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Sample records for single-crystalline rutile tio2

  1. Transport properties in single-crystalline rutile TiO2 nanorods

    NASA Astrophysics Data System (ADS)

    Chen, R. S.; Chen, C. A.; Wang, W. C.; Tsai, H. Y.; Huang, Y. S.

    2011-11-01

    Electronic transport properties of the single-crystalline titanium dioxide (TiO2) nanorods (NRs) with single rutile phase have been investigated. The conductivity values for the individual TiO2 NRs grown by metal-organic chemical vapor deposition are in the range of 1-10 Ω-1 cm-1. The temperature-dependent measurement shows the presence of two shallow donor levels/bands with activation energies at 8 and 28 meV, respectively. On the photoconductivity (PC), the TiO2 NRs exhibit the much higher normalized PC gain and sensitive excitation-power dependence than the polycrystalline nanotubes. The results demonstrate the superior photoconduction efficiency and distinct mechanism in the monocrystalline one-dimensional TiO2 nanostructures in comparison to the polycrystalline or nanoporous counterparts.

  2. Achievement of 6.03% conversion efficiency of dye-sensitized solar cells with single-crystalline rutile TiO2 nanorod photoanode

    NASA Astrophysics Data System (ADS)

    Yang, Weiguang; Wan, Farong; Wang, Yali; Jiang, Chunhua

    2009-09-01

    The rutile TiO2 nanorods (RTNs) with the length of 40-130 nm and diameters approximately 8-15 nm, containing some 300-500 nm sized RTN aggregates and 6% of anatase TiO2 nanocrystals, were prepared by surfactant-assisted hydrothermal method. The dye-sensitized solar cell (DSC) based on the RTNs exhibited power conversion efficiency of 6.03%. As compared to P25 TiO2 based DSC, RTNs based DSC shows improved light-harvesting and Brunauer-Emmett-Teller surface area, leading to an increase in short-circuit current (Jsc) by 40.6%.

  3. Growth of aligned single-crystalline rutile TiO2 nanowires on arbitrary substrates and their application in dye-sensitized solar cells

    SciTech Connect

    Kumar, Akshay; Madaria, Anuj R.; Zhou, Chongwu

    2010-05-06

    TiO{sub 2} is a wide band gap semiconductor with important applications in photovoltaic cells and photocatalysis. In this paper, we report synthesis of single-crystalline rutile phase TiO{sub 2} nanowires on arbitrary substrates, including fluorine-doped tin oxide (FTO), glass slides, tin-doped indium oxide (ITO), Si/SiO{sub 2}, Si(100), Si(111), and glass rods. By controlling the growth parameters such as growth temperature, precursor concentrations, and so forth, we demonstrate that anisotropic growth of TiO{sub 2} is possible leading to various morphologies of nanowires. Optimization of the growth recipe leads to well-aligned vertical array of TiO{sub 2} nanowires on both FTO and glass substrates. Effects of various titanium precursors on the growth kinetics, especially on the growth rate of nanowires, are also studied. Finally, application of vertical array of TiO{sub 2} nanowires on FTO as the photoanode is demonstrated in dye-sensitized solar cell with an efficiency of 2.9 ± 0.2%.

  4. Antibacterial activity of single crystalline silver-doped anatase TiO2 nanowire arrays

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangyu; Li, Meng; He, Xiaojing; Hang, Ruiqiang; Huang, Xiaobo; Wang, Yueyue; Yao, Xiaohong; Tang, Bin

    2016-05-01

    Well-ordered, one-dimensional silver-doped anatase TiO2 nanowire (AgNW) arrays have been prepared through a hydrothermal growth process on the sputtering-deposited AgTi layers. Electron microscope analyses reveal that the as-synthesized AgNW arrays exhibit a single crystalline phase with highly uniform morphologies, diameters ranging from 85 to 95 nm, and lengths of about 11 μm. Silver is found to be doped into TiO2 nanowire evenly and mainly exists in the zerovalent state. The AgNW arrays show excellent efficient antibacterial activity against Escherichia coli (E. coli), and all of the bacteria can be killed within 1 h. Additionally, the AgNW arrays can still kill E. coli after immersion for 60 days, suggesting the long-term antibacterial property. The technique reported here is environmental friendly for formation of silver-containing nanostructure without using any toxic organic solvents.

  5. Ultrahigh efficient single-crystalline TiO2 nanorod photoconductors

    NASA Astrophysics Data System (ADS)

    Chen, R. S.; Chen, C. A.; Tsai, H. Y.; Wang, W. C.; Huang, Y. S.

    2012-03-01

    Photoconductive gain and normalized gain, which determine the device and material properties on photoconduction, respectively, have been defined for single-crystalline titanium dioxide (TiO2) nanorods (NRs) with various diameter sizes. The gain values of the NR photodetectors can reach 105 easily at a low bias of 0.1 V. By excluding the contributions of experimental parameters, the optimal normalized gain of the indirect-bandgap TiO2 NRs at 5.4 × 10-5 m2V-1 is comparable with that estimated from the direct-bandgap ZnO nanowires. The average normalized gain value at 3.3 ± 2.2 × 10-5 m2V-1 obtained from eight individual TiO2 NRs with diameters ranging from 120 to 1250 nm is also over three orders of magnitude higher than the polycrystalline nanotube counterpart. The results demonstrate the superior photoconductivity efficiency in boundary-free titania one-dimensional nanostructure, which is crucial for ultraviolet photodetector, dye-sensitized solar cell, and photochemical device applications.

  6. Growth Morphologies of Nanostructured Rutile TiO2

    NASA Astrophysics Data System (ADS)

    Huang, Yuan-Sheng; Liu, Hong-Wei

    2014-04-01

    The morphological and structural characteristics of nanostructure rutile TiO2 were investigated by using x-ray diffraction, scanning electron microscopy, electron diffraction, conventional and high resolution transmission electron microscopy. As a product of the precursor template of hydrogen titanate nanofibers, rutile could exhibit forms like tree, sheaf, or bundle. Both the branch and trunk of tree-like rutile have the same growth axis of [001]. The sheaf-like rutile forms while it grows along both [001] and [] directions. The bundle-like rutile grows along only one [001] direction. Tree-like morphology of nanocrystals rutile is revealed to be controlled by (101) twin structure. Twin formation is a possible mechanism to decrease the density of defects and reduce the system energy as the crystal grows.

  7. Band alignment of rutile and anatase TiO2

    NASA Astrophysics Data System (ADS)

    Scanlon, David O.; Dunnill, Charles W.; Buckeridge, John; Shevlin, Stephen A.; Logsdail, Andrew J.; Woodley, Scott M.; Catlow, C. Richard A.; Powell, Michael. J.; Palgrave, Robert G.; Parkin, Ivan P.; Watson, Graeme W.; Keal, Thomas W.; Sherwood, Paul; Walsh, Aron; Sokol, Alexey A.

    2013-09-01

    The most widely used oxide for photocatalytic applications owing to its low cost and high activity is TiO2. The discovery of the photolysis of water on the surface of TiO2 in 1972 launched four decades of intensive research into the underlying chemical and physical processes involved. Despite much collected evidence, a thoroughly convincing explanation of why mixed-phase samples of anatase and rutile outperform the individual polymorphs has remained elusive. One long-standing controversy is the energetic alignment of the band edges of the rutile and anatase polymorphs of TiO2 (ref. ). We demonstrate, through a combination of state-of-the-art materials simulation techniques and X-ray photoemission experiments, that a type-II, staggered, band alignment of ~ 0.4 eV exists between anatase and rutile with anatase possessing the higher electron affinity, or work function. Our results help to explain the robust separation of photoexcited charge carriers between the two phases and highlight a route to improved photocatalysts.

  8. Hydrogen Impurity Defects in Rutile TiO2

    PubMed Central

    Mo, Li-Bin; Wang, Yu; Bai, Yang; Xiang, Qing-Yun; Li, Qun; Yao, Wen-Qing; Wang, Jia-Ou; Ibrahim, Kurash; Wang, Huan-Hua; Wan, Cai-Hua; Cao, Jiang-Li

    2015-01-01

    Hydrogen-related defects play crucial roles in determining physical properties of their host oxides. In this work, we report our systematic experimental and theoretical (based on density functional theory) studies of the defect states formed in hydrogenated-rutile TiO2 in gaseous H2 and atomic H. In gas-hydrogenated TiO2, the incorporated hydrogen tends to occupy the oxygen vacancy site and negatively charged. The incorporated hydrogen takes the interstitial position in atom-hydrogenated TiO2, forming a weak O-H bond with the closest oxygen ion, and becomes positive. Both states of hydrogen affect the electronic structure of TiO2 mainly through changes of Ti 3d and O 2p states instead of the direct contributions of hydrogen. The resulted electronic structures of the hydrogenated TiO2 are manifested in modifications of the electrical and optical properties that will be useful for the design of new materials capable for green energy economy. PMID:26627134

  9. CdS/CdSe cosensitized oriented single-crystalline TiO2 nanowire array for solar cell application

    NASA Astrophysics Data System (ADS)

    Li, Ming; Liu, Yong; Wang, Hai; Shen, Hui; Zhao, Wenxia; Huang, Hong; Liang, Chaolun

    2010-11-01

    Vertically oriented single-crystalline TiO2 nanowires array was grown on transparent conductive oxide glass substrate, and then CdS and CdSe quantum dots (QDs) were deposited on nanowires to form a TiO2/CdS/CdSe core-shell structure films. The optical properties of films with different layers of QDs were compared. The QD sensitized solar cells (QD-SSCs) were assembled and the effect of coating cycles of QDs on the photovoltaic performance was investigated. Under optimum parameters, QD-SSCs assembled with 5 μm thick TiO2 nanowires film exhibited a short-circuit current density of 7.92 mA cm-2, an open-circuit voltage of 0.40 V, and a power conversion efficiency of 1.14%.

  10. Infrared dielectric anisotropy and phonon modes of rutile TiO2

    NASA Astrophysics Data System (ADS)

    Schöche, S.; Hofmann, T.; Korlacki, R.; Tiwald, T. E.; Schubert, M.

    2013-04-01

    Spectroscopic ellipsometry in the mid-infrared and far-infrared spectral range and generalized ellipsometry in the mid-infrared spectral range are used to investigate the anisotropic dielectric response of rutile TiO2. The ordinary and extraordinary dielectric function tensor components and all infrared active phonon mode parameters of single crystalline rutile TiO2 are determined with high accuracy for wavelengths from 3 μm to 83 μm. The data were acquired from samples of (001), (100), and (111) surfaces cut from bulk single crystals. A factorized model dielectric function is employed in order to determine the frequencies and damping parameters of the transverse and longitudinal phonon modes with A2u and Eu symmetries. The bands of total reflection of s- and p-polarized light in dependence of the angle of incidence for highly symmetric sample cuts and orientations are derived. Excellent agreement with phonon modes reported in literature is obtained. Introduction of two additional modes for ordinary as well as extraordinary component of the dielectric function tensor was necessary to most accurately match the experimental data. The spectral position of the additional modes is compared to the calculated phonon density of states. The low-frequency dielectric constants are calculated from the determined phonon mode parameters and the high-frequency dielectric constants by applying the Lyddanne-Sachs-Teller relation. The presented data revise existing infrared optical function data and will be suitable for interpretation of any kind of infrared spectra for bulk TiO2 single crystal substrates, thin films, and TiO2 nanostructures.

  11. Dielectric and Infrared Properties of TiO2 Films Containing Anatase and Rutile

    DTIC Science & Technology

    2005-07-18

    properties of TiO2 films containing anatase and rutile 2. Experimental details Thin films of TiO2 were deposited onto Si(1 0 0) wafers...annealed) and 7.4 nm (225 nm, deposited with a bias 872 Dielectric and infrared properties of TiO2 films containing anatase and rutile then annealed...Article POSTPRINT 3. DATES COVERED (From - To) 2001 - 2004 4. TITLE AND SUBTITLE Dielectric and infrared properties of TiO2 films

  12. Determination of electron and hole lifetimes of rutile and anatase TiO2 single crystals

    NASA Astrophysics Data System (ADS)

    Yamada, Yasuhiro; Kanemitsu, Yoshihiko

    2012-09-01

    The dynamical behavior of photoexcited states of TiO2 governs the activities of TiO2-based solar cells and photocatalysts. We determined the lifetimes of photoexcited electrons and holes in rutile and anatase TiO2 single crystals by combining advantages of time-resolved photoluminescence, photoconductance, and transient absorption spectroscopy. Electrons and holes in rutile show exponential decays with the lifetime of a few tens of nanoseconds, while non-exponential decays are observed in anatase, indicating the presence of multiple carrier trapping processes. We revealed the generic features of the carrier recombination processes in rutile and anatase TiO2.

  13. Surface structures of rutile TiO2(114)

    NASA Astrophysics Data System (ADS)

    Kubo, Toshitaka; Orita, Hideo; Nozoye, Hisakazu

    2016-11-01

    The surface structures of rutile TiO2(114) have been studied using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Depending on the sample preparation, the surface exhibits many complicated local nanostructures, e.g., dot-like, missing row, row-like (1 × 3), and twin dotted (2 × 2) structures. After several cycles of sputtering and high-temperature annealing, all samples exhibit triangular pyramidal structure. Microfaceted structural models, which are composed of combinations of {111} and (001) microfacets, can explain all experimental results as well as the structural variety. The calculated STM images are in good agreement with the experimental results. The decreasing density of dangling bonds, the increasing coordination number, and the evolution of non-polar structures stabilize the surface energy, which results in the microfaceted reconstructions. The formation of various nanostructures and the surface stoichiometric changes are discussed.

  14. Well-Defined Nanostructured, Single-Crystalline TiO2 Electron Transport Layer for Efficient Planar Perovskite Solar Cells.

    PubMed

    Choi, Jongmin; Song, Seulki; Hörantner, Maximilian T; Snaith, Henry J; Park, Taiho

    2016-06-28

    An electron transporting layer (ETL) plays an important role in extracting electrons from a perovskite layer and blocking recombination between electrons in the fluorine-doped tin oxide (FTO) and holes in the perovskite layers, especially in planar perovskite solar cells. Dense TiO2 ETLs prepared by a solution-processed spin-coating method (S-TiO2) are mainly used in devices due to their ease of fabrication. Herein, we found that fatal morphological defects at the S-TiO2 interface due to a rough FTO surface, including an irregular film thickness, discontinuous areas, and poor physical contact between the S-TiO2 and the FTO layers, were inevitable and lowered the charge transport properties through the planar perovskite solar cells. The effects of the morphological defects were mitigated in this work using a TiO2 ETL produced from sputtering and anodization. This method produced a well-defined nanostructured TiO2 ETL with an excellent transmittance, single-crystalline properties, a uniform film thickness, a large effective area, and defect-free physical contact with a rough substrate that provided outstanding electron extraction and hole blocking in a planar perovskite solar cell. In planar perovskite devices, anodized TiO2 ETL (A-TiO2) increased the power conversion efficiency by 22% (from 12.5 to 15.2%), and the stabilized maximum power output efficiency increased by 44% (from 8.9 to 12.8%) compared with S-TiO2. This work highlights the importance of the ETL geometry for maximizing device performance and provides insights into achieving ideal ETL morphologies that remedy the drawbacks observed in conventional spin-coated ETLs.

  15. TiO2-Based Nanomaterials for Gas Sensing-Influence of Anatase and Rutile Contributions.

    PubMed

    Zakrzewska, K; Radecka, M

    2017-12-01

    The paper deals with application of three nanomaterial systems: undoped TiO2, chromium-doped TiO2:Cr and TiO2-SnO2 synthesized by flame spray synthesis (FSS) technique for hydrogen sensing. The emphasis is put on the role of anatase and rutile polymorphic forms of TiO2 in enhancing sensitivity towards reducing gases. Anatase-to-rutile transformation is achieved by annealing of undoped TiO2 in air at 700 °C, specific Cr doping and modification with SnO2. Undoped TiO2 and TiO2-SnO2 exhibit n-type behaviour and while TiO2: 5 at.% Cr is a p-type semiconductor. X-ray diffraction (XRD) has been applied to determine anatase-to-rutile weight ratio as well as anatase and rutile crystal size. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used to characterize the structure and morphological parameters. Optical reflectometry enabled to find and compare the band gaps E g of anatase and rutile predominated compositions. Electrical properties, i.e. the electrical conductivity and values of constant phase element (CPE), have been established on the basis of impedance spectroscopy. Dynamic responses of the electrical resistance as a function of hydrogen concentration revealed that predominance of rutile in anatase/rutile mixture is beneficial for gas sensing. Partial transformation to rutile in all three material systems under study resulted in an increased sensitivity towards hydrogen. It is proposed that this effect can be explained in a similar way as in photocatalysis, i.e. by specific band alignment and electron transfer from rutile to anatase to facilitate oxygen preadsorption on the surface of anatase grains.

  16. Ti3+-self doped brookite TiO2 single-crystalline nanosheets with high solar absorption and excellent photocatalytic CO2 reduction

    PubMed Central

    Xin, Xiaoye; Xu, Tao; Wang, Lan; Wang, Chuanyi

    2016-01-01

    Black brookite TiO2 single-crystalline nanosheets with outstanding photocatalytic activity toward CO2 reduction is prepared by a facile oxidation-based hydrothermal reaction method combined with post-annealing treatment. Large amount of Ti3+ defects are introduced into the bulk of brookite nanoparticles, which increases the solar energy absorption and enhances the photocatalytic activity. PMID:27021203

  17. Ti3+-self doped brookite TiO2 single-crystalline nanosheets with high solar absorption and excellent photocatalytic CO2 reduction

    NASA Astrophysics Data System (ADS)

    Xin, Xiaoye; Xu, Tao; Wang, Lan; Wang, Chuanyi

    2016-03-01

    Black brookite TiO2 single-crystalline nanosheets with outstanding photocatalytic activity toward CO2 reduction is prepared by a facile oxidation-based hydrothermal reaction method combined with post-annealing treatment. Large amount of Ti3+ defects are introduced into the bulk of brookite nanoparticles, which increases the solar energy absorption and enhances the photocatalytic activity.

  18. Synthesis of anatase and rutile TiO2 nanostructures from natural ilmenite

    NASA Astrophysics Data System (ADS)

    Wahyuingsih, Sayekti; Ramelan, Ari Handono; Pramono, Edi; Sulistya, Ariantama Djati; Argawan, Panji Rofa; Dharmawan, Frenandha Dwi; Rinawati, Ludfiaastu; Hanif, Qonita Awliya; Sulistiyono, Eko; Firdiyono, Florentinus

    2016-02-01

    Nanostructure anatase and rutile type TiO2 were synthesized from dissolution roasted ilmenite from natural ilmenite sand as the starting materials. Anatase TiO2 and rutile TiO2 (high crystallinity) with the diameters of 20-100 nm were obtained by calcined soluble ilmenite sand produced by leaching process. Calcinations of the xerogel TiO2 from liquor products were conducted for 4 hours at temperature of 450 °C. The samples were characterized by XRD (X-ray diffraction), STA (simultant thermal analysis), TEM (Transmission Electron Microscopy), and BET surface area. Titania Anatase-Rutile form as a mixture were produced by titania slag with the hydrolysis product. While, in another route, complete titania anatase phase was produced through hydrolysis and condensation steps of leach liquors. This synthesis methods provide a simple route to fabricate nanostructure TiO2 from low cost material.

  19. Preparation and photoactivity of nanostructured anatase, rutile and brookite TiO2 thin films.

    PubMed

    Addamo, Maurizio; Bellardita, Marianna; Di Paola, Agatino; Palmisano, Leonardo

    2006-12-21

    Photoactive films consisting of pure anatase, brookite or rutile TiO2 were prepared by dip coating from water dispersions obtained by using TiCl4 as the precursor under similar mild experimental conditions.

  20. Ultralong Rutile TiO2 Nanowire Arrays for Highly Efficient Dye-Sensitized Solar Cells.

    PubMed

    Li, Hailiang; Yu, Qingjiang; Huang, Yuewu; Yu, Cuiling; Li, Renzhi; Wang, Jinzhong; Guo, Fengyun; Jiao, Shujie; Gao, Shiyong; Zhang, Yong; Zhang, Xitian; Wang, Peng; Zhao, Liancheng

    2016-06-01

    Vertically aligned rutile TiO2 nanowire arrays (NWAs) with lengths of ∼44 μm have been successfully synthesized on transparent, conductive fluorine-doped tin oxide (FTO) glass by a facile one-step solvothermal method. The length and wire-to-wire distance of NWAs can be controlled by adjusting the ethanol content in the reaction solution. By employing optimized rutile TiO2 NWAs for dye-sensitized solar cells (DSCs), a remarkable power conversion efficiency (PCE) of 8.9% is achieved. Moreover, in combination with a light-scattering layer, the performance of a rutile TiO2 NWAs based DSC can be further enhanced, reaching an impressive PCE of 9.6%, which is the highest efficiency for rutile TiO2 NWA based DSCs so far.

  1. Enhanced Photoelectrochemical Performance from Rationally Designed Anatase/Rutile TiO2 Heterostructures.

    PubMed

    Cao, Fengren; Xiong, Jie; Wu, Fangli; Liu, Qiong; Shi, Zhiwei; Yu, Yanhao; Wang, Xudong; Li, Liang

    2016-05-18

    In a photoelectrochemical (PEC) cell for water splitting, the critical issue is charge separation and transport, which is usually completed by designing semiconductor heterojunctions. TiO2 anatase-rutile mixed junctions could largely improve photocatalytic properties, but impairs PEC water splitting performance. We designed and prepared two types of TiO2 heterostructures with the anatase thin film and rutile nanowire phases organized in different sequences. The two types of heterostructures were used as PEC photoanodes for water splitting and demonstrated completely opposite results. Rutile nanowires on anatase film demonstrated enhanced photocurrent density and onset potential, whereas strong negative performance was obtained from anatase film on rutile nanowire structures. The mechanism was investigated by photoresponse, light absorption and reflectance, and electrochemical impedance spectra. This work revealed the significant role of phase sequence in performance gain of anatase-rutile TiO2 heterostructured PEC photoanodes.

  2. Low Temperature Synthesis of Rutile TiO2 Nanocrystals and Their Photovoltaic and Photocatalytic Properties.

    PubMed

    Roy, Subhasis; Han, Gill Sang; Shin, Hyunjung; Lee, Jin Wook; Mun, Jinsoo; Shin, Hyunho; Jung, Hyun Suk

    2015-06-01

    We report a novel method of synthesizing rutile TiO2 nanocrystals at low temperature (200 degrees C) via a butanol rinsing process followed by heat treatment in an O2 atmosphere. The rutile nanocrystals show uniform size distribution of approximately 20 nm and good crystallinity confirmed by X-ray diffraction and transmission electron microscopy. A mechanism for the low temperature synthesis of rutile nanocrystals is rationalized in terms of an explosive thermal decomposition reaction of butoxy groups on TiO2 powders with O2 gas. Characterizations of the photovoltaic and photocatalytic properties of rutile nanocrystals exhibited higher photoactivity than large-sized conventional rutile powder, which demonstrates that this novel synthesis technology could expand applications of rutile powders to various photoactive devices beyond solar cells and photocatalysts.

  3. Ti(3+) Self-Doped Blue TiO2(B) Single-Crystalline Nanorods for Efficient Solar-Driven Photocatalytic Performance.

    PubMed

    Zhang, Yan; Xing, Zipeng; Liu, Xuefeng; Li, Zhenzi; Wu, Xiaoyan; Jiang, Jiaojiao; Li, Meng; Zhu, Qi; Zhou, Wei

    2016-10-12

    Ti(3+) self-doped blue TiO2(B) single-crystalline nanorods (b-TR) are fabricated via a simple sol-gelation method, cooperated with hydro-thermal treatment and subsequent in situ treatment method, and afterward annealed at 350 °C in Ar. The structures are characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (UV-vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The prepared b-TR with narrow band gap possesses single-crystalline TiO2(B) phase, Ti(3+) self-doping, and one-dimensional (1D) rodlike nanostructure. In addition, the improved photocatalytic performance is studied by decomposition of Rhodamine B (RhB) and hydrogen evolution. The degradation rate of RhB by Ti(3+) self-doped blue TiO2(B) single-crystalline nanorods is ∼6.9- and 2.1-times higher compared with the rates of titanium dioxide nanoparticles and pristine TiO2(B) nanorods under visible light illumination, respectively. The hydrogen evolution rate of b-TR is 26.6 times higher compared with that of titanium dioxide nanoparticles under AM 1.5 irradiation. The enhanced photocatalytic performances arise from the synergetic action of the special TiO2(B) phase, Ti(3+) self-doping, and the 1D rod-shaped single-crystalline nanostructure, favoring the visible light utilization and the separation and transportation of photogenerated charge carriers.

  4. Rutile TiO2 nanowire-based perovskite solar cells.

    PubMed

    Jiang, Qinglong; Sheng, Xia; Li, Yingxuan; Feng, Xinjian; Xu, Tao

    2014-12-07

    Different lengths of rutile TiO2 nanowires (NW) with wide-open space for effective material filling were used as photoanodes for perovskite solar cells. Cells with 900 nm nanowires as photoanodes exhibit a current density of 22 mA cm(-2) and an efficiency of 11.7%, outperforming the reported TiO2 nanowire-based perovskite solar cells.

  5. Preparation and Characterization of Rutile-Type TiO2 Doped with Cu

    NASA Astrophysics Data System (ADS)

    Tryba, B.; Orlikowski, J.; Wróbel, R. J.; Przepiórski, J.; Morawski, A. W.

    2015-03-01

    Visible-light active photocatalysts were prepared by doping Cu-TiO2 through the sol-gel method. The influence of the preparation conditions such as pH of sol-gel solution and calcination temperature on the properties of TiO2-Cu was investigated. The presence of Cu caused reduction of band-gap energy, which was more visible in the rutile-type TiO2. Low pH of sol-gel solution such as pH 1.5 favorized formation of rutile during calcination and caused slower growth of the crystallites with increasing temperature of calcination in comparison with sol-gel prepared at pH 3. XPS measurements showed that Cu was placed mostly on the surface of TiO2. For sample calcined at 600 °C, the surface concentration of copper was 1.1 wt.%. The presence of both, rutile phase and Cu, increased adsorption of phenol and facilitated its photocatalytic decomposition. Moreover, reduced band-gap energy in rutile-type TiO2-Cu photocatalyst enabled phenol decomposition under visible light.

  6. Preparation of atomically flat rutile TiO2(001) surfaces for oxide film growth

    DOE PAGES

    Wang, Yang; Lee, Shinbuhm; Vilmercati, P.; ...

    2016-01-01

    The availability of low-index rutile TiO2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxialgrowth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO2(110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO2(001) surfaces can be prepared with an atomically ordered reconstructedsurface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surface energy associated withmore » the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxialgrowth of TiO2(001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.« less

  7. Photoconductive detection of hydrogen in ZnO and rutile TiO2

    NASA Astrophysics Data System (ADS)

    Lavrov, E. V.; Mchedlidze, T.; Herklotz, F.

    2016-08-01

    Hydrogen donors in ZnO and rutile TiO2 are probed by means of photoconductivity and IR absorption. It is shown that the O-H bonds giving rise to the local vibrational modes (LVMs) of interstitial hydrogen at 3611 and 3290 cm-1 in the case of ZnO and TiO2, respectively, also occur in the photoconductivity spectra as Fano resonances. The effects of isotope substitution, concentration, sample thickness, influence of other donors present in both oxides are considered. Based on the shape and frequency of these resonances, it is concluded that the apparent ionization energy of interstitial hydrogen in rutile TiO2 is less than 300 meV. By a direct comparison, we also demonstrate that photoconductive detection of LVMs of defects in thin semiconductor films is superior to the standard IR absorption.

  8. Photoemission Electron Microscopy of TiO2 Anatase Films Embedded with Rutile Nanocrystals

    SciTech Connect

    Xiong, Gang; Shao, Rui; Droubay, Timothy C.; Joly, Alan G.; Beck, Kenneth M.; Chambers, Scott A.; Hess, Wayne P.

    2007-09-03

    Photoemission electron microscopy (PEEM) excited by x-ray and UV sources is used to investigate epitaxial anatase thin films embedded with rutile nanocrystals, a model system for the study of heterocatalysis on mixed-phase TiO2. Both excitation sources show distinct contrast between the two TiO2 phases, however, the contrast is reversed. Rutile nanocrystals appear darker than the anatase film in X-ray PEEM images but brighter in UV-PEEM images. Topography-induced contrast is dominant X-ray PEEM imaging, whereas work function contrast, dominates for UV-PEEM. Work function contrast results from the differences in work function and surface defect state densities between the two phases near the Fermi level. This assertion is confirmed by UPS data that shows the rutile work function to be 0.2 eV lower and a greater occupied valence band density-of-states in rutile (100) than in anatase (001). Since the boundaries between rutile nanocrystals and the anatase film are clearly resolved, these results indicate that PEEM studies of excited state dynamics and heterocatalysis are possible at chemically intriguing mixed-phase TiO2 interfaces and grain boundaries.

  9. The synthesis of rutile nano-structured TiO2 composite under low temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Zheng, Yibo; Dong, Mofei; Li, Simian

    2012-11-01

    In this paper, in order to improve the photocatalytic application of TiO2, the low-density material such as Ps and TiCl4 is proposed to be the raw carrier, and the nana-structured TiO2 composite is obtained by combining the sol-gel technology and layer-by-layer self-assembly methods; The pure rutile nano-structured TiO2 whose diameter is about 0.25mm are prepared under different conditions at low temperature. By being calcined under 450 ℃ the hollow sphere TiO2 is prepared and its composition, size, structure analysis and characterization are studied by using X ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermal gravimetric analysis (DSC-TG) respectively.

  10. Dense and high-hydrophobic rutile TiO2 nanorod arrays

    NASA Astrophysics Data System (ADS)

    Peng, X.; Chen, A.

    2005-02-01

    Dense and well-oriented rutile TiO2 nanorod arrays were synthesized on a titanium substrate using the organic compound dibutyltin dilaurate as the oxygen source in the oxidation of Ti at 850 °C. The influence of temperature on the nanostructured TiO2 formation and the effect of the TiO2 structures on their wettability were also investigated. Polycrystalline TiO2 grains were formed at 800 °C; in contrast, TiO2 micro-whiskers were grown on the Ti substrate at 900 °C. The measurement of the water contact angle shows that the wetting property of the TiO2 films strongly depends on their surface structure. The surface of the dense well-oriented nanorod arrays is highly hydrophobic with a water contact angle of 130 °C. This study has demonstrated that the direct oxidation of Ti substrate using an organic oxygen source is a promising method for fabrication of large scale, uniform and well-aligned TiO2 nanorod arrays on titanium substrates.

  11. New understanding of the difference of photocatalytic activity among anatase, rutile and brookite TiO2.

    PubMed

    Zhang, Jinfeng; Zhou, Peng; Liu, Jianjun; Yu, Jiaguo

    2014-10-14

    In general, anatase TiO2 exhibits higher photocatalytic activities than rutile TiO2. However, the reasons for the differences in photocatalytic activity between anatase and rutile are still being debated. In this work, the band structure, density of states, and effective mass of photogenerated charge carriers for anatase, rutile and brookite TiO2 are investigated by the first-principle density functional theory calculation. The results indicate that anatase appears to be an indirect band gap semiconductor, while rutile and brookite belong to the direct band gap semiconductor category. Indirect band gap anatase exhibits a longer lifetime of photoexcited electrons and holes than direct band gap rutile and brookite because the direct transitions of photogenerated electrons from the conduction band (CB) to valence band (VB) of anatase TiO2 is impossible. Furthermore, anatase has the lightest average effective mass of photogenerated electrons and holes as compared to rutile and brookite. The lightest effective mass suggests the fastest migration of photogenerated electrons and holes from the interior to surface of anatase TiO2 particle, thus resulting in the lowest recombination rate of photogenerated charge carriers within anatase TiO2. Therefore, it is not surprising that anatase usually shows a higher photocatalytic activity than rutile and brookite. This investigation will provide some new insight into understanding the difference of photocatalytic activity among anatase, rutile and brookite.

  12. High photocatalytic activity of mixed anatase-rutile phases on commercial TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Ruu Siah, Wai; Lintang, Hendrik O.; Shamsuddin, Mustaffa; Yuliati, Leny

    2016-02-01

    Titanium dioxide (TiO2) is well-known as an active photocatalyst for degradation of various organic pollutants. Over the years, a wide range of TiO2 nanoparticles with different phase compositions, crystallinities, and surface areas have been developed. Due to the different methods and conditions used to synthesize these commercial TiO2 nanoparticles, the properties and photocatalytic performance would also be different from each other. In this study, the photocatalytic removal of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5- trichlorophenoxyacetic acid (2,4,5-T) was investigated on commercial Evonik P25, Evonik P90, Hombikat UV100 and Hombikat N100 TiO2 nanoparticles. Upon photocatalytic tests, it was found that overall, the photocatalytic activities of the P25 and the P90 were higher than the N100 and the UV100 for the removal of both 2,4-D and 2,4,5-T. The high activities of the P25 and the P90 could be attributed to their phase compositions, which are made up of a mixture of anatase and rutile phases of TiO2. Whereas, the UV100 and the N100 are made up of 100% anatase phase of TiO2. The synergistic effect of the anatase/rutile mixture was reported to slow down the recombination rate of photogenerated electron-hole pairs. Consequently, the photocatalytic activity was increased on these TiO2 nanoparticles.

  13. Growth and structure of MBE grown TiO2 anatase films with rutile nano-crystallites

    SciTech Connect

    Shao, Rui; Wang, Chong M.; McCready, David E.; Droubay, Timothy C.; Chambers, Scott A.

    2007-03-15

    We have grown TiO2 anatase films with rutile nanocrystalline inclusions using molecular beam epitaxy under different growth conditions. This model system is important for investigating the role of rutile/anatase interfaces in heterogeneous photocatalysis. To control the film structure, we grew a pure anatase (001) layer at a slow rate and then increased the growth rate to drive the nucleation of rutile particles. Structure analysis indicates that the rutile phase has four preferred orientations in the anatase film.

  14. Mechanism of Li+/electron conductivity in rutile and anatase TiO2 nanoparticles

    SciTech Connect

    Sushko, Maria L.; Rosso, Kevin M.; Liu, Jun

    2010-11-08

    Concurrent Li-ion and electron conductivity in rutile and anatase TiO2 nanoparticles was studied using multiscale simulations. We show that charge transport in titania nanoparticles is determined by the competition of charge redistribution towards the particle boundaries and constant Li+ and electron fluxes. In nanoparticles smaller than the Debye length the constant flux prevails and the conductivity has a dual ionic and electronic character, while for larger nanoparticles conductivity becomes predominately ionic. Simulations revealed that the temperature dependence of Li-ion conductivity in anatase is very weak, while in rutile the conductivity decreases with temperature in small nanoparticles and increases in large nanoparticles.

  15. Evaluation of Surface State Mediated Charge Recombination in Anatase and Rutile TiO2

    PubMed Central

    2016-01-01

    In nanostructured thin films, photogenerated charge carriers can access the surface more easily than in dense films and thus react more readily. However, the high surface area of these films has also been associated with enhanced recombination losses via surface states. We herein use transient absorption spectroscopy to compare the ultrafast charge carrier kinetics in dense and nanostructured TiO2 films for its two most widely used polymorphs: anatase and rutile. We find that nanostructuring does not enhance recombination rates on ultrafast time scales, indicating that surface state mediated recombination is not a key loss pathway for either TiO2 polymorph. Rutile shows faster, and less intensity-dependent recombination than anatase, which we assign to its higher doping density. For both polymorphs, we conclude that bulk rather than surface recombination is the primary determinant of charge carrier lifetime. PMID:27564137

  16. Hydrogen shallow donors in ZnO and rutile TiO2

    NASA Astrophysics Data System (ADS)

    Weber, Jörg; Lavrov, Edward V.; Herklotz, Frank

    2012-05-01

    A combined study of IR absorption, photoconductivity, photoluminescence and Raman measurements in ZnO samples supports the theoretical suggestions of a shallow bond-centered hydrogen donor and a shallow hydrogen donor within the oxygen vacancy. In rutile TiO2 we also identify a shallow hydrogen donor in contrast to recent theoretical predictions. A possible solution to this obvious discrepancy is proposed.

  17. Effect of highly ordered single-crystalline TiO2 nanowire length on the photovoltaic performance of dye-sensitized solar cells.

    PubMed

    Zhou, Zheng-ji; Fan, Jun-qi; Wang, Xia; Zhou, Wen-hui; Du, Zu-liang; Wu, Si-xin

    2011-11-01

    One-dimensional semiconductor nanostructures grown directly onto transparent conducting oxide substrates with a high internal surface area are most desirable for high-efficiency dye-sensitized solar cells (DSSCs). Herein, we present a multicycle hydrothermal synthesis process to produce vertically aligned, single crystal rutile TiO(2) nanowires with different lengths between 1 and 8 μm for application as the working electrode in DSSCs. Optimum performance was obtained with a TiO(2) nanowire length of 2.0 μm, which may be ascribed to a smaller nanowire diameter with a high internal surface area and better optical transmittance with an increase in the incident light intensity on the N719 dye; as well as a firm connection at the FTO/TiO(2) nanowire interface.

  18. Controlled formation of anatase and rutile TiO2 thin films by reactive magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Rafieian, Damon; Ogieglo, Wojciech; Savenije, Tom; Lammertink, Rob G. H.

    2015-09-01

    We discuss the formation of TiO2 thin films via DC reactive magnetron sputtering. The oxygen concentration during sputtering proved to be a crucial parameter with respect to the final film structure and properties. The initial deposition provided amorphous films that crystallise upon annealing to anatase or rutile, depending on the initial sputtering conditions. Substoichiometric films (TiOx<2), obtained by sputtering at relatively low oxygen concentration, formed rutile upon annealing in air, whereas stoichiometric films formed anatase. This route therefore presents a formation route for rutile films via lower (<500 °C) temperature pathways. The dynamics of the annealing process were followed by in situ ellipsometry, showing the optical properties transformation. The final crystal structures were identified by XRD. The anatase film obtained by this deposition method displayed high carriers mobility as measured by time-resolved microwave conductance. This also confirms the high photocatalytic activity of the anatase films.

  19. Modification of cellulose and rutile welding electrode coating by infiltrated TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Balos, Sebastian; Sidjanin, Leposava; Dramicanin, Miroslav; Labus, Danka; Pilic, Branka; Jovicic, Mirjana

    2016-05-01

    In this paper, a novel method of infiltration of TiO2 nanoparticles into the coating of the cellulose and rutile shielded metal arc welding electrode is shown. Tensile properties and strength of weld metals were correlated to the chemical composition of the weld metals, ferrite type, and non-metallic inclusion type, size and composition. As infiltration time is increased in the cellulose electrodes, the non-metallic inclusion count increases and their size decreases. They act as inoculants and lead to the replacement of Widmanstaetten with the finegrained acicular ferrite which increases the mechanical properties of the welds. The modification of rutile electrodes with low and medium infiltration time also refines the microstructure and increases the mechanical properties. Specimens welded with rutile electrodes infiltrated at maximum duration exhibited the lowest mechanical properties due to the relatively large non-metallic inclusions that act as void nucleation sites and the appearance of large grain allotriomorphic ferrite in the weld metal.

  20. Graphene Oxide-Assisted Synthesis of Microsized Ultrathin Single-Crystalline Anatase TiO2 Nanosheets and Their Application in Dye-Sensitized Solar Cells.

    PubMed

    Chen, Biao; Sha, Junwei; Li, Wei; He, Fang; Liu, Enzuo; Shi, Chunsheng; He, Chunnian; Li, Jiajun; Zhao, Naiqin

    2016-02-03

    High-quality microsized ultrathin single-crystalline anatase TiO2 nanosheets (MS-TiO2) with exposed {001} facets were synthesized by a facile and low-cost two-step process that combines a graphene oxide (GO)-assisted hydrothermal method with calcination. Both GO and HF play an important role in the formation of well dispersed MS-TiO2. As a novel microsized (1-4 μm) ultrathin two-dimensional (2D) material, MS-TiO2 possesses much higher lateral size and aspect ratio compared to common 2D nanosized (30-60 nm) ultrathin TiO2 nanosheets (NS-TiO2), resulting in excellent electronic conductivity and superior electron transfer and diffusion properties. Here, we fabricated MS-TiO2 and NS-TiO2, both of which were incorporated with the TiO2 nanoparticles (P25) to constitute the hybrid photoanode of dye-sensitized solar cells (DSSCs), and explored the effect of the lateral size (nano- and micro-) of ultrathin TiO2 nanosheets on their electron transfer and diffusion properties. Benefiting from the faster electron transfer rate and short diffusion path of the MS-TiO2, the MS-TiO2/P25 gains the more superior performance compared to pure P25 and NS-TiO2/P25 in the application of DSSCs. Moreover, it is expected that the novel high aspect ratio MS-TiO2 may be applied in diverse fields including photocatalysis, photodetectors, lithium-ion batteries and others concerning the environment and energy.

  1. Efficient phyto-synthesis and structural characterization of rutile TiO2 nanoparticles using Annona squamosa peel extract

    NASA Astrophysics Data System (ADS)

    Roopan, Selvaraj Mohana; Bharathi, A.; Prabhakarn, A.; Abdul Rahuman, A.; Velayutham, K.; Rajakumar, G.; Padmaja, R. D.; Lekshmi, Mohan; Madhumitha, G.

    2012-12-01

    In the present study, the biosynthesis of rutile TiO2 nanoparticles (TiO2 NPs) was achieved by a novel, biodegradable and convenient procedure using fruit peel Annona squamosa aqueous extract. This is the first report on the new, simple, rapid, eco-friendly and cheaper methods for the synthesis of rutile TiO2 NPs at lower temperature using agricultural waste. Rutile TiO2 NPs were characterized by UV, XRD, SEM, TEM and EDS studies. The UV-Vis spectrophotometer results were promising and showed a rapid production of TiO2 NPs with a surface plasmon resonance occurring at 284 nm. The formation of the TiO2 NPs as observed from the XRD spectrum is confirmed to be TiO2 particles in the rutile form as evidenced by the peaks at 2θ = 27.42°, 36.10°, 41.30° and 54.33° when compared with the literature. The TEM images showed polydisperse nanoparticles with spherical shapes and size 23 ± 2 nm ranges.

  2. Efficient phyto-synthesis and structural characterization of rutile TiO2 nanoparticles using Annona squamosa peel extract.

    PubMed

    Roopan, Selvaraj Mohana; Bharathi, A; Prabhakarn, A; Rahuman, A Abdul; Velayutham, K; Rajakumar, G; Padmaja, R D; Lekshmi, Mohan; Madhumitha, G

    2012-12-01

    In the present study, the biosynthesis of rutile TiO(2) nanoparticles (TiO(2) NPs) was achieved by a novel, biodegradable and convenient procedure using fruit peel Annona squamosa aqueous extract. This is the first report on the new, simple, rapid, eco-friendly and cheaper methods for the synthesis of rutile TiO(2) NPs at lower temperature using agricultural waste. Rutile TiO(2) NPs were characterized by UV, XRD, SEM, TEM and EDS studies. The UV-Vis spectrophotometer results were promising and showed a rapid production of TiO(2) NPs with a surface plasmon resonance occurring at 284 nm. The formation of the TiO(2) NPs as observed from the XRD spectrum is confirmed to be TiO(2) particles in the rutile form as evidenced by the peaks at 2θ=27.42°, 36.10°, 41.30° and 54.33° when compared with the literature. The TEM images showed polydisperse nanoparticles with spherical shapes and size 23±2 nm ranges.

  3. The electronic structure and optical response of rutile, anatase and brookite TiO2.

    PubMed

    Landmann, M; Rauls, E; Schmidt, W G

    2012-05-16

    In this study, we present a combined density functional theory and many-body perturbation theory study on the electronic and optical properties of TiO(2) brookite as well as the tetragonal phases rutile and anatase. The electronic structure and linear optical response have been calculated from the Kohn-Sham band structure applying (semi)local as well as nonlocal screened hybrid exchange-correlation density functionals. Single-particle excitations are treated within the GW approximation for independent quasiparticles. For optical response calculations, two-particle excitations have been included by solving the Bethe-Salpeter equation for Coulomb correlated electron-hole pairs. On this methodological basis, gap data and optical spectra for the three major phases of TiO(2) are provided. The common characteristics of brookite with the rutile and anatase phases, which have been discussed more comprehensively in the literature, are highlighted. Furthermore, the comparison of the present calculations with measured optical response data of rutile indicate that discrepancies discussed in numerous earlier studies are due to the measurements rather than related to an insufficient theoretical description.

  4. Wet chemically prepared rutile TiO2(110) and TiO2(011): Substrate preparation for surface studies under non-UHV conditions

    NASA Astrophysics Data System (ADS)

    Ahmed, M. H. M.; Lydiatt, F. P.; Chekulaev, D.; Wincott, P. L.; Vaughan, D. J.; Jang, J. H.; Baldelli, S.; Thomas, A. G.; Walters, W. S.; Lindsay, R.

    2014-12-01

    A procedure for wet chemical preparation of TiO2 single crystal surfaces is detailed. The potential of this procedure is demonstrated through application to rutile-TiO2(110) and rutile-TiO2(011) substrates. Characterisation with atomic force microscopy, low energy electron diffraction, auger electron spectroscopy, and vibrational sum frequency spectroscopy indicates that flat, well-ordered, carbon-free surfaces can be generated. Notably, in contrast to the (2 × 1) low energy electron diffraction pattern observed for TiO2(011) prepared in ultra-high vacuum, wet chemical preparation results in a (4 × 1) unit cell; wet chemically prepared TiO2(110) displays an unreconstructed (1 × 1) surface.

  5. Optical studies of cobalt implanted rutile TiO2 (110) surfaces

    NASA Astrophysics Data System (ADS)

    Joshi, Shalik Ram; Padmanabhan, B.; Chanda, Anupama; Mishra, Indrani; Malik, V. K.; Mishra, N. C.; Kanjilal, D.; Varma, Shikha

    2016-11-01

    Present study investigates the photoabsorption properties of single crystal rutile TiO2 (110) surfaces after they have been implanted with low fluences of cobalt ions. The surfaces, after implantation, demonstrate fabrication of nanostructures and anisotropic nano-ripple patterns. Creation of oxygen vacancies (Ti3+ states), development of cobalt nano-clusters as well as band gap modifications have also been observed. Results presented here demonstrate that fabrication of self organized nanostructures, upon implantation, along with the development of oxygen vacancies and ligand field transitions of cobalt ion promote the enhancement of photo-absorbance in both UV (∼2 times) and visible (∼5 times) regimes. These investigations on nanostructured TiO2 surfaces can be important for photo-catalysis.

  6. Field-programmable rectification in rutile TiO2 crystals

    NASA Astrophysics Data System (ADS)

    Jameson, John R.; Fukuzumi, Yoshiaki; Wang, Zheng; Griffin, Peter; Tsunoda, Koji; Meijer, G. Ingmar; Nishi, Yoshio

    2007-09-01

    The authors report "field-programmable rectification" in crystals of rutile TiO2. A "programming" voltage is applied between two Pt electrodes on the surface of a crystal. Afterwards, current can pass in the direction of the programming voltage, but not in the reverse direction. The polarity of the rectification can be reversed by applying a programming voltage of opposite sign. The effect was observed on the (110) and (100) surfaces, but not the (001) surface. The proposed mechanism is field-induced motion of oxygen vacancies, which pile up under the negative terminal, eliminating a Schottky barrier, but leaving one at the positive terminal intact.

  7. Synthesis and Characterization of Rutile TiO2Nanopowders Doped with Iron Ions

    PubMed Central

    2009-01-01

    Titanium dioxide nanopowders doped with different amounts of Fe ions were prepared by coprecipitation method. Obtained materials were characterized by structural (XRD), morphological (TEM and SEM), optical (UV/vis reflection and photoluminescence, and Raman), and analytical techniques (XPS and ICP-OES). XRD analysis revealed rutile crystalline phase for doped and undoped titanium dioxide obtained in the same manner. Diameter of the particles was 5–7 nm. The presence of iron ions was confirmed by XPS and ICP-OES. Doping process moved absorption threshold of TiO2into visible spectrum range. Photocatalytic activity was also checked. Doped nanopowders showed normal and up-converted photoluminescence. PMID:20596442

  8. Effect of TiO2 rutile nanorods on the photoelectrodes of dye-sensitized solar cells

    PubMed Central

    2013-01-01

    In order to enhance the electron transport on the photoelectrodes of dye-sensitized solar cells, one-dimensional rutile nanorods were prepared using electrospun TiO2 nanofibers. The grain size of the nanorods increased with increasing temperature. Electrochemical impedance spectroscopy measurements revealed reduced interface resistance of the cells with the one-dimensional rutile nanorods due to the improved electron transport and the enhanced electrolyte penetration. Intensity-modulated photocurrent/photovoltage spectroscopy showed that the one-dimensional rutile nanorods provided the electrons with a moving pathway and suppressed the recombination of photogenerated electrons. However, an excessive quantity of rutile nanorods created an obstacle to the electrons moving in the TiO2 thin film. The photoelectrode with 7 wt.% rutile nanorods optimized the performance of the dye-sensitized solar cells. PMID:23331863

  9. TiO2 single crystalline nanorod compact layer for high-performance CH3NH3PbI3 perovskite solar cells with an efficiency exceeding 17%

    NASA Astrophysics Data System (ADS)

    He, Xin; Wu, Jihuai; Tu, Yongguang; Xie, Yiming; Dong, Jia; Jia, Jinbiao; Wei, Yuelin; Lan, Zhang

    2016-11-01

    A TiO2 compact layer is crucial to a high-performance perovskite solar cell (PSC). Interestingly, there is a severe paucity of research on using one-dimensional nanostructure to fabricate the compact layer. In this study, anatase TiO2 single-crystalline nanorods (NRs) with a length of 30 ± 10 nm and a diameter of 4 ± 1 nm are synthesized via a one-pot solvothermal approach. A pinhole-free and thickness-controllable compact layer on PSC is fabricated by spin-coating the TiO2 nanorods on transparent conductive oxide substrate. Thanks to good electronic transport channel and less defects and interfaces, one-dimensional TiO2 NRs, with longer electron lifetime, shorter transport time and higher charge collection efficiency than TiO2 quantum dots (QDs) and TiO2 nanoparticles (NPs), can improve the photovoltaic performance of the PSC based on TiO2-NR compact layer. As a result, the PSC based on TiO2 NRs shows the best photovoltaic performance with a power conversion efficiency of 17.58%, which is enhanced by a factor of 1.16 and 1.30 respectively compared with the PSCs based on TiO2-QDs and TiO2-NPs.

  10. The acute proinflammatory and prothrombotic effects of pulmonary exposure to rutile TiO2 nanorods in rats.

    PubMed

    Nemmar, Abderrahim; Melghit, Khaled; Ali, Badreldin H

    2008-05-01

    Nanotechnology is extensively used in industry and is widely explored for possible applications in medicine. However, its potential respiratory and systemic adverse effects remain unknown. Here pure titanium dioxide (TiO2) nanorods with rutile structure were prepared at room temperature by using a soft chemistry technique. The structure of the TiO2 rutile nanorods was confirmed by powder X-ray diffraction, and the size was revealed by transmission electron microscopy. Thereafter, we investigated, in Wistar rats, the acute (24-hr) effects of intratracheal instillation of these rutile TiO2 nanorods (1 and 5 mg/kg) on lung inflammation (assessed by bronchoalveolar lavage), systemic inflammation, and platelet aggregation in whole blood. Compared with vehicle-exposed rats, rats that underwent intratracheal instillation of TiO2 nanorods experienced a dose-dependent increase in macrophage numbers at 1 (+50%) and 5 mg/kg (+81%; P < 0.05) and an influx of neutrophils at 1 (+294%) and 5 mg/kg (+4117%; P < 0.01) in their bronchoalveolar lavage fluid. Both doses of rutile TiO2 nanorods caused pulmonary and cardiac edema, assessed by analysis of the wet weight-to-dry weight ratios. Similarly, the numbers of monocytes and granulocytes in the blood were increased in a dose-dependent manner after exposure to rutile TiO2 nanorods. In contrast, the number of platelets was significantly reduced after pulmonary exposure to 5 mg/kg TiO2 nanorods; this result indicated the occurrence of platelet aggregation in vivo. The direct addition of TiO2 nanorods (0.4-10 microg/ml) to untreated rat blood significantly induced platelet aggregation in a dose-dependent fashion in vitro. It is concluded that the intratracheal instillation of rutile TiO2 nanorods caused upregulation of lung inflammation, pulmonary and cardiac edema, and systemic inflammation. Rutile TiO2 nanorods also triggered platelet aggregation in vivo and in vitro.

  11. Formation of swift heavy ion tracks on a rutile TiO2 (001) surface.

    PubMed

    Karlušić, Marko; Bernstorff, Sigrid; Siketić, Zdravko; Šantić, Branko; Bogdanović-Radović, Ivančica; Jakšić, Milko; Schleberger, Marika; Buljan, Maja

    2016-10-01

    Nanostructuring of surfaces and two-dimensional materials using swift heavy ions offers some unique possibilities owing to the deposition of a large amount of energy localized within a nanoscale volume surrounding the ion trajectory. To fully exploit this feature, the morphology of nanostructures formed after ion impact has to be known in detail. In the present work the response of a rutile TiO2 (001) surface to grazing-incidence swift heavy ion irradiation is investigated. Surface ion tracks with the well known intermittent inner structure were successfully produced using 23 MeV I ions. Samples irradiated with different ion fluences were investigated using atomic force microscopy and grazing-incidence small-angle X-ray scattering. With these two complementary approaches, a detailed description of the swift heavy ion impact sites, i.e. the ion tracks on the surface, can be obtained even for the case of multiple ion track overlap. In addition to the structural investigation of surface ion tracks, the change in stoichiometry of the rutile TiO2 (001) surface during swift heavy ion irradiation was monitored using in situ time-of-flight elastic recoil detection analysis, and a preferential loss of oxygen was found.

  12. Unique adsorption behaviors of carboxylic acids at rutile TiO2(110)

    NASA Astrophysics Data System (ADS)

    Yu, Yan-Yan; Gong, Xue-Qing

    2015-11-01

    The coverage-dependent adsorption behavior of acetic acid (CH3COOH) on rutile TiO2(110) was investigated by means of density functional theory (DFT) calculations, corrected by on-site Coulomb corrections and long-range dispersion interactions. The p(2 × 1) and c(2 × 2) domains of dissociatively adsorbed acetic acid under different coverages have been studied in detail regarding their structural and energetic properties. Adsorptions of formic acid (HCOOH) and carbonic acid (H2CO3) were also considered for better understanding the adsorption behaviors of carboxylic acids. Our calculation results show that carboxylic acids prefer to dissociatively adsorb in bridging bidentate configuration, and it induces significant surface relaxation at the adsorption site, which also affects other surface atoms nearby. Interestingly, we have shown that such adsorption-induced relaxations still maintain bond symmetries for surface Ti cations within the p(2 × 1) domain while they are drastically broken within the c(2 × 2) domain, giving rise to unstable Ti cations at the surface. This work not only explains the long-lasting puzzle of the preferable occurrence of p(2 × 1) domain for the adsorbed carboxylic acids at rutile TiO2(110), it also proposes a novel scheme that metal oxide surfaces may follow when they are involved in the processes like surface functionalization and self-assembly.

  13. Formation of swift heavy ion tracks on a rutile TiO2 (001) surface1

    PubMed Central

    Karlušić, Marko; Bernstorff, Sigrid; Siketić, Zdravko; Šantić, Branko; Bogdanović-Radović, Ivančica; Jakšić, Milko; Schleberger, Marika; Buljan, Maja

    2016-01-01

    Nanostructuring of surfaces and two-dimensional materials using swift heavy ions offers some unique possibilities owing to the deposition of a large amount of energy localized within a nanoscale volume surrounding the ion trajectory. To fully exploit this feature, the morphology of nanostructures formed after ion impact has to be known in detail. In the present work the response of a rutile TiO2 (001) surface to grazing-incidence swift heavy ion irradiation is investigated. Surface ion tracks with the well known intermittent inner structure were successfully produced using 23 MeV I ions. Samples irradiated with different ion fluences were investigated using atomic force microscopy and grazing-incidence small-angle X-ray scattering. With these two complementary approaches, a detailed description of the swift heavy ion impact sites, i.e. the ion tracks on the surface, can be obtained even for the case of multiple ion track overlap. In addition to the structural investigation of surface ion tracks, the change in stoichiometry of the rutile TiO2 (001) surface during swift heavy ion irradiation was monitored using in situ time-of-flight elastic recoil detection analysis, and a preferential loss of oxygen was found. PMID:27738417

  14. Fabrication of phase and morphology controlled pure rutile and rutile/anatase TiO2 nanostructures in functional ionic liquid/water

    NASA Astrophysics Data System (ADS)

    Shahi, Satwant Kaur; Kaur, Navneet; Singh, Vasundhara

    2016-01-01

    In this paper, pure rutile and anatase-rutile TiO2 nanoparticles have been successfully synthesised via a green route by hydrolysis of titanium tetrachloride with room temperature acidic ionic liquid 3-methyl-1-(3-sulfonylpropyl) imidazolium trifluoromethanesulfonate [HO3S(CH2)3MIM][CF3SO3] in aqueous medium. The influence of pH of the solution by varying molar ratio of substrate and ionic liquid has been investigated in both sol⿿gel and hydrothermal synthesis of TiO2 with significant variation in phase, phase composition (ratio of rutile to anatase) and morphology as indicated by various structural analysis such as XRD, TEM, BET, Raman and UV⿿vis absorption spectroscopy. The results indicate formation of a bunch of aligned thin flaky nano-rods of TiO2 which look like nano-flowers with a crystal size of 3⿿5 nm by sol⿿gel method, while in case of hydrothermal method well-defined rutile solid nanorods of TiO2 were formed with variable length in the range of 120⿿170 nm and 20⿿24 nm in width. The photocatalytic activity of the prepared TiO2 samples has been determined by the photodegradation of methyl orange dye (20 ppm) under UV light. Best photocatalytic activity was exhibited by sample S-2 prepared via sol⿿gel method.

  15. Adsorption of Nucleic Acid Components on Rutile (TiO2) Surfaces

    NASA Astrophysics Data System (ADS)

    Cleaves, H. James; Jonsson, Caroline M.; Jonsson, Christopher L.; Sverjensky, Dimitri A.; Hazen, Robert M.

    2010-04-01

    Nucleic acids, the storage molecules of genetic information, are composed of repeating polymers of ribonucleotides (in RNA) or deoxyribonucleotides (in DNA), which are themselves composed of a phosphate moiety, a sugar moiety, and a nitrogenous base. The interactions between these components and mineral surfaces are important because there is a tremendous flux of nucleic acids in the environment due to cell death and horizontal gene transfer. The adsorption of mono-, oligo-, and polynucleotides and their components on mineral surfaces may have been important for the origin of life. We have studied here interactions of nucleic acid components with rutile (TiO2), a mineral common in many terrestrial crustal rocks. Our results suggest roles for several nucleic acid functional groups (including sugar hydroxyl groups, the phosphate group, and extracyclic functional groups on the bases) in binding, in agreement with results obtained from studies of other minerals. In contrast with recent studies of nucleotide adsorption on ZnO, aluminum oxides, and hematite, our results suggest a different preferred orientation for the monomers on rutile surfaces. The conformations of the molecules bound to rutile surfaces appear to favor specific interactions, which in turn may allow identification of the most favorable mineral surfaces for nucleic acid adsorption.

  16. Comment on "Structure and dynamics of liquid water on rutile TiO2(110)

    SciTech Connect

    Wesolowski, David J; Sofo, Jorge O.; Bandura, Andrei V.; Zhang, Zhan; Mamontov, Eugene; Predota, M.; Kumar, Nitin; Kubicki, James D.; Kent, Paul R; Vlcek, Lukas; Machesky, Michael L.; Fenter, Paul; Cummings, Peter T; Anovitz, Lawrence {Larry} M; Skelton, A A; Rosenqvist, Jorgen K

    2012-01-01

    Liu and co-workers [Phys. Rev. B 82, 161415 (2010)] discussed the long-standing debate regarding whether H2O molecules on the defect-free (110) surface of rutile ( -TiO2) sorb associatively, or there is dissociation of some or all first-layer water to produce hydroxyl surface sites. They conducted static density functional theory (DFT) and DFT molecular dynamics (DFT-MD) investigations using a range of cell configurations and functionals. We have reproduced their static DFT calculations of the influence of crystal slab thickness on water sorption energies. However, we disagree with several assertions made by these authors: (a) that second-layer water structuring and hydrogen bonding to surface oxygens and adsorbed water molecules are weak ; (b) that translational diffusion of water molecules in direct contact with the surface approaches that of bulk liquid water; and (c) that there is no dissociation of adsorbed water at this surface in contact with liquid water. These assertions directly contradict our publishedwork, which compared synchrotron x-ray crystal truncation rod, second harmonic generation, quasielastic neutron scattering, surface charge titration, and classical MD simulations of rutile (110) single-crystal surfaces and (110)-dominated powders in contact with bulk water, and (110)-dominated rutile nanoparticles with several monolayers of adsorbed water.

  17. Surface-Electronic-State-Modulated, Single-Crystalline (001) TiO2 Nanosheets for Sensitive Electrochemical Sensing of Heavy-Metal Ions.

    PubMed

    Zhou, Wen-Yi; Liu, Jin-Yun; Song, Jie-Yao; Li, Jin-Jin; Liu, Jin-Huai; Huang, Xing-Jiu

    2017-03-21

    Intrinsically low conductivity and poor reactivity restrict many semiconductors from electrochemical detection. Usually, metal- and carbon-based modifications of semiconductors are necessary, making them complex, expensive, and unstable. Here, for the first time, we present a surface-electronic-state-modulation-based concept applied to semiconductors. This concept enables pure semiconductors to be directly available for ultrasensitive electrochemical detection of heavy-metal ions without any modifications. As an example, a defective single-crystalline (001) TiO2 nanosheet exhibits high electrochemical performance toward Hg(II), including a sensitivity of 270.83 μA μM(-1) cm(-2) and a detection limit of 0.017 μM, which is lower than the safety standard (0.03 μM) of drinking water established by the World Health Organization (WHO). It has been confirmed that the surface oxygen vacancy adsorbs an O2 molecule while the Ti(3+) donates an electron, forming the O2(•-) species that facilitate adsorption of Hg(II) and serve as active sites for electron transfer. These findings not only extend the electrochemical sensing applications of pure semiconductors but also stimulate new opportunities for investigating atom-level electrochemical behaviors of semiconductors by surface electronic-state modulation.

  18. The effect of Fe segregation on the photocatalytic growth of Ag nanoparticles on rutile TiO2(001)

    NASA Astrophysics Data System (ADS)

    Busiakiewicz, Adam; Kisielewska, Aneta; Piwoński, Ireneusz; Batory, Damian

    2017-04-01

    The photocatalytic growth of silver nanoparticles (AgNPs) on rutile TiO2(001) and Fe-modified rutile TiO2(001) monocrystals was investigated. Various amount of Fe was segregated in a controlled way from the doped TiO2 substrates in ultra-high vacuum conditions resulting in low- medium- and high- content of Fe on TiO2 substrates. AgNPs were grown on pristine TiO2 and substrates containing Fe by photoreduction of Ag+ ions under UV illumination. It was found that the size of AgNPs was larger on Fe/TiO2 than on TiO2 while the surface density exhibited the opposite behavior - a large number of AgNPs were present on the TiO2 surface but only a few AgNPs were visible on the Fe/TiO2 substrates. The reason for the differences in size and number of AgNPs on TiO2 and Fe/TiO2 is the limited access of Ag+ to the TiO2 surface caused by the large number of Fe grains segregated onto the TiO2 surface. Another possible reason for the various AgNPs morphologies is alteration in the mechanism of Ag+ photoreduction caused by iron present as Fe3+ ions and by newly formed AgNPs playing the role of electron traps. The surface elemental analysis of the investigated materials was performed with the use of X-ray photoelectron spectroscopy (XPS) and confirmed the composition of AgNPs/Fe/TiO2 systems. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed sizes, morphology and distribution of the nanostructures.

  19. Effect of rutile phase on V2O5 supported over TiO2 mixed phase for the selective catalytic reduction of NO with NH3

    NASA Astrophysics Data System (ADS)

    Zhang, Shule; Zhong, Qin; Wang, Yining

    2014-09-01

    A series of V2O5/TiO2 catalysts with different ratios of TiO2 rutile phase was prepared. Focusing on the effect of TiO2 rutile phase on V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3, the NO conversion for the different catalysts was investigated. The experimental results showed that a small amount of TiO2 rutile phase could improve the NO conversion significantly below 270 °C. Analysis by XRD, NH3-TPD, UV-vis, EPR and DFT calculation showed that the rutile phase of TiO2 supporter decreased the band gap, especially, the conduction band level. It improved the formation of reduced V species and superoxide ions that were important to the low-temperature SCR reaction.

  20. Niobium doped TiO2: Intrinsic transparent metallic anatase versus highly resistive rutile phase

    NASA Astrophysics Data System (ADS)

    Zhang, S. X.; Kundaliya, D. C.; Yu, W.; Dhar, S.; Young, S. Y.; Salamanca-Riba, L. G.; Ogale, S. B.; Vispute, R. D.; Venkatesan, T.

    2007-07-01

    We report on the structural, electrical, and optical properties of 5% niobium doped TiO2 thin films grown on various substrates by pulsed laser deposition. The epitaxial anatase Nb:TiO2 film on LaAlO3 is shown to be an intrinsic transparent metal and its metallic property arises from Nb substitution into Ti site as evidenced by the Rutherford backscattering channeling result. In contrast, the rutile Nb:TiO2 thin films show insulating behaviors with 2-3 orders higher room temperature electrical resistivity and ˜30 times lower mobility. A blueshift in the optical absorption edge is observed in both phases, though of differing magnitude.

  1. Stereospecific growth of densely populated rutile mesoporous TiO2 nanoplate films: a facile low temperature chemical synthesis approach

    NASA Astrophysics Data System (ADS)

    Lee, Go-Woon; Ambade, Swapnil B.; Cho, Young-Jin; Mane, Rajaram S.; Shashikala, V.; Yadav, Jyotiprakash; Gaikwad, Rajendra S.; Lee, Soo-Hyoung; Jung, Kwang-Deog; Han, Sung-Hwan; Joo, Oh-Shim

    2010-03-01

    We report for the first time, using a simple and environmentally benign chemical method, the low temperature synthesis of densely populated upright-standing rutile TiO2 nanoplate films onto a glass substrate from a mixture of titanium trichloride, hydrogen peroxide and thiourea in triply distilled water. The rutile TiO2 nanoplate films (the phase is confirmed from x-ray diffraction analysis, selected area electron diffraction, energy-dispersive x-ray analysis, and Raman shift) are 20-35 nm wide and 100-120 nm long. The chemical reaction kinetics for the growth of these upright-standing TiO2 nanoplate films is also interpreted. Films of TiO2 nanoplates are optically transparent in the visible region with a sharp absorption edge close to 350 nm, confirming an indirect band gap energy of 3.12 eV. The Brunauer-Emmet-Teller surface area, Barret-Joyner-Halenda pore volume and pore diameter, obtained from N2 physisorption studies, are 82 m2 g - 1, 0.0964 cm3 g - 1 and 3.5 nm, respectively, confirming the mesoporosity of scratched rutile TiO2 nanoplate powder that would be ideal for the direct fabrication of nanoscaled devices including upcoming dye-sensitized solar cells and gas sensors.

  2. Dehydration and Dehydrogenation of Ethylene Glycol on Rutile TiO2(110)

    SciTech Connect

    Li, Zhenjun; Kay, Bruce D.; Dohnalek, Zdenek

    2013-08-07

    The interactions of ethylene glycol (EG) with partially reduced rutile TiO2(110) surface have been studied using temperature programmed desorption (TPD). The saturation coverage on the surface Ti rows is determined to be 0.43 monolayer (ML), slightly less than one EG per two Ti sites. Most of the adsorbed ethanol (~80%) undergoes further reactions to other products. Two major channels are observed, dehydration yielding ethylene and water and dehydrogenation yielding acetaldehyde and hydrogen. Hydrogen formation is rather surprising as it has not been observed previously on TiO2(110) from simple organic molecules. The coverage dependent yields of ethylene and acetaldehyde correlate well with that of water and hydrogen, respectively. Dehydration dominates at lower EG coverages (< 0.2 ML) and plateaus as the coverage is increased to saturation. Dehydrogenation is observed primarily at higher EG coverages (>0.2 ML). Our results suggest that the observed dehydration and dehydrogenation reactions proceed via different surface intermediates.

  3. Role of Water in Methanol Photochemistry on Rutile TiO2(110)

    SciTech Connect

    Shen, Mingmin; Henderson, Michael A.

    2012-08-07

    Photochemistry of the molecularly and dissociatively adsorbed forms of methanol on the vacuum-annealed rutile TiO2(110) surface was explored using temperature programmed desorption (TPD), both with and without coadsorbed water. Methoxy, and not methanol, was confirmed as the photochemically active form of adsorbed methanol on this surface. UV irradiation of methoxy-covered TiO2(110) lead to depletion of the methoxy coverage and formation of formaldehyde and a surface OH group. Coadsorbed water did not promote either molecular methanol photochemistry or thermal decomposition of methanol to methoxy. However, terminal OH groups (OHt), prepared by coadsorption of water and oxygen atoms, thermally converted molecularly adsorbed methanol to methoxy at 120 K, thus enabling photoactivity. While chemisorbed water molecules had no influence on methoxy photochemistry, water molecules hydrogen-bonded in the second layer to bridging oxygen (Obr) sites inhibited the methoxy photodecomposition to formaldehyde. From this we conclude that Obr sites accept protons from the hole-mediated conversion of methoxy to formaldehyde. These results provide new fundamental understanding of the hole-scavenging role of methanol in photochemical processes on TiO2-based materials and how water influences this photochemistry. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle under contract DEAC05-76RL01830. The research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

  4. Room temperature synthesized rutile TiO(2) nanoparticles induced by laser ablation in liquid and their photocatalytic activity.

    PubMed

    Liu, Peisheng; Cai, Weiping; Fang, Ming; Li, Zhigang; Zeng, Haibo; Hu, Jinlian; Luo, Xiangdong; Jing, Weiping

    2009-07-15

    TiO(2) nanoparticles were prepared by one-step pulsed laser ablation of a titanium target immersed in a poly-(vinylpyrrolidone) solution at room temperature. The products were systematically characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). The results indicated that the rutile TiO(2) nanocrystalline particles were one-step synthesized at room temperature and the mean size in diameter is about 50 nm with a narrow size distribution. A probable formation process was proposed on the basis of the microstructure and the instantaneous plasma plume induced by the laser. Photocatalytic activity was monitored by degradation of a methylene blue solution. The as-prepared rutile TiO(2) nanoparticles demonstrate a good photocatalytic performance. This work shows that pulsed laser ablation in liquid media is a good method to synthesize some nanosized materials which are difficult to produce by other conventional methods.

  5. Vickers indentation hardness of stoichiometric and reduced single crystal TiO2 (rutile) from 25 to 800 C

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Deadmore, Daniel L.

    1993-01-01

    The indentation microhardness of stoichiometric and reduced single crystal rutile (TiO2) from 25 to 800 C is presented in this paper. The results serve two main purposes. One is to assess the effect of rutile's stoichiometry on its hardness. The other is to test recently suggested theory on solid lubrication with sub Stoichiometric rutile in an effort to better understand shear controlled phenomenon. Microhardness was measured using a Vickers diamond indentor on both vacuum and hydrogen reduced single crystal rutile from 25 to 800 C. The results indicate that stoichiometry and temperature have a pronounced effect on rutile's hardness. The measured effects lend support to theory on solid lubrication by enhanced crystallographic slip and suggest that solid lubricant materials may be produced by careful atomic level tailoring (stoichiometry control).

  6. Hydrothermal synthesis of a crystalline rutile TiO2 nanorod based network for efficient dye-sensitized solar cells.

    PubMed

    Yu, Hua; Pan, Jian; Bai, Yang; Zong, Xu; Li, Xinyong; Wang, Lianzhou

    2013-09-27

    One-dimensional (1D) TiO2 nanostructures are desirable as photoanodes in dye-sensitized solar cells (DSSCs) due to their superior electron-transport capability. However, making use of the DSSC performance of 1D rutile TiO2 photoanodes remains challenging, mainly due to the small surface area and consequently low dye loading. Herein, a new type of photoanode with a three-dimensional (3D) rutile-nanorod-based network structure directly grown on fluorine-doped tin oxide (FTO) substrates was developed by using a facile two-step hydrothermal process. The resultant photoanode possesses oriented rutile nanorod arrays for fast electron transport as the bottom layer and radially packed rutile head-caps with an improved large surface area for efficient dye adsorption. The diffuse reflectance spectra showed that with the radially packed top layer, the light-harvesting efficiency was increased due to an enhanced light-scattering effect. A combination of electrochemical impedance spectroscopy (EIS), dark current, and open-circuit voltage decay (OCVD) analyses confirmed that the electron-recombiantion rate was reduced on formation of the nanorod-based 3D network for fast electron transport. As a resut, a light-to-electricity conversion efficiency of 6.31% was achieved with this photoanode in DSSCs, which is comparable to the best DSSC efficiencies that have been reported to date for 1D rutile TiO2 .

  7. Photoluminescence and Raman spectroscopy studies of Eu3+-doped rutile TiO2 nanocrystals at high pressures

    NASA Astrophysics Data System (ADS)

    Zeng, Q. G.; Ding, Z. J.; Lei, B. F.; Sheng, Y. Q.; Zhang, Z. M.

    2012-09-01

    Nanocrystal samples (particle size about 90 nm) of Eu3+-doped rutile titanium dioxide (TiO2) nanocrystals (rutile Eu3+/TiO2 nanocrystals) were synthesized by the sol-gel method with hydrothermal treatment. The pressure effect on photoluminescence (PL) and Raman spectra of the rutile Eu3+/TiO2 nanocrystals was investigated with a diamond anvil cell under hydrostatic pressure condition. Raman spectra of the samples at high pressures indicated that the critical pressure for the transition from the rutile phase to a new baddeleyite-type phase was between 10 and 14.2 GPa. The position of Raman bands shifted to high wavenumbers and the PL intensity of 5D 0→7F 2 transition of Eu3+ decreased down to zero with the increase of pressure before the phase transition occurred. After releasing the pressure, the rutile phase was not recovered and a α-PbO2-type phase was observed at ambient pressure.

  8. Why is anatase a better photocatalyst than rutile?--Model studies on epitaxial TiO2 films.

    PubMed

    Luttrell, Tim; Halpegamage, Sandamali; Tao, Junguang; Kramer, Alan; Sutter, Eli; Batzill, Matthias

    2014-02-10

    The prototypical photocatalyst TiO2 exists in different polymorphs, the most common forms are the anatase- and rutile-crystal structures. Generally, anatase is more active than rutile, but no consensus exists to explain this difference. Here we demonstrate that it is the bulk transport of excitons to the surface that contributes to the difference. Utilizing high -quality epitaxial TiO2 films of the two polymorphs we evaluate the photocatalytic activity as a function of TiO2-film thickness. For anatase the activity increases for films up to ~5 nm thick, while rutile films reach their maximum activity for ~2.5 nm films already. This shows that charge carriers excited deeper in the bulk contribute to surface reactions in anatase than in rutile. Furthermore, we measure surface orientation dependent activity on rutile single crystals. The pronounced orientation-dependent activity can also be correlated to anisotropic bulk charge carrier mobility, suggesting general importance of bulk charge diffusion for explaining photocatalytic anisotropies.

