Rutile Titanium Research Articles

Simultaneous measurement of electric field gradient both at 111Cd and 181Ta sites in a single perturbed γ–γ angular correlation measurement

Present work demonstrates, for the first time, the use of multiple probes in a single time differential perturbed angular correlation (TDPAC) measurement. Two different probes, viz., 111In/111Cd and 181Hf/181Ta, simultaneously have been incorporated in both pure rutile and Hafnium (Hf)-doped rutile Titanium Dioxide (TiO2) systems following a soft chemical method. The rutile structure was identified by the hyperfine parameters, viz., quadrupole frequency (ω Q) and asymmetry (η). Due to the doping of Hf at 5 and 10 at.%, the sample partially lost the purity of the crystal and the fact has been reflected at both the probe sites.

A DFT+U investigation on methylamine decomposition catalyzed by Pt4 cluster supported on oxygen defective rutile(110) TiO2

The adsorption and decomposition mechanisms of methylamine catalyzed by Pt4 cluster supported on rutile(110) titania[namely, Pt4/TiO2-R(110)] were investigated via density functional theory slab calculations with Hubbard corrections(DFT+U). The adsorption energies under the most stable configuration of the possible species and the energy barriers of the possible elementary reactions involved in methylamine decomposition were obtained. Through systematic calculations for the reaction mechanism of methylamine decomposition on the Pt4/TiO2-R(110), the most possible decomposition path is CH3NH2→CH2NH2+H→CH2NH+2H→CHNH+3H→HCN+4H→ CN+5H, which is similar to that of methylamine dissociation catalyzed by Pt(100) surface.

Methanol Photo-Oxidation on Rutile TiO2 Nanowires: Probing Reaction Pathways on Complex Materials

Understanding photochemical processes on nanomaterials is key to developing effective photocatalysts. Herein, methanol oxidation and reduction is used to probe the thermal and photochemical properties of rutile titania nanowires grown using a hydrothermal method. The presence of oxygen vacancy defects leads to methoxy formation and subsequent disproportionation to formaldehyde and methanol at 700 K. Methane and dimethyl ether are also produced in minor quantities. Oxygen adatoms enhance the formation of methoxy, which led to an increase in the disproportionation products and dimethyl ether at high temperature and a decreased amount of methane. The thermal reactivity of the nanowires parallels that of rutile TiO2(110) single crystals. Photo-oxidation of methoxy using UV light produced formaldehyde and methyl formate. These product yields were enhanced on nanowires with oxygen adatoms, but a majority of methoxy (∼70%) is not photoactive. In contrast, all methoxy is photo-oxidized on rutile TiO2(110) when O-adatoms are present. This difference indicates that holes created in the nanowires during UV excitation do not migrate to most of the methoxy—a required step for methoxy photo-oxidation. This lack of activity could be due to either trapping of holes in the material or different binding of the inactive methoxy. These studies demonstrate that while charge carriers can be efficiently created in nanowires differences in chemical properties can suppress photo-oxidation.

Origin of the type-II band offset between rutile and anatase titanium dioxide: Classical and quantum-mechanical interactions between O ions

Titanium dioxide is one of the most promising semiconductors for photocatalytic splitting of water for hydrogen. The mixed rutile/anatase system shows even more favorable photocatalytic properties than the pristine ones. Band offset is a key factor that determines the photocatalytic activity of the mixed phase. However, the type of band alignment and the value of the band offset are still under debate both experimentally and theoretically. The difficulty of determining the band offset by commonly used core-level alignment calculation lies in the different symmetry and large lattice mismatch between the two phases. Here, we adopt our recently developed three-step method, which can overcome the lattice mismatch problem, to study the band offset with high accuracy. In the calculation, we used an intermediate phase $\mathrm{Ti}{\mathrm{O}}_{2}\mathrm{II}$ to build superlattice models of rutile(101)//$\mathrm{Ti}{\mathrm{O}}_{2}\mathrm{II}(001)$ and $\mathrm{Ti}{\mathrm{O}}_{2}\mathrm{II}(100)$//anatase(112) to determine the core-level alignment. Our studies show a type-II, staggered band alignment, with the valence band maximum (VBM) of rutile 0.80 eV above that of anatase, in agreement with recent experimental results. We further analyzed the electronic structure of the two phases, and found that the band offsets of the VBM originate from both the electrostatic interaction and electronic hybridization in rutile and anatase, which contribute 0.36 eV and 0.44 eV, respectively.

