Atoms In TiO2 Research Articles

Morphological Characterization and Optical Properties of CIGS/TiO2 Thin Films Using Sputtering Technique

Solar energy as a renewable energy source, is currently an important alternative to meet energy needs because of its unlimited amount and environmentally friendly. Almost the entire surface of the earth receives sunlight optimally, so breakthroughs are needed to transform the solar energy into electricity. In the research development process that was to develop advanced materials to support the development of alternative energy. Thin film synthesis was carried out using the Physical Vapor Deposition (PVD) of Direct Current (DC) Sputtering method on Indium Tin Oxide (ITO) substrates using Copper Indium Gallium Selenide (CIGS) and TiO2 with deposition time variations of 30, 45, and 60 minutes. Based on the test results, thin film surface with the largest grain size is 266.75 nm at CIGS/TiO2 45 minutes. This shows that more CIGS and TiO2 atoms are released from the target surface, forming clumps that cover the substrate surface along with the addition of deposition time. The longer the deposition time shows the higher the absorbance value. The highest absorbance value is 4.60873, which was achieved by 60 minutes CIGS/TiO2 sample with wavelength of 271 nm.

Adsorption Characteristics between Ti Atoms of TiO2(100) and Corrosive Species of CO2-H2S-Cl- System in Oil and Gas Fields.

The service environment of OCTG (Oil Country Tubular Goods) in oil and gas fields is becoming more and more severe due to the strong affinity between ions or atoms of corrosive species coming from solutions and metal ions or atoms on metals. While it is difficult for traditional technologies to accurately analyze the corrosion characteristics of OCTG in CO2-H2S-Cl- systems, it is necessary to study the corrosion-resistant behavior of TC4 (Ti-6Al-4V) alloys based on an atomic or molecular scale. In this paper, the thermodynamic characteristics of the TiO2(100) surface of TC4 alloys in the CO2-H2S-Cl- system were simulated and analyzed by first principles, and the corrosion electrochemical technologies were used to verify the simulation results. The results indicated that all of the best adsorption positions of corrosive ions (Cl-, HS-, S2-, HCO3-, and CO32-) on TiO2(100) surfaces were bridge sites. A forceful charge interaction existed between Cl, S, and O atoms in Cl-, HS-, S2-, HCO3-, CO32-, and Ti atoms in TiO2(100) surfaces after adsorption in a stable state. The charge was transferred from near Ti atoms in TiO2 to near Cl, S, and O atoms in Cl-, HS-, S2-, HCO3-, and CO32-. Electronic orbital hybridization occurred between 3p5 of Cl, 3p4 of S, 2p4 of O, and 3d2 of Ti, which was chemical adsorption. The effect strength of five corrosive ions on the stability of TiO2 passivation film was S2- > CO32- > Cl- > HS- > HCO3-. In addition, the corrosion current density of TC4 alloy in different solutions containing saturated CO2 was as follows: NaCl + Na2S + Na2CO3 > NaCl + Na2S > NaCl + Na2CO3 > NaCl. At the same time, the trends of Rs (solution transfer resistance), Rct (charge transfer resistance), and Rc (ion adsorption double layer resistance) were opposite to the corrosion current density. The corrosion resistance of TiO2 passivation film to corrosive species was weakened owing to the synergistic effect of corrosive species. Severe corrosion resulted, especially pitting corrosion, which further proved the simulation results mentioned above. Thus, this outcome provides the theoretical support to reveal the corrosion resistance mechanism of OCTG and to develop novel corrosion inhibitors in CO2-H2S-Cl- environments.

Preparation of N-TiO2/SiO2 composites by solvothermal method and their photocatalytic properties

In order to improve the visible light catalytic activity of titanium dioxide (TiO2) and ensure its long-term stability on the surface of concrete, an N-TiO2/SiO2 composite was prepared using tetrabutyl titanate, nitric acid, and modified SiO2 nanospheres as the precursors by a solvothermal method. The effect of nitric acid on the phase composition, morphology and photoelectric properties of the synthesized photocatalytic composites was systematically studied by various characterization methods. The results show that the optimum nitric acid/butyl titanate volume ratio is 1/6. The nitrogen-doped TiO2 nanoparticles were uniformly dispersed on the surface of spherical SiO2 with a diameter of 200 nm. The degradation rate of simulated pollutants (RhB) with pH 5 and 7 exceeded 95% within 30 min and the catalytic effect remained excellent after five repetitions without much weakening. The excellent visible photocatalytic performance can be attributed to the doping of N replacing part of the oxygen atoms in TiO2, forming the energy level of N 2p at the O 2p energy level and reducing the TiO2 energy band gap to 2.99 eV. At the same time, the better dispersion of N-TiO2/SiO2 prepared by this new synthesis method also plays an important role in the improvement of visible light photocatalytic activity.

