size was calculated. Raman Spectroscopy also used as the confirmation of phases formation of TiO2 coating films. Crystallite size of TiO2 films were obtained at 12.35 nm, 17.29 nm for anatase, 21.71 nm, 28.95 nm for rutile and 2.19 nm for brookite. Thus, the establishment of the desired phases, crystallinity and grain size of TiO2 thin films sol-gel can be controlled and encouraging to explore as an effort toward producing a sustainable photocatalytic.

Synthesis of nanosized TiO2 powder by sol gel method at low temperature

ABSTRACTNanotechnology is all about making products from very small constituents, components or subsystems to gain greatly enhanced material properties and functionality. Nanocrystalline anatase TiO2 was prepared by a facile sol–gel route at a temperature of 50°C under mild conditions. Titanium tetraisopropoxide (TTIP) was used as a titanium precursor, and 2-propanol was used as a solvent. XRD, TEM, SEM, FT-IR and BET were applied to characterize the crystal phase. The Crystalline size of TiO2 powder has been obtained with diameter < 30 nm for anatase at 500°C using an acid.

Effect of the TiO2 Crystallite Size, TiO2 Polymorph and Test Conditions on the Photo-Oxidation Rate of Aqueous Methylene Blue

This study systematically re-examines the titania-catalysed photo-oxidation of methylene blue (MB) in aqueous solution at 20 °C, placing particular emphasis on the effects of TiO2 crystallite size, TiO2 polymorph (anatase, brookite, rutile and combinations thereof) and experimental test conditions on the rate of MB photo-oxidation. For all TiO2 samples tested, the highest rate of MB photo-oxidation was observed at pH 6, slightly above the isoelectric point of TiO2 (~5.8 for P25 TiO2). Increasing the ionic strength at pH 6 induced MB dimer formation in solution, and lowered the rate of MB photo-oxidation by TiO2. For all TiO2 polymorphs, the surface area normalised rate increased with crystallite size reflecting the corresponding reduction in surface and bulk defects (electron–hole pair recombination sites). The optimum crystallite sizes were ~20–25 nm for anatase and ~50 nm for brookite. The photocatalytic activity of the different TiO2 powders followed the general order P25 > anatase > brookite ≫ rutile, with the high activity of P25 TiO2 providing strong evidence that anatase–rutile heterojunctions act as “hotspots” for MB photo-oxidation. Mixed phase anatase–rutile or brookite–rutile powders, each containing ~5 wt% rutile, demonstrated superior area normalized photocatalytic activities for MB photo-oxidation compared to pure phase anatase or brookite powders of comparable crystallite size. Finally, deposition of Pd, Pt or Au nanoparticles decreased the activity of P25 TiO2 for MB photo-oxidation. This paper clarifies long-standing confusion in the scientific literature about the photo-oxidation of aqueous MB over TiO2 and M/TiO2 (M = Pd, Pt and Au) photocatalysts.

Effect of acidic additives on the structure and performance of TiO2 films prepared by a commercial nanopowder for dye-sensitized solar cells

This work comprises an experimental study on the effect of various dispersing agents on the morphology of mesoporous TiO2 films prepared by the doctor blade method and on the performance of the resulting dye-sensitized solar cells. TiO2 films were prepared using a commercial nanopowder, Degussa P25, which was ground in a mortar, with different dispersing agents and under continuous grinding, in order to break the large agglomerates (>1 μm), present in the powder. These additives can be different acids or bases and must prevent also re-agglomeration of the nanoparticles, by forming a surface charge.Two strong acids (hydrochloric, HCl and nitric, HNO3), a weak one (acetic acid, CH3COOH) and a ketone (acetylacetone, C5H8O2) were used in turn. The properties of the films were dependent on the concentration and the kind of the acid. With increasing concentration the coagulation of the nanoparticles also increases, thus affecting the efficiency of the devices. Of all the additives used, HNO3 gave the best results and a 40% increment in efficiency was observed, compared to the standard dispersing agent that is acetylacetone. The improved homogeneity of the nanoparticle size (24 nm for anatase and 21.5 nm for rutile) and the better connectivity between them were responsible for the improvement in efficiency.