  9. Synthesis, phase to phase deposition and characterization of rutile nanocrystalline titanium dioxide (TiO2) thin films

    NASA Astrophysics Data System (ADS)

    Gupta, Sanjeev K.; Singh, Jitendra; Anbalagan, K.; Kothari, Prateek; Bhatia, Ravi Raj; Mishra, Pratima K.; Manjuladevi, V.; Gupta, Raj K.; Akhtar, J.

    2013-01-01

    In this work the preparation, deposition and structural properties of titanium oxide (TiO2) thin films were investigated. The films were deposited by means of the e-beam physical vapor deposition (EBPVD) method in high vacuum (10-7 Torr). A controlled deposition rate in the range of 0.1-0.3 Å/s was monitored in situ employing quartz crystal. The films were deposited on the oxidized Si (1 0 0) wafer, glass micro slides. These films were analyzed using Grazing Angle X-ray diffraction (GA-XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy (RAMAN), Atomic Force Microscopy (AFM) and UV-visible Spectroscopy (UV-vis). Structural characterization results showed mainly presence of the crystalline rutile phase, however an interfacial SiO2 layer between TiO2 and the substrate and the minor anatase crystalline phase of TiO2 was also identified in FTIR analysis. Grain size was found to be in the range of 100-125 nm while grain boundary was estimated to be 20 nm. Direct and indirect optical band gap was estimated to be 3.64 and 3.04 eV, respectively. A process induced self annealing of deposited film shows a strong effect on the structural, morphological and optical properties. Furthermore, low deposition rate and high vacuum allows rutile to rutile phase transformation from indigenously prepared TiO2 target to thin film.

  10. H2O-EG-assisted synthesis of uniform urchinlike rutile TiO2 with superior lithium storage properties.

    PubMed

    Chen, Jun Song; Liang, Yen Nan; Li, Yongmei; Yan, Qingyu; Hu, Xiao

    2013-10-23

    A facile green method to synthesize uniform nanostructured urchinlike rutile TiO2 is demonstrated. Titanium trichloride was selected as the TiO2 precursor, and a mixed solvent containing H2O and ethylene glycol was used. By using this binary medium, the nucleation and crystal growth of rutile TiO2 can be regulated, giving rise to very uniform urchinlike structures with tailorable sizes. As confirmed by the SEM and TEM analysis, large particles with dense aggregation of needle-like building blocks or small ones with loosely packed subunits could be obtained at different reaction conditions. The as-prepared samples were applied as the anode material for lithium-ion batteries, and they were shown to have superior properties with a high reversible capacity of 140 mA h g(-1) at a high current rate of 10 C for up to 300 cycles, which is almost unmatched by other rutile TiO2-based electrodes. A stable capacity of 88 mA h g(-1) can also be delivered at an extremely high rate of 50 C, suggesting the great potential of the as-prepared product for high-rate lithium-ion batteries.

  11. Electronic properties of atomic layer deposition films, anatase and rutile TiO2 studied by resonant photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Das, C.; Richter, M.; Tallarida, M.; Schmeisser, D.

    2016-07-01

    The TiO2 films are prepared by atomic layer deposition (ALD) method using titanium isopropoxide precursors at 250 °C and analyzed using resonant photoemission spectroscopy (resPES). We report on the Ti2p and O1s core levels, on the valence band (VB) spectra and x-ray absorption spectroscopy (XAS) data, and on the resonant photoelectron spectroscopy (resPES) profiles at the O1s and the Ti3p absorption edges. We determine the elemental abundance, the position of the VB maxima, the partial density of states (PDOS) in the VB and in the conduction band (CB) and collect these data in a band scheme. In addition, we analyze the band-gap states as well as the intrinsic states due to polarons and charge-transfer excitations. These states are found to cause multiple Auger decay processes upon resonant excitation. We identify several of these processes and determine their relative contribution to the Auger signal quantitatively. As our resPES data allow a quantitative analysis of these defect states, we determine the relative abundance of the PDOS in the VB and in CB and also the charge neutrality level. The anatase and rutile polymorphs of TiO2 are analyzed in the same way as the TiO2 ALD layer. The electronic properties of the TiO2 ALD layer are compared with the anatase and rutile polymorphs of TiO2. In our comparative study, we find that ALD has its own characteristic electronic structure that is distinct from that of anatase and rutile. However, many details of the electronic structure are comparable and we benefit from our spectroscopic data and our careful analysis to find these differences. These can be attributed to a stronger hybridization of the O2p and Ti3d4s states for the ALD films when compared to the anatase and rutile polymorphs.

  12. Interaction of CO2 with Oxygen Adatoms on Rutile TiO2(110)

    SciTech Connect

    Lin, Xiao; Wang, Zhitao; Lyubinetsky, Igor; Kay, Bruce D.; Dohnalek, Zdenek

    2013-01-10

    The interactions of CO2 with oxygen adatoms (Oa’s) on rutile TiO2(110) surfaces have been studied using scanning tunneling microscopy. At 50 K CO2 is found to adsorb preferentially on five-coordinated Ti sites (Ti5c’s) next to Oa’s rather than on oxygen vacancies (VO’s) (the most stable adsorption sites on reduced TiO2(110)). Temperature dependent studies show that after annealing to 100 - 150 K, VO’s become preferentially populated indicating the presence of a kinetic barrier for CO2 adsorption into the VO’s. The difference between the CO2 binding energy on VO’s and Ti5c sites next to the Oa’s are found to be only 0.009 - 0.025 eV. The barrier for CO2 diffusion away from Oa’s is estimated to be ~0.17 eV. Crescent-like feature of the images of CO2 adsorbed on Ti5c’s next to Oa’s are interpreted as a time average of terminally bound CO2 molecules switching between the configurations that are tilted towards Oa and/or towards one of the two neighboring bridging oxygen (Ob) rows. In the presence of VO defects, CO2 is found to tilt preferentially away from the VO containing Ob row. If another CO2 is present on the neighboring Ti5c row, both CO2 molecules tilt towards the common Ob row that separates them.

  13. Self-assembly of multilevel branched rutile-type TiO2 structures via oriented lateral and twin attachment

    PubMed Central

    Jordan, Vanja; Javornik, Uroš; Plavec, Janez; Podgornik, Aleš; Rečnik, Aleksander

    2016-01-01

    Recent breakthrough of novel hierarchic materials, orchestrated through oriented attachment of crystal subunits, opened questions on what is the mechanism of their self-assembly. Using rutile-type TiO2, synthesized by hydrothermal reaction of Ti(IV)-butoxide in highly acidic aqueous medium, we uncovered the key processes controlling this nonclassical crystallization process. Formation of complex branched mesocrystals of rutile is accomplished by oriented assembly of precipitated fibers along the two low-energy planes, i.e. {110} and {101}, resulting in lateral attachment and twinning. Phase analysis of amorphous material enclosed in pockets between imperfectly assembled rutile fibers clearly shows harmonic ordering resembling that of the adjacent rutile structure. To our understanding this may be the first experimental evidence indicating the presence of electromagnetic force-fields that convey critical structural information through which oriented attachment of nanocrystals is made possible. PMID:27063110

  14. Isotropic photo-decomposition of spherical organic polymers on rutile TiO2(110) surfaces

    NASA Astrophysics Data System (ADS)

    Ishida, Nobuyuki; Iwasaki, Tamaki; Fujita, Daisuke

    2011-04-01

    We observed the photo-decomposition process of polystyrene latex (PSL) spheres on a rutile TiO2(110) single crystal surface by using atomic force microscopy. During the decomposition process, both the height and width of the PSL spheres linearly decreased with the irradiation time in a similar way from the beginning, suggesting that the PSL spheres are isotropically decomposed. This indicates that the interface between the PSL spheres and the TiO2 surface is not a dominant reaction site, as expected from normal photocatalytic reactions.

  15. Threshold displacement energies in rutile TiO 2: A molecular dynamics simulation study

    NASA Astrophysics Data System (ADS)

    Thomas, B. S.; Marks, N. A.; Corrales, L. R.; Devanathan, R.

    2005-09-01

    Threshold displacement energies are determined for Ti and O in rutile TiO 2 using molecular dynamics simulations with an empirical model. The simulations involve the introduction of a primary knock-on atom (PKA) with a range of energies (30-150 eV) in various crystallographic directions at 160 K. We observe the formation of stable Frenkel defects, as well as defect recovery via low-energy interstitial migration mechanisms. The latter causes significant statistical variation between simulation outcomes, which leads to the definition of a defect formation probability. This probability is characterized as a function of PKA energy in order to define the threshold displacement energy and compare with experimental results. Using a probability of 10%, the average threshold displacement energy is around 40 eV for oxygen (comparable to experiment) and 105 eV for titanium. Using a probability of 50%, the values are 65 eV and 130 eV respectively, which may be more appropriate for use in TRIM calculations. In addition, we run a parallel set of calculations using a second empirical model, finding that the detailed results are highly model-dependent, particularly the oxygen defect structures and energies, which are compared to new ab initio data.

  16. Adsorption of small hydrocarbons on rutile TiO2(110)

    NASA Astrophysics Data System (ADS)

    Chen, Long; Smith, R. Scott; Kay, Bruce D.; Dohnálek, Zdenek

    2016-08-01

    Temperature programmed desorption and molecular beam scattering were used to study the adsorption and desorption of small hydrocarbons (n-alkanes, 1-alkenes and 1-alkynes of C1-C4) on rutile TiO2(110). We show that the sticking coefficients for all the hydrocarbons are close to unity (> 0.95) at an adsorption temperature of 60 K. The desorption energies for hydrocarbons of the same chain length increase from n-alkanes to 1-alkenes and to 1-alkynes. This trend is likely a consequence of additional dative bonding of the alkene and alkyne π system to the coordinatively unsaturated Ti5c sites. Similar to previous studies on the adsorption of n-alkanes on metal and metal oxide surfaces, we find that the desorption energies within each group (n-alkanes vs. 1-alkenes vs. 1-alkynes) from Ti5c sites increase linearly with the chain length. The absolute saturation coverages of each hydrocarbon on Ti5c sites were also determined. The saturation coverage of CH4, is found to be ~ 2/3 monolayer (ML). The saturation coverages of C2-C4 hydrocarbons are found nearly independent of the chain length with values of ~ 1/2 ML for n-alkanes and 1-alkenes and 2/3 ML for 1-alkynes. This result is surprising considering their similar sizes.

  17. Adsorption of small hydrocarbons on rutile TiO2(110)

    DOE PAGES

    Chen, Long; Smith, R. Scott; Kay, Bruce D.; ...

    2015-11-21

    Here, temperature programmed desorption and molecular beam scattering were used to study the adsorption and desorption of small hydrocarbons (n-alkanes, 1-alkenes and 1-alkynes of C1–C4) on rutile TiO2(110). We show that the sticking coefficients for all the hydrocarbons are close to unity (> 0.95) at an adsorption temperature of 60 K. The desorption energies for hydrocarbons of the same chain length increase from n-alkanes to 1-alkenes and to 1-alkynes. This trend is likely a consequence of additional dative bonding of the alkene and alkyne π system to the coordinatively unsaturated Ti5c sites. Similar to previous studies on the adsorption ofmore » n-alkanes on metal and metal oxide surfaces, we find that the desorption energies within each group (n-alkanes vs. 1-alkenes vs. 1-alkynes) from Ti5c sites increase linearly with the chain length. The absolute saturation coverages of each hydrocarbon on Ti5c sites were also determined. The saturation coverage of CH4, is found to be ~ 2/3 monolayer (ML). The saturation coverages of C2–C4 hydrocarbons are found nearly independent of the chain length with values of ~ 1/2 ML for n-alkanes and 1-alkenes and 2/3 ML for 1-alkynes. This result is surprising considering their similar sizes.« less

  18. Adsorption of small hydrocarbons on rutile TiO2(110)

    SciTech Connect

    Chen, Long; Smith, R. Scott; Kay, Bruce D.; Dohnálek, Zdenek

    2016-08-01

    Temperature programmed desorption and molecular beam scattering were used to study the adsorption and desorption of small hydrocarbons (n-alkanes, 1-alkenes and 1-alkynes with 1 - 4 carbon atoms of C1-C4) on rutile TiO2(110). We show that the sticking coefficients for all the hydrocarbons are close to unity (> 0.95) at an adsorption temperature of 60 K. The desorption energies for hydrocarbons of the same chain length increase from n-alkanes to 1-alkenes and to 1-alkynes. This trend is likely a consequence of an additional dative bonding of the alkene and alkyne π system to the coordinatively unsaturated Ti5c sites. Similar to previous studies on the adsorption of n-alkanes on metal and metal oxide surfaces, we find the desorption energies within each group (n-alkanes vs. 1-alkenes vs. 1-alkynes) from Ti5c sites increase linearly with the chain length. The absolute saturation coverages of each hydrocarbon on Ti5c sites were also determined. The saturation coverage of CH4, is found to be ~ 2/3 monolayer (ML). The saturation coverages of C2-C4 hydrocarbons are found nearly independent of the chain length with values of ~1/2 ML for n-alkanes and 1-alkenes and 2/3 ML for 1-alkynes. This result is surprising considering their similar sizes.

  19. A novel and efficient surfactant-free synthesis of Rutile TiO2 microflowers with enhanced photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Nair, Radhika V.; Jijith, M.; Gummaluri, Venkata Siva; Vijayan, C.

    2016-05-01

    Rutile TiO2 microflowers with three-dimensional spiky flower like architecture at the nanometer level are obtained by a fast single step surfactant free ethylene glycol based solvothermal scheme of synthesis. These structures are characterized by X-ray Diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and Raman spectroscopy. These measurements confirm Rutile phase of TiO2 flowers with very high crystallinity. Photodegradation of Rhodamine B with UV exposure is investigated by UV-Visible spectroscopy measurements in the presence of these samples. They are shown to have high photocatalytic activity due to the large surface area contributed by the highly dense spiky nanostructures. The plasmonic (Au) loading in these structures are shown to significantly enhance the photocatalytic activity.

  20. Degradation of polycyclic aromatic hydrocarbons in crumb tyre rubber catalysed by rutile TiO2 under UV irradiation.

    PubMed

    Yu, Kai; Huang, Linyue; Lou, Lan-Lan; Chang, Yue; Dong, Yanling; Wang, Huan; Liu, Shuangxi

    2015-01-01

    The polycyclic aromatic hydrocarbons (PAHs) in crumb tyre rubber were firstly degraded under UV irradiation in the presence of rutile TiO2 and hydrogen peroxide. The effects of light intensity, catalyst amount, oxidant amount, initial pH value, co-solvent content, and reaction time on degradation efficiency of typical PAHs in crumb tyre rubber were studied. The results indicated that UV irradiation, rutile TiO2, and hydrogen peroxide were beneficial to the degradation of PAHs and co-solvent could accelerate the desorption of PAHs from crumb tyre rubber. Up to 90% degradation efficiency of total 16 PAHs could be obtained in the presence of rutile TiO2 (1 wt%) and hydrogen peroxide (1.0 mL) under 1800 µW cm(-2) UV irradiation for 48 h. The high molecular weight PAHs (such as benz(a)pyrene) were more difficult to be degraded than low molecular weight PAHs (such as phenanthrene, chrysene). Moreover, through the characterization of reaction solution and degradation products via GC-MS, it was proved that the PAHs in crumb tyre rubber were successfully degraded.

  1. Controlling the Al-doping profile and accompanying electrical properties of rutile-phased TiO2 thin films.

    PubMed

    Jeon, Woojin; Rha, Sang Ho; Lee, Woongkyu; Yoo, Yeon Woo; An, Cheol Hyun; Jung, Kwang Hwan; Kim, Seong Keun; Hwang, Cheol Seong

    2014-05-28

    The role of Al dopant in rutile-phased TiO2 films in the evaluation of the mechanism of leakage current reduction in Al-doped TiO2 (ATO) was studied in detail. The leakage current of the ATO film was strongly affected by the Al concentration at the interface between the ATO film and the RuO2 electrode. The conduction band offset of the interface increased with the increase in the Al dopant concentration in the rutile TiO2, which reduced the leakage current in the voltage region pertinent to the next-generation dynamic random access memory application. However, the Al doping in the anatase TiO2 did not notably increase the conduction band offset even with a higher Al concentration. The detailed analyses of the leakage conduction mechanism based on the quantum mechanical transfer-matrix method showed that Schottky emission and Fowler-Nordheim tunneling was the dominant leakage conduction mechanism in the lower and higher voltage regions, respectively. The chemical analyses using X-ray photoelectron spectroscopy corroborated the electrical test results.

  2. IR and quantum-chemical studies of carboxylic acid and glycine adsorption on rutile TiO2 nanoparticles.

    PubMed

    Ojamäe, Lars; Aulin, Christian; Pedersen, Henrik; Käll, Per-Olov

    2006-04-01

    Nanocrystalline TiO2 powders of the rutile polymorph, synthesized by a sol-gel method, were treated with water solutions containing, respectively, formic, acetic, and citric acid and glycine in order to study the adsorption properties of these organic species. The samples were characterized by FTIR, Raman, powder XRD, and TEM. It was found that HCOOH, CH3COOH and HOC(COOH)(CH2COOH)2--but not NH2CH2COOH--adsorbed onto TiO2. The adsorption of HCOOH, CH3COOH and NH2CH2COOH onto the (110) surface of rutile was also studied by quantum-chemical periodic density functional theory (DFT) calculations. The organic molecules were from the computations found to adsorb strongly to the surfaces in a bridge-coordinating mode, where the two oxygens of the deprotonated carboxylic acid bind to two surface titanium ions. Surface relaxation is found to influence adsorption geometries and energies significantly. The results from DFT calculations and ab initio molecular-dynamics simulations of formic acid adsorption onto TiO2 are compared and match well with the experimental IR measurements, supporting the bridge-binding geometry of carboxylic-acid adsorption on the TiO2 nanoparticles.

  3. Ultrathin single-crystalline TiO2 nanosheets anchored on graphene to be hybrid network for high-rate and long cycle-life sodium battery electrode application

    NASA Astrophysics Data System (ADS)

    Shoaib, Anwer; Huang, Yongxin; Liu, Jia; Liu, Jiajia; Xu, Meng; Wang, Ziheng; Chen, Renjie; Zhang, Jiatao; Wu, Feng

    2017-02-01

    In view of the growing concern about energy management issues, sodium ion batteries (SIBs) as cheap and environmentally friendly devices have increasingly received wide research attentions. The high current rate and long cycle-life of SIBs are considered as two key parameters determining its potential for practical applications. In this work, the rigid single-crystalline anatase TiO2 nanosheets (NSs) with a thickness of ∼4 nm has been firstly prepared, based on which a stable nanostructured network consisting of ultrathin anatase TiO2 NSs homogeneously anchored on graphene through chemical bonding (TiO2 NSs-G) has fabricated by hydrothermal process and subsequent calcination treatment. The morphology, crystallization, chemical compositions and the intimate maximum contact between TiO2 NSs and graphene are confirmed by TEM, SEM, XRD, XPS and Raman characterizations. The results of electrochemical performance tests indicated that the TiO2 NSs-G hybrid network could be consider as a promising anode material for SIBs, in assessment of its remarkably high current rate and long cycle-life aside from the improved specific capacity, rate capability and cycle stability.

  4. In situ scanning tunneling microscopy study of Ca-modified rutile TiO2(110) in bulk water.

    PubMed

    Serrano, Giulia; Bonanni, Beatrice; Kosmala, Tomasz; Di Giovannantonio, Marco; Diebold, Ulrike; Wandelt, Klaus; Goletti, Claudio

    2015-01-01

    Despite the rising technological interest in the use of calcium-modified TiO2 surfaces in biomedical implants, the Ca/TiO2 interface has not been studied in an aqueous environment. This investigation is the first report on the use of in situ scanning tunneling microscopy (STM) to study calcium-modified rutile TiO2(110) surfaces immersed in high purity water. The TiO2 surface was prepared under ultrahigh vacuum (UHV) with repeated sputtering/annealing cycles. Low energy electron diffraction (LEED) analysis shows a pattern typical for the surface segregation of calcium, which is present as an impurity on the TiO2 bulk. In situ STM images of the surface in bulk water exhibit one-dimensional rows of segregated calcium regularly aligned with the [001] crystal direction. The in situ-characterized morphology and structure of this Ca-modified TiO2 surface are discussed and compared with UHV-STM results from the literature. Prolonged immersion (two days) in the liquid leads to degradation of the overlayer, resulting in a disordered surface. X-ray photoelectron spectroscopy, performed after immersion in water, confirms the presence of calcium.

  5. Temperature-programmed desorption study of NO reactions on rutile TiO2(110)-1×1

    SciTech Connect

    Kim, Boseong; Dohnálek, Zdenek; Szanyi, János; Kay, Bruce D.; Kim, Yu Kwon

    2016-10-01

    Systematic temperature-programmed desorption (TPD) studies of NO adsorption and reactions on rutile TiO2(110)-1×1 surface reveal several distinct reaction channels in a temperature range of 50 – 500 K. NO readily reacts on TiO2(110) to form N2O which desorbs between 50 and 200 K (LT N2O channels), which leaves the TiO2 surface populated with adsorbed oxygen atoms (Oa) as a byproduct of N2O formation. In addition, we observe simultaneous desorption peaks of NO and N2O at 270 K (HT1 N2O) and 400 K (HT2 N2O), respectively, both of which are attributed to reaction-limited processes. No N-derived reaction product desorbs from TiO2(110) surface above 500 K or higher, while the surface may be populated with Oa’s and oxidized products such as NO2 and NO3. The adsorbate-free TiO2 surface with oxygen vacancies can be regenerated by prolonged annealing at 850 K or higher. Detailed analysis of the three N2O desorption yields reveals that the surface species for the HT channels are likely to be various forms of NO dimers.

  6. Temperature-programmed desorption study of NO reactions on rutile TiO2(110)-1×1

    DOE PAGES

    Kim, Boseong; Dohnalek, Zdenek; Szanyi, Janos; ...

    2016-02-24

    In this study, systematic temperature-programmed desorption (TPD) studies of NO adsorption and reactions on rutile TiO2(110)-1 × 1 surface reveal several distinct reaction channels in a temperature range of 50–500 K. NO readily reacts on TiO2(110) to form N2O, which desorbs between 50 and 200 K (LT N2O channels), which leaves the TiO2 surface populated with adsorbed oxygen atoms (Oa) as a by-product of N2O formation. In addition, we observe simultaneous desorption peaks of NO and N2O at 270 K (HT1 N2O) and 400 K (HT2 N2O), respectively, both of which are attributed to reaction-limited processes. No N-derived reaction productmore » desorbs from TiO2(110) surface above 500 K or higher, while the surface may be populated with Oa's and oxidized products such as NO2 and NO3. The adsorbate-free TiO2 surface with oxygen vacancies can be regenerated by prolonged annealing at 850 K or higher. Detailed analysis of the three N2O desorption yields reveals that the surface species for the HT channels are likely to be various forms of NO dimers.« less

  7. Chemical bath deposited rutile TiO2 compact layer toward efficient planar heterojunction perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Liang, Chao; Wu, Zhenhua; Li, Pengwei; Fan, Jiajie; Zhang, Yiqiang; Shao, Guosheng

    2017-01-01

    TiO2 is a best choice of electron transport layers in perovskite solar cells, due to its high electron mobility and stability. However, traditional TiO2 processing method requires rather high annealing temperature (>500 °C), preventing it from application to flexible devices. Here, we show that TiO2 thin films can be synthesized via chemical bath deposition below 100 °C. Typically, a compact layer of rutile TiO2 is deposited onto fluorine-doped tin oxide (FTO) coated substrates, in an aqueous TiCl4 solution at 70 °C. Through the optimization of precursor concentration and ultraviolet-ozone surface modification, over 12% power conversion efficiency can be achieved for CH3NH3PbI3 based perovskite solar cells. These findings offer a potential low-temperature technical solution in using TiO2 thin film as an effective transport layer for flexible perovskite solar cells.

  8. Temperature-programmed desorption study of NO reactions on rutile TiO2(110)-1 × 1

    NASA Astrophysics Data System (ADS)

    Kim, Boseong; Dohnálek, Zdenek; Szanyi, János; Kay, Bruce D.; Kim, Yu Kwon

    2016-10-01

    Systematic temperature-programmed desorption (TPD) studies of NO adsorption and reactions on rutile TiO2(110)-1 × 1 surface reveal several distinct reaction channels in a temperature range of 50-500 K. NO readily reacts on TiO2(110) to form N2O, which desorbs between 50 and 200 K (LT N2O channels), which leaves the TiO2 surface populated with adsorbed oxygen atoms (Oa) as a by-product of N2O formation. In addition, we observe simultaneous desorption peaks of NO and N2O at 270 K (HT1 N2O) and 400 K (HT2 N2O), respectively, both of which are attributed to reaction-limited processes. No N-derived reaction product desorbs from TiO2(110) surface above 500 K or higher, while the surface may be populated with Oa's and oxidized products such as NO2 and NO3. The adsorbate-free TiO2 surface with oxygen vacancies can be regenerated by prolonged annealing at 850 K or higher. Detailed analysis of the three N2O desorption yields reveals that the surface species for the HT channels are likely to be various forms of NO dimers.

  9. Anatase (101)-like Structural Model Revealed for Metastable Rutile TiO2(011) Surface.

    PubMed

    Xu, Meiling; Shao, Sen; Gao, Bo; Lv, Jian; Li, Quan; Wang, Yanchao; Wang, Hui; Zhang, Lijun; Ma, Yanming

    2017-03-08

    Titanium dioxide has been widely used as an efficient transition metal oxide photocatalyst. However, its photocatalytic activity is limited to the ultraviolet spectrum range due to the large bandgap beyond 3 eV. Efforts to reduce the bandgap to achieve a broader spectrum range of light absorption have been successfully attempted via the experimental synthesis of dopant-free metastable surface structures of rutile-type TiO2 (011) 2 × 1. This new surface phase possesses a reduced bandgap of ∼2.1 eV, showing great potential for an excellent photocatalyst covering a wide range of visible light. There is a need to establish the atomistic structure of this metastable surface to understand the physical cause for the bandgap reduction and to improve the future design of photocatalysts. Here, we report computational investigations in an effort to unravel this surface structure via swarm structure-searching simulations. The established structure adopts the anatase (101)-like structure model, where the topmost 2-fold O atoms form a quasi-hexagonal surface pattern and bond with the unsaturated 5-fold and 4-fold Ti atoms in the next layer. The predicted anatase (101)-like surface model can naturally explain the experimental observation of the STM images, the electronic bandgap, and the oxidation state of Ti(4+). Dangling bonds on the anatase (101)-like surface are abundant making it a superior photocatalyst. First-principles molecular dynamics simulations have supported the high photocatalytic activity by showing that water and formic acid molecules dissociate spontaneously on the anatase (101)-like surface.

  10. Rapid charge transport in dye-sensitized solar cells made from vertically aligned single-crystal rutile TiO(2) nanowires.

    PubMed

    Feng, Xinjian; Zhu, Kai; Frank, Arthur J; Grimes, Craig A; Mallouk, Thomas E

    2012-03-12

    A rapid solvothermal approach was used to synthesize aligned 1D single-crystal rutile TiO(2) nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. The NW arrays showed a more than 200 times faster charge transport and a factor four lower defect state density than conventional rutile nanoparticle films.

  11. Rapid Charge Transport in Dye-Sensitized Solar Cells Made from Vertically Aligned Single-Crystal Rutile TiO2 Nanowires

    SciTech Connect

    Feng, X.; Zhu, K.; Frank, A. J.; Grimes, C. A.; Mallouk, T. E.

    2012-03-12

    A rapid solvothermal approach was used to synthesize aligned 1D single-crystal rutile TiO2 nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. The NW arrays showed a more than 200 times faster charge transport (see picture) and a factor four lower defect state density than conventional rutile nanoparticle films.

  12. Rapid (∼10 min) synthesis of single-crystalline, nanorice TiO2 mesoparticles with a high photovoltaic efficiency of above 8%.

    PubMed

    Parmar, K P S; Ramasamy, Easwaramoorthi; Lee, Jinwoo; Lee, Jae Sung

    2011-08-14

    A novel rapid (∼10 min) microwave-hydrothermal synthesis is demonstrated for nanorice TiO(2) mesoparticles as an anode of a dye-sensitized solar cell with an excellent photovoltaic efficiency of above 8%.

  13. Visible Light-Driven H2 Production over Highly Dispersed Ruthenia on Rutile TiO2 Nanorods

    DOE PAGES

    Nguyen-Phan, Thuy-Duong; Luo, Si; Vovchok, Dimitriy; ...

    2015-12-02

    The immobilization of miniscule quantities of RuO2 (~0.1%) onto one-dimensional (1D) TiO2 nanorods (NRs) allows H2 evolution from water under visible light irradiation. In addition, rod-like rutile TiO2 structures, exposing preferentially (110) surfaces, are shown to be critical for the deposition of RuO2 to enable photocatalytic activity in the visible region. The superior performance is rationalized on the basis of fundamental experimental studies and theoretical calculations, demonstrating that RuO2(110) grown as 1D nanowires on rutile TiO2(110), which occurs only at extremely low loads of RuO2, leads to the formation of a heterointerface that efficiently adsorbs visible light. The surface defects,more » band gap narrowing, visible photoresponse, and favorable upward band bending at the heterointerface drastically facilitate the transfer and separation of photogenerated charge carriers.« less

  14. First-principles study of relative stability of rutile and anatase TiO2 using the random phase approximation.

    PubMed

    Cui, Zhi-Hao; Wu, Feng; Jiang, Hong

    2016-11-02

    The relative stability of TiO2 in the rutile and anatase structure is wrongly described by density functional theory in various local, semilocal, or even hybrid functional approximations. In this work, we have found that by considering high-order correlations in the adiabatic connection fluctuation-dissipation theory with the random phase approximation (ACFDT-RPA), rutile is correctly predicted to be more stable than anatase, which can be physically attributed to different characters in the electronic band structure of rutile and anatase, including, in particular, that rutile has a smaller band gap than anatase. We further consider the zero-point energy and finite-temperature effects based on the harmonic approximation, and we found that the inclusion of the zero-point energy correction can further increase the relative stability of rutile, and leads to a better quantitative agreement with available experimental measurements. Our study indicates the importance of considering high-order dynamical correlation effects to correctly predict the relative phase stability of polymorphic materials, especially for those systems in which the less stable phase as predicted by conventional local, semilocal or even hybrid density functional approximations has a smaller band gap than the more stable one.

  15. Eu(III) sorption to TiO2 (anatase and rutile): batch, XPS, and EXAFS studies.

    PubMed

    Tan, Xiaoli; Fan, Qiaohui; Wang, Xiangke; Grambow, Bernd

    2009-05-01

    The sorption of Eu(III) on anatase and rutile was studied as a function of ionic strength, humic acid (HA, 7.5 mg/L), and electrolyte anions over a large range of pH (2-12). The presence of HA significantly affected Eu(III) sorption to anatase and rutile. The sorption of Eu(III) on anatase and rutile was independent of ionic strength. Results of an X-ray photoelectron spectroscopy (XPS) analysis showed that Eu(III) was chemically present within the near-surface of TiO2 due to the formation of triple bond SOEu and triple bond SOHAEu complexes. An extended X-ray absorption fine structure (EXAFS) technique was applied to characterize the local structural environment of the adsorbed Eu(III), and the results indicated that Eu(III) was bound to about seven or eight O atoms at a distance of about 2.40 A. The functional groups of surface-bound HA were expected to be involved in the sorption process. The measured Eu-Ti distance confirmed the formation of inner-sphere sorption complexes on a TiO2 surface.

  16. Localized Excitation of Ti(3+) Ions in the Photoabsorption and Photocatalytic Activity of Reduced Rutile TiO2.

    PubMed

    Wang, Zhiqiang; Wen, Bo; Hao, Qunqing; Liu, Li-Min; Zhou, Chuanyao; Mao, Xinchun; Lang, Xiufeng; Yin, Wen-Jin; Dai, Dongxu; Selloni, Annabella; Yang, Xueming

    2015-07-22

    In reduced TiO2, electronic transitions originating from the Ti(3+)-induced states in the band gap are known to contribute to the photoabsorption, being in fact responsible for the material's blue color, but the excited states accessed by these transitions have not been characterized in detail. In this work we investigate the excited state electronic structure of the prototypical rutile TiO2(110) surface using two-photon photoemission spectroscopy (2PPE) and density functional theory (DFT) calculations. Using 2PPE, an excited resonant state derived from Ti(3+) species is identified at 2.5 ± 0.2 eV above the Fermi level (EF) on both the reduced and hydroxylated surfaces. DFT calculations reveal that this excited state is closely related to the gap state at ∼1.0 eV below EF, as they both result from the Jahn-Teller induced splitting of the 3d orbitals of Ti(3+) ions in reduced TiO2. Localized excitation of Ti(3+) ions via 3d → 3d transitions from the gap state to this empty resonant state significantly increases the TiO2 photoabsorption and extends the absorbance to the visible region, consistent with the observed enhancement of the visible light induced photocatalytic activity of TiO2 through Ti(3+) self-doping. Our work reveals the physical origin of the Ti(3+) related photoabsorption and visible light photocatalytic activity in prototypical TiO2 and also paves the way for the investigation of the electronic structure and photoabsorption of other metal oxides.

  17. Influence of anatase and rutile phase in TiO2 upon the photocatalytic degradation of methylene blue under solar irradiation in presence of activated carbon.

    PubMed

    Matos, J; Montaña, R; Rivero, E; Escudero, A; Uzcategui, D

    2014-01-01

    The influence of activated carbon (AC) on the photocatalytic activity of different crystalline TiO2 phases was verified in the photocatalytic degradation of methylene blue under UV and solar irradiation. The results showed a volcano trend with a maximum photoactivity for the crystalline phase ratio of anatase:rutile equal to 80:20 both under UV or solar irradiation. By contrast, in presence of AC the photocatalytic activity of the binary materials of TiO2/AC followed an exponential trend, increasing as a function of the increase in anatase proportion in the TiO2 framework. The increase in the photoactivity of the binary material TiO2/AC relative to neat TiO2 was up to 22 and about 17 times higher under UV and visible irradiation, respectively. The present results suggest that AC interacts more efficiently with anatase phase than with rutile phase.

  18. Rutile TiO2 nano-branched arrays on FTO for dye-sensitized solar cells.

    PubMed

    Wang, Hua; Bai, Yusong; Wu, Qiong; Zhou, Wei; Zhang, Hao; Li, Jinghong; Guo, Lin

    2011-04-21

    Hierarchical TiO(2) nanostructures would be desirable for preparing dye-sensitized solar cells because of their large amount of dye adsorption and superior light harvesting efficiency, as well as efficient charge separation and transport properties. In this study, rutile TiO(2) nano-branched arrays grown directly on transparent conductive glass (FTO) were prepared by a facile two-step wet chemical synthesis process, using a simple aqueous chemical growth method involving immersing the TiO(2) nanorod arrays in an aqueous TiCl(4) solution as seeds, which were prepared by a hydrothermal method. The dye-sensitized solar cells based on the TiO(2) nano-branched arrays which were only about 3 μm in length show a short-circuit current intensity of 10.05 mA cm(-2) and a light-to-electricity conversion efficiency of 3.75%, which is nearly three times as high as that of bare nanorod arrays, due to the preferable nanostructure, which not only retains the efficient charge separation and transport properties of the nanorod arrays, but also can improve the amount of dye adsorption due to the increased specific surface area from the nanobranches.

  19. Unravelling Site-Specific Photo-Reactions of Ethanol on Rutile TiO2(110)

    PubMed Central

    Hansen, Jonas Ø.; Bebensee, Regine; Martinez, Umberto; Porsgaard, Soeren; Lira, Estephania; Wei, Yinying; Lammich, Lutz; Li, Zheshen; Idriss, Hicham; Besenbacher, Flemming; Hammer, Bjørk; Wendt, Stefan

    2016-01-01

    Finding the active sites of catalysts and photo-catalysts is crucial for an improved fundamental understanding and the development of efficient catalytic systems. Here we have studied the photo-activated dehydrogenation of ethanol on reduced and oxidized rutile TiO2(110) in ultrahigh vacuum conditions. Utilizing scanning tunnelling microscopy, various spectroscopic techniques and theoretical calculations we found that the photo-reaction proceeds most efficiently when the reactants are adsorbed on regular Ti surface sites, whereas species that are strongly adsorbed at surface defects such as O vacancies and step edges show little reaction under reducing conditions. We propose that regular Ti surface sites are the most active sites in photo-reactions on TiO2. PMID:26915303

  20. Transformations of PTCDA structures on rutile TiO2 induced by thermal annealing and intermolecular forces.

    PubMed

    Godlewski, Szymon; Prauzner-Bechcicki, Jakub S; Glatzel, Thilo; Meyer, Ernst; Szymoński, Marek

    2015-01-01

    Transformations of molecular structures formed by perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules on a rutile TiO2(110) surface are studied with low-temperature scanning tunnelling microscopy. We demonstrate that metastable molecular assemblies transform into differently ordered structures either due to additional energy provided by thermal annealing or when the influence of intermolecular forces is increased by the enlarged amount of deposited molecules. Proper adjustment of molecular coverage and substrate temperature during deposition allows for fabrication of desired assemblies. Differences between PTCDA/TiO2(110) and PTCDA/TiO2(011) systems obtained through identical experimental procedures are discussed.

  1. Effect of the rutile content on the photovoltaic performance of the dye-sensitized solar cells composed of mixed-phase TiO2 photoelectrodes.

    PubMed

    Yun, Tae Kwan; Park, Sung Soo; Kim, Duckhyun; Shim, Jae-Hyun; Bae, Jae Young; Huh, Seong; Won, Yong Sun

    2012-01-28

    The effect of the rutile content on the photovoltaic performance of dye-sensitized solar cells (DSSCs) composed of mixed-phase TiO(2) photoelectrode has been investigated. The mixed-phase TiO(2) particles with varied amounts of rutile, relative to anatase phase, are synthesized by an in situ method where the concentration of sulfate ion is used as a phase-controlling parameter in the formation of TiO(2) using TiCl(4) hydrolysis. The surface area (S(BET)) varies from 33 (pure rutile) to 165 (pure anatase) m(2) g(-1). Generally, both the current density (J(sc)) and photo-conversion efficiency (η) decrease as the rutile content increases. The incorporation of rod-shaped rutile particles causes low uptake of dye due to the reduced surface area, as well as slow electron transport in less efficiently-stacked structure. However, maximum J(sc) (14.63 mA cm(-2)) and η (8.69%) appear when relatively low rutile content (16%) is employed. The reported synergistic effect by the efficient interparticle electron transport from rutile to anatase seems to overbalance the decrease of surface area when small amount of rutile particles is incorporated.

  2. Influence of deposition temperature on the growth of rutile TiO2 nanostructures by CBD method on seed layer prepared by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Selman, Abbas M.; Hassan, Z.

    2013-12-01

    Rutile titanium dioxide (TiO2) nanostructures were successfully fabricated using the simple chemical bath deposition method at various deposition temperatures. These nanostructures were fabricated on (100 ± 10 nm) TiO2 seed layer coated glass, which was prepared via radio frequency (RF) magnetron sputtering at a substrate temperature of 350 °C. The synthesized TiO2 nanostructures were annealed at 550 °C for 2 h and examined via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), and Raman spectroscopy. The XRD patterns showed the presence of the peaks characteristic of rutile phase. The band gap of the TiO2 nanostructures was calculated using the UV-vis absorption spectrum and was determined to be between 3.15 and 3.24 eV. The Raman spectra contained three characteristic bands at 232, 446 and 612 cm-1, which correspond to the tetragonal TiO2 rutile. The results showed good quality of nanocrystalline TiO2 rutile phase.

  3. Hierarchical rutile TiO2 flower cluster-based high efficiency dye-sensitized solar cells via direct hydrothermal growth on conducting substrates.

    PubMed

    Ye, Meidan; Liu, Hsiang-Yu; Lin, Changjian; Lin, Zhiqun

    2013-01-28

    Dye-sensitized solar cells (DSSCs) based on hierarchical rutile TiO(2) flower clusters prepared by a facile, one-pot hydrothermal process exhibit a high efficiency. Complex yet appealing rutile TiO(2) flower films are, for the first time, directly hydrothermally grown on a transparent conducting fluorine-doped tin oxide (FTO) substrate. The thickness and density of as-grown flower clusters can be readily tuned by tailoring growth parameters, such as growth time, the addition of cations of different valence and size, initial concentrations of precursor and cation, growth temperature, and acidity. Notably, the small lattice mismatch between the FTO substrate and rutile TiO(2) renders the epitaxial growth of a compact rutile TiO(2) layer on the FTO glass. Intriguingly, these TiO(2) flower clusters can then be exploited as photoanodes to produce DSSCs, yielding a power conversion efficiency of 2.94% despite their rutile nature, which is further increased to 4.07% upon the TiCl(4) treatment.

  4. Comparison of Dye-Sensitized Rutile- and Anatase-Based TiO2 Solar Cells

    SciTech Connect

    Park, N. G.; van de Lagemaat, J.; Frank, A. J.

    2000-01-01

    The objective of this work is to develop and optimize the new dye-sensitized solar cell technology. In view of the infancy of rutile material development for solar cells, the PV response of the dye-sensitized rutile-based solar cell is remarkably close to that of the anatase-based cell.

  5. Solvothermal synthesis of hedgehog-like mesoporous rutile TiO2 with improved lithium storage properties

    NASA Astrophysics Data System (ADS)

    Wang, Dongdong; Shan, Zhongqiang; Na, Ren; Huang, Wenlong; Tian, Jianhua

    2017-01-01

    Hedgehog-like mesoporous rutile TiO2 (HLR-TiO2) composed of well-defined nanoneedles is fabricated in a solvothermal system containing tetrabutyl titanate, hydrochloric acid aqueous solution and diethylene glycol with a proper volume ratio. A possible formation mechanism of the HLR-TiO2 is proposed on the basis of different experimental results and three different morphologies are obtained by changing the solvent with other conditions unchanged. Given its unique hierarchical mesoporous nanostructures, the HLR-TiO2 shows superior lithium storage properties with excellent discharge specific capacity of 243.3 mA h g-1 obtained after 100 cycles at a current rate of 1 C among the three samples, which is almost unparalleled to other rutile TiO2-based electrodes. In particular, a specific capacity of 80.2 mA h g-1 is still maintained after 2000 cycles even at a high current rate of 20 C, indicating that great potential of HLR-TiO2 as an electrode material for lithium-ion batteries (LIBs).

  6. Correlation between Bonding Geometry and Band Gap States at Organic -- inorganic interfaces: Catechol on Rutile TiO2 (110)

    NASA Astrophysics Data System (ADS)

    Diebold, Ulrike; Li, Shao-Chun; Wang, Jian-Guo; Jacobson, Peter; Gong, Xue-Qing; Selloni, Annabella

    2009-03-01

    Adsorbate-induced band gap states in semiconductors are of particular interest due to the potential of increased light absorption and photoreactivity. A combined theoretical (DFT) and experimental (STM, photoemission) study of the molecular-scale factors involved in the formation of gap states in TiO2 is presented. Using the organic catechol on rutile TiO2(110) as a model system it is found that the bonding geometry strongly affects the molecular electronic structure. At saturation catechol forms an ordered 4 x 1 overlayer. This structure is attributed to catechol adsorbed on rows of surface Ti atoms with the molecular plane tilted from the surface normal by about ±27 in an alternating fashion. In the lowest-energy structure one of the two terminal OH groups at each catechol dissociates and the O binds to a surface Ti atom in a monodentate configuration, while the other OH group forms a H-bond to the next catechol neighbor. Through proton exchange with the surface this structure transforms into one where both OH groups dissociate and the catechol is bound to two surface Ti in a bidentate configuration. Only bidendate catechol introduces states in the band gap of TiO2.

  7. Optical properties of rutile and anatase phases of TiO2 thin films grown by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Naik, V. M.; Haddad, D.; Naik, R.; Benci, J.; Auner, G. W.

    2002-03-01

    There has been a great interest in preparing both rutile (R) and anatase (A) forms of TiO2 films for various optical, electrical, photocatalysis, photovoltaics, and biosensor applications. The R-TiO2 is superior in optical properties and thermodynamically more stable than A-TiO_2. However, the latter has attracted much attention recently as the most promising photocatalytic material. In general, the formation of R-phase of TiO2 films requires a higher substrate temperature (> 300 ^circC), whereas a lower substrate temperature results in either A-phase or an amorphous structure. In the present work, we have prepared A- and R-TiO2 films ( ~ 500 nm thick) on unheated glass substrates by RF magnetron sputtering by controlling the total pressure of sputtering gases (Ar + O_2). The crystal structures of the films were confirmed by x-ray diffraction and Raman scattering. The analysis of optical transmission and reflection data measured in the UV-Visible region (175 nm- 2500 nm) show an optical bandgap of ~ 3.1 eV (direct) for R-phase, and ~ 3.2 eV (indirect) for A-phase of TiO2 films.

  8. Ammonia formation from NO reaction with surface hydroxyls on rutile TiO2 (110) - 1×1

    SciTech Connect

    Kim, Boseong; Kay, Bruce D.; Dohnalek, Zdenek; Kim, Yu Kwon

    2015-01-15

    The reaction of NO with hydroxylated rutile TiO2(110)-1×1 surface (h-TiO2) was investigated as a function of NO coverage using temperature-programmed desorption. Our results show that NO reaction with h-TiO2 leads to formation of NH3 which is observed to desorb at ~ 400 K. Interestingly, the amount of NH3 produced depends nonlinearly on the coverage of NO. The yield increases up to a saturation value of ~1.3×1013 NH3/cm2 at a NO dose of 5×1013 NO/cm2, but subsequently decreases at higher NO doses. Preadsorbed H2O is found to have a negligible effect on the NH3 desorption yield. Additionally, no NH3 is formed in the absence of surface hydroxyls (HOb’s) upon coadsorption of NO and H2O on a stoichiometric TiO2(110) (s-TiO2(110)). Based on these observations, we conclude that nitrogen from NO has a strong preference to react with HOb’s on the bridge-bonded oxygen rows (but not with H2O) to form NH3. The absolute NH3 yield is limited by competing reactions of HOb species with titanium-bound oxygen adatoms to form H2O. Our results provide new mechanistic insight about the interactions of NO with hydroxyl groups on TiO2(110) .

  9. Low temperature chemically synthesized rutile TiO2 photoanodes with high electron lifetime for organic dye-sensitized solar cells.

    PubMed

    Ambade, Swapnil B; Ambade, Rohan B; Mane, Rajaram S; Lee, Go-Woon; Shaikh, ShoyebMohamad F; Patil, Supriya A; Joo, Oh-Shim; Han, Sung-Hwan; Lee, Soo-Hyoung

    2013-04-11

    Electron lifetime in mesoporous nanostructured rutile TiO2 photoanodes, synthesized via a simple, cost-effective, low temperature (50-55 °C) wet chemical process, annealed at 350 °C for 1 h and not employing any sprayed TiO2 compact layer, was successfully tailored with 0.2 mM TiCl4 surface treatment that resulted in light to electric power conversion efficiency up to 4.4%.

  10. Ethanol photocatalysis on rutile TiO2(110): the role of defects and water

    PubMed Central

    Walenta, Constantin A.; Kollmannsberger, Sebastian L.; Kiermaier, Josef; Winbauer, Andreas; Tschurl, Martin

    2015-01-01

    In this work we present a stoichiometric reaction mechanism for the photocatalytic ethanol oxidation on TiO2(110). The reaction products are analyzed either under reaction conditions or after irradiation at lower temperatures. Water is identified as a quantitative by-product, which resides in a defect site. These water molecules cause a blocking of the defect sites which results in poisoning of the catalyst. By different preparation techniques of the TiO2(110) surface, the role of surface defects is further elucidated and the role of molecular oxygen is investigated. Based on the investigation, a complete photochemical reaction mechanism is given, which provides insights into general photon driven oxidation mechanisms on TiO2. PMID:26264863

  11. First-principles real-space study of electronic and optical excitations in rutile TiO2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Hung, Linda; Baishya, Kopinjol; Ã-ǧüt, Serdar

    2014-10-01

    We model rutile titanium dioxide nanocrystals (NCs) up to ˜1.5 nm in size to study the effects of quantum confinement on their electronic and optical properties. Ionization potentials (IPs) and electron affinities (EAs) are obtained via the perturbative GW approximation (G0W0) and ΔSCF method for NCs up to 24 and 64 TiO2 formula units, respectively. These demanding GW computations are made feasible by using a real-space framework that exploits quantum confinement to reduce the number of empty states needed in GW summations. Time-dependent density functional theory (TDDFT) is used to predict the optical properties of NCs up to 64 TiO2 units. For a NC containing only 2 TiO2 units, the offsets of the IP and the EA from the corresponding bulk limits are of similar magnitude. However, as NC size increases, the EA is found to converge more slowly to the bulk limit than the IP. The EA values computed at the G0W0 and ΔSCF levels of theory are found to agree fairly well with each other, while the IPs computed with ΔSCF are consistently smaller than those computed with G0W0 by a roughly constant amount. TDDFT optical gaps exhibit weaker size dependence than GW quasiparticle gaps, and result in exciton binding energies on the order of eV. Altering the dimensions of a fixed-size NC can change electronic and optical excitations up to several tenths of an eV. The largest NCs modeled are still quantum confined and do not yet have quasiparticle levels or optical gaps at bulk values. Nevertheless, we find that classical Mie-Gans theory can quite accurately reproduce the line shape of TDDFT absorption spectra, even for (anisotropic) TiO2 NCs of subnanometer size.

  12. UV and visible light synergetic photodegradation using rutile TiO2 nanorod arrays based on a p-n Junction.

    PubMed

    Ji, Tao; Cui, Ze; Zhang, Wenlong; Cao, Yunjiu; Zhang, Yongfang; He, Shu-Ang; Xu, Mingdong; Sun, Yangang; Zou, Rujia; Hu, Junqing

    2017-03-27

    Herein, we report a photocatalytic heterojunction device of rutile TiO2 nanorod arrays based on a p-n silicon junction (TiO2@PN) and its full absorption of ultraviolet and visible light for synergistic photodegradation. The fabricated TiO2@PN had excellent photocatalytic degradation of methyl orange (MO) under irradiation of a 300 W Xe lamp, and its pseudo-first-order rate constant k was 0.221 h(-1), which was greatly higher than that for TiO2 nanorod arrays based on an n-p silicon junction (TiO2@NP, 0.078 h(-1)) and glass (TiO2@G, 0.032 h(-1)). The higher photocatalytic performance of TiO2@PN could be attributed to the fact that the photovoltage (PV) of the p-n junction promotes separation of the electron-hole pairs of the TiO2, and the holes are thus left within the TiO2 nanorods to produce a strong oxidant of hydroxyl radicals (˙OH). Moreover, this heterojunction device could be easily fabricated in a large size for easy recovery and recycling, which shows its promise in the solar-driven degradation of environmental pollution.

  13. DFT computational study of the RGD peptide interaction with the rutile TiO2 (110) surface

    NASA Astrophysics Data System (ADS)

    Muir, J. M. R.; Costa, D.; Idriss, H.

    2014-06-01

    Planewave DFT calculations including ab initio molecular dynamics (AIMD) were used to model the adsorption of a biologically relevant peptide sequence, arginine-glycine-aspartic acid (RGD), upon a rutile TiO2 (110) surface. It was found that binding is solely through the aspartic acid end of the RGD. The carboxy groups bind through dissociative bridging and molecular forms, similar to formic acid. The energy of adsorption is much smaller (0.5-0.77 eV) than seen for formic acid and the molecular adsorption is the strongest adsorption mode. Neutral adsorption is favoured over zwitterionic adsorption and adsorption through the carboxy group of the aspartic acid side chain rather than the terminal carboxy group is favoured due to a configuration allowing an additional surface-carbonyl bond. The RGD backbone is not significantly disrupted upon adsorption.

  14. Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2

    NASA Astrophysics Data System (ADS)

    Mandal, Suman; Pal, Somnath; Kundu, Asish K.; Menon, Krishnakumar S. R.; Hazarika, Abhijit; Rioult, Maxime; Belkhou, Rachid

    2016-08-01

    Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.

  15. Transformations of PTCDA structures on rutile TiO2 induced by thermal annealing and intermolecular forces

    PubMed Central

    Godlewski, Szymon; Glatzel, Thilo; Meyer, Ernst; Szymoński, Marek

    2015-01-01

    Summary Transformations of molecular structures formed by perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules on a rutile TiO2(110) surface are studied with low-temperature scanning tunnelling microscopy. We demonstrate that metastable molecular assemblies transform into differently ordered structures either due to additional energy provided by thermal annealing or when the influence of intermolecular forces is increased by the enlarged amount of deposited molecules. Proper adjustment of molecular coverage and substrate temperature during deposition allows for fabrication of desired assemblies. Differences between PTCDA/TiO2(110) and PTCDA/TiO2(011) systems obtained through identical experimental procedures are discussed. PMID:26199854

  16. Rutile TiO2(011)-2 × 1 Reconstructed Surfaces with Optical Absorption over the Visible Light Spectrum.

    PubMed

    Zhou, Rulong; Li, Dongdong; Qu, Bingyan; Sun, Xiaorui; Zhang, Bo; Zeng, Xiao Cheng

    2016-10-12

    The stable structures of the reconstructed rutile TiO2(011) surface are explored based on an evolutionary method. In addition to the well-known "brookite(001)-like" 2 × 1 reconstruction model, three 2 × 1 reconstruction structures are revealed for the first time, all being more stable in the high Ti-rich condition. Importantly, the predicted Ti4O4-2 × 1 surface model not only is in excellent agreement with the reconstructed metastable surface detected by Tao et al. [Nat. Chem. 3, 296 (2011)] from their STM experiment but also gives a consistent formation mechanism and electronic structures with the measured surface. The computed imaginary part of the dielectric function suggests that the newly predicted reconstructed surfaces are capable of optical absorption over the entire visible light spectrum, thereby offering high potential for photocatalytic applications.

  17. Three-dimensional interaction force and tunneling current spectroscopy of point defects on rutile TiO2(110)

    NASA Astrophysics Data System (ADS)

    Baykara, Mehmet Z.; Mönig, Harry; Schwendemann, Todd C.; Ünverdi, Ã.-zhan; Altman, Eric I.; Schwarz, Udo D.

    2016-02-01

    The extent to which point defects affect the local chemical reactivity and electronic properties of an oxide surface was evaluated with picometer resolution in all three spatial dimensions using simultaneous atomic force/scanning tunneling microscopy measurements performed on the (110) face of rutile TiO2. Oxygen atoms were imaged as protrusions in both data channels, corresponding to a rarely observed imaging mode for this prototypical metal oxide surface. Three-dimensional spectroscopy of interaction forces and tunneling currents was performed on individual surface and subsurface defects as a function of tip-sample distance. An interstitial defect assigned to a subsurface hydrogen atom is found to have a distinct effect on the local density of electronic states on the surface, but no detectable influence on the tip-sample interaction force. Meanwhile, spectroscopic data acquired on an oxygen vacancy highlight the role of the probe tip in chemical reactivity measurements.

  18. A density functional theory study of atomic steps on stoichiometric rutile TiO2(110).

    PubMed

    Stausholm-Møller, Jess; Kristoffersen, Henrik Høgh; Martinez, Umberto; Hammer, Bjørk

    2013-12-21

    We present a detailed theoretical study of the energetics of stoichiometric steps on the (110) surface of rutile TiO2. Step structures running along the <001>, <111>, and <110> directions including bulk-terminations and possible reconstructions have been considered. A robust method for extracting surface and step energies of vicinal surfaces, where the surface energies converge slowly with respect to slab thickness, is outlined and used. Based on the calculated step energies a 2D Wulff-construction is presented from which it can be concluded that in equilibrium only oxygen terminated steps running along the <001> directions and reconstructed steps along the <111> directions should be present. Finally it is found that under conditions of stoichiometry the reconstructed <111> steps should be more than twice as abundant as oxygen terminated <001> steps.

  19. N incorporation and electronic structure in N-doped TiO2(110) rutile

    SciTech Connect

    Cheung, Sau H.; Nachimuthu, Ponnusamy; Joly, Alan G.; Engelhard, Mark H.; Bowman, Michael K.; Chambers, Scott A.

    2007-02-08

    Epitaxial TiO2-xNx film growth under anion-rich conditions is characterized by nearly balanced incorporation rates for substitutional N (NO) and interstitial Ti (Tii). Tii donors fully compensate and stabilize N3-, but preclude the formation of p-type material. Hybridization occurs between Tii(IV) and NO3-, but the value of x is limited to ~0.02 under these conditions. Tii(IV)-NO3- states occur above the valence band maximum of pure TiO2, riving rise to enhanced optical absorption in the visible up to ~2.5 eV. Much higher NO and Tii concentrations result from using cation-rich conditions.

  20. Transport and Retention of TiO2 Rutile Nanoparticles in Saturated Porous Media at Low-Ionic-Strength Conditions: Measurements and Mechanisms

    EPA Science Inventory

    The mechanisms governing the transport and retention kinetics of titanium dioxide (TiO2, rutile) nanoparticle (NP) aggregates were investigated in saturated porous media. Experiments were carried out under a range of well-controlled ionic strength (from DI water up to 1 mM) and...

  1. Transport and Retention of TiO2 Rutile Nanoparticles in Saturated Porous Media: Influence of Solution pH, Ionic Strength, and the Presence of Humic Acid

    EPA Science Inventory

    The influence of solution pH, ionic strength, and varying concentrations of the Suwannee River Humic Acid (SRHA) on the transport of titanium dioxide (TiO2, rutile) nanoparticle aggregates (nTiO2) in saturated porous media was investigated through systematically examining the tra...

  2. Characterization of individual molecular adsorption geometries by atomic force microscopy: Cu-TCPP on rutile TiO2 (110)

    NASA Astrophysics Data System (ADS)

    Jöhr, Res; Hinaut, Antoine; Pawlak, Rémy; Sadeghi, Ali; Saha, Santanu; Goedecker, Stefan; Such, Bartosz; Szymonski, Marek; Meyer, Ernst; Glatzel, Thilo

    2015-09-01

    Functionalized materials consisting of inorganic substrates with organic adsorbates play an increasing role in emerging technologies like molecular electronics or hybrid photovoltaics. For such applications, the adsorption geometry of the molecules under operating conditions, e.g., ambient temperature, is crucial because it influences the electronic properties of the interface, which in turn determine the device performance. So far detailed experimental characterization of adsorbates at room temperature has mainly been done using a combination of complementary methods like photoelectron spectroscopy together with scanning tunneling microscopy. However, this approach is limited to ensembles of adsorbates. In this paper, we show that the characterization of individual molecules at room temperature, comprising the determination of the adsorption configuration and the electrostatic interaction with the surface, can be achieved experimentally by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We demonstrate this by identifying two different adsorption configurations of isolated copper(ii) meso-tetra (4-carboxyphenyl) porphyrin (Cu-TCPP) on rutile TiO2 (110) in ultra-high vacuum. The local contact potential difference measured by KPFM indicates an interfacial dipole due to electron transfer from the Cu-TCPP to the TiO2. The experimental results are verified by state-of-the-art first principles calculations. We note that the improvement of the AFM resolution, achieved in this work, is crucial for such accurate calculations. Therefore, high resolution AFM at room temperature is promising for significantly promoting the understanding of molecular adsorption.

  3. Characterization of individual molecular adsorption geometries by atomic force microscopy: Cu-TCPP on rutile TiO2 (110).

    PubMed

    Jöhr, Res; Hinaut, Antoine; Pawlak, Rémy; Sadeghi, Ali; Saha, Santanu; Goedecker, Stefan; Such, Bartosz; Szymonski, Marek; Meyer, Ernst; Glatzel, Thilo

    2015-09-07

    Functionalized materials consisting of inorganic substrates with organic adsorbates play an increasing role in emerging technologies like molecular electronics or hybrid photovoltaics. For such applications, the adsorption geometry of the molecules under operating conditions, e.g., ambient temperature, is crucial because it influences the electronic properties of the interface, which in turn determine the device performance. So far detailed experimental characterization of adsorbates at room temperature has mainly been done using a combination of complementary methods like photoelectron spectroscopy together with scanning tunneling microscopy. However, this approach is limited to ensembles of adsorbates. In this paper, we show that the characterization of individual molecules at room temperature, comprising the determination of the adsorption configuration and the electrostatic interaction with the surface, can be achieved experimentally by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We demonstrate this by identifying two different adsorption configurations of isolated copper(ii) meso-tetra (4-carboxyphenyl) porphyrin (Cu-TCPP) on rutile TiO2 (110) in ultra-high vacuum. The local contact potential difference measured by KPFM indicates an interfacial dipole due to electron transfer from the Cu-TCPP to the TiO2. The experimental results are verified by state-of-the-art first principles calculations. We note that the improvement of the AFM resolution, achieved in this work, is crucial for such accurate calculations. Therefore, high resolution AFM at room temperature is promising for significantly promoting the understanding of molecular adsorption.

  4. Magnetic, specific heat and electrical transport properties of oxygen-deficient nanosized rutile TiO2‑δ

    NASA Astrophysics Data System (ADS)

    Tran, Vinh Hung; Thi Quynh Hoa, Nguyen

    2017-03-01

    An oxygen-deficient nanosized {{TiO}}2-δ , δ ∼ 0.7 sample was synthesized by a solvothermal method, and was characterized to have both ∼3 nm amorphous solid and ∼36–46 nm diameter rutile nanowires. Physical properties of the sample were investigated by measuring magnetic, specific heat, electrical resistance and magnetoresitance properties. DC magnetization M(H) data confirm ferromagnetic behavior previously reported for undoped TiO2. Furthermore, M(T) dependence follows the power-law relation M{(T)\\propto (1-T/{T}C)}β in the near-critical regime, yielding Curie temperature {T}C ∼ 415 K and critical exponent β = 0.2. Moreover, our results of AC magnetic susceptibility measurements suggest an additional phase transition at {T}* ∼ 310 K, presumably due to spin orientation. The metallic-like electrical resistance exhibits a distinct drop below {T}* with a strong thermal hysteresis in the temperature range 225–275 K. Specific heat in the temperature range 20–300 K is well described by the sum of contributions from acoustic phonons with Debye temperature 605 K and optical phonons with Einstein temperature 113 K. Below 10 K the specific heat divulges a large excess, which can be interpreted as an additional contribution originating from soft potentials.

  5. A DFT study of water adsorption on rutile TiO2 (110) surface: The effects of surface steps

    NASA Astrophysics Data System (ADS)

    Zheng, Ting; Wu, Chunya; Chen, Mingjun; Zhang, Yu; Cummings, Peter T.

    2016-07-01

    The associative and dissociative adsorption of water molecules at low-coverage situations on rutile TiO2 (110) surface with step defects was investigated by the density functional theory calculations. Structural optimization of the hydroxylated/hydrated configurations at step edges along the <" separators="1 1 ¯ 1 > crystal directions and the dynamic process of water dissociation were discussed to get a better description of the water/TiO2 interface. Our results indicate that steps on the TiO2 (110) surface could be an active site for water dissociation. The results of geometry optimization suggest that the stability of hydroxylated configuration is largely dependent on the locations of the H species and the recombination of water molecules from hydroxyls is observed in the fully hydroxylated condition. However, these hydroxyls can be stabilized by the associatively absorbed water nearby by forming competitive intermolecular hydrogen bonds. The dynamics of water dissociation and hydrogen diffusion were studied by the first principles molecular dynamics simulation and our results suggest that the hydrogen released by water dissociation can be transferred among the adsorbates, such as the unsaturated oxygen atoms-H2O-hydroxyl (TiO-H2O-OH) complex at step edges, or gradually diffuses to the bulk water system in the form of hydronium (H3O+) at higher water coverage.

  6. Growth and characterization of rutile TiO2 nanorods on various substrates with fabricated fast-response metal-semiconductor-metal UV detector based on Si substrate

    NASA Astrophysics Data System (ADS)

    Selman, Abbas M.; Hassan, Z.

    2015-07-01

    Rutile-phase titanium dioxide nanorods (NRs) were synthesized successfully on p-type silicon (Si) (1 1 1), c-plane sapphire (Al2O3), glass coated with fluorine-doped tin oxide (FTO), glass, and quartz substrates via chemical bath deposition method. All substrates were seeded with a TiO2 seed layer synthesized with a radio frequency reactive magnetron sputtering system prior to NRs growth. The effect of substrate type on structural, morphological, and optical properties of rutile TiO2 NRs was studied. X-ray diffraction, Raman spectroscopy, and field-emission scanning electron microscopy analyses showed the tetragonal rutile structure of the synthesized TiO2 NRs. Optical properties were examined with photoluminescence (PL) spectroscopy of the grown rutile NRs on all substrates, with the spectra exhibiting one strong ultraviolet emission peak intensity compared with broad visible peak. The optimal sample of rutile NRs was grown on Si substrate. Thus, a fast-response metal-semiconductor-metal ultraviolet (UV) detector was fabricated. Upon exposure to 365 nm light (2.3 mW/cm2) at 5 V bias, the device displays 2.62 × 10-5 A photocurrent, and the response and recovery times are calculated as 18.5 and 19.1 ms, respectively. These results demonstrate that the fabricated high-quality photodiode is a promising candidate as a low-cost UV photodetector for commercially integrated photoelectronic applications.

  7. Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

    NASA Astrophysics Data System (ADS)

    Mayabadi, A. H.; Waman, V. S.; Kamble, M. M.; Ghosh, S. S.; Gabhale, B. B.; Rondiya, S. R.; Rokade, A. V.; Khadtare, S. S.; Sathe, V. G.; Pathan, H. M.; Gosavi, S. W.; Jadkar, S. R.

    2014-02-01

    Nanocrystalline thin films of TiO2 were prepared on glass substrates from an aqueous solution of TiCl3 and NH4OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO2 transition from a mixed anatase-rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO2 thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29-3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors.

  8. Self-induced synthesis of phase-junction TiO2 with a tailored rutile to anatase ratio below phase transition temperature

    PubMed Central

    Wang, Wei-Kang; Chen, Jie-Jie; Zhang, Xing; Huang, Yu-Xi; Li, Wen-Wei; Yu, Han-Qing

    2016-01-01

    The surface phase junction of nanocrystalline TiO2 plays an essential role in governing its photocatalytic activity. Thus, facile and simple methods for preparing phase-junction TiO2 photocatalysts are highly desired. In this work, we show that phase-junction TiO2 is directly synthesized from Ti foil by using a simple calcination method with hydrothermal solution as the precursor below the phase transition temperature. Moreover, the ratio of rutile to anatase in the TiO2 samples could be readily tuned by changing the ratio of weight of Ti foil to HCl, which is used as the hydrothermal precursor, as confirmed by the X-ray diffraction analysis. In the photocatalytic reaction by the TiO2 nanocomposite, a synergistic effect between the two phases within a certain range of the ratio is clearly observed. The results suggest that an appropriate ratio of anatase to rutile in the TiO2 nanocomposite can create more efficient solid-solid interfaces upon calcination, thereby facilitating interparticle charge transfer in the photocatalysis. PMID:26864501

  9. The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes

    NASA Astrophysics Data System (ADS)

    Ding, Jianning; Li, Yan; Hu, Hongwei; Bai, Li; Zhang, Shuai; Yuan, Ningyi

    2013-01-01

    High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO2 nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO2 DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO2 electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO2 nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6 wt.% rutile) TiO2 nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3 mA cm-2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO2 nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.

  10. The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes.

    PubMed

    Ding, Jianning; Li, Yan; Hu, Hongwei; Bai, Li; Zhang, Shuai; Yuan, Ningyi

    2013-01-03

    High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO2 nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO2 DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO2 electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO2 nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6 wt.% rutile) TiO2 nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3 mA cm-2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO2 nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.

  11. The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes

    PubMed Central

    2013-01-01

    High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO2 nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO2 DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO2 electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO2 nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6 wt.% rutile) TiO2 nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3 mA cm−2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO2 nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies. PMID:23286741

  12. Structural studies of TiO2/wood coatings prepared by hydrothermal deposition of rutile particles from TiCl4 aqueous solutions on spruce (Picea Abies) wood

    NASA Astrophysics Data System (ADS)

    Pori, Pavel; Vilčnik, Aljaž; Petrič, Marko; Sever Škapin, Andrijana; Mihelčič, Mohor; Šurca Vuk, Angela; Novak, Urban; Orel, Boris

    2016-05-01

    A low temperature approach was developed for the deposition of rutile TiO2 particles on a wood surface by hydrolysis of TiCl4 in aqueous solutions acidified with HCl, and crystallization at 75 and 90 °C (1 h). Prior to hydrothermal treatment, Picea Abies wood was first soaked in a 0.5 mmol/l aqueous solution containing anionic surfactant sodium dodecyl sulphate (SDS, Sigma Aldrich) for 2 h at 80 °C. The crystal structure of the hydrothermally made rutile particles was determined with XRD, while the morphology of the deposited TiO2 particles and their distribution in the wood were examined with SEM and EDX measurements. The penetration and amount of deposited rutile particles could be modified by changing the deposition conditions. Thicker layers were obtained from more concentrated aqueous TiCl4 solutions with and without added HCl, and with longer deposition times and higher temperatures of the hydrothermal treatment. The interaction of TiO2 particles with hemicellulose and lignin in wood was established from infrared attenuated total reflection (FT-IR ATR) and Raman spectra measurements, from which the spectra of wood were subtracted. Analysis of the subtraction spectra showed the presence of titania particles on the wood surface, revealing also the establishment of TiO2-wood coordinative bonds of titanium ions with hemicellulose and lignin. The red frequency shift of the OH stretching modes suggested interaction of the TiO2 particles with water molecules of wood. TiO2 deposited on wood treated with SDS became hydrophobic (water contact angles (WCA) of 150°), contrasting the properties of untreated wood with a deposited TiO2 particle coating, which remained hydrophilic.

  13. Growth of anatase and rutile phase TiO2 nanoparticles using pulsed laser ablation in liquid: Influence of surfactant addition and ablation time variation

    NASA Astrophysics Data System (ADS)

    Chaturvedi, Amita; Joshi, M. P.; Mondal, P.; Sinha, A. K.; Srivastava, A. K.

    2017-02-01

    Titanium dioxide (TiO2) nanoparticles were grown using nanosecond pulsed laser ablation of Ti target in DI water and in 0.001 M sodium dodecyl sulfate (SDS) surfactant aqueous solution. Growth was carried out with varying ablation times i. e. 30 min, 60 min and 90 min. The objective of our study was to investigate the influence of variations in liquid ambience conditions on the growth of the nanoparticles in a pulsed laser ablation in liquid (PLAL) process. Size, composition and optical properties of the grown TiO2 nanoparticles were investigated using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), optical absorption, photoluminescence (PL) spectroscopy and X-ray diffraction (XRD) studies. The obtained nanoparticles of TiO2 were found almost spherical in shape and polycrystalline in nature in both the liquid mediums i.e. DI water and aqueous solution of surfactant. Nanoparticles number density was also found to increase with increasing ablation time in both the liquid mediums. However crystalline phase of the grown TiO2 nanoparticles differs with the change in liquid ambience conditions. Selected area electron diffraction (SAED), PL and XRD studies suggest that DI water ambience is favorable for the growth of anatase phase TiO2 nanoparticles for all ablation times. While Surfactant added water ambience is favorable for the growth of rutile phase TiO2 nanoparticles but for shorter ablation times of 30 min and 60 min only, for longer ablation time of 90 min anatase phase was also observed along with the rutile phase TiO2 nanoparticles. The formation of anatase phase in DI water and rutile and anatase phase in aqueous solution of surfactant is explained on the basis of varying thermodynamic conditions with the two different liquid ambiences and different ablation times.

  14. On the consistency of QCBED structure factor measurements for TiO2 (Rutile)

    DOE PAGES

    Jiang, Bin; Zuo, Jian -Min; Friis, Jesper; ...

    2003-09-16

    The same Bragg reflection in TiO2 from twelve different CBED patterns (from different crystals, orientations and thicknesses) are analysed quantitatively in order to evaluate the consistency of the QCBED method for bond-charge mapping. The standard deviation in the resulting distribution of derived X-ray structure factors is found to be an order of magnitude smaller than that in conventional X-ray work, and the standard error (0.026% for FX(110)) is slightly better than obtained by the X-ray Pendellosung method applied to silicon. This is sufficiently accuracy to distinguish between atomic, covalent and ionic models of bonding. We describe the importance of extractingmore » experimental parameters from CCD camera characterization, and of surface oxidation and crystal shape. Thus, the current experiments show that the QCBED method is now a robust and powerful tool for low order structure factor measurement, which does not suffer from the large extinction (multiple scattering) errors which occur in inorganic X-ray crystallography, and may be applied to nanocrystals. Our results will be used to understand the role of d electrons in the chemical bonding of TiO2.« less

  15. Conversion of 1,2-Propylene Glycol on Rutile TiO2(110)

    SciTech Connect

    Chen, Long; Li, Zhenjun; Smith, R. Scott; Kay, Bruce D.; Dohnalek, Zdenek

    2014-07-17

    We have studied the reactions of 1,2-propylene glycol (1,2-PG), DOCH(CH3)CH2OD, on partially reduced, hydroxylated and oxidized TiO2(110) surfaces using temperature programmed desorption. On reduced TiO2(110), propylene, propanal, and acetone are identified as primary carbon-containing products. While the propylene formation channel dominates at low 1,2-PG coverages, all of the above-mentioned products are observed at high coverages. The carbon-containing products are accompanied by the formation of D2O and D2. The observation of only deuterated products shows that the source of hydrogen (D) is from the 1,2-PG hydroxyls. The role of bridging oxygen vacancy (VO) sites was further investigated by titrating them via hydroxylation and oxidation. The results show that hydroxylation does not change the reactivity because the VO sites are regenerated at 500 K, which is a temperature lower than the 1,2-PG product formation temperature. In contrast, surface oxidation causes significant changes in the product distribution, with increased acetone and propanal formation and decreased propylene formation. Additionally D2 is completely eliminated as an observed product at the expense of D2O formation.

  16. Density functional theory study on the structural and electronic properties of low index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems.

