TiO2 Compounds Research Articles

Dye-sensitized solar cells based on a single layer deposition of TiO2 from a new formulation paste and their photovoltaic performance

A new strategy for enhancing the efficiency and reducing the production cost of TiO2 solar cells by design of a new formulated TiO2 paste with tailored crystal structure and morphology is reported. The conventional three- or four-fold layer deposition process was eliminated and replaced by a single layer deposition of TiO2 compound. Different TiO2 pastes with various crystal structures, morphologies and crystallite sizes were prepared by an aqueous particulate sol–gel process. Based on simultaneous differential thermal (SDT) analysis the minimum annealing temperature to obtain organic-free TiO2 paste was determined at 400°C, being one of the lowest crystallization temperatures of TiO2 photoanode electrodes for solar cell application. Photovoltaic measurements showed that TiO2 solar cell with pure anatase crystal structure had higher power conversion efficiency (PCE) than that made of pure rutile-TiO2. However, the PCE of solar cells depends on the anatase to rutile weight ratio, reaching a maximum at a specific value due to the synergic effect between anatase and rutile TiO2 nanoparticles. Moreover, it was found that the PCE of solar cells made of crystalline TiO2 powders was much higher, increasing in the range 32–84% depending on anatase to rutile weight ratio, than that of prepared by amorphous powders. TiO2 solar cell with the morphology of mixtures of nanoparticles and microparticles had higher PCE than the solar cell with the same phase composition containing TiO2 nanoparticles due to the role of TiO2 microparticles as light scattering particles. The presented strategy would open up new insight into fabrication and structural design of low-cost TiO2 solar cells with high power conversion efficiency.

Elaboration, charge-carrier lifetimes and activity of Pd-TiO2 photocatalysts obtained by gamma radiolysis

Abstract The surface of four commercial TiO2 compounds (Cristal Global PC-series) has been modified by Pd nanoparticles induced by gamma radiolysis. Their photocatalytic properties have been followed by phenol and rhodamine B photocatalytic degradation in aqueous suspensions under UV and visible light. Their electronic properties have been studied by time resolved microwave conductivity (TRMC) method to follow the charge-carrier dynamics. The experiments evidence a complex behavior of the surface-Pd. Its influence depends on the pollutant and on the irradiation. The modification may be strongly favorable to the photocatalytic activity. The results have been interpreted in terms of modification of charge-carrier dynamics with TRMC measurements. The surface-Pd plays a role in charge-carrier separations, increasing the photocatalytic activity under UV-light, but shows no effect on the absorption properties, preventing the creation of an activity under visible light.

An X-ray Photoelectron Spectroscopy Investigation of Redeposition from Fluorine-based Plasma Etch on Magnetic Recording Slider Head Substrate

Re-deposition is an etched by-product in the Reactive Ion Etching (RIE) process well known the causing dirty on etching work piece. In this work, we aim to investigate the re-deposition of fluorine-based plasma etch on the Al2O3-TiC substrate. To select the suitable chemical solution for cleaning, it's necessary to know that the chemical bonding of the re-deposition material. Thermodynamic theory is used to predict the potential of re-deposition compounds which should be found in our experiment. The real re-deposition is prepared by the RIE etching system. The morphology of the re-deposition is investigated by scanning electron microscope (SEM). The elemental composition and chemical bonding are characterized by X-ray photoelectron spectroscopy (XPS).Thermodynamic predicts that the re-deposition presented in our experiment should be composed of AlF3(s), TiF4(s), TiF3(s) and TiF2(s). The result showed XPS could detect the prepared re-deposition contained fluorine 31.2 At%, oxygen 23.7 At%, carbon 23.7 At%, aluminium 16.0 At% and titanium 5.4 At%. The chemical bonding; AlF3, AlF6, CF, CO, C2 and TiO2 are formed to be the re-deposition material. The in-coincidence between thermodynamic prediction of forming Ti-F compounds versus Ti-O compound as found in the experiment was able to explain via the oxidation state of atoms; the oxidation state of the sputtered Ti atoms is +4 is suitable to have the reaction with sputtered oxygen atoms (from the substrate) that have an oxidation number +2, forming the TiO2 compound.