Transformation of diffusive to capacitive kinetics in nanoscale modified Co-TiO2@CNTs composites safeguarding steady reversible capacity as sodium-ion battery anode

The effective diffusion-controlled performance of the SIB anode, CoxTi1−xO2/CNTs, presented here offers high reversible sodium uptake. Kinetic studies of the samples conducted through cyclic voltammetry at various scan rates suggest that by increasing the mass ratio of Co atoms in TiO2 lattice the mechanism is shifted from a slow diffusive charge contribution to a fast capacitive charge contribution. Partial amorphization of the crystalline TiO2 diffraction planes revealed by ex-situ XRD along with the attenuation of the crystal lattice reflects the ability of the electrodes for high reversible sodium uptake. The synchronous effect of CNTs and Co loading enhance the porosity with multiple electronic/ionic conducting channels favouring high sodium storage and stability from 109.3 mAh g–1 in TiO2 to 168.5 mAh g–1 in Co0.03Ti0.97O2/CNT electrode after 80 cycles at a current rate of 0.05 C.

One‐step synthesis of Cu/N co‐doped TiO 2 nanocomposites with enhanced photocatalytic activities under visible‐light irradiation

In this research, a one-step hydrothermal method is used to prepare Cu-doped, N-doped and Cu/N co-doped titanium dioxide (TiO2) composites, and the doping effects on the structures, absorption and photocatalytic performance are investigated. All the products are in anatase structure. The substitution of Cu atoms in TiO2 and distribution of N in the crystal lattice have been identified by X-ray diffraction, which lead to the decrease of grain size. Hollow micro-nanospheres of Cu-TiO2 samples, which make them have strong dark adsorption properties, can be observed. Cu/N co-doped samples exhibit the maximum light absorption in the visible light region, and a red-shift which is responsible for narrow band gap energy owing to the presence of N-atoms and Cu-atoms in the TiO2 lattice. The synergistic effect of Cu and N results in the enhanced photocatalytic activity for degradation of methyl orange under visible light irradiation.

Doping of Chlorine from a Neoprene Adhesive Enhances Degradation Efficiency of Dyes by Structured TiO2-Coated Photocatalytic Fabrics

We demonstrate that using neoprene as a binder during the fabrication of TiO2-coated fabrics enhances the rates of photodegradation of dyes by the fabrics. The neoprene binder simultaneously modifies the surface of the TiO2 particles with Cl and dopes the TiO2 with Cl, without requiring high temperatures or other harsh laboratory treatments. The adsorption of chlorine on the surface and doping of the lattice with chlorine were confirmed by X-ray photoelectron spectroscopy. The chloride ions adsorbed onto the TiO2 surface introduces a negative surface charge that enhances electrostatic adsorption of cationic dyes, and greatly improves the self-sensitizing degradation performance of the dyes. Chloride ions replace lattice oxygen atoms in TiO2, inducing lattice oxygen vacancies, that reduce the apparent band gap of the TiO2 particles, enhancing its absorption of visible light, and further increasing the photocatalytic activity of the composite-coated fabric. The degradation rates of RhB and MB over 50 min were 95.2% and 96.0%, respectively. The degradation rate for MO reached 95.4% after 180 min. We also show that •OH and •O2− are active agents in the dye-degradation mechanism. Moreover, the photocatalytic performance of the composite-coated fabric was unchanged after eight cycles of photocatalytic degradation of RhB, demonstrating that the photocatalyst-coated fabrics was highly recyclable.

Doping of TiO2 nanotubes with nitrogen by annealing in ammonia for visible light activation: Influence of pre- and post-annealing in air

The ∼60 nm wide and ∼2 μm long TiO2 nanotubes were obtained by anodization of Ti films sputtered on F-doped tin oxide glass. For N-doping the samples were annealed in ammonia atmosphere. The effect of pre- and post-annealing in air on the nature and amount of incorporated N was studied by X-ray photoelectron spectroscopy. By measuring the absorption spectra of the obtained samples and interpreting the corresponding Tauc plots it was shown that the sample annealed just in ammonia showed the highest visible light absorption even after sputtering cleaning and a decrease of N amount from 3.8% to 1%. Pre and/or post annealing in air led to smaller amount of incorporated N, that caused less pronounced absorption enhancement and smaller band gap narrowing compared to the sample annealed only in ammonia. By fitting of N 1 s line, the contribution that was assigned to substitutional N was detected only in the samples that did not sustained post-annealing. The study showed that post-annealing in air might lead to partial conversion of N atoms in TiO2 to oxidized nitrogen species that are easily removed with sputtering. It is also possible that substitutional nitrogen was suppressed by oxygen from air to move to interstitial site. Weakly bonded NOx surface species, which are cleaned away by sputtering, can be removed by post-annealing in air. Those surface species could act as sensitizers and when their amounts are reduced, the core absorption properties, as a result of interstitial incorporation of N in TiO2 structure, were revealed. Much lower visible light sensitization was achieved in the case of pre-annealed sample in comparison to sample without pre-annealing, regardless the same quantity and type of incorporated nitrogen.