Regularities Of Photoelectrochemical Oxidation Of Glycerol Using Electrophoretically Deposited Tio2 Coatings On Steel

The aim of this work was to study glycerol photoelectrochemical oxidation by using electrophoretically deposited nanosized TiO2 coatings on AISI 304 type stainless steel.The structure and morphology of the prepared coatings were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It has been determined that the coatings contain 73 % of anatase and 27 % of rutile. The average crystallite size was calculated to be 21 and 54 nm for anatase and rutile, respectively. The photoelectrochemical behaviour of TiO2 coatings was investigated by photovoltammetry. The n-type TiO2 coatings were found to generate the photocurrents which are greatly enhanced by the presence of glycerol in 0.1 M Na2SO4 aqueous electrolyte. An increase in glycerol concentration causes a decrease in the photocurrent. The presence of pure glycerol results in higher photocurrents as compared with the technical glycerol.DOI: http://dx.doi.org/10.5755/j01.ct.62.4.3228

Toward a Low-Temperature Sol−Gel Synthesis of TiO2(B) Using Mixtures of Surfactants and Ionic Liquids

An approach toward the synthesis of nanocrystalline TiO2(B) in surfactant/ionic liquid systems at low temperature (100 °C) by means of sol−gel chemistry is presented. As reaction medium, a solution of imidazolium- and ammonium-based surfactants in ionic liquids was applied. Interestingly, TiO2(B), in coexistence with anatase, was observed only in cases where the ionic liquid is based on imidazolium moieties. The final product contained up to 60 wt % TiO2(B), depending on the initial amount of surfactant. X-ray powder diffraction measurements and transmission electron microscopy revealed small particle sizes (ca. 2 nm for TiO2(B), around 6 nm for anatase) as well as a high crystallinity of the material. The materials possessed surface areas up to 300 m2/g. Electrochemical studies further confirmed the presence of the two titania polymorphs anatase and TiO2(B) in similar proportions. Small-angle X-ray scattering experiments gave insight into the phase behavior of the surfactant in the ionic liquid under reaction conditions. The formation of TiO2(B) is discussed based on systematic variation of diverse parameters.

BIOLOGICAL EFFECT OF INTRANASALLY INSTILLED TITANIUM DIOXIDE NANOPARTICLES ON FEMALE MICE

The toxicological effect of TiO 2 nanoparticles with different crystal structure (80 nm for rutile and 155 nm for anatase) on female mice was investigated through intranasal instillation. After exposure for 30 days at the dose of 50 mg/kg body weight, no abnormal activity and mortality were observed with the normally increasing body weight of mice. The coefficients of tissues to body weight also show no obvious difference from the control except the increased coefficient of kidneys in mice exposed to 80 nm TiO 2 nanoparticles. Titanium contents and histopathology examination indicate the no pathological response in the lung was induced by the increased TiO 2 deposition, and the liver, heart, and spleen were not influenced. The severe pathology changes in kidneys suggest that TiO 2 nanoparticles may be excreted out by kidneys via system circulation. However, the serum biochemical parameters were not changed compared with the control, which means no obvious functional impairment induced by the nasal exposure for 30 days. In addition, the higher titanium contents in the brain tissues imply that the translocation and deposition of nanoparticles through intranasal instilling pathway is different from the other routes such as intratracheal inhalation or intratracheal instillation. The influence of deposited nanoparticles on central nervous system needs further investigation and is underway.

