Narrow Results

${\mathrm{\text{TiO}}}_2$ nanomaterials with different content of ${\mathrm{\text{Ce}}}^{4+}$ ion were synthesized by the chemical method from solutions and demonstrated improved photocatalytic and optical properties with significant redshift compared to pristine ${\mathrm{\text{TiO}}}_2$. According to X-ray phase analysis and transmission electron microscopy, all synthesized materials are characterized by anatase modification, which holds up to $800^{\circ }$C, the particle size for all materials is 12–21 nm. X-ray diffraction spectra revealed that the anatase to rutile phase transition for materials doped with ${\mathrm{\text{Ce}}}^{4+}$ ions begins at a higher temperature of $800^{\circ }$C compared to pristine ${\mathrm{\text{TiO}}}_2$. The influence of synthesis conditions and ${\mathrm{\text{Ce}}}^{4+}$ content (0.1–2 mol.%) on characteristics and photocatalytic activity were investigated. The Ce-doped ${\mathrm{\text{TiO}}}_2$ nanomaterial, containing 0.1% ${\mathrm{\text{Ce}}}^{4+}$ provides an extremely high degree of methylene blue decomposition by 93% within visible light irradiation for 3 h. The stability of the catalyst over four cycles has been shown, which makes it possible to use it in the purification of water resources from dyes or other pollutants.

Titanium dioxide nanoparticles were prepared by precipitation of aqueous TiCl₄ solution with ammonium hydroxide as precipitation agent. Freshly prepared Titania gel is allowed to crystallize under refluxing and stirring condition for 6 h over 90°C and oven dried over night in temperature above 100 C. X-ray diffraction studies on oven dried powder indicate formation of anatase phase TiO₂ with average crystalline size of 4.5 nm. Powders with variable amount of anatase and rutile phase were prepared by calcination of pure anatase in the temperature range 400-1000 c for 4 h. the XRD patterns show that phase transition from anatase to rutile occur in calcination above 600°C. The morphology and microstructure characteristics were obtained by XRD, TEM. and TGA.

The effect of doping with boron, carbon and nitrogen on crystal lattice parameters, electronic band structure and optical absorption of anatase has been studied by means of an ab initio density functional theory approach. The investigations included optimization of crystal structure based on the pseudo-potential plane-wave approach. The spin-polarized calculations of the band structure with the account of on-site Coulomb correlations (LSDA+U) employing the tight-binding linear muffin-tin orbitals method (TB-LMTO) have also been performed. The evaluations of optical absorption were based on the calculations of dielectric function with local field effects taken into account. We find that the crystal lattice relaxation around the doping atoms produces noticeable changes in the band structure, magnetic state and optical properties of the doped compounds. The most considerable effects are the collapse of magnetic moment on carbon atom and an essential reduction of the optical absorption in the region of the impurity band — impurity band transitions. Comparing optical absorption for different kinds of doping and taking into account the intensity distribution of the solar light we come to the conclusion than the doping with boron is the most promising kind of doping for photocatalytic applications of the doped anatase.

TiO₂ sol-gel thin films were deposited on glass substrates by dip coating method. Nanocrystalline TiO₂ thin films were prepared at 300°C. The effect of annealing temperature on optical properties of nanocrystalline TiO₂ thin films was studied. The films were characterized by different techniques: XRD, UV-visible spectroscopy, FTIR spectroscopy and FESEM. The characterization studies revealed that the films are crystallized as anatase phase and are nano-structured. The optical measurements were showed the indirect band gap between 3.31 and 3.35 eV with corresponding crystallite sizes between 8.9 and 3.7 nm at the temperatures 300, 400 and 500°C. The FESEM images of film were showed spherical nanocrystalline structure of TiO₂ particles with the crystallite sizes between 30 and 100 nm. It is also observed that refractive index of the film increases with increasing the annealing temperature. The smaller crystallite size gives larger band gap due to quantum size effects.

