Papers by Keyword: Anatase

Abstract: Chemical synthesis of nanocomposite particles based on titanium dioxide modified with iron and gold was carried out. It was shown that, depending on the mass content of the doping species, the phase transformation of titanium hydroxide at T = 700 °C proceeds with the formation of either anatase (2 wt.%) or anatase and rutile (8 wt.%). The doping species form a hematite phase and gold clusters on the metal-oxide surface. A weakly crystalline anatase obtained by the transformation of metatitanic acid (MTA), with a particle size of 8 nm and a sulfur content of 0.036%, was selected as the co-catalyst. The anatase co-catalyst exhibits photocatalytic activity in the destruction of organic dyes. Its introduction into the TiO₂&Fe₂O₃&Au nanocomposite suspension promotes the catalytic degradation of cationic and anionic dyes at temperatures ranging from 35 to 60 °C. It was observed that the degradation degree of the solutions after 150 min of catalytic process is the following: Methyl Orange (MO) – 72 %, Methylene Blue (MB) – 71.5 %, Rhodamine B (RhB) – 63.5 %, and Orange G (OG) – 47 %. The reaction rate constant depends on the composition of the dye, varying from 6.5·10^-4 min^-1 for OG to 2.56·10^-3 min^-1 for MB. The prospect of creating heterostructures based on TiO₂ modified with hematite and gold, and their further adaptation for photocatalytic hydrogen production, is considered.

Abstract: Kinetic studies of the photocatalytic decomposition of cationic dyes MB (Methylene Blue) and RhB (Rhodamine B), and hydrogen generation from a water–methanol mixture were carried out using nanosized particles of anatase and binary composites based on it with 2 wt.% of palladium or cerium. Nanocomposites were synthesized by a chemical method using TTIP (Titanium TetraIsoPropoxide) in the presence of aqueous salt solutions containing doping metals. The paper briefly describes the structure, morphology, and chemical composition of the anatase-based nanoparticles using modern physical-chemical methods. In the presence of TiO₂&Pd particles, the destruction degree of RhB and MB under the UV irradiation during 60 min reached 81.0–85.5%, and in the presence of TiO₂&CeO₂ particles – 95%. The dye destruction process was accompanied by a hypsochromic shift of chromophoric peaks, which indicated the decomposition products formation. The reactions are pseudo-first order, and the rate constants are within 10^-2. Photocatalytic activity for hydrogen generation using UV radiation showed increased activity (H₂ 3519 μmol·g^-1) for TiO₂&2wt.%Pd due to the possible penetration of palladium atoms into the anatase lattice with efficient separation of photogenerated charge carriers in this system.

Abstract: In this work, photoelectron nanocomposites of TiO₂&CeO₂&Ag were synthesized by a co-deposition method using TTIP (Titanium TetraIsoPropoxide) and water solutions of Ce(NO₃)₃ and AgNO₃. Heat treatment of the precipitates at 600°C led to the formation of an anatase phase with the primary particles’ size of 14.1–15.2 nm. Molecules of Malachite green and Methylene blue are intensively adsorbed on the surface of nanocomposites. TiO₂&CeO₂&Ag nanocomposites show high photocatalytic activity to cationic dyes and weak – to anionic ones. The photocatalytic decomposition of cationic dyes is accompanied by a hypsochromic shift of chromophoric bands. Only the chromophoric part of the dye molecules is destroyed by temperature (catalytic process). Nanocomposites based on anatase containing 1–2 wt.% of Ag and Ce show the highest photocatalytic activity for the destruction of organic dyes.

Abstract: The effect of biaxial and uniaxial strains on the electronic structure of anatase is studied using Density Functional Theory (DFT) calculation with ultrasoft pseudopotential and a generalized gradient approximation (GGA) Perdew-Burke Ernzerhof (PBE) exchange-correlation. The lattice constant is optimized using the Birch-Murnaghan equation of states (BM-EOS) to get an optimized geometric structure of anatase TiO₂. We apply biaxial and uniaxial strains to this optimized structure up to 16% and find that the applied strains change the band gap energy compared to a pure anatase with a different band gap energy up to 1.61 eV for biaxial strain and 0.35 eV for uniaxial strain. The biaxial strains increase gap energies except at +16% tensile strain, decreasing the gap energy to 0.04 eV. Uniaxial strains tend to increase as the strains increase except at-12 and-16%; their gap energy differences are 0.08 and 0.20 eV, respectively, smaller than that of the zero strain. The results also show that the applied 16% tensile strain significantly lengthens the atomic bonds; thus, we conclude that the maximum strain applied to anatase TiO₂ is 16%.

