TiO2 In Air Research Articles

Atomic Layer Deposition of Gold Nanoparticles with Controlled Size and Distribution on Titania Support

AbstractNano‐sized gold particles have shown unique merits in the field of catalysis, sensing and imaging, whereas their controllable synthesis with sub‐nanometer size and narrow distribution on a support still remains a challenge. Herein, we developed a facile and controllable process of atomic layer deposition (ALD) using dimethyl(acetylacetonate)gold (Me2Au(acac)) and ozone as the precursor reactants to directly synthesize ultrafine Au nanoparticles on titania support. The size of Au nanoparticles could be precisely controlled via the modulation of depositing temperature and the counter reactant. Additionally, the dispersion of Au nanoparticles on the support is decreased by pre‐calcining TiO2 in air, which is due to the decreased surface hydroxyls concentration on support, leading to less adsorption sites of gold precursor. Moreover, we demonstrated that Au nanoparticles prepared by this method on TiO2 could function as an effective co‐catalyst for photocatalytic hydrogen evolution reaction.

TiO2 NANOTUBES FOR PHOTOCATALYTIC DEGRADATION OF METHYLENE BLUE

Titanium dioxide remains one of the most studied semiconductor for photocatalytic applications due to its low cost production, reduced toxicity, ability to break down the organic pollutants and possibility to achieve complete mineralization. In this work, we report on results of the photocatalytic activity of titanium dioxide nanotubes fabricated by electrochemical anodization technique in an electrolyte solution containing a mixture of hydrofluoric acid, ethylene glycol and phosphoric acid. The morphology and crystallinity of the obtained nanotubes were investigated by means of electron microscopy and it was found that nanotubes have a constant outer diameter of 200 nm and an internal conical shape where the diameter gradually decreases from 120 nm at the wide end to 50 nm at the narrow end. The transmission electron microscopy investigation defined two different phases of titanium dioxide obtained after annealing of amorphous TiO2 in air at 650 °C and 850 °C. Photocatalytic activity of the samples have been evaluated in methylene blue solution in the presence of dispersed nanotubes under visible and UV irradiation by means of UV/Vis spectroscopy. Anatase phase TiO2 shows the best performance degrading 85 % of dye in 25 min under UV illumination, while rutile phase with anatase inclusions shows the best results with a 50 % decay of dye concentration in 25 min under visible light illumination.

ChemInform Abstract: Structural Studies of CaAl12O19, SrAl12O19, La2/3+δAl12‐δO19, and CaAl10NiTiO19 with the Hibonite Structure; Indications of an Unusual Type of Ferroelectricity.

AbstractThe title hibonite‐type compounds are prepared by repeated firing of appropriate quantities of CaCO3, SrCO3, La2O3, NiO, Al2O3, and TiO2 in air (1300 °C for CaAl12O19, 1500 °C for all other compounds).

ChemInform Abstract: Low‐Cost Orthorhombic Na[FeTi]O4 (x = 1 and 4/3) Compounds as Anode Materials for Sodium‐Ion Batteries.

AbstractNax[FeTi]O4 (x = 1 and 4/3) anode materials are prepared by calcining stoichiometric amounts of Na2CO3, FeC2O4, and TiO2 in air (900 °C, 12 h).

ChemInform Abstract: NaTi3FeO8: A Novel Anode Material for Sodium‐Ion Batteries.

AbstractNaTi3FeO8 is prepared by calcination of stoichiometric amounts of Na2CO3, Fe2O3, and TiO2 in air (950 °C, 12 h).

Interplay of dopants and defects in making Cu doped TiO2 nanoparticle a ferromagnetic semiconductor

Here we have studied the role of oxygen defects and Cu dopants on ferromagnetism in Cu doped TiO2 nanoparticles with nominal Cu concentration of 2%, 4% and 6 mol%. Electron paramagnetic resonance (EPR) spectra analysis reveals the presence of Cu2+ in the distorted octahedral coordination of TiO2. Cu d-states undergo strong p-d coupling with the valence band O 2p state of TiO2 resulting the extended absorption hump in the visible region. Photoluminescence results reveal the presence of oxygen defect related emission peaks in Cu doped TiO2. Room temperature ferromagnetism is observed in all the Cu doped TiO2 nanoparticles. Saturation magnetization is the highest at 4 mol% and then there is a decrease in magnetization at 6 mol%. Ferromagnetism completely disappears on calcinations of 4% Cu doped TiO2 in air at 450 °C for 8 h. It is speculated that both oxygen vacancies and Cu d-states are involved in the room temperature ferromagnetism. Spin polarization occurs by the formation of bound magnetic polaron between electrons in Cu2+d-states and the unpaired spins in oxygen vacancies. Presence of Cu2+-Cu2+d-d exchange interaction and Cu2+-O2−-Cu2+ antiferromagnetic superexchange interactions might have resulted in the reduction in magnetization at 6 mol% Cu.