Preparation and Photocatalytic Properties of Magnetic TiO<sub>2</sub> Compounds

In this paper, magnetic composite photocatalysts were prepared through depositing TiO2 on the surface of NiFe2O4 by sol-gel method. The composition, structure and magnetism of the samples are tested by XRD, TEM and VSM, respectively. The photoactivity of the as-prepared photocatalysts was investigated by degrading methyl orange under UV light. The effect of NiFe2O4 and SiO2 intermediate layer on the activity of photocatalyst was also studied. It has been found that NiFe2O4 has a negative influence on the photocatalytic activity of magnetic TiO2 compounds. The middle layer of SiO2 can effectively improve the photocatalytic activity of magnetic TiO2 compounds.

Non-magnetic impurity induced magnetism in rutile TiO2:K compounds

Recent ab initio studies have theoretically predicted room temperature ferromagnetism in several oxide materials of the type AO2 in which the cation A4+ is substituted by a non-magnetic element of the 1 A column. Our purpose is to address experimentally the possibility of magnetism in Ti1−xKxO2 compounds. The samples have been synthesized via the solid state route method at equilibrium. Our study has shown that Ti1−xKxO2 is thermodynamically unstable and leads to a phase separation, in contradiction with the hypothesis of ab initio calculations. In particular, the crystalline TiO2 grains appear to be surrounded by K-based phase. The oxidization state of the Ti ion is found to be in Ti4+ as confirmed from the x-ray photoelectron spectra measurement. Nevertheless, K:TiO2 compounds exhibit weak paramagnetism with the highest magnetic moment of ∼0.5 μB K−1 but no long-range ferromagnetic order. The observed moment in these compounds remains much smaller than the predicted moment of 3 μB by ab initio calculation. The apparent contradictions between our experiments and first-principles studies are discussed.

Charge–discharge properties of a layered-type Li(Ni,Co,Ti)O2 powder library

A powder library of layered Li(Ni,Co,Ti)O2 (Ni ≤ 0.8, Ti ≤ 0.2) compounds was prepared by electrostatic spray deposition. From powder x-ray diffraction patterns, most of the powder library sintered at 700 ○C was indexed as a single phase belonging to the space group Rm. These results were almost identical to those obtained from a study by combinatorial exploration. We investigated the charge–discharge characteristics of the Li(Ni,Co,Ti)O2 powder library in a voltage range from 4.2 to 2.8 V at 1 C and found favorable cycling properties in the LiNixCo0.9-xTi0.1O2 (0 ≤x ≤ 0.6) compounds.

The magnetic phase transition in titanium oxide induced by proton irradiation

We have studied the magnetic properties of 57Fe-doped TiO2 compounds irradiated by proton with 0, 5 and 10pC/μm2. We have observed the enhancement of the magnetic moment, measured by superconducting quantum interference device magnetometer, with increasing proton irradiation ranging from 0 to 10pC/μm2. Mössbauer spectra of proton irradiated Ti0.9957Fe0.01O2 samples were taken at room temperature. Two sites of the wing (sextet) and the central (doublet) are shown in the spectra, which suggest the magnetically ordered phase and the paramagnetic phase, respectively. With increasing proton irradiation, the part of Fe3+ ions was converted to Fe2+ ions by compensation charge. This clearly suggests that the enhancement of magnetic moment after proton irradiation is contributed to the moment by the spin-orbit coupling of Fe2+ ions.

A novel resonant inductive magnetic coupling wireless charger with TiO2 compound interlayer

A nonradiative energy transformer exploiting TiO2 nano-powder and (C4H6O2)x latex as a combined interlayer is proposed. The transformer works on ‘strong coupling’ between two coils (i.e., resonators), which are physically separated from each other by distances that are longer than the characteristic sizes of each resonator, to realize efficient wireless energy transfer. Nonradiative energy transfer between the two resonators is facilitated through the coupling of their resonant-field evanescent tails. Finite element analysis and experiments have been carried out to facilitate quantitative comparison. The efficiency of the proposed system is 70.6% at 5 cm and 26.3% at 15 cm at an operating frequency of 1.74 MHz. When compared with typical magnetic inductive coupling energy transmission devices with low dielectric constants, the efficiency of the proposed system is much higher.