Abstract: In this work, the Sol-Gel dip-coating technique is used to report the effect of thickness and annealing temperature on structural and optical properties of TiO₂ thin films. To study the effect of the annealing temperature, the prepared samples were annealed at different temperatures: 300, 400, and 500 °C for 1 h. By increasing the annealing temperature, an amelioration of the crystalline quality is observed. The best crystalline quality was obtained at 500 °C. Additionally, the band gap value E_g, evaluated from transmission spectra, does not vary with the increasing of the annealing temperature. All the films with different thicknesses present crystalize in the Anatase structure, and the crystallite size value does not practically change with thickness increase. It was also found that the TiO₂ film band gap value decreases with the film thickness increase, demonstrating the possibility of band gap tuning by varying the TiO₂ film thickness.

Abstract: Due to its to its optical, thermal, photocatalytic and electrophysical properties, nanocrystalline titanium oxide (TiO₂) is widely used in various fields. In the present work, a series of pure and Gd-modified (0.5, 5, 50 mol%) TiO₂ nanocrystalline powders were prepared by a novel synthesis approach – extraction-pyrolytic method (EPM). Metal containing extracts on the basis of valeric acid were used as precursors. Thermal behavior of produced individual and mixed precursors were investigated by thermogravimetric analysis (TGA) and high temperature differential scanning colometry (HDSC). Phase composition of pure and Gd-modified TiO₂ powders were studied as a function of pyrolysis temperature (450^o -850°C ) and gadolinium content by X-ray diffraction (XRD) method. Photocatalytic activity of produced powders was studied by photocatalytic degradation of methylene blue (MB) under UV/VIS light irradiation.

Abstract: The purpose of the plasma oxidation process is to increase the hardness, corrosion resistance and to improve the biocompatibility properties of Ti6Al4V alloys by thickening the natural oxide in the material, which is produced by this treatment. The aim of this work is to verify the effect of temperature on the thickness, hardness and wear resistance of the Ti6Al4V alloy treated with plasma oxidation. The treatment was performed using a Pulsed DC vacuum reactor, with a gas ratio of 60% Ar and 40% O₂ and 1.65 torr pressure for 1 hour of treatment, at temperatures of 480°C, 520°C, 670°C and 705°C. In regards to the multilayer formation of anatase and rutile, it was observed that the layer thickness increased as the treatment temperature increased. The increase of surface hardness provided by the treatment caused a considerable increase in the wear resistance of the studied material. The greatest layer thickness and surface hardness were obtained for the material treated at 705°C, but the lowest wear volume was obtained for the material treated at 520°C.

Abstract: Herein, Ag-anatase photocatalysts were synthesized though chemical reduction method under room temperature by using PVP and NaBH₄ as stabilizer and strong reducing agent, respectively. The prepared photocatalysts were characterized by the following technique: XRD, SEM, HR-TEM, EDX, and UV-Vis-NIR. The photocatalytic performance of 0.05 g of photocatalysts were performed under UV irradiation within 1 h by using 10 mg/L of rhodamine B as the representative of organic pollutant. The results demonstrated that the optimum Ag loading contents were 2 %wt (2-ST) which can degrade rhodamine B up to 98.54%. Therefore, the photocatalytic performance of bare anatase could be enhanced by deposited Ag nanoparticles. Further, this prepared Ag-anatase could be suitable for environmental application.

Abstract: In this study, titanium dioxide nanoparticles were synthesized for possible application in enhanced oil recovery. Sol-gel method was employed with titanium (IV) isopropoxide as the precursor. The prepared materials were characterized using Powder X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), High-Resolution Transmission electron microscopy (HRTEM) and Brunauer–Emmet–Teller (BET) techniques. Reaction parameter such as calcination temperature was varied during the preparation to obtain the uniform TiO₂ nanoparticles with the smallest particle size and high surface area. The results of study revealed that 400 °C is the optimum calcination temperature in preparing TiO₂ nanoparticles producing the smallest crystallite and particle sizes. XRD results indicated that the nanoparticles have formed anatase phase at 400 °C and achieved low crystallite size of 7.27 nm with the smallest average particle size of 19.53 nm through FESEM and HRTEM observations. BET analysis had achieved the highest surface area 103.64 m²/g.

Abstract: Titanium dioxide has a special feature: anatase, to rutile transformation which was considered in our investigations. It is especially important to keep anatase form of titanium dioxide for photocatalytic materials, different ceramics with tribo-chemical properties, self-cleaning coatings and self-sterilizing coatings. For that only one of the titanium dioxide forms is more suitable – anatase, which is more active but not stable, because it transforms to rutile during the time or with the temperature increase loses its activity. Different methods of stabilising anatase have been considered in the paper. Several doping agents have been determined and it was chosen fluorine ion to modify titanium dioxide. Stabilization of anatase is achieved by preparing the reaction mixture by a sol-gel method with hydrofluoric acid. It has shown thermodynamic data, results of experiment, temperatures of anatase to rutile transformation of non-doped and doped titanium dioxide, its X-Ray diffraction and TGA. It is proved that titanium dioxide doped by fluorine ion keeps anatase form till the temperature is more than 1000 °C.