Stability of V2O5 Supported on Titania in the Presence of Water, Bulk Oxygen Vacancies, and Adsorbed Oxygen Atoms

A catalyst consisting of vanadium oxide submonolayers supported on rutile titanium dioxide is used for a variety of reactions. One important question is the difference between the activity of monomeric clusters (having one vanadium atom) and polymeric clusters (having more than one vanadium atom). In the case of oxidative dehydrogenation of alkanes and methanol, the reaction produces water, oxygen vacancies, and hydrogen atoms bound to the surface. For this article we use density functional theory to examine how the presence of these species on the surface affects a V2O5 cluster, which we assume to be a representative of a polymeric species. We find that often the presence of other species on the surface can change the composition of the cluster or break it up into two monomeric clusters.

Improving the photovoltaic parameters in Quantum dot sensitized solar cells through employment of chemically deposited compact titania blocking layer

Incorporation of compact blocking layer at the Transparent Conducting Oxide (TCO)/Electrolyte interface is an effective method to improve the device performance in QDSSC through mitigation of electron recombinations at this interface. This paper reports the most facile and cost effective method of depositing a rutile titania Compact Layer (CL) over Fluorine doped Tin Oxide (FTO) substrate and its application in titania based CdS QD sensitized solar cells. The deposited compact layers are characterized to study their structural, optical, morphological and electrochemical properties using X-Ray Diffractometry, UV–Visible spectroscopy, Scanning electron microscopy, Cyclic Voltammetry and Contact Angle measurements. Sandwich solar cells are fabricated using these CL based electrodes and characterized using Electrochemical Impedance Spectroscopy, Open Circuit Voltage Decay and J-V characteristics. The CL incorporated CdS QDSSC showed more than 100% increase in the photoconversion efficiency (1.68%) as compared to its bare FTO counterpart (0.73%) proving the efficacy of employed strategy.

Investigation of chemical tooth mechanism in chemical mechanical planarization of germanium

The effect of pH on germanium (Ge) chemical mechanical planarization (CMP) removal rate (RR) using polymorphs of titania was investigated. Rutile and anatase polymorphs of titania were used to study the removal rate of germanium in absence of oxidizer. Polishing experiments performed using rutile titania showed highest removal rate at pH 3, and subsequently decreased with pH and became negligible at pH 11. However, no material removal was observed with anatase polymorph for the entire pH range investigated in this work. Higher Ge removal using rutile abrasive can be attributed to the formation of Ti-O-Ge bond due to the structural similarity of polishing surface and abrasive. Ge RR showed a linear relationship with pressure and table speed, following Prestonian behavior.

Three-dimensional flower-like rutile TiO2 microsphere composed of nanorods: a potential material as light scattering layer for DSSCs

The low spectrum utilization and the recombination of photo-generated electrons are the main challenges for improving the performance of dye sensitized solar cells(DSSCs). In this article, a three-dimensional flower-like rutile titanium dioxide(TDF-TiO2) was successfully synthesized via a simple sol-thermal process. X-Ray diffraction patterns(XRD) and scan electron microscopy(SEM) images exhibit that the TDF-TiO2 are the rutile TiO2 microsphere composed of lots of regular cuboid nanorods. Applying this TDF-TiO2 as light scattering layer on the photoanode of DSSCs, the devices present an excellent photovoltage performance, yielding a power conversion efficiency(PCE) of 7.69%, which can be mainly attributed to the enhanced light utilization and the reduced recombination of pho-to-generated electrons upon a combined analysis of electrochemical impedance spectroscopy(EIS), open-circuit vol-tage decay(OCVD), and intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spec-troscopy(IMPS/IMVS), etc. As a conclusion, TDF-TiO2 is a potential material as light scattering layer and optical transition medium to improve the performance of DSSCs, and this work further demonstrated that regulating the morphology and particle size of TiO2 is an efficient approach for enhancing the performance of DSSCs by optimizing the utilization of light and the transporting behaviors of photo-generated electrons.

100-fold improvement in carrier drift mobilities in alkanephosphonate-passivated monocrystalline TiO2 nanowire arrays