    PubMed

    Beltrán, A; Andrés, J; Sambrano, J R; Longo, E

    2008-09-25

    The present study is concerned with the structural and electronic properties of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems. Periodic quantum mechanical method with density functional theory at the B3LYP level has been carried out. Relaxed surface energies, structural characteristics and electronic properties of the (110), (010), (101) and (00) low-index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 models are studied. For comparison purposes, the bare rutile TiO2 and SnO2 structures are also analyzed and compared with previous theoretical and experimental data. The calculated surface energy for both rutile TiO2 and SnO2 surfaces follows the sequence (110) < (010) < (101) < (001) and the energy increases as (010) < (101) < (110) < (001) and (010) approximately = (110) < (101) < (001) for SnO2/TiO2/SnO2 and TiO2/SnO2/TiO2 composite systems, respectively. SnO2/TiO2/SnO2 presents larger values of surface energy than the individual SnO2 and TiO2 metal oxides and the TiO2/SnO2/TiO2 system renders surface energy values of the same order that the TiO2 and lower than the SnO2. An analysis of the electronic structure of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 systems shows that the main characteristics of the upper part of the valence bands for all the studied surfaces are dominated by the external layers, i.e., by the TiO2 and the SnO2, respectively, and the topology of the lower part of the conduction bands looks like the core layers. There is an energy stabilization of both valence band top and conduction band bottom for (110) and (010) surfaces of the SnO2/TiO2/SnO2 composite system in relation to their core TiO2, whereas an opposite trend is found for the same surfaces of the TiO2/SnO2/TiO2 composite system in relation to the bare SnO2. The present theoretical results may explain the growth of TiO2@SnO2 bimorph composite nanotape.

  17. Thermodynamic Properties of Rutile (TiO2) Within the Phonon Calculations

    NASA Astrophysics Data System (ADS)

    Kangarlou, Haleh; Abdollahi, Arash

    2016-11-01

    Full phonon calculations have been performed to estimate the thermal properties of rutile (titanium dioxide). Calculations have been carried out using the pseudo-potential method within the local density approximation. Thermodynamic properties including the thermal expansion, thermal expansion coefficient, heat capacity and entropy were calculated as a function of temperature in the framework of quasi-harmonic approximation. Also, to compare the results with the results of other approaches, we apply Debye-Slater and Debye-Gruneisen approaches with the same parameters for electronic calculations. It is found that the phonon calculations provide more accurate estimates in comparison with the other two models.

  18. Adhesion of sodium dodecyl sulfate surfactant monolayers with TiO2 (rutile and anatase) surfaces

    SciTech Connect

    Darkins, Robert; Sushko, Maria L.; Liu, Jun; Duffy, Dorothy M.

    2013-09-17

    Surfactants are widely used as templates to control the nucleation and growth of nanostructured metal oxides such as titania. To gain insight into the origin of surfactant-titania interactions responsible for polymorph and orientation selection, we simulate the self-assembly of an anionic surfactant monolayer on various low-index titania surfaces and for a range of densities. We characterize the binding in each case and compute the adhesion energies, finding anatase (100) and rutile (110) to be the strongest-binding surfaces. The sodium counterions in the monolayer are found to dominate the adhesion. It is also observed that the assembly is directed predominantly by surface-monolayer electrostatic complementarity.

  19. High-pressure polymorphic transformation of rutile to alpha-PbO2-type TiO2 at {011}R twin boundaries.

    PubMed

    Meng, D W; Wu, X L; Sun, F; Huang, L W; Liu, F; Han, Y J; Zheng, J P; Meng, X; Mason, R

    2008-01-01

    The presence of nano-scale lamellae of the alpha-PbO2-type polymorph of TiO2 sandwiched between twinned rutile inclusions in jadeite has been confirmed by electron diffraction and high-resolution transmission electron microscopy, backed up by image simulation techniques, from ultrahigh-pressure jadeite quartzite at Shuanghe in the Dabie Mountains, China. The crystal structure is orthorhombic with lattice parameters a=4.58 A, b=5.42 A, c=5.02 A and space group Pbcn. A three-dimensional structural model has been constructed for the rutile to alpha-PbO2-type TiO2 phase transformation based on high-resolution electron microscopic images. Computer image simulation and structural model analysis reveal that rutile {011}R twin interface is a basic structural unit of alpha-PbO2-type TiO2. Nucleation of alpha-PbO2-type TiO2 lamellae 1-2 nm thick is caused by the displacement of one half of the titanium cations within the {011}R twin slab. This displacement reduces the Ti-O-Ti distance and is favored by high pressure.

  20. Effect of rutile TiO2 on the photocatalytic performance of g-C3N4/brookite-TiO2-xNy photocatalyst for NO decomposition

    NASA Astrophysics Data System (ADS)

    Li, Huihui; Wu, Xiaoyong; Yin, Shu; Katsumata, Kenichi; Wang, Yuhua

    2017-01-01

    Novel g-C3N4/rutile-brookite TiO2-xNy composite photocatalysts were fabricated through a facile solvothermal approach. The effect of rutile phase TiO2 with brookite TiO2 and g-C3N4 on the photocatalytic activity of g-C3N4/nitrogen-doped TiO2 composite was studied. The photocatalytic performance of the photocatalyst was evaluated by measuring the degradation of NO gas under visible and UV light irradiation. It is suggested that g-C3N4/rutile-brookite TiO2-xNy forms a Z-scheme photocatalytic system, which shows improvement on the photocatalytic activity than that of g-C3N4/single brookite TiO2-xNy. By importing rutile phase TiO2-xNy, the photogenerated electrons can efficiently transfer from rutile TiO2 to g-C3N4, which results in the separation of electron and hole pairs, enhancing the photocatalytic ability. However, single brookite TiO2-xNy can not remove the photogenerated electrons efficiently and the photocatalytic performances of composites decrease with g-C3N4 amount increase.

  1. Probing the charge recombination in rGO decorated mixed phase (anatase-rutile) TiO2 multi-leg nanotubes

    NASA Astrophysics Data System (ADS)

    Rambabu, Y.; Jaiswal, Manu; Roy, Somnath C.

    2016-11-01

    Recombination of photo-generated charges is one of the most significant challenges in designing efficient photo-anode for photo electrochemical water oxidation. In the case of TiO2, mixed phase (anatase-rutile) junctions often shown to be more effective in suppressing electron-hole recombination compared to a single (anatase or rutile) phase. Here, we report the study of bulk and surface recombination process in TiO2 multi-leg nanotube (MLNTs) anatase-rutile (A-R) junctions decorated with reduced graphene oxide (rGO) layers, through an analysis of the photo-current and impedance characteristics. To quantify the charge transport/transfer process involved in these junctions, holes arriving at the interface of semiconductor/electrolyte were collected by adding H2O2 to the electrolyte. This enabled us to interpret the bulk and surface recombination process involved in anatase/rutile/rGO junctions for photo-electrochemical water oxidation. We correlated this quantification to the electrochemical impedance spectroscopy (EIS) measurements, and showed that in anatase/rutile junction the increase in PEC performance was due to suppression in electron-hole recombination rate at the surface states that effectively enhances the hole transfer rate to the electrolyte. On the other hand, in rGO wrapped A-R MLNTs junction it was due to both phenomenon i.e decrease in bulk recombination rate as well as increase in hole transfer rate to the electrolyte at the semiconductor/electrolyte interface.

  2. DFT + U investigation on the adsorption and initial decomposition of methylamine by a Pt single-atom catalyst supported on rutile (110) TiO2

    NASA Astrophysics Data System (ADS)

    Lv, Cun-Qin; Liu, Jian-Hong; Guo, Yong; Li, Xue-Mei; Wang, Gui-Chang

    2016-12-01

    The adsorption and initial decomposition for methylamine catalyzed by a single Pt atom supported on rutile (110) titania (namely, Pt1/TiO2-R(110)) surface have been investigated by the density functional theory slab calculations with Hubbard corrections (DFT + U). The main purpose of the work is to better understand the role of dispersed platinum metal on the surface of rutile (110) titania in the initial decomposition of methylamine. Our calculated results show that the barriers increased with the order of Csbnd H < Nsbnd H < Csbnd N, which indicates that the Csbnd H bond is the easiest to decompose and the Csbnd N bond is the most difficult to break.

  3. Conversion of 1,3-Propylene Glycol on Rutile TiO2(110)

    SciTech Connect

    Chen, Long; Li, Zhenjun; Smith, R. Scott; Kay, Bruce D.; Dohnalek, Zdenek

    2014-10-09

    The adsorption of 1,3-propylene glycol (1,3-PG) on partially reduced TiO2(110) and its conversion to products have been studied by a combination of molecular beam dosing and temperature programmed desorption (TPD). When the Ti surface sites are saturated by 1,3-PG, ~80% of the molecules undergo further reactions to yield products that are liberated during the TPD ramp. In contrast to ethylene glycol (EG) and 1,2- propylene glycol (1,2-PG) that yield only alkenes and water at very low coverages (< 0.05 ML), two additional products, HCHO and C2H4, along with propylene (CH3CHCH2) and water are observed for 1,3-PG. Identical TPD line shapes and desorption yields for HCHO and C2H4 suggest that these products result from C-C bond cleavage and are coupled. At higher 1,3-PG coverages (> 0.1 ML), propanal (CH3CH2CHO) and two additional products, 1-propanol (CH3CH2CH2OH) and acrolein (CH2CHCHO), are observed. The desorption of 1-propanol is found to be coupled with the desorption of acrolein, suggesting that these products are formed by the disproportionation of two 1,3-PG molecules. The coverage dependent TPD results further show that propylene formation dominates at low coverages (< 0.3 ML), while the decomposition and disproportionation channels increase rapidly at higher coverages and reach yields comparable to that of propylene at the 1,3-PG saturation coverage of 0.5 ML. The observed surface chemistry clearly shows how the molecular structure of glycols influences their reaction pathways on oxide surfaces.

  4. Low temperature EPR investigation of Co2+ ion doped into rutile TiO2 single crystal: Experiments and simulations

    NASA Astrophysics Data System (ADS)

    Zerentürk, A.; Açıkgöz, M.; Kazan, S.; Yıldız, F.; Aktaş, B.

    2017-02-01

    In this paper, we present the results of X-band EPR spectra of Co2+ ion doped rutile (TiO2) which is one of the most promising memristor material. We obtained the angular variation of spectra in three mutually perpendicular planes at liquid helium (7-13 K) temperatures. Since the impurity ions have ½ effective spin and 7/2 nuclear spin, a relatively simple spin Hamiltonian containing only electronic Zeeman and hyperfine terms was utilized. Two different methods were used in theoretical analysis. Firstly, a linear regression analysis of spectra based on perturbation theory was studied. However, this approach is not sufficient for analyzing Co+2 spectra and leads to complex eigenvectors for G and A tensors due to large anisotropy of eigenvalues. Therefore, all spectra were analyzed again with exact diagonalization of spin Hamiltonian and the high accuracy eigenvalues and eigenvectors of G and A tensors were obtained by taking into account the effect of small sample misalignment from the exact crystallographic planes due to experimental conditions. Our results show that eigen-axes of g and A tensors are parallel to crystallographic directions. Hence, our EPR experiments proves that Co2+ ions substitute for Ti4+ ions in lattice. The obtained principal values of g tensor are gx=2.110(6), gy=5.890(2), gz=3.725(7) and principal values of hyperfine tensor are Ax=42.4, Ay=152.7, Az=26 (in 10-4/cm).

  5. Fabrication of nanosized Pt on rutile TiO2 using a standing wave sonochemical reactor (SWSR)--observation of an enhanced catalytic oxidation of CO.

    PubMed

    Sivakumar, Manickam; Towata, Atsuya; Yasui, Kyuichi; Tuziuti, Toru; Kozuka, Teruyuki; Tsujimoto, Masahiko; Zhong, Ziyi; Iida, Yasuo

    2010-01-01

    Fine particles of rutile TiO2 supporting nanosized particles of Pt were prepared by a simultaneous in situ sonochemical reduction and deposition method using a standing wave sonochemical reactor (SWSR). The mean diameter of sonochemically obtained Pt particles are of 2 nm. Following this sonochemical technique, rutile TiO2 was also deposited with different weight percentages of Pt. Catalytic function of the prepared composite catalysts were tested by the oxidation of CO to CO(2). From the catalytic activity results, it has been found out that the catalysts prepared by the sonochemical method exhibited higher catalytic activity for CO oxidation, probably attributed to the higher Pt particle distribution achieved under sonication. Transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), and diffuse reflectance spectroscopy (DRS) were employed to characterize the resulting material.

  6. Hydrothermal Etching Treatment to Rutile TiO2 Nanorod Arrays for Improving the Efficiency of CdS-Sensitized TiO2 Solar Cells

    NASA Astrophysics Data System (ADS)

    Wan, Jingshu; Liu, Rong; Tong, Yuzhu; Chen, Shuhuang; Hu, Yunxia; Wang, Baoyuan; Xu, Yang; Wang, Hao

    2016-01-01

    Highly ordered TiO2 nanorod arrays (NRAs) were directly grown on an F:SnO2 (FTO) substrate without any seed layer by hydrothermal route. For a larger surface area, the second-step hydrothermal treatment in hydrochloric acid was carried out to the as-prepared TiO2 NRAs. The results showed that the center portion of the TiO2 nanorods were dissolved in the etching solution to form a nanocave at the initial etching process. As the etching time extended, the tip parts of the nanocave wall split into lots of nanowires with a reduced diameter, giving rise to a remarkable increase of specific surface area for the TiO2 NRAs. The TiO2 films after etching treatment were sensitized by CdS quantum dots (QDs) to fabricate quantum dot-sensitized solar cells (QDSSCs), which exhibited a significant improvement in the photocurrent density in comparison with that of the un-treated device, this mainly attributed to the enhancement of QD loading and diffused reflectance ability. Through modifying the etching TiO2 films with TiCl4, a relatively high power conversion efficiency (PCE) of 3.14 % was obtained after optimizing the etching time.

  7. Hydrothermal Etching Treatment to Rutile TiO2 Nanorod Arrays for Improving the Efficiency of CdS-Sensitized TiO2 Solar Cells.

    PubMed

    Wan, Jingshu; Liu, Rong; Tong, Yuzhu; Chen, Shuhuang; Hu, Yunxia; Wang, Baoyuan; Xu, Yang; Wang, Hao

    2016-12-01

    Highly ordered TiO2 nanorod arrays (NRAs) were directly grown on an F:SnO2 (FTO) substrate without any seed layer by hydrothermal route. For a larger surface area, the second-step hydrothermal treatment in hydrochloric acid was carried out to the as-prepared TiO2 NRAs. The results showed that the center portion of the TiO2 nanorods were dissolved in the etching solution to form a nanocave at the initial etching process. As the etching time extended, the tip parts of the nanocave wall split into lots of nanowires with a reduced diameter, giving rise to a remarkable increase of specific surface area for the TiO2 NRAs. The TiO2 films after etching treatment were sensitized by CdS quantum dots (QDs) to fabricate quantum dot-sensitized solar cells (QDSSCs), which exhibited a significant improvement in the photocurrent density in comparison with that of the un-treated device, this mainly attributed to the enhancement of QD loading and diffused reflectance ability. Through modifying the etching TiO2 films with TiCl4, a relatively high power conversion efficiency (PCE) of 3.14 % was obtained after optimizing the etching time.

  8. Effective charge separation in the rutile TiO2 nanorod-coupled α-Fe2O3 with exceptionally high visible activities

    PubMed Central

    Luan, Peng; Xie, Mingzheng; Liu, Dening; Fu, Xuedong; Jing, Liqiang

    2014-01-01

    Herein, we have fabricated rutile TiO2 nanorod-coupled α-Fe2O3 by a wet-chemical process. It is demonstrated that the visible activities for photoelectrochemical water oxidation and for degrading pollutant of α-Fe2O3 are greatly enhanced after coupling a proper amount of rutile nanorods. The enhanced activity is attributed to the prolonged lifetime and improved separation of photogenerated charges mainly by the transient surface photovoltage responses. Interestingly, the observed EPR signals (with g⊥ = 1.963 and g|| = 1.948) of Ti3+ in the fabricated TiO2-Fe2O3 nanocomposite at ultra low temperature (1.8 k) after visible laser excitation, along with the electrochemical impedance spectra and the normalized photocurrent action spectra, testify evidently that the spacial transfers of visible-excited high-energy electrons of α-Fe2O3 to TiO2 could happen. Moreover, it is confirmed that it is more favorable for the uncommon electron transfers of α-Fe2O3 to rutile than to anatase. This is responsible for the much obvious enhancement of visible activity of Fe2O3 after coupling with rutile TiO2, compared with anatase and phase-mixed P25 ones. This work would help us to deeply understand the uncommon photophysical processes, and also provide a feasible route to improve the photocatalytic performance of visible-response semiconductor photocatalyst for water splitting and pollutant degradation. PMID:25154460

  9. Vibrational relaxation dynamics of catalysts on TiO2 Rutile (1 1 0) single crystal surfaces and anatase nanoporous thin films

    NASA Astrophysics Data System (ADS)

    Ricks, Allen M.; Anfuso, Chantelle L.; Rodríguez-Córdoba, William; Lian, Tianquan

    2013-08-01

    Time-resolved vibrational sum frequency generation (VSFG) spectroscopy has been used to investigate the vibrational relaxation dynamics of the rhenium bipyridyl CO2-reduction catalyst Re(CO)3Cl(dcbpy) [dcbpy = 4,4‧-dicarboxy-2,2‧-bipyridine] adsorbed onto the (1 1 0) surface of a Rutile TiO2 single crystal. IR pump-VSFG probe spectra of the a‧(1) CO stretching mode indicate a ultrafast population equilibration between three CO stretching modes followed by their population relaxation via intramolecular vibrational energy transfer. Similar vibational relaxation dynamics was also observed for the same complex on anatase TiO2 nanocrystalline thin films measured by IR pump-IR probe transient absorption spectroscopy. The relaxation dynamics of ReCOA on TiO2, in DMF solution, and immobilized on Au through alkane thiol linkers were compared to examine possible effects of adsorbate-TiO2 interaction.

  10. Effect of N and F doping on the electronic properties of rutile TiO2 quantum dot solar cells: A first principle study

    NASA Astrophysics Data System (ADS)

    Salehi-Abar, Parvin; Kazempour, Amir

    2017-04-01

    Titanium dioxide phases are important due to their special potential for use in a broad range of applications particularly low-cost solar cells. However, this potential is actually restricted by the wide band gaps of TiO2 phases. A way to overcome this limitation is to reduce the band gap by incorporating nonmetal dopants into TiO2. For this purpose, in this paper, the effect of F and N doping on different sizes of rutile TiO2 quantum dots (QDs) was investigated using density functional theory (DFT) calculations. The results indicated that unlike nitrogen, doping of fluorine increases the efficiency of the quantum dot solar cells as a consequence of reducing auger recombination. Moreover, it was observed that when the size of QDs increases, shifting of the Fermi level towards the conduction band occurs as a favorable effect for solar cells.

  11. Facile oxidative conversion of TiH2 to high-concentration Ti(3+)-self-doped rutile TiO2 with visible-light photoactivity.

    PubMed

    Grabstanowicz, Lauren R; Gao, Shanmin; Li, Tao; Rickard, Robert M; Rajh, Tijana; Liu, Di-Jia; Xu, Tao

    2013-04-01

    TiO2, in the rutile phase with a high concentration of self-doped Ti(3+), has been synthesized via a facile, all inorganic-based, and scalable method of oxidizing TiH2 in H2O2 followed by calcinations in Ar gas. The material was shown to be photoactive in the visible-region of the electromagnetic spectrum. Powdered X-ray diffraction (PXRD), transmission electron microscopy (TEM), ultraviolet-visible-near-infrared (UV-vis-NIR), diffuse reflectance spectroscopy (DRS), and Brunauer-Emmett-Teller (BET) methods were used to characterize the crystalline, structural, and optical properties and specific surface area of the as-synthesized Ti(3+)-doped rutile, respectively. The concentration of Ti(3+) was quantitatively studied by electron paramagnetic resonance (EPR) to be as high as one Ti(3+) per ~4300 Ti(4+). Furthermore, methylene blue (MB) solution and an industry wastewater sample were used to examine the photocatalytic activity of the Ti(3+)-doped TiO2 which was analyzed by UV-vis absorption, Fourier transform infrared spectroscopy (FT-IR), and electrospray ionization mass spectrometry (ESI-MS). In comparison to pristine anatase TiO2, our Ti(3+) self-doped rutile sample exhibited remarkably enhanced visible-light photocatalytic degradation on organic pollutants in water.

  12. CO2 Capture and Conversion on Rutile TiO2(110) in the Water Environment: Insight by First-Principles Calculations.

    PubMed

    Yin, Wen-Jin; Krack, Matthias; Wen, Bo; Ma, Shang-Yi; Liu, Li-Min

    2015-07-02

    The conversion of CO2 by the virtue of sunlight has the great potential to produce useful fuels or valuable chemicals while decreasing CO2 emission from the traditional fossil fuels. Here, we use the first-principles calculations combined with the periodic continuum solvation model (PCSM) to explore the adsorption and reactivity of CO2 on rutile TiO2(110) in the water environment. The results exhibit that both adsorption structures and reactivity of CO2 are greatly affected by water coadsorption on rutile TiO2(110). In particular, the solvation effect can change the most stable adsorption configuration of CO2 and H2O on rutile TiO2(110). In addition, the detailed conversion mechanism of CO2 reduction is further explored in the water environment. The results reveal that the solvation effect cannot only greatly decrease the energy barrier of CO2 reduction but also affect the selectivity of the reaction processes. These results presented here show the importance of the aqueous solution, which should be helpful to understand the detailed reaction processes of photocatalysts.

  13. Comparison between sol-gel-derived anatase- and rutile-structured TiO2 coatings in soft-tissue environment.

    PubMed

    Rossi, S; Moritz, N; Tirri, T; Peltola, T; Areva, S; Jokinen, M; Happonen, R-P; Närhi, T

    2007-09-15

    The bioactivity of the surface reactive TiO(2) coatings for medical implants can be locally modified by CO(2) laser processing to match with the properties of surrounding tissues. The TiO(2) coatings heat-treated at 500 degrees C exhibit in vitro bioactivity. With further CO(2) laser treatment they exhibit enhanced in vitro bioactivity. The aim of this in vivo study was to compare the performance of heat-treated anatase-structured TiO(2) coatings with preheat-treated and CO(2) laser-treated rutile-structured coatings in terms of their ability to attach soft connective tissues. The coatings were characterized with TF-XRD and AFM. TiO(2)-coated discs were implanted in rats. The samples were analyzed with routine histology, SEM-EDS, and TEM. In both groups, already at 3 days, soft connective tissues were in immediate contact with the surface. No thick crystalline CaP layer was detected by SEM-EDS, but a thin amorphous CaP layer was detected by XPS. No gap between the cell membrane and the coating could be observed in TEM pictures. No differences were observed between the anatase- and rutile-structured coatings in terms of tissue responses. Further studies are needed to verify if the tissues are adherent to the surface of the implant.

  14. Reduced Step Edges on Rutile TiO2(110) as Competing Defects to Oxygen Vacancies on the Terraces and Reactive Sites for Ethanol Dissociation

    NASA Astrophysics Data System (ADS)

    Martinez, U.; Hansen, J. Ø.; Lira, E.; Kristoffersen, H. H.; Huo, P.; Bechstein, R.; Lægsgaard, E.; Besenbacher, F.; Hammer, B.; Wendt, S.

    2012-10-01

    The rutile TiO2(110) surface is the most studied surface of titania and considered as a prototype of transition metal oxide surfaces. Reactions on flat TiO2(110)-(1×1) surfaces are well studied, but the processes occurring on the step edges have barely been considered. Based on scanning tunneling microscopy studies, we here present experimental evidence for the existence of O vacancies along the ⟨11¯1⟩R step edges (OS vac.’s) on rutile TiO2(110). Both the distribution of bridging O vacancies on the terraces and temperature-programed reaction experiments of ethanol-covered TiO2(110) point to the existence of the OS vac.’s. Based on experiments and density functional theory calculations, we show that OS vac.’s are reactive sites for ethanol dissociation via O-H bond scission. Implications of these findings are discussed.

  15. Locating structures and evolution pathways of reconstructed rutile TiO2(011) using genetic algorithm aided density functional theory calculations.

    PubMed

    Ding, Pan; Gong, Xue-Qing

    2016-05-01

    Titanium dioxide (TiO2) is an important metal oxide that has been used in many different applications. TiO2 has also been widely employed as a model system to study basic processes and reactions in surface chemistry and heterogeneous catalysis. In this work, we investigated the (011) surface of rutile TiO2 by focusing on its reconstruction. Density functional theory calculations aided by a genetic algorithm based optimization scheme were performed to extensively sample the potential energy surfaces of reconstructed rutile TiO2 structures that obey (2 × 1) periodicity. A lot of stable surface configurations were located, including the global-minimum configuration that was proposed previously. The wide variety of surface structures determined through the calculations performed in this work provide insight into the relationship between the atomic configuration of a surface and its stability. More importantly, several analytical schemes were proposed and tested to gauge the differences and similarities among various surface structures, aiding the construction of the complete pathway for the reconstruction process.

  16. TiO2 thin films with rutile phase prepared by DC magnetron co-sputtering at room temperature: Effect of Cu incorporation

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Li, Yujie; Ba, Xin; Huang, Lin; Yu, Ying

    2015-08-01

    The thin films for pure TiO2 and that incorporated with Cu ion were deposited by DC magnetron co-sputtering with Ar gas. The crystal texture, surface morphology, energy gap and optical properties of the prepared films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectrometer (XPS), UV-vis spectrophotometer, and Raman spectroscopy. The results show that as-deposited TiO2 film mainly possesses anatase structure at room temperature with pure Ar gas, but the introduction of Cu can alter the phase structure of crystallite TiO2. XRD patterns and Raman spectra indicate that the Cu incorporation with high concentration (ACu/ATi + ACu ≈ 20%) favors the formation of rutile phase. Moreover, the Cu incorporation into TiO2 lattice induces band gap narrowing. Band structures and density of states have been analyzed based on density functional theory (DFT) and periodic models in order to investigate the influence of the Cu incorporation on the electronic structure of TiO2. Both experimental data and electronic structure calculations evidence the fact that the change in film structure from the anatase to the rutile phase can be ascribed to the possible incorporation of Cu1+ in the sites previously occupied by Ti4+, and the presence of Cu results in important effect on the electronic states, which is mainly related to the 3d Cu orbitals in the gap and in the vicinity of the valence band edges for TiO2.

  17. Adsorption and dissociation of NH3 on clean and hydroxylated TiO2 rutile (110) surfaces: a computational study.

    PubMed

    Chang, Jee-Gong; Chen, Hsin-Tsung; Ju, Shin-Pon; Chang, Ching-Sheng; Weng, Meng-Hsiung

    2011-04-30

    The adsorption and dissociation of NH(3) on the clean and hydroxylated TiO(2) rutile (110) surfaces have been investigated by the first-principles calculations. The monodentate adsorbates such as H(3)N-Ti(a), H(2)N-Ti(a), N-Ti(a), H(2)N-O(a), HN-O(a), N-O(a) and H-O(a), as well as the bidentate adsorbate, Ti-N-Ti(a) can be formed on the clean surface. It is found that the hydroxyl group enhances the adsorption of certain adsorbates on the five-fold-coordinated Ti atoms (5c-Ti), namely H(2)N-Ti(a), HN-Ti(a), N-Ti(a) and Ti-N-Ti(a). In addition, the adsorption energy increases as the number of hydroxyl groups increases. On the contrary, the opposite effect is found for those on the two-fold-coordinated O atoms (2c-O). The enhanced adsorption of NH(x) (x = 1-2) on the 5c-Ti is due to the large electronegativity of the OH group, increasing the acidity of the Ti center. This also contributes to diminish the adsorption of NH(x) (x = 1-2) on the two-fold-coordinated O atoms (2c-O) decreasing its basicity. According to potential energy profile, the NH(3) dissociation on the TiO(2) surface is endothermic and the hydroxyl group is found to lower the energetics of H(2)N-Ti(a)+H-O(a) and HN-Ti(a)+2{H-O(a)}, but slightly raise the energetic of Ti-N-Ti(a)+3{H-O(a)} compare to those on the clean surface. However, the dissociation of NH(3) is found to occur on the hydroxylated surface with an overall endothermic by 31.8 kcal/mol and requires a barrier of 37.5 kcal/mol. A comparison of NH(3) on anatase surface has been discussed. The detailed electronic analysis is also carried out to gain insights into the interaction nature between adsorbate and surface.

  18. Carbon as amorphous shell and interstitial dopant in mesoporous rutile TiO2: Bio-template assisted sol-gel synthesis and photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Mohamed, Mohamad Azuwa; Wan Salleh, Wan Norharyati; Jaafar, Juhana; Rosmi, Mohamad Saufi; Mohd. Hir, Zul Adlan; Abd Mutalib, Muhazri; Ismail, Ahmad Fauzi; Tanemura, Masaki

    2017-01-01

    Regenerated cellulose membrane was used as bio-template nanoreactor for the formation of rutile TiO2 mesoporous, as well as in-situ carbon dopant in acidified sol-gel system. The effects of calcination temperature on the physicochemical characteristic of core-shell nanostructured of bio-templated C-doped mesoporous TiO2 are highlighted in this study. By varying the calcination temperature, the thickness of the carbon shell coating on TiO2, crystallinity, surface area, and optical properties could be tuned as confirmed by HRTEM, nitrogen adsorption/desorption measurement, XRD and UV-vis-NIR spectroscopy. The results suggested that increment in the calcination temperature would lead to the band gap narrowing from 2.95 to 2.80 eV and the thickness of carbon shell increased from 0.40 to 1.20 nm. The x-ray photoelectron spectroscopy showed that the visible light absorption capability was mainly due to the incorporation of carbon dopant at interstitial position in the TiO2 to form Osbnd Tisbnd C or Tisbnd Osbnd C bond. In addition, the formation of the carbon core-shell nanostructured was due to carbonaceous layer grafted onto the surface of TiO2 via Tisbnd Osbnd C and Tisbnd OCO bonds. The result indicated that bio-templated C-doped core-shell mesoporous TiO2 prepared at 300 °C exhibited the highest photocatalytic activity. It is worthy to note that, the calcination temperature provided a huge impact towards improving the physicochemical and photocatalytic properties of the prepared bio-templated C-doped core-shell mesoporous TiO2.

  19. Moving into advanced nanomaterials. Toxicity of rutile TiO2 nanoparticles immobilized in nanokaolin nanocomposites on HepG2 cell line.

    PubMed

    Bessa, Maria João; Costa, Carla; Reinosa, Julian; Pereira, Cristiana; Fraga, Sónia; Fernández, José; Bañares, Miguel A; Teixeira, João Paulo

    2017-02-01

    Immobilization of nanoparticles on inorganic supports has been recently developed, resulting in the creation of nanocomposites. Concerning titanium dioxide nanoparticles (TiO2 NPs(1)), these have already been developed in conjugation with clays, but so far there are no available toxicological studies on these nanocomposites. The present work intended to evaluate the hepatic toxicity of nanocomposites (C-TiO2(2)), constituted by rutile TiO2 NPs immobilized in nanokaolin (NK(3)) clay, and its individual components. These nanomaterials were analysed by means of FE-SEM(4) and DLS(5) analysis for physicochemical characterization. HepG2 cells were exposed to rutile TiO2 NPs, NK clay and C-TiO2 nanocomposite, in the presence and absence of serum for different exposure periods. Possible interferences with the methodological procedures were determined for MTT,(6) neutral red uptake, alamar blue (AB), LDH,(7) and comet assays, for all studied nanomaterials. Results showed that MTT, AB and alkaline comet assay were suitable for toxicity analysis of the present materials after slight modifications to the protocol. Significant decreases in cell viability were observed after exposure to all studied nanomaterials. Furthermore, an increase in HepG2 DNA damage was observed after shorter periods of exposure in the absence of serum proteins and longer periods of exposure in their presence. Although the immobilization of nanoparticles in micron-sized supports could, in theory, decrease the toxicity of single nanoparticles, the selection of a suitable support is essential. The present results suggest that NK clay is not the appropriate substrate to decrease TiO2 NPs toxicity. Therefore, for future studies, it is critical to select a more appropriate substrate for the immobilization of TiO2 NPs.

  20. Tm-doped TiO2 and Tm2Ti2O7 pyrochlore nanoparticles: enhancing the photocatalytic activity of rutile with a pyrochlore phase

    PubMed Central

    De los Santos, Desiré M; Aguilar, Teresa; Sánchez-Coronilla, Antonio; Fernández-Lorenzo, Concha; Alcántara, Rodrigo; Piñero, Jose Carlos; Blanco, Ginesa; Martín-Calleja, Joaquín

    2015-01-01

    Summary Tm-doped TiO2 nanoparticles were synthesized using a water-controlled hydrolysis reaction. Analysis was performed in order to determine the influence of the dopant concentration and annealing temperature on the phase, crystallinity, and electronic and optical properties of the resulting material. Various characterization techniques were utilized such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and UV–vis spectroscopy. For the samples annealed at 773 and 973 K, anatase phase TiO2 was obtained, predominantly internally doped with Tm3+. ICP–AES showed that a doping concentration of up to 5.8 atom % was obtained without reducing the crystallinity of the samples. The presence of Tm3+ was confirmed by X-ray photoelectron spectroscopy and UV–vis spectroscopy: the incorporation of Tm3+ was confirmed by the generation of new absorption bands that could be assigned to Tm3+ transitions. Furthermore, when the samples were annealed at 1173 K, a pyrochlore phase (Tm2Ti2O7) mixed with TiO2 was obtained with a predominant rutile phase. The photodegradation of methylene blue showed that this pyrochlore phase enhanced the photocatalytic activity of the rutile phase. PMID:25821701

  1. A comparative study of optical absorption and photocatalytic properties of nanocrystalline single-phase anatase and rutile TiO2 doped with transition metal cations

    NASA Astrophysics Data System (ADS)

    Kernazhitsky, L.; Shymanovska, V.; Gavrilko, T.; Naumov, V.; Kshnyakin, V.; Khalyavka, T.

    2013-02-01

    The effect of nanocrystalline TiO2 doping with transition metal cations (Cu2+, Fe3+, Co2+, Cr3+) on their optical absorption and photocatalytic properties was investigated. The obtained metal-doped TiO2 samples were characterized by X-ray diffraction, scanning electron microscopy, and UV-vis absorption spectroscopy. It is shown that doping effect on anatase (A) and rutile (R) properties is quite different, being much stronger and complicated on A than on R. Contrary to doped R, doped A revealed a significant red shift of the absorption edge along with the band gap narrowing. Photocatalytic activity of anatase increases upon doping in the order: Arutile samples decreases upon doping in the series R>R/Co>R/Cu>R/Fe>R/Cr, indicating the inhibitory effect of impurity cations. This fact correlates with the decrease in the UV absorption of the doped rutile in the region of the Hg-lamp irradiation at 4.88 eV.

  2. Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile TiO2

    DOE PAGES

    Lan, Tian; Li, Chen W.; Hellman, O.; ...

    2015-08-11

    Although the rutile structure of TiO2 is stable at high temperatures, the conventional quasiharmonic approximation predicts that several acoustic phonons decrease anomalously to zero frequency with thermal expansion, incorrectly predicting a structural collapse at temperatures well below 1000 K. In this paper, inelastic neutron scattering was used to measure the temperature dependence of the phonon density of states (DOS) of rutile TiO2 from 300 to 1373 K. Surprisingly, these anomalous acoustic phonons were found to increase in frequency with temperature. First-principles calculations showed that with lattice expansion, the potentials for the anomalous acoustic phonons transform from quadratic to quartic, stabilizingmore » the rutile phase at high temperatures. In these modes, the vibrational displacements of adjacent Ti and O atoms cause variations in hybridization of 3d electrons of Ti and 2p electrons of O atoms. Finally, with thermal expansion, the energy variation in this “phonon-tracked hybridization” flattens the bottom of the interatomic potential well between Ti and O atoms, and induces a quarticity in the phonon potential.« less

  3. Growth and characterization of well-aligned densely-packed rutile TiO(2) nanocrystals on sapphire substrates via metal-organic chemical vapor deposition.

    PubMed

    Chen, C A; Chen, Y M; Korotcov, A; Huang, Y S; Tsai, D S; Tiong, K K

    2008-02-20

    Well-aligned densely-packed rutile TiO(2) nanocrystals (NCs) have been grown on sapphire (SA) (100) and (012) substrates via metal-organic chemical vapor deposition (MOCVD), using titanium-tetraisopropoxide (TTIP, Ti(OC(3)H(7))(4)) as a source reagent. The surface morphology as well as structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAED), x-ray diffraction (XRD) and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned NCs were grown on SA(100), whereas the NCs on the SA(012) were grown with a tilt angle of ∼33° from the normal to substrates. TEM and SAED measurements showed that the TiO(2) NCs on SA(100) with square cross section have their long axis directed along the [001] direction. The XRD results reveal TiO(2) NCs with either (002) orientation on SA(100) substrate or (101) orientation on SA(012) substrate. A strong substrate effect on the alignment of the growth of TiO(2) NCs has been demonstrated and the probable mechanism for the formation of these NCs has been discussed.

  4. High-permittivity metal-insulator-metal capacitors with TiO2 rutile dielectric and RuO2 bottom electrode

    NASA Astrophysics Data System (ADS)

    Hudec, B.; Husekova, K.; Dobrocka, E.; Lalinsky, T.; Aarik, J.; Aidla, A.; Frohlich, K.

    2010-02-01

    We describe properties of MIM capacitor structures with the RuO2 bottom electrode, TiO2 dielectric film and various top electrodes. The TiO2 films were grown by atomic layer deposition (ALD) at temperature 425 °C on metal organic chemical vapour deposited (MOCVD) RuO2 bottom electrodes grown at 300 °C. Due to local epitaxial growth on the RuO2 rutile structure, TiO2 films with the permittivity 135 and equivalent oxide thickness 0.58 nm were obtained. Capacitance density as high as 60 fF/μm2 was achieved. Au and Ni films for top electrodes were prepared by evaporation at room temperature. RuO2 films for top electrodes were grown by MOCVD. Strong effect of top electrode material on capacitance and leakage currents was observed. In addition, the stacks with TiO2 dielectric were found to be very sensitive to oxygen post-deposition treatment.

  5. Growth and characterization of well-aligned densely-packed rutile TiO2 nanocrystals on sapphire substrates via metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Chen, C. A.; Chen, Y. M.; Korotcov, A.; Huang, Y. S.; Tsai, D. S.; Tiong, K. K.

    2008-02-01

    Well-aligned densely-packed rutile TiO2 nanocrystals (NCs) have been grown on sapphire (SA) (100) and (012) substrates via metal-organic chemical vapor deposition (MOCVD), using titanium-tetraisopropoxide (TTIP, Ti(OC3H7)4) as a source reagent. The surface morphology as well as structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAED), x-ray diffraction (XRD) and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned NCs were grown on SA(100), whereas the NCs on the SA(012) were grown with a tilt angle of ~33° from the normal to substrates. TEM and SAED measurements showed that the TiO2 NCs on SA(100) with square cross section have their long axis directed along the [001] direction. The XRD results reveal TiO2 NCs with either (002) orientation on SA(100) substrate or (101) orientation on SA(012) substrate. A strong substrate effect on the alignment of the growth of TiO2 NCs has been demonstrated and the probable mechanism for the formation of these NCs has been discussed.

  6. Multiple step growth of single crystalline rutile nanorods with the assistance of self-assembled monolayer for dye sensitized solar cells.

    PubMed

    Yang, Mengjin; Neupane, Suman; Wang, Xuewen; He, Jin; Li, Wenzhi; Pala, Nezih

    2013-10-09

    A novel multiple step growth (MSG) process has been developed to synthesize rutile nanorods (NRs) on fluorine-doped tin oxide (FTO) glass with the assistance of a self-assembled monolayer (SAM) aiming to increase the internal surface area of the 1D materials for dye sensitized solar cell (DSSC) applications. The experimental result reveals that the SAM layer can be selectively decomposed at the tip of the nanorod, namely the rutile (001) surface, due to the anisotropic photocatalytic property of the rutile. The remaining SAM layer on the side-wall of the NRs remains intact and serves as water repellent which prevents the radial growth of the NRs during the next step hydrothermal synthesis; therefore, the spacing between the NRs and the porosity of the NR array can be retained after additional growth cycles. On the other hand, introduction of a middle layer formed via TiCl4 solution treatment before the next growth cycle is found to be an effective way to control the diameters of the newly grown NRs. The performance of DSSC made from the rutile NRs grown using the MSG technique has been examined, and it is significantly affected by the internal surfaces of the NRs. Furthermore, the MSG combined with NR etching treatment by acid at low temperature (150 °C) leads to a significant enhancement in the solar cell performance. The gigantic wettability difference of the NRs before and after the SAM treatment as well as the MSG method could be adapted to prepare superhydrophobic and superhydrophilic nanostructured patterns for other applications.

  7. Exceptional performance of photoelectrochemical water oxidation of single-crystal rutile TiO2 nanorods dependent on the hole trapping of modified chloride.

    PubMed

    Zhang, Xuliang; Cui, Haiqin; Humayun, Muhammad; Qu, Yang; Fan, Naiying; Sun, Xiaojun; Jing, Liqiang

    2016-02-24

    It is highly desired to effectively trap photogenerated holes for efficient photoelectrochemical (PEC) water oxidation to evolve O2 on oxide semiconductors. Herein, it is found for the first time mainly based on the time-resolved- and atmosphere-controlled- surface photovoltage responses that the modified chloride would effectively trap photogenerated holes so as to prolong the charge lifetime and hence promote charge separation of single-crystal rutile TiO2 nanorods. Its strong capacity to trap holes, comparable to the widely-used methanol and Co(II) phosphate, is well responsible for the exceptional photoactivities for PEC water oxidation to evolve O2 on rutile nanorods with a proper amount of chloride modified, about 2.5-time high as that on the resulting anatase nanoparticles, even 10-time if the surface area is considered. Moreover, it is suggested that the hole trapping role of chemically-adsorbed chloride is related to its lonely-pair electrons, and to the subsequently-produced intermediate Cl atoms with proper electronegativity for evolving O2. Interestingly, this finding is also applicable to the chloride-modified anatase TiO2. This work will provide a feasible strategy to design high-activity nanostructured semiconductor photoanodes for PEC water oxidation, even for overall water splitting.

  8. The unexpectedly rich reconstructions of rutile TiO2(011)-(2 × 1) surface and the driving forces behind their formation: an ab initio evolutionary study.

    PubMed

    Wang, Qinggao; Oganov, Artem R; Feya, Oleg D; Zhu, Qiang; Ma, Dongwei

    2016-07-20

    In this paper, we employ state-of-the-art theoretical approaches to elucidate the structures of the (011) surface of rutile (R-)TiO2. An unexpectedly rich chemistry has been uncovered. Titanyl-TiO2 and titanyl-Ti2O3 reconstructions can be used for rationalizing the experimental findings, matching the STM images and the changes in the band gap. From the viewpoint of thermodynamics, the predicted MF(111)-TiO reconstruction is more reasonable than the previously proposed MF(111)-TiO3 model, although there is a structural similarity. The richness of surface phases, the formation of which is driven by thermodynamic conditions and surface stress release, implies the multifunctionality of the R-TiO2(011) surface. After the clarification of TiO2(011) and TiO2(110) surface structures {PRL, 2014, 113, 266101} (the most important surfaces of rutile), the origin of the Brønsted acidity of R-TiO2, which has remained a mystery at the atomic level, can also be addressed in the near future.

  9. Exceptional performance of photoelectrochemical water oxidation of single-crystal rutile TiO2 nanorods dependent on the hole trapping of modified chloride

    NASA Astrophysics Data System (ADS)

    Zhang, Xuliang; Cui, Haiqin; Humayun, Muhammad; Qu, Yang; Fan, Naiying; Sun, Xiaojun; Jing, Liqiang

    2016-02-01

    It is highly desired to effectively trap photogenerated holes for efficient photoelectrochemical (PEC) water oxidation to evolve O2 on oxide semiconductors. Herein, it is found for the first time mainly based on the time-resolved- and atmosphere-controlled- surface photovoltage responses that the modified chloride would effectively trap photogenerated holes so as to prolong the charge lifetime and hence promote charge separation of single-crystal rutile TiO2 nanorods. Its strong capacity to trap holes, comparable to the widely-used methanol and Co(II) phosphate, is well responsible for the exceptional photoactivities for PEC water oxidation to evolve O2 on rutile nanorods with a proper amount of chloride modified, about 2.5-time high as that on the resulting anatase nanoparticles, even 10-time if the surface area is considered. Moreover, it is suggested that the hole trapping role of chemically-adsorbed chloride is related to its lonely-pair electrons, and to the subsequently-produced intermediate Cl atoms with proper electronegativity for evolving O2. Interestingly, this finding is also applicable to the chloride-modified anatase TiO2. This work will provide a feasible strategy to design high-activity nanostructured semiconductor photoanodes for PEC water oxidation, even for overall water splitting.

  10. Exceptional performance of photoelectrochemical water oxidation of single-crystal rutile TiO2 nanorods dependent on the hole trapping of modified chloride

    PubMed Central

    Zhang, Xuliang; Cui, Haiqin; Humayun, Muhammad; Qu, Yang; Fan, Naiying; Sun, Xiaojun; Jing, Liqiang

    2016-01-01

    It is highly desired to effectively trap photogenerated holes for efficient photoelectrochemical (PEC) water oxidation to evolve O2 on oxide semiconductors. Herein, it is found for the first time mainly based on the time-resolved- and atmosphere-controlled- surface photovoltage responses that the modified chloride would effectively trap photogenerated holes so as to prolong the charge lifetime and hence promote charge separation of single-crystal rutile TiO2 nanorods. Its strong capacity to trap holes, comparable to the widely-used methanol and Co(II) phosphate, is well responsible for the exceptional photoactivities for PEC water oxidation to evolve O2 on rutile nanorods with a proper amount of chloride modified, about 2.5-time high as that on the resulting anatase nanoparticles, even 10-time if the surface area is considered. Moreover, it is suggested that the hole trapping role of chemically-adsorbed chloride is related to its lonely-pair electrons, and to the subsequently-produced intermediate Cl atoms with proper electronegativity for evolving O2. Interestingly, this finding is also applicable to the chloride-modified anatase TiO2. This work will provide a feasible strategy to design high-activity nanostructured semiconductor photoanodes for PEC water oxidation, even for overall water splitting. PMID:26906953

  11. Correlation between bonding geometry and band gap states at organic-inorganic interfaces: catechol on rutile TiO2(110).

    PubMed

    Li, Shao-Chun; Wang, Jian-guo; Jacobson, Peter; Gong, X-Q; Selloni, Annabella; Diebold, Ulrike

    2009-01-28

    Adsorbate-induced band gap states in semiconductors are of particular interest due to the potential of increased light absorption and photoreactivity. A combined theoretical and experimental (STM, photoemission) study of the molecular-scale factors involved in the formation of gap states in TiO(2) is presented. Using the organic catechol on rutile TiO(2)(110) as a model system, it is found that the bonding geometry strongly affects the molecular electronic structure. At saturation catechol forms an ordered 4 x 1 overlayer. This structure is attributed to catechol adsorbed on rows of surface Ti atoms with the molecular plane tilted from the surface normal in an alternating fashion. In the computed lowest-energy structure, one of the two terminal OH groups at each catechol dissociates and the O binds to a surface Ti atom in a monodentate configuration, whereas the other OH group forms an H-bond to the next catechol neighbor. Through proton exchange with the surface, this structure can easily transform into one where both OH groups dissociate and the catechol is bound to two surface Ti in a bidentate configuration. Only bidendate catechol introduces states in the band gap of TiO(2).

  12. Insights into Acetone Photochemistry on Rutile TiO2(110). 1. Off-Normal CH3 Ejection from Acetone Diolate.

    SciTech Connect

    Petrik, Nikolay G.; Henderson, Michael A.; Kimmel, Gregory A.

    2015-06-04

    Thermal- and photon-stimulated reactions of acetone co-adsorbed with oxygen on rutile TiO2(110) surface are studied with infrared reflection-adsorption spectroscopy (IRAS) combined with temperature programmed desorption and angle-resolved photon stimulated desorption. IRAS results show that n2-acetone diolate ((CH3)2COO) is produced via thermally-activated reactions between the chemisorbed oxygen with co-adsorbed acetone. Formation of acetone diolate is also consistent with 18O / 16O isotopic exchange experiments. During UV irradiation at 30 K, CH3 radicals are ejected from the acetone diolate with a distribution that is peaked at .-. +- 66 degrees from the surface normal along the azimuth (i.e. perpendicular to the rows of bridging oxygen and Ti5c ions). This distribution is also consistent with the orientation of the C–CH3 bonds in the n2-acetone diolate on TiO2(110). The acetone diolate peaks disappear from the IRAS spectra after UV irradiation and new peaks are observed and associated with n2-acetate. The data presented here demonstrate direct signatures of the proposed earlier 2-step mechanism for acetone photooxidation on TiO2(110)

  13. The mechanism of emerging catalytic activity of gold nano-clusters on rutile TiO2(110) in CO oxidation reaction

    NASA Astrophysics Data System (ADS)

    Mitsuhara, K.; Tagami, M.; Matsuda, T.; Visikovskiy, A.; Takizawa, M.; Kido, Y.

    2012-03-01

    This paper reveals the fact that the O adatoms (Oad) adsorbed on the 5-fold Ti rows of rutile TiO2(110) react with CO to form CO2 at room temperature and the oxidation reaction is pronouncedly enhanced by Au nano-clusters deposited on the above O-rich TiO2(110) surfaces. The optimum activity is obtained for 2D clusters with a lateral size of ˜1.5 nm and two-atomic layer height corresponding to ˜50 Au atoms/cluster. This strong activity emerging is attributed to an electronic charge transfer from Au clusters to O-rich TiO2(110) supports observed clearly by work function measurement, which results in an interface dipole. The interface dipoles lower the potential barrier for dissociative O2 adsorption on the surface and also enhance the reaction of CO with the Oad atoms to form CO2 owing to the electric field of the interface dipoles, which generate an attractive force upon polar CO molecules and thus prolong the duration time on the Au nano-clusters. This electric field is screened by the valence electrons of Au clusters except near the perimeter interfaces, thereby the activity is diminished for three-dimensional clusters with a larger size.

  14. The mechanism of emerging catalytic activity of gold nano-clusters on rutile TiO2(110) in CO oxidation reaction.

    PubMed

    Mitsuhara, K; Tagami, M; Matsuda, T; Visikovskiy, A; Takizawa, M; Kido, Y

    2012-03-28

    This paper reveals the fact that the O adatoms (O(ad)) adsorbed on the 5-fold Ti rows of rutile TiO(2)(110) react with CO to form CO(2) at room temperature and the oxidation reaction is pronouncedly enhanced by Au nano-clusters deposited on the above O-rich TiO(2)(110) surfaces. The optimum activity is obtained for 2D clusters with a lateral size of ∼1.5 nm and two-atomic layer height corresponding to ∼50 Au atoms∕cluster. This strong activity emerging is attributed to an electronic charge transfer from Au clusters to O-rich TiO(2)(110) supports observed clearly by work function measurement, which results in an interface dipole. The interface dipoles lower the potential barrier for dissociative O(2) adsorption on the surface and also enhance the reaction of CO with the O(ad) atoms to form CO(2) owing to the electric field of the interface dipoles, which generate an attractive force upon polar CO molecules and thus prolong the duration time on the Au nano-clusters. This electric field is screened by the valence electrons of Au clusters except near the perimeter interfaces, thereby the activity is diminished for three-dimensional clusters with a larger size.

  15. Phosphate modified N/Si co-doped rutile TiO2 nanorods for photoelectrochemical water oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaofan; Zhang, Bingyan; Luo, Yanping; Lv, Xiaowei; Shen, Yan

    2017-01-01

    Surface modification of TiO2 film provides possibilities to improve photoelectrochemical (PEC) activity. In this study, we report on phosphate modified N/Si co-doped TiO2 nanorods films (Pi-N/Si-TiO2 NRs) for PEC water oxidation. Compared to the pristine TiO2 NRs, the Pi-N/Si-TiO2 NRs photoanode shows a 4.65-fold enhanced photocurrent density (1.44 mA cm-2) under light illumination. This significant improvement can be attributed to the synergistic effect of phosphate modification and the N and Si co-dopants. In addition to the improvement of ultraviolet and visible light response by N and Si co-dopants, phosphate modification is mainly responsible for charge transfer at the interface of the photoanode/electrolyte.

  16. Release of Phosphorous Impurity from TiO2 Anatase and Rutile Nanoparticles in Aquatic Environments and Its Implications

    EPA Science Inventory

    Phosphorus-bearing materials as an additive have been popularly used in nanomaterial synthesis and the residual phosphorus within the nanoparticles (NPs) can be of an environmental concern. For instance, phosphorus within pristine commercial TiO2 NPs greatly influences the surfac...

  17. Silicon Impurity Release and Surface Transformation of TiO2 Anatase and Rutile Nanoparticles in Water Environments

    EPA Science Inventory

    Surface transformation can affect the stability, reactivity, and toxicity of titanium dioxide (TiO2) nanoparticles (NPs) when released to water environments. Herein, we investigated the release kinetics of Si impurity frequently introduced during NP synthesis and the resulting ef...

  18. Effect of subsurface Ti-interstitials on the bonding of small gold clusters on rutile TiO(2)(110).

    PubMed

    Madsen, Georg K H; Hammer, Bjørk

    2009-01-28

    The density functional theory is used to examine the electronic structure of small Au clusters, supported on rutile TiO(2)(110) surfaces having subsurface Ti-interstitials. The interstitials reduce the surface and we find that negatively charged gold clusters are stabilized with respect to the stoichiometric surface. The behavior of the open-shell gold clusters can be rationalized in terms of the highest occupied molecular orbitals and the resulting electron affinities. The relative stabilities of closed-shell gold clusters led to recent disagreements in the literature. We show that they are very dependent on the density functional used. As expected, a redshift in the CO stretch vibration is calculated for CO adsorbed on a negatively charged cluster. Somewhat surprisingly a larger redshift is found for CO adsorbed on an overall positively charged Au(3) cluster. This is explained by CO being a local probe of the individual Au charges and one Au atom having an electron accumulation.

  19. Densely-packed ZnTPPs Monolayer on the Rutile TiO2(110)-(1×1) Surface: Adsorption Behavior and Energy Level Alignment.

    PubMed

    Rangan, Sylvie; Ruggieri, Charles; Bartynski, Robert; Martínez, José Ignacio; Flores, Fernando; Ortega, José

    2016-03-03

    The adsorption of a densely packed Zinc(II) tetraphenylporphyrin monolayer on a rutile TiO2(110)-(1×1) surface has been studied using a combination of experimental and theoretical methods, aimed at analyzing the relation between adsorption behavior and barrier height formation. The adsorption configuration of ZnTPP was determined from scanning tunnel microscopy (STM) imaging, density functional theory (DFT) calculations and STM image simulation. The corresponding energy alignment was experimentally determined from X-ray and UV-photoemission spectroscopies and inverse photoemission spectroscopy. These results were found in good agreement with an appropriately corrected DFT model, pointing to the importance of local bonding and intermolecular interactions in the establishment of barrier heights.

  20. Adsorption and stability of malonic acid on rutile TiO2 (110), studied by near edge X-ray absorption fine structure and photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Syres, Karen L.; Thomas, Andrew G.; Graham, Darren M.; Spencer, Ben F.; Flavell, Wendy R.; Jackman, Mark J.; Dhanak, Vinod R.

    2014-08-01

    The adsorption of malonic acid on rutile TiO2 (110) has been studied using photoelectron spectroscopy and C K-edge, near edge X-ray fine structure spectroscopy (NEXAFS). Analysis of the O 1s and Ti 2p spectra suggest that the molecule adsorbs dissociatively in a doubly-bidentate adsorption geometry as malonate. The data are unable to distinguish between a chelating bonding mode with the backbone of the molecule lying along the [001] azimuth or a bridging geometry along the direction. Work carried out on a wiggler beamline suggests that the molecule is unstable under irradiation by high-flux synchrotron radiation from this type of insertion device.

  1. Densely-packed ZnTPPs Monolayer on the Rutile TiO2(110)-(1×1) Surface: Adsorption Behavior and Energy Level Alignment

    PubMed Central

    Rangan, Sylvie; Ruggieri, Charles; Bartynski, Robert; Martínez, José Ignacio; Flores, Fernando; Ortega, José

    2016-01-01

    The adsorption of a densely packed Zinc(II) tetraphenylporphyrin monolayer on a rutile TiO2(110)-(1×1) surface has been studied using a combination of experimental and theoretical methods, aimed at analyzing the relation between adsorption behavior and barrier height formation. The adsorption configuration of ZnTPP was determined from scanning tunnel microscopy (STM) imaging, density functional theory (DFT) calculations and STM image simulation. The corresponding energy alignment was experimentally determined from X-ray and UV-photoemission spectroscopies and inverse photoemission spectroscopy. These results were found in good agreement with an appropriately corrected DFT model, pointing to the importance of local bonding and intermolecular interactions in the establishment of barrier heights. PMID:26998188

  2. Distinct Effects of Humic Acid on Transport and Retention of TiO2 Rutile Nanoparticles in Saturated Sand Columns

    EPA Science Inventory

    The distinct effects of humic acid (HA, 0−10 mg L−1) on the transport of titanium dioxide (rutile) nanoparticles (nTiO2) through saturated sand columns were observed under conditions of environmental relevance (ionic strength 3−200 mM NaCl, pH 5.7 and 9.0). Specifically, the tra...

  3. Distinct Effects of Humic Acid on Transport and Retention of TiO2 Rutile Nanoparticles in Saturated Sand Column

    EPA Science Inventory

    Distinct effects of humic acid (HA, 0 – 10 mg L-1) on the transport of titanium dioxide (rutile) nanoparticles (nTiO2) through saturated sand columns were observed under conditions of environmental relevance (ionic strength 3 – 200 mM NaCl, pH 5.7 and 9.0). Specifical...

  4. Covalent O-H bonds as electron traps in proton-rich rutile TiO2 nanoparticles.

    PubMed

    Zhang, Jing; Steigerwald, Michael; Brus, Louis; Friesner, Richard A

    2014-01-01

    The cation in the electrolyte of the dye-sensitized solar cell (DSSC) has a profound effect on electron trapping and transport behavior in TiO2 nanocrystalline film; this is one of the important factors that determines the overall efficiency of DSSCs. Here, we present a quantum mechanical investigation on the structures and energetics of proton-induced electron trap states and the thermodynamical barrier heights for the ambipolar diffusion of proton/electron pair using a large cluster model for the computations. Our calculations indicate that protons react with TiO2 to form covalent O-H bonds. This is in contrast to the reaction of Li(+) with TiO2, in which case the alkali metal is more accurately described as a simple coordinating cation. The covalent O-H bonding leads both to deeper electron trap states and to significantly higher barriers for the diffusion of carriers. These results are qualitatively consistent with experimental observations, and they extend our understanding of the cation effect in DSSCs at an atomic level of detail.

  5. Direct Low-Temperature Growth of Single-Crystalline Anatase TiO2 Nanorod Arrays on Transparent Conducting Oxide Substrates for Use in PbS Quantum-Dot Solar Cells.

    PubMed

    Chung, Hyun Suk; Han, Gill Sang; Park, So Yeon; Shin, Hee-Won; Ahn, Tae Kyu; Jeong, Sohee; Cho, In Sun; Jung, Hyun Suk

    2015-05-20

    We report on the direct growth of anatase TiO2 nanorod arrays (A-NRs) on transparent conducting oxide (TCO) substrates that can be directly applied to various photovoltaic devices via a seed layer mediated epitaxial growth using a facile low-temperature hydrothermal method. We found that the crystallinity of the seed layer and the addition of an amine functional group play crucial roles in the A-NR growth process. The A-NRs exhibit a pure anatase phase with a high crystallinity and preferred growth orientation in the [001] direction. Importantly, for depleted heterojunction solar cells (TiO2/PbS), the A-NRs improve both electron transport and injection properties, thereby largely increasing the short-circuit current density and doubling their efficiency compared to TiO2 nanoparticle-based solar cells.

  6. Effect of Ar ion irradiation on the room temperature ferromagnetism of undoped and Cu-doped rutile TiO2 single crystals

    NASA Astrophysics Data System (ADS)

    Xu, Nan-Nan; Li, Gong-Ping; Lin, Qiao-Lu; Liu, Huan; Bao, Liang-Man

    2016-11-01

    Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO2 single crystals (SCs). To tune their magnetism, Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively. The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO2. Meanwhile, a new CuO-like species present in the sample was found to be dissolved after the post-irradiation. Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions, while these ions are directly involved in boosting the absorption in the visible region. Project supported by the National Natural Science Foundation of China (Grant No. 11575074), the Open Project of State Key laboratory of Crystal Material, Shandong University, China (Grant No. KF1311), the Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, China (Grant No. LZUMMM2012003), the Open Project of Key Laboratory of Beam Technology and Material Modification of Ministry of Education, Beijing Normal University, China (Grant No. 201204), and the Fundamental Research Funds for the Central Universities, China (Grant No. lzujbky-2015-240).

  7. The effect of oxygen vacancies on the binding interactions of NH3 with rutile TiO2(110) -1×1

    SciTech Connect

    Kim, Boseong; Li, Zhenjun; Kay, Bruce D.; Dohnalek, Zdenek; Kim, Yu Kwon

    2012-11-21

    A series of NH3 temperature-programmed desorption (TPD) spectra was taken after the NH3 dose at 70 K on rutile TiO2(110)-1×1 surfaces with the oxygen vacancy (VO) concentrations of ~0% (p-TiO2) and 5% (r-TiO2), respectively, to study the effect of VO’s on the desorption energy of NH3 as a function of the coverage, θ. Our results show that at zero coverage limit, the desorption energy of NH3 on r-TiO2 is 115 kJ/mol, which is 10 kJ/mol less than that on p-TiO2. The desorption energy from the Ti4+ sites decreases with increasing θ due to the repulsive NH3 - NH3 interactions and approaches ~ 55 kJ/mol upon the saturation of Ti4+ sites (θ = 1 monolayer, ML) on both p- and r-TiO2. The absolute saturation coverage is determined to be about 10% smaller on r-TiO2 than that on p-TiO2. Further, the trailing edges of the NH3 TPD spectra on the hydroxylated TiO2(110) (h-TiO2) appear to be the same as that on r-TiO2 while those on oxidized TiO2(110) (o-TiO2) shift to higher temperatures. We present the detailed analysis of the results and reconcile the observed differences based on the repulsive adsorbate-adsorbate interactions between neighboring NH3 molecules and the surface charge associated with the presence of VO’s. Besides NH3, no other reaction products are observed in the TPD spectra.

  8. Formation of surface nanostructures on rutile (TiO2): comparative study of low-energy cluster ion and high-energy monoatomic ion impact

    NASA Astrophysics Data System (ADS)

    Popok, V. N.; Jensen, J.; Vučković, S.; Mackova, A.; Trautmann, C.

    2009-10-01

    The formation of nanostructures on rutile (TiO2) surfaces formed after the implantation of kiloelectronvolt-energy Ar_n^+ cluster ions and megaelectronvolt- to gigaelectronvolt-energy multiply charged heavy ions (Iq+, Taq+ and Uq+) is studied. Despite the differences in stopping and energy transfer mechanisms between the kiloelectronvolt-energy cluster ions and megaelectronvolt-energy monoatomic ions, their impacts lead to a similar type of surface damage, namely craters. For the cluster ion implantation the craters are caused by the multiple-collision effect (dominated by nuclear stopping) and the high density of energy and momentum transferred to the target, while for the case of megaelectronvolt multiply charged ions the craters are probably formed due to the Coulomb explosion and fast energy transfer caused by the electronic stopping. At ion energies in the gigaelectronvolt range, nanosize protrusions, so-called hillocks, are observed on the surface. It is suggested that electronic stopping leads to the formation of continuous tracks and the transferred energy is high enough to melt the material along the whole projectile path. Elastic rebound of the tension between the molten and solid state phases leads to liquid flow, expansion and quenching of the melt, thus forming the hillocks. Atomic force microscopy measurements carried out under different environmental conditions (temperature and atmosphere) suggest that the damaged material at the nanosize impact spots has very different water affinity properties (higher hydrophilicity or water adsorption) compared with the non-irradiated rutile surface.

  9. Modification of the microstructure and electronic properties of rutile TiO2 thin films with 79 MeV Br ion irradiation

    NASA Astrophysics Data System (ADS)

    Rath, Haripriya; Dash, P.; Singh, U. P.; Avasthi, D. K.; Kanjilal, D.; Mishra, N. C.

    2015-12-01

    Modifications induced by 79 MeV Br ions in rutile titanium dioxide thin films, synthesized by dc magnetron sputtering are presented. Irradiations did not induce any new XRD peak corresponding to any other phase. The area and the width of the XRD peaks were considerably affected by irradiation, and peaks shifted to lower angles. But the samples retained their crystallinity at the highest fluence (1 × 1013 ions cm-2) of irradiation even though the electronic energy loss of 79 MeV Br ions far exceeds the reported threshold value for amorphization of rutile TiO2. Fitting of the fluence dependence of the XRD peak area to Poisson equation yielded the radius of ion tracks as 2.4 nm. Ion track radius obtained from the simulation based on the thermal spike model matches closely with that obtained from the fluence dependence of the area under XRD peaks. Williamson-Hall analysis of the XRD spectra indicated broadening and shifting of the peaks are a consequence of irradiation induced defect accumulation leading to microstrains, as was also indicated by Raman and UV-Visible absorption study.

  10. Low-frequency dielectric properties of intrinsic and Al-doped rutile TiO2 thin films grown by the atomic layer deposition technique

    NASA Astrophysics Data System (ADS)

    Kassmi, M.; Pointet, J.; Gonon, P.; Bsiesy, A.; Vallée, C.; Jomni, F.

    2016-06-01

    Dielectric spectroscopy is carried out for intrinsic and aluminum-doped TiO2 rutile films which are deposited on RuO2 by the atomic layer deposition technique. Capacitance and conductance are measured in the 0.1 Hz-100 kHz range, for ac electric fields up to 1 MVrms/cm. Intrinsic films have a much lower dielectric constant than rutile crystals. This is ascribed to the presence of oxygen vacancies which depress polarizability. When Al is substituted for Ti, the dielectric constant further decreases. By considering Al-induced modification of polarizability, a theoretical relationship between the dielectric constant and the Al concentration is proposed. Al doping drastically decreases the loss in the very low frequency part of the spectrum. However, Al doping has almost no effect on the loss at high frequencies. The effect of Al doping on loss is discussed through models of hopping transport implying intrinsic oxygen vacancies and Al related centers. When increasing the ac electric field in the MVrms/cm range, strong voltage non-linearities are evidenced in undoped films. The conductance increases exponentially with the ac field and the capacitance displays negative values (inductive behavior). Hopping barrier lowering is proposed to explain high-field effects. Finally, it is shown that Al doping strongly improves the high-field dielectric behavior.

  11. Alcohol Chemistry on Rutile TiO2(110): The Influence of Alkyl Substituents on Reactivity and Selectivity

    SciTech Connect

    Kim, Yu Kwon; Kay, Bruce D.; White, J. M.; Dohnalek, Zdenek

    2007-12-13

    Product yields and selectivities, based on ultra high vacuum temperature programmed desorption, are compared for ten C2 to C8 aliphatic alcohols dosed at 100 K on highly-ordered TiO2(110) with a 3.5 % concentration of surface oxygen vacancies. Dehydration to form an alkene and water typically dominates while two other channels, dehydrogenation to form aldehydes, and reformation of alcohol, make detectable contributions for primary alcohols. Depending on the alcohol there are two distinct dehydration pathways, one operative at low temperature (LT, 300 to 425 K) and the other at high temperature (HT, 480 to 650 K). The HT dehydration pathway is common, while the LT channel is not observed for tertiary butanol and 3- and 4-octanol. The observed trends are accounted for in terms of the inductive and steric effects of the alkyl substituents.

  12. Influence of hydroxyls on Pd atom mobility and clustering on rutile TiO(2)(011)-2 × 1.

    PubMed

    Addou, Rafik; Senftle, Thomas P; O'Connor, Nolan; Janik, Michael J; van Duin, Adri C T; Batzill, Matthias

    2014-06-24

    Understanding agglomeration of late transition metal atoms, such as Pd, on metal oxide supports, such as TiO2, is critical for designing heterogeneous catalysts as well as for controlling metal/oxide interfaces in general. One approach for reducing particle sintering is to modify the metal oxide surface with hydroxyls that decrease adatom mobility. We study by scanning tunneling microscopy experiments, density functional theory (DFT) calculations, and Monte Carlo (MC) computer simulations the atomistic processes of Pd sintering on a hydroxyl-modified TiO2(011)-2 × 1 surface. The formation of small 1-3 atom clusters that are stable at room temperature is achieved on the hydroxylated surface, while much larger clusters are formed under the same conditions on a hydroxyl-free surface. DFT shows that this is a consequence of stronger binding of Pd atoms adjacent to hydroxyls and increased surface diffusion barriers for Pd atoms on the hydroxylated surface. DFT, kinetic MC, and ReaxFF-based NVT-MC simulations show that Pd clusters larger than single Pd monomers can adsorb the hydrogen from the oxide surface and form Pd hydrides. This depletes the surface hydroxyl coverage, thus allowing Pd to more freely diffuse and agglomerate at room temperature. Experimentally, this causes a bimodal cluster size distribution with 1-3 atom clusters prevalent at low Pd coverage, while significantly larger clusters become dominant at higher Pd concentrations. This study demonstrates that hydroxylated oxide surfaces can significantly reduce Pd cluster sizes, thus enabling the preparation of surfaces populated with metal clusters composed of single to few atoms.

  13. Effect of 17β-estradiol on stability and mobility of TiO2 rutile nanoparticles.

    PubMed

    Lee, Jaewoong; Bartelt-Hunt, Shannon L; Li, Yusong; Morton, Martha

    2015-04-01

    Contaminants including titanium dioxide nanoparticles (n-TiO2), as well as organic wastewater contaminants (OWCs), have been detected in wastewater treatment plant effluents, however, no information is yet available on how OWCs may modify the surface properties of TiO2 nanoparticles, or influence their stability in water and subsequent mobility in porous media. In this study, 17β-estradiol (E2) was chosen as a representative OWC to investigate the interaction between OWCs and n-TiO2. Batch and kinetic sorption experiments and Fourier Transform Infrared (FTIR) Spectrometer measurements confirmed that E2 was quickly sorbed onto the surface of n-TiO2 aggregates in water. Aggregation experiments showed that the presence of E2 has a minor influence on the size of n-TiO2 aggregates under lower ionic strength conditions at natural pH. In high ionic strength solution, the presence of E2 led to an increased average hydrodynamic diameter and a wider distribution of n-TiO2 aggregate sizes. Interaction energy analyses indicated that steric repulsion likely contributed to the stability of the n-TiO2 suspension in the presence of E2. Mobility analysis based on the clean bed filtration theory indicated that the impact of E2 on the mobility of n-TiO2 in porous media is minimal in comparison to the influence of solution ionic strength.

  14. The Adsorption and Reactions of the Amino Acid Proline on Rutile TiO2(110) Surfaces

    SciTech Connect

    Fleming,G.; Adib, K.; Rodriquez, J.; Barteau, M.; White, J.; Idriss, H.

    2008-01-01

    The reaction of the amino acid dl-proline is studied over stoichiometric and Ar-ions sputtered (reduced) TiO2(1 1 0) single crystal surfaces by synchrotron High Resolution X-ray Photoelectron Spectroscopy (HRXPS). On the stoichiometric surface proline gives two different species at 300 K: dissociated and zwitterionic. Upon heating the zwitterionic structure is removed first from the surface followed by the dissociated form. The C1s signal for the COO function is found close to 288.5 eV for both forms while the N 1s for the dissociated form is found at 400.0 eV and that of the zwitterionic from close to 401.8 eV. From the attenuation of the Ti 2p signal the surface coverage was estimated less than 1/2 (about 0.35). This smaller coverage than dissociatively adsorbed carboxylic acids on this surface (usually close to 1/2), is attributed to lateral repulsion caused by the ring of adjacent proline molecules adsorbed on five-fold coordinated Ti cations along the [0 0 1] direction. On the reduced surface the amount of zwitterion structure is found two times higher than that on the stoichiometric surface, at 300 K, most likely due to the considerable decrease of the amount of surface oxygen available. The stability of the zwitterionic structure on this surface is however found similar to that found on the stoichiometric surface. In addition, evidence of oxidation of reduced Ti cations upon adsorption at 300 K is noticed and explained as breaking of the carbon-oxygen bond of a fraction of adsorbed proline. Variable temperature HRXPS has been collected and results indicated that proline is more stable on the reduced surface compared to the stoichiometric surface.

  15. H2O2-assisted photocatalysis on flower-like rutile TiO2 nanostructures: Rapid dye degradation and inactivation of bacteria

    NASA Astrophysics Data System (ADS)

    Kőrösi, László; Prato, Mirko; Scarpellini, Alice; Kovács, János; Dömötör, Dóra; Kovács, Tamás; Papp, Szilvia

    2016-03-01

    Hierarchically assembled flower-like rutile TiO2 (FLH-R-TiO2) nanostructures were successfully synthesized from TiCl4 at room temperature without the use of surfactants or templates. An initial sol-gel synthesis at room temperature allowed long-term hydrolysis and condensation of the precursors. The resulting FLH-R-TiO2 possessed relatively high crystallinity (85 wt%) and consisted of rod-shaped subunits assembling into cauliflower-like nanostructures. Hydrothermal evolution of FLH-R-TiO2 at different temperatures (150, 200 and 250 °C) was followed by means of X-ray diffraction, transmission and scanning electron microscopy. These FLH-R-TiO2 nanostructures were tested as photocatalysts under simulated daylight (full-spectrum lighting) in the degradation of methyl orange and in the inactivation of a multiresistant bacterium, Klebsiella pneumoniae. The effects of hydrothermal treatment on the structure, photocatalytic behavior and antibacterial activity of FLH-R-TiO2 are discussed.

  16. Adsorption of CO on the rutile TiO2(110) surface: a dispersion-corrected density functional theory study.

    PubMed

    Prates Ramalho, João P; Illas, Francesc; Gomes, José R B

    2017-01-18

    The geometry, energy and stretching frequency of carbon monoxide on the rutile TiO2(110) surface for coverages between 0.125 and 1.5 ML are investigated by means of density functional theory calculations. Four different approaches were considered, namely, the PBE exchange-correlation functional and the PBE-D2, vdW-DF and vdW-DF2 methods incorporating van der Waals dispersion interactions of different theoretical complexity and empiricism. It is found that upon the increase of the surface coverage, the adsorption becomes less favorable due to lateral destabilizing interactions between adsorbed molecules. The preferred geometry for CO changes from an upright configuration at 0.125 ML to tilted configurations at 1.5 ML and the tilting of the C-O axis from the surface normal increases with the increase of the surface coverage. At 1 ML, all computational approaches predict alternate tilted configurations which contradict the interpretation of recent experimental infrared reflection-absorption spectroscopic findings suggesting upright CO geometries. Encouragingly, a very good agreement between calculated and experimental shifts of the C-O stretching frequency of adsorbed CO at different coverages with respect to gaseous CO species was reached.

  17. Water adsorption on rutile TiO2(110) for applications in solar hydrogen production: A systematic hybrid-exchange density functional study

    NASA Astrophysics Data System (ADS)

    Patel, M.; Mallia, G.; Liborio, L.; Harrison, N. M.