TiO2 thin films prepared by sol–gel method for waveguiding applications: Correlation between the structural and optical properties

Thin films of transparent titanium oxide (TiO2) are prepared by the sol–gel dip-coating technique. Structural and optical properties of TiO2 thin films are investigated for different annealing temperatures and different number of coatings. X-ray diffraction (XRD) and Raman spectroscopy analysis show that the anatase crystalline phase appears beyond 350°C for the four layers TiO2 film. At higher temperatures and for thicker films, we observe in addition to anatase the formation of brookite and rutile phases. The grain size calculated from XRD patterns increases as the temperature of annealing and number of dipping increase, from 11.9 to 17.1nm for anatase and decreases as the number of dipping increases, from 24.2 to 10.2nm for brookite. Film thickness, refractive index, and porosity are found to vary with treatment temperature and the number of coating. The obtained films are transparent in the visible range and opaque in the UV region. Waveguiding properties are studied using m-lines spectroscopy. The best results indicate that our films are monomodes TE0 at 632.8nm with optical losses of 2dBcm−1.

Effect of γ-irradiation and ZnO-doping of CuO/TiO 2 system on its catalytic activity in ethanol and isopropanol conversion

The effects of γ-irradiation (0.4–1.6 MGy) and ZnO-doping (1–6 mol%) of CuO/TiO 2 system on its surface and catalytic properties were investigated using XRD, nitrogen adsorption at−196 °C and ethanol and isopropanol conversion. The catalytic reactions were carried out at 250–400 °C using micro pulse technique. The results revealed that all investigated solids heated at 400 and 600 °C consisted of TiO 2 (anatase) as major phase besides TiO 2 (rutile) as minor phase together with CuO phase. The anatase and CuO phases existed as nano-crystallized solids having crystallite size varying between 5.5 and 21.3 nm and between 8.2 and 23.5 nm for anatase and CuO phases, respectively. ZnO-doping and γ-irradiation brought about a progressively significant decrease in the crystallite size of TiO 2 and CuO phases which increased by increasing the calcination temperature of the system investigated from 400 to 600 °C. ZnO-doping and γ-irradiation increased the specific surface areas of the treated solids to an extent proportional to the amount of dopant added and the dose of γ-rays absorbed. All solids investigated were highly selective in ethanol and isopropanol conversion reactions, which proceed via dehydration yielding only ethene and propene, respectively. The catalytic activity of all solids was found to decrease by increasing the calcination temperature from 400 to 600 °C. ZnO-doping conducted at 400 °C exerted no significant change in the activity of doped solids. γ-Irradiation of the solids calcined at 400 °C led to a limited increase in their catalytic activities. On the other hand, ZnO-doping and γ-irradiation (0.4 MGy) of solids calcined at 600 °C resulted in an increase in their catalytic activities. The increase was, however, more pronounced in case of γ-irradiation at a dose of 0.4 MGy.

Controllable Crystalline Nano-TiO2 by Homogeneous Hydrolysis with Toluene-p-Sulfonic Acid

The homogeneous hydrolysis method was proposed to synthesize nano-TiO 2 with mixed crystal of anatase and rutile. It is remarkable that the crystal-form-controllable nanosize TiO 2 was obtained by the addition of toluene-p-sulfonic acid (TSA). Two processes of the rutile phase formation were proposed. TiO 2 was pure anatase crystalline in the absence of TSA. The sample with 0.2 mole ratio of TSA was mixed crystal of anatase and rutile, and characterized that the size of nanocrystalline was 19.5 nm for rutile and 13.5 nm for anatase, the specific surface area was 72.7 m 2 /g, and the energy of band gap was 2.83 eV. And the mechanism of the development of rutile nano-TiO 2 was presented in homogeneous hydrolysis system with TSA.

Structure and properties of crystalline titanium oxide layers deposited by reactive pulse magnetron sputtering