Photocatalytic oxide films in the built environment

The possibility to increase human comfort in buildings is a powerful driving force for the introduction of new technology. Among other things our sense of comfort depends on air quality, temperature, lighting level, and the possibility of having visual contact between indoors and outdoors. Indeed there is an intimate connection between energy, comfort, and health issues in the built environment, leading to a need for intelligent building materials and green architecture. Photocatalytic materials can be applied as coatings, filters, and be embedded in building materials to provide self-cleaning, antibacterial, air cleaning, deodorizing, and water cleaning functions utilizing either solar light or artificial illumination sources – either already present in buildings, or by purposefully designed luminaries. Huge improvements in indoor comfort can thus be made, and also alleviate negative health effects associated with buildings, such as the sick-house syndrome. At the same time huge cost savings can be made by reducing maintenance costs. Photocatalytic oxides can be chemically modified by changing their acid-base surface properties, which can be used to overcome deactivation problems commonly encountered for TiO2 in air cleaning applications. In addition, the wetting properties of oxides can be tailored by surface chemical modifications and thus be made e.g. oleophobic and water repellent. Here we show results of surface acid modified TiO2 coatings on various substrates by means of photo-fixation of surface sulfate species by a method invented in our group. In particular, we show that such surface treatments of photocatalytic concrete made by mixing TiO2 nanoparticles in reactive concrete powders result in concrete surfaces with beneficial self-cleaning properties. We propose that such approaches are feasible for a number of applications in the built environment, including glass, tiles, sheet metals, plastics, etc.

Influences of Calcination Ambiences on Morphologies, Phase Composition and Contents of the Elements of Ceramic Coatings on Ti Alloy by Micro-Arc Oxidation

Compound ceramic coatings with the main crystal phase of Al2TiO5 (as-coated samples) were prepared in situ on the surface of Ti-6Al-4V alloy by means of pulsed bi-polar micro-arc oxidation (MAO) in an NaAlO2 solution. The coated samples were calcined in argon and air at 1000 oC, respectively. The phase composition, surface and section morphology, and element contents of the ceramic coatings were investigated by X-ray diffractometry (XRD), Scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). The samples were treated in argon and the as-coated ones were calcined in air at 1000 oC to study the anti-oxidation properties of the samples. The results show that Al2TiO5 had been decomposed in an hour and transformed into α-Al2O3 and rutile TiO2 in air. However, Al2TiO5 had been decomposed in four hours in argon and the final coating surface was completely composed of α-Al2O3. The content of Al2O3 was decreased from outside to inside layers and Ti2O3 was formed in the coating. Furthermore, the morphology of the ceramic coatings after the calcination was different. The coatings calcined in argon were finer; the grains and pores were smaller than those in air.

Influences of Argon Ambience on Phase Composition and High Temperature Oxidation Resistance Property of Ceramic Coatings on Ti Alloy by Micro-Arc Oxidation

Abstract. Compound ceramic coatings with the main crystal phase of Al2TiO5 (as-coated samples) were prepared in situ on the surface of Ti-6Al-4V alloy by means of pulsed bi-polar micro-arc oxidation (MAO) in an NaAlO2 solution. The coated samples were calcined in argon and air at 1000 oC, respectively. The phase composition, surface and section morphology, and element contents of the ceramic coatings were investigated by X-ray diffractometry(XRD), Scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). The samples were treated in argon and the as-coated ones were calcined in air at 1000 oC to study the anti-oxidation properties of the samples. The results show that Al2TiO5 had been decomposed in an hour and transformed into α-Al2O3 and rutile TiO2 in air. However, Al2TiO5 had been decomposed in four hours in argon and the final coating surface was completely composed of α-Al2O3. The content of Al2O3 was decreased from outside to inside layers and Ti2O3 was formed in the coating. Furthermore, the morphology of the ceramic coatings after the calcination was different. The coatings calcined in argon were finer; the grains and pores were smaller than those in air. The high oxidation reaction of the TC4 substrate was the fiercest and the weight gains of the coated samples treated in argon was the lowest. The weight gains of the ceramic coatings were nearly changing in the form of parabola law.