    2012-07-01

    Periodic hybrid-exchange density functional theory calculations are used to predict the structure of water on the rutile TiO2(110) surface (Θ⩽ 1 ML), which is an important first step towards understanding the photocatalytic processes that occur in solar water splitting. A detailed model describing the water-water and water-surface interactions is developed by exploring thoroughly the adsorption energetics. The possible adsorption mode—molecular, dissociative, or mixed—and the binding energy are studied as a function of coverage and arrangement, thus separation, of adsorbed species. These dependencies (coverage and arrangement) have a significant influence on the nature of the interactions involved in the H2O-TiO2 system. The importance of both direct intermolecular and surface-mediated interactions between surface species is emphasized. Finally, to gain insight into the photooxidation of adsorbed species at the surface, the electronic structure of the predicted adsorbate-substrate geometries is analyzed in terms of total and projected density of states.

  18. Fe(II)Ti(IV)O3 mixed oxide monolayer at rutile TiO2(011): Structures and reactivities

    NASA Astrophysics Data System (ADS)

    Wen, Zhan-Hui; Halpegamage, Sandamali; Gong, Xue-Qing; Batzill, Matthias

    2016-11-01

    Mixed-metal oxide monolayer grown at an oxide support is of great potential in applications like heterogeneous catalysis. In this work, the experimentally obtained ordered mixed FeTiO3 oxide monolayer supported by rutile TiO2(011) surface has been carefully studied with density functional theory calculations. The genetic algorithm based optimization scheme has been employed to improve the searching capacity for possible structures, and a well ordered mixed Fe(II)Ti(IV)O3 monolayer oxide structure much more stable than the one proposed previously has been successfully located. The new surface structure consists of uniformly distributed Ti and Fe cations in the ratio of 2:1. The simulated Scanning Tunneling Microscopy image based on this model is well consistent with the experimental one. Our calculations have shown that the O vacancy formation energy is rather high at the surface. We have also studied the adsorption of O2 and CO at the exposed Fe sites on the surface as well as their reactions. The adsorption energies of O2 are generally higher than those of CO. The catalytic cycle of CO oxidation following an Eley-Rideal type mechanism has been located for CO to react with surface adsorbed O2 and O.

  19. Comparison of photovoltaic properties of TiO2 electrodes prepared with nanoparticles and nanorods.

    PubMed

    Nam, Sang-Hun; Ju, Dong-Woo; Boo, Jin-Hyo

    2014-12-01

    In this report, single crystalline rutile TiO2 nanoparticles and nanorods were synthesized via the hydrothermal method using titanium tetra-isopropoxide as a precursor then, these were coated on top of a fluorine-doped tin oxide (FTO) substrate by using a doctor blade and direct deposition, respectively. Consequently, TiO2 nanorods-based dye-sensitized solar cells (DSSC) exhibit a J(sc) of 3.37 mA/cm2, a V(oc) of 0.82 V and fill factor of 60.1% with an overall conversion efficiency of 1.66%. This result shows an increase of around 38% for current density and 35% for conversion efficiency. Also, with respect to the impedance data, TiO2 nanorods-based DSSCs had smaller semicircles than did the nanoparticles-based DSSCs. These results demonstrate that the nanorod structure can have fast electron transport and reduced charge recombination.

  20. Study of paramagnetic defect centers in as-grown and annealed TiO2 anatase and rutile nanoparticles by a variable-temperature X-band and high-frequency (236 GHz) EPR

    PubMed Central

    Misra, S.K.; Andronenko, S.I.; Tipikin, D.; Freed, J. H.; Somani, V.; Prakash, Om

    2016-01-01

    Detailed EPR investigations on as-grown and annealed TiO2 nanoparticles in the anatase and rutile phases were carried out at X-band (9.6 GHz) at 77, 120–300 K and at 236 GHz at 292 K. The analysis of EPR data for as-grown and annealed anatase and rutile samples revealed the presence of several paramagnetic centers: Ti3+, O−, adsorbed oxygen (O2−) and oxygen vacancies. On the other hand, in as-grown rutile samples, there were observed EPR lines due to adsorbed oxygen (O2−) and the Fe3+ ions in both Ti4+ substitutional positions, with and without coupling to an oxygen vacancy in the near neighborhood. Anatase nanoparticles were completely converted to rutile phase when annealed at 1000° C, exhibiting EPR spectra similar to those exhibited by the as-grown rutile nanoparticles. The high-frequency (236 GHz) EPR data on anatase and rutile samples, recorded in the region about g = 2.0 exhibit resolved EPR lines, due to O− and O2− ions enabling determination of their g-values with higher precision, as well as observation of hyperfine sextets due to Mn2+ and Mn4+ ions in anatase. PMID:27041794

  1. Polarizable Site Charge Model at Liquid/Solid Interfaces for Describing Surface Polarity: Application to Structure and Molecular Dynamics of Water/Rutile TiO2(110) Interface.

    PubMed

    Nakamura, Hisao; Ohto, Tatsuhiko; Nagata, Yuki

    2013-02-12

    We present a novel scheme to construct a polarizable force field for liquid/solid interfaces, which takes into account the effect of the surface polarity induced by liquid-solid interactions explicitly. We extend the charge response kernel (CRK) method for molecules to solid surfaces by introducing the surface CRK. The CRK parameters are systematically determined by the first-principles calculations in the slab model with the dipole-correction method. Our methodology is applied to the water/clean rutile TiO2(110) interface. Structures and induced charges of a single water molecule attached to the TiO2 surface optimized by our polarizable force field show good agreement with those predicted by the first-principles calculations. Further, we carried out MD simulations for the liquid water/TiO2 interface and found three stable structures of water attached to the TiO2 surface. Two of them are predicted by both the polarizable and the nonpolarizable force fields, while the polarizable force field model predicts a structure of water with the hydrogen and oxygen atoms interacting with the oxygen atom of the surface TiO2 and the hydrogen atom of the other water molecule, respectively, which was reported by the previous first-principles MD simulation. This indicates that the dipole moments of water and TiO2 induced by the water-TiO2 interactions have significant impact on molecular conformations of the water/TiO2 interface.

  2. Physical Mechanism Behind Enhanced Photoelectrochemical and Photocatalytic Properties of Superhydrophilic Assemblies of 3D-TiO2 Microspheres with Arrays of Oriented, Single-Crystalline TiO2 Nanowires as Building Blocks Deposited on Fluorine-Doped Tin Oxide.

    PubMed

    Sadhu, Subha; Gupta, Preeti; Poddar, Pankaj

    2017-03-29

    In comparison to the one-dimensional (1D) semiconductor nanostructures, the hierarchical, three-dimensional (3D) microstructures, composed of the arrays of 1D nanostructures as building blocks, show quite unique physicochemical properties due to efficient photon capture and enhanced surface to volume ratio, which aid in advancing the performance of various optoelectronic devices. In this contribution, we report the fabrication of surfactant-free, radially assembled, 3D titania (rutile-phase) microsphere arrays (3D-TMSAs) composed of bundles of single-crystalline titania nanowires (NWs) directly on fluorine-doped conducting oxide (FTO) substrates with tunable architecture. The effects of growth parameters on the morphology of the 3D-TMSAs have been studied thoroughly. The 3D-TMSAs grown on the FTO-substrate showed superior photon-harvesting owing to the increase in light-scattering. The photocatalytic and photon to electron conversion efficiency of dye-sensitized solar cells (DSSC), where the optimized 3D-TMSAs were used as an anode, showed around 44% increase in the photoconversion efficiency compared to that of Degussa P-25 as a result of the synergistic effect of higher surface area and enhanced photon scattering probability. The TMSA film showed superhydrophilicity without any prior UV irradiation. In addition, the presence of bundles of almost parallel NWs led to the formation of arrays of microcapacitors, which showed stable dielectric performance. The fabrication of single-crystalline, oriented, self-assembled TMSAs with bundles of titania nanowires as their building blocks deposited on transparent conducting oxide (TCO) substrates has vast potential in the area of photoelectrochemical research.

  3. Electrodeposited Ag nanoparticles on TiO2 nanorods for enhanced UV visible light photoreduction CO2 to CH4

    NASA Astrophysics Data System (ADS)

    Kong, Dan; Tan, Jeannie Ziang Yie; Yang, Fei; Zeng, Jieliang; Zhang, Xiwen

    2013-07-01

    We employed the double-potentiostatic methodology to electrodeposit Ag nanoparticles on oriented single-crystalline rutile TiO2 nanorods synthesized by hydrothermal method. The synthesized composites were used as the photocatalyst to reduce CO2 to CH4 under UV irradiation, and tested by SEM, XRD, TEM, XPS, UV-vis and photoluminescence. Deposition with Ag nanoparticles was observed to enhance the photocatalytic activity (≈1.5-2.64 μmol (gcatal h)-1) up to 5 times with respect to undecorated TiO2 nanorods (≈0.5 μmol (gcatal h)-1). The increase in the CH4 yield was correlated with the surface morphology and structure of TiO2 nanorods.

  4. Single crystalline magnetite nanotubes.

    PubMed

    Liu, Zuqin; Zhang, Daihua; Han, Song; Li, Chao; Lei, Bo; Lu, Weigang; Fang, Jiye; Zhou, Chongwu

    2005-01-12

    We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inner cores of MgO/Fe3O4 core-shell nanowires. Homogeneous Fe3O4 nanotubes with controllable length, diameter, and wall thickness have been obtained. Resistivity of the Fe3O4 nanotubes was estimated to be approximately 4 x 10-2 Omega cm at room temperature. Magnetoresistance of approximately 1% was observed at T = 77 K when a magnetic field of B = 0.7 T was applied. The synthetic strategy presented here may be extended to a variety of materials such as YBCO, PZT, and LCMO which should provide ideal candidates for fundamental studies of superconductivity, piezoelectricity, and ferromagnetism in nanoscale structures.

  5. O2 evolution on a clean partially reduced rutile TiO2(110) surface and on the same surface precovered with Au1 and Au2: the importance of spin conservation.

    PubMed

    Chrétien, Steeve; Metiu, Horia

    2008-08-21

    We have used spin-polarized density functional theory (DFT) to study O(2) evolution on a clean partially reduced rutile TiO(2)(110) surface (i.e., a surface having oxygen vacancies) and its interaction with Au(1) or Au(2) cluster adsorbed on it. We assume that the total spin of the electronic wave function is related to the number of unpaired spins (N(s)) and calculate the binding and the activation energies involved in O(2) evolution for fixed values of N(s). In addition to keeping N(s) constant, we assume that reactions in which the N(s) of the reactants differs from that of the products are very slow. The potential energy surfaces obtained in this way depend strongly on N(s). For example, O(2) dissociation at the vacancy site on a clean partially reduced TiO(2)(110) surface is exothermic by 0.85 eV in the triplet state and the highest activation energy in the chain of reactions leading to the O(2) dissociation is 0.67 eV. In the singlet state, O(2) dissociation is endothermic by 0.11 eV and the activation energy leading to dissociation is 1.30 eV. These observations are in qualitative agreement with scanning tunneling microscopy experiment in which O(2) dissociation on a partially reduced rutile TiO(2)(110) surface is observed at temperature as low as 120 K. In contrast, O(2) dissociation is predicted to be endothermic and is prevented by an activation barrier larger than 1 eV in all the previous DFT calculations, in which the DFT program varies N(s) to get the lowest energy state. We find that on a partially reduced rutile TiO(2)(110) with Au(1) and Au(2) preadsorbed on its surface, O(2) dissociates at the vacancy site: One oxygen atom fills the oxygen vacancy and the other becomes available for oxidation chemistry. This means that Au(1) and Au(2) supported on a partially reduced TiO(2)(110) surface is not an oxidation catalyst since the presence of oxygen turns it into a stoichiometric Au(n)/TiO(2)(110) surface. Finally, we find that the evolution of oxygen on

  6. Quasi-intrinsic colossal permittivity in Nb and In co-doped rutile TiO2 nanoceramics synthesized through a oxalate chemical-solution route combined with spark plasma sintering.

    PubMed

    Han, HyukSu; Dufour, Pascal; Mhin, Sungwook; Ryu, Jeong Ho; Tenailleau, Christophe; Guillemet-Fritsch, Sophie

    2015-07-14

    Nb and In co-doped rutile TiO2 nanoceramics (n-NITO) were successfully synthesized through a chemical-solution route combined with a low temperature spark plasma sintering (SPS) technique. The particle morphology and the microstructure of n-NITO compounds were nanometric in size. Various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG)/differential thermal analysis (DTA), Fourier transform infrared (FTIR), and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compound. The results indicated that the as-synthesized n-NITO oxalate as well as sintered ceramic have a co-doped single phase of titanyl oxalate and rutile TiO2, respectively. Broadband impedance spectroscopy revealed that novel colossal permittivity (CP) was achieved in n-NITO ceramics exhibiting excellent temperature-frequency stable CP (up to 10(4)) as well as low dielectric loss (∼5%). Most importantly, detailed impedance data analyses of n-NITO compared to microcrystalline NITO (μ-NITO) demonstrated that the origin of CP in NITO bulk nanoceramics might be related with the pinned electrons in defect clusters and not to extrinsic interfacial effects.

  7. Effect of gas flow rates on the anatase-rutile transformation temperature of nanocrystalline TiO2 synthesised by chemical vapour synthesis.

    PubMed

    Ahmad, Md Imteyaz; Bhattacharya, S S; Fasel, Claudia; Hahn, Horst

    2009-09-01

    Of the three crystallographic allotropes of nanocrystalline titania (rutile, anatase and brookite), anatase exhibits the greatest potential for a variety of applications, especially in the area of catalysis and sensors. However, with rutile being thermodynamically the most stable phase, anatase tends to transform into rutile on heating to temperatures in the range of 500 degrees C to 700 degrees C. Efforts made to stabilize the anatase phase at higher temperatures by doping with metal oxides suffer from the problems of having a large amorphous content on synthesis as well as the formation of secondary impurity phases on doping. Recent studies have suggested that the as-synthesised phase composition, crystallite size, initial surface area and processing conditions greatly influence the anatase to rutile transformation temperature. In this study nanocrystalline titania was synthesised in the anatase form bya chemical vapour synthesis (CVS) method using titanium tetra iso-propoxide (TTIP) as a precursor under varying flow rates of oxygen and helium. The anatase to rutile transformation was studied using high temperature X-ray diffraction (HTXRD) and simultaneous thermogravimetric analysis (STA), followed by transmission electron microscopy (TEM). It was demonstrated that the anatase-rutile transformation temperatures were dependent on the oxygen to helium flow rate ratio during CVS and the results are presented and discussed.

  8. A DFT+U study of acetylene selective hydrogenation on oxygen defective anatase (101) and rutile (110) TiO2 supported Pd4 cluster

    NASA Astrophysics Data System (ADS)

    Yang, Jie; Lv, Cun-Qin; Guo, Yong; Wang, Gui-Chang

    2012-03-01

    The reaction mechanisms for selective acetylene hydrogenation on three different supports, Pd4 cluster, oxygen defective anatase (101), and rutile (110) titania supported Pd4, cluster are studied using the density functional theory calculations with a Hubbard U correction (DFT+U). The present calculations show that the defect anatase support binds Pd4 cluster more strongly than that of rutile titania due to the existence of Ti3+ in anatase titania. Consequently, the binding energies of adsorbed species such as acetylene and ethylene on Pd4 cluster become weaker on anatase supported catalysts compared to the rutile supported Pd4 cluster. Anatase catalyst has higher selectivity of acetylene hydrogenation than rutile catalyst. On the one hand, the activation energies of ethylene formation are similar on the two catalysts, while they vary a lot on ethyl formation. The rutile supported Pd catalyst with lower activation energy is preferable for further hydrogenation. On the other hand, the relatively weak adsorption energy of ethylene is gained on anatase surface, which means it is easier for ethylene desorption, hence getting higher selectivity. For further understanding, the energy decomposition method and micro-kinetic analysis are also introduced.

  9. Preparation of Highly Crystalline TiO(2) Nanostructures by Acid-assisted Hydrothermal Treatment of Hexagonal-structured Nanocrystalline Titania/Cetyltrimethyammonium Bromide Nanoskeleton.

    PubMed

    Dai, Shuxi; Wu, Yanqiang; Sakai, Toshio; Du, Zuliang; Sakai, Hideki; Abe, Masahiko

    2010-08-11

    Highly crystalline TiO(2) nanostructures were prepared through a facile inorganic acid-assisted hydrothermal treatment of hexagonal-structured assemblies of nanocrystalline titiania templated by cetyltrimethylammonium bromide (Hex-ncTiO(2)/CTAB Nanoskeleton) as starting materials. All samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of hydrochloric acid concentration on the morphology, crystalline and the formation of the nanostructures were investigated. We found that the morphology and crystalline phase strongly depended on the hydrochloric acid concentrations. More importantly, crystalline phase was closely related to the morphology of TiO(2) nanostructure. Nanoparticles were polycrystalline anatase phase, and aligned nanorods were single crystalline rutile phase. Possible formation mechanisms of TiO(2) nanostructures with various crystalline phases and morphologies were proposed.

  10. Preparation of Highly Crystalline TiO2 Nanostructures by Acid-assisted Hydrothermal Treatment of Hexagonal-structured Nanocrystalline Titania/Cetyltrimethyammonium Bromide Nanoskeleton

    PubMed Central

    2010-01-01

    Highly crystalline TiO2 nanostructures were prepared through a facile inorganic acid-assisted hydrothermal treatment of hexagonal-structured assemblies of nanocrystalline titiania templated by cetyltrimethylammonium bromide (Hex-ncTiO2/CTAB Nanoskeleton) as starting materials. All samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of hydrochloric acid concentration on the morphology, crystalline and the formation of the nanostructures were investigated. We found that the morphology and crystalline phase strongly depended on the hydrochloric acid concentrations. More importantly, crystalline phase was closely related to the morphology of TiO2 nanostructure. Nanoparticles were polycrystalline anatase phase, and aligned nanorods were single crystalline rutile phase. Possible formation mechanisms of TiO2 nanostructures with various crystalline phases and morphologies were proposed. PMID:21124640

  11. Electron transport and recombination in dye-sensitized solar cells made from single-crystal rutile TiO2 nanowires.

    PubMed

    Enache-Pommer, Emil; Liu, Bin; Aydil, Eray S

    2009-11-14

    Contrary to expectations, the electron transport rate in dye-sensitized solar cells made from single-crystal rutile titanium dioxide nanowires is found to be similar to that measured in dye-sensitized solar cells made from titanium dioxide nanoparticles.

  12. Comparison of the Activity and the Stability in CO Oxidation of Au-Cu Catalysts Supported on TiO2 in Anatase or Rutile Phase.

    PubMed

    Zanella, Rodolfo; Bokhimi, Xim; Maturano, Viridiana; Morales, Antonio

    2015-09-01

    Au-Cu catalysts supported on anatase or rutile phases were prepared by deposition-precipitation method. The titania polymorph used as the support determined the catalytic behavior. For the Au-Cu/rutile catalysts, the metallic phase had smaller dimensions than for the Au-Cu/anatase catalysts. The catalysts supported on anatase, however, were more active and stable than those supported on rutile. A systematic study of the catalytic activity for CO oxidation as a function of the temperature of activation and the aging time was performed. The catalytic properties were correlated with the properties of the catalysts analyzed with X-ray powder diffraction, refinement of the crystalline structures with the Rietveld method, and transmission electron microscopy. When the support was anatase, a pretreatment at 400 degrees C in air led to the most active catalysts, whereas when the support was rutile, a pretreatment between 200 and 300 degrees C in air led to the most active catalysts; activation under hydrogen generated less active catalysts. The Au-Cu catalysts activated in air were more active for the oxidation of CO than the respective monometallic gold catalysts, indicating a promoting effect between gold and copper to catalyze this reaction.

  13. Synergistic manipulation of micro-nanostructures and composition: anatase/rutile mixed-phase TiO2 hollow micro-nanospheres with hierarchical mesopores for photovoltaic and photocatalytic applications.

    PubMed

    Zhu, Qing; Qian, Jieshu; Pan, Hao; Tu, Luo; Zhou, Xingfu

    2011-09-30

    The construction of nanocrystals with controllable composition and desirable micro-nanostructures is a well-known challenge. A combination of favorable composition and optimized micro-nanostructures can enhance the performance of a material significantly. Using TiO(2) as an example, we demonstrate here a facile approach to prepare anatase/rutile mixed-phase TiO(2) hollow micro-nanospheres with hierarchical mesopores. Our strategy relies on polymer-assisted assembly of ∼ 5 nm nano-building blocks into three-dimensional hierarchical hollow micro-nanospheres in a mixed alcohol-water solution. This superior micro-nanostructure endows the sample with hierarchical mesopores and a high surface area of 106 m(2) g(-1). We also show that, due to the synergetic effects of the mixed-phase composition and the micro-nanostructures, the sample exhibited significantly improved photovoltaic performance and similar photocatalytic performance compared with the commercial Degussa P25. These results suggested that our sample has great potential for future photovoltaic and photocatalytic applications.

  14. High efficiency solid-state sensitized solar cell-based on submicrometer rutile TiO2 nanorod and CH3NH3PbI3 perovskite sensitizer.

    PubMed

    Kim, Hui-Seon; Lee, Jin-Wook; Yantara, Natalia; Boix, Pablo P; Kulkarni, Sneha A; Mhaisalkar, Subodh; Grätzel, Michael; Park, Nam-Gyu

    2013-06-12

    We report a highly efficient solar cell based on a submicrometer (~0.6 μm) rutile TiO2 nanorod sensitized with CH3NH3PbI3 perovskite nanodots. Rutile nanorods were grown hydrothermally and their lengths were varied through the control of the reaction time. Infiltration of spiro-MeOTAD hole transport material into the perovskite-sensitized nanorod films demonstrated photocurrent density of 15.6 mA/cm(2), voltage of 955 mV, and fill factor of 0.63, leading to a power conversion efficiency (PCE) of 9.4% under the simulated AM 1.5G one sun illumination. Photovoltaic performance was significantly dependent on the length of the nanorods, where both photocurrent and voltage decreased with increasing nanorod lengths. A continuous drop of voltage with increasing nanorod length correlated with charge generation efficiency rather than recombination kinetics with impedance spectroscopic characterization displaying similar recombination regardless of the nanorod length.

  15. A method for the concentration of fine-grained rutile (TiO2) from sediment and sedimentary rocks by chemical leaching

    USGS Publications Warehouse

    Commeau, Judith A.; Valentine, Page C.

    1991-01-01

    Most of the sample analyzed by the method described were marine muds collected from the Gulf of Maine (Valentine and Commeau, 1990). The silt and clay fraction (up to 99 wt% of the sediment) is composed of clay minerals (chiefly illite-mica and chlorite), silt-size quartz and feldspar, and small crystals (2-12 um) of rutile and hematite. The bulk sediment samples contained an average of 2 to 3 wt percent CaCO3. Tiher samples analyzed include red and gray Carboniferous and Triassic sandstones and siltstones exposed around the Bay of Fundy region and Paleozoic sandstones, siltstones, and shales from northern Maine and New Brunswick. These rocks are probable sources for the fine-grained rutile found in the Gulf of Maine.

  16. Structural characterization of mineral with rutile inclusions (TiO2) and manganocolumbite (MnNb2O6) by means of X-ray

    NASA Astrophysics Data System (ADS)

    Arcila, J. F.; Hincapié, A. F.

    2013-11-01

    A sample of mineral obtained in the department of Vichada was characterized by the technique of X-ray diffraction in powder samples, in order to determine the crystallographic phases present. After analyzing diffraction patterns, as a result, the mineral had inclusions of Rutile (86.3%) and Manganocolumbita (13.7%). Next, a simulation of the crystal structure of these minerals from the data entered in the databases was carried on. Later, the Rietveld method was used, from this refinement, the new diffraction pattern and the new network parameters were obtained. For the Rutile it was obtained a tetragonal structure, and for the Manganocolumbita an orthorhombic structure was obtained. The characterization is justified among other aspects due to the important applications of these materials in industry and technology, such as Rutile is used in welding rod coatings, in Industries cardboard paper and ink impression among many other uses, the Manganocolumbita is used in special alloys resistant to high temperatures, it also is directly related to the tantalite in coltan formation.

  17. Hydrogen-Treated Rutile TiO2 Shell in Graphite-Core Structure as a Negative Electrode for High-Performance Vanadium Redox Flow Batteries.

    PubMed

    Vázquez-Galván, Javier; Flox, Cristina; Fàbrega, Cristian; Ventosa, Edgar; Parra, Andres; Andreu, Teresa; Morante, Joan Ramón

    2017-03-01

    Hydrogen-treated TiO2 as an electrocatalyst has shown to boost the capacity of high-performance all-vanadium redox flow batteries (VRFBs) as a simple and eco-friendly strategy. The graphite felt-based GF@TiO2 :H electrode is able to inhibit the hydrogen evolution reaction (HER), which is a critical barrier for operating at high rate for long-term cycling in VRFBs. Significant improvements in charge/discharge and electron-transfer processes for the V(3+) /V(2+) reaction on the surface of reduced TiO2 were achieved as a consequence of the formation of oxygen functional groups and oxygen vacancies in the lattice structure. Key performance indicators of VRFB have been improved, such as high capability rates and electrolyte-utilization ratios (82 % at 200 mA cm(-2) ). Additionally, high coulombic efficiencies (ca. 100 % up to the 96th cycle, afterwards >97 %) were obtained, demonstrating the feasibility of achieving long-term stability.

  18. Solid state perovskite solar modules by vacuum-vapor assisted sequential deposition on Nd:YVO4 laser patterned rutile TiO2 nanorods

    NASA Astrophysics Data System (ADS)

    Fakharuddin, Azhar; Palma, Alessandro L.; Di Giacomo, Francesco; Casaluci, Simone; Matteocci, Fabio; Wali, Qamar; Rauf, Muhammad; Di Carlo, Aldo; Brown, Thomas M.; Jose, Rajan

    2015-12-01

    The past few years have witnessed remarkable progress in solution-processed methylammonium lead halide (CH3NH3PbX3, X = halide) perovskite solar cells (PSCs) with reported photoconversion efficiency (η) exceeding 20% in laboratory-scale devices and reaching up to 13% in their large area perovskite solar modules (PSMs). These devices mostly employ mesoporous TiO2 nanoparticles (NPs) as an electron transport layer (ETL) which provides a scaffold on which the perovskite semiconductor can grow. However, limitations exist which are due to trap-limited electron transport and non-complete pore filling. Herein, we have employed TiO2 nanorods (NRs), a material offering a two-fold higher electronic mobility and higher pore-filing compared to their particle analogues, as an ETL. A crucial issue in NRs’ patterning over substrates is resolved by using precise Nd:YVO4 laser ablation, and a champion device with η ∼ 8.1% is reported via a simple and low cost vacuum-vapor assisted sequential processing (V-VASP) of a CH3NH3PbI3 film. Our experiments showed a successful demonstration of NRs-based PSMs via the V-VASP technique which can be applied to fabricate large area modules with a pin-hole free, smooth and dense perovskite layer which is required to build high efficiency devices.

  19. In situ study of photo- and thermo-induced color centers in photochromic rutile TiO2 in the temperature range 90-720 K.

    PubMed

    Kuznetsov, V N; Glazkova, N I; Mikhaylov, R V; Serpone, N

    2016-10-05

    This article reports an in situ UV-Vis-NIR diffuse reflectance (DR) spectroscopic and kinetic study of the photoformation and thermal annealing of light absorbing electronic point defects (color centers) in photochromic TiO2 in the temperature range 90-720 K using a simple laboratory-made cryostat-type accessory (for a Cary 5000 spectrophotometer equipped with an integrating sphere). The accessory also allowed for UV-Vis-NIR DR studies to be undertaken either in vacuum or in an oxygen atmosphere at significantly high temperatures (to 720 K) to assess dark chemical events occurring in photochromic titania with the participation of color centers. The DR spectral and kinetic measurements provided the opportunity to examine the separation of photoinduced charge carriers at traps and thermally stimulated carrier detrapping and recombination, as well as the response of color centers to oxidative/reductive treatments of photochromic TiO2. Kinetic results also demonstrate the applicability of the fabricated DR accessory as a high-temperature reaction cell in the systematic study of the principal regularities in the formation and destruction of color centers in titania at various temperatures and gaseous atmospheres.

  20. Single crystalline mesoporous silicon nanowires.

    PubMed

    Hochbaum, Allon I; Gargas, Daniel; Hwang, Yun Jeong; Yang, Peidong

    2009-10-01

    Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. These porous nanowires also retain the crystallographic orientation of the wafer from which they are etched. Electron microscopy and diffraction confirm their single-crystallinity and reveal the silicon surrounding the pores is as thin as several nanometers. Confocal fluorescence microscopy showed that the photoluminescence (PL) of these arrays emanate from the nanowires themselves, and their PL spectrum suggests that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices.

  1. Single crystalline mesoporous silicon nanowires

    SciTech Connect

    Hochbaum, A.I.; Gargas, Daniel; Jeong Hwang, Yun; Yang, Peidong

    2009-08-04

    Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. These porous nanowires also retain the crystallographic orientation of the wafer from which they are etched. Electron microscopy and diffraction confirm their single-crystallinity and reveal the silicon surrounding the pores is as thin as several nanometers. Confocal fluorescence microscopy showed that the photoluminescence (PL) of these arrays emanate from the nanowires themselves, and their PL spectrum suggests that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices.

  2. Adsorption sites of single noble metal atoms on the rutile TiO2 (1 1 0) surface influenced by different surface oxygen vacancies.

    PubMed

    Matsunaga, Katsuyuki; Chang, Teng-Yuan; Ishikawa, Ryo; Dong, Qian; Toyoura, Kazuaki; Nakamura, Atsutomo; Ikuhara, Yuichi; Shibata, Naoya

    2016-05-05

    Atomic adsorption of Au and Pt on the rutile (1 1 0) surface was investigated by atomic-resolution aberration-corrected scanning transmission electron microscopy (STEM) measurements combined with density functional theory calculations. Au single atoms were deposited on the surface in a vacuum condition, and the observed results were compared with Pt single atoms on the same surface prepared by the same experimental manner. It was found that Au single atoms are stably adsorbed only at the bridging oxygen vacancy sites, which is quite different from Pt single atoms exhibiting the most frequently observed adsorption at the basal oxygen vacancy sites. Such a difference in oxygen-vacancy effect between Au and Pt can be explained by electronic structures of the surface vacancies as well as characters of outermost atomic orbitals of Au and Pt.

  3. Reverse micelles directed synthesis of TiO2-CeO2 mixed oxides and investigation of their crystal structure and morphology

    NASA Astrophysics Data System (ADS)

    Matějová, Lenka; Valeš, Václav; Fajgar, Radek; Matěj, Zdeněk; Holý, Václav; Šolcová, Olga

    2013-02-01

    The synthesis of TiO2-CeO2 mixed oxides based on the sol-gel process controlled within reverse micelles of non-ionic surfactant Triton X-114 in cyclohexane is reported. The crystallization, phase composition, trends in nanoparticles growth and porous structure properties are studied as a function of Ti:Ce molar composition and annealing temperature by in-situ X-ray diffraction, Raman spectroscopy and physisorption. The brannerite-type CeTi2O6 crystallizes as a single crystalline phase at Ti:Ce molar composition of 70:30 and in the mixture with cubic CeO2 and anatase TiO2 for composition 50:50. At Ti:Ce molar ratios 90:10 and 30:70 the mixtures of TiO2 anatase, rutile and cubic CeO2 appear. In these mixtures TiO2 rutile is formed at higher temperatures than conventionally. Additionally, the amount of a present amorphous phase in individual mixtures was estimated from diffraction data. The porous structure morphology depends both on molar composition and annealing temperature. This is correlated with the presence of carbon impurities of different character.

  4. A Strategy for Synthesis of Nanosheets Consisting of Alternating Spinel Li4Ti5O12 and Rutile TiO2 Lamellas for High-Rate Anodes of Lithium-Ion Batteries.

    PubMed

    Wu, Libo; Leng, Xuning; Liu, Yan; Wei, Sufeng; Li, Chunlin; Wang, Guoyong; Lian, Jianshe; Jiang, Qing; Nie, Anmin; Zhang, Tong-Yi

    2017-02-08

    Ultrathin dual phase nanosheets consisting of alternating spinel Li4Ti5O12 (LTO) and rutile TiO2 (RT) lamellas are synthesized through a facile and scalable hydrothermal method, and the formation mechanism is explored. The thickness of constituent lamellas can be controlled exactly by adjusting the mole ratio of Li:Ti in the original reactants. Alternating insertion of the RT lamellas significantly improves the electrochemical performance of LTO nanosheets, especially at high charge/discharge rates. As anodes in lithium-ion batteries (LIBs), the dual phase nanosheet electrode with the optimized phase ratio can deliver stable discharge capacities of 178.5, 154.9, 148.4, 142.3, 138.2, and 131.4 mA h g(-1) at current densities of 1, 10, 20, 30, 40, and 50 C, respectively. Meanwhile, they inherit the excellent cyclic stability of pure spinel LTO and exhibit a capacity retention of 93.1% even after 500 cycles at 50 C. Our results indicate that the alternating nanoscaled lamella structure is a good alternative to facilitate the transfer of both the Li ions and electrons into the spinel LTO, giving rise to an excellent cyclability and fast rate performance. Therefore, the newly prepared carbon-free LTO-RT nanosheets with high safety provide a new opportunity to develop high-power anodes for LIBs.

  5. Oxygen-Induced Restructuring of Rutile TiO(2)(110): Formation Mechanism, Atomic Models, and Influence on Surface Chemistry

    SciTech Connect

    Li, Min; Hebenstreit, Wilhelm; Diebold, Ulrike; Henderson, Michael A.; Jennison, Dwight R.

    1999-07-07

    The rutile TiO{sub 2} (110) (1x1) surface is considered the prototypical ''well-defined'' system in the surface science of metal oxides. Its popularity results partly from two experimental advantages: bulk-reduced single crystals do not exhibit charging, and stoichiometric surfaces--as judged by electron spectroscopes--can be prepared reproducibly by sputtering and annealing in oxygen. We present results that show that this commonly-applied preparation procedure may result in a surface structure that is by far more complex than generally anticipated. Flat, (1x1) terminated surfaces are obtained by sputtering and annealing in ultrahigh vacuum. When re-annealed in oxygen at moderate temperatures (470 K to 660 K), irregular networks of partially-connected, pseudohexagonal rosettes (6.5 x 6 {angstrom} wide), one-unit cell wide strands, and small ({approximately} tens of {angstrom}) (1x1) islands appear. This new surface phase is formed through reaction of oxygen gas with interstitial Ti from the reduced bulk. Because it consists of an incomplete, kinetically-limited (1x1) layer, this phenomenon has been termed restructuring. We report a combined experimental and theoretical study that systematically explores this restructuring process. The influence of several parameters (annealing time, temperature, pressure, sample history, gas) on the surface morphology is investigated using STM. The surface coverage of the added phase as well as the kinetics of the restructuring process are quantified by LEIS and SSIMS measurements in combination with annealing in {sup 18}O-enriched gas. Atomic models of the essential structural elements are presented and are shown to be stable with first-principles density functional calculations. The effect of oxygen-induced restructuring on surface chemistry and its importance for TiO{sub 2} and other bulk-reduced oxide materials is briefly discussed.

  6. Charge separation in branched TiO2 nanorod array homojunction aroused by quantum effect for enhanced photocatalytic decomposition of gaseous benzene

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoxia; Ni, Qian; Zeng, Dawen; Liao, Guanglan; Xie, Changsheng

    2016-12-01

    As known, the electron transfer behavior in photocatalysis is short-distance transportation, which leads the photo-induced electrons and holes to be localized. The temporarily separated electrons and holes will recombine with each other in the localized region. In this paper, we successfully achieved electron transfer in a homojunction of branched rutile TiO2 nanorod @nanoparticle core-shell architecture by quantum confinement effect aroused by the nanoparticle, which is proved by the blue-shifting in UV-vis absorption spectrum of the homojunction. Meanwhile, an absolute charge separation is also achieved by the long-distance electron transfer along the single-crystalline rutile TiO2 nanorod as uninterrupted high-speed electron transfer channel to FTO substrates. Based on the effective charge separation, the photocatalytic decomposition of gaseous benzene by the homojunction is significantly enhanced, yielding 10 times CO2 than that of the nanorod array. This homojunction interfacial charge separation, aroused by quantum effect, through long-distance transfer along the single-crystalline nanorod gives us inspiration to achieve efficient charge separation with defect-less interfaces, which might can be utilized for real-time environmental abatement and energy generation simultaneously.

  7. Single crystalline mesoporous silicon nanowires

    SciTech Connect

    Hochbaum, Allon; Dargas, Daniel; Hwang, Yun Jeong; Yang, Peidong

    2009-08-18

    Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. The photoluminescence of these nanowires suggest they are composed of crystalline silicon with small enough dimensions such that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices. A better understanding of this electroless route to mesoporous silicon could lead to facile and general syntheses of different narrow bandgap semiconductor nanostructures for various applications.

  8. Single-crystalline self-branched anatase titania nanowires for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Li, Zhenquan; Yang, Huang; Wu, Fei; Fu, Jianxun; Wang, Linjun; Yang, Weiguang

    2016-12-01

    The morphology of the anatase titania plays an important role in improving the photovoltaic performance in dye-sensitized solar cells. In this work, single-crystalline self-branched anatase TiO2 nanowires have been synthesized by hydrothermal method using TBAH and CTAB as morphology controlling agents. The obtained self-branched TiO2 nanowires dominated by a large percentage of (010) facets. The photovoltaic conversion efficiency (6.37%) of dye-sensitized solar cell (DSSC) based on the self-branched TiO2 nanowires shows a significant improvement (26.6%) compared to that of P25 TiO2 (5.03%). The enhanced performance of the self-branched TiO2 nanowires-based DSSC is due to heir large percent of exposed (010) facets which have strong dye adsorption capacity and effective charge transport of the self-branched 1D nanostructures.

  9. Single-crystalline self-branched anatase titania nanowires for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Li, Zhenquan; Yang, Huang; Wu, Fei; Fu, Jianxun; Wang, Linjun; Yang, Weiguang

    2017-03-01

    The morphology of the anatase titania plays an important role in improving the photovoltaic performance in dye-sensitized solar cells. In this work, single-crystalline self-branched anatase TiO2 nanowires have been synthesized by hydrothermal method using TBAH and CTAB as morphology controlling agents. The obtained self-branched TiO2 nanowires dominated by a large percentage of (010) facets. The photovoltaic conversion efficiency (6.37%) of dye-sensitized solar cell (DSSC) based on the self-branched TiO2 nanowires shows a significant improvement (26.6%) compared to that of P25 TiO2 (5.03%). The enhanced performance of the self-branched TiO2 nanowires-based DSSC is due to heir large percent of exposed (010) facets which have strong dye adsorption capacity and effective charge transport of the self-branched 1D nanostructures.

  10. Anatase TiO2 sheet-assisted synthesis of Ti(3+) self-doped mixed phase TiO2 sheet with superior visible-light photocatalytic performance: Roles of anatase TiO2 sheet.

    PubMed

    Zhang, Xiaojie; Zuo, Guoqing; Lu, Xin; Tang, Changqing; Cao, Shuo; Yu, Miao

    2017-03-15

    On the basis of measurements, such as field emission scanning electron microscope, UV-Vis diffuse reflectance spectra, X-ray diffraction, electron paramagnetic resonance, photoluminescence spectra, and photocurrent measurements, the roles of anatase TiO2 sheet on synthesizing Ti(3+) self-doped mixed phase TiO2 nanosheets (doped TiO2 (A/R, TiO2 (A))) and on improving the performance for photocatalytic CO2 reduction were explored systematically. High surface area anatase TiO2 nanosheets (TiO2 (A)) as a substrate, structure directing agent, and inhibitor, mediated the synthesis of Ti(3+) self-doped mixed phase TiO2 nanosheets. Addition of TiO2 (A) significantly improved not only visible light absorption of doped TiO2 (A/R, TiO2 (A)), but also the efficiency of photo-excited charges separations due to the existence of interfacial regions of anatase-rutile TiO2 junctions. Finally, a possible mechanism for interfacial charge transfer at the anatase-rutile TiO2 interface and for photocatalytic CO2 reduction over Pt loaded doped TiO2 (A/R, TiO2 (A)) were proposed.

  11. Size-tunable TiO2 nanorod microspheres synthesised via a one-pot solvothermal method and used as the scattering layer for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Rui, Yichuan; Li, Yaogang; Zhang, Qinghong; Wang, Hongzhi

    2013-11-01

    TiO2 microspheres assembled by single crystalline rutile TiO2 nanorods were synthesized by one-pot solvothermal treatment at 180 °C based on an aqueous-organic mixture solution containing n-hexane, distilled water, titanium n-butoxide and hydrochloric acid. The spheres had a radiative structure from the center, and their diameters were controlled in the range from 1 to 5 μm by adjusting the volume of the reactant water. Nitrogen adsorption-desorption isotherms showed that all the as-prepared microspheres had relatively high specific surface areas of about 50 m2 g-1. The 1 μm sized TiO2 nanorod microspheres were fabricated as a scattering overlayer in DSSCs, leading to a remarkable improvement in the power conversion efficiency: 8.22% of the bi-layer DSSCs versus 7.00% for the reference cell made of a single-layer film prepared from nanocrystalline TiO2. Such improvement was mainly attributed to the enhanced light harvesting and dye loading brought by the effective scattering centers.TiO2 microspheres assembled by single crystalline rutile TiO2 nanorods were synthesized by one-pot solvothermal treatment at 180 °C based on an aqueous-organic mixture solution containing n-hexane, distilled water, titanium n-butoxide and hydrochloric acid. The spheres had a radiative structure from the center, and their diameters were controlled in the range from 1 to 5 μm by adjusting the volume of the reactant water. Nitrogen adsorption-desorption isotherms showed that all the as-prepared microspheres had relatively high specific surface areas of about 50 m2 g-1. The 1 μm sized TiO2 nanorod microspheres were fabricated as a scattering overlayer in DSSCs, leading to a remarkable improvement in the power conversion efficiency: 8.22% of the bi-layer DSSCs versus 7.00% for the reference cell made of a single-layer film prepared from nanocrystalline TiO2. Such improvement was mainly attributed to the enhanced light harvesting and dye loading brought by the effective scattering

  12. Thermo-selective Tm(x)Ti(1-x)O(2-x/2) nanoparticles: from Tm-doped anatase TiO2 to a rutile/pyrochlore Tm2Ti2O7 mixture. An experimental and theoretical study with a photocatalytic application.

    PubMed

    Navas, Javier; Sánchez-Coronilla, Antonio; Aguilar, Teresa; De los Santos, Desireé M; Hernández, Norge C; Alcántara, Rodrigo; Fernández-Lorenzo, Concha; Martín-Calleja, Joaquín

    2014-11-07

    This is an experimental and theoretical study of thulium doped TiO2 nanoparticles. From an experimental perspective, a method was used to synthesize thulium-doped TiO2 nanoparticles in which Tm(3+) replaces Ti(4+) in the lattice, which to our knowledge has neither been reported nor studied theoretically so far. Different proportions of anatase and rutile phases were obtained at different annealing temperatures, and XRD and Raman spectroscopy also revealed the presence of a pyrochlore phase (Tm2Ti2O7) at 1173 K. Thus, the structure of the Tm-doped nanoparticles was thermally-controlled. Furthermore, XPS showed the presence of Tm(3+) in the samples synthesized, which produces oxygen vacancies to maintain the local neutrality in the lattice. The presence of Tm(3+) in the samples led to changes in the UV-Vis absorption spectra, so they showed photoluminescence properties and new states in the band gap, which produce a new lower energy electronic transition than the main TiO2 one. Periodic DFT calculations were performed to understand the experimentally produced structures. The production of oxygen vacancies was analysed and the changes generated in the structure were fully detailed. The DOS and PDOS analyses confirmed the experimental results obtained using UV-Vis spectroscopy, and showed that the new electronic states in the band gap are due to interactions of the f state of Tm and the p state of O. Likewise, the charge study and the ELF analysis indicate that when Tm is introduced into the TiO2 structure, the Ti-O bond around the oxygen vacancy is strengthened. Finally, an example of a photocatalytic application was developed to show the high efficiency of the samples due to the heterojunction in the interfaces of the phases in the samples, which improved the charge separation and the good charge carrier mobility due to the presence of the pyrochlore phase, as was also shown theoretically.

  13. Instability of Hydrogenated TiO2

    SciTech Connect

    Nandasiri, Manjula I.; Shutthanandan, V.; Manandhar, Sandeep; Schwarz, Ashleigh M.; Oxenford, Lucas S.; Kennedy, John V.; Thevuthasan, Suntharampillai; Henderson, Michael A.

    2015-11-06

    Hydrogenated TiO2 (H-TiO2) is toted as a viable visible light photocatalyst. We report a systematic study on the thermal stability of H-implanted TiO2 using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). Protons (40 keV) implanted at a ~2 atom % level within a ~120 nm wide profile of rutile TiO2(110) were situated ~300 nm below the surface. NRA revealed that this H-profile broadened preferentially toward the surface after annealing at 373 K, dissipated out of the crystal into vacuum at 473 K, and was absent within the beam sampling depth (~800 nm) at 523 K. Photoemission showed that the surface was reduced in concert with these changes. Similar anneals had no effect on pristine TiO2(110). The facile bulk diffusivity of H in rutile, as well as its activity toward interfacial reduction, significantly limits the utilization of H-TiO2 as a photocatalyst. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. The research was performed using the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

  14. A maskless synthesis of TiO2-nanofiber-based hierarchical structures for solid-state dye-sensitized solar cells with improved performance

    PubMed Central

    2014-01-01

    TiO2 hierarchical nanostructures with secondary growth have been successfully synthesized on electrospun nanofibers via surfactant-free hydrothermal route. The effect of hydrothermal reaction time on the secondary nanostructures has been studied. The synthesized nanostructures comprise electrospun nanofibers which are polycrystalline with anatase phase and have single crystalline, rutile TiO2 nanorod-like structures growing on them. These secondary nanostructures have a preferential growth direction [110]. UV–vis spectroscopy measurements point to better dye loading capability and incident photon to current conversion efficiency spectra show enhanced light harvesting of the synthesized hierarchical structures. Concomitantly, the dye molecules act as spacers between the conduction band electrons of TiO2 and holes in the hole transporting medium, i.e., spiro-OMeTAD and thus enhance open circuit voltage. The charge transport and recombination effects are characterized by electrochemical impedance spectroscopy measurements. As a result of improved light harvesting, dye loading, and reduced recombination losses, the hierarchical nanofibers yield 2.14% electrochemical conversion efficiency which is 50% higher than the efficiency obtained by plain nanofibers. PMID:24410851

  15. Size-tunable TiO2 nanorod microspheres synthesised via a one-pot solvothermal method and used as the scattering layer for dye-sensitized solar cells.

    PubMed

    Rui, Yichuan; Li, Yaogang; Zhang, Qinghong; Wang, Hongzhi

    2013-12-21

    TiO2 microspheres assembled by single crystalline rutile TiO2 nanorods were synthesized by one-pot solvothermal treatment at 180 °C based on an aqueous-organic mixture solution containing n-hexane, distilled water, titanium n-butoxide and hydrochloric acid. The spheres had a radiative structure from the center, and their diameters were controlled in the range from 1 to 5 μm by adjusting the volume of the reactant water. Nitrogen adsorption-desorption isotherms showed that all the as-prepared microspheres had relatively high specific surface areas of about 50 m(2) g(-1). The 1 μm sized TiO2 nanorod microspheres were fabricated as a scattering overlayer in DSSCs, leading to a remarkable improvement in the power conversion efficiency: 8.22% of the bi-layer DSSCs versus 7.00% for the reference cell made of a single-layer film prepared from nanocrystalline TiO2. Such improvement was mainly attributed to the enhanced light harvesting and dye loading brought by the effective scattering centers.

  16. Remarkable Charge Separation and Photocatalytic Efficiency Enhancement through Interconnection of TiO2 Nanoparticles by Hydrothermal Treatment.

    PubMed

    Ide, Yusuke; Inami, Nozomu; Hattori, Hideya; Saito, Kanji; Sohmiya, Minoru; Tsunoji, Nao; Komaguchi, Kenji; Sano, Tsuneji; Bando, Yoshio; Golberg, Dmitri; Sugahara, Yoshiyuki

    2016-03-07

    Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2 , which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2 , inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.

  17. Influence of annealing on optical and photovoltaic properties of nanostructured TiO2 films

    NASA Astrophysics Data System (ADS)

    Serikov, T. M.; Ibrayev, N. Kh; Smagulov, Zh Kh; Kuterbekov, К. А.

    2017-01-01

    Spectral and kinetic characteristics of the photoluminescence of TiO2 films obtained from TiO2 nanoparticles and nanotubes were studied. Luminescence spectra typical for the TiO2 with anatase structure were observed under UV excitation of the films. Heat treatment of the films at T=1273 K leads to a long-wavelength shift of the photoluminescence band with maximum at 850 nm, which corresponds to the rutile structure. The luminescence duration of rutile films is longer than the luminescence duration of the anatase films as for nanoparticles and for nanotubes. The photovoltaic properties of TiO2 films with different structures were investigated. It was established that anatase structured films have a higher photocurrent than the rutile structured film. By impedance spectroscopy method it was found that the electron transport resistance in the nanotube films is higher but the recombination rate is lower than in the TiO2 nanoparticle films.

  18. Effect of TiO2 blocking layer on TiO2 nanorod arrays based dye sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Sivakumar, R.; Paulraj, M.

    2016-05-01

    Highly ordered rutile titanium dioxide nanorod (TNR) arrays (1.2 to 6.2 μm thickness) were grown on TiO2 blocking layer chemically deposited on fluorine doped tin oxide (FTO) substrate and were used as photo-electrodes to fabricate dye sensitized solar cells (DSSC's). Homogeneous layer of TiO2 on FTO was achieved by using aqueous peroxo- titanium complex (PTC) solutions via chemical bath deposition. Structural and morphological properties of the prepared samples were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) measurements. TNR arrays (6.2 μm) with TiO2 blocking layer showed higher energy conversion efficiency (1.46%) than that without TiO2 blocking layer. The reason can be ascertained to the suppression of electron-hole recombination at the semiconductor/electrolyte interface by the effect of TiO2 blocking layer.

  19. Optimized nanostructured TiO2 photocatalysts

    NASA Astrophysics Data System (ADS)

    Topcu, Selda; Jodhani, Gagan; Gouma, Pelagia

    2016-07-01

    Titania is the most widely studied photocatalyst. In it’s mixed-phase configuration (anatase-rutile form) -as manifested in the commercially available P25 Degussa material- titania was previously found to exhibit the best photocatalytic properties reported for the pure system. A great deal of published research by various workers in the field have not fully explained the underlying mechanism for the observed behavior of mixed-phase titania photocatalysts. One of the prevalent hypothesis in the literature that is tested in this work involves the presence of small, active clusters of interwoven anatase and rutile crystallites or “catalytic “hot-spots””. Therefore, non-woven nanofibrous mats of titania were produced and upon calcination the mats consisted of nanostructured fibers with different anatase-rutile ratios. By assessing the photocatalytic and photoelectrochemical properties of these samples the optimized photocatalyst was determined. This consisted of TiO2 nanostructures annealed at 500˚C with an anatase /rutile content of 90/10. Since the performance of this material exceeded that of P25 complete structural characterization was employed to understand the catalytic mechanism involved. It was determined that the dominant factors controlling the photocatalytic behavior of the titania system are the relative particle size of the different phases of titania and the growth of rutile laths on anatase grains which allow for rapid electron transfer between the two phases. This explains how to optimize the response of the pure system.

  20. Thermo-selective TmxTi1-xO2-x/2 nanoparticles: from Tm-doped anatase TiO2 to a rutile/pyrochlore Tm2Ti2O7 mixture. An experimental and theoretical study with a photocatalytic application

    NASA Astrophysics Data System (ADS)

    Navas, Javier; Sánchez-Coronilla, Antonio; Aguilar, Teresa; de Los Santos, Desireé M.; Hernández, Norge C.; Alcántara, Rodrigo; Fernández-Lorenzo, Concha; Martín-Calleja, Joaquín

    2014-10-01

    This is an experimental and theoretical study of thulium doped TiO2 nanoparticles. From an experimental perspective, a method was used to synthesize thulium-doped TiO2 nanoparticles in which Tm3+ replaces Ti4+ in the lattice, which to our knowledge has neither been reported nor studied theoretically so far. Different proportions of anatase and rutile phases were obtained at different annealing temperatures, and XRD and Raman spectroscopy also revealed the presence of a pyrochlore phase (Tm2Ti2O7) at 1173 K. Thus, the structure of the Tm-doped nanoparticles was thermally-controlled. Furthermore, XPS showed the presence of Tm3+ in the samples synthesized, which produces oxygen vacancies to maintain the local neutrality in the lattice. The presence of Tm3+ in the samples led to changes in the UV-Vis absorption spectra, so they showed photoluminescence properties and new states in the band gap, which produce a new lower energy electronic transition than the main TiO2 one. Periodic DFT calculations were performed to understand the experimentally produced structures. The production of oxygen vacancies was analysed and the changes generated in the structure were fully detailed. The DOS and PDOS analyses confirmed the experimental results obtained using UV-Vis spectroscopy, and showed that the new electronic states in the band gap are due to interactions of the f state of Tm and the p state of O. Likewise, the charge study and the ELF analysis indicate that when Tm is introduced into the TiO2 structure, the Ti-O bond around the oxygen vacancy is strengthened. Finally, an example of a photocatalytic application was developed to show the high efficiency of the samples due to the heterojunction in the interfaces of the phases in the samples, which improved the charge separation and the good charge carrier mobility due to the presence of the pyrochlore phase, as was also shown theoretically.This is an experimental and theoretical study of thulium doped TiO2 nanoparticles. From

  1. Shock induced phase transition of different TiO2 precursors

    NASA Astrophysics Data System (ADS)

    Chen, Pengwan; Gao, Xiang; Liu, Jianjun; Zhou, Qiang

    2011-06-01

    To investigate the effects of phase composition and particle size on shock-induced phase transition of TiO2, different TiO2 precursors including MC-150 TiO2(pure anatase,5nm), P25 TiO2(85% anatase/15% rutile,15nm), T2 TiO2(pure anatase,35nm) and T1 TiO2(pure rutile, 24nm) were impacted by detonation-driven high velocity flyers. Powder X-ray diffraction(XRD) was used to characterize the phase composition of recovered samples. Two types of phase transition were observed, including anatase to rutile transition and anatase to high pressure phase of srilankite transition. The phase transition mechanisms and effects of shock conditions, initial phase composition and particle size were analyzed. Complete transition from anatase to srilankite can be obtained by adjusting the shock conditions. In the case of impacting pure P25 TiO2, anatase to srilankite transition was hardly observed, which may be due to the restraint of initial phase of thermodynamically stable rutile. However, in the case of impacting a mixture of P25 TiO2 and dicyandiamide(C2N4H4) , it is interesting to observe anatase to srilankite transition and the mechanisms was analyzed. National Natural Science Foundation of China

  2. Controlled synthesis of single-crystalline graphene

    SciTech Connect

    Xueshen, Wang Jinjin, Li Qing, Zhong; Yuan, Zhong; Mengke, Zhao; Yonggang, Liu

    2014-03-15

    This paper reports the controlled synthesis of single-crystalline graphene on the back side of copper foil using CH{sub 4} as the precursor. The influence of growth time and the pressure ratio of CH{sub 4}/H{sub 2} on the structure of graphene are examined. An optimized polymer-assisted method is used to transfer the synthesized graphene onto a SiO{sub 2}/Si substrate. Scanning electron microscopy and Raman spectroscopy are used to characterize the graphene.

  3. AC conductivity studies of Fe doped TiO2 nanotubes

    NASA Astrophysics Data System (ADS)

    Vijayan, P. P.; Thomas, M.; George, K. C.

    2015-02-01

    Fe-doped TiO2 nanotubes are prepared by the combination of sol-gel process with hydrothermal treatment. The morphology and crystalline structure of TiO2 nanotubes are characterized by transmission electron microscopy (TEM), X-ray diffraction respectively (XRD). Fe doping induces a structural transformation from anatase to rutile. The temperature dependence of the ac electrical conductivity is investigated in the temperature range 303-413 K. Positive temperature coefficient of resistance is observed in the Fe doped TiO2 nanotubes. PL spectrum shows the presence of oxygen vacancies and self trapped excitons in Fe doped TiO2 nanotubes and undoped samples.

  4. Microscale material testing of single crystalline silicon

    NASA Astrophysics Data System (ADS)

    Yi, Taechung

    The mechanical properties of single crystalline silicon (SCS) in microscale are characterized using a uniaxial tension test. The samples are prepared using, various micromachining techniques. The dimensions of the tension specimen at the maximum stress region are 5 to 10 mum in thickness and 20 to 100 mum in width. The sample has two illumination marks on the top surface for strain measurement. The uniaxial tension test setup has been built to accommodate requirements such as sample handling, sample alignment, and friction elimination. Stress is measured using a commercial load cell. Strain is measured by laser interferometry. All the components are connected to a data acquisition board and controlled by a personal computer. Measured Young's moduli in three directions agree well with the reference values and verify the reliability of the setup and measurement procedure. The measured fracture strength is 0.6 GPa to 1.2 GPa, depending on sample preparation methods and loading directions. Preliminary work for fracture toughness measurements using a sharp initial crack is also presented. Future works include further investigation of fracture surfaces, fracture toughness measurement using crack opening criteria, and improvement of the testing apparatus.

  5. Searching for new TiO2 crystal phases with better photoactivity

    NASA Astrophysics Data System (ADS)

    Shang, Cheng; Zhao, Wei-Na; Liu, Zhi-Pan

    2015-04-01

    Using the recently developed stochastic surface walking global optimization method, this work explores the potential energy surface of TiO2 crystals aiming to search for likely phases with higher photocatalytic activity. Five new phases of TiO2 are identified and the lowest energy phase transition pathways connecting to the most abundant phases (rutile and anatase) are determined. Theory shows that a high-pressure phase, α-PbO2-like form (TiO2II) acts as the key intermediate in between rutile and anatase. The phase transition of anatase to rutile belongs to the diffusionless Martensitic phase transition, occurring through a set of habit planes, rutile(101)//TiO2II(001), and TiO2II(100)//anatase(112). With regard to the photocatalytic activity, three pure phases (#110, pyrite and fluorite) are found to possess the band gap narrower than rutile, but they are unstable at the low-pressure condition. Instead, a mixed anatase-TiO2II phase is found to have good stability and narrower band gap than both parent phases. Because of the phase separation, the mixed phase is also expected to improve the photocatalytic performance by reducing the probability of the electron-hole pair recombination.

  6. Electronic and optical properties of TiO2 and its polymorphs by Z-scan method

    NASA Astrophysics Data System (ADS)

    Divya, S.; V, P. N. Nampoori; P, Radhakrishnan; A, Mujeeb

    2014-08-01

    TiO2 is a material which has attracted considerable attention from the scientific community for its innumerable properties. TiO2 is known to exist in nature in three different crystalline structures: rutile, anatase, and brookite. Anatase and rutile TiO2 films have been widely characterized for their potential applications in solar cells, self-cleaning coatings, and photocatalysis. In the present report, the third-order nonlinear susceptibilities of TiO2 and its polymorphs, anatase, and rutile, prepared by the sol—gel technique followed by heat treatment are investigated using the Z-scan technique at a wavelength of 532 nm with a duration of 7 ns. Imaginary and real values of χ(3) for amorphous, anatase, and rutile are also calculated and found to be 5 × 10-19 m2/V2, 27 × 10-19 m2/V2, 19 × 10-19 m2/V2, respectively. It is found that the values of the optical constants of amorphous TiO2 after heat treatment vary considerably. It is assumed that this could be due to the variation in the electronic structure of TiO2 synchronous with the formation of its polymorphs, anatase, and rutile. Amorphous TiO2 is marked by the localization of the tail states near the band gap, whereas its crystalline counterparts are characterized by completely delocalized tail states.

  7. BIOLOGICAL RESPONSE TO NANO-SCALE TIO2: ROLE OF PARTICLE DOSE, SHAPE AND RETENTION

    PubMed Central

    Silva, Rona M.; TeeSy, Christel; Franzi, Lisa; Weir, Alex; Westerhoff, Paul; Evans, James E.; Pinkerton, Kent E.

    2015-01-01

    TiO2 is one of the most widely used nanomaterials, valued for its highly refractive, photocatalytic and pigmenting properties. TiO2 is also classified by the International Agency for Research on Cancer (IARC) as a possible human carcinogen. The objectives of this study were to establish a lowest observed effect level (LOEL) for nano-scale TiO2, determine TiO2 uptake in the lungs, and estimate toxicity based on physico-chemical properties and retention in the lungs. In vivo lung toxicity of nano-scale TiO2 using varying forms of well-characterized, highly-dispersed TiO2 was assessed. Anatase/rutile P25 spheres (TiO2-P25), pure anatase spheres (TiO2-A), and anatase nanobelts (TiO2-NB) were tested. To determine the effects of dose and particle characteristics, male Sprague-Dawley rats were given TiO2 (0, 20, 70, or 200 µg) via intratracheal instillation. Broncho-alveolar lavage fluid (BALF) and lung tissue were obtained for analysis 1 and 7 days post exposure. Despite abundant TiO2 inclusions in all exposed animals, only TiO2-NB elicited any significant degree of inflammation seen in BALF at the 1-day time-point. This inflammation resolved by 7 days; although, TiO2 particles had not cleared from alveolar macrophages recovered from the lung. Histological examination showed TiO2-NB caused cellular changes at day 1 which were still evident at day 7. We conclude TiO2-NB is the most inflammatory with a lowest observable effect level of 200 µg at 1 day post instillation. PMID:24156719

  8. Multiphoton Effects in Rutile.

    NASA Astrophysics Data System (ADS)

    Royce, Gerald A.

    Multiphoton effects are investigated in crystalline rutile TiO(,2) using Nd:YAG laser photons. The 1.06 micron laser is operated in Q-switched mode with intensities up to 1.4 x 10('6) watts/cm('2) on the rutile crystal. Photoconductivity measurements provide data indicating a mixture of modes for electrons to be photoionized. Assuming aluminum impurity as the contributing sites, the first order photionization cross section is found to be 1.5 x 10('-26) cm('2) and second order cross section is found to be 7.7 x 10('-51) cm('4)-s. No appreciable change in cross section is observed for circular versus linear polarization of the laser. Observations of the photo-emission of the laser illuminated crystal provide radiative relaxation times on the order of 100 nanoseconds with emission peaks at 4500 and 5000 angstroms plus a near infrared continuum out to 1 micron. The thermoluminescence of rutile shows a number of trapping levels between 0.4 and 0.8 eV below the conduction band. These are attributed to an aluminum impurity.

  9. Hierarchical Oriented Anatase TiO2 Nanostructure arrays on Flexible Substrate for Efficient Dye-sensitized Solar Cells

    PubMed Central

    Wu, Wu-Qiang; Rao, Hua-Shang; Xu, Yang-Fan; Wang, Yu-Fen; Su, Cheng-Yong; Kuang, Dai-Bin

    2013-01-01

    The vertically oriented anatase single crystalline TiO2 nanostructure arrays (TNAs) consisting of TiO2 truncated octahedrons with exposed {001} facets or hierarchical TiO2 nanotubes (HNTs) consisting of numerous nanocrystals on Ti-foil substrate were synthesized via a two-step hydrothermal growth process. The first step hydrothermal reaction of Ti foil and NaOH leads to the formation of H-titanate nanowire arrays, which is further performed the second step hydrothermal reaction to obtain the oriented anatase single crystalline TiO2 nanostructures such as TiO2 nanoarrays assembly with truncated octahedral TiO2 nanocrystals in the presence of NH4F aqueous or hierarchical TiO2 nanotubes with walls made of nanocrystals in the presence of pure water. Subsequently, these TiO2 nanostructures were utilized to produce dye-sensitized solar cells in a backside illumination pattern, yielding a significant high power conversion efficiency (PCE) of 4.66% (TNAs, JSC = 7.46 mA cm−2, VOC = 839 mV, FF = 0.75) and 5.84% (HNTs, JSC = 10.02 mA cm−2, VOC = 817 mV, FF = 0.72), respectively. PMID:23715529

  10. Gel-sol synthesis of rutile nanoparticles.

    PubMed

    Verhovšek, Dejan; Lešnik, Maja; Veronovski, Nika; Samardžija, Zoran; Žagar, Kristina; Čeh, Miran

    2014-01-01

    Titanium dioxide (TiO(2)) rutile nanoparticles were synthesized at temperatures below 100 °C using a gel-sol process that provides control of the final particles' characteristics, such as the nanoparticle size, morphology, crystal structure and crystallinity. The synthesized rutile nanoparticles were analyzed using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the gel-sol process allows control over the final nanoparticle characteristics with the proper choice of reaction parameters. The most profound influence on the nanoparticles' properties is achieved by the type and concentration of the acid used in the reaction mixture. The gel-sol synthesis resulted in anisotropic rutile nanoparticles that are 60-160 nm long, depending on the reaction parameters, and have an aspect ratio of about 5. A reaction mechanism is presented, explaining the influence of various reaction parameters on the characteristics of the TiO(2) nanoparticles.

  11. Structural analysis of TiO2 and TiO2-Ag thin films and their antibacterial behaviors

    NASA Astrophysics Data System (ADS)

    Hsieh, J. H.; Yu, R. B.; Chang, Y. K.; Li, C.

    2012-01-01

    TiO2 (rutile and anatase) thin films was first prepared using reactive sputtering, in an Ar+O2 plasma. In the 2nd stage of the experiment, various amounts (3, 7, and 10 at. %) of Ag was doped into the rutile film in order to form TiO2-Ag thin films. These films were annealed for one hour in Ar atmosphere, at 300, 400, and 500 °C. The films' structures were then examined using X-ray diffractometry. FESEM (field-emission scaning electron microscopy) was used to investigate the surface emergence of Ag particles. As for the examination of optical band gaps and absorption of these films, UV-Vis-NIR photometer was used. The results show that, in as-deposited condition, the addition of Ag might disrupt the growth of crystalline structure and cause the formation of amorphous films. After annealing, it is found that the structure tends to become anatase phase which is a metastable phase between amorphous titanium oxide and rutile. More importantly, the absorption of the Ag-doped films would be enhanced in the visible-light range. Some of the enhancement is clearly due to plasmon resonance effect. The Ag-doped samples have shown some antibacterial effect in dark. When irradiated with light, the samples show a synergistic behavior combining the bactericidal effect of Ag ions and photocatalytic effect of TiO2.

  12. Influence of terbium on structure and luminescence of nanocrystalline TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Wojcieszak, Damian; Kaczmarek, Danuta; Domaradzki, Jaroslaw; Lukowiak, Anna; Strek, Wieslaw

    2013-02-01

    In this work analysis of the structural and optical properties of TiO2 thin films doped with terbium has been described. Samples were prepared by a high energy reactive magnetron sputtering process under low pressure of oxygen plasma. X-ray diffraction results have shown that different TiO2 crystal forms have been produced, depending on the amount of Tb dopant. The undoped matrix had rutile structure with crystallites with a size of 8.7 nm, while incorporation of 0.4 at. % of Tb into the film during the sputtering process resulted in anatase structure with bigger crystallites (11.7 nm). Increasing the amount of terbium up to 2 at. % and 2.6 at. % gave rutile structure with crystallites with a size of 6.6 nm for both films. However, Raman spectroscopy has revealed that in the case of TiO2:(2 at. % Tb), except for the rutile form, the presence of fine-crystalline anatase was observed. Moreover, the lack of Raman peaks shift attests to the lack of stress in the titania lattice of all of the TiO2:Tb films. This fact indicates localization of Tb3+ ions on the surface of TiO2 nanocrystals. In the case of optical investigation, results have shown that doping with terbium has a significant influence on the properties of TiO2, but it does not decrease the high transparency of the matrix. The observed changes of the transmission characteristics were produced only due to modification of the TiO2:Tb structure. Photoluminescence measurements have shown that emission of light from TiO2:Tb films occurs when the amount of terbium is 2.6 at. %. Based on the obtained results a scheme of direct energy transfer from titanium dioxide matrix (with rutile structure) to Tb3+ ions has been proposed.

  13. Comparison study on photocatalytic oxidation of pharmaceuticals by TiO2-Fe and TiO2-reduced graphene oxide nanocomposites immobilized on optical fibers.

    PubMed

    Lin, Lu; Wang, Huiyao; Jiang, Wenbin; Mkaouar, Ahmed Radhi; Xu, Pei

    2017-03-08

    Incorporating reduced graphene oxide (rGO) or Fe(3+) ions in TiO2 photocatalyst could enhance photocatalytic degradation of organic contaminants in aqueous solutions. This study characterized the photocatalytic activities of TiO2-Fe and TiO2-rGO nanocomposites immobilized on optical fibers synthesized by polymer assisted hydrothermal deposition method. The photocatalysts presented a mixture phase of anatase and rutile in the TiO2-rGO and TiO2-Fe nanocomposites. Doping Fe into TiO2 particles (2.40eV) could reduce more band gap energy than incorporating rGO (2.85eV), thereby enhancing utilization efficiency of visible light. Incorporating Fe and rGO in TiO2 decreased significantly the intensity of TiO2 photoluminescence signals and enhanced the separation rate of photo-induced charge carriers. Photocatalytic performance of the synthesized nanocomposites was measured by the degradation of three pharmaceuticals under UV and visible light irradiation, including carbamazepine, ibuprofen, and sulfamethoxazole. TiO2-rGO exhibited higher photocatalytic activity for the degradation of pharmaceuticals under UV irradiation, while TiO2-Fe demonstrated more suitable for visible light oxidation. The results suggested that the enhanced photocatalytic performance of TiO2-rGO could be attributed to reduced recombination rate of photoexcited electrons-hole pairs, but for TiO2-Fe nanocomposite, narrower band gap would contribute to increased photocatalytic activity.

  14. Photocatalytic antibacterial performance of TiO2 and Ag-doped TiO2 against S. aureus. P. aeruginosa and E. coli

    PubMed Central

    Gupta, Kiran; Singh, R P; Pandey, Ashutosh

    2013-01-01

    Summary This paper reports the structural and optical properties and comparative photocatalytic activity of TiO2 and Ag-doped TiO2 nanoparticles against different bacterial strains under visible-light irradiation. The TiO2 and Ag-doped TiO2 photocatalysts were synthesized by acid catalyzed sol–gel technique and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis spectroscopy and photoluminescence (PL). The XRD pattern revealed that the annealed sample of TiO2 has both anatase and rutile phases while only an anatase phase was found in Ag-doped TiO2 nanoparticles. The decreased band-gap energy of Ag-doped TiO2 nanoparticles in comparison to TiO2 nanoparticles was investigated by UV–vis spectroscopy. The rate of recombination and transfer behaviour of the photoexcited electron–hole pairs in the semiconductors was recorded by photoluminescence. The antimicrobial activity of TiO2 and Ag-doped TiO2 nanoparticles (3% and 7%) was investigated against both gram positive (Staphylococcus aureus) and gram negative (Pseudomonas aeruginosa, Escherichia coli) bacteria. As a result, the viability of all three microorganisms was reduced to zero at 60 mg/30 mL culture in the case of both (3% and 7% doping) concentrations of Ag-doped TiO2 nanoparticles. Annealed TiO2 showed zero viability at 80 mg/30 mL whereas doped Ag-TiO2 7% showed zero viability at 40 mg/30 mL culture in the case of P. aeruginosa only. PMID:23844339

  15. Photocatalytic antibacterial performance of TiO2 and Ag-doped TiO2 against S. aureus. P. aeruginosa and E. coli.

    PubMed

    Gupta, Kiran; Singh, R P; Pandey, Ashutosh; Pandey, Anjana

    2013-01-01

    This paper reports the structural and optical properties and comparative photocatalytic activity of TiO2 and Ag-doped TiO2 nanoparticles against different bacterial strains under visible-light irradiation. The TiO2 and Ag-doped TiO2 photocatalysts were synthesized by acid catalyzed sol-gel technique and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis spectroscopy and photoluminescence (PL). The XRD pattern revealed that the annealed sample of TiO2 has both anatase and rutile phases while only an anatase phase was found in Ag-doped TiO2 nanoparticles. The decreased band-gap energy of Ag-doped TiO2 nanoparticles in comparison to TiO2 nanoparticles was investigated by UV-vis spectroscopy. The rate of recombination and transfer behaviour of the photoexcited electron-hole pairs in the semiconductors was recorded by photoluminescence. The antimicrobial activity of TiO2 and Ag-doped TiO2 nanoparticles (3% and 7%) was investigated against both gram positive (Staphylococcus aureus) and gram negative (Pseudomonas aeruginosa, Escherichia coli) bacteria. As a result, the viability of all three microorganisms was reduced to zero at 60 mg/30 mL culture in the case of both (3% and 7% doping) concentrations of Ag-doped TiO2 nanoparticles. Annealed TiO2 showed zero viability at 80 mg/30 mL whereas doped Ag-TiO2 7% showed zero viability at 40 mg/30 mL culture in the case of P. aeruginosa only.

  16. Vapor-phase hydrothermal transformation of HTiOF3 intermediates into {001} faceted anatase single-crystalline nanosheets.

    PubMed

    Liu, Porun; Wang, Yun; Zhang, Haimin; An, Taicheng; Yang, Huagui; Tang, Zhiyong; Cai, Weiping; Zhao, Huijun

    2012-12-07

    For the first time, a facile, one-pot hydrofluoric acid vapor-phase hydrothermal (HF-VPH) method is demonstrated to directly grow single-crystalline anatase TiO(2) nanosheets with 98.2% of exposed {001} faceted surfaces on the Ti substrate via a distinctive two-stage formation mechanism. The first stage produces a new intermediate crystal (orthorhombic HTiOF(3) ) that is transformed into anatase TiO(2) nanosheets during the second stage. The findings reveal that the HF-VPH reaction environment is unique and differs remarkably from that of liquid-phase hydrothermal processes. The uniqueness of the HF-VPH conditions can be readily used to effectively control the nanostructure growth.

  17. Preparation of TiO2 Nanocrystallite Powders Coated with 9 mol% ZnO for Cosmetic Applications in Sunscreens

    PubMed Central

    Ko, Horng-Huey; Chen, Hui-Ting; Yen, Feng-Ling; Lu, Wan-Chen; Kuo, Chih-Wei; Wang, Moo-Chin

    2012-01-01

    The preparation of TiO2 nanocrystallite powders coated with and without 9 mol% ZnO has been studied for cosmetic applications in sunscreens by a co-precipitation process using TiCl4 and Zn(NO3)2·6H2O as starting materials. XRD results show that the phases of anatase TiO2 and rutile TiO2 coexist for precursor powders without added ZnO (T-0Z) and calcined at 523 to 973 K for 2 h. When the T-0Z precursor powders are calcined at 1273 K for 2 h, only the rutile TiO2 appears. In addition, when the TiO2 precursor powders contain 9 mol% ZnO (T-9Z) are calcined at 873 to 973 K for 2 h, the crystallized samples are composed of the major phase of rutile TiO2 and the minor phases of anatase TiO2 and Zn2Ti3O8. The analyses of UV/VIS/NIR spectra reveal that the absorption of the T-9Z precursor powders after being calcined has a red-shift effect in the UV range with increasing calcination temperature. Therefore, the TiO2 nanocrystallite powders coated with 9 mol% ZnO can be used as the attenuate agent in the UV-A region for cosmetic applications in sunscreens. PMID:22408415

  18. Impact of bimetal electrodes on dielectric properties of TiO2 and Al-doped TiO2 films.

    PubMed

    Kim, Seong Keun; Han, Sora; Jeon, Woojin; Yoon, Jung Ho; Han, Jeong Hwan; Lee, Woongkyu; Hwang, Cheol Seong

    2012-09-26

    Rutile structured Al-doped TiO(2) (ATO) and TiO(2) films were grown on bimetal electrodes (thin Ru/thick TiN, Pt, and Ir) for high-performance capacitors. The work function of the top Ru layer decreased on TiN and increased on Pt and Ir when it was thinner than ~2 nm, suggesting that the lower metal within the electrodes influences the work function of the very thin Ru layer. The use of the lower electrode with a high work function for bottom electrode eventually improves the leakage current properties of the capacitor at a very thin Ru top layer (≤2 nm) because of the increased Schottky barrier height at the interface between the dielectric and the bottom electrode. The thin Ru layer was necessary to achieve the rutile structured ATO and TiO(2) dielectric films.