A systematic study of unrelaxed and relaxed surface characters on the TiO₂ (101) surface has been carried out by first-principles calculations using plane-wave pseudopotential method. We find that O_2c atoms have an inward relaxation of 0.012 Å and Ti_5c atoms have an outward relaxation of 0.155 Å by taking a 24-layer slab with 5 Å vacuum width to consider the atomic relaxations, in good agreement with other theoretical values. The slab thickness has significant effect on the quality of band structure and density of states, and 24-layer slab is sufficient to present the electronic properties of TiO₂ (101) surface. Atomic relaxations result in a large transfer of surface charges from outermost layer to inner layer, and the surface bonds have a rehybridization, which makes the ionization reduce and the covalence increase; we believe that it causes the surface bond shorten. A fine analysis of band structure and density of states of the TiO₂ (101) surface shows that the surface relaxation induces the transformation from semi-metallic to semiconducting characteristic.

Titanium dioxide has been extensively studied in recent decades for its important photocatalytic application in environmental purification. The search for a method to narrow the optical band gap of TiO₂ plays a key role for enhancing its photocatalytic application. The optical band gap of epitaxial rutile and anatase TiO₂ thin films deposited by helicon magnetron sputtering on sapphire and on SrTiO₃ substrates was correlated to the lattice constants. The optical band gap of 3.03 eV for bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of 3.20 eV for bulk-anatase increases to 3.51 on SrTiO₃. In order to interpret this expansion, ab-initio calculations were performed using the Vienna ab-initio software. The calculations for rutile as well anatase show an almost linear increase of the band gap width with decreasing volume or increasing lattice constant a. The calculated band gap fits well with the experimental values. The conclusion from these calculations is, in order to achieve a smaller band gap for both, rutile or anatase, the lattice constant c has to be compressed, and a has to be expanded.

Nanoparticles of titanium dioxide (TiO₂) doped with 5 at.% Sc³⁺ ions were synthesized using the sol–gel method and calcined at 500°C to obtain better anatase phase. The crystal structures of the doped TiO₂ nanoparticles were characterized by X-ray powder diffraction (XRD), Raman, UV-vis, FT-IR spectroscopy, high resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). XRD patterns and Raman spectra of TiO₂ + 5 at.% Sc-500°C show the anatase phase and the average particle size of the sample calculated from XRD patterns was determined as 5.9 nm. Well-resolved rings of SAED of TiO₂ doped with Sc³⁺ ions are easily indexed to those from XRD pattern. HRTEM shows the well-defined lattice fringes and the lattice spacing measured from HRTEM is 0.33 nm, which is in well agreement with the distance between the (101) planes in anatase TiO₂. Energy-dispersive X-ray (EDX) spectrum of the doped TiO₂ confirms the presence of Sc element in the TiO₂ matrix.

Co doped TiO₂ nanopowder has been synthesized by a simple sol–gel route. XRD and TEM analysis confirms anatase phase of TiO₂ with crystallite and particle sizes of 10 and 15 nm respectively. Presence of Co is confirmed by EDX. FTIR shows a slight shift in the Ti-O bonding vibration to lower frequency suggesting dopant incorporation on Ti site. For magnetic measurements the sample with dopant amount x = 0.075 is annealed both in vacuum and air. Weak ferromagnetism and a blocking temperature of 39 K is obtained for vacuum annealed sample while ferromagnetism is lost in the air annealed sample and shows only paramagnetic behavior. Temperature dependent magnetic measurements for air annealed sample shows antiferromagnetic behavior with a Neel temperature of 36.51 K. Here we report that oxygen vacancy and cobalt aggregates is a key factor for inducing ferromagnetism–superparamagnetism in vacuum annealed sample. Appearance of Neel temperature reveals the presence of antiferromagnetic Co₃O₄ which is the oxidation results of metallic Co or cobalt clusters present on host TiO₂ surface.