Characterization of Co:TiO2 Thin Film Grown by MOCVD Technique

The Co:TiO2 thin film was grown on n-type Si(100) by metal organic chemical vapor deposition (MOCVD) technique. The film’s growth parameters are as follow: substrate temperature of 450°C, bubbler temperature of 70°C, reactor chamber pressure of 2 militorr, and growth time of 2 hours. We characterized the structure of film by X-ray Difractometer (XRD), the morphology was characterized by Scanning Electron Microscope (SEM), and the fraction of Co atoms in TiO2 was characterized by Energy Dispersive x-ray Spectroscopy (EDS). The XRD result shows that the Co:TiO2 thin film is an anatase phase crystal dominated by A(213) orientation. Using Warren-Scherrer’s formula, the average grain size of Co:TiO2 is 169 nm. The SEM result shows that the Co:TiO2 film surface is quite coarse with relatively homogeneous grain shape. the average growth rate of Co:TiO2 film is 0.78 μm/h. In addition, the EDS result shows that Co atoms have been incorporated into the film replacing a portion of the Ti atoms by 0.085%.

TDPAC study of Fe-implanted titanium dioxide thin films

Fe-doping in TiO2 has been proven to improve several of its properties, including the photocatalytic activity. Time-differential perturbed angular correlation (TDPAC) as the applied spectroscopy method is particularly interesting because it can probe the electric and magnetic interactions on a local atomic scale. In this work the hyperfine interactions on 111Cd atoms substituting Ti atoms in TiO2 due to nearby Fe atoms also diluted within the TiO2 lattice were measured as a function of temperature. The results review two fractions with distinct quadrupole interaction parameters. One site, occupied by the 111Cd probes, presents the smaller quadrupole interaction frequency, namely υq1 = 45 MHz, and can be ascribed to sites that are more distant from the Fe substitutional site whereas the second site characterized with υq2 = 62 MHz is related to Cd probe atoms that are closer to the Fe defect. Additionally, the system has been characterized using electron dispersive spectroscopy.

Passivated co-doping approach to bandgap narrowing of titanium dioxide with enhanced photocatalytic activity

Aiming for the enhanced photocatalytic activity of titanium dioxide (TiO2), we probe various co-doping pairs of impurity atoms in TiO2 in search of the right co-dopants which can reduce the bandgap without creating recombination centers. To confirm the band edges and the relative positions of impurity levels, we perform first-principles density-functional-theory calculations within the local density approximation as well as the hybrid functional approach. From the analysis of the bandgaps of doped-TiO2 and the defect levels, we propose that the vanadium-nitrogen (V-N) pair is a suitable passivated co-dopant in TiO2. By doping TiO2 with the V-N pair, the bandgap of TiO2 is reduced; enhancing the visible light absorption. The calculated band edges after doping also matches the redox potentials of hydroxyl radical (OH) and superoxide anion (O2−); enhancing the photocatalytic activity for the degradation of organic pollutants and acting as antibacterial agents as well.

Group 4 Metal Oxynitride Nanocatalysts for Oxygen Reduction Reaction in Acidic Media