  19. Effects of TiO2 structures in dye-sensitized solar cell.

    PubMed

    Kim, Bok-Min; Rho, Seon-Gyun; Kang, Choon-Hyoung

    2011-02-01

    In this work, the effects of crystalline structure of the TiO2, which is incorporated in fabrication of the n-type electrode, on the DSSC performance were investigated in terms of the energy conversion efficiency. In this effort, TiO2 nanoparticle pastes with varying contents of rutile and anatase structures were prepared by using the ethanol mixing method. The most efficient photo-electro-chemical performance was achieved for the DSSC fabricated with the TiO2 paste in which the anatase form of the nanocrystal extends to 90%.

  20. Local Bonding Analysis of the Valence and Conduction Band Features of TiO2

    DTIC Science & Technology

    2007-01-01

    nanocrystalline samples tenuous at best. Hence, the phase of the unannealed TiO2 films cannot conclusively be identified as either anatase or rutile...reveals the local physical origin of the electronic structure in nanocrystalline films . TiO2 has further been chosen as a natural starting point to...thickness ratio is 2:1 for TiO2 . This assump- tion has been verified by XPS studies of the substrate Si 2p core-level spectra with film thickness. The

  1. Photoconductivity studies on amorphous and crystalline TiO2 films doped with gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Valverde-Aguilar, G.; García-Macedo, J. A.; Rentería-Tapia, V.; Aguilar-Franco, M.

    2011-06-01

    In this work, amorphous and crystalline TiO2 films were synthesized by the sol-gel process at room temperature. The TiO2 films were doped with gold nanoparticles. The films were spin-coated on glass wafers. The crystalline samples were annealed at 100°C for 30 minutes and sintered at 520°C for 2 h. All films were characterized using X-ray diffraction, transmission electronic microscopy and UV-Vis absorption spectroscopy. Two crystalline phases, anatase and rutile, were formed in the matrix TiO2 and TiO2/Au. An absorption peak was located at 570 nm (amorphous) and 645 nm (anatase). Photoconductivity studies were performed on these films. The experimental data were fitted with straight lines at darkness and under illumination at 515 nm and 645 nm. This indicates an ohmic behavior. Crystalline TiO2/Au films are more photoconductive than the amorphous ones.

  2. One-Step Solvothermal Synthesis of Black TiO2 Films for Enhanced Visible Absorption.

    PubMed

    Chen, Shanlong; Tao, Jie; Tao, Haijun; Wang, Chen; Shen, Yizhou; Jiang, Jiajia; Zhu, Lumin; Zeng, Xiaofei; Wang, Tao

    2016-03-01

    An economic and facile solvothermal method was reported to prepare black TiO2 films on Ti foils that possessed the property of optical absorption in the visible region. The UV-vis spectra showed that the black TiO2 samples exhibited highly enhanced visible-light absorption from 400-600 nm. The black TiO2 films were compact and uniform, composed of nanoparticles and nanosheets. Moreover, a mixed structure of anatase and rutile was present in black TiO2 films. The electron paramagnetic resonance (EPR) spectra confirmed the presence of Ti3+ in samples, which accounted for longer wavelength optical absorption. The results showed that the TiO2 films had retained their black color upon storage in ambient atmosphere for more than one month. Therefore, it was supposed that the ethylene glycol in solvothermal reaction was the key factor for the extension of the absorption spectrum.

  3. Effects of annealed temperature on the properties of TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Avesh

    2016-05-01

    In this work, the structural, morphological and electrical properties of TiO2 thin films are studied. The phase transformation of TiO2 from anatase to rutile is occurred at a certain temperature. This transformation increases defects concentration onthe surface of the film which acts as trapping sites for carriers, thereby affecting the Fermi level of TiO2 film.Quantitative estimation of Fermi level shifting is measured in terms of work function measurement using scanning Kelvin probe measurement. Work function of TiO2 was found to decrease with increasing annealed temperature indicating shifting of Fermi level towards conduction band. Position of Fermi level plays an important role in phase transformation and electronic properties of TiO2.

  4. Natural dye sensitized TiO2 nanorods assembly of broccoli shape based solar cells.

    PubMed

    Yuvapragasam, Akila; Muthukumarasamy, N; Agilan, S; Velauthapillai, Dhayalan; Senthil, T S; Sundaram, Senthilarasu

    2015-07-01

    TiO2 nanorods based thin films with rutile phase have been synthesized using template free low temperature hydrothermal method. The scanning electron microscope images showed that the prepared TiO2 samples were made of TiO2 nanorods and the nanorods had arranged by itself to form a broccoli like shape. The X-ray diffraction studies revealed that the prepared TiO2 samples exhibit rutile phase. The grown TiO2 nanorods had been sensitized using the flowers of Sesbania (S) grandiflora, leaves of Camellia (C) sinensis and roots of Rubia (R) tinctorum. Dye sensitized solar cells had been fabricated using the natural dye sensitized TiO2 nanorods based thin film photoelectrode and the open circuit voltage and short circuit current density were found to lie in the range of 0.45-0.6 V and 5.6-6.4 mA/cm(2) respectively. The photovoltaic performance of all the fabricated natural dye sensitized TiO2 solar cells indicate that natural dyes have the potential to be used as effective sensitizer in dye sensitized solar cells.

  5. Enhanced photocatalytic activity in anodized WO3-loaded TiO2 nanotubes

    NASA Astrophysics Data System (ADS)

    Nazari, M.; Golestani-Fard, F.; Bayati, R.; Eftekhari-Yekta, B.

    2015-04-01

    In this work, TiO2 and WO3-grafted TiO2 nanotubes were grown via anodizing of titanium substrates in tungstate containing electrolytes. The samples were characterized in detail by XRD, XPS, SEM, EDX, and UV-Vis spectrophotometry techniques. Besides, photocatalytic characteristics were evaluated through measuring the degradation rate of 4-chlorophenol to establish a correlation between structure and photochemical properties. We were able to control morphology and growth mode of nanotubes from a tubular to a worm-like structure by changing the electrolyte composition. The samples possessed an anatase-rutile matrix where the anatase/rutile ratio was found to increase with the concentration of tungstate in the electrolyte. We attributed this observation to change in electrical conductivity of the electrolyte and the heat generated on the substrates. It was unambiguously revealed that a composite of WO3 and TiO2 forms and, in parallel, tungsten is doped into the crystalline lattice of TiO2. The maximum photocatalytic reaction rate constant for TiO2 and WO3-TiO2 samples was determined to be 0.0131 and 0.0174 min-1 respectively. The grafting TiO2 nanotubes with WO3 enhances the photocatalytic activity mainly due to the hindrance of charge carrier recombination and the formation of a more acidic surface. We established a correlation between structure, stoichiometry, and photocatalytic characteristics of nanotubes.

  6. Raman study of TiO2 coatings modified by UV pulsed laser

    NASA Astrophysics Data System (ADS)

    Belka, Radosław; Keczkowska, Justyna; Sek, Piotr

    2016-12-01

    The TiO2 coatings were prepared by simple sol-gel method and modified by UV pulsed laser. TiO2, also know as titania, is a ceramic compound, existing in numerous polymorphic forms, mainly as tetragonal rutile and anatase, and rhomboidal brookite. Rutile is the most stable form of titanium dioxide, whereas anatase is a metastable form, created in lower temperatures than rutile. Anatase is marked with higher specific surface area, porosity and a higher number of surface hydroxyl groups as compared to rutile. The unique optical and electronic properties of TiO2 results in its use as semiconductors dielectric mirrors, sunscreen and UV-blocking pigments and especially as photocatalyst. In this paper, the tetraisopropoxide was used as Ti precursor according to sol-gel method. An organic base was applied during sol preparation. Prepared gel was coated on glass substrates and calcined in low temperature to obtain amorphous phase of titania. Prepared coatings were modified by UV picosecond pulse laser with different pulse repetition rate and pulse power. Physical modification of the coatings using laser pulses was intended in order change the phase content of the produced material. Raman spectroscopy (RS) method was applied to studies of modified coatings as it is one of the basic analytical techniques, supporting the identification of compounds and obtaining information about the structure. Especially, RS is a useful method for distinguishing the anatase and rutile phases. In these studies, anatase to rutile transformation was observed, depending on laser parameters.

  7. High efficiency dye-sensitized solar cell based on novel TiO2 nanorod/nanoparticle bilayer electrode.

    PubMed

    Hafez, Hoda; Lan, Zhang; Li, Qinghua; Wu, Jihuai

    2010-08-26

    High light-to-energy conversion efficiency was achieved by applying novel TiO2 nanorod/nanoparticle (NR/NP) bilayer electrode in the N719 dye-sensitized solar cells. The short-circuit current density (J SC), the open-circuit voltage (V OC), the fill factor (FF), and the overall efficiency (η) were 14.45 mA/cm(2), 0.756 V, 0.65, and 7.1%, respectively. The single-crystalline TiO2 NRs with length 200-500 nm and diameter 30-50 nm were prepared by simple hydrothermal methods. The dye-sensitized solar cells with pure TiO2 NR and pure TiO2 NP electrodes showed only a lower light-to-electricity conversion efficiency of 4.4% and 5.8%, respectively, compared with single-crystalline TiO2 NRs. This can be attributed to the new NR/NP bilayer design that can possess the advantages of both building blocks, ie, the high surface area of NP aggregates and rapid electron transport rate and the light scattering effect of single-crystalline NRs.

  8. Improvement of solar energy conversion with Nb-incorporated TiO2 hierarchical microspheres.

    PubMed

    Hoang, Son; Ngo, Thong Q; Berglund, Sean P; Fullon, Raymond R; Ekerdt, John G; Mullins, C Buddie

    2013-07-22

    Niobium-modified TiO2 hierarchical spherical micrometer-size particles, which consist of many nanowires, are synthesized by solvothermal synthesis and studied as photoelectrodes for water photo-oxidation and dye-sensitized solar cell (DSSC) applications. Incorporation of Nb leads to a rutile-to-anatase TiO2 phase transition in the TiO2 hierarchical spheres (HSs), with the anatase percentage increasing from 0% for the pristine TiO2 HSs to 47.6% for the 1.82 at.% Nb-incorporated TiO2 sample. Incorporation of Nb leads to significant improvements in water photo-oxidation with the photocurrents reaching 70.5 μA cm(-2) at 1.23 V versus the reversible hydrogen electrode, compared with 28.3 μA cm(-2) for the pristine TiO2 sample. The photoconversion efficiency of Nb:TiO2 HS-based DSSCs reaches 6.09±0.15% at 0.25 at.% Nb, significantly higher than that for the pristine TiO2 HS cells (3.99±0.02%). In addition, the incident-photon-to-current efficiency spectra for DSSCs show that employing TiO2 and Nb:TiO2 HSs provides better light harvesting, especially of long-wavelength photons, than anatase TiO2 nanoparticle-based DSSCs.

  9. Controllable Synthesis and Tunable Photocatalytic Properties of Ti(3+)-doped TiO2.

    PubMed

    Ren, Ren; Wen, Zhenhai; Cui, Shumao; Hou, Yang; Guo, Xiaoru; Chen, Junhong

    2015-06-05

    Photocatalysts show great potential in environmental remediation and water splitting using either artificial or natural light. Titanium dioxide (TiO2)-based photocatalysts are studied most frequently because they are stable, non-toxic, readily available, and highly efficient. However, the relatively wide band gap of TiO2 significantly limits its use under visible light or solar light. We herein report a facile route for controllable synthesis of Ti(3+)-doped TiO2 with tunable photocatalytic properties using a hydrothermal method with varying amounts of reductant, i.e., sodium borohydride (NaBH4). The resulting TiO2 showed color changes from light yellow, light grey, to dark grey with the increasing amount of NaBH4. The present method can controllably and effectively reduce Ti(4+) on the surface of TiO2 and induce partial transformation of anatase TiO2 to rutile TiO2, with the evolution of nanoparticles into hierarchical structures attributable to a high pressure and strong alkali environment in the synthesis atmosphere; in this way, the photocatalytic activity of Ti(3+)-doped TiO2 under visible-light can be tuned. The as-developed strategy may open up a new avenue for designing and functionalizing TiO2 materials for enhancing visible light absorption, narrowing band gap, and improving photocatalytic activity.

  10. Controllable Synthesis and Tunable Photocatalytic Properties of Ti3+-doped TiO2

    PubMed Central

    Ren, Ren; Wen, Zhenhai; Cui, Shumao; Hou, Yang; Guo, Xiaoru; Chen, Junhong

    2015-01-01

    Photocatalysts show great potential in environmental remediation and water splitting using either artificial or natural light. Titanium dioxide (TiO2)-based photocatalysts are studied most frequently because they are stable, non-toxic, readily available, and highly efficient. However, the relatively wide band gap of TiO2 significantly limits its use under visible light or solar light. We herein report a facile route for controllable synthesis of Ti3+-doped TiO2 with tunable photocatalytic properties using a hydrothermal method with varying amounts of reductant, i.e., sodium borohydride (NaBH4). The resulting TiO2 showed color changes from light yellow, light grey, to dark grey with the increasing amount of NaBH4. The present method can controllably and effectively reduce Ti4+ on the surface of TiO2 and induce partial transformation of anatase TiO2 to rutile TiO2, with the evolution of nanoparticles into hierarchical structures attributable to a high pressure and strong alkali environment in the synthesis atmosphere; in this way, the photocatalytic activity of Ti3+-doped TiO2 under visible-light can be tuned. The as-developed strategy may open up a new avenue for designing and functionalizing TiO2 materials for enhancing visible light absorption, narrowing band gap, and improving photocatalytic activity. PMID:26044406

  11. A comparative study of TiO2 nanoparticles synthesized in premixed and diffusion flames

    NASA Astrophysics Data System (ADS)

    Ma, Hsiao-Kang; Yang, Hsiung-An

    2010-12-01

    Previous studies have been shown that synthesis of titania (TiO2) crystalline phase purity could be effectively controlled by the oxygen concentration through titanium tetra-isopropoxide (TTIP) via premixed flame from a Bunsen burner. In this study, a modified Hencken burner was used to synthesize smaller TiO2 nanoparticles via short diffusion flames. The frequency of collisions among particles would decrease and reduce TiO2 nanoparticle size in a short diffusion flame height. The crystalline structure of the synthesized nanoparticles was characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Barrett-Joyner-Halenda (BJH) and Brunauer-Emmett-Teller (BET) measurements. The characteristic properties of TiO2 nanoparticles synthesized from a modified Hencken burner were compared with the results from a Bunsen burner and commercial TiO2 (Degussa P25). The results showed that the average particle size of 6.63 nm from BET method was produced by a modified Hencken burner which was smaller than the TiO2 in a Bunsen burner and commercial TiO2. Moreover, the rutile content of TiO2 nanoparticles increased as the particle collecting height increased. Also, the size of TiO2 nanoparticles was highly dependent on the TTIP loading and the collecting height in the flame.

  12. Optical properties of hierarchical-nanostructured TiO2 and its time-dependent photo-degradation of gaseous acetaldehyde

    NASA Astrophysics Data System (ADS)

    Ahn, Kyun; Kim, Min-Sun; Kim, Soon-Hyun; Hyun Kim, Jae; Jeong, Se-Young; Kim, Jong-Pil; Sung Jin, Jong; Cho, Chae-Ryong

    2013-12-01

    The TiO2 hierarchical nanostructures (HNs) composed of rutile TiO2 nanowires on anatase TiO2 nanofibers had higher photocatalytic activities of 62% and 48% than the commercial TiO2 nanoparticles (˜21 nm diameter) in the continuous flow mode and closed-circulation mode, respectively, leading to an efficient degradation of gaseous acetaldehyde under UV-light irradiation. This behavior may be attributed to the effective TiO2 HNs with specific surface area of 85.1 m2/g and lower radiative recombination of self-trapped excitons, enabling an effective electron-hole separation.

  13. Synthesis and characterization of structural and optical properties of single crystalline a-TiO2 films on MgAl2O4(111) substrate

    NASA Astrophysics Data System (ADS)

    Xu, Haisheng; Feng, Xianjin; Luan, Caina; Ma, Jin

    2017-01-01

    Anatase phase TiO2 (a-TiO2) films have been deposited on MgAl2O4(111) substrates by the metal organic chemical vapor deposition (MOCVD) method at the substrate temperatures of 500-650°C. The structural analyses showed that the films were highly (004) oriented with tetragonal anatase structure and the epitaxial relationship was given as a-TiO2(004)||MgAl2O4 (111). The sample prepared at 600°C exhibited the best crystallization with a single-crystalline epitaxial film. The average transmittance of every TiO2 film in the visible range exceeded 90% excluding the influence of the substrate. The morphology and composition of the TiO2 films have also been studied in detail.

  14. Absence of ferromagnetism in Fe-doped TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Balcells, Ll.; Frontera, C.; Sandiumenge, F.; Roig, A.; Martínez, B.; Kouam, J.; Monty, C.

    2006-09-01

    The structural and magnetic properties of Ti1-xFexO2-ɛ (x≈0.13) nanoparticles prepared by vaporization-condensation method are analyzed. Samples, mainly of rutile phase, exhibit a pronounced mosaic structure and are free of secondary phases or impurities. Mössbauer spectroscopy evidences the absence of magnetic ordering and shows features indicative of the existence of two doublets assigned to two different structural arrangements of Fe3+ ions substituting for Ti4+ ions in the rutile structure. The application of the Goodenough-Kanamori rules clearly indicates that conventional FM ordering should not be expected in Fe-doped TiO2 with rutile structure.

  15. Photocatalytical Antibacterial Activity of Mixed-Phase TiO2 Nanocomposite Thin Films against Aggregatibacter actinomycetemcomitans.

    PubMed

    Yeniyol, Sinem; Mutlu, Ilven; He, Zhiming; Yüksel, Behiye; Boylan, Robert Joseph; Ürgen, Mustafa; Karabuda, Zihni Cüneyt; Basegmez, Cansu; Ricci, John Lawrence

    2015-01-01

    Mixed-phase TiO2 nanocomposite thin films consisting of anatase and rutile prepared on commercially pure Ti sheets via the electrochemical anodization and annealing treatments were investigated in terms of their photocatalytic activity for antibacterial use around dental implants. The resulting films were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD). The topology was assessed by White Light Optical Profiling (WLOP) in the Vertical Scanning Interferometer (VSI) mode. Representative height descriptive parameters of roughness R a and R z were calculated. The photocatalytic activity of the resulting TiO2 films was evaluated by the photodegradation of Rhodamine B (RhB) dye solution. The antibacterial ability of the photocatalyst was examined by Aggregatibacter actinomycetemcomitans suspensions in a colony-forming assay. XRD showed that anatase/rutile mixed-phase TiO2 thin films were predominantly in anatase and rutile that were 54.6 wt% and 41.9 wt%, respectively. Craters (2-5 µm) and protruding hills (10-50 µm) on Ti substrates were produced after electrochemical anodization with higher R a and R z surface roughness values. Anatase/rutile mixed-phase TiO2 thin films showed 26% photocatalytic decolorization toward RhB dye solution. The number of colonizing bacteria on anatase/rutile mixed-phase TiO2 thin films was decreased significantly in vitro. The photocatalyst was effective against A. actinomycetemcomitans colonization.

  16. Photocatalytical Antibacterial Activity of Mixed-Phase TiO2 Nanocomposite Thin Films against Aggregatibacter actinomycetemcomitans

    PubMed Central

    Yeniyol, Sinem; Mutlu, Ilven; He, Zhiming; Yüksel, Behiye; Boylan, Robert Joseph; Ürgen, Mustafa; Karabuda, Zihni Cüneyt; Basegmez, Cansu; Ricci, John Lawrence

    2015-01-01

    Mixed-phase TiO2 nanocomposite thin films consisting of anatase and rutile prepared on commercially pure Ti sheets via the electrochemical anodization and annealing treatments were investigated in terms of their photocatalytic activity for antibacterial use around dental implants. The resulting films were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD). The topology was assessed by White Light Optical Profiling (WLOP) in the Vertical Scanning Interferometer (VSI) mode. Representative height descriptive parameters of roughness Ra and Rz were calculated. The photocatalytic activity of the resulting TiO2 films was evaluated by the photodegradation of Rhodamine B (RhB) dye solution. The antibacterial ability of the photocatalyst was examined by  Aggregatibacter actinomycetemcomitans suspensions in a colony-forming assay. XRD showed that anatase/rutile mixed-phase TiO2 thin films were predominantly in anatase and rutile that were 54.6 wt% and 41.9 wt%, respectively. Craters (2–5 µm) and protruding hills (10–50 µm) on Ti substrates were produced after electrochemical anodization with higher Ra and Rz surface roughness values. Anatase/rutile mixed-phase TiO2 thin films showed 26% photocatalytic decolorization toward RhB dye solution. The number of colonizing bacteria on anatase/rutile mixed-phase TiO2 thin films was decreased significantly in vitro. The photocatalyst was effective against A. actinomycetemcomitans colonization. PMID:26576430

  17. Hydrogen plasma reduced black TiO2sbnd B nanowires for enhanced photoelectrochemical water-splitting

    NASA Astrophysics Data System (ADS)

    Tian, Zhangliu; Cui, Huolei; Zhu, Guilian; Zhao, Wenli; Xu, JiJian; Shao, Feng; He, Jianqiao; Huang, Fuqiang

    2016-09-01

    Black TiO2 with various nanostructures and phase constitutions have been reported to exhibit excellent photocatalytic and photoelectrochemical (PEC) performance. Here, we report the fabrication of black nanostructured TiO2sbnd B through hydrogen plasma assisted reduction and its enhanced PEC properties for the first time. Both the obtained TiO2sbnd B and black TiO2sbnd B are single crystalline nanowires, while the black TiO2sbnd B samples exhibit much stronger visible and infrared light absorption. The optimal black TiO2sbnd B sample obtained by hydrogen plasma treatment at 425 °C yields a photocurrent density of 0.85 mA cm-2, a rather low onset potential of -0.937 VAg/AgCl and a high applied bias photon-to-current efficiency (ABPE) of 0.363%, which is far superior to the TiO2sbnd B (0.15 mA cm-2 photocurrent, -0.917 VAg/AgCl onset potential and 0.138% ABPE). The significantly enhanced PEC performance of the black TiO2sbnd B is ascribed to the introduction of moderate surface oxygen vacancies. These results indicate that the black TiO2sbnd B is a promising material for PEC application and solar energy utilization.

  18. Photocatalytic performance of nitrogen, osmium co-doped TiO2 for removal of eosin yellow in water under simulated solar radiation.

    PubMed

    Kuvarega, Alex T; Krause, Rui W M; Mamba, Bhekie B

    2013-07-01

    Nitrogen, osmium co-doped TiO2 photocatalysts were prepared by a modified sol-gel method using ammonia as the nitrogen source and osmium tetroxide as the source of osmium. The role of rutile phase OsO2 in enhancing the photocatalytic activity of rutile TiO2 towards the degradation of Eosin Yellow was investigated. The materials were characterised by various techniques that include FTIR, Raman, XRD, SEM, EDS, TEM, TGA and DRUV-Vis. The amorphous, oven dried sample was transformed to the anatase and then the rutile phase with increasing calcination temperature. DRUV-Vis analysis revealed a red shift in absorption with increasing calcination temperature, confirmed by a decrease in the band gap of the material. The photocatalytic activity of N, Os co-doped TiO2 was evaluated using eosin yellow degradation and activity increased with increase in calcination temperature under simulated solar irradiation. The rutile phase of the co-doped TiO2 was found to be more effective in degrading the dye (k(a) = 1.84 x 10(-2) min(-1)) compared to the anatase co-doped phase (k(a) = 9.90 x 10(-3) min(-1)). The enhanced photocatalytic activity was ascribed to the synergistic effects of rutile TiO2 and rutile OsO2 in the N, Os co-doped TiO2.

  19. Temperature dependent tuning of the flat band voltages of TiO2/Si interfaces

    NASA Astrophysics Data System (ADS)

    Nasim, F.; Ali, A.; Bhatti, A. S.; Naseem, S.

    2011-12-01

    In this work, we present study of charge accumulation at the TiO2/Si interfaces and its variation in the TiO2 thin films sputter-deposited on n-Si, p-Si, and B-implanted Si substrates at various growth temperatures. TiO2 films, deposited in an oxygen deficient environment, showed significant growth of rutile phase and absence of anatase phase in the as-grown films. Annealing in air resulted in emergence of anatase phase, thus improving the ratio of anatase to rutile phase in TiO2 films. The flatband voltages determined from capacitance-voltage measurements were observed to be high in the rutile phase TiO2 and dropped considerably on annealing, due to formation of the anatase phase. The drop in the flatband voltages on annealing was also observed to depend strongly on the initial growth temperature. Films grown at high temperatures showed relatively low flatband voltages as compared to the films grown at room temperature. It is demonstrated that VFB strongly depends on the interface traps, and oxide-related defects were two orders of magnitude smaller than interface traps. The amount of depletion of the interface charge was found to depend on annealing. In the end, we also demonstrate that interface traps and oxide defects are not the only factors affecting the band bending, but the underlying substrate also plays an important role.

  20. Plasma sprayed rutile titania-nanosilver antibacterial coatings

    NASA Astrophysics Data System (ADS)

    Gao, Jinjin; Zhao, Chengjian; Zhou, Jingfang; Li, Chunxia; Shao, Yiran; Shi, Chao; Zhu, Yingchun

    2015-11-01

    Rutile titania (TiO2) coatings have superior mechanical properties and excellent stability that make them preferential candidates for various applications. In order to prevent infection arising from bacteria, significant efforts have been focused on antibacterial TiO2 coatings. In the study, titania-nanosilver (TiO2/Ag) coatings with five different kinds of weight percentages of silver nanoparticles (AgNPs) were prepared by plasma spray. The feedstock powders, which had a composition of rutile TiO2 powders containing 1-10,000 ppm AgNPs, were double sintered and deposited on stainless steel substrates with optimized spraying parameters. X-Ray diffraction and scanning electron microscopy were used to analysize the phase composition and surface morphology of TiO2/Ag powders and coatings. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were employed to examine the antibacterial activity of the as-prepared coatings by bacterial counting method. The results showed that silver existed homogeneously in the TiO2/Ag coatings and no crystalline changed happened in the TiO2 structure. The reduction ratios on the TiO2/Ag coatings with 10 ppm AgNPs were as high as 94.8% and 95.6% for E. coli and S. aureus, respectively, and the TiO2/Ag coatings with 100-1000 ppm AgNPs exhibited 100% bactericidal activity against E. coli and S. aureus, which indicated the TiO2/Ag coatings with more than 10 ppm AgNPs had strong antibacterial activity. Moreover, the main factors influencing the antibacterial properties of TiO2/Ag coatings were discussed with grain size and the content of silver as well as the microstructure of the coatings.

  1. Unprecedented coloration of rutile titanium dioxide nanocrystalline thin films.

    PubMed

    Mane, Rajaram S; Joo, Oh-Shim; Lee, Won Joo; Han, Sung-Hwan

    2007-01-01

    In this communication, TiO2 nanocrystalline thin films synthesized by a room temperature (27 degrees C) chemical dip process. To our knowledge, this is first report of the preparation of nanoscale rutile TiO2 particles from common inorganic salt at such low temperature. Interestingly, unprecedented dynamic color change accompanies with titanium dioxide grain size, which can be seen with the naked eye that generated curiosity in our mind to check UV-vis absorption, where significant changes were observed. The room temperature synthesized thin films of rutile titanium dioxide make it a potential candidate for high-compatibility material, which can be used in artificial heart valves.

  2. A single crystalline InP nanowire photodetector

    NASA Astrophysics Data System (ADS)

    Yan, Xin; Li, Bang; Wu, Yao; Zhang, Xia; Ren, Xiaomin

    2016-08-01

    Single crystalline nanowires are critical for achieving high-responsivity, high-speed, and low-noise nanoscale photodetectors. Here, we report a metal-semiconductor-metal photodetector based on a single crystalline InP nanowire. The nanowires are grown by a self-catalyzed method and exhibit stacking-fault-free zinc blende crystal structure. The nanowire exhibits a typical n-type semiconductor property and shows a low room temperature dark current of several hundred pA at moderate biases. A photoresponsivity of 6.8 A/W is obtained at a laser power density of 0.2 mW/cm2. This work demonstrates that single crystalline InP nanowires are good candidates for future optoelectronic device applications.

  3. Solar-light photocatalytic disinfection using crystalline/amorphous low energy bandgap reduced TiO2

    PubMed Central

    Kim, Youngmin; Hwang, Hee Min; Wang, Luyang; Kim, Ikjoon; Yoon, Yeoheung; Lee, Hyoyoung

    2016-01-01

    A generation of reactive oxygen species (ROS) from TiO2 under solar light has been long sought since the ROS can disinfect organic pollutants. We found that newly developed crystalline/amorphous reduced TiO2 (rTiO2) that has low energy bandgap can effectively generate ROS under solar light and successfully remove a bloom of algae. The preparation of rTiO2 is a one-pot and mass productive solution-process reduction using lithium-ethylene diamine (Li-EDA) at room temperature. Interestingly only the rutile phase of TiO2 crystal was reduced, while the anatase phase even in case of both anatase/rutile phased TiO2 was not reduced. Only reduced TiO2 materials can generate ROS under solar light, which was confirmed by electron spin resonance. Among the three different types of Li-EDA treated TiO2 (anatase, rutile and both phased TiO2), the both phased rTiO2 showed the best performance to produce ROS. The generated ROS effectively removed the common green algae Chlamydomonas. This is the first report on algae degradation under solar light, proving the feasibility of commercially available products for disinfection. PMID:27121120

  4. Solar-light photocatalytic disinfection using crystalline/amorphous low energy bandgap reduced TiO2.

    PubMed

    Kim, Youngmin; Hwang, Hee Min; Wang, Luyang; Kim, Ikjoon; Yoon, Yeoheung; Lee, Hyoyoung

    2016-04-28

    A generation of reactive oxygen species (ROS) from TiO2 under solar light has been long sought since the ROS can disinfect organic pollutants. We found that newly developed crystalline/amorphous reduced TiO2 (rTiO2) that has low energy bandgap can effectively generate ROS under solar light and successfully remove a bloom of algae. The preparation of rTiO2 is a one-pot and mass productive solution-process reduction using lithium-ethylene diamine (Li-EDA) at room temperature. Interestingly only the rutile phase of TiO2 crystal was reduced, while the anatase phase even in case of both anatase/rutile phased TiO2 was not reduced. Only reduced TiO2 materials can generate ROS under solar light, which was confirmed by electron spin resonance. Among the three different types of Li-EDA treated TiO2 (anatase, rutile and both phased TiO2), the both phased rTiO2 showed the best performance to produce ROS. The generated ROS effectively removed the common green algae Chlamydomonas. This is the first report on algae degradation under solar light, proving the feasibility of commercially available products for disinfection.

  5. Single-crystalline monolayer and multilayer graphene nano switches

    SciTech Connect

    Li, Peng; Cui, Tianhong; Jing, Gaoshan; Zhang, Bo; Sando, Shota

    2014-03-17

    Growth of monolayer, bi-layer, and tri-layer single-crystalline graphene (SCG) using chemical vapor deposition method is reported. SCG's mechanical properties and single-crystalline nature were characterized and verified by atomic force microscope and Raman spectroscopy. Electro-mechanical switches based on mono- and bi-layer SCG were fabricated, and the superb properties of SCG enable the switches to operate at pull-in voltage as low as 1 V, and high switching speed about 100 ns. These devices exhibit lifetime without a breakdown of over 5000 cycles, far more durable than any other graphene nanoelectromechanical system switches reported.

  6. Lithium insertion in nanostructured TiO(2)(B) architectures.

    PubMed

    Dylla, Anthony G; Henkelman, Graeme; Stevenson, Keith J

    2013-05-21

    Electric vehicles and grid storage devices have potentialto become feasible alternatives to current technology, but only if scientists can develop energy storage materials that offer high capacity and high rate capabilities. Chemists have studied anatase, rutile, brookite and TiO2(B) (bronze) in both bulk and nanostructured forms as potential Li-ion battery anodes. In most cases, the specific capacity and rate of lithiation and delithiation increases as the materials are nanostructured. Scientists have explained these enhancements in terms of higher surface areas, shorter Li(+) diffusion paths and different surface energies for nanostructured materials allowing for more facile lithiation and delithiation. Of the most studied polymorphs, nanostructured TiO2(B) has the highest capacity with promising high rate capabilities. TiO2(B) is able to accommodate 1 Li(+) per Ti, giving a capacity of 335 mAh/g for nanotubular and nanoparticulate TiO2(B). The TiO2(B) polymorph, discovered in 1980 by Marchand and co-workers, has been the focus of many recent studies regarding high power and high capacity anode materials with potential applications for electric vehicles and grid storage. This is due to the material's stability over multiple cycles, safer lithiation potential relative to graphite, reasonable capacity, high rate capability, nontoxicity, and low cost (Bruce, P. G.; Scrosati, B.; Tarascon, J.-M. Nanomaterials for Rechargeable Lithium Batteries. Angew. Chem., Int. Ed.2008, 47, 2930-2946). One of the most interesting properties of TiO2(B) is that both bulk and nanostructured forms lithiate and delithiate through a surface redox or pseudocapacitive charging mechanism, giving rise to stable high rate charge/discharge capabilities in the case of nanostructured TiO2(B). When other polymorphs of TiO2 are nanostructured, they still mainly intercalate lithium through a bulk diffusion-controlled mechanism. TiO2(B) has a unique open crystal structure and low energy Li

  7. Hydroxyapatite growth on anodic TiO2 nanotubes.

    PubMed

    Tsuchiya, Hiroaki; Macak, Jan M; Müller, Lenka; Kunze, Julia; Müller, Frank; Greil, Peter; Virtanen, Sannakaisa; Schmuki, Patrik

    2006-06-01

    In the present work, we study the growth of hydroxyapatite formation on different TiO(2) nanotube layers. The nanotube layers were fabricated by electrochemical anodization of titanium in fluoride-containing electrolytes. To study various nanotube lengths, layers with an individual tube diameter of 100 nm were grown to a thickness of approximately 2 mum or 500 nm. The ability to form apatite on the nanotube layers was examined by immersion tests combined with SEM, XRD and FT-IR investigations. For reference, experiments were also carried out on compact anodic TiO(2) layers. The results clearly show that the presence of the nanotubes on a titanium surface enhances the apatite formation and that the 2-mum thick nanotube layer triggers deposition faster than the thinner layers. Tubes annealed to anatase, or a mixture of anatase and rutile are clearly more efficient in promoting apatite formation than the tubes in their "as-formed" amorphous state.

  8. Size effect on thermal stability of nanocrystalline anatase TiO2

    NASA Astrophysics Data System (ADS)

    Wang, Junwei; Mishra, Ashish Kumar; Zhao, Qing; Huang, Liping

    2013-06-01

    Thermal stability of nanocrystalline anatase TiO2 against coarsening and anatase-rutile phase transformation was studied using both a pyroprobe heater and a conventional furnace. The pyroprobe heater, because of the programmable control and the ultra-fast heating rate (up to 20 000 °C s-1), for the first time, allows us to access the very early stage of the sintering and phase-transformation processes. Our short time (0-30 s) heat treatments reveal that rapid grain growth takes place first in anatase nanoparticles (NPs) upon the initial heating due to the lower activation energy compared with that for the anatase-rutile phase transformation. Meanwhile, rutile-like structural elements develop at the interface between anatase NPs during the fast grain growth period, which evolve into rutile nuclei with time, followed by nuclei growth, to convert nanocrystalline anatase into rutile rapidly in the temperature range where the phase transformation does not occur in coarse anatase TiO2. Overall, both grain growth and phase transformation in smaller anatase NPs happen at lower temperatures and faster than in bigger ones. The coupled sintering-phase-transformation mechanism can be exploited to design thermally stable nanocrystalline anatase TiO2 by reducing the sintering kinetics, for example, via minority additives.

  9. Thermally induced superhydrophilicity in TiO2 films prepared by supersonic aerosol deposition.

    PubMed

    Park, Jung-Jae; Kim, Do-Yeon; Latthe, Sanjay S; Lee, Jong-Gun; Swihart, Mark T; Yoon, Sam S

    2013-07-10

    Superhydrophilic and superhydrophobic surfaces enable self-cleaning phenomena, either forming a continuous water film or forming droplets that roll off the surface, respectively. TiO2 films are well-known for their extreme hydrophilicity and photocatalytic characteristics. Here, we describe nanostructured TiO2 thin films prepared by supersonic aerosol deposition, including a thorough study of the effects of the annealing temperature on the crystal structure, surface morphology, surface roughness, and wetting properties. Powder X-ray diffraction showed that supersonic deposition resulted in fragmentation and amorphization of the micrometer-size anatase (60%)-rutile (40%) precursor powder and that, upon annealing, a substantial fraction of the film (~30%) crystallized in the highly hydrophilic but metastable brookite phase. The film morphology was also somewhat modified after annealing. Scanning electron microscopy and atomic force microscopy revealed rough granular films with high surface roughness. The as-deposited TiO2 films were moderately hydrophilic with a water contact angle (θ) of ~45°, whereas TiO2 films annealed at 500 °C became superhydrophilic (θ ~ 0°) without UV illumination. This thermally induced superhydrophilicity of the TiO2 films can be explained on the basis of the combined effects of the change in the crystal structure, surface microstructure, and surface roughness. Supersonic aerosol deposition followed by annealing is uniquely able to produce these nanostructured films containing a mixture of all three TiO2 phases (anatase, rutile, and brookite) and exhibiting superhydrophilicity without UV illumination.

  10. The adsorption and photo-degradation of oxalic acid at the TiO2 surface.

    NASA Astrophysics Data System (ADS)

    Mendive, Cecilia; Blesa, Miguel; Bahnemann, Detlef

    2006-03-01

    Oxalic acid is the simplest model compound to study the heterogeneous photocatalytic oxidation of pollutants on TiO2 containing more than one carboxylate group. We have carried out a study of a system of an oxalic acid solution in contact with a thin film of TiO2 particles employing ATR - FTIR in combination with quantum chemical calculations. Thus, possible adsorption structures have been identified and molecular dynamic simulations have been used to compare their predictions with the experimental data. It was found that the adsorption of oxalic acid on TiO2 in the dark can be explained in terms of two surface complexation modes for the anatase phase and only one surface complexation mode for the rutile phase. We have found that under illumination one of the complexes on the anatase phase preferably undergoes photo-degradation. At the same time water molecules are desorbed from the TiO2 surface by a thermal mechanism induced by the absorption of photons. Both processes favor the adsorption of more molecules of oxalic acid at the TiO2 surface which is thus enriched in the second complexation mode. A similar mechanism was found to occur on the rutile phase. The only complexation mode appears not to be photo-sensitive but the TiO2 surface is enriched in oxalic acid under illumination due to the replacement of photo-desorbed water molecules.

  11. Design of Novel Visible Light Active Photocatalyst Materials: Surface Modified TiO2.

    PubMed

    Nolan, Michael; Iwaszuk, Anna; Lucid, Aoife K; Carey, John J; Fronzi, Marco

    2016-07-01

    Work on the design of new TiO2 based photocatalysts is described. The key concept is the formation of composite structures through the modification of anatase and rutile TiO2 with molecular-sized nanoclusters of metal oxides. Density functional theory (DFT) level simulations are compared with experimental work synthesizing and characterizing surface modified TiO2 . DFT calculations are used to show that nanoclusters of metal oxides such as TiO2 , SnO/SnO2 , PbO/PbO2 , ZnO and CuO are stable when adsorbed at rutile and anatase surfaces, and can lead to a significant red shift in the absorption edge which will induce visible light absorption; this is the first requirement for a useful photocatalyst. The origin of the red shift and the fate of excited electrons and holes are determined. For p-block metal oxides the oxidation state of Sn and Pb can be used to modify the magnitude of the red shift and its mechanism. Comparisons of recent experimental studies of surface modified TiO2 that validate our DFT simulations are described. These nanocluster-modified TiO2 structures form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with a correct choice of nanocluster modified can be applied to other reactions.

  12. Oxygen release and structural changes in TiO2 films during photocatalytic oxidation

    NASA Astrophysics Data System (ADS)

    Yoshida, Kenta; Nanbara, Takahiro; Yamasaki, Jun; Tanaka, Nobuo

    2006-04-01

    Changes in the crystal structure and grain modifications in titanium oxide (TiO2) thin films were observed during the photocatalytic oxidation of hydrocarbons. When the hydrocarbon and collodion films were irradiated, single crystalline titanium oxide transformed into polycrystals. The titanium oxide films gradually became network aggregates. These changes were analyzed with a dedicated in situ transmission electron microscope and observed three dimensionally by electron tomography. A detailed analysis of electron energy loss spectra of the samples also revealed that the changes were associated with the loss of oxygen atoms in the TiO2 crystal lattice. Correlations between the polycrystalline grain size of TiO2 and its catalyst activity were discussed based on the measured data.

  13. Growth of single-crystalline particles of metallic copper

    NASA Astrophysics Data System (ADS)

    Guo, Jinlei; Shen, Shaobo; Zhao, Yingshi; Wang, Fuming

    2016-10-01

    Most of ultrafine particles of metallic copper reported so far were of polycrystalline structures. Here, some ultrafine particles of metallic copper of single-crystalline structure were synthesized in gas phase. Some mixtures of a raw copper powder (about 79 μm) and sodium chloride powder were used as the precursor materials. The materials were chlorinated by dry chlorine at 400 °C. Some anhydrous eutectics composed of copper chlorides and sodium chloride were thus obtained. The eutectics were first heated in situ up to 900 °C and then carried to a gas space by evaporation using a flowing Argon, where they met H2 and were reduced to metallic copper particles. It was found that all these copper particles prepared were of single-crystalline structure irrespective of the molar ratio of raw copper and sodium chloride. When the molar ratio of NaCl to Cu in the precursor materials was 1 to 3, some dispersed octahedral particles of single-crystalline copper with an average size of 776 nm were prepared. However, when the ratio was increased to 4 to 1, some dispersed spherical particles of single-crystalline copper with a size of 92 nm were obtained. No impurities from the two shapes of copper particles were detected. The mechanisms involved in controlling the shape and size of copper particles were proposed.

  14. Influence of TiO2 Nanorod Arrays on the Bilayered Photoanode for Dye-Sensitized Solar Cells

    NASA Astrophysics Data System (ADS)

    Cao, Ya; Li, Zhen; Wang, Yang; Zhang, Tao; Li, Yinchang; Liu, Xueqin; Li, Fei

    2016-10-01

    A TiO2 bilayered structure consisting of TiO2 nanoparticles (TiO2NP) as an overlayer and single-crystal rutile TiO2 nanorods (TiO2 NRs) as an underlayer on a transparent conductive fluorine-doped tin oxide substrate was designed as the photoanode of dye-sensitized solar cells (DSSCs) through a facile hydrothermal treatment followed by a doctor-blade method. DSSCs based on the hierarchical TiO2 nano-architecture photoelectrode shows a power conversion efficiency of 7.39% because the relatively large specific surface area of TiO2NP increased the dye absorption, and oriented one-dimensional TiO2 NRs enhanced the light harvesting capability, accelerating interfacial electron transport. In particular, we observed the growth morphology of the TiO2 nanorod arrays in the bilayered photoanode and the influence of the whole solar cell. The result indicated that the TiO2 NRs layer clearly impacted the photoelectron chemical properties, while the vertical and intensive nanorod arrays significantly increased their performance.

  15. Phase stability frustration on ultra-nanosized anatase TiO2.

    PubMed

    Patra, Snehangshu; Davoisne, Carine; Bouyanfif, Houssny; Foix, Dominique; Sauvage, Frédéric

    2015-06-04

    This work sheds light on the exceptional robustness of anatase TiO2 when it is downsized to an extreme value of 4 nm. Since at this size the surface contribution to the volume becomes predominant, it turns out that the material becomes significantly resistant against particles coarsening with temperature, entailing a significant delay in the anatase to rutile phase transition, prolonging up to 1000 °C in air. A noticeable alteration of the phase stability diagram with lithium insertion is also experienced. Lithium insertion in such nanocrystalline anatase TiO2 converts into a complete solid solution until almost Li1TiO2, a composition at which the tetragonal to orthorhombic transition takes place without the formation of the emblematic and unwished rock salt Li1TiO2 phase. Consequently, excellent reversibility in the electrochemical process is experienced in the whole portion of lithium content.

  16. Effect of construction of TiO2 nanotubes on platelet behaviors: Structure-property relationships.

    PubMed

    Huang, Qiaoling; Yang, Yun; Zheng, Dajiang; Song, Ran; Zhang, Yanmei; Jiang, Pinliang; Vogler, Erwin A; Lin, Changjian

    2017-03-15

    Blood compatibility of TiO2 nanotubes (TNTs) has been assessed in rabbit platelet-rich plasma (PRP), which combines activation of both blood plasma coagulation and platelets. We find that (i) amorphous TiO2 nanotubes (TNTs) with relatively larger outer diameters led to reduced platelet adhesion/activation, (ii) TNTs with relatively smaller outer diameters in a predominately rutile phase also inhibited platelet adhesion and activation, and (iii) a pervasive fibrin network formed on larger outer diameter TNTs in a predominately anatase phase. Thus, this study suggests that combined effect of crystalline phase and surface chemistry controls blood-contact behavior of TNTs. A more comprehensive mechanism is proposed for understanding hemocompatibility of TiO2 which might prove helpful as a guide to prospective design of TiO2-based biomaterials.

  17. Phase stability frustration on ultra-nanosized anatase TiO2

    PubMed Central

    Patra, Snehangshu; Davoisne, Carine; Bouyanfif, Houssny; Foix, Dominique; Sauvage, Frédéric

    2015-01-01

    This work sheds light on the exceptional robustness of anatase TiO2 when it is downsized to an extreme value of 4 nm. Since at this size the surface contribution to the volume becomes predominant, it turns out that the material becomes significantly resistant against particles coarsening with temperature, entailing a significant delay in the anatase to rutile phase transition, prolonging up to 1000 °C in air. A noticeable alteration of the phase stability diagram with lithium insertion is also experienced. Lithium insertion in such nanocrystalline anatase TiO2 converts into a complete solid solution until almost Li1TiO2, a composition at which the tetragonal to orthorhombic transition takes place without the formation of the emblematic and unwished rock salt Li1TiO2 phase. Consequently, excellent reversibility in the electrochemical process is experienced in the whole portion of lithium content. PMID:26042388

  18. Mesoporous TiO2 single crystals: facile shape-, size-, and phase-controlled growth and efficient photocatalytic performance.

    PubMed

    Zheng, Xiaoli; Kuang, Qin; Yan, Keyou; Qiu, Yongcai; Qiu, Jianhang; Yang, Shihe

    2013-11-13

    In this work, we have succeeded in preparing rutile and anatase TiO2 mesoporous single crystals with diverse morphologies in a controllable fashion by a simple silica-templated hydrothermal method. A simple in-template crystal growth process was put forward, which involved heterogeneous crystal nucleation and oriented growth within the template, a sheer spectator, and an excluded volume, i.e., crystal growth by faithful negative replication of the silica template. A series of mesoporous single-crystal structures, including rutile mesoporous TiO2 nanorods with tunable sizes and anatase mesoporous TiO2 nanosheets with dominant {001} facets, have been synthesized to demonstrate the versatility of the strategy. The morphology, size, and phase of the TiO2 mesoporous single crystals can be tuned easily by varying the external conditions such as the hydrohalic acid condition, seed density, and temperature rather than by the silica template, which merely serves for faithful negative replication but without interfering in the crystallization process. To demonstrate the application value of such TiO2 mesoporous single crystals, photocatalytic activity was tested. The resultant TiO2 mesoporous single crystals exhibited remarkable photocatalytic performance on hydrogen evolution and degradation of methyl orange due to their increased surface area, single-crystal nature, and the exposure of reactive crystal facets coupled with the three-dimensionally connected mesoporous architecture. It was found that {110} facets of rutile mesoporous single crystals can be considered essentially as reductive sites with a key role in the photoreduction, while {001} facets of anatase mesoporous single crystals provided oxidation sites in the oxidative process. Such shape- and size-controlled rutile and anatase mesoporous TiO2 single crystals hold great promise for building energy conversion devices, and the simple solution-based hydrothermal method is extendable to the synthesis of other

  19. Photoresponse and Donor Concentration of Plasma-Sprayed TiO2 and TiO2-ZnO Electrodes

    NASA Astrophysics Data System (ADS)

    Ye, F.-X.; Ohmori, A.; Li, C.-J.

    2005-12-01

    The photoelectrochemical characteristics of plasma-sprayed porous TiO2, TiO2-5%ZnO, and TiO2-10%ZnO electrodes in 0.1 N NaOH solution were studied through a three-electrode cell system. The microstructure, morphology, and composition of the electrodes were analyzed using an electron probe surface roughness analyzer (ERA-8800FE), scanning electron microscopy, and x-ray diffraction. The results indicate that the sprayed electrodes have a porous microstructure, which is affected by the plasma spray parameters and composition of the powders. The TiO2-ZnO electrodes consist of anatase TiO2, rutile TiO2, and Zn2Ti3O8 phase. The photoresponse characteristics of the plasma-sprayed electrodes are comparable to those of single-crystal TiO2, but the breakdown voltage is close to 0.5 V (versus that of a saturated calomel electrode). The short-circuit photocurrent density ( J SC) increases with a decrease of donor concentration, which was calculated according to the Gartner-Butler model. For the lowest donor concentration of a TiO2-5%ZnO electrode sprayed under an arc current of 600 A, the short-circuit J SC is approximately 0.4 mA/cm2 higher than that of the TiO2 electrodes under 30 mW/cm2 xenon light irradiation. The J SC increases linearly with light intensity.

  20. Hydrogen donor in anatase TiO2

    NASA Astrophysics Data System (ADS)

    Lavrov, E. V.

    2016-01-01

    An IR absorption study of hydrogen-related defects in natural single-crystalline anatase TiO2 has been carried out. A complex with IR absorption lines at 3412 and 3417 cm-1 is shown to act as a donor with ionization energy of tens of meV. The two lines are identified as stretching local vibrational modes of the O-H bonds of the donor in the neutral and positive charge states, respectively. The defect is unstable against annealing at approximately 300 ∘C and a storage at room temperature on the time scale of a few weeks. These findings suggest that interstitial hydrogen is a plausible model of this defect.

  1. Synthesis of TiO2/WO3 nanoparticles via sonochemical approach for the photocatalytic degradation of methylene blue under visible light illumination.

    PubMed

    Anandan, Sambandam; Sivasankar, Thirugnanasambandam; Lana-Villarreal, Teresa

    2014-11-01

    Through an ultrasound assisted method, TiO2/WO3 nanoparticles were synthesized at room temperature. The XRD pattern of as-prepared TiO2/WO3 nanoparticles matches well with that of pure monoclinic WO3 and rutile TiO2 nanoparticles. TEM images show that the prepared TiO2/WO3 nanoparticles consist of mixed square and hexagonal shape particles about 8-12nm in diameter. The photocatalytic activity of TiO2/WO3 nanoparticles was tested for the degradation of a wastewater containing methylene blue (MB) under visible light illumination. The TiO2/WO3 nanoparticles exhibits a higher degradation rate constant (6.72×10(-4)s(-1)) than bare TiO2 nanoparticles (1.72×10(-4)s(-1)) under similar experimental conditions.

  2. A novel 3D structure composed of strings of hierarchical TiO2 spheres formed on TiO2 nanobelts with high photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Jiang, Yongjian; Li, Meicheng; Song, Dandan; Li, Xiaodan; Yu, Yue

    2014-03-01

    A novel hierarchical titanium dioxide (TiO2) composite nanostructure with strings of anatase TiO2 hierarchical micro-spheres and rutile nanobelts framework (TiO2 HSN) is successfully synthesized via a one-step hydrothermal method. Particularly, the strings of hierarchical spheres are assembled by very thin TiO2 nanosheets, which are composed of highly crystallized anatase nanocrystals. Meanwhile, the HSN has a large surface area of 191 m2/g, which is about 3 times larger than Degussa P25. More importantly, the photocatalytic activity of HSN and P25 were evaluated by the photocatalytic oxidation decomposition of methyl orange (MO) under UV light illumination, and the TiO2 HSN shows enhanced photocatalytic activity compared with Degussa P25, as result of its continuous hierarchical structures, special conductive channel and large specific surface area. With these features, the hierarchical TiO2 may have more potential applications in the fields of dye-sensitized solar cells and lithium ion batteries.

  3. Preparation of hollow TiO2 nanoparticles through TiO2 deposition on polystyrene latex particles and characterizations of their structure and photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Wang, Jingang; Yu, Jiemei; Zhu, Xiaoli; Kong, Xiang Zheng

    2012-11-01

    In a mixed solvent of water and ethanol, polystyrene/titanium dioxide (PSt/TiO2) composite particles of core-shell structure were prepared by hydrolysis of tetrabutyl titanate in the presence of cationic PSt particles or anionic PSt particles surface-treated using γ-aminopropyl triethoxysilane. Hollow TiO2 particles were obtained through calcination of the PSt/TiO2 core-shell particles to burn off the PSt core or through dissolution of the core by tetrahydrofuran (THF). An alternative process constituted of preheating the PSt/TiO2 particles at 200°C to allow partial crystallization followed by calcination or PSt dissolution by THF. The outcome TiO2 particles thus prepared were examined by TEM, and hollow TiO2 particles were observed. The crystalline phase structure and phase transformation were characterized, which revealed that preheating before the removal of the PSt core was useful to achieve the desired hollow TiO2 particles, and the calcination process was beneficial to the formation of anatase and rutile structures. The tests of TiO2 particles as catalyst in the photodegradation of Rhodamine B demonstrated that a much higher catalytic activity was observed with the TiO2 hollow particles prepared through calcination combined with preheating.

  4. Density functional theory study of dopants in polycrystalline TiO2

    NASA Astrophysics Data System (ADS)

    Körner, Wolfgang; Elsässer, Christian

    2011-05-01

    We present a density functional theory (DFT) study of doped rutile and anatase TiO2 in which we investigate the impact of grain boundaries on the physics of atomic defects. The main goal is to obtain information about the positions of the defect levels generated by an oxygen vacancy, a titanium interstitial, cation dopants Nb, Al, and Ga, and an anion dopant N in the electronic band gap having in mind the application of TiO2 as a transparent conducting oxide (TCO) or its use in heterogeneous catalysis. Due to the known deficiency of the local density approximation (LDA) of DFT to yield accurate values for band gap energies for insulators such as TiO2, a self-interaction correction (SIC) to the LDA is employed. The main result of our study is that grain boundaries do affect the defect formation energies as well as the position and shape of the dopant-induced electronic energy levels significantly with respect to the single crystal. According to our study Nb doping may lead to n-conducting TiO2 whereas doping with N, Al, or Ga is not promising in order to achieve p-conducting TiO2. Furthermore an increase in the photoconductivity of TiO2:N and the colorlessness of TiO2:Al may be explained by our results.

  5. Light-induced antifungal activity of TiO 2 nanoparticles/ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Haghighi, N.; Abdi, Y.; Haghighi, F.

    2011-09-01

    Antifungal activity of TiO2/ZnO nanostructures under visible light irradiation was investigated. A simple chemical method was used to synthesize ZnO nanowires. Zinc acetate dihydrate, Polyvinyl Pyrrolidone and deionized water were used as precursor, capping and solvent, respectively. TiO2 nanoparticles were deposited on ZnO nanowires using an atmospheric pressure chemical vapor deposition system. X-ray diffraction pattern of TiO2/ZnO nano-composite has represented the diffraction peaks relating to the crystal planes of the TiO2 (anatase and rutile) and ZnO. TiO2/ZnO nanostructure antifungal effect on Candida albicans biofilms was studied and compared with the activity of TiO2 nanoparticles and ZnO nanowires. The high efficiency photocatalytic activity of TiO2 nanoparticles leads to increased antifungal activity of ZnO nanowires. Scanning electron microscope was utilized to study the morphology of the as prepared nanostructures and the degradation of the yeast.

  6. Whiter, brighter, and more stable cellulose paper coated with TiO2 /SiO2 core/shell nanoparticles using a layer-by-layer approach.

    PubMed

    Cheng, Fei; Lorch, Mark; Sajedin, Seyed Mani; Kelly, Stephen M; Kornherr, Andreas

    2013-08-01

    To inhibit the photocatalytic degradation of organic material supports induced by small titania (TiO2 ) nanoparticles, four kinds of TiO2 nanoparticles, that is, commercial P25-TiO2 , commercial rutile phase TiO2 , rutile TiO2 nanorods and rutile TiO2 spheres, prepared from TiCl4 , were coated with a thin, but dense, coating of silica (SiO2 ) using a conventional sol-gel technique to form TiO2 /SiO2 core/shell nanoparticles. These core/shell particles were deposited and fixed as a very thin coating onto the surface of cellulose paper samples by a wet-chemistry polyelectrolyte layer-by-layer approach. The TiO2 /SiO2 nanocoated paper samples exhibit higher whiteness and brightness and greater stability to UV-bleaching than comparable samples of blank paper. There are many potential applications for this green chemistry approach to protect cellulosic fibres from UV-bleaching in sunlight and to improve their whiteness and brightness.

  7. A pseudo-single-crystalline germanium film for flexible electronics

    SciTech Connect

    Higashi, H.; Yamada, S.; Kanashima, T.; Hamaya, K.; Kasahara, K.; Park, J.-H.; Miyao, M.; Kudo, K.; Okamoto, H.; Moto, K.; Tsunoda, I.

    2015-01-26

    We demonstrate large-area (∼600 μm), (111)-oriented, and high-crystallinity, i.e., pseudo-single-crystalline, germanium (Ge) films at 275 °C, where the temperature is lower than the softening temperature of a flexible substrate. A modulated gold-induced layer exchange crystallization method with an atomic-layer deposited Al{sub 2}O{sub 3} barrier and amorphous-Ge/Au multilayers is established. From the Raman measurements, we can judge that the crystallinity of the obtained Ge films is higher than those grown by aluminum-induced-crystallization methods. Even on a flexible substrate, the pseudo-single-crystalline Ge films for the circuit with thin-film transistor arrays can be achieved, leading to high-performance flexible electronics based on an inorganic-semiconductor channel.

  8. Imparting amphiphobicity on single-crystalline porous materials.

    PubMed

    Sun, Qi; He, Hongming; Gao, Wen-Yang; Aguila, Briana; Wojtas, Lukasz; Dai, Zhifeng; Li, Jixue; Chen, Yu-Sheng; Xiao, Feng-Shou; Ma, Shengqian

    2016-10-31

    The sophisticated control of surface wettability for target-specific applications has attracted widespread interest for use in a plethora of applications. Despite the recent advances in modification of non-porous materials, surface wettability control of porous materials, particularly single crystalline, remains undeveloped. Here we contribute a general method to impart amphiphobicity on single-crystalline porous materials as demonstrated by chemically coating the exterior of metal-organic framework (MOF) crystals with an amphiphobic surface. As amphiphobic porous materials, the resultant MOF crystals exhibit both superhydrophobicity and oleophobicity in addition to retaining high crystallinity and intact porosity. The chemical shielding effect resulting from the amphiphobicity of the MOFs is illustrated by their performances in water/organic vapour adsorption, as well as long-term ultrastability under highly humidified CO2 environments and exceptional chemical stability in acid/base aqueous solutions. Our work thereby pioneers a perspective to protect crystalline porous materials under various chemical environments for numerous applications.

  9. A pseudo-single-crystalline germanium film for flexible electronics

    NASA Astrophysics Data System (ADS)

    Higashi, H.; Kasahara, K.; Kudo, K.; Okamoto, H.; Moto, K.; Park, J.-H.; Yamada, S.; Kanashima, T.; Miyao, M.; Tsunoda, I.; Hamaya, K.

    2015-01-01

    We demonstrate large-area (˜600 μm), (111)-oriented, and high-crystallinity, i.e., pseudo-single-crystalline, germanium (Ge) films at 275 °C, where the temperature is lower than the softening temperature of a flexible substrate. A modulated gold-induced layer exchange crystallization method with an atomic-layer deposited Al2O3 barrier and amorphous-Ge/Au multilayers is established. From the Raman measurements, we can judge that the crystallinity of the obtained Ge films is higher than those grown by aluminum-induced-crystallization methods. Even on a flexible substrate, the pseudo-single-crystalline Ge films for the circuit with thin-film transistor arrays can be achieved, leading to high-performance flexible electronics based on an inorganic-semiconductor channel.

  10. Imparting amphiphobicity on single-crystalline porous materials

    NASA Astrophysics Data System (ADS)

    Sun, Qi; He, Hongming; Gao, Wen-Yang; Aguila, Briana; Wojtas, Lukasz; Dai, Zhifeng; Li, Jixue; Chen, Yu-Sheng; Xiao, Feng-Shou; Ma, Shengqian

    2016-10-01

    The sophisticated control of surface wettability for target-specific applications has attracted widespread interest for use in a plethora of applications. Despite the recent advances in modification of non-porous materials, surface wettability control of porous materials, particularly single crystalline, remains undeveloped. Here we contribute a general method to impart amphiphobicity on single-crystalline porous materials as demonstrated by chemically coating the exterior of metal-organic framework (MOF) crystals with an amphiphobic surface. As amphiphobic porous materials, the resultant MOF crystals exhibit both superhydrophobicity and oleophobicity in addition to retaining high crystallinity and intact porosity. The chemical shielding effect resulting from the amphiphobicity of the MOFs is illustrated by their performances in water/organic vapour adsorption, as well as long-term ultrastability under highly humidified CO2 environments and exceptional chemical stability in acid/base aqueous solutions. Our work thereby pioneers a perspective to protect crystalline porous materials under various chemical environments for numerous applications.

  11. Nanometer-size alpha-PbO(2)-type TiO(2) in garnet: A thermobarometer for ultrahigh-pressure metamorphism

    PubMed

    Hwang; Shen; Chu; Yui

    2000-04-14

    A high-pressure phase of titanium dioxide (TiO(2)) with an alpha-PbO(2)-type structure has been identified in garnet of diamondiferous quartzofeldspathic rocks from the Saxonian Erzgebirge, Germany. Analytical electron microscopy indicates that this alpha-PbO(2)-type TiO(2) occurred as an epitaxial nanometer-thick slab between twinned rutile bicrystals. Given a V-shaped curve for the equilibrium phase boundary of alpha-PbO(2)-type TiO(2) to rutile, the stabilization pressure of alpha-PbO(2)-type TiO(2) should be 4 to 5 gigapascals at 900 degrees to 1000 degrees C. This suggests a burial of continental crustal rocks to depths of at least 130 kilometers. The alpha-PbO(2)-type TiO(2) may be a useful pressure and temperature indicator in the diamond stability field.

  12. Synthesis and characterization of single crystalline selenium nanowire arrays

    SciTech Connect

    Zhang, X.Y. . E-mail: apzhxy@polyu.edu.hk; Xu, L.H.; Dai, J.Y.; Cai, Y.; Wang, N.

    2006-09-14

    Ordered selenium nanowire arrays with diameters about 40 nm have been fabricated by electrodeposition using anodic porous alumina templates. As determined by X-ray diffraction, Raman spectra, electron diffraction and high-resolution transmission electron microscopy, selenium nanowires have uniform diameters, which are fully controllable. Single crystalline trigonal selenium nanowires have been obtained after postannealing at 180 deg. C. These nanowires are perfect with a c-axis growth orientation. The optical absorption spectra reveal two types of electron transition activity.

  13. A one-step process for the antimicrobial finishing of textiles with crystalline TiO2 nanoparticles.

    PubMed

    Perelshtein, Ilana; Applerot, Guy; Perkas, Nina; Grinblat, Judith; Gedanken, Aharon

    2012-04-10

    Titanium oxide (TiO(2)) nanoparticles (NPs) in their two forms, anatase and rutile, were synthesized and deposited onto the surface of cotton fabrics by using ultrasonic irradiation. The structure and morphology of the nanoparticles were analyzed by using characterization methods such as XRD, TEM, STEM, and EDS. The antimicrobial activities of the TiO(2)-cotton composites were tested against Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) strains, as well as against Candida albicans. Significant antimicrobial effect was observed, mainly against Staphylococcus aureus. In addition, the combination of visible light and TiO(2) NPs showed enhanced antimicrobial activity.

  14. The effect of silica thickness on nano TiO2 particles for functional polyurethane nanocomposites.

    PubMed

    Chen, Chao; Wu, Wei; Xu, William Z; Charpentier, Paul A

    2017-03-17

    In order to help reduce the agglomeration of TiO2 nanoparticles in polyurethane coatings while enhancing their photoactivity and mechanical/physical properties, this work examined encapsulating TiO2 nanoparticles in a thin layer of SiO2, prior to their nanocomposite polymerization. By applying a Stöber process, varying thicknesses of SiO2 were successfully coated onto the surface of anatase and rutile TiO2 nanoparticles. The methylene blue results showed that different loadings of SiO2 onto the TiO2 surface significantly influenced their photocatalytic activity. When the loading weight of SiO2 was lower than 3.25 wt%, the photocatalytic activity was enhanced, while with higher loadings, it gave lower photocatalytic activity. When the rutile phase TiO2 surface was fully covered with SiO2, an enhanced photocatalytic activity was observed. When these silica coated nanoparticles were applied in polyurethane coatings, increasing the amount of SiO2 on the titania surface increased the coatings contact angle from 75° to 87° for anatase phase and 70°-78° for rutile phase. The Young's modulus was also increased from 1.06 GPa to 2.77 GMPa for anatase phase and 1.06-2.17 GPa for rutile phase, attributed to the silica layer giving better integration. The thermal conductivity of the polyurethane coatings was also successfully decreased by encapsulating SiO2 on the titania surface for next generation high performance coatings.

  15. The effect of silica thickness on nano TiO2 particles for functional polyurethane nanocomposites

    NASA Astrophysics Data System (ADS)

    Chen, Chao; Wu, Wei; Xu, William Z.; Charpentier, Paul A.

    2017-03-01

    In order to help reduce the agglomeration of TiO2 nanoparticles in polyurethane coatings while enhancing their photoactivity and mechanical/physical properties, this work examined encapsulating TiO2 nanoparticles in a thin layer of SiO2, prior to their nanocomposite polymerization. By applying a Stöber process, varying thicknesses of SiO2 were successfully coated onto the surface of anatase and rutile TiO2 nanoparticles. The methylene blue results showed that different loadings of SiO2 onto the TiO2 surface significantly influenced their photocatalytic activity. When the loading weight of SiO2 was lower than 3.25 wt%, the photocatalytic activity was enhanced, while with higher loadings, it gave lower photocatalytic activity. When the rutile phase TiO2 surface was fully covered with SiO2, an enhanced photocatalytic activity was observed. When these silica coated nanoparticles were applied in polyurethane coatings, increasing the amount of SiO2 on the titania surface increased the coatings contact angle from 75° to 87° for anatase phase and 70°–78° for rutile phase. The Young’s modulus was also increased from 1.06 GPa to 2.77 GMPa for anatase phase and 1.06–2.17 GPa for rutile phase, attributed to the silica layer giving better integration. The thermal conductivity of the polyurethane coatings was also successfully decreased by encapsulating SiO2 on the titania surface for next generation high performance coatings.

  16. Structure and Formation Mechanism of Black TiO2 Nanoparticles.

    PubMed

    Tian, Mengkun; Mahjouri-Samani, Masoud; Eres, Gyula; Sachan, Ritesh; Yoon, Mina; Chisholm, Matthew F; Wang, Kai; Puretzky, Alexander A; Rouleau, Christopher M; Geohegan, David B; Duscher, Gerd

    2015-10-27

    The remarkable properties of black TiO2 are due to its disordered surface shell surrounding a crystalline core. However, the chemical composition and the atomic and electronic structure of the disordered shell and its relationship to the core remain poorly understood. Using advanced transmission electron microscopy methods, we show that the outermost layer of black TiO2 nanoparticles consists of a disordered Ti2O3 shell. The measurements show a transition region that connects the disordered Ti2O3 shell to the perfect rutile core consisting first of four to five monolayers of defective rutile, containing clearly visible Ti interstitial atoms, followed by an ordered reconstruction layer of Ti interstitial atoms. Our data suggest that this reconstructed layer presents a template on which the disordered Ti2O3 layers form by interstitial diffusion of Ti ions. In contrast to recent reports that attribute TiO2 band-gap narrowing to the synergistic action of oxygen vacancies and surface disorder of nonspecific origin, our results point to Ti2O3, which is a narrow-band-gap semiconductor. As a stoichiometric compound of the lower oxidation state Ti(3+) it is expected to be a more robust atomic structure than oxygen-deficient TiO2 for preserving and stabilizing Ti(3+) surface species that are the key to the enhanced photocatalytic activity of black TiO2.

  17. Immobilized TiO2 nanoparticles produced by flame spray for photocatalytic water remediation

    NASA Astrophysics Data System (ADS)

    Bettini, Luca Giacomo; Diamanti, Maria Vittoria; Sansotera, Maurizio; Pedeferri, Maria Pia; Navarrini, Walter; Milani, Paolo

    2016-08-01

    Anatase/rutile mixed-phase titanium dioxide (TiO2) photocatalysts in the form of nanostructured powders with different primary particle size, specific surface area, and rutile content were produced from the gas-phase by flame spray pyrolysis (FSP) starting from an organic solution containing titanium (IV) isopropoxide as Ti precursor. Flame spray-produced TiO2 powders were characterized by means of X-ray diffraction, Raman spectroscopy, and BET measurements. As-prepared powders were mainly composed of anatase crystallites with size ranging from 7 to 15 nm according to the synthesis conditions. TiO2 powders were embedded in a multilayered fluoropolymeric matrix to immobilize the nanoparticles into freestanding photocatalytic membranes. The photocatalytic activity of the TiO2-embedded membranes toward the abatement of hydrosoluble organic pollutants was evaluated employing the photodegradation of rhodamine B in aqueous solution as test reaction. The photoabatement rate of best performing membranes significantly overcomes that of membranes produced by the same method and incorporating commercial P25-TiO2.

  18. Efficient Photocatalytic Activities of TiO2 Hollow Fibers with Mixed Phases and Mesoporous Walls

    PubMed Central

    Hou, Huilin; Shang, Minghui; Wang, Lin; Li, Wenge; Tang, Bin; Yang, Weiyou

    2015-01-01

    Currently, Degussa P25, with the typical mixed phases of anatase and rutile TiO2, is widely applied as the commercial photocatalysts. However, there are still some of obstacles for the P25 nanoparticles with totally high photocatalytic activities, especially for the catalytic stability due to their inevitable aggregation of the nanoparticles when used as the photocatalysts. In the present work, we reported the exploration of a novel TiO2 photocatalyst, which could offer an ideal platform for synergetic combination of the mixed-phase composition, hollow architecture and mesoporous walls for the desired excellent photocatalytic efficiency and robust stability. The mesoporous TiO2 hollow nanofibers were fabricated via a facile single capillary electrospinning technique, in which the foaming agents were used for creating mesopores throughout the walls of the hollow fibers. The obtained hollow fibers exhibit a high purity and possess the mixed phases of 94.6% anatase and 5.4% rutile TiO2. As compared to P25, the as-fabricated mesoporous TiO2 hollow fibers exhibited much higher efficient photocatalytic activities and stabilities toward the hydrogen evolution with a rate of ~499.1 μmol g−1·h−1 and ~99.5% degradation Rhodamine B (RhB) in 60 min, suggesting their promising application in efficient photocatalysts. PMID:26470013

  19. Mn-doped TiO2 thin films with significantly improved optical and electrical properties

    NASA Astrophysics Data System (ADS)

    Lu, Liu; Xia, Xiaohong; Luo, J. K.; Shao, G.

    2012-12-01

    TiO2 thin films with various Mn doping contents were fabricated by reactive magnetron sputtering deposition at 550 °C and their structural, optical and electrical properties were characterized. All films were made of densely packed columnar grains with a fibrous texture along the normal direction of the substrate. The as-deposited structure in the pure TiO2 film consisted of anatase grains with the [1 0 1] texture. Mn incorporation stabilized the rutile phase and induced lattice contraction in the [1 0 0] direction. The texture in the Mn-doped films changed from [1 1 0] to [2 0 0] with increasing Mn content. The incorporation of Mn in the TiO2 lattice introduced intermediate bands into its narrowed forbidden gap, leading to remarkable red-shifts in the optical absorption edges, together with significantly improved electrical conductivity of the thin films. Hall measurement showed that the incorporation of Mn-induced p-type conductivity, with hole mobility in heavily doped TiO2 (˜40% Mn) being about an order higher than electron mobility in single-crystal rutile TiO2. Oxygen vacancies, on the other hand, interacted with substitutional Mn atoms to reduce its effect on optical and electrical properties.

  20. Colloidal TiO2 nanocrystals prepared from peroxotitanium complex solutions: phase evolution from different precursors.

    PubMed

    Seok, Sang Il; Vithal, Muga; Chang, Jeong Ah

    2010-06-01

    We report the preparation of nanocrystalline anatase and rutile TiO(2) from aqueous peroxotitanium complex (PTC) solutions and their characterization by powder X-ray diffraction (XRD), infrared spectroscopy, and Raman spectroscopy. The phase evolution of TiO(2) prepared using PTC derived from different precursors, i.e., TiCl(4) and titanium tetraisopropoxide (TTIP), is related to the nature of the intermediate steps. Phase-pure nanoanatase was formed in PTC solution derived from TiCl(4), while a mixture of minor anatase and dominant rutile were prepared from PTC when TTIP was used as precursor. On the other hand, in the case of calcining PTC powders in air, a pure anatase phase of TiO(2) was obtained, regardless of the precursor used. Thus, the formation and attachment of hydrated TiO(6) units or TiO(2)·xH(2)O under a different environment, especially pH, plays a critical role in determining the phase during the crystallization of TiO(2).