Single crystal rutile titania nanowires grown by solvothermal synthesis are actively being researched for use as electron transporting scaffolds in perovskite solar cells, in low detection limit ultraviolet photodetectors, in photoelectrochemical water-splitting, and in chemiresistive and electrochemical sensing. The electron drift mobility (μn) in solution-grown TiO2 nanowires is very low due to a high density of deep traps, and reduces performance in optoelectronic devices. In this study, the effects of molecular passivation of the nanowire surface by octadecylphosphonic acid (ODPA), on carrier transport in TiO2 nanowire ensembles, were investigated using transient space charge limited current measurements. Infrared spectroscopy indicated the formation of a highly ordered phosphonate monolayer with a high likelihood of bidentate binding of ODPA to the rutile surface. We report the hole drift mobility (μp) for the first time in unpassivated solvothermal rutile nanowires to be 8.2 × 10−5 cm2 V−1 s−1 and the use of ODPA passivation resulted in μp improving by nearly two orders of magnitude to 7.1 × 10−3 cm2 V−1 s−1. Likewise, ODPA passivation produced between a 2 and 3 order of magnitude improvement in μn from ∼10−5–10−6 cm2 V−1 s−1 to ∼10−3 cm2 V−1 s−1. The bias dependence of the post-transit photocurrent decays in ODPA-passivated nanowires indicated that minority carriers were lost to trapping and/or monomolecular recombination for small values of bias (<5 V). Bimolecular recombination was indicated to be the dominant recombination mechanism at higher bias values.

Study of conversion of butadiene to CO2 by rTiO2 nanoparticles: ZINDO/S

One of the pollutants emitted from automobile exhaust is unburned hydrocarbons that include benzene, propane, formaldehyde, butadiene, etc. Due to the carcinogenicity of these substances, eliminating and reducing them in the source of production is essential. Catalytic converters have been developed to reduce these pollutions to low-risk materials in automobile exhaust. In this study, the mechanism of converting butadiene to carbon dioxide is simulated and calculated by rutile titanium dioxide (Titania) nanoparticles (rTiO2-NP). Then the geometric structure of simulated steps (the conversion butadiene to carbon dioxide) is optimized by DFT method and semi-empirical (ZINDO/S) method is used to calculate the thermodynamic properties. There are three different locations of physical chemistry on the rTiO2-NPs to get closer pollutants, namely Ti–O (1), Ti–O (2), and Ti–Ti. The results show the approaching possibility of butadiene to Ti–O (1) is more than other locations, because the bond length, electronegativity and spatial structure of this position are different from others.

Interfacial Interaction of Titania Nanoparticles and Ligated Uranyl Species: A Relativistic DFT Investigation.

To understand interfacial behavior of actinides adsorbed onto mineral surfaces and unravel their structure-property relationship, the structures, electronic properties, and energetics of various ligated uranyl species adsorbed onto TiO2 surface nanoparticle clusters (SNCs) were examined using relativistic density functional theory. Rutile (110) and anatase (101) titania surfaces, experimentally known to be stable, were fully optimized. For the former, models studied include clean and water-free Ti27O64H20 (dry), partially hydrated (Ti27O64H20)(H2O)8 (sol) and proton-saturated [(Ti27O64H20)(H2O)8(H)2]2+ (sat), while defect-free and defected anatase SNCs involving more than 38 TiO2 units were considered. The aquouranyl sorption onto rutile SNCs is energetically preferred, with interaction energies of -8.54, -10.36, and -2.39 eV, respectively. Energy decomposition demonstrates that the sorption is dominated by orbital attractive interactions and modified by steric effects. Greater hydrogen-bonding involvement leads to increased orbital interactions (i.e., more negative energy) from dry to sol/sat complexes, while much larger steric interaction in the sat complex significantly reduces the sorption interaction (i.e., more positive energy). For dry SNC, adsorbates were varied from aquo to aquo-carbonato, to carbonato, to hydroxo uranyl species. Longer U-Osurf/U-Ti distances and more positive sorption energies were calculated upon introducing carbonato and hydroxo ligands, indicative of weaker uranyl sorption onto the substrate. This is consistent with experimental observations that the uranyl sorption rate decreases upon raising solution pH value or adding carbon dioxide. Anatase SNCs adsorbing aquouranyl are even more exothermic, because more bonds are formed than in the case of rutile. Moreover, the anatase sorption can be tuned by surface defects as well as its Ti and O stoichiometry. All the aquouranyl-SNC complexes show similar character of molecular orbitals and energetic order although differing in highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps and orbital energy levels, but changes can be accomplished by adding carbonato and hydroxo ligands.

Cobalt Oxide Nanoclusters on Rutile Titania as Bifunctional Units for Water Oxidation Catalysis and Visible Light Absorption: Understanding the Structure-Activity Relationship.