CO2 Absorption and Desorption Abilities of Li2O–TiO2 Compounds

As an initial stage of the creation of a new solid material for carbon dioxide capture and storage (CCS), the behaviors of CO2 absorption and desorption were investigated in terms of Li2O–TiO2 compounds. The Li4TiO4 specimen began to absorb CO2 at 250°C with the formation of Li2TiO3 and Li2CO3 phases. The absorption rate was significantly enhanced at 710°C by the formation of the Li2CO3-based liquid phase. Decomposition of Li2CO3 was observed above 960°C in CO2 atmosphere and above 900°C in Ar-10%CO2 atmosphere. In the formation of solid Li2CO3 after Li4TiO4/CO2 reaction below 700°C, the reaction rate of CO2 absorption increased with the decreasing diameter of Li4TiO4 particles. The area ratio of the Li4TiO4 phase decreased and that of the Li2TiO3 phase increased in the Li4TiO4 sample after repeating the reaction path of CO2 absorption and desorption.

Synthesis and characterization of photosensitive TiO2 nanorods by controlled precipitation route

Nanocrystalline TiO2 thin films have been successfully synthesized by controlled precipitation route. These films are further annealed at 623 K for 2 h. The change in structural, morphological, optical, and wettability properties are studied by means of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM), optical absorption, and contact angle measurement. From the XRD pattern it is clear that the as-grown TiO2 films are amorphous in nature which becomes polycrystalline after annealing. The FTIR study reveals the formation of TiO2 compound. Scanning electron micrographs shows that the as-grown TiO2 film consists of agglomerated nanograins well covered to the substrate surface which gets converted into vertical nanorods after annealing. As-deposited and annealed TiO2 films showed hydrophilic behavior as water contact angles were 24° and 32°, respectively. The optical absorption study reveals the small red shift due to annealing and attributed to grain size. The annealed TiO2 film showed conversion efficiency of 0.037% in photoelectrochemical cell with 1 M NaOH electrolyte.

Nanoparticles dispersion in processing functionalised PP/TiO2 nanocomposites: distribution and properties

Future innovations in textiles and fibrous materials are likely to demand fibres with enhanced multifunctionality. The fibres can be functionalized by dispersing nanoadditives into the polymer during melt compounding/spinning. TiO2 nanoparticles have the potential to improve UV resistance, antistatic, as well as impart self-cleaning by photocatalysis and thereby de-odour and antimicrobial effects. In this study, a micro-lab twin-screw extruder was used to produce samples of polypropylene (PP) nanocomposite monofilaments, doped with nano titanium oxide (TiO2)/manganese oxide (MnO) compound having size ranging from 60 to 200 nm. As a control sample, PP filaments without additives were also extruded. Three samples were produced containing different concentrations (wt%) of the TiO2 compound, i.e. 0.95, 1.24 and 1.79%. Nano metal-oxide distribution in the as-spun and drawn nanocomposite filaments was analysed. Although, there are small clusters of the nanoparticles, the characterizing techniques showed good dispersion and distribution of the modified TiO2 along and across the processed filaments. From UV spectroscopy and TGA, a significant enhancement of polypropylene UV protection and thermal stability were observed: PP with higher percentage of TiO2 absorbed UV wavelength of 387 nm and thermally decomposed at 320.16 °C accompanied by 95% weight loss.

SYNTHESIS OF ANISOTROPIC LEAD TITANATE POWDERS FOR TEMPLATED GRAIN GROWTH OF TEXTURED PIEZOELECTRIC CERAMICS

Needle-shaped PbTiO3 (PT) template particles were successfully synthesized using two different types of approaches, molten salt synthesis (MSS) and thermal synthesis method. In eutectic NaCl–KCl molten salt system, homogeneous and nonagglomerated needle-shaped PT particles were produced from PbO and needle-like TiO2 compound heated at 800–850°C for 2 h. The effect of heating temperature on the morphology of formed powders was studied in order to identify the optimum processing parameters. The template formation mechanism is discussed. Using thermal synthesis method, comparable needle-shaped PT crystalline particles were also obtained in one step. Plate-shaped PT powders were derived via flux synthesis. The effect of additives such as MnCl2 and LiF on the morphology of derived PT was studied. Adding a certain amount of MnCl2 led to the formation of well-defined plate-shaped PT particles. The structure and morphology of synthesized powders were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM).