  1. TiO2 hierarchical nanostructures: Hydrothermal fabrication and application in dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Liang, Jia; Zhang, Gengmin; Yang, Jin; Sun, Wentao; Shi, Mingji

    2015-01-01

    Arrays of TiO2 hierarchical nanostructures that consisted of rutile nanorods and anatase branches were hydrothermally fabricated and employed as photoanodes in dye-sensitized solar cells (DSSCs). Each hierarchical nanostructure array was attained in two steps. First, a primary nanorod array was synthesized in aqueous solutions of hydrochloric acid (HCl) and tetrabutyl titanate (C16H36O4Ti); subsequently, secondary branches were grown on the nanorods in aqueous solutions of ammonium hexafluorotitanate ((NH4)2TiF6) and boric acid (H3BO3). The secondary anatase branches filled part of the space among the primary rutile nanorods and gave rise to a larger surface area. Light-harvesting capability of the DSSCs with TiO2 hierarchical nanostructures as photoanodes was appreciably improved because more dye molecules could be loaded on the photoanodes and more light could be scattered inside the DSSCs. Therefore, the conversion efficiencies of the DSSCs were doubled by replacing the photoanode of primary TiO2 nanorod array with the photoanodes of TiO2 hierarchical nanostructure arrays. Furthermore, in order to reach a compromise between the photoanode surface area and the inter-nanorod space volume, the growth time of the secondary TiO2 anatase branches was optimized.

  2. Structure and Formation Mechanism of Black TiO2 Nanoparticles

    DOE PAGES

    Tian, Mengkun; Mahjouri-Samani, Masoud; Eres, Gyula; ...

    2015-10-27

    The remarkable properties of black TiO2 are due to its disordered surface shell surrounding a crystalline core. However, the chemical composition and the atomic and electronic structure of the disordered shell and its relationship to the core remain poorly understood. Using advanced transmission electron microscopy methods, we show that the outermost layer of black TiO2 nanoparticles consists of a disordered Ti2O3 shell. The measurements show a transition region that connects the disordered Ti2O3 shell to the perfect rutile core consisting first of four to five monolayers of defective rutile, containing clearly visible Ti interstitial atoms, followed by an ordered reconstructionmore » layer of Ti interstitial atoms. Our data suggest that this reconstructed layer presents a template on which the disordered Ti2O3 layers form by interstitial diffusion of Ti ions. In contrast to recent reports that attribute TiO2 band-gap narrowing to the synergistic action of oxygen vacancies and surface disorder of nonspecific origin, our results point to Ti2O3, which is a narrow-band-gap semiconductor. In conclusion, as a stoichiometric compound of the lower oxidation state Ti3+ it is expected to be a more robust atomic structure than oxygen-deficient TiO2 for preserving and stabilizing Ti3+ surface species that are the key to the enhanced photocatalytic activity of black TiO2.« less

  3. Enhanced photocatalytic activity of TiO2 nanobarbed fibers treated with atmospheric pressure plasma using O2 gas

    NASA Astrophysics Data System (ADS)

    Lee, Hyun-Uk; Ahn, Kyun; Jeong, Se-Young; Cho, Chae-Ryong; Kim, Jong-Pil; Bae, Jong-Seong; Kim, Hyun-Gyu; Kwon, Se-Hun; Lee, Hyung Woo

    2010-11-01

    TiO2 nanobarbed fibers (NBFs) were prepared by growing rutile TiO2 nanorods on anatase TiO2 nanofibers via electrospinning and hydrothermal reaction processes. There was a large increase in the photocatalytic activity of O2-plasma-treated (OP)-TiO2 NBFs relative to that of the TiO2 NBFs; this is due to the hydroxylation of the surface of the TiO2 NBFs by OP treatment. The repeatability of the photocatalytic activity of the OP-TiO2 NBFs was found to be high and the decolorization rate after ten cycles was 88.3% of the initial value. These results indicate that OP-TiO2 NBFs have great potential for use as a photocatalyst.

  4. Synthesis of Nanoscale TiO2 and Study of the Effect of Their Crystal Structure on Single Cell Response

    PubMed Central

    Ismagilov, Z. R.; Shikina, N. V.; Mazurkova, N. A.; Tsikoza, L. T.; Tuzikov, F. V.; Ushakov, V. A.; Ishchenko, A. V.; Rudina, N. A.; Korneev, D. V.; Ryabchikova, E. I.

    2012-01-01

    To study the effect of nanoscale titanium dioxide (TiO2) on cell responses, we synthesized four modifications of the TiO2 (amorphous, anatase, brookite, and rutile) capable of keeping their physicochemical characteristics in a cell culture medium. The modifications of nanoscale TiO2 were obtained by hydrolysis of TiCl4 and Ti(i-OC3H7)4 (TIP) upon variation of the synthesis conditions; their textural, morphological, structural, and dispersion characteristics were examined by a set of physicochemical methods: XRD, BET, SAXS, DLS, AFM, SEM, and HR-TEM. The effect of synthesis conditions (nature of precursor, pH, temperature, and addition of a complexing agent) on the structural-dispersion properties of TiO2 nanoparticles was studied. The hydrolysis methods providing the preparation of amorphous, anatase, brookite, and rutile modifications of TiO2 nanoparticles 3–5 nm in size were selected. Examination of different forms of TiO2 nanoparticles interaction with MDCK cells by transmission electron microscopy of ultrathin sections revealed different cell responses after treatment with different crystalline modifications and amorphous form of TiO2. The obtained results allowed us to conclude that direct contact of the nanoparticles with cell plasma membrane is the primary and critical step of their interaction and defines a subsequent response of the cell. PMID:22623903

  5. Tricrystalline TiO2 with enhanced photocatalytic activity and durability for removing volatile organic compounds from indoor air.

    PubMed

    Chen, Kunyang; Zhu, Lizhong; Yang, Kun

    2015-06-01

    It is important to develop efficient and economic techniques for removing volatile organic compounds (VOCs) in indoor air. Heterogeneous TiO2-based semiconductors are a promising technology for achieving this goal. Anatase/brookite/rutile tricrystalline TiO2 with mesoporous structure was synthesized by a low-temperature hydrothermal route in the presence of HNO3. The obtained samples were characterized by X-ray diffraction and N2 adsorption-desorption isotherm. The photocatalytic activity was evaluated by photocatalytic decomposition of toluene in air under UV light illumination. The results show that tricrystalline TiO2 exhibited higher photocatalytic activity and durability toward gaseous toluene than bicrystalline TiO2, due to the synergistic effects of high surface area, uniform mesoporous structure and junctions among mixed phases. The tricrystalline TiO2 prepared at RHNO3=0.8, containing 80.7% anatase, 15.6% brookite and 3.7% rutile, exhibited the highest photocatalytic activity, about 3.85-fold higher than that of P25. The high activity did not significantly degrade even after five reuse cycles. In conclusion, it is expected that our study regarding gas-phase degradation of toluene over tricrystalline TiO2 will enrich the chemistry of the TiO2-based materials as photocatalysts for environmental remediation and stimulate further research interest on this intriguing topic.

  6. Simultaneous phase- and size-controlled synthesis of TiO(2) nanorods via non-hydrolytic sol-gel reaction of syringe pump delivered precursors.

    PubMed

    Koo, Bonil; Park, Jongnam; Kim, Yukyeong; Choi, Sang-Hyun; Sung, Yung-Eun; Hyeon, Taeghwan

    2006-12-07

    The simultaneous phase- and size-controlled synthesis of TiO(2) nanorods was achieved via the non-hydrolytic sol-gel reaction of continuously delivered two titanium precursors using two separate syringe pumps. As the injection rate was decreased, the length of the TiO(2) nanorods was increased and their crystalline phase was simultaneously transformed from anatase to rutile. When the reaction was performed by injecting titanium precursors contained in two separate syringes into a hot oleylamine surfactant solution with an injection rate of 30 mL/h, anatase TiO(2) nanorods with dimensions of 6 nm (thickness) x 50 nm (length) were produced. When the injection rate was decreased to 2.5 mL/h, star-shaped rutile TiO(2) nanorods with dimensions of 25 nm x 200 nm and a small fraction of rod-shaped anatase TiO(2) nanorods with dimensions of 9 nm x 100 nm were synthesized. Pure star-shaped rutile TiO(2) nanorods with dimensions of 25 nm x 450 nm were synthesized when the injection rate was further decreased to 1.25 mL/h. The simultaneous phase transformation and length elongation of the TiO(2) nanorods were achieved. Under optimized reaction conditions, as much as 3.5 g of TiO(2) nanorods were produced. The TiO(2) nanorods were used to produce dye-sensitized solar cells, and the photoconversion efficiency of the mixture composed of star-shaped rutile TiO(2) nanorods and a small fraction of anatase nanorods were comparable to that of Degussa P-25.

  7. Nanostructured TiO2 films for dye-sensitized solar cells prepared by the sol-gel method.

    PubMed

    Jin, Young Sam; Kim, Kyung Hwan; Park, Sang Joon; Yoon, Hyon Hee; Choi, Hyung Wook

    2011-12-01

    TiO2 films were prepared on glass substrates using the sol-gel process for a dye-sensitized solar cell application. The TiO2 sol was prepared using hydrolysis/polycondensation. Titanium (IV) Tetra Isopropoxide (TTIP) was used as precursor and Nitric acid (HNO3) was used as a catalyst for the peptization. The crystal structure and morphology of the prepared materials were characterized by XRD, and an SEM. The observations confirmed the nanocrystalline nature of the TiO2. The reaction parameters, such as the catalyst concentrations, the calcination time, and the calcination temperature were varied during the synthesis in order to achieve nanosize TiO2 particles. The prepared TiO2 particles were coated onto FTO glass using a screen printing technique. The prepared TiO2 films were characterized by UV-vis. The TiO2 particles calcinated at low temperatures showed an anatase phase they grew into a rutile phase when the calcination temperature increased. The size and structure of the TiO2 particles were adjusted to specific surface areas. It was found that the conversion efficiency of the DSSC was highly affected by the properties of the TiO2 particles.

  8. Photocatalytic activity and characterization of sol-gel-derived Ni-doped TiO2-coated active carbon composites

    NASA Astrophysics Data System (ADS)

    Bhosale, R. R.; Pujari, S. R.; Lande, M. K.; Arbad, B. R.; Pawar, S. B.; Gambhire, A. B.

    2012-11-01

    Ni-doped, TiO2-coated active carbon (Ni-TiO2/AC) were prepared by a sol-gel method. The effect of supports, including TiO2 and active carbon (AC), on the molecular structure and photocatalytic activity of nickel oxide for complete decomposition of methylene blue has been examined with respect to the content of Ni on the catalyst surface. The photocatalytic activities of the Ni-TiO2/AC composites were evaluated in the decomposition of methylene blue solution under visible-light irradiation. The results indicate that Ni-TiO2/AC has a higher efficiency in decomposition of methylene blue than TiO2 and TiO2/AC. This was attributed to the different functions of active carbon and nickel species. First, nanosize TiO2 particles on composites were not reunited, possible because active carbon retards transformation of anatase into rutile and decrease the crystallite size. Second, production of high concentrations of organic compound near Ni-TiO2. Third, carbon in active carbon causes some of the TiO2 to reduce to Ti3+ ions, which prevents electron-hole pair recombination. It was found that the addition of Ni to TiO2 sol could suppress the grain growth of TiO2 crystals and increase the hydroxyl content on the surface of TiO2/AC. The photocatalytic efficiency and activity of the composites remained good, even after three cycles.

  9. Novel TiO2/C nanocomposites: synthesis, characterization, and application as a photocatalyst for the degradation of organic pollutants.

    PubMed

    da Costa, Elias; Zamora, Patricio P; Zarbin, Aldo J G

    2012-02-15

    Novel TiO(2)/carbon nanocomposites were prepared through the pyrolysis of TiO(2)/poly(furfuryl alcohol) hybrid materials, which were obtained by the sol-gel method, starting from titanium tetraisopropoxide (TTIP) and furfuryl alcohol (FA) precursors. Six different TiO(2)/C samples were prepared based on different TiO(2) nanoparticle sizes and TiO(2)/FA ratios. All of the samples were characterized using X-ray diffraction, infrared, and Raman spectroscopy. The results indicated effective FA polymerization onto the TiO(2) (anatase) nanoparticles, polymer conversion to disordered carbon following the pyrolysis, and a simultaneous TiO(2) anatase-rutile phase transition. The resulting TiO(2)/carbon composites were used as photocatalysts in the advanced oxidative process (AOP) for the degradation of reactive organic dyes in aqueous solution. The results indicate excellent photocatalytic performance (degradation of 99% of the dye after 60 min) with several advantages over traditional TiO(2)-based photocatalysts.

  10. Synthesis and characterization of LaFeO3/TiO2 nanocomposites for visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Dhinesh Kumar, R.; Thangappan, R.; Jayavel, R.

    2017-02-01

    LaFeO3/TiO2 nanocomposites were successfully synthesized by hydrothermal method. The as-prepared nanoparticles were characterized by TGA, XRD, HRSEM, EDS, TEM, VSM and UV-Vis techniques. Thermal stability of the material was studied by thermal analysis. XRD studies confirm the orthorhombic and rutile phase for pure LaFeO3 and TiO2 nanoparticles. The LaFeO3/TiO2 composite shows the coexistence of LaFeO3 and TiO2 phases with no extra peaks. Morphological analysis shows the spherical nanoparticles and the average particle size of LaFeO3, TiO2 and LaFeO3/TiO2 was around 60 nm. The LaFeO3/TiO2 nanocomposites show a significant shift in the UV-vis absorption spectra in comparison with both TiO2 and LaFeO3 nanoparticles. The photocatalytic activity of the samples were tested for the degradation of methyl orange (MO) in aqueous solutions under visible light irradiations for 180 min. The LaFeO3/TiO2 composite exhibits enhanced visible light photocatalytic properties in comparison with that of LaFeO3 nanoparticles.

  11. Electron and Hole Behavior in Powdered TiO2 - Photoluminescence and Infrared Studies

    DTIC Science & Technology

    2014-04-01

    39. Winder, E. J.; Moore, D. E.; Neu, D. R.; Ellis, A. B.; Geisz, J. F.; Kuech, T. F., Detection of Ammonia , Phosphine, and Arsine Gases by... Ammonia on the (011) Surface of Rutile Tio2. Langmuir 2008, 24, 97- 104. 59. Wilson, J. N.; Idriss, H., Reactions of Ammonia on Stoichiometric and... Ammonia Adsorption on Anatase Tio2 (001) Slab. Surf. Sci. 2010, 604, 1029–1033. 61. Raupp, G. B.; Dumesic, J. A., Adsorption of Co, Co2, H-2, and H2o on

  12. TiO2 Nanorods Preparation from Titanyl Sulphate Produced by Dissolution of Ilmenite

    NASA Astrophysics Data System (ADS)

    Wahyuningsih, S.; Rinawati, L.; Munifa, R. M. I.; Ramelan, A. H.; Sulistyono, Eko

    2017-02-01

    One-dimensional titanium oxides (TiO2) nanorods have substantial applications in photocatalytic, nanoelectronic, and photoelectrochemical solar cells. These applications require large quantities of materials and a production technique suitable for future industry fabrication. We demonstrate here a new method of TiO2 nanorods production from ilmenite sands (FeTiO3). In this process, the roasted ilmenite sand was separated from the iron content and dissolved in the sulphuric acid solution. Separation process of TiO2 from ilmenite has been carried out by roasting, leaching and precipitation processes. The roasting process was conducted by the addition of Na2S at a temperature of 800°C that had been deomposed ilmenite into hematite (Fe2O3), anatase TiO2, rutile TiO2, Na2SO4, NaFeS2 and NaFeO2. Separation TiO2 from titanyl sulfate (TiOSO4) after leaching in H2SO4 solution was conducted by hydrolysis-condensation step and complexation step of Fe2+ content. KCNS solution was used as a complexing agent. The xerogel synthesized TiO2 then was prepared to 1-D nanostructure of TiO2 nanorods by hydrothermal process under alkaline condition. By the two-step method, we finally gain the 1D nanorods TiO2 extracted from ilmenite sand. The characterization using the Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) obtained the nanorod morphology at a diameter about 9.6 nm.

  13. Synergistic effects of F and Fe in co-doped TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Yufei; Shen, Huiyuan; Liu, Yanhua

    2016-03-01

    TiO2 photocatalysts co-doped with F and Fe were synthesized by a sol-gel method. Synergistic effects of F and Fe in the co-doped TiO2 were verified by NH3 decomposition, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible (UV-Vis) absorption spectroscopy, and was analyzed by the simulation based on the density functional theory (DFT). The results from NH3 decomposition confirmed that the cooperation of F and Fe broadened the optical response of TiO2 to visible light region and also enhanced the photocatalytic activity of TiO2 under ultraviolet light. XRD patterns, SEM and HRTEM images showed that the co-doped samples were nanometric anatase with an average particle size of 25 nm. Co-doping with F and Fe inhibited the grain growth of TiO2 from anatase to rutile and resulted in a larger lattice defect. XPS analysis exhibited that the doped F and Fe atoms were into the TiO2 lattice. UV-Vis absorption spectra showed that its optical absorption edge was moved up to approximately 617 nm and its ultraviolet absorption was also enhanced. The DFT results indicated that the cooperation of Fe 3d and O 2p orbits narrowed the band gap of TiO2 and F 2p orbit widened the upper valence bands. The synergistic electron density around F and Fe in co-doped TiO2 was capable to enhance the photo-chemical stability of TiO2.

  14. Beneficial surface passivation of hydrothermally grown TiO2 nanowires for solar water oxidation

    NASA Astrophysics Data System (ADS)

    Yun, Gun; Song, Gwang Yeom; Ahn, Bo-Eun; Lee, Sang-Kwon; Heo, Jaeyeong; Ahn, Kwang-Soon; Kang, Soon Hyung

    2016-03-01

    Rutile TiO2 nanowires (TONWs) with a length of 2.0 μm were synthesized using a facile hydrothermal method in a strong acid solution. To investigate the effect of surface passivation of TONW arrays, a TiO2 layer with a thickness varying from 5 to 20 nm on TONW arrays was applied by atomic layer deposition (ALD). No distinct morphological modification was observed in all prepared TONW arrays in the environment where the diameter of the TONW arrays was systematically increased from 10 to 40 nm. In this study, Mott-Schottky analysis revealed that 10 nm TiO2-coated TONW (denoted as TiO2(10 nm)/TONW) arrays showed the highest electronic conductivity, followed by the 5 nm, 20 nm, and 0 nm TiO2/TONW arrays. The photoelectrochemical (PEC) performance was assessed in 0.1 M KOH, which revealed that TiO2(10 nm)/TONW arrays displayed a photocurrent density (3.92 mA/cm2 at 0.5 VNHE) higher than that (2.72 mA/cm2) of TONW arrays. This may be ascribed to the surface passivation of trap or defect sites by the thin TiO2 surface coating, leading to the increased electron densities and improving the PEC performance. For a more definitive examination, photovoltage decay measurement was performed to calculate the decay lifetime, which is closely correlated to the electron-hole recombination reaction. In this study, TiO2(10 nm)/TONW arrays exhibited a decay lifetime (0.7 s) shorter than that (1.1 s) of TONW arrays, proving the suppressed charge recombination in the thin TiO2/TONW arrays.

  15. Effect of TiO2 Nanoparticles on Tensile Strength of Dental Acrylic Resins

    PubMed Central

    Shirkavand, Saeed; Moslehifard, Elnaz

    2014-01-01

    Background and aims. Adding further fillers to dental resins may enhance their physical characteristics. The aim of this study was to evaluate the tensile strength of heat-curing acrylic resin reinforced by TiO2nanoparticles added into the resin matrix. Materials and methods. Commercially available TiO2 nanoparticles were obtained and characterized using X-ray diffrac-tion (XRD) and scanning electron microscopy (SEM) to determine their crystalline structure, particle size and morphology. TiO2-acrylic resin nanocomposite was prepared by mixing 0.5, 1 and 2 (wt%) of surface modified TiO2 nanoparticles in an amalgamator providing three groups of samples. Before curing, the obtained paste was packed into steel molds. After cur-ing, the specimens were removed from the molds. The tensile strength test samples were prepared according to ISO 1567. Results. Two crystalline phases were found in TiO2 nanoparticles including: (i) anatase as the major one, and (ii) rutile. The average particle size calculated according to the Scherrer equation was 20.4 nm, showing a normal size distribution. According to SEM images, the nanocomposite with 1wt% TiO2 nanoparticles had a better distribution compared to other groups. In addition, the group by 1wt% TiO2 exhibited higher tensile strength with a significant difference compared to other groups. ANOVA showed significant differences between the contents of TiO2 particles in acrylic resin (F = 22.19; P < 0.001). Conclusion. A considerable increase in tensile strength was observed with titania NPs reinforcement agents in 1wt% by weight. Further increase of TiO2 nanoparticles decreased the tensile strength. PMID:25587380

  16. Photodegradation of phenanthrene by N-doped TiO2 photocatalyst.

    PubMed

    Sirisaksoontorn, Weekit; Thachepan, Surachai; Songsasen, Apisit

    2009-07-15

    The photodegradation of phenanthrene has been catalyzed by nanostructures of TiO2 doped with nitrogen, N-doped TiO2. The N-doped TiO2 was prepared from the sol-gel reaction of Titanium(IV) bis(ethyl acetoacetato)diisopropoxide with 25% ammonia solution. The N-doped TiO2 was calcined at various temperatures from 300 to 700 degrees C. X-ray diffraction (XRD) results showed that N-doped TiO2 remained amorphous at 300 degrees C but anatase-to-rutile transformation started at 400 degrees C and was complete at 700 degrees C. The average particle size calculated from Scherrer's equation was in the range of 9-51 nm with surface area (S(BET)) of 253.7-4.8 m2/g. X-ray photoelectron spectroscopy (XPS) results confirmed the incorporation of nitrogen atoms (Ti-N bond) in the N-doped catalyst. Moreover, the percentage of nitrogen determined by Elemental analysis was 0.236% of N-doped calcined at 400 degrees C. UV-Vis reflection spectra indicated that N-doped TiO2 calcined at 400 degrees C shifted to the higher absorption edge in the range of visible light. N-doped TiO2 calcined at 400 degrees C successfully catalyzed the photodegradation of phenanthrene (80% conversion) whereas N-doped TiO2 calcined at 500 degrees C and P25 TiO2 failed as catalysts.

  17. The provenance of rutile.

    USGS Publications Warehouse

    Force, E.R.

    1980-01-01

    Most coarse detrital rutile is derived from high-grade metamorphic rocks. Contrary to a conventional assumption, independent rutile grains are particularly rare in igneous rocks except alkalic rocks. The use of rutile in the zircon-tourmaline-rutile index of mineralogic maturity is only partially valid, owing to its restricted provenance. -Author

  18. Degradation of the ammonia wastewater in aqueous medium with ozone in combination with mesoporous TiO2 catalytic

    NASA Astrophysics Data System (ADS)

    Liu, Zhiwu; Qiu, Jianping; Zheng, Chaocan; Li, Liqing

    2017-03-01

    TiO2 mesoporous nanomaterials are now widely used in catalytic ozone technology. In this paper, the market P25 as precursor hydrothermal method to prepare TiO2 mesoporous materials, ozone catalyst material characterization by transmission electron microscopy, surface area analyzers, and X-ray diffraction technique and found that nanotubes, nanosheets, nanorods through characterization results, nano-particles of different morphology and anatase and rutile proportion of the ozone catalytic material can be controlled by the calcination temperature and the temperature of hot water to give, and with the hot water temperature and calcination temperature, the catalyst becomes small aperture size larger catalyst crystalline phase from anatase to rutile gradually shift. Catalytic materials have been prepared by the Joint ozone degradation of ammonia wastewater to evaluate mesoporous TiO2 nanomaterials ozone catalytic performance, the results showed that: ammonia wastewater removal efficiency of various catalytic materials relatively separate ozone and markets P25 effects are significantly improved, and TiO2 nanotubes cooperate with ozone degradation ammonia wastewater highest efficiency, in addition, rutile TiO2 catalysts, the more the better the performance of their ozone catalysis.

  19. Effect of the crystalline constitution of TiO2 substrates on the growth of ultrathin Mo layer

    NASA Astrophysics Data System (ADS)

    Noirfalise, X.; Renaux, F.; Cossement, D.; Sebaihi, Noham; Lazzaroni, Roberto; Snyders, R.

    2012-11-01

    Metallic molybdenum was deposited by magnetron sputtering on amorphous and (110) rutile TiO2 substrates. An interfacial reaction between the deposited Mo and the TiO2 substrates generating Ti3 +, Ti2 + oxidation states is evidenced by X-ray photoelectron spectroscopy. Our XPS data suggest, as compared to the (110) rutile substrate, a higher reactivity of the amorphous TiO2 leading to a stronger Mo oxidation. In both cases, this reaction, leads to the formation of MoOx nanostructures at the interfaces. The growth mechanism of the Mo deposit as a function of the crystalline constitution of the TiO2 substrate was analyzed by processing the XPS data using the Quases ® software. The data reveal a layer-by-layer growth of the Mo deposit on the (110) rutile substrate and a Stranski-Krastanov growth on the amorphous one. We explain these different growth modes based on the TiO2 surface reactivity and electronic structure using the Cabrera-Mott theory. This explanation is supported by Time-of-Flight Secondary Ion Mass spectrometry profiling.

  20. Synthesis and visible light photoactivity of anatase Ag, and garlic loaded TiO2 nanocrystalline catalyst

    EPA Science Inventory

    An excellent visible light activated Ag and S doped TiO2 nanocatalyst was prepared by using AgNO3 and garlic (Allium sativum) as Ag+ and sulfur sources, respectively. The catalyst resisted the change from anatase to rutile phase even at calcination at 700 oC. The photocatalytic e...

  1. Enhanced bolometric properties of TiO2-x thin films by thermal annealing

    NASA Astrophysics Data System (ADS)

    Ashok Kumar Reddy, Y.; Shin, Young Bong; Kang, In-Ku; Lee, Hee Chul; Sreedhara Reddy, P.

    2015-07-01

    The effect of thermal annealing on the bolometric properties of TiO2-x films was investigated. The test-patterned TiO2-x samples were annealed at 300 °C temperature in order to enhance their structural and electrical properties for effective infrared image sensor device applications. The crystallinity was changed from amorphous to rutile/anatase in annealed TiO2-x films. Compared to the as-deposited samples, a decrement of the band gap and a decrease of the electrical resistivity were perceived in annealed samples. We found that the annealed samples show linear current-voltage (I-V) characteristic performance, which implies that ohmic contact was well formed at the interface between the TiO2-x and the Ti electrode. Moreover, the annealed TiO2-x sample had a significantly low 1/f noise parameter (1.21 × 10-13) with a high bolometric parameter (β) value compared to those of the as-deposited samples. As a result, the thermal annealing process can be used to prepare TiO2-x film for a high-performance bolometric device.

  2. Exposure to TiO2 nanoparticles increases Staphylococcusaureusinfection of HeLa cells

    NASA Astrophysics Data System (ADS)

    Xu, Yan; Wei, Ming-Tzo; Walker, Stephen. G.; Wang, Hong Zhan; Gondon, Chris; Brink, Peter; Guterman, Shoshana; Zawacki, Emma; Applebaum, Eliana; Rafailovich, Miriam; Ou-Yang, H. Daniel; Mironava, Tatsiana

    TiO2 is one of the most common nanoparticles in industry from food additives to energy generation. Even though TiO2 is also used as an anti-bacterial agent in combination with UV, we found that, in the absence of UV, exposure of HeLa cells to TiO2 nanoparticles largely increased their risk of bacterial invasion. HeLa cells cultured with low dosage rutile and anatase TiO2 nanoparticles (0.1 mg/ml) for 24 hrs prior to exposure to bacteria had 350% and 250% respectively more bacteria infected per cell. The increase was attributed to increased LDH leakage, and changes in the mechanical response of the cell membrane. On the other hand, macrophages exposed to TiO2 particles ingested 40% fewer bacteria, further increasing the risk of infection. In combination, these two factors raise serious concerns regarding the impact of exposure to TiO2 nanoparticles on the ability of organisms to resist bacterial infection.

  3. ZnFe2O4-TiO2 Nanoparticles within Mesoporous MCM-41

    PubMed Central

    Tang, Aidong; Deng, Yuehua; Jin, Jiao; Yang, Huaming

    2012-01-01

    A novel nanocomposite ZnFe2O4-TiO2/MCM-41 (ZTM) was synthesized by a sol-gel method and characterized through X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N2 adsorption-desorption, Raman spectroscopy, and ultraviolet visible (UV-vis) spectrophotometry. The results confirmed the incorporation of ZnFe2O4-TiO2 nanoparticles inside the pores of the mesoporous MCM-41 host without destroying its integrity. ZnFe2O4 nanoparticles can inhibit the transformation of anatase into rutile phase of TiO2. Incorporation of ZnFe2O4-TiO2 within MCM-41 avoided the agglomeration of nanoparticles and reduced the band gap energy of TiO2 to enhance its visible light photocatalytic activity. UV-vis absorption edges of ZTM nanocomposites redshifted with the increase of Zn/Ti molar ratio. The nanocomposite approach could be a potential choice for enhancing the photoactivity of TiO2, indicating an interesting application in the photodegradation and photoelectric fields. PMID:22919325

  4. Growth of TiO2 with thermal and plasma enhanced atomic layer deposition.

    PubMed

    Tallarida, Massimo; Friedrich, Daniel; Städter, Matthias; Michling, Marcel; Schmeisser, Dieter

    2011-09-01

    We show a comparative study of the TiO2 ALD with TTIP and either O2 or O2-plasma on Si/SiO2 substrates. In particular we compare the surface morphology and crystalline phase by means of Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) for different O2-plasma procedures upon changing the time between cycles and the N2-purging pressure. The AFM images show that already these parameters may induce structural changes in the TiO2 films grown by ALD, with the formation of crystallites with average lateral width varying between 15 and 80 nm. By means of XAS we also found that the crystallites have mixed anatase and rutile crystalline phases and that smaller crystallites have a greater rutile component than the larger ones.

  5. Electronic structure and room temperature ferromagnetism of C doped TiO2

    NASA Astrophysics Data System (ADS)

    Ablat, Abduleziz; Wu, Rong; Mamat, Mamatrishat; Ghupur, Yasin; Aimidula, Aimierding; Bake, Muhammad Ali; Gholam, Turghunjan; Wang, Jiaou; Qian, Haijie; Wu, Rui; Ibrahim, Kurash

    2016-10-01

    C-doped TiO2 nanoparticles were successfully synthesized using a simple hydrothermal synthesis method. After this preparation, a portion of the samples were annealed separately in air on the one hand, and in argon on the other, and another portion remained untreated. The results of X-ray diffraction show that the untreated samples primarily display anatase and rutile structures. However, after annealing, the samples displayed the rutile structure only. The Ti K-edge and L-edge Near Edge X-ray Absorption Fine Structure analyses clearly show that C atoms were successfully incorporated into the TiO2 host lattice. All doped samples exhibit ferromagnetism at room temperature. The saturation magnetization (Ms) and coercive fields (Hc) tend to decrease after the samples are annealed in argon and in air. The maximum Ms of the untreated samples was approximately 0.038 emu/g.

  6. Formation of titanium monoxide (001) single-crystalline thin film induced by ion bombardment of titanium dioxide (110)

    NASA Astrophysics Data System (ADS)

    Pabón, B. M.; Beltrán, J. I.; Sánchez-Santolino, G.; Palacio, I.; López-Sánchez, J.; Rubio-Zuazo, J.; Rojo, J. M.; Ferrer, P.; Mascaraque, A.; Muñoz, M. C.; Varela, M.; Castro, G. R.; de La Fuente, O. Rodríguez

    2015-02-01

    A plethora of technological applications justify why titanium dioxide is probably the most studied oxide, and an optimal exploitation of its properties quite frequently requires a controlled modification of the surface. Low-energy ion bombardment is one of the most extended techniques for this purpose and has been recently used in titanium oxides, among other applications, to favour resistive switching mechanisms or to form transparent conductive layers. Surfaces modified in this way are frequently described as reduced and defective, with a high density of oxygen vacancies. Here we show, at variance with this view, that high ion doses on rutile titanium dioxide (110) induce its transformation into a nanometric and single-crystalline titanium monoxide (001) thin film with rocksalt structure. The discovery of this ability may pave the way to new technical applications of ion bombardment not previously reported, which can be used to fabricate heterostructures and interfaces.

  7. Epitaxial growth of homogeneous single-crystalline AlN films on single-crystalline Cu (1 1 1) substrates

    NASA Astrophysics Data System (ADS)

    Wang, Wenliang; Yang, Weijia; Liu, Zuolian; Lin, Yunhao; Zhou, Shizhong; Qian, Huirong; Gao, Fangliang; Yang, Hui; Li, Guoqiang

    2014-03-01

    The homogeneous and crack free single-crystalline AlN thin films have been epitaxially grown on single-crystalline Cu (1 1 1) substrates with an in-plane alignment of AlN [11-20]//Cu [1-10] by pulsed laser deposition (PLD) technology with an integrated laser rastering program. The as-grown AlN films are studied by spectroscopic ellipsometry, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), polarized light microscopy, high-resolution X-ray diffraction, and high-resolution transmission electron microscopy (HRTEM). The spectroscopic ellipsometry reveals the excellent thickness uniformity of as-grown AlN films on the Cu (1 1 1) substrates with a root-mean-square (RMS) thickness inhomogeneity less than 2.6%. AFM and FESEM measurements indicate that very smooth and flat surface AlN films are obtained with a surface RMS roughness of 2.3 nm. The X-ray reflectivity image illustrates that there is a maximum of 1.2 nm thick interfacial layer existing between the as-grown AlN and Cu (1 1 1) substrates and is confirmed by HRTEM measurement, and reciprocal space mapping shows that almost fully relaxed AlN films are achieved only with a compressive strain of 0.48% within ∼321 nm thick films. This work demonstrates a possibility to obtain homogeneous and crack free single-crystalline AlN films on metallic substrates by PLD with optimized laser rastering program, and brings up a broad prospect for the application of acoustic filters that require abrupt hetero-interfaces between the AlN films and the metallic electrodes.

  8. Imparting amphiphobicity on single-crystalline porous materials

    PubMed Central

    Sun, Qi; He, Hongming; Gao, Wen-Yang; Aguila, Briana; Wojtas, Lukasz; Dai, Zhifeng; Li, Jixue; Chen, Yu-Sheng; Xiao, Feng-Shou; Ma, Shengqian

    2016-01-01

    The sophisticated control of surface wettability for target-specific applications has attracted widespread interest for use in a plethora of applications. Despite the recent advances in modification of non-porous materials, surface wettability control of porous materials, particularly single crystalline, remains undeveloped. Here we contribute a general method to impart amphiphobicity on single-crystalline porous materials as demonstrated by chemically coating the exterior of metal-organic framework (MOF) crystals with an amphiphobic surface. As amphiphobic porous materials, the resultant MOF crystals exhibit both superhydrophobicity and oleophobicity in addition to retaining high crystallinity and intact porosity. The chemical shielding effect resulting from the amphiphobicity of the MOFs is illustrated by their performances in water/organic vapour adsorption, as well as long-term ultrastability under highly humidified CO2 environments and exceptional chemical stability in acid/base aqueous solutions. Our work thereby pioneers a perspective to protect crystalline porous materials under various chemical environments for numerous applications. PMID:27796363

  9. Epitaxial single crystalline ferrite films for high frequency applications

    SciTech Connect

    Suzuki, Y.; Dover, R.B. van; Korenivski, V.; Werder, D.; Chen, C.H.; Felder, R.J.; Phillips, J.M.

    1996-11-01

    The successful growth of single crystal ferrites in thin film form is an important step towards their future incorporation into integrated circuits operating at microwave frequencies. The authors have successfully grown high quality single crystalline spinel ferrite thin films of (Mn,Zn)Fe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} on (100) and (110) SrTiO{sub 3} and MgAl{sub 2}O{sub 4} at low temperature. These ferrite films are buffered with spinel structure layers that are paramagnetic at room temperature. In contrast to ferrite films grown directly on the substrates, ferrite films grown on buffered substrates exhibit excellent crystallinity and bulk saturation magnetization values, thus indicating the importance of lattice match and structural similarity between the film and the immediately underlying layer. X-ray, RBS, AFM and TEM analysis provide a consistent picture of the structural properties of these ferrite films. The authors then use this technique to grow exchange-coupled bilayers of single crystalline CoFe{sub 2}O{sub 4} and (Mn,Zn)Fe{sub 2}O{sub 4}. In these bilayers, they observe strong exchange coupling across the interface that is similar in strength to the exchange coupling in the individual layers.

  10. A novel method for formation of single crystalline tungsten nanotip

    NASA Astrophysics Data System (ADS)

    Hayashi, Shigeki; Ono, Masashi; Tomonaga, Shinya; Nakanishi, Haruka

    2016-12-01

    A point electron source is desired to improve performance of high brightness electron beam instruments. It is valuable to create nano-sized tungsten (W) tip from sharp ordinary polycrystalline W needle. The sharp W needle, which is manufactured by electrochemical etching, has been practically utilized as a cold field emission electron source. A novel method for formation of single crystalline W nanotip on the top of h-BN coated conventional polycrystalline tungsten, by supplying high voltage, has been found. The W nanotip with an apex radius as small as a few times 10 nm would be grown on the top of the polycrystalline W needle. Field emission characteristics of obtained W nanotip are measured, and the field emission microscopic (FEM) and transmission emission microscopic (TEM) images are observed. The emission current from the W nanotip is measured to exceed 0.1 mA. The FEM image shows significant electron emission from the crystallographic facets of the W single crystal. From these results, the present method for formation of the single crystalline W nanotip would be expected as a key technology to realize a point electron source with a nano-sized apex which makes it possible to improve the performance of high brightness electron beam instruments, especially tiny X-ray tubes for medical use, as well as a cantilever of scanning probe microscope.

  11. The nanocrystalline structure of TiO2 film deposited by DC magnetron sputtering at room temperature

    NASA Astrophysics Data System (ADS)

    Liu, Jindong; Ding, Wanyu; Wang, Hualin; Liu, Shimin; Jiang, Weiwei; Liu, Chaoqian; Wang, Nan; Chai, Weiping

    2014-10-01

    At room temperature, titanium dioxide (TiO2) films were deposited by the direct current pulse magnetron sputtering technique. Varying O2/Ar flow ratio, TiO2 films with different nanocrystalline structures were obtained. The high resolution transmission electron microscopy results show that with O2/Ar = 6/14, the nanocrystalline in rutile phase appears in as-deposited film. Then X-ray diffraction patterns of annealed films revealed that with O2/Ar = 6/14, the higher weight fractions of rutile TiO2 appear in films. The optical emission spectroscopy results show that with O2/Ar < 6/14, O element was mainly existed as O-/O+ ions, instead of excited state of O atoms.

  12. Morphological and phase evolution of TiO 2 nanocrystals prepared from peroxotitanate complex aqueous solution: Influence of acetic acid

    NASA Astrophysics Data System (ADS)

    Chang, Jeong Ah; Vithal, Muga; Baek, In Chan; Seok, Sang Il

    2009-04-01

    Nanosized anatase and rutile TiO 2 having different shape, phase and size have been prepared from aqueous solutions of peroxo titanium complex starting from titanium(IV) isopropoxide (TTIP), acetic acid and hydrogen peroxide (H 2O 2) in water/isopropanol media by a facile sol-gel process. The TiO 2 nanocrystals are characterized by powder X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy, TEM, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques. The influence of pH and the sequence of addition of reaction contents on the phase and morphology of TiO 2 are studied. The reasons for the observation of only anatase and/or mixture of anatase and rutile are given.

  13. Fungus-mediated biosynthesis and characterization of TiO2 nanoparticles and their activity against pathogenic bacteria

    NASA Astrophysics Data System (ADS)

    Rajakumar, G.; Rahuman, A. Abdul; Roopan, S. Mohana; Khanna, V. Gopiesh; Elango, G.; Kamaraj, C.; Zahir, A. Abduz; Velayutham, K.

    2012-06-01

    In the present study, the biosynthesis of TiO2 nanoparticles (TiO2 NPs) was achieved by a novel, biodegradable and convenient procedure using Aspergillus flavus as a reducing and capping agent. Research on new, simple, rapid, eco-friendly and cheaper methods has been initiated. TiO2 NPs were characterized by FTIR, XRD, AFM, SEM and TEM studies. The X-ray diffraction showed the presence of increased amount of TiO2 NPs which can state by the presence of peaks at rutile peaks at 1 0 0, 0 0 2, 1 0 0 and anatase forms at 1 0 1 respectively. SEM observations revealed that synthesized TiO2 NPs were spherical, oval in shape; individual nanoparticles as well as a few aggregate having the size of 62-74 nm. AFM shows crystallization temperature was seen on the roughness of the surface of TiO2. The Minimum inhibitory concentration value for the synthesized TiO2 NPs was found to be 40 μg ml-1 for Escherichia coli, which was corresponding to the value of well diffusion test. This is the first report on antimicrobial activity of fungus-mediated synthesized TiO2 NPs, which was proved to be a good novel antibacterial material.

  14. Synthesis and Modification of Zn-doped TiO2 Nanoparticles for the Photocatalytic Degradation of Tetracycline.

    PubMed

    Pang, Shuo; Huang, Ji-Guo; Su, Yun; Geng, Bo; Lei, Su-Yuan; Huang, Yu-Ting; Lyu, Cong; Liu, Xing-Juan

    2016-09-01

    The synthesis of Zn-doped TiO2 nanoparticles by solgel method was investigated in this study, as well as its modification by H2 O2 . The catalyst was characterized by transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller, UV-visible reflectance spectra and X-ray photoelectron spectroscopy (XPS). The results indicated that doping Zn into TiO2 nanoparticles could inhibit the transformation from anatase phase to rutile phase. Zn existed as the second valence oxidation state in the Zn-doped TiO2 . Zn-doped TiO2 that was synthesized by 5% Zn doping at 450°C exhibited the best photocatalytic activity. Then, the H2 O2 modification further enhanced the photocatalytic activity. Zn doping and H2 O2 modifying narrowed the band gap and efficiently increased the optical absorption in visible region. The optimal degradation rate of tetracycline by Zn-doped TiO2 and H2 O2 modified Zn-doped TiO2 was 85.27% and 88.14%. Peroxide groups were detected in XPS analysis of H2 O2 modified Zn-doped TiO2 , favoring the adsorption of visible light. Furthermore, Zn-doped TiO2 modified by H2 O2 had relatively good reusability, exhibiting a potential practical application for tetracycline's photocatalytic degradation.

  15. Osteoconductivity and Hydrophilicity of TiO(2) Coatings on Ti Substrates Prepared by Different Oxidizing Processes.

    PubMed

    Yamamoto, Dai; Kawai, Ikki; Kuroda, Kensuke; Ichino, Ryoichi; Okido, Masazumi; Seki, Azusa

    2012-01-01

    Various techniques for forming TiO(2) coatings on Ti have been investigated for the improvement of the osteoconductivity of Ti implants. However, it is not clear how the oxidizing process affects this osteoconductivity. In this study, TiO(2) coatings were prepared using the following three processes: anodizing in 0.1 M H(3)PO(4) or 0.1 M NaOH aqueous solution; thermal oxidation at 673 K for 2 h in air; and a two-step process of anodizing followed by thermal oxidation. The oxide coatings were evaluated using SEM, XRD, and XPS. The water contact angle on the TiO(2) coatings was measured as a surface property. The osteoconductivity of these samples was evaluated by measuring the contact ratio of formed hard tissue on the implanted samples (defined as the R(B-I) value) after 14 d implantation in rats' tibias. Anatase was formed by anodizing and rutile by thermal oxidation, but the difference in the TiO(2) crystal structure did not influence the osteoconductivity. Anodized TiO(2) coatings were hydrophilic, but thermally oxidized TiO(2) coatings were less hydrophilic than anodized TiO(2) coatings because they lacked in surface OH groups. The TiO(2) coating process using anodizing without thermal oxidation gave effective improvement of the osteoconductivity of Ti samples.

  16. Osteoconductivity and Hydrophilicity of TiO2 Coatings on Ti Substrates Prepared by Different Oxidizing Processes

    PubMed Central

    Yamamoto, Dai; Kawai, Ikki; Kuroda, Kensuke; Ichino, Ryoichi; Okido, Masazumi; Seki, Azusa

    2012-01-01

    Various techniques for forming TiO2 coatings on Ti have been investigated for the improvement of the osteoconductivity of Ti implants. However, it is not clear how the oxidizing process affects this osteoconductivity. In this study, TiO2 coatings were prepared using the following three processes: anodizing in 0.1 M H3PO4 or 0.1 M NaOH aqueous solution; thermal oxidation at 673 K for 2 h in air; and a two-step process of anodizing followed by thermal oxidation. The oxide coatings were evaluated using SEM, XRD, and XPS. The water contact angle on the TiO2 coatings was measured as a surface property. The osteoconductivity of these samples was evaluated by measuring the contact ratio of formed hard tissue on the implanted samples (defined as the RB-I value) after 14 d implantation in rats' tibias. Anatase was formed by anodizing and rutile by thermal oxidation, but the difference in the TiO2 crystal structure did not influence the osteoconductivity. Anodized TiO2 coatings were hydrophilic, but thermally oxidized TiO2 coatings were less hydrophilic than anodized TiO2 coatings because they lacked in surface OH groups. The TiO2 coating process using anodizing without thermal oxidation gave effective improvement of the osteoconductivity of Ti samples. PMID:23316128

  17. Plasmonic Ag deposited TiO2 nano-sheet film for enhanced photocatalytic hydrogen production by water splitting

    NASA Astrophysics Data System (ADS)

    Liu, Enzhou; Kang, Limin; Yang, Yuhao; Sun, Tao; Hu, Xiaoyun; Zhu, Changjun; Liu, Hanchen; Wang, Qiuping; Li, Xinghua; Fan, Jun

    2014-04-01

    TiO2 nano-sheet film (TiO2 NSF) was prepared by a hydrothermal method. Ag nanoparticles (NPs) were then deposited on the surface of TiO2 NSF (Ag/TiO2 NSF) under microwave-assisted chemical reduction. The prepared samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible (UV-vis) absorption spectroscopy, x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, and Raman scattering spectroscopy. The results revealed that the Ag NPs were well dispersed on the anatase/rutile mixed-phase TiO2 nano-sheet surface with a metallic state. The visible light absorption and Raman scattering of TiO2 were enhanced by Ag NPs based on its surface plasmon resonance effect. Besides, Ag NPs could also effectively restrain the recombination of photogenerated electrons and holes. Photocatalytic water splitting was conducted on the films to obtain hydrogen, and the experimental results indicated that plasmonic Ag NPs could greatly enhance the photocatalytic activity of TiO2 due to the synergistic effect between electron transfer and surface plasmon resonance enhanced absorption. The hydrogen yield obtained from the optimal sample reached 8.1 μmol cm-2 and the corresponding energy efficiency was about 0.47%, which was 8.5 times higher than that of pure TiO2 film. Additionally, the formation mechanism of TiO2 nano-sheet film is preliminarily discussed.

  18. Metal oxide nanocluster-modified TiO2 as solar activated photocatalyst materials

    NASA Astrophysics Data System (ADS)

    Fronzi, Marco; Iwaszuk, Anna; Lucid, Aoife; Nolan, Michael

    2016-02-01

    In this review we describe our work on new TiO2 based photocatalysts. The key concept in our work is to form new composite structures by the modification of rutile and anatase TiO2 with nanoclusters of metal oxides and our density functional theory (DFT) level simulations are validated by experimental work synthesizing and characterizing surface-modified TiO2. We use DFT to show that nanoclusters of different metal oxides, TiO2, SnO/SnO2, PbO/PbO2, NiO and CuO can be adsorbed at rutile and anatase surfaces and can induce red shifts in the absorption edge to enable visible light absorption which is the first key requirement for a practical photocatalyst. We furthermore determine the origin of the red shift and discuss the factors influencing this shift and the fate of excited electrons and holes. For p-block metal oxides we show how the oxidation state of Sn and Pb can be used to tune both the magnitude of the red shift and also its mechanism. Finally, aiming to make our models more realistic, we present some new results on the stability of water at rutile and anatase surfaces and the effect of water on oxygen vacancy formation and on nanocluster modification. These nanocluster-modified TiO2 structures form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with the suitable choice of nanocluster modifier can be applied to CO2 reduction.

  19. Metal oxide nanocluster-modified TiO2 as solar activated photocatalyst materials.

    PubMed

    Fronzi, Marco; Iwaszuk, Anna; Lucid, Aoife; Nolan, Michael

    2016-02-24

    In this review we describe our work on new TiO2 based photocatalysts. The key concept in our work is to form new composite structures by the modification of rutile and anatase TiO2 with nanoclusters of metal oxides and our density functional theory (DFT) level simulations are validated by experimental work synthesizing and characterizing surface-modified TiO2. We use DFT to show that nanoclusters of different metal oxides, TiO2, SnO/SnO2, PbO/PbO2, NiO and CuO can be adsorbed at rutile and anatase surfaces and can induce red shifts in the absorption edge to enable visible light absorption which is the first key requirement for a practical photocatalyst. We furthermore determine the origin of the red shift and discuss the factors influencing this shift and the fate of excited electrons and holes. For p-block metal oxides we show how the oxidation state of Sn and Pb can be used to tune both the magnitude of the red shift and also its mechanism. Finally, aiming to make our models more realistic, we present some new results on the stability of water at rutile and anatase surfaces and the effect of water on oxygen vacancy formation and on nanocluster modification. These nanocluster-modified TiO2 structures form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with the suitable choice of nanocluster modifier can be applied to CO2 reduction.

  20. Nanoscale strain engineering on the surface of a bulk TiO2 crystal.

    PubMed

    Potapenko, Denis V; Li, Zhisheng; Kysar, Jeffery W; Osgood, Richard M

    2014-11-12

    Arrays of highly strained 5-25 nm-wide regions have been prepared on rutile TiO2(110) surface through a low energy Ar ion bombardment technique. Using scanning tunneling microscopy (STM) and an innovative STM tip-triggered nanoexplosion approach we show experimentally that the protrusions arise from subsurface Ar-filled pockets. Continuum mechanics modeling gives good estimates of the corresponding elastic deformation. Surface strain values of up to 4% have been deduced.

  1. The influence of temperature, pressure and Ag doping on the physical properties of TiO2 nanoceramics.

    PubMed

    Tran, V H; Głuchowski, P; Łukowiak, A; Stre Combining Cedilla K, W

    2016-12-01

    Undoped and Ag-doped TiO2 ceramics have been prepared at temperatures between 500-1000 °C and under pressures up to 8 GPa. Their crystal structures and physical properties were investigated by means of EDX, SEM, TEM, X-ray powder diffraction, and magnetization M, specific heat Cp and electrical resistance ρ measurements. It is found that the anatase-structured As-cast powder transforms into rutile and columbite-type at 500 °C and 5.5 GPa. The stabilization of the latter phase is fulfilled under a pressure of 8 GPa and at temperatures above 800 °C. On the basis of experimental results, we conclude that the physical properties of TiO2 can be tailored along with its crystal structure. In particular, magnetic properties change from paramagnetic in anatase and rutile to magnetic correlations and in all likelihood magnetic-field-induced antiferromagnetic short-range order in columbite-structured TiO2. Contrasting behaviour in the temperature dependences of specific heat between anatase/rutile and columbite-type TiO2 is obvious. Differently from anatase/rutile, the Cp of columbite-type TiO2 exhibits a low-temperature excess, being interpreted as due to magnetic correlations, or else the prevalence of soft modes. An analysis of ρ(T) for columbite-type TiO2 in the temperature range of 280-400 K reveals the presence of a new trapping state at an energy level of ∼28 meV within the originally forbidden gap. Furthermore, thermal fluctuation-induced tunnelling and hopping conductivities are suggested to govern in a lower temperature range. We recognize that the Ag-doped contents do not alter the crystal structure but considerably enhance magnetic correlations, compared to undoped samples.

  2. Synthesis, characterization and photocatalytic behavior of Ag doped TiO2 thin film

    NASA Astrophysics Data System (ADS)

    Bensouici, F.; Souier, T.; Dakhel, A. A.; Iratni, A.; Tala-Ighil, R.; Bououdina, M.

    2015-09-01

    In this study, structure, microstructure, optical properties and photocatalytic degradation of Rhodamine B (RhB) have been investigated in an aqueous heterogeneous media containing pure and Ag doped TiO2 nanostructures thin films which were prepared by a simple sol-gel route. Thermal analysis demonstrated that Ag content decreased the temperature of anatase-to-rutile phase transformation. X-ray diffraction analysis confirmed that the prepared nanostructures crystallize within anatase-type structure and that the dopant Ag ions were not fully incorporated within TiO2 host lattice, meanwhile both the refractive index and optical band gap were affected by Ag concentration. The photodegradation of Rhodamine B under UV-C radiation by using pure and Ag-doped TiO2 nanostructures showed that Ag played an important role in a significant improvement of the photodegradation efficiency and that the optimum content of Ag ions was found to be 0.5% molar ratio.

  3. A novel sol-gel method for preparing favorable TiO2 thin film

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoyi; Zhang, Dainan; Li, Jie; Zhong, Zhiyong; Jia, Lijun; Wen, Tianlong; Zhang, Huaiwu; Liao, Yulong

    2016-01-01

    Nanocrystalline TiO2 thin films were synthesized by the sol-gel spin-coating method with different variables. Tetrabutyl titanate (TBOT) proportion and C5H8O2: TBOT molar ratio were confirmed to be influential on the gelation time. X-ray diffraction analysis indicated that the samples presented rutile TiO2 phases, which is a basis for subsequent experiments. Scanning electron microscope results revealed that TiO2 thin films with homogeneous and compact surfaces were synthesized successfully when adding moderate TBOT. It was found the thickness of films could reach about 60 nm when sintered at 750 °C, and the influence of sintering temperature was also investigated.

  4. Raman spectral analysis of TiO2 thin films doped with rare-earth samarium.

    PubMed

    Yang, Chang-Hu; Ma, Zhong-Quan

    2012-08-01

    TiO(2) thin films doped with rare-earth samarium were prepared on a quartz plate by the sol-gel/spin-coating technique. The samples were annealed at 700 °C to 1100 °C, and the Raman spectra of the samples were obtained. Analyses of Raman spectra show that samarium doping can inhibit the anatase-rutile phase transition. Samarium doping can refine grains of TiO(2) thin films and increase the internal stress, thereby preventing lattice vibration. Nanocrystalline TiO(2) thin films obviously show the phonon confinement effect, i.e., the blueshift of characteristic Raman peak and full width at half-height increase, and the peak shapes asymmetrically broaden with a decrease in the grain sizes of the samples.

  5. Non-Band-Gap Photoexcitation of Hydroxylated TiO2.

    PubMed

    Zhang, Yu; Payne, Daniel T; Pang, Chi L; Fielding, Helen H; Thornton, Geoff

    2015-09-03

    The photochemistry of TiO2 has been studied intensively since it was discovered that TiO2 can act as a photocatalyst. Nevertheless, it has proven difficult to establish the detailed charge-transfer processes involved, partly because the excited states involved are difficult to study. Here we present evidence of the existence of hydroxyl-induced excited states in the conduction band region. Using two-photon photoemission, we show that stepwise photoexcitation from filled band gap states lying 0.8 eV below the Fermi level of rutile TiO2(110) excites hydroxyl-induced states 2.73 eV above the Fermi level that has an onset energy of ∼3.1 eV. The onset is shifted to lower energy by the coadsorption of molecular water, which suggests a means of tuning the energy of the excited state.

  6. Hydrogen donors in ZnO and TiO2

    NASA Astrophysics Data System (ADS)

    Lavrov, Eduard V.

    2016-02-01

    The results of combined IR absorption and photoconductivity studies on hydrogen donors in ZnO and TiO2 are presented. It is shown that hydrogen donors in ZnO and rutile TiO2 can be detected as Fano resonances in the photoconductivity spectra at the frequencies corresponding to the vibrational modes of these defects. In the case of anatase TiO2 IR absorption lines at 3412 and 3417 cm-1 are assigned to the stretching local vibrational modes of a donor in the neutral and the positive charge states, respectively. Interstitial hydrogen is suggested as a tentative model for the defect giving rise to these vibrational modes.

  7. Antibacterial activity of TiO2 nanotubes: Influence of crystal phase, morphology and Ag deposition

    NASA Astrophysics Data System (ADS)

    Li, Huirong; Cui, Qiang; Feng, Bo; Wang, Jianxin; Lu, Xiong; Weng, Jie

    2013-11-01

    TiO2 nanotubes on Ti substrate were fabricated by electrochemical anodization. Ag nanoparticles were deposited on the TiO2 nanotubes by a silver mirror reaction. Antibacterial activity of the nanotubes with different structural features was evaluated by a culture test with Escherichia coli bacteria. The anatase nanotubes showed the highest antibacterial activity among three crystal phases including anatase, rutile and amorphous titania. The diameters of the nanotubes affected the antibacterial activity. The two nanotubes with 200 nm and 50 nm diameters had higher antibacterial rate than those with other diameters. The antibacterial activity of the nanotubes was independent on their lengths. Ag-deposited nanotubes exhibited excellent antibacterial activity and its antibacterial rate was up to approximately 100%. TiO2 nanotubes and Ag-deposited nanotubes on titanium should be potential for antibacterial applications in clinics and industry, especially regarding with their reusability.

  8. Microstructure and Transport properties of epitaxial VO2 thin films on TiO2 substrates

    NASA Astrophysics Data System (ADS)

    Lu, Jiwei

    2008-10-01

    Vanadium oxides are paradigms of strongly correlated oxides and have attracted attention because of the metal insulator transitions (MIT) that several of the oxides and sub-oxides exhibit. In particular, VO2 has a metal--semiconductor transition at 340 K. This transition in VO2 combines the properties of a pure Mott Hubbard electronic transition with those of a Peierls structural transition. The Mott transition is responsible for the extreme speed of the optical switching that has been observed (faster than 100 fs). Understanding this transition and how to control it remains a challenge for both theory and experimental physics. We used a novel deposition technique, Reactive Bias Target Ion Beam Deposition, to grow 40 nm epitaxial VO2 thin films on rutile TiO2 substrates with various crystal orientations. X-ray diffraction (XRD) was used to explore the epitaxy of VO2 and we found that all VO2 thin films on TiO2 substrates showed tetragonal symmetry at room temperature due to the constrain from rutile substrates. We also characterized the metal-insulator transition of VO2 films as the function of the crystal orientation of rutile TiO2. We also characterized the anisotropy of VO2 thin films. In collaboration with Kevin West and Stuart Wolf, University of Virginia.

  9. Theoretical investigations of Ni- and Cu-doped TiO2

    NASA Astrophysics Data System (ADS)

    Esakki muthuraju, M.; Mahesh, R.; Sreekanth, T.; Venugopal Reddy, P.

    2014-03-01

    The electronic, magnetic and optical properties of rutile Ti1-xTMxO2 (where TM: Ni, Cu and x = 0.25) have been investigated by the density functional theory with the plane wave self consistent field method. For the calculation of exchange correlation potential, the local density approximation along with Hubbard correction (LDA +U) was used. Electronic, magnetic and optical properties were calculated using 12 atoms supercell of rutile TiO2 with one Ti atom replaced by a dopant transition metal atom. The band structure of doped rutile phase indicates the reduction of band gap leading to improvement in the photocatalytic properties of TiO2 as well as enhancement in its magnetic properties. The observed magnetism is explained on the basis of spin polarization of d states of Ti with dopants. Optical calculations by full potential, linear augmented plane wave plus local orbital (FP-LAPW+lo) method with ELK code established the presence of optical transitions in the visible light region. These theoretical calculations gave a meaningful information and excellent prediction to develop TiO2 for spintronics applications and photocatalytic applications in the visible region.

  10. The preparation of nitrogen-doped TiO 2- xN x photocatalyst coated on hollow glass microbeads

    NASA Astrophysics Data System (ADS)

    Shifu, Chen; Xuqiang, Liu; Yunzhang, Liu; Gengyu, Cao

    2007-01-01

    In this paper, the effective method for nitrogen-doped TiO 2- xN x photocatalyst coated on hollow glass microbeads is described, which uses titanium tetraisopropoxide [Ti( iso-OC 3H 7) 4] as the raw materials and gaseous ammonia as a heat treatment atmosphere. The effects of heat treatment temperature and time on the photocatalytic activity of TiO 2- xN x/beads are studied. The photocatalyst is characterized by the UV-vis diffuse reflection spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis and scanning electron microscopy (SEM). The results show that when the TiO 2- xN x/beads is heated at 650 °C for 5 h, the photocatalytic activity of the TiO 2- xN x/beads is the best. Compared with TiO 2, the photoabsorption wavelength range of nitrogen-doped TiO 2- xN x red shifts of about 60 nm, and the photoabsorption intensity increases as well. The photocatalytic activity of the TiO 2- xN x/beads is higher than that of the TiO 2/beads under visible light irradiation. The presence of nitrogen neither influences on the transformation of anatase to rutile, nor creates new crystal phases. When the TiO 2- xN x/beads is heated at 650 °C for 5 h, the amount of nitrogen-doped is 0.53 wt.% in the TiO 2- xN x. As the density of TiO 2- xN x/beads prepared is lower than 1.0 g/cm 3, it may float on water surface and use broader sunlight spectrum directly.

  11. Photocatalytic Activity of W-Doped TiO2 Nanofibers for Methylene Blue Dye Degradation.

    PubMed

    Song, Yo-Seung; Cho, Nam-Ihn; Lee, Myung-Hyun; Kim, Bae-Yeon; Lee, Deuk Yong

    2016-02-01

    Photocatalytic degradation of methylene blue (MB) in water was examined using W-doped TiO2 nanofibers prepared by a sol-gel derived electrospinning and subsequent calcination for 4 h at 550 degrees C. Different concentrations of W dopant in the range of 0 to 8 mol% were synthesized to evaluate the effect of W concentration on the photocatalytic activity of TiO2. XRD results indicated that the undoped TiO2 is composed of anatase and rutile phases. The rutile phase was transformed to anatase phase completely with the W doping. Among W-TiO2 catalysts, the 2 mol% W-TiO2 catalyst showed the highest MB degradation rate. The degradation kinetic constant increased from 1.04 x 10(-3) min(-1) to 3.54 x 10(-3) min(-1) with the increase of W doping from 0 to 2 mol%, but decreased down to 1.77 x 10(-3) min(-1) when the W content was 8 mol%. It can be concluded that the degradation of MB under UV radiation was more efficient with W-TiO2 catalysts than with pure TiO2-

  12. Crystallization kinetics and phase transformations in aluminum ion-implanted electrospun TiO2 nanofibers

    NASA Astrophysics Data System (ADS)

    Albetran, H.; Low, I. M.

    2016-12-01

    Electrospun TiO2 nanofibers were implanted with aluminum ions, and their crystallization kinetics, phase transformations, and activation energies were investigated from 25 to 900 °C by in situ high-temperature synchrotron radiation diffraction. The amorphous non-implanted and Al ion-implanted TiO2 nanofibers transformed to crystalline anatase at 600 °C and to rutile at 700 °C. The TiO2 phase transformation of the Al ion-implanted material was accelerated relative to non-implanted sample. Compared with non-implanted nanofibers, the Al-implanted materials yielded a decreased activation energies from 69(17) to 29(2) kJ/mol for amorphous-to-anatase transformation and from 112(15) to 129(5) kJ/mol for anatase-to-rutile transformation. A substitution of smaller Al ions for Ti in the TiO2 crystal structure results in accelerated titania phase transformation and a concomitant reduction in the activation energies.

  13. Influences of TiO2 phase structures on the structures and photocatalytic hydrogen production of CuOx/TiO2 photocatalysts

    NASA Astrophysics Data System (ADS)

    Liu, Yuanxu; Wang, Zhonglei; Huang, Weixin

    2016-12-01

    CuOx/TiO2 photocatalysts employing TiO2 with different phase structures as well as P25 as supports were prepared, and their structures and activity for photocatalytic H2 production in methanol/water solution under simulated solar light were comparatively studied. Structural characterization results demonstrated that the TiO2 phase structure strongly affects the CuOx-TiO2 interaction and copper species in various CuOx/TiO2 photocatalysts. The Cu2O-rutile TiO2 interaction is much stronger than the Cu2O-anatase TiO2 interaction, facilitates the interfacial charge transfer process within the Cu2O-rutile TiO2 heterojunction but disables supported Cu2O to catalyze the hole-participated methanol oxidation. The Cu2O-anatase TiO2 heterojunction with the appropriate Cu2O-anatase TiO2 interaction and thus the balancing efficiencies between the interfacial charge transfer process and hole-participated methanol oxidation is most photocatalytic active, and CuOx/P25 with the largest population of Cu2O-anatase TiO2 heterojunction exhibits the highest photocatalytic H2 production. These results provide novel insights in the applied surface science of CuOx/TiO2 photocatalysts.

  14. Thin films of TiO2:N for photo-electrochemical applications.

    PubMed

    Trenczek-Zajac, A; Pamula, E; Radecka, M; Kowalski, K; Reszka, A; Brudnik, A; Kusior, E; Zakrzewska, K

    2012-06-01

    Dc-pulsed magnetron sputtering from Ti target in reactive Ar+O2+N2 atmosphere was used to grow stoichiometric TiO2:N and non-stoichiometric TiO2-x:N thin films. X-ray diffraction at glancing incidence, atomic force microscopy AFM, scanning electron microscopy SEM, X-ray photoelectron spectroscopy XPS, and optical spectrophotometry were applied for sample characterization. Measurements of photocurrent versus voltage and wavelength over the ultraviolet uv and visible vis ranges of the light spectrum were performed in order to assess the performance of nitrogen-doped titanium dioxide thin films as photoanodes for hydrogen generation in photoelectrochemical cells, PEC. Undoped TiO2 and TiO2-x films were found to be composed of anatase and rutile mixture with larger anatase crystallites (25-35 nm) while the growth of smaller rutile crystallites (6-10 nm) predominated at higher nitrogen flow rates etaN2 as measured in standard cubic centimeters, sccm. Nitrogen-to-titanium ratio increased from N/Ti = 0.05 at etaN2 = 0.8 sccm for stoichiometric TiO2:N to N/Ti = 0.11 at etaN2 = 0.8 sccm for nonstoichiometric TiO2-x:N thin films. A red-shift in the optical absorbance was observed with an increase in etaN2. Doping with nitrogen improved photoelectrochemical properties over the visible range of the light spectrum in the case of nonstoichiometric samples.

  15. CdSe nanocrystal sensitized anatase TiO2 (001) tetragonal nanosheet-array films for photovoltaic application.

    PubMed

    Feng, Shuanglong; Yang, Junyou; Liu, Ming; Liu, Yong

    2013-02-01

    CdSe nanocrystal sensitized TiO2 nanosheet array heterostructure films were fabricated by a two-step method. Firstly, a single crystalline anatase TiO2 tetragonal nanosheet-array film on a transparent conductive fluorine-doped tin oxide (FTO) substrate was successfully prepared by hydrothermal method. Then, CdSe nanocrystalline sensitizers were deposited on the TiO2 nanosheet array by CBD method. The products were characterized with XRD, SEM, TEM and UV-vis absorption spectroscopy. The effect of the CdSe nanocrystal deposition time and the length of the TiO2 sheet on the photovoltaic performance of the resulting CdSe/TiO2 nanosheet array electrodes were also investigated. In comparison with the non-sensitized TiO2 nanosheet array, the photocurrent of CdSe sensitized TiO2 nanosheet has a great enhancement, which gives some insight to the fundamental mechanism of the performance improvement.

  16. TiS2 transformation into S-doped and N-doped TiO2 with visible-light catalytic activity

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chen; Chien, Tzu-En; Lai, Po-Chih; Chiang, Yu-Hsien; Li, Kun-Lin; Lin, Jong-Liang

    2015-12-01

    S-doped rutile has been prepared for the first time by hydrothermal reaction of TiS2 in hydrochloric acid at a low temperature (180 °C), with the S atoms in three states of Tisbnd Ssbnd Ti, Tisbnd Ssbnd O and SO4. TiS2 in nitric acid can also be transformed into TiO2, but with mixed phases of anatase and rutile, containing nitrogen atoms at interstitial sites in the form of Tisbnd Osbnd N or Tisbnd Nsbnd O. The Ssbnd TiO2 catalyst shows a better visible-light reactivity toward adsorbed methylene blue (MB) photodegradation and hydroxylation of terephthalic acid with respect to the Nsbnd TiO2. The possible reasons leading to the high photoactivity of the Ssbnd TiO2 are discussed in terms of the incorporated sulfur states.

  17. Electronic coupling in iron oxide-modified TiO2 leads to a reduced band gap and charge separation for visible light active photocatalysis.

    PubMed

    Nolan, Michael

    2011-10-28

    In recent experiments Tada et al. have shown that TiO(2) surfaces modified with iron oxide display visible light photocatalytic activity. This paper presents first principles simulations of iron oxide clusters adsorbed at the rutile TiO(2) (110) surface to elucidate the origin of the visible light photocatalytic activity of iron oxide modified TiO(2). Small iron oxide clusters adsorb at rutile (110) surface and their presence shifts the valence band so that the band gap of the composite is narrowed towards the visible, thus confirming the origin of the visible light activity of this composite material. The presence of iron oxide at the TiO(2) surface leads to charge separation, which is the origin of enhanced photocatalytic efficiency, consistent with experimental photoluminesence and photocurrent data. Surface modification of a metal oxide is thus an interesting route in the development of visible light photocatalytic materials.

  18. Influence of the oxygen concentration on the formation of crystalline phases of TiO2 during the low-pressure arc-discharge plasma synthesis

    NASA Astrophysics Data System (ADS)

    Ushakov, A. V.; Karpov, I. V.; Lepeshev, A. A.

    2016-02-01

    The synthesis of titanium dioxide (TiO2) nanoparticles with different percentage of anatase and rutile phases is investigated. The synthesis is performed by controlling the oxygen percentage in the gas mixture in the plasmachemical evaporation-condensation process employing a low-pressure arc discharge. In all our experiments, the pressure in the plasmachemical reactor and the average size of particles remain constant and are 60 Pa and 6 nm, respectively. The crystal structure of synthesized TiO2 is studied using X-ray diffraction; the morphology of the particles is analyzed employing transmission electron microscopy. Using X-ray phase analysis, it is established that the concentration of the TiO2 anatase phase decreases upon a decrease in the oxygen concentration in the gas mixture. It is shown that the TiO2 anatase phase is more efficient for photocatalytic decomposition of methylene blue than the rutile phase.

  19. Photocatalytic activity of magnetically anatase TiO2 with high crystallinity and stability for dyes degradation: Insights into the dual roles of SiO2 interlayer between TiO2 and CoFe2O4

    NASA Astrophysics Data System (ADS)

    Yang, Zewei; Shi, Yingying; Wang, Bing

    2017-03-01

    A novel magnetically separable photocatalyst comprising hollow TiO2-SiO2-CoFe2O4 (TSC) was prepared. In the TSC photocatalyst, an SiO2 interlayer between CoFe2O4 core and TiO2 shell is used to both weaken adverse influence of the magnetic core on photocatalysis and increase the temperature of the transition from anatase to rutile phase TiO2, thus increasing the anatase TiO2 crystallinity. Such an interlayer promotes photocatalytic activity by changing the competition between the injecting process and reacting process of the photogenerated carriers. The photocatalytic activity of TSC was determined for degradation of dye molecules in water under either UV or visible light. The photocatalytic reaction of cationic dyes was governed by rad OH radicals, while O2rad - was the main active species in the initial photoreaction of anionic dyes.

  20. Fatigue crack propagation behavior of a single crystalline superalloy

    NASA Technical Reports Server (NTRS)

    Lerch, B. A.; Antolovich, Stephen D.

    1990-01-01

    Crack propagation mechanisms occurring at various temperatures in a single crystalline Ni-base alloy, Rene N4, were investigated. The rates of crack growth at 21, 704, 927, 1038, and 1093 C were measured in specimens with 001-line and 110-line directions parallel to the load axis and the machined notch, respectively, using a pulsed dc potential drop apparatus, and the fracture surfaces at each temperature were examined using SEM. Crack growth rates (CGRs) for specimens tested at or below 927 C were similar, while at two higher temperatures, the CGRs were about an order of magnitude higher than at the lower temperatures. Results of SEM observations showed that surface morphologies depended on temperature.

  1. Physical properties of single crystalline BaSn{sub 5}

    SciTech Connect

    Lin, Xiao; Budko, Sergey; Canfield, Paul

    2012-01-30

    We present a comprehensive study of the binary intermetallic superconductor, BaSn{sub 5}. High-quality single crystalline BaSn{sub 5} was grown out of a Sn flux. Detailed thermodynamic and transport measurements were performed to study BaSn{sub 5}'s normal and superconducting state properties. This material appears to be a strongly coupled, multiband superconductor. H{sub c2}(T) is almost isotropic. De Haas–van Alphen oscillations were observed and two effective masses were estimated from the FFT spectra. Hydrostatic pressure causes a decrease in the superconducting transition temperature at the rate of ≈−0.053 ± 0.001 K/kbar.

  2. Performance of single crystalline silicon solar cell with irradiance

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Purohit, A.; Nehra, Anshu; Nehra, S. P.; Dhaka, M. S.

    2015-06-01

    In this paper, the effect of irradiance on the performance parameters of single crystalline silicon solar cell is undertaken. The experiment was carried out employing solar cell simulator with varying irradiance in the range 115-550W/m2 at constant cell temperature 25°C. The results show that the short circuit current is found to be increased linearly with irradiance and the open circuit voltage is increased slightly. The fill factor, maximum power and cell efficiency are also found to be increased with irradiance. The efficiency is increased linearly at lower irradiance while slightly increased at higher. The results revealed that the irradiance has a dominant effect on the performance parameters. The results are in good agreement with the available literature.

  3. Photocatalytic investigations of TiO2-P25 nanocomposite thin films prepared by peroxotitanic acid modified sol-gel method

    NASA Astrophysics Data System (ADS)

    Oshani, Fatemeh; Marandi, Reza; Rasouli, Sousan; Farhoud, Mitra Keramati

    2014-08-01

    TiO2 thin films and TiO2-P25 nanocomposite thin films were synthesized by sol-gel method utilizing peroxotitanic acid sol (PTA). Films were obtained by three dip coatings of sol on borosilicate glasses. The crystalline size and the variation in phase of thin films were determined through X-ray diffraction. The average crystalline size of the films that was in the range of 42 nm showed a reduction in the value by increasing the rutile content. The surface morphology of the films has been characterized utilizing Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Contact-mode atomic force microscopy (AFM). The results of the morphological investigations were completely coincided with the formation of TiO2-P25 nanocomposite. The optical property of the films has been evaluated by Diffuse Reflection Spectrophotometer (DRS) at the room temperature. The obtained UV-vis spectra for both TiO2 and TiO2-P25 thin films had similar maximum wavelengths. The band gap values for the direct and indirect transitions have been measured for the TiO2 and TiO2-P25 thin films and the results showed negligible variations. The photocatalytical activity of the films was studied by photodegradation of Reactive Red 222 (RR222) under UV irradiation. The results showed that the photocatalytic efficiency of TiO2-P25 nanocomposite thin films had enhanced by the addition of rutile phase which was obviously due to the cooperation of TiO2 and P25 nanoparticles in effective charge transfer process. Additionally, photodegradation rate constant result calculations for the TiO2-P25 nanocomposite thin films can well exhibit the increase in its photocatalytic performance in comparison with TiO2 thin films.

  4. TiO2 film properties as a function of processing temperature, volume 3

    NASA Technical Reports Server (NTRS)

    Fitzgibbons, E. T.; Sladek, K. J.; Hartwig, W. H.