The structure of cobalt oxide (CoOx) nanoparticles dispersed on rutile TiO2 (R-TiO2) was characterized by X-ray diffraction, UV-vis-NIR diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, X-ray absorption fine-structure spectroscopy, and X-ray photoelectron spectroscopy. The CoOx nanoparticles were loaded onto R-TiO2 by an impregnation method from an aqueous solution containing Co(NO3)2·6H2O followed by heating in air. Modification of the R-TiO2 with 2.0 wt % Co followed by heating at 423 K for 1 h resulted in the highest photocatalytic activity with good reproducibility. Structural analyses revealed that the activity of this photocatalyst depended strongly on the generation of Co3O4 nanoclusters with an optimal distribution. These nanoclusters are thought to interact with the R-TiO2 surface, resulting in visible light absorption and active sites for water oxidation.

Surfactants assisted solvothermal derived titania nanoparticles: synthesis and simulation

Solvothermal method was used to prepare titanium dioxide (TiO2) nanoparticles (NP’s) of various morphologies at 180 °C growth temperature. Acetic acid and oley amine were used as surfactants. The powder of TiO2 was annealed at 550 and 950 °C for 18 and 24 h. The influence of surfactants on the morphology of titania NP’s was investigated using transmission electron microscopy (TEM). The structural, optical, and molecular properties of titania NP’s are investigated by means of X-ray diffraction, UV–visible, Photoluminescence, and Fourier Transform Infrared. The physical properties, surface area and pore volume, of the samples were investigated by Brunauer-Emmett-Teller and Barrett-Joyner-Halenda measurement. The results illustrated type IV adsorption isotherms for all samples, implying the characteristics of mesoporous materials (2–50 nm). Furthermore, the hysteresis loops shifted to higher relative pressure, indicating that the specific surface area increases and the pore size decreases after heat treatment. Micrograph images acquired from TEM portrayed different shapes such as irregular spherical, rounded rectangular, truncated rhombic, and rod-like for titania NP’s when various surfactants were used. Monte-Carlo simulation carried out for pristine and rutile titania NP’s as representative samples explained the growth mechanism of titania NP’s and corroborated the formation of spherical and rod-like structures due to attractive and repulsive interactions among particle respectively.

Morphologically tuned 3D/1D rutile TiO2 hierarchical hybrid microarchitectures engineered by one-step surfactant free hydrothermal method

Present investigation reports on the surfactant free hydrothermal synthesize of the morphologically tuned hierarchical hybrid rutile titanium oxide (TiO2) microarchitectures showing three dimensional microflower structures and cook pine tree like structures on the one dimensional nanorods formed over TiO2 seed layer coated glass substrates by tuning growth temperature. TiO2 seed layer of ∼100nm thick was coated on the glass substrates employing sol–gel spin coating method and then rutile TiO2 microarchitectures were synthesized on the TiO2 seed layer by one-step surfactant free hydrothermal method. Deposited samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, UV–vis spectroscopy and photoluminescence spectroscopy techniques. Influence of the growth temperature on the crystallinity, morphology and optical properties along with the growth mechanism to achieve hierarchical microarchitectures was investigated. Present work revealed that the structural, morphological and optical properties of the TiO2 hierarchical microarchitectures strongly depend on the growth temperature. Further we proposed a model for the cause to effect possible morphological changes of rutile TiO2 microarchitectures as a function of growth temperatures on the TiO2 seeded glass substrates.

Hydroxyl-Induced Partial Charge States of Single Porphyrins on Titania Rutile

The adsorption of Cu–porphyrin derivatives terminated with peripheral carboxyphenyl side groups on hydroxylated TiO2(110) surfaces is investigated by combined scanning tunneling microscopy (STM), atomic force microscopy (AFM), and density functional theory (DFT). Two distinct contrasts of the molecules are revealed by STM and tunneling spectroscopy. Via single-molecule manipulations, the origin of these peculiar contrasts is found to arise from the presence or not of hydroxyl groups below the molecules. Hence, the electronic coupling of the molecule with the underlying TiO2 surface is locally modified altering the amount of charge transfer and thus their charge state at the molecular scale. Our results particularly underline the fundamental role of hydroxyls of TiO2 on the charge state of adsorbed organic molecules potentially used in dye-sensitized solar cells.