Crystalline TiO2 layers could be deposited on glass and silicon substrates by reactive pulse magnetron sputtering without additional substrate heating using a long-term stable process with high deposition rate. XRD investigations have revealed that the variation of pulse mode between unipolar and bipolar allows the deposition of layers with anatase and rutile structures, respectively. The SEM micrographs of anatase layers show faceted crystallites on the surface as well as in the fracture. In comparison the rutile layers have a smoother surface and a more glassy like fracture. Cross-section TEM investigations on samples with anatase or rutile phase have shown that the growth of the layers starts with an amorphous sub-layer. With increasing distance from the substrate the nucleation of first crystallites can be recognized. The lateral size of the columnar grains ranges between 100 and 200 nm for anatase and rutile films. In contrast, the defect density of the rutile phase is drastically higher than in films with anatase structure. Spectroscopic ellipsometry measurements have shown that no absorption is present in the visible spectrum range. The refractive index at 550 nm is approximately 2.55 for anatase and 2.68 for rutile phase, respectively. The hardness and Young's modulus measured by nanoindentation is approximately 8 and 170 GPa for anatase and 17 and 260 GPa for rutile layers. Layers with an anatase structure are well suited for photocatalytic applications using the hydrophilic, self-cleaning and antifogging properties. Rutile layers can be used as optical layers with high refractive index and as protective layers with good mechanical properties.

Preparation of Controllable Crystalline Nano-TiO2 by Homogeneous Hydrolysis

Abstract The crystal-form-controllable nanosize TiO2 was obtained using homogeneous hydrolysis method by the addition of toluene-p-sulfonic acid (TSA). Two processes of the rutile phase formation were proposed. The sample with 0.2 mole ratio of toluene-p-sulfonic acid was a mixed crystal of anatase and rutile, and characterised that the size of nano-crystalline was 19.5 nm for rutile, and 13.5 nm for anatase, the specific surface area was 72.7 m2/g, and the energy of band gap was 2.83 eV. The mechanism of development of rutile nanosize TiO2 was presented in homogeneous hydrolysis system with TSA.

Structure and properties of crystalline titanium oxide layers deposited by reactive pulse magnetron sputtering

Crystalline TiO 2 layers could be deposited on glass and silicon substrates by reactive pulse magnetron sputtering without additional substrate heating using a long-term stable process with high deposition rate. XRD investigations have revealed that the variation of pulse mode between unipolar and bipolar allows the deposition of layers with anatase and rutile structures, respectively. The SEM micrographs of anatase layers show faceted crystallites on the surface as well as in the fracture. In comparison the rutile layers have a smoother surface and a more glassy like fracture. Cross-section TEM investigations on samples with anatase or rutile phase have shown that the growth of the layers starts with an amorphous sub-layer. With increasing distance from the substrate the nucleation of first crystallites can be recognized. The lateral size of the columnar grains ranges between 100 and 200 nm for anatase and rutile films. In contrast, the defect density of the rutile phase is drastically higher than in films with anatase structure. Spectroscopic ellipsometry measurements have shown that no absorption is present in the visible spectrum range. The refractive index at 550 nm is approximately 2.55 for anatase and 2.68 for rutile phase, respectively. The hardness and Young's modulus measured by nanoindentation is approximately 8 and 170 GPa for anatase and 17 and 260 GPa for rutile layers. Layers with an anatase structure are well suited for photocatalytic applications using the hydrophilic, self-cleaning and antifogging properties. Rutile layers can be used as optical layers with high refractive index and as protective layers with good mechanical properties.

Effect of Thermal and Mechanical Treatments on the Cathodoluminescence of Tin and Titanium Oxides

ABSTRACTThe luminescence of titanium oxide and tin oxide has been investigated by cathodoluminescence in the SEM, as a function of the structural changes induced by thermal treatments. The evolution of the luminescence of TiO2 rutile, anatase and mixture phase with the annealing temperature is related to the process of thermal induced grain texture and to transition of metastables phases to the stable rutile. The emission band is peaked at 480 nm for the composite phase and at 580 nm for anatase and rutile phases respectively. A broad band in the 520–560 nm region is present in the spectra of both anatase and rutile phase. Thermal annealing leads to a red shift of the luminescence emission, with the emission band peaked at around 820 nm. In sintered tin oxide the main emission bands appear centered at about 480 nm and 630 nm. The intensity of these bands increases with annealing temperature up to 1200°, whereas for samples annealed at 1500° these emissions are quenched. Mechanical ball milling has been used to produce nanocrystalline SnO2 grains to investigate the influence of the presence of nanocrystals on the CL emission.