The nanocrystalline TiO₂ powder was synthesized by sol–gel method. The XRD analysis reveals that TiO₂ powder was highly crystalline (anatase phase) and nanostructured with tetragonal system. The average crystallite size after calcined at 673K is found to be 7.7nm. The surface morphological studies using scanning electron microscopy (SEM) exhibit that the formation of nanosized TiO₂ particles with less densification nature. Atomic force microscopy (AFM) topography exhibits the uniform distribution of spherical-shaped particles. The energy dispersive X-ray spectroscopy (EDX) confirms the presence of Titanium and Oxygen in synthesized TiO₂ nanopowder. The value of optical bandgap of TiO₂ nanopowder calculated from UV-Visible spectrum is 3.45eV. The presence of TiO₂ particles is confirmed from the dominant fourier transform infrared (FTIR) peaks at 621cm${}^{-1}$ and 412cm${}^{-1}$.

C-doped Ti–O films with different titanium suboxide contents are prepared by DC magnetron sputtering deposition at different sputtering powers. The films with different phases are formed after annealing at 873K in air. The structure of the films is characterized by X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The optical properties and surface roughness of the films are investigated by UV–vis spectroscopy and atomic force microscopy, respectively. Photocatalytic activity of the thin films is studied by degrading the methyl orange solution under xenon lamp (300W) irradiation. The results show that the C-doped Ti–O thin films with higher titanium suboxide contents (${\text{Ti}}^{4+}<45.4$%) tend to form the rutile phase after annealing, whereas the films with a lower titanate content (${\text{Ti}}^{4+}>54.8$%) are easy to form anatase phase by annealing.

Thin TiO₂-films were synthesized for the first time by solid-phase low-temperature pyrolysis technique onto quartz glasses or silicon substrates. The obtained films are nanoscale; crystallize in a mixed anatase-rutile modification, which was confirmed by X-ray diffraction, scanning electron and atomic force microscopy (AFM) methods. The three-layer films’ thickness was 140 nm. The TiO₂-films consist of crystallites 12–27 nm, depending on the temperature treatment and phase composition. In addition, all of the obtained TiO₂-films are optically transparent regardless of synthesis conditions; the calculated band gap was 3.55 eV, which makes it possible to recommend TiO₂-films for use in optical filters and gas sensors.

Sn-doped TiO₂ nanomaterials were synthesized by sol–gel method. It was shown the phase compositions and phase transitions change with the introduction of different tin amounts (0.5–20mol.%). X-ray powder diffraction was used to study the effect of different tin amounts on the anatase–rutile phase transition. It was found that the introduction of ions increases the thermal stability of anatase modifications. The material’s photocatalytic activity was studied in reaction with a model pollutant (methylene blue) photodegradation under UV and visible light activation. The best photocatalytic properties were shown for material, which contains 5mol.% of Sn.

TiO₂ thin films were deposited on glass substrates by sol-gel method. Nanocrystalline TiO₂ thin films were prepared at ambient conditions and titanium tetraisopropoxide [C₁₂H₂₈O₄Ti] was used as a Ti-precursor. The effect of annealing temperature on optical properties of nanocrystalline TiO₂ thin films was studied. The as-deposited films were dried at 100 °C for 1 hr. The films formed were further heated in temperature between 200 and 500 °C for 1 hr. The films were characterized by different techniques: XRD, UV-visible spectroscopy, FTIR spectroscopy and FESEM. The characterization studies revealed that the films are crystallized as anatase phase and nano-structured with better optical properties α = 0.89 as compared to reported data. The optical measurement showed the indirect band gap between 3.31 and 3.35 eV with corresponding crystallite sizes between 8.9 and 3.7 nm. The FESEM image of film annealed at 400 °C showed spherical nanocrystalline structure of TiO₂ particles. The crystallite sizes obtained from FESEM image are found to be between 30 and 100 nm. It is also observed that refractive index of the film increases with increasing the annealing temperature. The smaller crystallite size gives larger band gap due to quantum size effects.

Anatase TiO₂ aqueous sols were prepared below 70 °C by sol method. The influences of preparing conditions on the crystal structures and stability of the sols were investigated with X-ray diffraction (XRD) and Zeta potential. The photocatalytic activities of the anatase TiO₂ aqueous sols were characterized by degradation of methyl orange and methylene blue under ultraviolet light, fluorescent light and sunlight. The sols demonstrate higher photocatalytic activity than that of Degussa P25-TiO₂.