    1972-01-01

    Thin film TiO2 was produced at 150 C by chemical vapor deposition using hydrolysis of tetraisopropyl titanate. Films were amorphous as grown, but annealing in air caused crystallization, with anatase formed beginning at 350 C and rutile at 700 C. Density and index of refraction increased substantially with increasing anneal temperature, while etch susceptibility in HF and H2SO4 decreased. Comparison with literature data showed two groups of processes. One group yields films having properties that gradually approach those of rutile with increasing process temperature. The other group gives rutile directly at moderate temperatures. Deposition of amorphous film followed by etching and annealing is suggested as a means for pattern definition.

  5. Monoethanolamine adsorption on TiO2 (110) for solid supported CO2 capture

    NASA Astrophysics Data System (ADS)

    Lu, Deyu; Muller, Kathrin; Senanayake, Sanjaya; Starr, David

    2012-02-01

    Solid supported CO2 capture materials are drawing substantial attention as a promising, cost-effective and environmentally friendly alternative to aqueous amine based CO2 capture. Recently CO2 capture was observed from monoethanolamine (MEA) adsorbed TiO2 powders. In order to facilitate the rational design of future solid CO2 capture materials, it is very important to understand the interaction between MEA and the TiO2 surface at the atomic level and how it affects the CO2 capture capabilities. In this work, we report a combined experimental and theoretical study of MEA adsorption on rutile TiO2 (110). We found that 1 ML of MEAs can form a stable and ordered patten on TiO2 (110). However, the amine group in MEA (the CO2 capture site) binds preferably to the TiO2 surface in the gauche mode. The binding energy of the gauche mode is about 0.8 eV larger than the trans mode, where the amine group is free, causing the present MEA/TiO2 system unable to capture CO2. We found that this large binding energy difference is originated from a combination of surface donor-acceptor bonds, H-bonds, and dipole-induced dipole interaction. Our study suggests that these effects are key factors to design future amine-based solid supported CO2 capture materials.

  6. Selective defunctionalization by TiO2 of monomeric phenolics from lignin pyrolysis into simple phenols.

    PubMed

    Mante, Ofei D; Rodriguez, Jose A; Babu, Suresh P

    2013-11-01

    This study is focused on defunctionalizing monomeric phenolics from lignin into simple phenols for applications such as phenol/formaldehyde resins, epoxidized novolacs, adhesives and binders. Towards this goal, Titanium dioxide (TiO2) was used to selectively remove hydroxyl, methoxy, carbonyl and carboxyl functionalities from the monomeric phenolic compounds from lignin to produce mainly phenol, cresols and xylenols. The results showed that anatase TiO2 was more selective and active compared to rutile TiO2. Catechols were found to be the most reactive phenolics and 4-ethylguaiacol the least reactive with anatase TiO2. An overall conversion of about 87% of the phenolics was achieved at 550°C with a catalyst-to-feed ratio of 5 w/w. Over 97% conversion of phenolics is achievable at moderate temperatures (550°C or ≤ 600°C) and a moderate catalyst-to-feed ratio of 6.5:1. The reactivity of catechols on TiO2 suggests that titania is a promising catalyst in the removal of hydroxyl moiety.

  7. Interface feature characterization and Schottky interfacial layer confirmation of TiO2 nanotube array film

    NASA Astrophysics Data System (ADS)

    Li, Hongchao; Tang, Ningxin; Yang, Hongzhi; Leng, Xian; Zou, Jianpeng

    2015-11-01

    We report here characterization of the interfacial microstructure and properties of titanium dioxide (TiO2) nanotube array films fabricated by anodization. Field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), nanoindentation, atomic force microscopy (AFM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the interface of the film. With increasing annealing temperature from 200 °C to 800 °C, the interfacial fusion between the film and the Ti substrate increased. The phase transformation of the TiO2 nanotube film from amorphous to anatase to rutile took place gradually; as the phase transformation progressed, the force needed to break the film increased. The growth of TiO2 nanotube arrays occurs in four stages: barrier layer formation, penetrating micropore formation, regular nanotube formation, and nanofiber formation. The TiO2 nanotubes grow from the Schottky interface layer rather than from the Ti substrate. The Schottky interface layer's thickness of 35-45 nm was identified as half the diameter of the corresponding nanotube, which shows good agreement to the Schottky interface layer growth model. The TiO2 nanotube film was amorphous and the Ti substrate was highly crystallized with many dislocation walls.

  8. Nanostructured TiO2-based gas sensors with enhanced sensitivity to reducing gases.

    PubMed

    Maziarz, Wojciech; Kusior, Anna; Trenczek-Zajac, Anita

    2016-01-01

    2D TiO2 thin films and 3D flower-like TiO2-based nanostructures, also decorated with SnO2, were prepared by chemical and thermal oxidation of Ti substrates, respectively. The crystal structure, morphology and gas sensing properties of the TiO2-based sensing materials were investigated. 2D TiO2 thin films crystallized mainly in the form of rutile, while the flower-like 3D nanostructures as anatase. The sensor based on the 2D TiO2 showed the best performance for H2 detection, while the flower-like 3D nanostructures exhibited enhanced selectivity to CO(CH3)2 after sensitization by SnO2 nanoparticles. The sensor response time was of the order of several seconds. Their fast response, high sensitivity to selected gas species, improved selectivity and stability suggest that the SnO2-decorated flower-like 3D nanostructures are a promising material for application as an acetone sensor.

  9. Shape Dependent Thermal Conductivity of TiO2-Deionized Water and Ethylene Glycol Dispersion.

    PubMed

    Pal, Bhupender; Mallick, Soumya Suddha; Pal, Bonamali

    2015-05-01

    This paper presents the importance of different shapes and crystal phases of TiO2 nanostructures such as TiO2 P-25 (70:30 anatase and rutile), as-prepared nanorods (pure anatase) and sodium titanate nanotubes (orthorhombic Na2Ti2O5 x H2O crystal) on the thermal conductivity of de-ionized water and ethylene glycol. It revealed that TiO2 nanorods (L x W = 81-134 nm x 8-13 nm and surface area = 79 m2 g(-1)) showed always higher thermal conductivity than porous nanotubes (L x W = 85-115 nm x 9-12 nm and surface area = 176 m2 g(-1)) and commercial TiO2 P-25 (30-55 nm surface area = 56 m2 g(-1)), which was explained by their differences in crystallinity, crystal phases, compactness, surface exposed atoms, surface area and much greater mean free path of longitudinal phonon vibrations along its lateral dimensions. The subsequent effect of sonication time from 5-10 h results into the breakdown of TiO2 nanorods cluster (42 to 28 nm) with the instantaneous increase in negative zeta potential values from -31 to -45 mV, respectively, seems to be an additional cause for enhancement in its thermal conductivity.

  10. Bi2O3 cocatalyst improving photocatalytic hydrogen evolution performance of TiO2

    NASA Astrophysics Data System (ADS)

    Xu, Difa; Hai, Yang; Zhang, Xiangchao; Zhang, Shiying; He, Rongan

    2017-04-01

    Photocatalytic hydrogen production using water splitting is of potential importance from the viewpoint of renewable energy development. Herein, Bi2O3-TiO2 composite photocatalysts presented as Bi-Bi2O3-anatase-rutile TiO2 multijunction were first fabricated by a simple impregnation-calcination method using Bi2O3 as H2-production cocatalysts. The obtained multijunction samples exhibit an obvious enhancement in photocatalytic H2 evolution activity in the presence of glycerol. The effect of Bi2O3 amount on H2-evolution activity of TiO2 was investigated and the optimal Bi2O3 content was found to be 0.89 mol%, achieving a H2-production rate of 920 μmol h-1, exceeding that of pure TiO2 by more than 73 times. The enhanced mechanism of photocatalytic H2-evolution activity is proposed. This study will provide new insight into the design and fabrication of TiO2-based hydrogen-production photocatalysts using low-cost Bi2O3 as cocatalyst.

  11. Bioactive TiO2 fiber films prepared by electrospinning method.

    PubMed

    Chen, S J; Yu, H Y; Yang, B C

    2013-01-01

    Electrospining method was used to prepare bioactive TiO(2) fibers films in this study. The acetic acid/ethanol/tetrabutyl titanate/polyvinylpyrrolidone (PVP) solvent system was used as precursor for the electrospining. The TiO(2) fiber structures (including its fiber diameter, morphology, and phase composition) could be controlled by changing feeding rate, PVP concentration and sinter temperature. The fiber films were subjected to simulated body fluid soaking experiments and MG63 cells culture experiments to study their bioactivity. According to the X-ray diffraction and MTT assay results, the fiber containing with anatase showed better apatite formation ability than that without anatase at the early stage, while cell proliferated on anatase-rutile TiO(2) fiber was better than that on other samples (p < 0.05).Some string beads in the fiber were beneficial for apatite formation, while the cell proliferated best on the fiber film without string beads (p < 0.05). The fiber with a diameter of 200 nm had the best apatite formation ability and osteoblast compatibility (p < 0.05). The results showed that the TiO(2) fiber film structure had great influence on its bioactivity. It indicated that the electronspining method is an effective way to prepare bioactive titania fiber films, and it is possible to control the structure of the films in the spinning process to optimize the bioactivity of TiO(2) fiber.

  12. Nanostructured TiO2-based gas sensors with enhanced sensitivity to reducing gases

    PubMed Central

    Kusior, Anna; Trenczek-Zajac, Anita

    2016-01-01

    2D TiO2 thin films and 3D flower-like TiO2-based nanostructures, also decorated with SnO2, were prepared by chemical and thermal oxidation of Ti substrates, respectively. The crystal structure, morphology and gas sensing properties of the TiO2-based sensing materials were investigated. 2D TiO2 thin films crystallized mainly in the form of rutile, while the flower-like 3D nanostructures as anatase. The sensor based on the 2D TiO2 showed the best performance for H2 detection, while the flower-like 3D nanostructures exhibited enhanced selectivity to CO(CH3)2 after sensitization by SnO2 nanoparticles. The sensor response time was of the order of several seconds. Their fast response, high sensitivity to selected gas species, improved selectivity and stability suggest that the SnO2-decorated flower-like 3D nanostructures are a promising material for application as an acetone sensor. PMID:28144521

  13. Synthesis and Characterization of Photocatalytic TiO 2 -ZnFe 2 O 4 Nanoparticles

    DOE PAGES

    Srinivasan, Sesha S.; Wade, Jeremy; Stefanakos, Elias K.

    2006-01-01

    A new coprecipimore » tation/hydrolysis synthesis route is used to create a TiO 2 -ZnFe 2 O 4 nanocomposite that is directed towards extending the photoresponse of TiO 2 from UV to visible wavelengths ( > 400   nm ). The effect of TiO 2 's accelerated anatase-rutile phase transformation due to the presence of the coupled ZnFe 2 O 4 narrow-bandgap semiconductor is evaluated. The transformation's dependence on pH, calcinations temperature, particle size, and ZnFe 2 O 4 concentration has been analyzed using XRD, SEM, and UV-visible spectrometry. The requirements for retaining the highly photoactive anatase phase present in a ZnFe 2 O 4 nanocomposite are outlined. The visible-light-activated photocatalytic activity of the TiO 2 -ZnFe 2 O 4 nanocomposites has been compared to an Aldrich TiO 2 reference catalyst, using a solar-simulated photoreactor for the degradation of phenol.« less

  14. Microporous Ni-doped TiO2 film photocatalyst by plasma electrolytic oxidation.

    PubMed

    Yao, Zhongping; Jia, Fangzhou; Tian, Shujun; Li, ChunXiang; Jiang, Zhaohua; Bai, Xuefeng

    2010-09-01

    Ni-doped TiO2 film catalysts were prepared by a plasma electrolytic oxidation (PEO) method and were mainly characterized by means of SEM, EDS, XRD, XPS, and DRS, respectively. The effects of Ni doping on the structure, composition and optical absorption property of the film catalysts were investigated along with their inherent relationships. The results show that the film catalyst is composed of anatase and rutile TiO2 with microporous structure. Doping Ni changes the phase composition and the lattice parameters (interplanar crystal spacing and cell volume) of the films. The optical absorption range of TiO2 film gradually expands and shifts to the red with increasing dosages. Both direct and indirect transition band gaps of the TiO2 films are deduced consequently. Moreover, the photocatalytic activity of the film catalysts for splitting Na2S+Na2SO3 solution into H2 is enhanced by doping with an appropriate amount of Ni. The as-prepared TiO2 film catalyst doping with 10 g/L of Ni(Ac)2 presents the highest photocatalytic reducing activity.

  15. Influence of Ti nanocrystallization on microstructure, interface bonding, surface energy and blood compatibility of surface TiO 2 films

    NASA Astrophysics Data System (ADS)

    Shao, Honghong; Yu, Chunhang; Xu, Xiaojing; Wang, Ji; Zhai, Rui; Wang, Xiaojing

    2010-12-01

    Recent progress in ultrafine-grained/nano-grained (UFG/NG) titanium permits a consideration for TiO 2 films deposited on nano-grained titanium for antithrombogenic application such as artificial valves and stents. For this paper, the microstructure, interface bonding, surface energy, and blood compatibility features of TiO 2 films deposited by direct current magnetron reactive sputtering technology on NG titanium and coarse-grained (CG) titanium were investigated. The results show that the nanocrystallization of titanium substrate has a significant influence on TiO 2 films. At the same deposition parameters, the content of rutile phase of TiO 2 film was increased from 47% (on the CG titanium substrate) to 72% (on the NG titanium substrate); the adhesion of TiO 2 film was improved from 5.8 N to 17 N; the surface energy was reduced from 6.37 dyn/cm to 3.01 dyn/cm; the clotting time was improved from 18 min to 28 min; the platelets accumulation and pseudopodium of adherent platelets on TiO 2 film on NG titanium were considerably reduced compared to that on CG titanium. The present results demonstrate the possibility of improving the blood compatibility of TiO 2 film through the approach of substrate nanocrystallization. Also it may provide an attractive idea to prepare stents with biological coatings of more outstanding blood compatibility and interface bonding.

  16. TiO2-assisted degradation of a perfluorinated surfactant in aqueous solutions treated by gliding arc discharge.

    PubMed

    Marouf-Khelifa, Kheira; Abdelmalek, Fatiha; Khelifa, Amine; Addou, Ahmed

    2008-02-01

    The plasma-chemical degradation of Forafac 1110, a perfluorinated non-ionic surfactant, in aqueous solutions was investigated using TiO2 catalysts. The considered plasma was the gliding arc in humid air, which results from an electric discharge at atmospheric pressure and quasi-ambient temperature. Two titanium dioxide powders were used and their synergistic effects on the Forafac degradation were compared. The results were discussed through the evolution of the pH, the conductivity, the fluoride ions concentration released in solutions, the surfactant concentration remaining after treatment and the chemical oxygen demand (COD) measurement. The combination of the plasma-chemical treatment with heterogeneous catalysis through the use of TiO2 accelerated the Forafac degradation, since only 60 min was sufficient to remove 96% instead of 360 min needed in the absence of TiO2. The use of anatase and rutile under the trade-name of Rhodia TiO2 and Merck TiO2, respectively, led to different results, because Rhodia TiO2 has proven to be more efficient. It would seem that the crystalline phase as well as the crystallite size, explain the efficiency of anatase. The advantage of the plasma-catalysis is due to the fact that there is a significant production of the OH* radicals not only generated by the gliding arc discharge but also by TiO2.

  17. [Preparation, characterization of Si doped TiO2 nanotubes and its application in photocatalytic oxidation of VOCs].

    PubMed

    Zou, Xue-Jun; Li, Xin-Yong; Qu, Zhen-Ping; Wang, Jiang-Jiang

    2011-12-01

    The Si-doped TiO2 nanotubes photocatalysts was synthesized by anodic oxidation method, which used Na2SiF6/HF as an electrolyte, and was characterized by means of SEM, XRD, DRS and EDX. TiO2 nanotubes composed of anatase phase and rutile phase, and Si was highly dispersed on the wall of TiO2 nanotubes. The photocatalytic activity of the Si-doped TiO2 nanotubes was investigated for photocatalytic degradation of gaseous toluene. It was found that the photocatalytic activity of Si-doped TiO2 nanotubes, which prepared by 0.03 mol x L x (-1) Na2SiF6/HF and calcined at 400 degrees C for 1 h, was the highest. The conversion of toluene was 60% over the prepared Si doped TiO2 nanotubes under UV light, which was one times higher than that of pure TiO2 nanotubes.

  18. Influence of Nd dopant amount on microstructure and photoluminescence of TiO2:Nd thin films

    NASA Astrophysics Data System (ADS)

    Wojcieszak, Damian; Mazur, Michal; Kaczmarek, Danuta; Morgiel, Jerzy; Zatryb, Grzegorz; Domaradzki, Jaroslaw; Misiewicz, Jan

    2015-10-01

    TiO2 and TiO2:Nd thin films were deposited using reactive magnetron sputtering process from mosaic Ti-Nd targets with various Nd concentration. The thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectroscopic techniques. Photoluminescence (PL) in the near infrared obtained upon 514.5 nm excitation was also examined. The relationship between the Nd concentration, structural, optical and photoluminescence properties of prepared thin films was investigated and discussed. XRD and TEM measurements showed that an increase in the Nd concentration in the thin films hinders the crystal growth in the deposited coatings. Depending on the Nd amount in the thin films, TiO2 with the rutile, mixed rutile-amorphous or amorphous phase was obtained. Transmittance measurements revealed that addition of Nd dopant to titania matrix did not deteriorate optical transparency of the coatings, however it influenced on the position of the fundamental absorption edge and therefore on the width of optical band gap energy. All TiO2:Nd thin films exhibited PL emission that occurred at ca. 0.91, 1.09 and 1.38 μm. Finally, results obtained for deposited coatings showed that titania with the rutile structure and 1.0 at.% of Nd was the most efficient in VIS to NIR photon conversion.

  19. CNTs threaded (001) exposed TiO2 with high activity in photocatalytic NO oxidation

    NASA Astrophysics Data System (ADS)

    Xiao, Shuning; Zhu, Wei; Liu, Peijue; Liu, Fanfan; Dai, Wenrui; Zhang, Dieqing; Chen, Wei; Li, Hexing

    2016-01-01

    A microwave-ionothermal strategy was developed for in situ synthesis of CNTs threaded TiO2 single crystal with a tunable percentage of surface exposed (001) active facets. The CNTs were used as microwave antennas to create local ``super hot'' dots to induce Ti3+ adsorption and hydrolysis, thereby leading to a good assembly of (001) facets exposed single crystalline TiO2 threaded by the CNTs in the presence of Hmim[BF4] ionic liquid. Due to the high percentage of the active (001) facets of single crystal TiO2 and the direct electron transfer property of the CNTs, the as-prepared CNTs-TiO2 composite showed a photocatalytic NO removal ratio of up to 76.8% under UV irradiation. In addition, with self-doped Ti3+, the CNTs-TiO2 composite also exhibited an enhanced activity under irradiation with either solar lights or visible lights, showing good potential in practical applications for environmental remediation.A microwave-ionothermal strategy was developed for in situ synthesis of CNTs threaded TiO2 single crystal with a tunable percentage of surface exposed (001) active facets. The CNTs were used as microwave antennas to create local ``super hot'' dots to induce Ti3+ adsorption and hydrolysis, thereby leading to a good assembly of (001) facets exposed single crystalline TiO2 threaded by the CNTs in the presence of Hmim[BF4] ionic liquid. Due to the high percentage of the active (001) facets of single crystal TiO2 and the direct electron transfer property of the CNTs, the as-prepared CNTs-TiO2 composite showed a photocatalytic NO removal ratio of up to 76.8% under UV irradiation. In addition, with self-doped Ti3+, the CNTs-TiO2 composite also exhibited an enhanced activity under irradiation with either solar lights or visible lights, showing good potential in practical applications for environmental remediation. Electronic supplementary information (ESI) available: TG, FTIR, Raman, EPR and additional photocatalytic performance data. See DOI: 10.1039/c5nr07589k

  20. Hydrogen Assisted Nano-crystallization in TiO2 Thin Film Prepared by Hot-Wire Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Iida, Tamio; Koie, Ryousuke; Masuda, Toshiro; Ueno, Hiroyuki; Nonomura, Shuichi

    2009-03-01

    Preparations and structural studies of TiO2 thin films using hot-wire chemical vapor deposition (CVD) (hot-filament CVD) are reported for the first time. Titanium tetra-isopropoxide [Ti(OC3H7)4] was used as a source gas and decomposed on a heated rhenium filament. The film deposited at the filament temperature (Tf) of 1300 °C shows amorphous structure with the substrate temperature (Ts) of 300 °C, and X-ray diffraction (XRD) peaks originated from nano-crystalline with anatase structure appeared over Ts of 400-700 °C. The optical band gap energies of the nano-crystalline TiO2 films with anatase structure were ˜3.4 eV. An increase of Ts from 400 to 700 °C enhanced the XRD peak intensity of (112) orientation. Meanwhile, an increase of Tf up to 1500 °C induces nano-crystalline TiO2 with rutile structure. Furthermore, the hydrogen dilution realizes the nano-crystallite growth of rutile structure even in the deposition at Tf = 1300 °C. During this deposition, the actual substrate surface temperature (Tsuf) was 305 °C. In bulk TiO2 materials, the anatase structure changes to the rutile structure by thermal annealing up to about 800 °C. We propose for the first time that atomic hydrogen contributes to the low temperature nucleation of rutile structure in the deposition of oxide system, TiO2 films.

  1. Modification mechanism of praseodymium doping for the photocatalytic performance of TiO2: a combined experimental and theoretical study.

    PubMed

    Duan, Zhi-Gang; Zhao, Zong-Yan; Shi, Qing-Nan

    2015-07-15

    Impurity doping is a simple and efficient modification method to improve the photocatalytic performance of wide band gap photocatalysts. However, some basic and important issues about the mechanism of impurity doping modification still need to be further confirmed and explained. In the present work, Pr-doped TiO2 with a mono-phase crystal structure was prepared by a sol-gel method. Then, the crystal structure, binding information, optical absorption, and photocatalytic activity were systematically investigated. The experimental results show that Pr doping could significantly enhance the photocatalytic activity of TiO2, and the effects of modification on rutile TiO2 are more obvious than for anatase TiO2. In order to understand the underlying mechanism, density functional theory was utilized to calculate the crystal structure and electronic structure of pure and Pr-doped TiO2. The differences in electronic structure between anatase and rutile phases lead to the above photocatalytic performance. The experimental measurements and theoretical calculations mutually support each other in the present work. Two points are confirmed: the position of the band edge determines the redox activity of the photocatalyst, and the shallow energy bands induced by impurity doping could improve the photocatalytic performance.

  2. A new form of chemisorbed photo- and electro-active atomic H species on the TiO2(110) surface

    NASA Astrophysics Data System (ADS)

    Zhang, Zhen; Yates, John T.

    2016-10-01

    Hydrogen adsorption on TiO2 is of importance in chemical and photochemical reduction processes. Using several surface science methods, we clearly distinguish two kinds of H species on the surface of rutile TiO2(110)-1 × 1. In contrast with the well-studied bridge-bonded OH species (α-H) originating from H2O dissociation on the surface oxygen vacancy site on TiO2(110), atomic H adsorption on the TiO2(110) (denoted as β-H) exhibits special high sensitivity to the electronic excitation of the TiO2(110) by either electrons or UV photons. The formation of molecular H2 gas by photoexcitation of β-H/TiO2(110) surfaces has been observed, which may shed light on the basic understanding of the processes of photocatalytic H2 production by splitting water.

  3. Unveiling the formation pathway of single crystalline porous silicon nanowires.

    PubMed

    Zhong, Xing; Qu, Yongquan; Lin, Yung-Chen; Liao, Lei; Duan, Xiangfeng

    2011-02-01

    Porous silicon nanowire is emerging as an interesting material system due to its unique combination of structural, chemical, electronic, and optical properties. To fully understand their formation mechanism is of great importance for controlling the fundamental physical properties and enabling potential applications. Here we present a systematic study to elucidate the mechanism responsible for the formation of porous silicon nanowires in a two-step silver-assisted electroless chemical etching method. It is shown that silicon nanowire arrays with various porosities can be prepared by varying multiple experimental parameters such as the resistivity of the starting silicon wafer, the concentration of oxidant (H(2)O(2)) and the amount of silver catalyst. Our study shows a consistent trend that the porosity increases with the increasing wafer conductivity (dopant concentration) and oxidant (H(2)O(2)) concentration. We further demonstrate that silver ions, formed by the oxidation of silver, can diffuse upwards and renucleate on the sidewalls of nanowires to initiate new etching pathways to produce a porous structure. The elucidation of this fundamental formation mechanism opens a rational pathway to the production of wafer-scale single crystalline porous silicon nanowires with tunable surface areas ranging from 370 to 30 m(2) g(-1) and can enable exciting opportunities in catalysis, energy harvesting, conversion, storage, as well as biomedical imaging and therapy.

  4. Facile morphological control of single-crystalline silicon nanowires

    NASA Astrophysics Data System (ADS)

    Wu, Shao-long; Zhang, Ting; Zheng, Rui-ting; Cheng, Guo-an

    2012-10-01

    To realize wider potentials of silicon nanowires (SiNWs), the morphological controllability is desirable. In this paper, we synthesized well vertically- and slantingly-aligned SiNWs with ultra-high aspect ratio in metal-assisted chemical etching method, and wafer-scale zigzag SiNWs with three types of turning angle were also obtained. The formation of the curved SiNWs is a result of the alternation of moving direction of Ag nanoparticles between the preferred <1 0 0> and other directions in Si substrates. The as-prepared SiNWs are single-crystalline and their orientations are mostly along the <1 0 0> or <1 1 1> directions. The surface of the resulting SiNWs can be controlled to be smooth or rough, with or without mesopores, by adjusting the etching conditions and using various Si substrates with different crystal orientations and doping levels. Moreover, the effects of the etching conditions (etching time, oxidant concentration, deposition time of Ag nanoparticles and etching temperature) and substrate properties (crystal orientation and doping level) on the as-prepared SiNWs have been discussed.

  5. Single-crystalline aluminum film for ultraviolet plasmonic nanolasers

    NASA Astrophysics Data System (ADS)

    Chou, Bo-Tsun; Chou, Yu-Hsun; Wu, Yen-Mo; Chung, Yi-Cheng; Hsueh, Wei-Jen; Lin, Shih-Wei; Lu, Tien-Chang; Lin, Tzy-Rong; Lin, Sheng-Di

    2016-01-01

    Significant advances have been made in the development of plasmonic devices in the past decade. Plasmonic nanolasers, which display interesting properties, have come to play an important role in biomedicine, chemical sensors, information technology, and optical integrated circuits. However, nanoscale plasmonic devices, particularly those operating in the ultraviolet regime, are extremely sensitive to the metal and interface quality. Thus, these factors have a significant bearing on the development of ultraviolet plasmonic devices. Here, by addressing these material-related issues, we demonstrate a low-threshold, high-characteristic-temperature metal-oxide-semiconductor ZnO nanolaser that operates at room temperature. The template for the ZnO nanowires consists of a flat single-crystalline Al film grown by molecular beam epitaxy and an ultrasmooth Al2O3 spacer layer synthesized by atomic layer deposition. By effectively reducing the surface plasmon scattering and metal intrinsic absorption losses, the high-quality metal film and the sharp interfaces formed between the layers boost the device performance. This work should pave the way for the use of ultraviolet plasmonic nanolasers and related devices in a wider range of applications.

  6. Single-crystalline aluminum film for ultraviolet plasmonic nanolasers

    PubMed Central

    Chou, Bo-Tsun; Chou, Yu-Hsun; Wu, Yen-Mo; Chung, Yi-Cheng; Hsueh, Wei-Jen; Lin, Shih-Wei; Lu, Tien-Chang; Lin, Tzy-Rong; Lin, Sheng-Di

    2016-01-01

    Significant advances have been made in the development of plasmonic devices in the past decade. Plasmonic nanolasers, which display interesting properties, have come to play an important role in biomedicine, chemical sensors, information technology, and optical integrated circuits. However, nanoscale plasmonic devices, particularly those operating in the ultraviolet regime, are extremely sensitive to the metal and interface quality. Thus, these factors have a significant bearing on the development of ultraviolet plasmonic devices. Here, by addressing these material-related issues, we demonstrate a low-threshold, high-characteristic-temperature metal-oxide-semiconductor ZnO nanolaser that operates at room temperature. The template for the ZnO nanowires consists of a flat single-crystalline Al film grown by molecular beam epitaxy and an ultrasmooth Al2O3 spacer layer synthesized by atomic layer deposition. By effectively reducing the surface plasmon scattering and metal intrinsic absorption losses, the high-quality metal film and the sharp interfaces formed between the layers boost the device performance. This work should pave the way for the use of ultraviolet plasmonic nanolasers and related devices in a wider range of applications. PMID:26814581

  7. Liquid crystal deposition on poled, single crystalline lithium niobate

    NASA Astrophysics Data System (ADS)

    Bharath, S. C.; Pimputkar, K. R.; Pronschinske, A. M.; Pearl, T. P.

    2008-01-01

    For the purpose of elucidating the mechanisms for molecular organization at poled ferroelectric surfaces, single crystalline lithium niobate (LN), 'Z-cut' along the (0 0 0 1) plane, has been prepared and characterized and subsequently exposed to liquid crystal molecules. As a model system we chose to study the anchoring of 4- n-octyl-4'-cyanobiphenyl (8CB) to LN. Liquid crystalline films are of interest because of their useful electronic and optical properties as well as chemical sensing attributes. Low-energy electron diffraction (LEED), atomic force microscopy (AFM), surface contact angle measurements (CA), and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of lithium niobate as well as the nature of 8CB films grown on the surface. Atomically flat LN surfaces were prepared as a support for monolayer thick, 8CB molecular domains. 8CB liquid crystal molecules were deposited by an ambient vaporization technique and the films were analyzed using XPS and CA. Understanding electrostatic anchoring mechanisms and thin film organization for this molecule on uniformly poled surfaces allows for a fuller appreciation of how molecular deposition of other polarizable molecules on periodically poled and patterned poled lithium niobate surfaces would occur.

  8. Development of novel UV emitting single crystalline film scintillators

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu; Gorbenko, V.; Savchyn, V.; Voznyak, T.; Nikl, M.; Mares, J. A.; Martin, T.; Douissard, P.-A.

    2011-04-01

    The work is dedicated to development of new types of UV -emitting scintillators based on single crystalline films (SCF) of aluminimum perovskites and garnets grown by the liquid phase epitaxy (LPE) method. The development of the following three types of UV SCF scintillators is considered in this work: i) Ce-doped SCF of Y-Lu-Al-perovskites with Ce3+ emission in the 360-370 nm range with a decay time of 16-17 ns; ii) Pr-doped SCF of Y-Lu-Al garnets with Pr3+ emission in the 300-400 nm range with a decay time of 13-17 ns; iii) La3+ and Sc3+ doped SCF of Y-Lu-Al-garnets, emitting in the 290-400 nm range due to formation of the LaY,Lu, ScY,Lu and ScAl centers with decay time of 250-575 ns. The results of testing the several novel UV-emitting SCFs scintillators for visualization of X-ray images at ESFR are presented. It is shown that the UV emission of the LuAG:Sc, LuAG:La and LuAG:Pr SCFs is efficient enough for conversion of X-ray to the UV light and that these scintillators can be used for improvement of the resolution of imaging detectors in synchrotron radiation applications.

  9. Effect of heat treatment on morphology, crystalline structure and photocatalysis properties of TiO 2 nanotubes on Ti substrate and freestanding membrane

    NASA Astrophysics Data System (ADS)

    Fang, Dong; Luo, Zhiping; Huang, Kelong; Lagoudas, Dimitris C.

    2011-05-01

    Highly ordered titanium oxide (TiO 2) nanotubes were prepared by electrolytic anodization of titanium electrodes. Morphological evolution and phase transformations of TiO 2 nanotubes on a Ti substrate and that of freestanding TiO 2 membranes during the calcinations process were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction microscopy. The detailed results and mechanisms on the morphology and crystalline structure were presented. Our results show that a compact layer exists between the tubular layer and Ti substrate at 600 °C, and the length of the nanotubes shortens dramatically at 750 °C. The freestanding membranes have many particles on their tubes during calcinations from 450 to 900 °C. The TiO 2 nanotubes on the Ti substrate transform to rutile crystals at 600 °C, while the freestanding TiO 2 membranes retain an anatase crystal with increasing temperature to 800 °C. The photocatalytic activity of TiO 2 nanotubes on a Ti substrate annealed at different temperatures was investigated by the degradation of methyl orange in aqueous solution under UV light irradiation. Due to the anatase crystals in the tubular layer and rutile crystals in the compact layer, TiO 2 nanotubes annealed at 450 °C with pure anatase crystals have a better photocatalytic activity than those annealed at 600 °C or 750 °C.

  10. Effects of TiO2 crystal structure on the luminescence quenching of [Ru(bpy)2(dppz)](2+)-intercalated into DNA.

    PubMed

    Chen, Linlin; Wang, Yi; Huang, Minggao; Li, Xiaodan; Zhu, Licai; Li, Hong

    2017-03-22

    The intercalation of [Ru(bpy)2(dppz)](2+) labeled as Ru(II) (bpy=2,2'-bipyridine and dppz=dipyrido[3,2,-a:2',3'-c]phenazine) into herring sperm DNA leads to the formation of emissive Ru(II)-DNA dyads, which can be quenched by TiO2 nanoparticles (NPs) and sol-gel silica matrices at heterogeneous interfaces. The calcinations temperature exhibits a remarkable influence on the luminescence quenching of the Ru(II)-DNA dyads by TiO2 NPs. With increasing calcinations temperature in the range from 200 to 850°C, the anatase-to-rutile TiO2 crystal structure transformation increases the average particle size and hydrodynamic diameter of TiO2 and DNA@TiO2. The anatase TiO2 has the stronger ability to unbind the Ru(II)-DNA dyads than the rutile TiO2 at room temperature. The TiO2 NPs and sol-gel silica matrices can quench the luminescence of the Ru(II) complex intercalated into DNA by selectively capturing the negatively DNA and positively charged Ru(II) complex to unbind the dyads, respectively. This present results provide new insights into the luminescence quenching and competitive binding of dye-labeled DNA dyads by inorganic NPs.

  11. An effective method for the preparation of high temperature stable anatase TiO2 photocatalysts

    NASA Astrophysics Data System (ADS)

    Fagan, Rachel; Synnott, Damian W.; McCormack, Declan E.; Pillai, Suresh C.

    2016-05-01

    An efficient, rapid and straightforward method for the preparation of nitrogen and fluorine (N, F) codoped high temperature stable anatase using a microwave pre-treatment is reported. Using a single source, ammonium fluoride (NH4F) for both nitrogen and fluorine, effective doping of the precursor titanium isopropoxide (TTIP) was possible. These samples were characterised for their structural and optical properties using X-ray diffraction (XRD), Fourier Transform IR (FTIR), Raman spectroscopy and UV-vis spectroscopy. In terms of the anatase to rutile transition enhancement using a novel microwave assisted technique, the sample prepared in a composition of 1:8 TiO2: NH4F at 1200 °C was seen to be most effective, having stable anatase present at 57.1% compared to undoped TiO2 being 100% rutile from 900 °C. This method involves the production of ammonium oxofluorotitanates (NH4TiOF3) at low temperatures. The inclusion of these intermediates greatly reduces the particle size growth and delays the anatase to rutile transition. The photocatalytic activity of these materials was studied by analysing the degradation of an organic dye, rhodamine 6G as a model system and the rate constant was calculated by pseudo-first-order kinetics. These results showed that the doped sample (0.0225 min-1) was three times more active than the undoped sample (0.0076 min-1) and over seven times faster than the commercial TiO2 photocatalyst standard Degussa P-25 calcined at 1200 °C (0.0030 min-1). The formation of intermediate compounds, oxofluorotitanates, was identified as the major reason for a delay in the anatase to rutile transition.

  12. TiO2-based nanopowders and thin films for photocatalytical applications.

    PubMed

    Radecka, M; Rekas, M; Kusior, E; Zakrzewska, K; Heel, A; Michalow, K A; Graule, T

    2010-02-01

    TiO2-based nanopowders are elaborated by flame spray synthesis, FSS from organic precursors of titanium and chromium with the Cr content changing from 0 to 15 at.%. Well-crystallized nanopowders with high specific surface area SSA reaching 107 m2/g for undoped TiO2 and 177 m2/g for TiO2 + 15 at.% Cr are obtained. Thin films are deposited by rf reactive sputtering from metallic Ti and Ti-Cr targets in Ar + O2 flow controlled atmosphere. The adjustable area of Cr/Ti allows to obtain up to 16 at.% Cr in TiO2 thin films. X-ray diffraction, transmission electron spectroscopy, TEM, atomic force microscopy, AFM and optical spectrophotometry over the ultraviolet UV and visible VIS range of the light spectrum have been performed in order to characterize the nanomaterials. The particle size of nanopowders is within the range of 5-42 nm. Anatase is the predominating polymorphic form while the amount of rutile increases with Cr content to reach of about 25 wt.% at 15 at.% Cr. The post-deposition annealing of thin films in air at temperatures from 770 K to 1280 K modifies the phase composition, leads to irreversible transformation from anatase to rutile and affects the surface roughness. Structural and optical properties of TiO2-based nanopowders and thin films are compared. The effect of grain size and the level of chromium doping on the band gap E(g) is discussed. Photocatalytic activity of the nanopowders is tested for degradation of methylene blue, MB.

  13. A shock-induced polymorph of anatase and rutile from the Chesapeake Bay impact structure, Virginia, U.S.A

    USGS Publications Warehouse

    Jackson, J.C.; Horton, J.W.; Chou, I.-Ming; Belkin, H.E.

    2006-01-01

    A shock-induced polymorph (TiO2II) of anatase and rutile has been identified in breccias from the late Eocene Chesapeake Bay impact structure. The breccia samples are from a recent, partially cored test hole in the central uplift at Cape Charles, Virginia. The drill cores from 744 to 823 m depth consist of suevitic crystalline-clast breccia and brecciated cataclastic gneiss in which the TiO2 phases anatase and rutile are common accessory minerals. Electron-microprobe imaging and laser Raman spectroscopy of TiO2 crystals, and powder X-ray diffraction (XRD) of mineral concentrates, confirm that a high-pressure, ??-PbO2 structured polymorph of TiO2 (TiO2II) coexists with anatase and rutile in matrix-hosted crystals and in inclusions within chlorite. Raman spectra of this polymorph include strong bands at wavenumbers (cm-1) 175, 281, 315, 342, 356, 425, 531, 571, and 604; they appear with anatase bands at 397, 515, and 634 cm-1, and rutile bands at 441 and 608 cm-1. XRD patterns reveal 12 lines from the polymorph that do not significantly interfere with those of anatase or rutile, and are consistent with the TiO2II that was first reported to occur naturally as a shock-induced phase in rutile from the Ries crater in Germany. The recognition here of a second natural shock-induced occurrence of TiO2II suggests that its presence in rocks that have not been subjected to ultrahigh-pressure regional metamorphism can be a diagnostic indicator for confirmation of suspected impact structures.

  14. Cytotoxicity of TiO2 nanoparticles to mussel hemocytes and gill cells in vitro: Influence of synthesis method, crystalline structure, size and additive.

    PubMed

    Katsumiti, Alberto; Berhanu, Deborah; Howard, Kieren T; Arostegui, Inmaculada; Oron, Miriam; Reip, Paul; Valsami-Jones, Eugenia; Cajaraville, Miren P

    2015-01-01

    Increasing the production and applications of TiO2 nanoparticles (NPs) has led to grow concerns about the consequences for the environment. In this study, we investigated the effects of a set of TiO2 NPs on the viability of mussel hemocytes and gill cells using neutral red and thiazolyl tetrazolium bromide assays. For this, we compared the cytotoxicity of TiO2 NPs (0.1-100 mg Ti/L) produced by different techniques: rutile NPs (60 nm) produced by milling and containing disodium laureth sulfosuccinate (DSLS), rutile NPs (10, 40 and 60 nm) produced by wet chemistry and anatase/rutile NPs (∼100 nm) produced by plasma synthesis. The commercially available P25 anatase/rutile NPs (10-20 nm) were also tested. Exposures were performed in parallel with their respective bulk forms and the cytotoxicity of the additive DSLS was also tested. Z potential values in distilled water indicated different stabilities depending on the NP type and all NPs tested formed agglomerates/aggregates in cell culture media. In general, TiO2 NPs showed a relatively low and dose-dependent toxicity for both cell models with the two assays tested. NPs produced by milling showed the highest effects, probably due to the toxicity of DSLS. Size-dependent toxicity was found for NPs produced by wet chemistry (10 nm > 40 nm and 60 nm). All TiO2 NPs tested were more toxic than bulk forms excepting for plasma produced ones, which were the least toxic TiO2 tested. The mixture bulk anatase/rutile TiO2 was more toxic than bulk rutile TiO2. In conclusion, the toxicity of TiO2 NPs varied with the mode of synthesis, crystalline structure and size of NPs and can also be influenced by the presence of additives in the suspensions.

  15. Nanocrystalline TiO2/SnO2 heterostructures for gas sensing

    PubMed Central

    Kusior, Anna; Rekas, Mieczylaw; Zukrowski, Jan; Gajewska, Marta; Michalow-Mauke, Katarzyna; Graule, Thomas; Radecka, Marta; Zakrzewska, Katarzyna

    2017-01-01

    The aim of this research is to study the role of nanocrystalline TiO2/SnO2 n–n heterojunctions for hydrogen sensing. Nanopowders of pure SnO2, 90 mol % SnO2/10 mol % TiO2, 10 mol % SnO2/90 mol % TiO2 and pure TiO2 have been obtained using flame spray synthesis (FSS). The samples have been characterized by BET, XRD, SEM, HR-TEM, Mössbauer effect and impedance spectroscopy. Gas-sensing experiments have been performed for H2 concentrations of 1–3000 ppm at 200–400 °C. The nanomaterials are well-crystallized, anatase TiO2, rutile TiO2 and cassiterite SnO2 polymorphic forms are present depending on the chemical composition of the powders. The crystallite sizes from XRD peak analysis are within the range of 3–27 nm. Tin exhibits only the oxidation state 4+. The H2 detection threshold for the studied TiO2/SnO2 heterostructures is lower than 1 ppm especially in the case of SnO2-rich samples. The recovery time of SnO2-based heterostructures, despite their large responses over the whole measuring range, is much longer than that of TiO2-rich samples at higher H2 flows. TiO2/SnO2 heterostructures can be intentionally modified for the improved H2 detection within both the small (1–50 ppm) and the large (50–3000 ppm) concentration range. The temperature T max at which the semiconducting behavior begins to prevail upon water desorption/oxygen adsorption depends on the TiO2/SnO2 composition. The electrical resistance of sensing materials exhibits a power-law dependence on the H2 partial pressure. This allows us to draw a conclusion about the first step in the gas sensing mechanism related to the adsorption of oxygen ions at the surface of nanomaterials. PMID:28144570

  16. Nanocrystalline TiO2/SnO2 heterostructures for gas sensing.

    PubMed

    Lyson-Sypien, Barbara; Kusior, Anna; Rekas, Mieczylaw; Zukrowski, Jan; Gajewska, Marta; Michalow-Mauke, Katarzyna; Graule, Thomas; Radecka, Marta; Zakrzewska, Katarzyna

    2017-01-01

    The aim of this research is to study the role of nanocrystalline TiO2/SnO2 n-n heterojunctions for hydrogen sensing. Nanopowders of pure SnO2, 90 mol % SnO2/10 mol % TiO2, 10 mol % SnO2/90 mol % TiO2 and pure TiO2 have been obtained using flame spray synthesis (FSS). The samples have been characterized by BET, XRD, SEM, HR-TEM, Mössbauer effect and impedance spectroscopy. Gas-sensing experiments have been performed for H2 concentrations of 1-3000 ppm at 200-400 °C. The nanomaterials are well-crystallized, anatase TiO2, rutile TiO2 and cassiterite SnO2 polymorphic forms are present depending on the chemical composition of the powders. The crystallite sizes from XRD peak analysis are within the range of 3-27 nm. Tin exhibits only the oxidation state 4+. The H2 detection threshold for the studied TiO2/SnO2 heterostructures is lower than 1 ppm especially in the case of SnO2-rich samples. The recovery time of SnO2-based heterostructures, despite their large responses over the whole measuring range, is much longer than that of TiO2-rich samples at higher H2 flows. TiO2/SnO2 heterostructures can be intentionally modified for the improved H2 detection within both the small (1-50 ppm) and the large (50-3000 ppm) concentration range. The temperature Tmax at which the semiconducting behavior begins to prevail upon water desorption/oxygen adsorption depends on the TiO2/SnO2 composition. The electrical resistance of sensing materials exhibits a power-law dependence on the H2 partial pressure. This allows us to draw a conclusion about the first step in the gas sensing mechanism related to the adsorption of oxygen ions at the surface of nanomaterials.

  17. Characterization and environmental implications of nano- and larger TiO(2) particles in sewage sludge, and soils amended with sewage sludge.

    PubMed

    Kim, Bojeong; Murayama, Mitsuhiro; Colman, Benjamin P; Hochella, Michael F

    2012-04-01

    Titanium dioxide (TiO(2)) is the most extensively used engineered nanoparticle to date, yet its fate in the soil environment has been investigated only rarely and is poorly understood. In the present study, we conducted two field-scale investigations to better describe TiO(2) nano- and larger particles in their most likely route of entry into the environment, i.e., the application of biosolids to soils. We particularly concentrated on the particles in the nano-size regime due to their novel and commercially useful properties. First, we analyzed three sewage sludge products from the US EPA TNSSS sampling inventory for the occurrence, qualitative abundance, and nature of TiO(2) nano- and larger particles by using analytical scanning electron microscopy and analytical (scanning) transmission electron microscopy. Nano- and larger particles of TiO(2) were repeatedly identified across the sewage sludge types tested, providing strong evidence of their likely concentration in sewage sludge products. The TiO(2) particles identified were as small as 40 nm, and as large as 300 nm, having faceted shapes with the rutile crystal structure, and they typically formed small, loosely packed aggregates. Second, we examined surface soils in mesocosms that had been amended with Ag nanoparticle-spiked biosolids for the occurrence of TiO(2) particles. An aggregate of TiO(2) nanoparticles with the rutile structure was again identified, but this time TiO(2) nanoparticles were found to contain Ag on their surfaces. This suggests that TiO(2) nanoparticles from biosolids can interact with toxic trace metals that would then enter the environment as a soil amendment. Therefore, the long-term behavior of TiO(2) nano- and larger particles in sewage sludge materials as well as their impacts in the soil environment need to be carefully considered.

  18. Growth of TiO2 nanofibers on FTO substrates and their application in dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Suryana, R.; Rahmawati, L. R.; Triyana, K.

    2016-11-01

    Growth of TiO2 nanofibers on fluorine-doped tin oxide (FTO) substrates have been performed using electrospinning method. Homogenous TiO2 solution as nanofibers material was prepared with titanium tetraisopropoxide (TTIP), ethanol, acetic acid and polyvinyl pyrrolidone (PVP) which was stirred for 24 h. TiO2 solution was loaded into the syringe pump. Electrospun voltage was operated under 15 kV with optimum distance between syringe tip and collector was 15 cm. FTO substrates were attached on the collector surface. Electrospinning coating time was varied at 15 min, 30 min, 45 min, and 60 min. Then TiO2 nanofibers layer was annealed at temperature of 450° C for 3 h. X-ray diffraction spectrum of TiO2 nanofibers showed major anatase peaks at 25.3°, 48.0° and 37.8° correlating crystal orientation of (101), (200), and (004), respectively while only one rutile peak at 27.5°(110). TiO2 nanofibers diameter was measured using atomic force microscopy (AFM). TiO2 nanofibers have diameter in range of 100-1000 nm. The obtained-TiO2 nanofibers were applied in dye-sensitized solar cell (DSSC) with beta-carotene as dye, carbon as catalyst, and I-/I3- redox couple as electrolyte. DSSC performance was analyzed from I-V characterization. Growth of TiO2 nanofibers at electrospinning time for 45 min has highest efficiency that is 0.016%. It is considered that TiO2 nanofibers at electrospinning time for 45 min can produce optimum thickness so that it is speculated many dyes adsorb on the nanofiber surfaces and many electrons diffuse toward the electrodes.

  19. Desulphurization performance of TiO2-modified activated carbon by a one-step carbonization-activation method.

    PubMed

    Zhang, Chuanjun; Yang, Danni; Jiang, Xia; Jiang, Wenju

    2016-08-01

    In this study, TiO2 powder was used as the additive to directly blend with raw bituminous coal and coking coal for preparing modified activated carbon (Ti/AC) by one-step carbonization-activation method. The Ti/AC samples were prepared through blending with different ratios of TiO2 (0-12 wt%) and their desulphurization performance was evaluated. The results show that the desulphurization activity of all Ti/AC samples was higher than that of the blank one, and the highest breakthrough sulphur capacity was obtained at 200.55 mg/g C when the blending ratio of TiO2 was 6 wt%. The Brunauer-Emmett-Temer results show that the micropores were dominant in the Ti/AC samples, and their textual properties did not change evidently compared with the blank one. The X-ray photoelectron spectroscopy results show that the loaded TiO2 could influence the relative content of surface functional groups, with slightly higher content of π-π* transitions groups on the Ti/AC samples, and the relative contents of C=O and π-π* transitions groups decreased evidently after the desulphurization process. The X-ray diffraction results show that the anatase TiO2 and rutile TiO2 co-existed on the surface of the Ti/AC samples. After the desulphurization process, TiO2 phases did not change and Ti(SO4)2 was not observed on the Ti/AC samples, while sulphate was the main desulphurization product. It can be assumed that SO2 could be catalytically oxidized into SO3 by TiO2 indirectly, rather than TiO2 directly reacted with SO2 to Ti(SO4)2.

  20. Active hydrogen species on TiO2 for photocatalytic H2 production.

    PubMed

    Wu, Zongfang; Zhang, Wenhua; Xiong, Feng; Yuan, Qing; Jin, Yuekang; Yang, Jinlong; Huang, Weixin

    2014-04-21

    Photocatalytic H2 production over TiO2 has attracted tremendous attention and achieved great progress, but the active hydrogen species is still unknown. Employing a rutile TiO2(110) surface as a model catalyst we report here for the first time the direct observation of photocatalytic H2 production under ultrahigh vacuum conditions during UV-light irradiation at 115 K and the identification of negatively-charged hydride-type H-Ti species as the corresponding photoactive surface species by means of thermal desorption spectroscopy, photon-stimulated desorption spectroscopy, X-ray photoelectron spectroscopy and DFT calculations. The formation and stability of H-Ti species are closely related to available surplus electrons on the rutile TiO2(110) surface that can be created by the formation of surface BBO vacancies or by the formation of surface hydroxyls via the adsorption of atomic H or molecular H2 on O sites. The photocatalytic H2 production from H-Ti species is hole-mediated and co-existing water exerts a negative effect on this process.

  1. Influence of laser modification of TiO2 films for its photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Sawczak, Mirosław; Górski, Michał; Rachubiński, Hubert; Cenian, Adam

    2013-01-01

    The photocatalytic activity of TiO2 layer modified by laser radiation is discussed in the paper. Commercially available nanopowder P25(Degussa) was used, which consists of a mixture of anatase and rutile - two crystallographic forms of TiO2 . The spin-coating technique was applied to produce thin layers on glass. After drying and calcination the layer was thermally modified using a pulsed (6 ns) Nd:YAG laser (FHG 266 nm). This caused a clearly visible surface darkening effect. The XRD spectra show that phase change transition (from anatase to rutile) took place partially. This was also confirmed by Raman spectra. The main peak of Raman-spectra shifts from 142,84 to 145,22 cm-1, probably due to decreasing size of TiO2 nanoparticles or more probably due to a defects generation in nanocrystallite structure. Defects have been reported in the literature as surface oxygen depletion and generation valance states Ti3+ and Ti4+. Eventually, kinetics of methylene-blue decay and CO2 to methane conversion were examined. In both cases an increase of catalytic activity was observed.

  2. Core-shell TiO2@ZnO nanorods for efficient ultraviolet photodetection

    NASA Astrophysics Data System (ADS)

    Panigrahi, Shrabani; Basak, Durga

    2011-05-01

    Core-shell TiO2@ZnO nanorods (NRs) have been fabricated by a simple two step method: growth of ZnO NRs' array by an aqueous chemical technique and then coating of the NRs with a solution of titanium isopropoxide [Ti(OC3H7)4] followed by a heating step to form the shell. The core-shell nanocomposites are composed of single-crystalline ZnO NRs, coated with a thin TiO2 shell layer obtained by varying the number of coatings (one, three and five times). The ultraviolet (UV) emission intensity of the nanocomposite is largely quenched due to an efficient electron-hole separation reducing the band-to-band recombinations. The UV photoconductivity of the core-shell structure with three times TiO2 coating has been largely enhanced due to photoelectron transfer between the core and the shell. The UV photosensitivity of the nanocomposite becomes four times larger while the photocurrent decay during steady UV illumination has been decreased almost by 7 times compared to the as-grown ZnO NRs indicating high efficiency of these core-shell structures as UV sensors.

  3. Core-shell TiO2@ZnO nanorods for efficient ultraviolet photodetection.

    PubMed

    Panigrahi, Shrabani; Basak, Durga

    2011-05-01

    Core-shell TiO(2)@ZnO nanorods (NRs) have been fabricated by a simple two step method: growth of ZnO NRs' array by an aqueous chemical technique and then coating of the NRs with a solution of titanium isopropoxide [Ti(OC(3)H(7))(4)] followed by a heating step to form the shell. The core-shell nanocomposites are composed of single-crystalline ZnO NRs, coated with a thin TiO(2) shell layer obtained by varying the number of coatings (one, three and five times). The ultraviolet (UV) emission intensity of the nanocomposite is largely quenched due to an efficient electron-hole separation reducing the band-to-band recombinations. The UV photoconductivity of the core-shell structure with three times TiO(2) coating has been largely enhanced due to photoelectron transfer between the core and the shell. The UV photosensitivity of the nanocomposite becomes four times larger while the photocurrent decay during steady UV illumination has been decreased almost by 7 times compared to the as-grown ZnO NRs indicating high efficiency of these core-shell structures as UV sensors.

  4. Niobian rutile in an Apollo 14 KREEP fragment.

    NASA Technical Reports Server (NTRS)

    Hlava, P. F.; Prinz, M.; Keil, K.

    1972-01-01

    Niobian rutile was found in a KREEP lithic fragment of basaltic texture. The niobian rutile contains 85.3% TiO2, 7.1% Nb2O5, 2.65% Cr2O3, 0.70% ZrO2, 0.61% SiO2, 0.82% Al2O3 0.61% FeO, 0.52% CaO, 0.22% V2O3 in addition to minor amounts of MnO, MgO, and CeO2. Rare-earth elements were not detected, in contrast with lunar niobian rutile of Marvin (1971). Coexisting minerals in the KREEP fragment are major amounts of plagioclase and orthopyroxene, and minor amounts of olivine, ilmenite, augite, barian K-feldspar, whitlockite, troilite, Ni-Fe, zirkelite, and chromite.

  5. Reactive wetting properties of TiO2 nanoparticles predicted by ab initio molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Brandt, Erik G.; Agosta, Lorenzo; Lyubartsev, Alexander P.

    2016-07-01

    coordination numbers); radial distribution functions for all O-Ti pairs over the entire data domain; comparison of coordination number distributions for dry and wet nanoparticles; dynamics of water reactivity; high-resolution electron density for the rutile NP. A movie of the simulation trajectory for the rutile (TiO2)24.30H2O system. See DOI: 10.1039/C6NR02791A

  6. Compositional Variability of Rutile in Hydrothermal Ore Deposits

    NASA Astrophysics Data System (ADS)

    Clark, J. R.; Williams-Jones, A. E.

    2009-05-01

    Rutile is a relatively common accessory phase in many geological environments, and although it is almost always composed dominantly of TiO2, it is also associated with a wide range of minor and trace element substitutions. The most prominent minor elements that occur in rutile are Fe, Cr, V, Nb and Ta. Like Ti, the latter two elements are essentially immobile in most non-magmatic metallic ore deposits, and their concentrations in rutile are largely influenced by precursor mineral compositions. Iron, Cr and V concentrations vary considerably in rutile hosted by ore deposits, and reflect combinations of precursor mineral composition and the bulk chemistry of the local mineralized or altered rock environment. However, in hydrothermal alteration zones, rutile compositions are clearly anomalous compared to those in unaltered host rocks, and have distinctive elemental associations and substitutions in different types of ore deposits. We have evaluated the mineral chemistry of rutile in >40 ore deposits worldwide. In general, rutile in volcanogenic massive sulfide deposits contains Sn (and locally W, Sb and/or Cu). Rutile from mesothermal and related gold deposits invariably contains W, and in some of the larger and more important deposits, also contains Sb and/or V. Tungsten-bearing detrital rutile grains from the Witwatersrand suggest that paleoplacer mineralization may have had a mesothermal/orogenic gold source. In some magmatic-hydrothermal Pd-Ni-Cu deposits, rutile contains Ni and Cu. Rutile associated with granite-related Sn deposits has strongly elevated concentrations of Sn and W, and granite-pegmatite W-Sn deposits contain rutile with these elements plus Nb and Ta. The Olympic Dam deposit hosts rutile that is enriched in W, Sn and Cu. Rutile associated with porphyry and skarn Cu and Cu-Au deposits tends to contain elevated W, Cu (and sometimes V). Although many ore deposits have well-defined and diagnostic rutile compositions, there are some compositional

  7. Optical response of columnar TiO2:Co on Si substrate

    NASA Astrophysics Data System (ADS)

    Anggraeni, G. P.; Saripudin, A.; Rusydi, A.; Darma, Y.

    2015-09-01

    Vertically arranged columnar TiO2:Co structure has been deposited on Si (100) substrate using the metal organic chemical vapor deposition (MOCVD) technique. SEM images confirm the columnar structure of the TiO2:Co layer on Si (100). Concentration of the Co dopant has been defined by means of the energy dispersive x-ray (EDX) spectra. Co concentrations are varied at 0.18, 0.33, and 0.68 at. % using pure TiO2 as the reference. X-ray diffraction (XRD) spectra show that the TiO2:Co layer have a rutile phase. Further analysis of this structure has been performed by using room temperature spectroscopic ellipsometry (SE) measurements in the energy range of 0.5 - 6.5 eV. This optical response shows the unique feature of significantly high density fringe especially below the band gap energy region (lower than 3.3 eV) in contrast to the conventional TiO2 thin film structure. This unique feature is interpreted as a dominant contribution of the vertical interfaces at columnar boundaries towards reflected light from the sample. The evolution of Ψ and Δ will be discussed as the function of Co concentration and some optical properties will be extracted after reasonably well data fitting by multilayer modelling. Furthermore, by comparing the SE data from different measurement orientations, it has been shown that TiO2:Co tends to be anisotropic. This study enables us to further evaluate structural properties through optical responses given by SE measurement.

  8. Nanoporous SiO2/TiO2 coating with enhanced interfacial compatibility for orthopedic applications

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaobing; Cao, Hengchun; You, Jing; Cheng, Xingbao; Xie, Youtao; Cao, Huiliang; Liu, Xuanyong

    2015-11-01

    Topographic modification in nanoscale is one of the most often used strategies to enhance the interfacial biocompatibility of implant materials. The aim of this work is to produce SiO2/TiO2 coatings with nanoporous structures and favorable biological properties by atmospheric plasma spraying technology and subsequently hydrothermal etching method in hydrogen fluoride solution. The effects of hydrothermal time and temperature on the microstructures and osteoblast behavior of the SiO2/TiO2 coatings were investigated. Results demonstrated that the as-sprayed SiO2/TiO2 coating was mainly composed of rutile and quartz phases. After etching, nanoporous topographies were formed on the surface of the coatings and the hydrothermal parameters had important influences on the size and shape of the pores. The interconnected network pores on the coating surface could only produce at the appropriate hydrothermal conditions (the hydrothermal time and temperature were 60 min and 100 °C, respectively). Compared to TiO2 and SiO2/TiO2 coatings, nanoporous SiO2/TiO2 coatings could enhance osteoblast adhesion and promote cell proliferation. The results suggested the potential application of the porous coatings for enhancing the biological performance of the currently used dental and orthopedic implant materials.

  9. CdS quantum dot-sensitized solar cells based on nano-branched TiO2 arrays

    PubMed Central

    2014-01-01

    Nano-branched rutile TiO2 nanorod arrays were grown on F:SnO2 conductive glass (FTO) by a facile, two-step wet chemical synthesis process at low temperature. The length of the nanobranches was tailored by controlling the growth time, after which CdS quantum dots were deposited on the nano-branched TiO2 arrays using the successive ionic layer adsorption and reaction method to make a photoanode for quantum dot-sensitized solar cells (QDSCs). The photovoltaic properties of the CdS-sensitized nano-branched TiO2 solar cells were studied systematically. A short-circuit current intensity of approximately 7 mA/cm2 and a light-to-electricity conversion efficiency of 0.95% were recorded for cells based on optimized nano-branched TiO2 arrays, indicating an increase of 138% compared to those based on unbranched TiO2 nanorod arrays. The improved performance is attributed to a markedly enlarged surface area provided by the nanobranches and better electron conductivity in the one-dimensional, well-aligned TiO2 nanorod trunks. PMID:24597830

  10. CdS quantum dot-sensitized solar cells based on nano-branched TiO2 arrays

    NASA Astrophysics Data System (ADS)

    Liu, Chang; Li, Yitan; Wei, Lin; Wu, Cuncun; Chen, Yanxue; Mei, Liangmo; Jiao, Jun

    2014-03-01

    Nano-branched rutile TiO2 nanorod arrays were grown on F:SnO2 conductive glass (FTO) by a facile, two-step wet chemical synthesis process at low temperature. The length of the nanobranches was tailored by controlling the growth time, after which CdS quantum dots were deposited on the nano-branched TiO2 arrays using the successive ionic layer adsorption and reaction method to make a photoanode for quantum dot-sensitized solar cells (QDSCs). The photovoltaic properties of the CdS-sensitized nano-branched TiO2 solar cells were studied systematically. A short-circuit current intensity of approximately 7 mA/cm2 and a light-to-electricity conversion efficiency of 0.95% were recorded for cells based on optimized nano-branched TiO2 arrays, indicating an increase of 138% compared to those based on unbranched TiO2 nanorod arrays. The improved performance is attributed to a markedly enlarged surface area provided by the nanobranches and better electron conductivity in the one-dimensional, well-aligned TiO2 nanorod trunks.

  11. A mini-review on rare earth metal-doped TiO2 for photocatalytic remediation of wastewater.

    PubMed

    Saqib, Najm Us; Adnan, Rohana; Shah, Irfan

    2016-08-01

    Titanium dioxide (TiO2) has been considered a useful material for the treatment of wastewater due to its non-toxic character, chemical stability and excellent electrical and optical properties which contribute in its wide range of applications, particularly in environmental remediation technology. However, the wide band gap of TiO2 photocatalyst (anatase phase, 3.20 eV) limits its photocatalytic activity to the ultraviolet region of light. Besides that, the electron-hole pair recombination has been found to reduce the efficiency of the photocatalyst. To overcome these problems, tailoring of TiO2 surface with rare earth metals to improve its surface, optical and photocatalytic properties has been investigated by many researchers. The surface modifications with rare earth metals proved to enhance the efficiency of TiO2 photocatalyts by way of reducing the band gap by shifting the working wavelength to the visible region and inhibiting the anatase-to-rutile phase transformations. This review paper summarises the attempts on modification of TiO2 using rare earth metals describing their effect on the photocatalytic activities of the modified TiO2 photocatalyst.

  12. Amorphous and crystalline TiO2 nanotube arrays for enhanced Li-ion intercalation properties.

    PubMed

    Guan, Dongsheng; Cai, Chuan; Wang, Ying

    2011-04-01

    We have employed a simple process of anodizing Ti foils to prepare TiO2 nanotube arrays which show enhanced electrochemical properties for applications as Li-ion battery electrode materials. The lengths and pore diameters of TiO2 nanotubes can be finely tuned by varying voltage, electrolyte composition, or anodization time. The as-prepared nanotubes are amorphous and can be converted into anatase nanotubes with heat treatment at 480 degrees C. Rutile crystallites emerge in the anatase nanotube when the annealing temperature is increased to 580 degrees C, resulting in TiO2 nanotubes of mixed phases. The morphological features of nanotubes remain unchanged after annealing. Li-ion insertion performance has been studied for amorphous and crystalline TiO2 nanotube arrays. Amorphous nanotubes with a length of 3.0 microm and an outer diameter of 125 nm deliver a capacity of 91.2 microA h cm(-2) at a current density of 400 microA cm(-2), while those with a length of 25 microm and an outer diameter of 158 nm display a capacity of 533 microA h cm-2. When the 3-microm long nanotubes become crystalline, they deliver lower capacities: the anatase nanotubes and nanotubes of mixed phases show capacities of 53.8 microA h cm-2 and 63.1 microA h cm(-2), respectively at the same current density. The amorphous nanotubes show excellent capacity retention ability over 50 cycles. The cycled nanotubes show little change in morphology compared to the nanotubes before electrochemical cycling. All the TiO2 nanotubes demonstrate higher capacities than amorphous TiO2 compact layer reported in literature. The amorphous TiO2 nanotubes with a length of 1.9 microm exhibit a capacity five times higher than that of TiO2 compact layer even when the nanotube array is cycled at a current density 80 times higher than that for the compact layer. These results suggest that anodic TiO2 nanotube arrays are promising electrode materials for rechargeable Li-ion batteries.

  13. Enhanced photovoltaic performance of novel TiO2 photoelectrode on TCO substrates for dye-sensitized solar cells.

    PubMed

    Nam, Jung Eun; Kwon, Soon Jin; Jo, Hyo Jeong; Yi, Kwang Bok; Kim, Dae-Hwan; Kang, Jin-Kyu

    2014-12-01

    In this study, we report synthesis and growth of rutile-anatase TiO2 thin film on fluorine-doped tin oxide (FTO) glass by a two-step hydrothermal method. The effects of additional treatments (i.e., TiCl4 post-treatment and seed layer formation were also studied. Photocurrent-voltage (I-V) measurement of rutile-anatase TiO2 thin film was performed under 1.5 G light illumination. Photovoltaic performance was investigated by incident photon-to-electron conversion efficiency (IPCE), electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent/photovoltage spectroscopy (IMVS/IMPS) and open-circuit photovoltage decay (OCVD).

  14. Fabrication and characterization of TiO 2-ZnO composite nanofibers

    NASA Astrophysics Data System (ADS)

    Lotus, A. F.; Tacastacas, S. N.; Pinti, M. J.; Britton, L. A.; Stojilovic, N.; Ramsier, R. D.; Chase, G. G.

    2011-02-01

    Tetraisopropyl titanate, zinc acetate dihydrate, and polyvinylpyrrolidone (PVP) were mixed to obtain a composite solution for producing TiO 2-ZnO nanofibers. Electrospinning and subsequent calcination at 973 K were employed to produce composite metal-oxide nanofibers with diameters ranging from 50 to 150 nm. Characterization of the TiO 2-ZnO composite nanofibers was carried out by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (XEDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible (UV-vis) spectrophotometry. TGA reveals a total weight loss of 49% and no change in mass above 873 K. The nanofibers are predominantly made of titania and exhibit two different energy band gap values of 3.0 and 3.5 eV. Our findings indicate that in the composite TiO 2-ZnO nanofibers three different phases (anatase and rutile TiO 2 and wurtzite ZnO) can co-exist and retain their individual characteristic properties.

  15. Electronic structures and optical properties of TiO2: Improved density-functional-theory investigation

    NASA Astrophysics Data System (ADS)

    Gong, Sai; Liu, Bang-Gui

    2012-05-01

    TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors. In fact, it has been widely used for a long time as white pigment and sunscreen because of its whiteness, high refractive index, and excellent optical properties. However, its electronic structures and the related properties have not been satisfactorily understood. Here, we use Tran and Blaha's modified Becke-Johnson (TB-mBJ) exchange potential (plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2. Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation (LDA) and generalized gradient approximation (GGA), in contrast with substantially overestimated values from many-body perturbation (GW) calculations. As for optical dielectric functions (both real and imaginary parts), refractive index, and extinction coefficients as functions of photon energy, our mBJ calculated results are in excellent agreement with the experimental curves. Our further analysis reveals that these excellent improvements are achieved because mBJ potential describes accurately the energy levels of Ti 3d states. These results should be helpful to understand the high temperature ferromagnetism in doped TiO2. This approach can be used as a standard to understand electronic structures and the related properties of such materials as TiO2.

  16. Tunability of morphological properties of Nd-doped TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Rehan, Imran; Sultana, Sabiha; Khan, Nauman; Qamar, Zahid; Rehan, Kamran

    2016-11-01

    In this work, an endeavor is made toward structural assessment and morphological variation of titanium dioxide (TiO2) thin films when doped with neodymium (Nd). The electron beam deposition technique was employed to fabricate Nd-based TiO2 thin films on n-Type Si substrates. Nd concentration was varied from 0.0 to 2.0 atomic percent (at.%) under identical growth environments. The films were deposited in an oxygen-deficient environment to cause the growth of rutile phases. Energy dispersive x-ray spectroscopy confirmed the presence and variation of Nd dopant in TiO2. X-ray diffraction analysis showed the transformation of amorphous structures of the as-grown samples to anatase polycrystalline after annealing at 500 °C, while atomic force microscopy exposed linearity in grain density in as-grown samples with doping until 1 at.%. Raman spectrums of as-grown and annealed samples revealed the growth of the anatase phase in the annealed samples. Based on these results it can be proposed that Nd doping has pronounced effects on the structural characteristics of TiO2 thin films.

  17. Fe-Doped TiO2 Thin Films for CO Gas Sensing

    NASA Astrophysics Data System (ADS)

    Kumar, Mukesh; Kumar, Dinesh; Gupta, Anil Kumar

    2015-01-01

    Fe-doped TiO2 thin films were prepared by the sol-gel technique on silicon substrate. The thin films were evaluated for detection of carbon monoxide (CO) gas at room temperature. The TiO2 films were characterized by x-ray diffraction (XRD) analysis, field-emission scanning electron microscopy, and ultraviolet-visible (UV) spectroscopy. The characterization revealed that, as the doping concentration was increased, the grain size decreased. XRD patterns revealed the phase transition from rutile to anatase with addition of different percentages (weight/volume) of Fe. The bandgap determined from UV spectroscopy was found to decrease with increasing Fe doping concentration. Fe doping was observed to have a significant effect on the resistivity of the doped TiO2 thin films. The gas sensing behavior of the films was studied by exposure to different concentrations of CO gas with measurement of the electrical resistance. It was observed that Fe-doped (7% weight/volume) TiO2 exhibited high sensitivity and good response/recovery on exposure to CO gas in the concentration range from 100 ppm to 900 ppm in Ar.

  18. Genotoxic potential of TiO2 on bottlenose dolphin leukocytes.

    PubMed

    Bernardeschi, Margherita; Guidi, Patrizia; Scarcelli, Vittoria; Frenzilli, Giada; Nigro, Marco

    2010-01-01

    Titanium dioxide is extensively used in a variety of products, including industrial materials and cosmetics. Studies mainly performed on human cell lines and in vivo exposure on experimental animals have raised concern about the toxic effects of ultrafine titanium dioxide; however, scarce information is available about its impact on aquatic life. The aim of this article was to assess the genotoxic potential of TiO(2) (anatase and rutile) on bottlenose dolphin leukocytes. Blood samples were obtained from four male and one female specimens reared at the Adriatic SeaWorld "Oltremare" (Riccione, Italy). Leukocytes were isolated by the lyses procedure and in vitro exposed to TiO(2) in RPMI. Experimental solutions were sonicated immediately before dosing the cells. Three exposure times (4, 24 and 48 h) and three doses (20, 50 and 100 microg/ml) were tested. Genotoxicity was detected by the single-cell gel electrophoresis (or comet assay) at pH > or = 13, assessing single/double-strand breaks and alkali-labile sites. Cytotoxicity was also detected by the Trypan blue exclusion method. Results showed that both the crystalline forms of TiO(2) were genotoxic for bottlenose dolphin leukocytes, with a statistically significant increase of DNA fragmentation after exposure to 50 and 100 microg/ml for 24 and 48 h. Although preliminary, these are the first data regarding the genetic susceptibility of toothed cetaceans toward an "emerging" pollutant, such as TiO(2) particles.

  19. Annealing effect on Sb2S3-TiO2 nanostructures for solar cell applications

    PubMed Central

    2013-01-01

    Nanostructures composited of vertical rutile TiO2 nanorod arrays and Sb2S3 nanoparticles were prepared on an F:SnO2 conductive glass by hydrothermal method and successive ionic layer adsorption and reaction method at low temperature. Sb2S3-sensitized TiO2 nanorod solar cells were assembled using the Sb2S3-TiO2 nanostructure as the photoanode and a polysulfide solution as an electrolyte. Annealing effects on the optical and photovoltaic properties of Sb2S3-TiO2 nanostructure were studied systematically. As the annealing temperatures increased, a regular red shift of the bandgap of Sb2S3 nanoparticles was observed, where the bandgap decreased from 2.25 to 1.73 eV. At the same time, the photovoltaic conversion efficiency for the nanostructured solar cells increased from 0.46% up to 1.47% as a consequence of the annealing effect. This improvement can be explained by considering the changes in the morphology, the crystalline quality, and the optical properties caused by the annealing treatment. PMID:23421351

  20. Characterization of sprayed TiO2 on ITO substrates for solar cell applications.

    PubMed

    Arunachalam, A; Dhanapandian, S; Manoharan, C; Sridhar, R

    2015-10-05

    Titanium dioxide (TiO2) thin films had been deposited with various substrate temperatures by spray pyrolysis technique onto ITO substrates. All films exhibited polycrystalline nature with the preferred orientation along (101) plane. At the substrate temperature 450 °C, the film favored the formation of anatase phase. The higher substrate temperature (475 °C) favored the appearance of rutile structure. The SEM image of the film at substrate temperature (Ts=450 °C) showed high structural quality with the porous nature. The typical AFM image of TiO2 film deposited at the substrate temperature, 450 °C depicted the regular arrangement of fine closely packed tetragonal structured grains. The transmittance of the spectra exhibited above 85% with energy band gap of 3.6 eV. From the study of photoluminescence, the emission at 417 nm, 437 nm and with weak emission at 551 nm was observed, which confirmed the lesser defects in the samples. The electrical resistivity was found to be 6.856×10(1) Ω cm for the substrate temperature 450 °C. The efficiency of anatase TiO2 photoelectrode deposited at the substrate temperature 450 °C based cell was much higher than the efficiency of TiO2 photoelectrode deposited at the substrate temperature 475 °C based cell.