Influences of Different Calcination Ambiences on Phase Composition, Morphologies of Ceramic Coatings on Ti–6Al–4V Alloy by Micro-Arc Oxidation

Compound ceramic coatings with the main crystal phase of Al2TiO5(as-coated samples) were prepared in situ on the surface of Ti-6Al-4V alloy by means of pulsed bi-polar micro-arc oxidation (MAO) in an NaAlO2solution. The coated samples were calcined in argon and air at 1000°C, respectively. The phase composition, surface and section morphology, and element contents of the ceramic coatings were investigated by X-ray diffractometry (XRD), Scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). The samples were treated in argon and the as-coated ones were calcined in air at 1000°C to study the anti-oxidation properties of the samples. The results show that Al2TiO5had been decomposed in an hour and transformed intoα-Al2O3and rutile TiO2in air. However, Al2TiO5had been decomposed in four hours in argon and the final coating surface was completely composed ofα-Al2O3. The content of Al2O3was decreased from outside to inside layers and Ti2O3was formed in the coating. Furthermore, the morphology of the ceramic coatings after the calcination was different. The coatings calcined in argon were finer; the grains and pores were smaller than those in air.

Influences of Different Calcinations Ambience on Phase Composition and Morphologies of Ceramic Coatings on Ti Alloy by Micro-Arc Oxidation

Compound ceramic coatings with the main crystalline of Al2TiO5 (as-coated samples) were prepared in situ on the surface Ti-6Al-4V alloy by means of pulsed bi-polar micro-arc oxidation (MAO) in a NaAlO2 solution. The coated samples were calcined in argon and air at 1000 oC, respectively. The phase composition, surface morphology of the ceramic coatings were investigated by XRD, SEM and XRF. The samples were treated in argon and the as-coated ones were calcined in air at 1000 oC to study the anti-oxidation properties of the samples. The results show that Al2TiO5 was decomposed very soon and transformed into α-Al2O3 and rutile TiO2 in air. However, Al2TiO5 was decomposed very slowly in argon and the final coating surface was completely α-Al2O3. Also, the morphology of the ceramic coatings after the calcination was different. The coatings calcined in argon were fined; grains and pores were smaller than those in air. High temperature oxidation occurred very strongly in the TC4 substrate, the weight gains of the as-coated ceramic coatings and the treated ones in argon were nearly changing in the form of parabola, and the weight gains of the coated samples treated in argon were comparatively lower than those of the as-coated samples.

Beiträge zur Kristallchemie und zum thermischen Verhalten von wasserfreien Phosphaten, XXXVII [1]. Synthese, Kristallstruktur und kernresonanzspektroskopische Untersuchung von In2Ti6(PO4)6[Si2O(PO4)6] – Eine Hybride aus den NASICON und M4[Si2O(PO4)6] Strukturtypen / Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phospates, XXXVII [1]. Synthesis, Crystal Structure and Nuclear Magnetic Resonance Investigation of In2Ti6(PO4)6- [Si2O(PO4)6] – A Hybride Built from Layers with NASICON

In2Ti6(PO4)6[Si2O(PO4)6] has been obtained by heating (1100 °C) stoichiometric amounts of In2O3, SiP2O7, TiP2O7, and TiO2 in air. Colourless crystals of the phosphate-silicophosphate suitable for a single crystal structure investigation have been grown by chemical vapour transport (1000°C → 900°C, mixture of 70 mg PtCl2 and 3.5 mg TiP as transport agent). In2Ti6(PO4)6[Si2O(PO4)6] adopts its own structure type (R3̅ (No. 148), Z = 3, a = 8.4380(10) Å , c = 44.295(1) Å , 1809 independent reflections, 109 variables, R1 = 0.044, wR2 = 0.112). The crystal structure represents a hybride built up from alternating layers (⟂ to the c-axis) of the NASICON structure-type and those showing the structure of silicophosphates M4[Si2O(PO4)6]. Isolated heteropolyanions [Si2O(PO4)6]12− and double-octahedra [InIIITiIVO9] occur as coordination polyhedra besides isolated octahedra [TiIVO6] and tetrahedral phosphate groups. The results of 29Si and 31P-MAS-NMR studies are in agreement with one crystallographically independent site for silicon and two sites for phosphorus. The phosphorus resonances can be related to the two sites by 2-dimensional cross-polarisation experiments, by the anisotropies of their chemical shifts, and by the observed line widths. All criteria lead to the same assignment. Substitution of In3+ by several trivalent transition metal ions leads to phosphate-silicophosphates M2Ti6(PO4)6[Si2O(PO4)6] (M = Ti3+, V3+, Cr3+, Fe3+)

Solid Solutions of the System V2O5-V2O4-TiO2 in Air

Gravimetry in combination with X-ray phase analysis, X-ray crystallography, and X-ray densitometry were used to determine the contents of V5+, V4+, and Ti4+ ions and vacancies in solid solutions formed by the reaction of V2O5 with TiO2 in air at atmospheric pressure.

Photocatalytic Activity and Electrochemical Impedance Spectroscopy of TiO<sub>2</sub> Thermally Treated by Hydrogen

Tio2 treated in hydrogen atmosphere showed enhanced photocatalytic activity in degrading the sulfosalicylic acid (ssal),the results of the electrochemical impedance spectroscopy (eis) investigation showed that the diameters of the capacitive arcs for the h-tio2 were much smaller than those of bare tio2 and thermally treated tio2 in air, indicating that the charge transfer of the h-tio2 occurs more rapidly, thus inviting a higher photocatalytic activity. when an external bias was applied on the h-tio2, the arc of the eis nyquist plot decreased obviously than without the bias, suggesting more efficient separation of the photo-generated carriers.