Titanium dioxide (TiO2) has attracted significant attention for the use in various applications; photocatalysts, dye-sensitized solar cells, lithium/sodium ion batteries, sensors, etc. Since the discovery of high visible-light photocatalytic activity by Asahi et al. in 2001,1 substitution of oxygen atoms in TiO2 by heteroatoms has been the hot topic in these fields. Recent work of Ota et al. opened a new application of TiO2: oxygen deficient TiO x showed the oxygen reduction reaction (ORR) activity in acidic media that simulate polymer electrolyte fuel cell (PEFC) cathodes.2 Other oxide catalysts containing group 4 or 5 metals also showed ORR activity in acidic media, whereas TiO2 is the most promising from the viewpoint of natural abundance. The oxygen defects in oxide catalysts have been acknowledged as active sites for ORR and they have been incorporated using various routes such as the pyrolysis under reductive atmosphere containing hydrogen,2 so-called carbothermal-reduction3 and nitrogen-doping.4-8 Rutile is more active for ORR than anatase,3,6,7 and this trend is opposite to that in photocatalytic activity. In this work, oxygen defects were incorporated into nanoparticles of rutile TiO2 and other group 4 metal oxides by substitutional nitrogen-doping using a recently developed solution phase combustion route.7,8 X-ray photoelectron spectroscopy analyses on TiO2 catalysts revealed that (1) charge imbalance caused by doped nitrogen atoms were compensated by the incorporation of oxygen defects, not the decrease in the valence of titanium on the surface and (2) the surface rutile was formed on TiN, yielding a core-shell structure. Many transition metal nitrides are well known to be unstable in water or even in air moisture, except for Ta3N5;9,10 however, the surface rutile successfully protected the TiN-core in 0.1 mol dm–3 H2SO4 solution not to change the ORR mechanism represented by Tafel slope after 20,000 potential cycles between 0.6 and 1.0 V versus the reversible hydrogen electrode. The active sites will be discussed at the meeting by comparing the activity of TiO2 and other group 4 metal oxides. Acknowledgments The authors gratefully acknowledge Mr. Yusei Tsushima for his help with acquisition of transmission electron microscopy images. This work was partially supported by a Grant-in-Aid for Scientific Research (C) (26420132) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan; an Adaptable and Seamless Technology Transfer Program through Target-driven R&D grant (AS262Z02037) from the Japan Science and Technology Agency; a research grant from the Takahashi Industrial and Economic Research Foundation of Japan; a research grant from the Naoji Iwatani Foundation of Japan; and a grant for chemical research from the Foundation for Japanese Chemical Research. The X-ray photoelectron spectra were acquired with the support by Nanotechnology Platform, 12024046 of the MEXT of Japan. References (1) R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, and Y. Taga, Science, 293, 269 (2001). (2) J. H. Kim, A. Ishihara, S. Mitsushima, N. Kamiya, and K. Ota, Electrochim. Acta, 52, 2492 (2007). (3) M. Chisaka and N. Itagaki, Electrochim. Acta, in press. Doi:10.1016/j.electacta.2015.10.184. (4) M. Chisaka, H. Sasaki and H. Muramoto, Phys. Chem. Chem. Phys., 16, 20419 (2014). (5) M. Chisaka, A. Ishihara, K. Suito, K. Ota and H. Muramoto, Electrochim. Acta, 88, 697 (2013). (6) M. Chisaka and H. Muramoto, ChemElectroChem, 1, 544 (2014). (7) M. Chisaka, Y. Ando and H. Muramoto, Electrochim. Acta, 183, 100 (2015) (8) M. Chisaka, Y. Ando and N. Itagaki, J. Mater Chem. A, in press. Doi:10.1039/C5TA08235H (9) M. Hara, E. Chiba, A. Ishikawa, T. Takata, J. N. Kondo and K. Domen, J. Phys. Chem. B, 107, 13441 (2003). (10) M. Chisaka, A. Ishihara, N. Uehara, M. Matsumoto and K. Ota, J. Mater Chem. A, 3, 16414 (2015).

Impact of Ga-V Codoping on Interfacial Electron Transfer in Dye-Sensitized TiO2.

The improvement of charge transfer between an organic molecule and a semiconductor is an important and challenging goal in the fields of photovoltaics and photocatalysis. In this work, we present a time-dependent density functional theory investigation of the impact of Ga-V codoping of TiO2 on the excited-state electron injection from perylene-3-carboxylic acid. The doping is shown to raise the charge-transfer efficiency for the highest possible surface dye uptake by ∼16%. The strength of the effect depends on the dopant-pair-dye separation, dopant concentration, and distribution of Ga, V atoms in TiO2. The doping of the superficial level turns out to be more favorable than those in the bulk. The changes in electron injection dynamics are attributed to the modification of accepting semiconductor levels and hybridization profile between molecular and semiconductor states.

Tailoring Band Structure of TiO2 To Enhance Photoelectrochemical Activity by Codoping S and Mg

Doping with foreign element is an effective method to narrow the band gap of TiO2. Here, the S doping and (S, Mg) codoping effects on the electronic structure and optical properties of the anatase TiO2 were investigated at the HSE06 hybrid functional level. The hybridization of the O 2p, Ti-t2g, and S 3p states creates the intermediate band for the doped TiO2, which makes the absorption onset extend into the visible-light region. The introduction of Mg promotes the corporation of S into TiO2. The heavy doping with S further improves the absorption efficiency and eliminates the unoccupied intermediate band. The band alignment confirms that the (S, Mg) codoping with two O atoms substituted by S atoms in TiO2 is desirable for the overall water splitting.