  1. Generation of Organic Radicals During Photocatalytic Reactions on TiO2

    SciTech Connect

    Henderson, Michael A.; Deskins, N. Aaron; Zehr, Robert T.; Dupuis, Michel

    2011-04-01

    Using a variety of organic carbonyl molecules (R1C(O)R2) and the rutile TiO2(110) surface as a model photocatalyst, we demonstrate both experimentally and theoretically that ejection of organic radicals from TiO2 surfaces is likely a prevalent reaction process occurring during heterogeneous photooxidationof organic molecules. Organic carbonyls react with coadsorbed oxygen species to form organic diolates which are more strongly bound to TiO2 than are the parent carbonyls. The parent carbonyls, when bound to TiO2(110) in an η1 configuration, are photo-inactive. However, the diolates are shown to photodecompose by ejection one of the two R substituents from the surface into the gas phase, leaving behind the carboxylate of the other R group. Theoretical calculations using DFT show that in most cases the choice of which R group is ejected can be predicted based on the C-R bond energies and, to a lesser extent, the stability of the ejected R group.

  2. Ag-Si Co-doped TiO2 photocatalyst synthesized via a nonaqueous method.

    PubMed

    Chen, Qifeng; Shi, Weimei; Xu, Yao; Wu, Dong; Sun, Yuhan

    2010-11-01

    Ag-Si/TiO2 photocatalysts were synthesized in a nonaqueous system at 140 degrees C, and then annealed at different temperatures. The obtained photocatalysts were characterized by XRD, TEM, BET, TG-DTA, XPS, as well as UV-vis DRS. The results showed that All Ag-Si/TiO2 held an anatase phase and high thermal stability and the phase transformation from anatase to rutile was retarded to about 900 degrees C. The Ag-Si/TiO2 particles were highly mono-dispersed and the particles size became smaller compared to TiO2. Additionally, UV-vis light absorption shifted to visible region after Ag doping. Si weaved into the matrix of TiO2, while Ag dispersed on the surface of TiO2 particles. The visible light photocatalytic activity was evaluated by Rhodamine B (RhB) degradation in an aqueous solution under visible light irradiation. It was found that the photccatalytic activities of the obtained Ag-Si/TiO2 samples were all higher than those of pure TiO2 and Ag/TiO2, reaching the maximum at the Ag and Si content of 0.5 mol% and 20.0 mol%, respectively. The enhanced visible photocatalytic activity may be attributed to the simultaneous effects of silver and silicon co-doping.

  3. The result of synthesis analysis of the powder TiO2/ZnO as a layer of electrodes for dye sensitized solar cell applications

    NASA Astrophysics Data System (ADS)

    Retnaningsih, Lilis; Muliani, Lia

    2016-04-01

    This study has been conducted synthesis of TiO2 nanoparticle powders and ZnO nanoparticle powder into a paste to be in this research, dye-sensitive solar cells (DSSC) was produced by TiO2 nanopowder and ZnO nanopowder synthesis to make paste that is applied as electrode. This electrode works based on photon absorbed by dye and transferred to different composition of TiO2/ ZnO particle. Properties of DSSC are affected by fabrication method, parameter and dimension of TiO2 / ZnO nanoparticles, technique and composition of TiO2 / ZnO paste preparation is important to get the higher performance of DSSC. Doctor blade is a method for electrode coating on glass substrate. The electrode was immersed into dye solution of Z907 and ethanol. From the experiment, the effect of TiO2 and ZnO nanopowder mixture for electrode was investigated. XRD characterization show anatase and rutile phase, which sintered TiO2/ZnO has intensity more than 11,000. SEM characterization shows the composition of 20% TiO2 / 80% ZnO has better porosity. Higher efficiency that is investigated by I-V measurement using Sun Simulator.

  4. Hydrothermal Synthesis of TiO2@SnO2 Hybrid Nanoparticles in a Continuous-Flow Dual-Stage Reactor.

    PubMed

    Hellstern, Henrik L; Bremholm, Martin; Mamakhel, Aref; Becker, Jacob; Iversen, Bo B

    2016-03-08

    TiO2@SnO2 hybrid nanocomposites were successfully prepared in gram scale using a dual-stage hydrothermal continuous-flow reactor. Temperature and pH in the secondary reactor were found to selectively direct nucleation and growth of the secondary material into either heterogeneous nanocomposites or separate intermixed nanoparticles. At low pH, 2 nm rutile SnO2 nanoparticles were deposited on 9 nm anatase TiO2 particles; the presence of TiO2 was found to suppress formation of larger SnO2 particles. At high pH SnO2 formed separate particles and no deposition on TiO2 was observed. Ball-milling of TiO2 and SnO2 produced no TiO2@SnO2 composites. This verifies that the composite particles must be formed by nucleation and growth of the secondary precursor on the TiO2 . High concentration of secondary precursor led to formation of TiO2 particles embedded in aggregates of SnO2 nanoparticles. The results demonstrate how nanocomposites may be produced in high yield by green chemistry.

  5. Synthesis of TiO2 visible light catalysts with controllable crystalline phase and morphology from Ti-bearing electric arc furnace molten slag.

    PubMed

    Li, Yang; Liu, Lulu; Guo, Min; Zhang, Mei

    2016-09-01

    TiO2 visible light catalysts with different crystalline phases and morphologies were synthesized from titanium-bearing electric arc furnace molten slag (Ti-bearing EAF slag) by using a simple acidolysis process. The effects of the pH of the HCl solution, liquid to solid ratio (RL/S, HCl solution to the residue ratio, mL/g) and acidolysis time on the micro-morphology and crystalline phase of as-prepared TiO2 photocatalysts were systematically investigated. The results indicated that with decreasing pH in the HCl solution and increasing RL/S, the crystalline phase and micro-morphology of the obtained TiO2 nanostructures tended to transform from anatase type TiO2 with spherical nanoparticle structures to rutile type TiO2 with needle-like nanorod structures. The acidolysis time had little influence on the crystalline phase but great impact on the size of the obtained TiO2. The growth mechanism of TiO2 from Ti-bearing EAF slag during the acidolysis process was also discussed. In addition, the influence of RL/S on the photocatalytic properties of the synthesized nanostructured TiO2 was studied. The results showed that the photodegradation efficiency for Rhodamine B solution could reach 91.00% in 120min when the RL/S was controlled at 50:1.

  6. Structure and photoluminescence of the TiO2 films grown by atomic layer deposition using tetrakis-dimethylamino titanium and ozone.

    PubMed

    Jin, Chunyan; Liu, Ben; Lei, Zhongxiang; Sun, Jiaming

    2015-01-01

    TiO2 films were grown on silicon substrates by atomic layer deposition (ALD) using tetrakis-dimethylamino titanium and ozone. Amorphous TiO2 film was deposited at a low substrate temperature of 165°C, and anatase TiO2 film was grown at 250°C. The amorphous TiO2 film crystallizes to anatase TiO2 phase with annealing temperature ranged from 300°C to 1,100°C in N2 atmosphere, while the anatase TiO2 film transforms into rutile phase at a temperature of 1,000°C. Photoluminescence from anatase TiO2 films contains a red band at 600 nm and a green band at around 515 nm. The red band exhibits a strong correlation with defects of the under-coordinated Ti(3+) ions, and the green band shows a close relationship with the oxygen vacancies on (101) oriented anatase crystal surface. A blue shift of the photoluminescence spectra reveals that the defects of under-coordinated Ti(3+) ions transform to surface oxygen vacancies in the anatase TiO2 film annealing at temperature from 800°C to 900°C in N2 atmosphere.

  7. Identification of the Active Species in Photochemical Hole Scavenging Reactions of Methanol on TiO2

    SciTech Connect

    Shen, Mingmin; Henderson, Michael A.

    2011-11-03

    Molecular and dissociative methanol adsorption species were prepared on rutile TiO2(110) surfaces to study photocatalytic oxidation of methanol in ultrahigh vacuum (UHV) using temperature-programmed desorption (TPD). Adsorbed methoxy groups (CH3O-) were found to be the photoactive form of adsorbed methanol converted to adsorbed formaldehyde and a surface OH group by hole-mediated C-H bond cleavage. These results suggest that adsorbed methoxy is the effective hole scavenger in photochemical reactions involving methanol.

  8. Charge storage in oxygen deficient phases of TiO2: defect Physics without defects

    PubMed Central

    Padilha, A. C. M.; Raebiger, H.; Rocha, A. R.; Dalpian, G. M.

    2016-01-01

    Defects in semiconductors can exhibit multiple charge states, which can be used for charge storage applications. Here we consider such charge storage in a series of oxygen deficient phases of TiO2, known as Magnéli phases. These Magnéli phases (TinO2n−1) present well-defined crystalline structures, i.e., their deviation from stoichiometry is accommodated by changes in space group as opposed to point defects. We show that these phases exhibit intermediate bands with an electronic quadruple donor transitions akin to interstitial Ti defect levels in rutile TiO2. Thus, the Magnéli phases behave as if they contained a very large pseudo-defect density: ½ per formula unit TinO2n−1. Depending on the Fermi Energy the whole material will become charged. These crystals are natural charge storage materials with a storage capacity that rivals the best known supercapacitors. PMID:27364139

  9. Photocatalytic activity and reusability study of nanocrystalline TiO2 films prepared by sputtering technique

    NASA Astrophysics Data System (ADS)

    Barrocas, B.; Monteiro, O. C.; Jorge, M. E. Melo; Sério, S.

    2013-01-01

    The photocatalytic activity of nanocrystalline titanium dioxide (TiO2) films deposited on unheated glass substrates by DC reactive magnetron sputtering at different oxygen partial pressures was tested on the decolorization of Rhodamine 6G (Rh6G) aqueous solutions. The dye photodecolorization process was studied considering the influence of the crystallinity and preferred orientation of growth of the prepared films. It was found that the higher photocatalytic activity was achieved by the film with preferred orientation of growth along the (1 0 1) crystal direction and showing a vestigial rutile phase in a mainly anatase phase. The recycling catalytic ability of the TiO2 films was also evaluated and a promising photocatalytic performance has been revealed with a very low variation of the decay rate after five consecutive usages. Structural and morphological characterization revealed high photochemical stability of the films after successive photodegradations assays.

  10. Charge storage in oxygen deficient phases of TiO2: defect Physics without defects

    NASA Astrophysics Data System (ADS)

    Padilha, A. C. M.; Raebiger, H.; Rocha, A. R.; Dalpian, G. M.

    2016-07-01

    Defects in semiconductors can exhibit multiple charge states, which can be used for charge storage applications. Here we consider such charge storage in a series of oxygen deficient phases of TiO2, known as Magnéli phases. These Magnéli phases (TinO2n-1) present well-defined crystalline structures, i.e., their deviation from stoichiometry is accommodated by changes in space group as opposed to point defects. We show that these phases exhibit intermediate bands with an electronic quadruple donor transitions akin to interstitial Ti defect levels in rutile TiO2. Thus, the Magnéli phases behave as if they contained a very large pseudo-defect density: ½ per formula unit TinO2n-1. Depending on the Fermi Energy the whole material will become charged. These crystals are natural charge storage materials with a storage capacity that rivals the best known supercapacitors.

  11. Transmission Electron Microscopy and Scanning Transmission X-Ray Microscopy Studies on the Bioaccumulation and Tissue Level Absorption of TiO2 Nanoparticles in Daphnia magna.

    PubMed

    Kwon, Dongwook; Nho, Hyun Woo; Yoon, Tae Hyun

    2015-06-01

    In this study, bioaccumulation and tissue-level absorption of TiO2 nanoparticles (NPs) in freshwater invertebrates were investigated using transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM). The TiO2 NPs were used to test impacts of core sizes (i.e., 5 ± 2 nm and 23 ± 7 nm for TiO2(SYN) and TiO2(P25), respectively) and agglomerations (i.e., well dispersed vs. highly agglomerated) on the uptake of TiO2 NPs in Daphnia magna (D. magna). Highly agglomerated TiO2 NPs, regardless of their core sizes, were heavily taken up into the digestive tract of D. magna and no detectable penetration of both TiO2 NPs into the gut epithelial cells of D. magna was observed in TEM and STXM images. However, significant damages involving morphological changes in the microvilli and gut epithelial cells (e.g., irregular shaped microvilli, epithelial cell protrusion, and dilatation of cytoplasmic inclusion) were observed only with the commercial TiO2 NPs (TiO2(P25)) with larger core size and mixed crystalline phase, while the laboratory synthesized TiO2 NPs (TiO2(Syn)) with smaller core size and single crystalline phase showed slight morphological changes in the gut microvilli and epithelial cells. In the case of D. magna exposed to the well dispersed synthetic TiO2 NP ((Cit)TiO2(Syn)), only a negligible amount of TiO2 NPs were found within the digestive tract of the D. magna without any significant damages in the gut microvilli and epithelial cells and any detectable penetrations of TiO2 NPs into epithelial cells of D. magna gut. These TEM and STXM observations confirmed us that uptake of NP into D. magna are strongly dependent on their agglomeration (i.e., hydrodynamic sizes), rather than their core sizes, while direct penetration of NPs into tissues of digestive tract seems unlikely without significant morphological changes (e.g., collapse of the epithelial tissue) caused by high toxicity of NPs or released metal ions.

  12. TF-XRD examination of surface-reactive TiO2 coatings produced by heat treatment and CO2 laser treatment.

    PubMed

    Moritz, Niko; Areva, Sami; Wolke, Joop; Peltola, Timo

    2005-07-01

    When surface-reactive (bioactive) coatings are applied to medical implants by means of CO2 laser processing, the bioactivity of the surface of the implant can be locally modified to match the properties of the surrounding tissues to provide a firm fixation of the implant. The aim of this study was to compare the heat treated TiO2 coatings with the laser-treated TiO2 coatings in terms of amorphous-crystalline-phase development. The coatings were characterized with thin-film X-ray diffraction (TF-XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The TiO2 coatings heat treated at 500 degrees C known to be bioactive in SBF (simulated body fluid) consisted mainly of anatase with some rutile-phase, suggesting a predominant effect of anatase on reactivity of coatings. However, the coatings preheat-treated at 500 degrees C with further laser treatment exhibited enhanced bioactivity while consisting mainly of rutile. These findings indicated a key role of both rutile and anatase for the reactivity of the coatings. Without preheat treatment, by laser treatment alone, the amorphous titania coatings developed into mixed anatase/rutile containing coatings. This structural organization and the increase in crystal size are thus considered to be the reasons for their bioactivity. The SBF results indicate the possibility to control bioactivity by altering laser power used through the anatase/rutile crystallinity enhancement.

  13. Oxygen vacancy induced phase formation and room temperature ferromagnetism in undoped and Co-doped TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Mohanty, P.; Mishra, N. C.; Choudhary, R. J.; Banerjee, A.; Shripathi, T.; Lalla, N. P.; Annapoorni, S.; Rath, Chandana

    2012-08-01

    TiO2 and Co-doped TiO2 (CTO) thin films deposited at various oxygen partial pressures by pulsed laser deposition exhibit room temperature ferromagnetism (RTFM) independent of their phase. Films deposited at 0.1 mTorr oxygen partial pressure show a complete rutile phase confirmed from glancing angle x-ray diffraction and Raman spectroscopy. At the highest oxygen partial pressure, i.e. 300 mTorr, although the TiO2 film shows a complete anatase phase, a small peak corresponding to the rutile phase along with the anatase phase is identified in the case of CTO film. An increase in O to Ti/(Ti+Co) ratio with increase in oxygen partial pressure is observed from Rutherford backscattering spectroscopy. It is revealed from x-ray photoelectron spectroscopy (XPS) that oxygen vacancies are found to be higher in the CTO film than TiO2, while the valency of cobalt remains in the +2 state. Therefore, the CTO film deposited at 300 mTorr does not show a complete anatase phase unlike the TiO2 film deposited at the same partial pressure. We conclude that RTFM in both films is not due to impurities/contaminants, as confirmed from XPS depth profiling and cross-sectional transmission electron microscopy (TEM), but due to oxygen vacancies. The magnitude of moment, however, depends not only on the phase of TiO2 but also on the crystallinity of the films.

  14. The FTIR studies of gels and thin films of Al2O3-TiO2 and Al2O3-TiO2-SiO2 systems.

    PubMed

    Adamczyk, Anna; Długoń, Elżbieta

    2012-04-01

    In this work, samples in form of bulk ones and thin films were obtained using the sol-gel method. The bulk samples were heated at different temperatures (500 °C, 850 °C and 1100 °C) corresponding to the annealing process of coatings, deposited on different substrates by dipping and pulling out samples from the proper sol with the stable speed. Thin films of both Al2O3-TiO2 and Al2O3-TiO2-SiO2 systems were deposited on carbon, steel and titanium substrates in two different ways: as single layers obtained from Al2O3 sol, TiO2 sol and Al2O3 sol or deposited as mixed coatings from Al2O3-TiO2 sol as well as Al2O3-TiO2-SiO2 one. All bulk samples were studied by the FTIR spectroscopy and the X-ray diffractometry while thin films were also investigated by the electron microscopy. In the IR spectra of Al2O3-TiO2 samples, as well as gels and coatings, bands due to the vibrations of AlO bonds of the octahedrally and tetrahedrally coordinated aluminum were observed. The IR spectra of samples of Al2O3-TiO2-SiO2 system differ from that of Al2O3-TiO2 ones in presence of bands assigned to the SiO bond vibrations and in positions of bands due to AlO bond vibrations. In all spectra of bulk samples and coatings, the positions of TiO bond vibrations were ascribed basing on the IR spectra of the pure anatase and rutile.

  15. Rietveld analysis of the effect of annealing atmosphere on phase evolution of nanocrystalline TiO2 powders.

    PubMed

    Salari, M; Rezaee, M; Chidembo, A T; Konstantinov, K; Liu, H K

    2012-06-01

    The structural evolution of nanocrystalline TiO2 was studied by X-ray diffraction (XRD) and the Rietveld refinement method (RRM). TiO2 powders were prepared by the sol-gel technique. Post annealing of as-synthesized powders in the temperature range from 500 degrees C to 800 degrees C under air and argon atmospheres led to the formation of TiO2 nanoparticles with mean crystallite size in the range of 37-165 nm, based on the Rietveld refinement results. It was found that the phase structure, composition, and crystallite size of the resulting particles were dependent on not only the annealing temperature, but also the annealing atmosphere. Rietveld refinement of the XRD data showed that annealing the powders under argon atmosphere promoted the polymorphic phase transformation from anatase to rutile. Field emission scanning electron microscopy (FESEM) was employed to investigate the morphology and size of the annealed powders.

  16. Hydrothermal synthesis of Mo-doped VO2/TiO2 composite nanocrystals with enhanced thermochromic performance.

    PubMed

    Li, Dengbing; Li, Ming; Pan, Jing; Luo, Yuanyuan; Wu, Hao; Zhang, Yunxia; Li, Guanghai

    2014-05-14

    This paper reports a one-step TiO2 seed-assistant hydrothermal synthesis of Mo-doped VO2(M)/TiO2 composite nanocrystals. It was found that excess Mo doping can promote formation of the VO2(M) phase, and rutile TiO2 seed is beneficial to morphology control, size reduction, and infrared modulation of Mo-doped VO2(M) nanocrystals. The Mo-doped VO2 nanocrystals epitaxially grow on TiO2 seeds and have a quasi-spherical shape with size down to 20 nm and a nearly 35% infrared modulation near room temperature. The findings of this work demonstrate important progress in the near-room-temperature thermochromic performance of VO2(M) nanomaterials, which will find potential application in constructing VO2(M) nanocrystal-based smart window coatings.

  17. Photochromism-based detection of volatile organic compounds by W-doped TiO2 nanofibers.

    PubMed

    Jin, Ming; Zhang, Xintong; Pu, Hongting; Nishimoto, Shunsuke; Murakami, Taketoshi; Fujishima, Akira

    2011-10-01

    W-doped TiO(2) nanofibers with various compositions (W/Ti: 2-8%) were fabricated by the electrospinning method from respective precursor solutions containing tungsten(V) pentaethoxide, titanium tetraisopropoxide (TTIP), and polyvinylpyrrolidone (PVP), followed with calcination at 550 °C. Morphological and structural characteristics of these nanofibers were studied with SEM, XRD and XPS. W-doping inhibited the crystal growth and anatase-to-rutile transformation of TiO(2) nanofibers. W-doped TiO(2) nanofiber mats showed good photocatalytic oxidation abilities for acetone. Obvious color change from white to blue of mats during the photocatalysis process can be detected by naked eyes, which provides a good way in detection of pollutants in indoor air, especially for the volatile organic compounds (VOCs).

  18. Atomic-Scale Surface Local Structure of TiO2 and Its Influence on the Water Photooxidation Process.

    PubMed

    Imanishi, Akihito; Fukui, Ken-Ichi

    2014-06-19

    The water photooxidation reaction on TiO2 and related metal oxides has been attracting strong attention from the point of view of solar water splitting. The water photooxidation reaction (i.e., oxygen evolution reaction) accompanies three other kinds of side reactions (photoluminescence (PL), surface roughening, and nonradiative recombination). These reactions are competitive with each other, and the ratio of their quantum efficiencies strongly depends on the atomic-scale surface local structure. This Perspective focuses on the atomic-scale surface local structure dependence of those four kinds of competitive reactions on a TiO2 (rutile) single-crystal electrode on which not only a terrace structure but also step structures were strictly controlled. The experimental results are discussed based on the reaction model of water photooxidation that we previously proposed. The photocatalytic activity of the TiO2 surface roughened by the photoinduced roughening process is also focused on.

  19. Large-Scale Synthesis of Transition-Metal-Doped TiO2 Nanowires with Controllable Overpotential

    SciTech Connect

    Liu, Bin; Chen, HaoMing; Liu, Chong; Andrews, Sean; Han, Chris; Yang, Peidong

    2013-03-13

    Practical implementation of one-dimensional semiconductors into devices capable of exploiting their novel properties is often hindered by low product yields, poor material quality, high production cost, or overall lack of synthetic control. Here, we show that a molten-salt flux scheme can be used to synthesize large quantities of high-quality, single-crystalline TiO2 nanowires with controllable dimensions. Furthermore, in situ dopant incorporation of various transition metals allows for the tuning of optical, electrical, and catalytic properties. With this combination of control, robustness, and scalability, the molten-salt flux scheme can provide high-quality TiO2 nanowires to satisfy a broad range of application needs from photovoltaics to photocatalysis.

  20. Nb-doped rutile TiO₂: a potential anode material for Na-ion battery.

    PubMed

    Usui, Hiroyuki; Yoshioka, Sho; Wasada, Kuniaki; Shimizu, Masahiro; Sakaguchi, Hiroki

    2015-04-01

    The electrochemical properties of the rutile-type TiO2 and Nb-doped TiO2 were investigated for the first time as Na-ion battery anodes. Ti(1-x)Nb(x)O2 thick-film electrodes without a binder and a conductive additive were prepared using a sol-gel method followed by a gas-deposition method. The TiO2 electrode showed reversible reactions of Na insertion/extraction accompanied by expansion/contraction of the TiO2 lattice. Among the Ti(1-x)Nb(x)O2 electrodes with x = 0-0.18, the Ti(0.94)Nb(0.06)O2 electrode exhibited the best cycling performance, with a reversible capacity of 160 mA h g(-1) at the 50th cycle. As the Li-ion battery anode, this electrode also attained an excellent rate capability, with a capacity of 120 mA h g(-1) even at the high current density of 16.75 A g(-1) (50C). The improvements in the performances are attributed to a 3 orders of magnitude higher electronic conductivity of Ti(0.94)Nb(0.06)O2 compared to that of TiO2. This offers the possibility of Nb-doped rutile TiO2 as a Na-ion battery anode as well as a Li-ion battery anode.

  1. Dielectric relaxation and conduction mechanisms in sprayed TiO2 thin films as a function of the annealing temperature

    NASA Astrophysics Data System (ADS)

    Juma, Albert; Acik, Ilona Oja; Mere, Arvo; Krunks, Malle

    2016-04-01

    The electrical properties of TiO2 thin films deposited by chemical spray pyrolysis onto Si substrates were investigated in the metal-oxide-semiconductor (MOS) configuration using current-voltage characteristics and impedance spectroscopy. The electrical properties were analyzed in relation to the changes in microstructure induced during annealing in air up to a temperature of 950 °C. Anatase to rutile transformation started after annealing at 800 °C, and at 950 °C, only the rutile phase was present. The dielectric relaxation strongly depended upon the microstructure of TiO2 with the dielectric constant for the anatase phase between 45 and 50 and that for the rutile phase 123. Leakage current was reduced by three orders of magnitude after annealing at 700 °C due to the densification of the TiO2 film. A double-logarithmic plot of the current-voltage characteristics showed a linear relationship below 0.12 V consistent with Ohmic conduction, while space-charge-limited conduction mechanism as described by Child's law dominated for bias voltages above 0.12 V.

  2. Adsorption Dynamics Of Water On The Surface Of TiO2 (110)

    NASA Astrophysics Data System (ADS)

    Bundaleski, B.; Silva, A. G.; Schröder, U.; Moutinho, A. M. C.; Teodoro, O. M. N. D.

    2010-07-01

    Rutile titanium dioxide TiO2 is used in a number of technological areas. Therefore, in surface science, it has become the most studied oxide surface, and it is generally used to model the TiO2 catalytic properties under ultra high vacuum conditions. While water adsorption on rutile TiO2 (110) has been mainly investigated using scanning tunnelling spectroscopy (STM), we use here a different approach based on the work function spectroscopy (WF): water adsorption induces formation of a dipole layer which locally changes the work function. The change can be experimentally monitored by the onset shift of the energy spectrum of secondary electrons. Although X-ray photoelectron spectroscopy is not sensitive enough to monitor water adsorption on TiO2 having low defect concentration, WF results clearly show the work function change which is undoubtedly attributed to the water adsorption. These measurements were done for different water vapour pressures, exposure times, sample temperatures and general surface conditions. Time evolution of the work function change, together with that of the H2O partial pressure, enable us to successfully model the adsorption dynamics and help us understand the observed results. This analysis clearly shows existence of at least three different adsorption mechanisms. The interplay between them governs the measured time evolution of the work function change. Their relative contributions depend on the surface temperature and, presumably, its topography. These results will be discussed in the light of several recent experimental (mainly using STM) and theoretical studies of this system done by other authors.

  3. Biopolymeric hydrogels - nanostructured TiO2 hybrid materials as potential injectable scaffolds for bone regeneration.

    PubMed

    Zazakowny, Karolina; Lewandowska-Łańcucka, Joanna; Mastalska-Popławska, Joanna; Kamiński, Kamil; Kusior, Anna; Radecka, Marta; Nowakowska, Maria

    2016-12-01

    The present work aims at development of novel hybrid materials from genipin crosslinked collagen or collagen/chitosan hydrogels containing various types of TiO2 nanoparticles characterized with different anatase/rutile ratios. Collagen and chitosan were selected as hydrogel components since they are biopolymers being, like collagen, the major compound present in extracellular matrix or exhibit structural similarity to glycosaminoglycans, like chitosan. TiO2 nanoparticles were introduced to the hydrogel matrices to improve their mechanical properties as well as bioactivity. A series of twelve novel hybrid materials were prepared and their physicochemical, mechanical and biological properties were evaluated. It was found that TiO2 nanostructures introduced to the hydrogels have significant influence on the swelling properties of the synthesized hybrids and their impact is strongly dependent on the type of matrices. The surfaces of hybrid materials were found to be more hydrophilic than these of corresponding hydrogel matrix. It was also observed that, the storage modulus values of the hybrids based on collagen-chitosan hydrogel are comparable to these for plain hydrogels what indicates that the mechanical properties of the materials obtained are satisfactory for possible biomedical application. The in vitro cell culture studies have shown that prepared materials are biocompatible as they can support mitochondrial activity of MEFs as well as MG-63 cells. In vitro experiments performed under simulated body fluid (SBF) conditions have revealed that all studied TiO2 nanoparticles present in hydrogel matrices, regardless of anatase/rutile ratio, successfully induced formation of apatite-like structures. The hybrid materials developed here are promising candidates for preparation of bioactive, injectable scaffolds for tissue engineering.

  4. Influence of acidic pH on the formulation of TiO2 nanocrystalline powders with enhanced photoluminescence property.

    PubMed

    Tsega, Moges; Dejene, F B

    2017-02-01

    Titanium dioxide (TiO2) nanoparticles were prepared by the sol-gel method at different pH values (3.2-6.8) with a hydrochloric acid (HCl) solution. Raw samples were calcined at 500 °C for 2 h. The effects of pH on the structural, morphological and optical properties of TiO2 nanoparticles were investigated. At pH 4.4-6.8, only the anatase phase of TiO2 was observed. Under strong acidic condition at pH 3.2 rutile, brookite and anatase co-exist, but rutile is the predominant phase. The strain value increased and the crystallite size decreased as the HCl content increased. The increased crystallite sizes in the range 21-24 nm and enhanced blue emission intensity around 432 nm was obtained for the sample at pH 5.0. Experimental results showed that TiO2 nanoparticles synthesized at pH 5.0 exhibited the best luminescence property with pure anatase phase.

  5. Formation of TiO2 Thin Films using NH3 as Catalyst by Metalorganic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Jung, Sung-Hoon; Kang, Sang-Won

    2001-05-01

    We have studied metalorganic chemical vapor deposition of TiO2 thin films using titanium tetra-isopropoxide [TTIP, Ti(O--C3H7)4] and NH3 as a catalyst at deposition temperatures ranging from 250 to 365°C. At deposition temperatures above 330°C, pyrolytic self-decomposition of TTIP is dominant regardless of the use of NH3, and the activation energy for TiO2 film formation is 152 kJ/mol. At deposition temperatures below 330°C, the films can be formed with the help of the catalytic activity of NH3, and the activation energy is reduced to 55 kJ/mol. TiO2 films deposited through the pyrolytic self-decomposition of TTIP have an anatase structure before and after performing post-deposition annealing in oxygen ambient for 30 min at 750°C. On the other hand, the as-deposited films formed through the catalytic reaction of TTIP with NH3 incorporate nitrogen impurities and have microcrystallites of the rutile structure within the amorphous matrix. However, the post-deposition annealing, the nitrogen impurities are completely removed from the films, and the films are converted into polycrystalline TiO2 films with the rutile structure, which have a high dielectric constant of 82 and a low leakage current.

  6. Preparation and characterization of Cu-doped TiO2 materials for electrochemical, photoelectrochemical, and photocatalytic applications

    NASA Astrophysics Data System (ADS)

    Ganesh, Ibram; Kumar, Polkampally P.; Annapoorna, Ibram; Sumliner, Jordan M.; Ramakrishna, Mantripragada; Hebalkar, Neha Y.; Padmanabham, Gade; Sundararajan, Govindan

    2014-02-01

    The Cu-doped TiO2 (Cu = 0-50 wt.%) powders and thin films were prepared by following a homogeneous co-precipitation method and sol-gel dip-coating technique, respectively, and were treated through 400-800 °C, and then thoroughly investigated by following various characterization techniques. The characterization results suggest that the pure TiO2 powder formed at 550 °C is in rutile phase, whereas the 0.1-10 wt.% Cu-doped TiO2 powders formed at 550 °C are mainly in anatase phase. These latter powders possess low band-gap energies (3.247-3.265 eV) and flat-band potentials amenable to water oxidation reaction. The 0.5-wt.% Cu-doped TiO2 thin film formed at 550 °C exhibited n-type semiconducting behavior and considerable photocurrent among various investigated powders. The CO2 reduction with a Faradaic efficiency of 82% and ˜ 96% CO selectivity in a two-compartment electrochemical cell was noted at -2500 mV (vs. Ag/Ag+) on pre-reduced (at -2000 mV vs. Ag/AgCl) 50 wt.% Cu-doped TiO2 thin film electrode in conjunction with an ionic liquid. The UV-light-induced TiO2 was found to be responsible for photocatalytic methylene blue (MB) degradation, and TiO2 is not sensitized by MB. The in situ formed compounds of TiO2 and CuO/Cu2O were found to absorb visible light, but showed little visible-light-induced photocatalytic activity.

  7. Influence of TiO2 nanoparticles on cellular antioxidant defense and its involvement in genotoxicity in HepG2 cells

    NASA Astrophysics Data System (ADS)

    Petković, Jana; Žegura, Bojana; Filipič, Metka

    2011-07-01

    We investigated the effects of two types of TiO2 nanoparticles (<25 nm anatase, TiO2-An; <100 nm rutile, TiO2-Ru) on cellular antioxidant defense in HepG2 cells. We previously showed that in HepG2 cells, TiO2 nanoparticles are not toxic, although they induce oxidative DNA damage, production of intracellular reactive oxygen species, and up-regulation of mRNA expression of DNA-damage-responsive genes (p53, p21, gadd45α and mdm2). In the present study, we measured changes in mRNA expression of several antioxidant enzymes: catalase, superoxide dismutase, glutathione peroxidase, nitric oxide synthase, glutathione reductase and glutamate-cysteine ligase. As reduced glutathione has a central role in cellular antioxidant defense, we determined the effects of TiO2 nanoparticles on changes in the intracellular glutathione content. To confirm a role for glutathione in protection against TiO2-nanoparticle-induced DNA damage, we compared the extent of TiO2-nanoparticle-induced DNA damage in HepG2 cells that were glutathione depleted with buthionine-(S,R)-sulfoximine pretreatment and in nonglutathione-depleted cells. Our data show that both types of TiO2 nanoparticles up-regulate mRNA expression of oxidative-stress-related genes, with TiO2-Ru being a stronger inducer than TiO2-An. Both types of TiO2 nanoparticles also induce dose-dependent increases in intracellular glutathione levels, and in glutathione-depleted cells, TiO2-nanoparticle-induced DNA damage was significantly greater than in nonglutathione-depleted cells. Interestingly, the glutathione content and the extent of DNA damage were significantly higher in TiO2-An- than TiO2-Ru-exposed cells. Thus, we show that TiO2 nanoparticles cause activation of cellular antioxidant processes, and that intracellular glutathione has a critical role in defense against this TiO2-nanoparticle-induced DNA damage.

  8. Ultra-long Pt nanolawns supported on TiO2-coated carbon fibers as 3D hybrid catalyst for methanol oxidation

    PubMed Central

    2012-01-01

    In this study, TiO2 thin film photocatalyst on carbon fibers was used to synthesize ultra-long single crystalline Pt nanowires via a simple photoreduction route (thermally activated photoreduction). It also acted as a co-catalytic material with Pt. Taking advantage of the high-aspect ratio of the Pt nanostructure as well as the excellent catalytic activity of TiO2, this hybrid structure has the great potential as the active anode in direct methanol fuel cells. The electrochemical results indicate that TiO2 is capable of transforming CO-like poisoning species on the Pt surface during methanol oxidation and contributes to a high CO tolerance of this Pt nanowire/TiO2 hybrid structure. PMID:22546416

  9. TiO2 Processed by pressurized hot solvents as a novel photocatalyst for photocatalytic reduction of carbon dioxide

    NASA Astrophysics Data System (ADS)

    Reli, Martin; Kobielusz, Marcin; Matějová, Lenka; Daniš, Stanislav; Macyk, Wojciech; Obalová, Lucie; Kuśtrowski, Piotr; Rokicińska, Anna; Kočí, Kamila

    2017-01-01

    Anatase-brookite TiO2 photocatalysts were prepared by the sol-gel process controlled within reverse micelles and processing by pressurized hot solvents-water/methanol/water (TiO2(M)) and water/ethanol/water (TiO2(E)), as an unconventional alternative to common calcination. The main goal of this work was to prepare anatase-brookite mixtures by processing by two different alcohols (methanol and ethanol) and evaluate the influence of the alcohol on the photocatalytic activity. Prepared photocatalysts were characterized by organic elemental analysis, nitrogen physisorption, XRD, UV-vis, photoelectrochemical and spectroelectrochemical measurements and XPS. The prepared photocatalysts efficiency was tested on the photocatalytic reduction of carbon dioxide and compared with commercial TiO2 Evonik P25. Both prepared nanocomposites were more efficient towards methane production but Evonik P25 was the most efficient towards hydrogen generated through water splitting. The higher performance of anatase-brookite mixture towards methane production can be explained by (i) a higher photocatalytic activity of brookite than rutile; (ii) a large surface area of anatase-brookite composites enabling better carbon dioxide adsorption; (iii) the photoinduced electron transfer from the brookite conduction band to the anatase conduction band. On the other hand, a higher production of hydrogen in the presence of Evonik P25 is caused by a better charge separation in anatase-rutile than anatase-brookite phase compositions. TiO2(M) appeared more active than TiO2(E) in the photocatalytic reduction of carbon dioxide due to a lower density of defects created in the crystal lattice.

  10. Enhanced photocatalytic performance of porous TiO2 nanobelts with phase junctions

    NASA Astrophysics Data System (ADS)

    Pang, Lai-xue; Wang, Xiao-ying; Tang, Xin-de

    2015-01-01

    Porous TiO2 nanobelts with rutile/anatase phase junctions are successfully prepared through a hydrothermal route and ion exchange process. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to characterize the products. The photocatalytic performance of the porous nanobelts was evaluated by measuring the degradation of methyl blue under UV light irradiation. The photocatalytic activity of the porous nanobelts is much superior to that of P-25 and pristine non-porous nanobelts. The excellent photocatalytic of porous nanobelts can be attributed to pores which enhanced ability in UV-light harvesting. What's more, the existence of rutile/anatase phase junction is favorable for the formation and separation of the hole-electron pair, resulting in a reduced electron-hole recombination.

  11. Fine-grained rutile in the Gulf of Maine - diagenetic origin, source rocks, and sedimentary environment of deposition

    USGS Publications Warehouse

    Valentine, P.C.; Commeau, J.A.

    1990-01-01

    The Gulf of Maine, an embayment of the New England margin, is floored by shallow, glacially scoured basins that are partly filled with late Pleistocene and Holocene silt and clay containing 0.7 to 1.0 wt percent TiO2 chiefly in the form of silt-size rutile. Much of the rutile in the Gulf of Maine mud probably formed diagenetically in poorly cemented Carboniferous and Triassic coarse-grained sedimentary rocks of Nova Scotia and New Brunswick after the dissolution of titanium-rich detrital minerals (ilmenite, ilmenomagnetite). The diagenesis of rutile in coarse sedimentary rocks (especially arkose and graywacke) followed by erosion, segregation, and deposition (and including recycling of fine-grained rutile from shales) can serve as a model for predicting and prospecting for unconsolidated deposits of fine-grained TiO2. -from Authors

  12. Electrodeposition of single-crystalline molybdenum layers from tungstate-molybdate melts

    SciTech Connect

    Esina, N.O.; Tarasova, K.P.; Baraboshkin, A.N.

    1987-07-01

    The structure and growth rates of single-crystalline molybdenum layers produced by electrolysis of tungstate-molybdate melts on single-crystalline substrates with the orientations (110), (112), (100), and (111) were investigated. Growth pyramids having a symmetry coincident with that of the substrate plane were revealed as the characteristic feature of surface structure of these layers. The change from single- to polycrystalline molybdenum structure occurs via the development of twinning defects.

  13. Increased visible-light photocatalytic activity of TiO2 via band gap manipulation

    NASA Astrophysics Data System (ADS)

    Pennington, Ashley Marie

    Hydrogen gas is a clean burning fuel that has potential applications in stationary and mobile power generation and energy storage, but is commercially produced from non-renewable fossil natural gas. Using renewable biomass as the hydrocarbon feed instead could provide sustainable and carbon-neutral hydrogen. We focus on photocatalytic oxidation and reforming of methanol over modified titanium dioxide (TiO2) nanoparticles to produce hydrogen gas. Methanol is used as a model for biomass sugars. By using a photocatalyst, we aim to circumvent the high energy cost of carrying out endothermic reactions at commercial scale. TiO2 is a semiconductor metal oxide of particular interest in photocatalysis due to its photoactivity under ultraviolet illumination and its stability under catalytic reaction conditions. However, TiO2 primarily absorbs ultraviolet light, with little absorption of visible light. While an effective band gap for absorbance of photons from visible light is 1.7 eV, TiO2 polymorphs rutile and anatase, have band gaps of 3.03 eV and 3.20 eV respectively, which indicate ultraviolet light. As most of incident solar radiation is visible light, we hypothesize that decreasing the band gap of TiO2 will increase the efficiency of TiO2 as a visible-light active photocatalyst. We propose to modify the band gap of TiO2 by manipulating the catalyst structure and composition via metal nanoparticle deposition and heteroatom doping in order to more efficiently utilize solar radiation. Of the metal-modified Degussa P25 TiO2 samples (P25), the copper and nickel modified samples, 1%Cu/P25 and 1%Ni/P25 yielded the lowest band gap of 3.05 eV each. A difference of 0.22 eV from the unmodified P25. Under visible light illumination 1%Ni/P25 and 1%Pt/P25 had the highest conversion of methanol of 9.9% and 9.6%, respectively.

  14. Effect of vanadium admixing on the surface structure of TiO2(110) under non-oxidizing conditions

    NASA Astrophysics Data System (ADS)

    Song, Xin; Primorac, Elena; Kuhlenbeck, Helmut; Freund, Hans-Joachim

    2016-11-01

    Single crystalline Ti + V mixed oxide layers have been prepared by doping vanadium into TiO2(110) thin films on TiO2(110) single crystal substrates with a Ti + Ta mixed oxide interlayer between the film and the substrate. The interlayer prevents the diffusion of vanadium into the substrate and also the diffusion of Ti3 + between substrate and overlayer. Mixing vanadium into the TiO2 lattice increases the reducibility of the host oxide as concluded from an appreciable degree of reduction produced by comparatively mild annealing. A high density of bridging oxygen vacancies was identified at the surface of films with a low vanadium content (2%) while a (1 × 2) reconstruction as also known for massively reduced TiO2(110) was observed for layers with 8% of vanadium. Studies of methanol adsorption indicate that the vanadium atoms are mostly located below the surface since there is no indication of a vanadium-methanol interaction. We provide evidence that the reducibility of the vanadium ions in the thin film is higher than that of the titanium ions and we suggest that this is the origin of the increased reducibility of the mixed oxide.

  15. Surface Compositional, Structural and Optical Properties of Nanohybrid TiO2/ZnO Coated Silicone Surface

    NASA Astrophysics Data System (ADS)

    Achoi, M. F.; Gambar, M. Z. M.; Rusop, M.; Abdullah, S.

    2013-04-01

    This paper reports on preparation and characterizations of nanohybrid TiO2/ZnO using sol-gel spin-coating techniques. The study involved of modification band-gap energy of Titanium dioxide (TiO2) at different precursor molecular concentration of Zinc oxide (ZnO). The Field Emission Scanning Electron Microscope (FESEM) for morphological characterization showed the existence of TiO2 and ZnO particles at 20 nm scale of magnification. The compositional of both particles were then confirmed using Energy Disperse Analyzer X-Ray (EDAX) analysis which indicates the elements of Ti, O and Zn exhibited EDAX spectras at about 0.5 and 1.0 keV while silicone (Si) at 1.75 keV. The X-Ray diffraction (XRD) characterized the structural properties of anatase and rutile for TiO2, and zincite for ZnO, then crystallite size for both elements. AT optimum molar concentration ratio of nanohybrid TiO2/ZnO is 1:4 (0.20M), the crystallite size, d, is 23.71 nm with peak of anatase found at diffraction angle of 48.05° and 62.50° while at 33.25° and 55.06° is rutile phase, respectively. We have found the distribution of nanohybrid TiO2/ZnO particles dispersed homogeneously since the particles were not bonded together with increasing ZnO molar concentration. From Ultra-Violet/Visible-near-infrared spectroscopy (UV-Vis-NiR), we have found the optical band-gap energy of nanohybrid TiO2/ZnO was increased at 3.38 eV, while the transmittance percentage is 88.67%. This studied was successfully improved the optical band-gap energy of TiO2 and the results suggests for improvement of optical band-gap energy TiO2.

  16. Molecular-Level Insights into Photocatalysis from Scanning Probe Microscopy Studies on TiO2(110)

    SciTech Connect

    Henderson, Michael A.; Lyubinetsky, Igor

    2013-06-12

    The field of heterogeneous photocatalysis has grown considerably in the decades since Fujishima and Honda's ground-breaking publications of photoelectrochemistry on TiO2. Numerous review articles continue to point to both progress made in the use of heterogeneous materials (such as TiO2) to perform photoconversion processes, and the many opportunities and challenges in heterogeneous photocatalysis research such as solar energy conversion and environmental remediation. The past decade has also seen an increase in the use of molecular-level approaches applied to model single crystal surfaces in an effort to obtain new insights into photocatalytic phenomena. In particular, scanning probe techniques (SPM) have enabled researchers to take a ‘nanoscale’ approach to photocatalysis that includes interrogation of the reactivities of specific sites and adsorbates on a model photocatalyst surface. The rutile TiO2(110) surface has become the prototypical oxide single crystal surface for fundamental studies of many interfacial phenomena. In particular, TiO2(110) has become an excellent model surface for probing photochemical and photocatalytic reactions at the molecular level. A variety of experimental approaches have emerged as being ideally suited for studying photochemical reactions on TiO2(110), including desorption-oriented approaches and electronic spectroscopies, but perhaps the most promising techniques for evaluating site-specific properties are those of SPM. In this review, we highlight the growing use of SPM techniques in providing molecular-level insights into surface photochemistry on the model photocatalyst surface of rutile TiO2(110). Our objective is to both illustrate the unique knowledge that scanning probe techniques have already provided the field of photocatalysis, and also to motivate a new generation of effort into the use of such approaches to obtain new insights into the molecular level details of photochemical events occurring at interfaces

  17. Photocatalytic degradation of methylene blue over nanosized TiO2 particles prepared using the self-propagating high-temperature synthesis method.

    PubMed

    Park, Chul-Min; Seo, Hyeong-Seok; Cho, Jung-Ho; Choi, Da-Hye; Jeong, Young-Shin; Chung, Min-Chul; Jung, Sang-Chul; Jeong, Woon-Jo; Ban, Jae-Sam; Ahn, Ho-Geun

    2013-08-01

    In order to reutilize the spent metallic titanium chips, TiO2 photocatalysts were prepared using the self-propagating high-temperature synthesis (SHS) method, and were characterized by N2 gas adsorption, X-ray diffraction, and scanning electron microscope, particle size distribution. Also, their photocatalytic activities were evaluated using methylene blue as a model organic compound. It was confirmed that the crystal structure of TiO2 prepared by SHS method was relatively homogeneous powder of rutile type. Optimum conditions for photocatalytic degradation of methylene blue under UV-C irradiation were methylene blue 9.5 ppm in solution and at amount of TiO2 added of 0.02 g/L. In addition, it was found that the photocatalytic activity for methylene blue degradation over the prepared TiO2 particles was positively related with BET specific surface area.

  18. Electrorheological behaviour under oscillatory shear of TiO2 rod-like particles prepared via microwave-assisted molten-salt synthesis

    NASA Astrophysics Data System (ADS)

    Sedlacik, M.; Mrlik, M.; Pavlinek, V.; Kozakova, Z.; Saha, P.

    2013-02-01

    Titanium dioxide (TiO2) rod-like particles were synthesized by a simple and rapid microwave-assisted molten-salt method. The X-ray diffraction analysis and electron microscopy provided information on particle composition and morphology, respectively. It was found that during the synthesis process the crystalline phase of TiO2 transformed from anatase into rutile while the morphology changed from nanospheres into micrometer sized rod-like particles. The electrorheological (ER) properties were investigated via oscillatory shear tests. It was found that TiO2 rod-like particles based silicone oil suspensions exhibited higher ER activity than those of original anatase TiO2 nanoparticles probably due to side-by-side solid friction between particles as well as shorter time of their polarization. The changes in ER properties of rod-like particle based suspensions as a function of the applied electric field strength and particles weight fraction were also investigated.

  19. Lattice strain alteration and activation energy of phase transformation of TiO2 nanorods doped with silver and iron oxides

    NASA Astrophysics Data System (ADS)

    Riazian, M.

    2013-10-01

    TiO2 nanorods are synthesized by a thermal corrosion. In present work, synthesis of TiO2 nanorods in anatase, rutile and Ti8O15 phases, TiO2 nanorods embedded with silver and iron oxides as dopant by using the sol-gel method and alkaline corrosion are reported. The morphologies and crystal structures of TiO2 nanorods are characterized by use of field emission scanning electron microscopy, atomic force microscopy and X-ray diffractometer techniques. The obtained results illustrate an aggregative structure at high calcined temperatures with production of spherical particles. The effects of chemical compositions and calcined temperatures on surface topography and crystallization of phases are studied. Moreover, activation energy of nanoparticles formation in pure and doped state are calculated during thermal treatment.

  20. Frictional Properties of Single Crystalline and Quasicrystalline Surfaces

    NASA Astrophysics Data System (ADS)

    Gellman, Andrew

    2000-03-01

    The use of ultra-high vacuum surface science methods has been aplied to the problem of studying friction between single srystalline and quasicrystalline metal surfaces. A experimental apparatus has been developed that combines the ability to perform surface preparation and analysis with the ability to make measurements of macroscopic friction forces between surfaces in sliding contact. This UHV chamber allows simultaneous preparation and characterization of two sample surfaces. These are usually single crystalline samples of the same metal and can be either perfectly clean or modified by adsorbed species such as atoms or molecules. Once prepared these two surfaces can be brought into contact under an applied normal load (Fn = 0.001 0.1 N) and sheared relative to one another at constant velocity (vs = 1 100 mm/s). Both normal and shear forces are measured simultaneously enabling one to determine a coefficient of friction. This unique apparatus has been used to study a number of problems in tribology. Adsorbed species on metal surfaces serve as a lubricants and prevent direct metal-metal contact. We have addressed the issue of surface coverage effects on interfacial friction. Surfaces have been prepared with adsorbed species ranging continuously in coverage from zero monolayers to many ( 100) monolayers. These experiments have been performed with pairs of both Ni(100) and Cu(111) surfaces. The interesting observation has been that adsorbed layers of atoms have little or no influence on friction coefficients between the two surfaces at coverages below one monolayer. Adsorbed molecules such as ethanol or trifluoroethanol are more interesting in this regard. They also have little influence on friction when adsorbed at coverages of < 1 monolayer, however, once the coverage exceeds 1 monolayer the coefficient of friction drops substantially. Friction reaches its limit at coverages of 5 10 monolayer. It is quite interesting to note that these metal single crystal surface

  1. Electrical and optical properties of TiO2 anatase thin films

    NASA Astrophysics Data System (ADS)

    Tang, H.; Prasad, K.; Sanjinès, R.; Schmid, P. E.; Lévy, F.

    1994-02-01

    Electrical and optical spectroscopic studies of TiO2 anatase thin films deposited by sputtering show that the metastable phase anatase differs in electronic properties from the well-known, stable phase rutile. Resistivity and Hall-effect measurements reveal an insulator-metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self-trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.

  2. Fano resonances in photoconductivity spectra of hydrogen donors in ZnO and rutile

    NASA Astrophysics Data System (ADS)

    Lavrov, E. V.; Herklotz, F.; Weber, J.

    2015-02-01

    The results of photoconductivity studies of hydrogen donors in ZnO and rutile TiO2 are presented. It is shown that local vibrational modes of O-H bonds comprising donors in both semiconductors can be detected in photoconductivity spectra as Fano resonances at 3611 and 3290 cm-1 in the case of ZnO and TiO2, respectively. The frequencies of these features red-shift in energy down to 2668 (ZnO) and 2445 cm-1 (TiO2) if hydrogen is substituted by deuterium. Based on the frequency of the deuterium resonance it is concluded that the ionization energy of the hydrogen donor in TiO2 is less than 300 meV, which is in variance with predictions of theory. The reasons for such a discrepancy are discussed.

  3. Effect of the nanocrystalline structure type on the optical properties of TiO2:Nd (1 at.%) thin films

    NASA Astrophysics Data System (ADS)

    Mazur, Michal; Wojcieszak, Damian; Kaczmarek, Danuta; Domaradzki, Jaroslaw; Zatryb, Grzegorz; Misiewicz, Jan; Morgiel, Jerzy

    2015-04-01

    Titanium dioxide thin films, each doped with the same amount of neodymium (1 at.%) were deposited by Low Pressure Hot Target Reactive Sputtering and High Energy Reactive Magnetron Sputtering processes in order to obtain anatase and rutile thin film structures respectively. The microstructure and phase composition were analyzed using the transmission electron microscopy method including high resolution electron microscopy imaging. The measurements of the optical properties showed, that both prepared thin films were transparent in the visible light range and had a low extinction coefficient of ca. 3 ṡ 10-3. The thin film with the anatase structure had a lower cut-off wavelength and refractive index and a higher value of optical energy band gap as-compared to the TiO2:Nd coating with the rutile structure. Simultaneously, more efficient photoluminescence emission was observed for the rutile thin films.

  4. Influence of pH on the formulation of TiO2 powder prepared by co-precipitation of TiCl3 and photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Yudoyono, Gatut; Zharvan, Vicran; Ichzan, Nur; Daniyati, Rizqa; Indarto, Bachtera; Pramono, Yono Hadi; Zainuri, Mochamad; Darminto

    2016-02-01

    Titanium dioxide (titania) nanoparticle were synthesized by coprecipitation process of titanium trichloride (TiCl3) in aqueous medium, with NH4OH as pH regulator. The pH solution was varied during the synthesis process between pH 3-8.4, and all samples were calcined temperature at 400°C for 3 hours. Characteristics and properties of the TiO2 powder were investigated using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM). XRD results show that the single-phase rutile formed when the pH is less than 5, anatase single phase formed began pH 8, and the pH of the solution between 5-8 formed mixed phase rutile-anatase-brookite, rutile-brookite or anatase-brookite. Methylene Blue (MB) photodegradation test were performed in order to evaluate photocatalytic activity. Nanoparticles TiO2 rutile, anatase phase, and mixed phase rutile-brookite, anatase-brookite used to test the photocatalytic activity by measuring the absorbance spectrum photodegradation using UV-Vis spectrometer. The test results showed that the mixture phase of rutile-brookite provide the greatest photodegradation than other phases.

  5. Structural, photoluminescent and photocatalytic properties of TiO2:Eu3+ coatings formed by plasma electrolytic oxidation

    NASA Astrophysics Data System (ADS)

    Stojadinović, Stevan; Radić, Nenad; Grbić, Boško; Maletić, Slavica; Stefanov, Plamen; Pačevski, Aleksandar; Vasilić, Rastko

    2016-05-01

    In this paper, we used plasma electrolytic oxidation (PEO) of titanium in water solution containing 10 g/L Na3PO4·12H2O + 2 g/L Eu2O3 powder for preparation of TiO2:Eu3+ coatings. The surfaces of obtained coatings exhibit a typical PEO porous structure. The energy dispersive X-ray spectroscopy analysis showed that the coatings are mainly composed of Ti, O, P, and Eu; it is observed that Eu content in the coatings increases with PEO time. The X-ray diffraction analysis indicated that the coatings are crystallized and composed of anatase and rutile TiO2 phases, with anatase being the dominant one. X-ray photoelectron spectroscopy revealed that Ti 2p spin-orbit components of TiO2:Eu3+ coatings are shifted towards higher binding energy, with respect to pure TiO2 coatings, suggesting that Eu3+ ions are incorporated into TiO2 lattice. Diffuse reflectance spectroscopy showed that TiO2:Eu3+ coatings exhibit evident red shift with respect to the pure TiO2 coatings. Photoluminescence (PL) emission spectra of TiO2:Eu3+ coatings are characterized by sharp emission bands in orange-red region ascribed to f-f transitions of Eu3+ ions from excited level 5D0 to lower levels 7FJ (J = 0, 1, 2, 3, and 4). The excitation PL spectra of TiO2:Eu3+ coatings can be divided into two regions: the broad band region from 250 nm to 350 nm associated with charge transfer state of Eu3+ and the series of sharp peaks in the range from 350 nm to 550 nm corresponding to direct excitation of the Eu3+ ions. It is observed that the intensity of peaks in excitation and emission PL spectra increases with the concentration of Eu3+, but the peak positions remain practically unchanged. The ratio of PL emission for electric and magnetic dipole transitions indicates highly asymmetric environment around Eu3+ ions. The photocatalytic activity (PA) of TiO2:Eu3+ coatings is evaluated by measuring the photodegradation of methyl orange under simulated sunlight conditions. It is shown that PEO time, i.e., the amount

  6. Optical and electrical properties of nanocrystalline TiO2:Pd semiconducting oxides

    NASA Astrophysics Data System (ADS)

    Sieradzka, Karolina; Kaczmarek, Danuta; Domaradzki, Jarosław; Prociów, Eugeniusz; Mazur, Michał; Górnicka, Barbara

    2011-04-01

    Electrical and optical properties of TiO2:Pd thin films deposited from Ti-Pd mosaic targets sputtered in reactive oxygen plasma have been studied. The properties were investigated for thin films with the Pd amount of 5.5 at. %, 8.4 at. % and 23 at. %. Based on resistivity measurements a drop from 103 down to almost 10-3Ωcm has been recorded when the Pd amount was varied from 5.5 at. % to 23 at. %, respectively. Moreover, it was shown that doping with different amounts of Pd results in the possibility of obtaining both types of electrical conduction: n-type for the TiO2 with 5.5 at. % and 8.4 at. % of Pd and p-type for the TiO2 with 23 at. % of Pd thin films. From optical measurements it has been found that as the Pd amount was increased the transmission through the thin films was reduced and position of the fundamental absorption edge was shifted toward a longer wavelength range of up to 600 nm. The optical band gap was calculated for direct and indirect transitions from optical absorption spectra. Structural properties were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The XRD patterns displayed occurrence of the crystalline, TiO2-rutile for lower Pd amounts (5.5 at. %, 8.4 at. %), while the TiO2:Pd (23 at. %) thin films displayed XRD-amorphous behaviour. Images obtained from AFM displayed dense, nanocrystalline structure with homogenous distribution of crystallites. Additionally performed secondary ion mass spectroscopy investigation confirmed homogenous distribution of Pd in the whole thickness of the prepared thin films.

  7. Novel Nanostructures of Rutile Fabricated by Templating against Yarns of Polystyrene Nanofibrils and Their Catalytic Applications

    PubMed Central

    Lu, Ping; Xia, Younan

    2013-01-01

    This article describes a facile approach to the synthesis of rutile nanostructures in the form of porous fibers or bundles of nanotubes by maneuvering the surface wettability of yarns made of polystyrene nanofibrils. Specifically, hierarchically porous fibers were obtained by hydrolyzing titanium tetraisopropoxide to form TiO2 nanoparticles in the void spaces among hydrophobic nanofibrils in each yarn. After calcination in air at 800 °C, the resultant fibers were comprised of many interconnected rutile nanoparticles whose diameters were in the range of 20–80 nm. After converting the nanofibrils and yarns into hydrophilic surfaces through plasma treatment, however, the TiO2 formed conformal coatings on the surfaces of nanofibrils in each yarn during hydrolysis instead of just filling the void spaces among the nanofibrils. As a result, bundles of rutile nanotubes were obtained after the sample had been calcined in air at 800 °C. The thermodynamically stable rutile nanostructures were then explored as supports for Pt nanoparticles whose catalytic activity was evaluated using the reduction of p-nitrophenol by NaBH4. The Pt supported on porous rutile fibers exhibited a better performance than the Pt on rutile nanotubes in terms of both induction time (tind) and apparent rate constant (kapp). PMID:23763369

  8. Dye-sensitized solar cells based on anatase TiO2 nanoparticle/nanowire composites.

    PubMed

    Tan, Bing; Wu, Yiying

    2006-08-17

    Dye-sensitized solar cells were fabricated based on the composites of anatase TiO2 nanoparticles and single crystalline anatase TiO2 nanowires. Nanoparticle/nanowire composites can possess the advantages of both building blocks, i.e., the high surface area of nanoparticle aggregates and the rapid electron transport rate and the light scattering effect of single-crystalline nanowires. Three different composites were prepared with 5 wt %, 20 wt %, and 77 wt % nanowires, respectively. The performances of composite solar cells were compared with pure nanoparticle cells at a series of film thickness. With low nanowire concentrations (5 wt % and 20 wt %), the composite films maintain similar specific surface area as the pure nanoparticle films, while the composite cells show higher short-circuit current density and open-circuit voltage. An enhancement of power efficiency from 6.7% for pure nanoparticle cells to 8.6% for the composite cell with 20 wt % nanowires has been achieved under 1 Sun AM1.5 illumination (100 mW/cm2). For the composite film with 77 wt % nanowires, the nanowires became the major phase. Their less compact packing resulted in significant decrease of the specific surface area, and thus the current density. However, with the increase of film thickness, the current density showed a continuous increase in the whole thickness range up to 17 microm, indicating the improved electron diffusion length due to the formed nanowire network. The nanowires also helped to preserve crack-free thick films. These results show that employing nanoparticle/nanowire composites represents a promising approach for further improving the efficiencies of sensitized solar cells.

  9. Porous TiO2 Assembled from Monodispersed Nanoparticles.

    PubMed

    Liu, Xu; Duan, Weijie; Chen, Yan; Jiao, Shihui; Zhao, Yue; Kang, Yutang; Li, Lu; Fang, Zhenxing; Xu, Wei; Pang, Guangsheng

    2016-12-01

    Porous TiO2 were assembled by evaporating or refluxing TiO2 colloid, which was obtained by dispersing the TiO2 nanoparticles with a crystallite size (d XRD) of 3.2 nm into water or ethanol without any additives. Porous transparent bulk TiO2 was obtained by evaporating the TiO2-C2H5OH colloid at room temperature for 2 weeks, while porous TiO2 nanospheres were assembled by refluxing the TiO2-H2O colloid at 80 °C for 36 h. Both of the porous TiO2 architectures were pore-size-adjustable depending on the further treating temperature. Porous TiO2 nanospheres exhibited enhanced photocatalysis activity compared to the nanoparticles.

  10. Photocatalitic Properties of Tio2 and ZnO Nanopowders / Tio2 un Zno Nanopulveru Fotokatalitiskās Īpašības

    NASA Astrophysics Data System (ADS)

    Grigorjeva, L.; Rikveilis, J.; Grabis, J.; Jankovica, Dz.; Monty, C.; Millers, D.; Smits, K.

    2013-08-01

    Photocatalytic activity of TiO2 and ZnO nanopowders is studied depending on the morphology, grain sizes and method of synthesizing. Photocatalysis of the prepared powders was evaluated by degradation of the methylene blue aqueous solution. Absorbance spectra (190-100 nm) were measured during exposure of the solution to UV light. The relationships between the photocatalytic activity and the particle size, crystal polymorph phases and grain morphology were analyzed. The photocatalytic activity of prepared TiO2 nanopowders has been found to depend of the anatase-to-rutile phase ratio. Comparison is given for the photocatalytic activity of ZnO nanopowders prepared by sol-gel and solar physical vapour deposition (SPVD) methods Darbā pētīta fotokatalīzes efektivitāte ar dažādām metodēm sintezētiem TiO2 and ZnO nanopulveriem, kuriem ir atšķirīga morfoloģija un grauda izmērs. Foto katalīzes process raksturots ar metilenzilā sagraušanu ūdens šķīdumā, to apstarojot ar UV gaismu. Analizēta fotokatalīzes efektivitātes atkarība no grauda izmēra, nanokristālu graudu morfoloģijas, TiO2 nanopulveru anatasa-rutīla fāžu svara attiecībām. Parādīts, ka fotokatalītiskā efektivitāte ir atšķirīga TiO2 nanopulveriem sintezētiem ar dažādām metodēm: sola-gēla un tvaicēšanu-kondensēšanu saules reaktorā. Salīdzināta fotokatalīzes efektivitāte ZnO un TiO2 nanopulveriem un secināts, ka ZnO nanopulveri ar tetrapodu morfoloģiju ir labs fotokatalizators

  11. Visible light induced electron transfer process over nitrogen doped TiO(2) nanocrystals prepared by oxidation of titanium nitride.

    PubMed

    Wu, Zhongbiao; Dong, Fan; Zhao, Weirong; Guo, Sen

    2008-08-30

    Nitrogen doped TiO(2) nanocrystals with anatase and rutile mixed phases were prepared by incomplete oxidation of titanium nitride at different temperatures. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), core level X-ray photoelectron spectroscopy (CL XPS), valence band X-ray photoelectron spectroscopy (VB XPS), UV-vis diffuse reflectance spectra (UV-vis DRS), and visible light excited photoluminescence (PL). The photocatalytic activity was evaluated for photocatalytic degradation of toluene in gas phase under visible light irradiation. The visible light absorption and photoactivities of these nitrogen doped TiO(2) nanocrystals can be clearly attributed to the change of the additional electronic (N(-)) states above the valence band of TiO(2) modified by N dopant as revealed by the VB XPS and visible light induced PL. A band gap structure model was established to explain the electron transfer process over nitrogen doped TiO(2) nanocrystals under visible light irradiation, which was consistent with the previous theoretical and experimental results. This model can also be applied to understand visible light induced photocatalysis over other nonmetal doped TiO(2).

  12. Optical properties of TiO2 thin film grown on quartz substrate by sol-gel method

    NASA Astrophysics Data System (ADS)

    Tian, Jianjun; Deng, Hongmei; Sun, Lin; Kong, Hui; Yang, Pingxiong; Chu, Junhao

    2011-11-01

    TiO2 film was deposited on quartz substrate by sol-gel method. X-ray diffraction analysis and Raman scattering measurement indicate that the TiO2 film is the pure rutile phase structure. From photoluminescence spectra, it is found that the TiO2 film shows a near-infrared luminescence band centered at about 832 nm, and two visible luminescence bands centered at about 426 nm and 524 nm, respectively. The refractive index n, extinct coefficient k, optical band gap EOBG and thickness d of TiO2 film were extracted by fitting transmission spectra with the Adachi's dielectric function model and a three-phase layered model. It is found that n value increases and then decreases with increasing wavelength, while k decreases continuously. The thickness of TiO2 film is about 297 nm. EOBG value is about 3.72eV and larger than that attained by Tauc's law, which is about 3.28eV.

  13. Optical properties of TiO2 thin film grown on quartz substrate by sol-gel method

    NASA Astrophysics Data System (ADS)

    Tian, Jianjun; Deng, Hongmei; Sun, Lin; Kong, Hui; Yang, Pingxiong; Chu, Junhao

    2012-02-01

    TiO2 film was deposited on quartz substrate by sol-gel method. X-ray diffraction analysis and Raman scattering measurement indicate that the TiO2 film is the pure rutile phase structure. From photoluminescence spectra, it is found that the TiO2 film shows a near-infrared luminescence band centered at about 832 nm, and two visible luminescence bands centered at about 426 nm and 524 nm, respectively. The refractive index n, extinct coefficient k, optical band gap EOBG and thickness d of TiO2 film were extracted by fitting transmission spectra with the Adachi's dielectric function model and a three-phase layered model. It is found that n value increases and then decreases with increasing wavelength, while k decreases continuously. The thickness of TiO2 film is about 297 nm. EOBG value is about 3.72eV and larger than that attained by Tauc's law, which is about 3.28eV.

  14. Development of high efficient visible light-driven N, S-codoped TiO2 nanowires photocatalysts

    NASA Astrophysics Data System (ADS)

    Zhang, Yanlin; Liu, Peihong; Wu, Honghai

    2015-02-01

    One-dimensional (1D) nanowire material (especially nonmetal doped 1D nanowires) synthesized by a facile way is of great significance and greatly desired as it has higher charge carrier mobility and lower carrier recombination rate. N, S-codoped TiO2 nanowires were synthesized using titanium sulfate as a precursor and isopropanol as a protective capping agent by a hydrothermal route. The obtained doped nanowires were characterized by XRD, SEM, HRTEM, SAED, XPS, BET and UV-vis absorption spectrum. The incorporation of N and S into TiO2 NWs can lead to the expansion of its lattice and remarkably lower its electron-transfer resistance. Photocatalytic activity measurement showed that the N, S-codoped TiO2 nanowires with high quantum efficiency revealed the best photocatalytic performance for atrazine degradation under visible light irradiation compared to N, S-codoped TiO2 nanoparticles and S-doped TiO2 nanowires, which was attributed to (i) the synergistic effect of N and S doping in narrowing the band gap, separating electron-hole pairs and increasing the photoinduced electrons, and (ii) extending the anatase-to-rutile transformation temperature above 600 °C.

  15. Linear and nonlinear optical studies of bare and copper doped TiO2 nanoparticles via sol gel technique.

    PubMed

    Rajamannan, B; Mugundan, S; Viruthagiri, G; Praveen, P; Shanmugam, N

    2014-01-24

    In general, the nanoparticles of TiO2 may exist in the phases of anatase, rutile and brookite. In the present work, we used titanium terta iso propoxide and 2-propanol as a common starting material to prepare the precursors of bare and copper doped nanosized TiO2. Then the synthesized products were calcinated at 500°C and after calcination the pure TiO2 nanoparticles in anatase phase were harvested. The crystallite sizes of bare and copper doped TiO2 nanoparticles were calculated from X-ray diffraction analysis. The existence of functional groups of the samples was identified by Fourier transform infrared spectroscopy. The optical properties of bare and doped samples were carried out using UV-DRS and photoluminescence measurements. The surface morphology and the element constitution of the copper doped TiO2 nanoparticles were studied by scanning electron microscope fitted with energy dispersive X-ray spectrometer arrangement. The nonlinear optical properties of the products were confirmed by Kurtz second harmonic generation (SHG) test and the output power generated by the nanoparticle was compared with that of potassium di hydrogen phosphate (KDP).

  16. Photocatalytic Activity and Photocurrent Properties of TiO2 Nanotube Arrays Influenced by Calcination Temperature and Tube Length

    NASA Astrophysics Data System (ADS)

    Hou, Jian; Zhang, Min; Yan, Guotian; Yang, Jianjun

    2012-06-01

    In this article, titanium oxide nanotube arrays (TiO2-NTAs) were fabricated by anodic oxidation in an ethylene glycol (EG) electrolyte solution containing 0.25 wt.% NH4F. By varying anodized time and annealed temperature, the obtained nanotube arrays behaved different photocatalytic (PC) activities and photocurrent properties. These samples were characterized by scanning electronic microscope (SEM), X-ray powder diffraction (XRD). It was indicated in SEM images that TiO2 nanotube manifests highly ordered structure which, however, has been completely destroyed when the temperature comes to 800°C. XRD manifested that TiO2 nanotubes with various kinds of length all possessed anatase crystallite when annealed at 500°C; meanwhile, with certain length, TiO2-NTAs annealed at series calcination temperature range of 300-600°C also presented anatase crystallite, which is gradually enhanced with the increment of temperature. At 700°C, mixed structure was observed which was made up of proportions of overwhelming anatase and toothful rutile. Methyl blue (MB) degradation and photocurrent measurement testified that TiO2-NTAs under 4 h oxidation and 3 h of 600°C calcination manifested the highest activity and photocurrent density.

  17. Microwave-assisted synthesis and photocatalytic properties of sulphur and platinum modified TiO2 nanofibers

    NASA Astrophysics Data System (ADS)

    Drunka, R.; Grabis, J.; Jankovica, Dz; Krumina, A.; Rasmane, Dz

    2015-03-01

    In the present work formation of active TiO2 nanofibers in microwave synthesis and their modification with platinum were studied. Mixture of anatase and rutile nanopowder and 10M KOH solution were used as raw materials. Microwave assisted synthesis method permitted to obtain TiO2 nanofibres with a diameter of 10nm and a specific surface area up to 40.2 m2/g. In order to modify TiO2 nanofibers with platinum it was stirred in H2PtCl6 solution and illuminated with UV irradiation or reduced with sodium boronhydride. To modify titania with sulphur and prepare co-doped nanofibers platinum doped samples were extra treated in hydrogen sulphide atmosphere. Photocatalytic activity was determined by degradation of the methylene blue (MB) solution under UV and visible light irradiation. The obtained samples showed higher photocatalytic activity with respect to pure TiO2 nanofibers. The doped TiO2 nanofibers were appropriate for degradation of harmful organic compounds.

  18. Anatase TiO2 Nanoparticles with Exposed {001} Facets for Efficient Dye-Sensitized Solar Cells

    PubMed Central

    Chu, Liang; Qin, Zhengfei; Yang, Jianping; Li, Xing’ao

    2015-01-01

    Anatase TiO2 nanoparticles with exposed {001} facets were synthesized from Ti powder via a sequential hydrothermal reaction process. At the first-step hydrothermal reaction, H-titanate nanowires were obtained in NaOH solution with Ti powder, and at second-step hydrothermal reaction, anatase TiO2 nanoparticles with exposed {001} facets were formed in NH4F solution. If the second-step hydrothermal reaction was carried out in pure water, the H-titanate nanowires were decomposed into random shape anatase-TiO2 nanostructures, as well as few impurity of H2Ti8O17 phase and rutile TiO2 phase. Then, the as-prepared TiO2 nanostructures synthesized in NH4F solution and pure water were applied to the photoanodes of dye-sensitized solar cells (DSSCs), which exhibited power conversion efficiency (PCE) of 7.06% (VOC of 0.756 V, JSC of 14.80 mA/cm2, FF of 0.631) and 3.47% (VOC of 0.764 V, JSC of 6.86 mA/cm2, FF of 0.662), respectively. The outstanding performance of DSSCs based on anatase TiO2 nanoparticles with exposed {001} facets was attributed to the high activity and large special surface area for excellent capacity of dye adsorption. PMID:26190140

  19. Passivation of pigment-grade TiO2 particles by nanothick atomic layer deposited SiO2 films

    NASA Astrophysics Data System (ADS)

    King, David M.; Liang, Xinhua; Burton, Beau B.; Kamal Akhtar, M.; Weimer, Alan W.

    2008-06-01

    Pigment-grade TiO2 particles were passivated using nanothick insulating films fabricated by atomic layer deposition (ALD). Conformal SiO2 and Al2O3 layers were coated onto anatase and rutile powders in a fluidized bed reactor. SiO2 films were deposited using tris-dimethylaminosilane (TDMAS) and H2O2 at 500 °C. Trimethylaluminum and water were used as precursors for Al2O3 ALD at 177 °C. The photocatalytic activity of anatase pigment-grade TiO2 was decreased by 98% after the deposition of 2 nm SiO2 films. H2SO4 digest tests were performed to exhibit the pinhole-free nature of the coatings and the TiO2 digest rate was 40 times faster for uncoated TiO2 than SiO2 coated over a 24 h period. Mass spectrometry was used to monitor reaction progress and allowed for dosing time optimization. These results demonstrate that the TDMAS-H2O2 chemistry can deposit high quality, fully dense SiO2 films on high radius of curvature substrates. Particle ALD is a viable passivation method for pigment-grade TiO2 particles.

  20. Surface modified TiO2 nanostructure with 3D urchin-like morphology for dye-sensitized solar cell application.

    PubMed

    Shin, Seong Sik; Kim, Dong Wook; Lee, Sangwook; Cho, In-Sun; Kim, Dong Hoe; Park, Jong Hoon; Hong, Kug Sun

    2012-02-01

    Three-dimensional (3D) urchin-like rutile TiO2 powders were synthesized by a mild hydrothermal method without any templates. An individual urchin-like TiO2 powder consists of self-assembled nanorods with a length of about 150 nm and width of about 10 nm. Additionally, the urchin-like TiO2 nanopowders were coated with an ultra-thin ZnO layer in order to modify the surface properties of the nanopowders, and the ZnO layer was confirmed by high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analysis. The ZnO-modified TiO2 was used as a photoelectrode of a dye-sensitized solar cell (DSSC) and the solar cell performances were investigated. In comparison with bare TiO2, ZnO-modified TiO2 improved the photovoltaic performances, i.e., energy conversion efficiency, open circuit voltage, and short circuit current were increased. The higher DSSC performance of ZnO-modified TiO2 was attributed to its higher dye loading and lower charge recombination rate.