Low-temperature chemical synthesis of rutile and anatase mixed phase TiO2 nanostructures for DSSCs photoanodes

Abstract Wet chemical deposition method by using copper salt doping approach is used to synthesize mixed phase (rutile and anatase) titanium dioxide (TiO 2 ) nanostructures. Pristine and Cu-doped TiO 2 photoanodes are analyzed for their physical properties. The results showed a significant influence of Cu-salt concentration in tuning the TiO 2 properties in terms of structural, morphological, porosity, optical and electrochemical properties. The Cu-free TiO 2 photoanode is rutile in structure whereas when Cu-doping level is increased, beyond 0.003 M, is transformed to mixed rutile-anatase structure. Presence of copper (Cu) in different weight percentages was confirmed from the surface energy dispersive X-ray analysis. Effect of Cu-doping on the power conversion efficiency of TiO 2 -based dye-sensitized solar cells is investigated. At 0.005 M Cu-doping level, both power conversion and incident-photon-to-current-conversion efficiencies of TiO 2 electrode are optimal i.e. 3.32% and 46% respectively; consistent to electron life time measurement where with increase in Cu-doping level from 0.001 to 0.005 M an electron life time of TiO 2 photoanode is increased from 0.1893 ms to 0.5967 ms.

CH3NH3PbI3 converted from reactive magnetron sputtered PbO for large area perovskite solar cells

Adopting DC reactive magnetron sputtering technique, PbO film was fabricated on FTO-glass substrate coated with a nanocrystalline rutile titania (NRT) by using a pure metallic lead target in an Ar/O2 mixture. Then the as-prepared PbO film was converted to CH3NH3PbI3 through the sequential reactions occurred in isopropanol solution of CH3NH3I. The as-prepared perovskite film exhibits a surface morphology of high uniformity and good coverage over a large scale; the crystal grains reach the size of up to 600nm, which is beneficial for enhancing light absorption and decreasing grain boundary. The solar cells with a structure of FTO/NRT/CH3NH3PbI3/Spiro-MeOTAD/Au were fabricated, where NRT was employed as the contact layer of the photovoltaic devices. Our champion cells with active area of 0.09cm2 and 1.07cm2 achieve the highest power conversion efficiency of 14.1% and 10.7%, respectively, under the standard AM 1.5 conditions. The present approach is competent for the fabrication of large area perovskite solar cells with the advantages of easy control, cost-saving, and less use of toxic reagents, and thus with potential applications.

Photocarrier dynamic measurement of rutile TiO2 films prepared by RF magnetron reactive sputtering

In this work, rutile titanium dioxide (TiO2) films were prepared on quartz and SiO2/Si substrates utilizing RF magnetron reactive sputtering technology. Crystal structure, surface morphology and optical property of these films were characterized to verify the obtainment of well crystalline rutile TiO2 films. The dynamics of photocarriers were studied by using temporally resolved transient absorption measurements. The differential reflectivity as a function of pump fluence was investigated. We also directly obtained a carrier lifetime of about 286 ps. The absorption cross-section and the absorption coefficient of free carrier at 800 nm were 1.87 × 10−17 cm2 and 32.9 cm−1, respectively.

Chemi-resistive response of rutile titania nano-particles towards isopropanol and formaldehyde: a correlation with the volatility and chemical reactivity of vapors

The performance of phase pure rutile titania nano-particles for gas/vapor sensing is not well explored in open literature, mostly because of their moderate chemical activity. However, the high thermal stability of rutile titania could be beneficial towards making a stable chemi-resistive sensor, operable generally at higher temperature. Herein, we have investigated the chemi-resistive response characteristics of rutile phase titania nano-particles for the detection of isopropanol and formaldehyde vapors. Titania nano-particles are synthesized through a hydrothermal route and characterized in terms of their phase formation behavior and micro-structural features. The sensing characteristics of the particles are measured by varying the operating temperature (275 °C–350 °C) of the sensor and concentrations (20–200 ppm) of the vapors, using a static flow gas sensing measurement set-up. The rutile titania particles are found more responsive towards isopropanol than formaldehyde. An attempt is made here to correlate the sensing performance of titania sensors with the volatility and chemical reactivity of studied vapors. The higher response of the sensor towards isopropanol is predicted, due to its comparatively lower volatility and more suitable chemical structure for oxidation on the sensor surface.

Enhanced Visible-Light-Sensitive Two-Step Overall Water-Splitting Based on Band Structure Controls of Titanium Dioxide and Strontium Titanate

Visible light-induced two-step overall water-splitting was achieved by combining two types of photocatalysts, which were prepared by introducing foreign elements into rutile titanium dioxide (TiO2) and strontium titanate (SrTiO3) with a controlled electronic band structure. Rutile TiO2 and SrTiO3 were doped with chromium and tantalum (Cr,Ta-TiO2) and with rhodium (Rh-SrTiO3), respectively, to introduce visible-light sensitivity. Under irradiation with only visible light from a 420-nm LED lamp, the simultaneous liberation of hydrogen and oxygen with a molar ratio of ~2:1 was achieved with these two types of photocatalysts in the presence of iodate ion/iodide ion as a redox mediator.