TiO2薄膜的硼掺杂对TiO2/p+-Si异质结器件电致发光的增强

TiO2/p+-Si and TiO2∶B / p+-Si heterostructures were formed by sputtering TiO2 films and boron-doped TiO2( TiO2∶ B) films on heavily boron-doped silicon( p+-Si) substrates,respectively,followed by annealing at 600 ℃ in O2 ambient. In contrast with the TiO2/ p+-Si heterostructured devices,the TiO2∶ B / p+-Si counterpart exhibits markedly enhanced electroluminescence( EL). It is derived that the doped B atoms in TiO2∶ B films enter into the interstitial sites of TiO2 lattice after annealing at high temperature,which introduces excess oxygen vacancies. The increase of the concentration of oxygen vacancies due to B-doping leads to the enhancement of EL from the TiO2∶ B / p+-Si heterostructured devices because oxygen vacancies are the light-emitting centers of the TiO2/p+-Si heterostructured devices.

Vectorial doping-promoting charge transfer in anatase TiO2 {0 0 1} surface

Doping-induced visible-light adsorption is often considered as the main reason for the enhanced photocatalytic activity of TiO2. However, this work provides a new understanding on the effect of doping on the photocatalytic activity of TiO2. The investigation on the C–F codoped anatase TiO2 {001} surface reveals that the impurity C and F atoms prefer to substitute for the outmost O atoms in the TiO2 {001} surface rather than those in the bulk TiO2. The exhibited vectorial doping of C and F atoms in TiO2 {001} surface produces a conducting layer with low electric resistance, which can promote the charge transfer in the photocatalytic reaction. This effectively inhibits the undesirable bulk recombination of photogenerated electron and hole. Hence, the optimized charge transfer in the C–F codoped TiO2 {001} surface makes a great contribution to the enhanced photocatalytic activity of TiO2. Further, the surface doping treatment is a potential method to improve the performance of photocatalyst.

Surface and interstitial transition barriers in rutile (110) surface growth

We present calculated surface and interstitial transition barriers for Ti, O, O-2, TiO, and TiO2 atoms and clusters at the rutile (110) surface. Defect structures involving these small clusters, including adcluster and interstitial binding sites, were calculated by energy minimization using density-functional theory (DFT). Transition energies between these defect sites were calculated using the NEB method. Additionally, a modified SMB-Q charge equilibration empirical potential and a fixed-charge empirical potential were used for a comparison of the transition energy barriers. Barriers of 1.2-3.5 eV were found for all studied small cluster transitions upon the surface except for transitions involving O-2. By contrast, the O-2 diffusion barriers along the [001] direction upon the surface are only 0.13 eV. The QEq charge equilibration model gave mixed agreement with the DFT calculations, with the barriers ranging between 0.8 and 5.8 eV.

Titanate biomaterials with enhanced antiinflammatory properties

While titanium implants are generally recognized as having excellent biocompatibility, the mechanistic basis for this has yet to be established. We previously demonstrated that TiO2, found on surfaces of titanium, has antioxidant properties that degrade the reactive oxygen species (ROS) which mediate the inflammatory response. We hypothesized that the antioxidant mechanism was similar to that known to mediate photocatalysis by titanium oxides. Specifically, we investigated whether the electronic or valence state of the surface titanium atoms mediates the catalytic degradation of ROS. Surface Ti(IV) atoms in TiO2 and SrTiO3 single crystal substrates were converted into Ti(III) while maintaining the bulk crystalline structure by vacuum annealing or Niobium doping. The degradation of both chemically-induced and neutrophil-derived ROS were significantly increased by changing the valence state of surface titanium. These results suggest that titanium-mediated degradation of ROS is through a catalytic mechanism. Furthermore, we describe a series of novel biomaterials that have antioxidant properties superior to those of titanium.

Spin polarization of oxygen atoms in ferromagnetic Co-doped rutile TiO2

Of central interest in the research of dilute magnetic semiconductors is the coupling mechanism leading to a ferromagnetic ground state. Using x-ray resonant magnetic scattering, we have analyzed the element specific magnetic hysteresis curves of Co, Ti, and oxygen in Co-doped TiO2 synthesized by ion implantation. Magnetic dichroism was observed at the Co L2,3 edges, as well as at the O K edge, indicative of a spin polarization of oxygen atoms in the TiO2 host matrix. The hysteretic shapes and the coercive field values measured at the Co L3 and O K edges are identical (1.9kOe at 30K).