Enhancing Effect of Iron Chlorides on the Anatase‐Rutile Transition in Titanium Dioxide

The effect of solid Fe2O3 and gaseous iron chlorides on the anatase‐rutile phase transition was investigated in the temperature range of 750°‐950°C via X‐ray diffractometry and scanning electron microscopy. In both cases, iron diffusion in the anatase lattice decreased the transition temperature and increased the anatase‐rutile transformation rate, in comparison with that in TiO2 fired in air. The enhancement effect of iron on the anatase‐rutile transition is understood on the basis of oxygen‐vacancy formation, which favors rutile nucleation. Solid‐state iron diffusion between the contact points of TiO2 and Fe2O3 particles and vapor mass transport through gaseous chlorides were the primary mechanisms of iron mass transport to the TiO2 surface in the presence of both Fe2O3 and gaseous iron chlorides, respectively. The transformation rate at a given reaction temperature increased in the following order of reaction conditions: pure TiO2 in air, TiO2 in the presence of Fe2O3 in air, TiO2 in the presence of Fe2O3 in chlorine, and TiO2 in the presence of gaseous iron chlorides.

Photocatalytic Activity of Amorphous−Anatase Mixture of Titanium(IV) Oxide Particles Suspended in Aqueous Solutions

Titanium(IV) oxide (TiO2) powders of various amorphous−anatase compositions were prepared by heat treatment (573−1073 K) of amorphous TiO2 in air and characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and BET surface area measurements. An exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction of amorphous phase. The fraction of anatase crystallites (f(anatase)) was calculated as the remainder after the amorphous phase and contaminated water or organic residue. The XRD data showed that the size of anatase crystallites was slightly decreased but almost constant along with the increase in f(anatase), being consistent with the small change in the BET surface area. These results suggest that each amorphous particle transforms into an anatase crystallite of similar size without sintering or crystal growth. The particles of mixture of amorphous and anatase were ...

Novel synthesis of microcrystalline titanium(IV) oxide having high thermal stability and ultra-high photocatalytic activity: thermal decomposition of titanium(IV) alkoxide in organic solvents

Thermal decomposition of titanium(IV) tetra-tert-butoxide (TTB) in inert organic solvents at 573 K yielded microcrystalline anatase (titanium(IV) oxide, TiO2) powders with a crystallite size of ca. 9 nm and a surface area of <100 m2 g-1. Primary and secondary alkoxides of titanium(IV), however, were not decomposed under similar conditions, indicating that the thermal stability of C-O bonds in the alkoxides was a decisive factor for their decomposition. The TiO2 prepared from TTB by this manner was thermally stable upon calcination in air and retained high surface area of ca. 100 m2 g-1 even after calcination at 823 K. The as-prepared TiO2 powders, without calcination, exhibited much higher rate of carbon dioxide formation than any other active photocatalysts such as Degussa P-25 and Ishihara ST-01 in the photocatalytic mineralization of acetic acid in aerated aqueous solutions. The higher activity of the present TiO2 photocatalysts is attributed to both high crystallinity and large surface of the present product. The calcination of the as-prepared TiO2 in air reduced the photocatalytic activity, but it was still higher than the other commercially available TiO2's.

ChemInform Abstract: A2Ln2Ti3O10 (A: K or Rb; Ln: La or Rare Earth Metal): A New Series of Layered Perovskites Exhibiting Ion Exchange.

AbstractThe title perovskites are synthesized by heating appropriate mixtures of A2CO3, Ln2O3 (Ln: La, Nd, Sm, Gd, Dy), and TiO2 in air at 1000 °C for 2 d. The hygroscopic compounds and their monohydrates both crystallize in a tetragonal structure similar to Sr4Ti3O10.

Formation of BaTiO3 from BaCO3 and TiO2 in Air and in CO2

The formation of BaTiO3 from equimolar BaCO3 and TiO2 (rutile) mixtures was studied in air and in CO2. A small amount of BaTiO3 is formed first directly from BaCO3 and TiO2 at the surface of contact. From then on it is a diffusion‐controlled reaction, and both BaTiO3 and Ba2TiO4 are produced, with Ba2TiO4 being formed in much larger amounts. In 1 atmosphere of CO2, the intermediate Ba2TiO4 was suppressed up to a temperature of about 1100°C. in agreement with thermodynamic calculations. Ba2TiO4 reacts fast with 1 atmosphere of CO2 below about 1100°C. to produce BaTiO3and BaCO3