The reactive gas pulsing process for tuneable properties of sputter deposited titanium oxide, nitride and oxynitride coatings

TiOx, TiNy and TiOxNy thin films were deposited by reactive sputtering. The reactive gas pulsing process was implemented to tune the chemical composition and consequently, the characteristics of the films. For TiOx coatings, oxygen concentration was progressively modified from pure titanium to TiO2 compound. Similarly, a gradual decrease of the deposition rate and a controlled modulation of the chemical composition of TiNy films (y between 0 and 1.05) were easily reached. A reverse evolution of the oxygen and nitrogen contents was produced in TiOxNy films, which was correlated with the smooth transition from metallic to semiconducting behaviours.

Molecular Models of Crystalline Materials. TiO2 and Copper Compounds

The featured molecules for this month come from two papers dealing with crystalline materials and include the three polymorphs of TiO2 (rutile, anatase, and brookite) as well Cu3N, Cu2O, CuS, Cu2S, and CuS3.

Is There a Nanosize for the Activity of TiO2 Compounds?

Reactivity of TiO2 compounds is investigated vs nanosize using atomic hydrogen adsorption as a probe. Small clusters with (TiO2)n stoichiometry (n = 1−24) of lowest energy are compared with infinite systems like polymers and surfaces. The binding energy for the most reactive clusters reaches ∼3.5 eV while it is 2.8 eV for the smallest one (the TiO2 molecule) and 2.30 eV for the most reactive surface (rutile-110). No systematic relation with size emerges from this analysis which predicts a large variety of individual structures. High H binding energy is associated with the presence of poorly coordinated O atom at the surface and with a favorable reducibility of the substrate. The local topology of the adsorption site and its flexibility play a major role in reactivity. However, the reactivity of nanosized TiO2 clusters is correlated with small electronic gap and low lying LUMOs.

Heat-regulating coatings based on BaTi(1-y)Sn y O3 powders

Only one of the three mechanisms of heat transfer (heat conductivity, convection, and radiation), namely, radiation is possible for space vehicles (SV), since they have contact neither with a solid body (there is no contact with other objects), nor with a gas (they operate in deep vacuum). To maintain the thermal mode, active and passive heatregulating systems are used. Passive systems are heat-regulating coatings (HRC) put on heat-regulating radiators or separate units and devices. According to the law of heat emission, the SV temperature is determined by the fourth root of the ratio of the integral solar radiation absorption coefficient (аs) to the emissivity (e): Т ~ (аs /e). During orbital flights, the absorption coefficient аs of the reflecting HRC increases due to the formation of photo-induced and radiative defects that absorb light in the solar range of the spectrum [1–3]. Since the emissivity of all known HRC either remains unchanged or decreases insignificantly (by 5%), the SV temperature increases in flight, which can cause overheating of the equipment and even its failure. This calls for the development of methods of temperature stabilization, one of which can be based on the emissivity increase with the absorption coefficient аs. Another situation in which the emissivity must be changed during an orbital flight is observed for the absorbing coatings. When the SV are in the Earth’s shadow zone or are rotated about their axes even in the zone illuminated by the sun, a fragment of their surface is screened by the airframe and is in the shadow zone, and the surface temperature here decreases because of the lack of the heat source – electromagnetic solar radiation. One of the methods of temperature stabilization at a preset level can be the emissivity decrease with the absorption coefficient аs remaining unchanged. To solve these problems of space materials science, compounds with phase transitions (PT) and general formula A(1-x)BxC(1-y)DyOz in which cations A and (or) C are partly substituted by ions B and D can be used as pigments of reflecting and absorbing coatings. These compounds without substitutes have phase transitions in the temperature dependences of the electric, dielectric, thermophysical, and other properties; after incorporation of substitutes, the phase transitions are displaced along the temperature scale. The displacement magnitude and rate, as well as some other PT characteristics, are determined by the type and concentration of substituting ions and conditions of their incorporation. Works studying the phase transitions in the temperature dependence of the emissivity are few in number, though the importance and practical necessity of such results are obvious. Works with ceramic samples [4] and powders of manganites of rare earth elements [5] should be mentioned here. The present work studies phase transitions in the temperature dependence of the emissivity of synthesized BaTi(1-y)SnyO3 powders to estimate the possibility of their application as pigments of heat-regulating coatings of space vehicles and household and technological enamels. To prepare solid solutions of barium titanate, BaCO3, SnO2, and TiO2 compounds were mixed by a magnetic mixer in bidistilled water; the mixture was evaporated for 1 h at a temperature of 100°C and put in a heat-treatment furnace for synthesis. The compounds with stannum cation concentrations of 10, 15, and 20 mass% were synthesized. The powder so obtained was then mixed with KO-596 lacquer in the 0.4 : 0.6 ratio, and the mixture was put on metal substrates. The

Preparation of TiO2-coated LiCo1/3Ni1/3Mn1/3O2 by electrostatic self-assembly method and its properties

A precursor of TiO2–LiCo1/3Ni1/3Mn1/3O2 was prepared by electrostatic self-assembly method. The final product was obtained by heating the precursor at 400–450 °C for 4–6 h in air. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical tests were used to examine the structural, morphology, elementary valence, and electrochemical characteristics. XRD indicated that the TiO2-coated material can be indexed by α-NaFeO2 layered structure, which belongs to hexagonal-type space group R3m. XPS results confirmed the existence of TiO2 compound on the surface of the coated sample. The SEM image showed that the material had spherically porous morphology with the uniform size about 6 μm. The initial charge–discharge capacity of the TiO2-coated LiCo1/3Ni1/3Mn1/3O2 material was 168.8/160.0 mAh/g. After 60 cycles, the discharge capacity of the TiO2-coated LiCo1/3Ni1/3Mn1/3O2 sample was 147.0 mAh/g, and the coulombic efficiency was 94.0%. Compared with the uncoated sample, the electrochemical performance of TiO2-coated LiCo1/3Ni1/3Mn1/3O2 was improved.

BaO-Nd<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub> Nano-Ceramics Prepared by SPS Technology

Fine grained and dense dielectric ceramics of the BaO-Nd2O3-TiO2 system have been fabricated by the most advanced Spark Plasma Sintering (SPS) technology, whose average grain size is about 100nm as determined by SEM. XRD showed that the diffractive peak of the sample was broadened clearly. The nano-ceramic microstructure formed by SPS is due to the high pressure up to 50 MPa, low temperature (1000°C) and fast sintering (1 minute). The BaO-Nd2O3-TiO2 ternary nanoceramic sample, which consists of the main phase Nd2Ti2O7 with perovskite-like layer structure (PLS) and the secondary phase BaNd2Ti4O12（Ba4.5Nd9Ti18O54）with perovskite-like tungsten bronze structure, was prepared for the first time by rapidly sintering nano-particles of the xBaO×(0.35-x)Nd2O3×0.65TiO2 compound. Those two phases are formed in BaO-Nd2O3-TiO2 micron-grained ceramics prepared by normal sintering of the nano-particles at 1300°C, resulting in good dielectric characteristics for microwave ceramics; however, dielectric characteristics are significantly degraded in the SPS-sintered samples probably due to the carbon contamination from the graphite SPS dies.

Synthesis, Structural Change upon Heating, and Electronic Structure of Ramsdellite‐Type TiO2.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Phenol Photodegradation on Platinized-TiO2 Photocatalysts Related to Charge-Carrier Dynamics

Three commercial TiO2 compounds (Degussa P25, Sachtleben UV100, and Millenium PC50) and their platinized forms have been studied by the time-resolved microwave conductivity (TRMC) method to follow their charge-carrier dynamics and to relate it to the photocatalytic activity for phenol degradation in TiO2 aqueous suspensions. The degradation reaction has been studied in detail, following the time evolution of the concentration of phenol and its intermediates by liquid chromatography. The results show that platinization has a distinct influence on the commercial compounds, decreasing globally the activity of P25 and increasing the activity of PC50 and UV100. An influence of charge-carrier lifetimes on the photoactivity of pure and platinized TiO2 samples has been evidenced.