Showing papers on "Rutile published in 2017"

UV and visible light photocatalytic activity of Au/TiO 2 nanoforests with Anatase/Rutile phase junctions and controlled Au locations.

Abstract: To magnify anatase/rutile phase junction effects through appropriate Au decorations, a facile solution-based approach was developed to synthesize Au/TiO2 nanoforests with controlled Au locations. The nanoforests cons®isted of anatase nanowires surrounded by radially grown rutile branches, on which Au nanoparticles were deposited with preferred locations controlled by simply altering the order of the fabrication step. The Au-decoration increased the photocatalytic activity under the illumination of either UV or visible light, because of the beneficial effects of either electron trapping or localized surface plasmon resonance (LSPR). Gold nanoparticles located preferably at the interface of anatase/rutile led to a further enhanced photocatalytic activity. The appropriate distributions of Au nanoparticles magnify the beneficial effects arising from the anatase/rutile phase junctions when illuminated by UV light. Under the visible light illumination, the LSPR effect followed by the consecutive electron transfer explains the enhanced photocatalysis. This study provides a facile route to control locations of gold nanoparticles in one-dimensional nanostructured arrays of multiple-phases semiconductors for achieving a further increased photocatalytic activity.

Structure sensitive photocatalytic reduction of nitroarenes over TiO 2 .

Abstract: It is a subject of exploration whether the phase pure anatase or rutile TiO2 or the band alignment due to the heterojunctions in the two polymorphs of TiO2 plays the determining role in efficacy of a photocatalytic reaction. In this work, the phase pure anatase and rutile TiO2 have been explored for photocatalytic nitroarenes reduction to understand the role of surface structures and band alignment towards the reduction mechanism. The conduction band of synthesized anatase TiO2 has been found to be more populated with electrons of higher energy than that of synthesized rutile. This has given the anatase an edge towards photocatalytic reduction of nitroarenes over rutile TiO2. The other factors like adsorption of the reactants and the proton generation did not play any decisive role in catalytic efficacy.

Ligand-free rutile and anatase TiO2 nanocrystals as electron extraction layers for high performance inverted polymer solar cells

Abstract: Ligand-free rutile and anatase TiO2 nanocrystals have been synthesized through a hydrolytic sol–gel reaction. The morphology, crystal structure, elemental composition and band structure of the obtained nanocrystals are characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and UV-visible absorption spectroscopy. These two kinds of nanocrystals could serve as electron extraction layers for improving the performance in inverted polymer solar cells. Compared with the device fabricated by using amorphous TiO2 (6.11%) and rutile TiO2 (6.93%), the device based on anatase TiO2 shows a significant enhancement in power conversion efficiency (7.85%). Meanwhile, the ideal current–voltage model for a single heterojunction solar cell is applied to clarify the junction property of the cell. The model demonstrates that the device based on anatase TiO2 has effective electron extraction and hole-blocking properties.

Low-Temperature Synthesis of Anatase/Rutile/Brookite TiO2 Nanoparticles on a Polymer Membrane for Photocatalysis

Abstract: Removing pollutants from water by using the photocatalyst TiO2 is a highly-promising method. A large amount of work has been done to increase the activity of TiO2, whereas the main two findings are increasing the surface area and applying mixed phase modifications (anatase, brookite, and rutile). Here, we present a method to directly synthesize non-agglomerated TiO2 nanoparticles with different crystal phase ratios via low temperature dissolution-precipitation (LTDRP) on a porous microfiltration membrane (polyethersulfone). The amount of hydrochloric acid and the temperature was varied between 0.1–1 M and 25–130 °C, respectively, while the concentration of titanium precursor (titanium(IV) isopropoxide) was kept unchanged. The TiO2 nanoparticles and the membrane were thoroughly characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), measuring the water contact angle and permeation flux, and examining the degradation of methylene blue. The mixed phase anatase/brookite with a main component being anatase exhibited the highest photocatalytic activity in removing methylene blue. Higher synthesis temperature induces enhanced crystallinity and, subsequently, the degradation rate of methylene blue was improved. Additionally, the photocatalytic activity remains high and unchanged for up to nine repeated cycles, i.e., full recovery of the photocatalytic properties is sustained.

Petrology and Geochronology of Rutile

Abstract: Rutile (TiO2) is an important accessory mineral that, when present, offers a rich source of information about the rock units in which it is incorporated It occurs in a variety of specific microstructural settings, contains significant amounts of several trace elements and is one of the classical minerals used for U–Pb age determination Here, we focus on information obtainable from rutile in its original textural context We do not present an exhaustive review on detrital rutile in clastic sediments, but note that an understanding of the petrochronology of rutile in its source rocks will aid interpretation of data obtained from detrital rutile For further information on the important role of rutile in provenance studies, the reader is referred to previous reviews (eg, Zack et al 2004b; Meinhold 2010; Triebold et al 2012) Coarse rutile is the only stable TiO2 polymorph under all crustal and upper mantle conditions, with the exception of certain hydrothermal environments (Smith et al 2009) As such, we will focus on rutile rather than the polymorphs brookite, anatase and ultrahigh-pressure modifications In this chapter, we first review rutile occurrences, trace element geochemistry, and U–Pb geochronology individually to illustrate the insights that can be gained from microstructures, chemistry and ages Then, in the spirit of petrochronology, we show the interpretational power of combining these approaches, using the Ivrea Zone (Italy) as a case study Finally, we suggest some areas of future research that would improve petrochronologic research using rutile Rutile is a characteristic mineral in moderate- to high pressure metapelitic rocks, in high pressure metamorphosed mafic rocks, and in sedimentary rocks (eg, Force 1980; Frost 1991; Zack et al 2004b; Triebold et al 2012) Rutile also occurs rarely in magmatic rocks, eg, anorthosites, as well as in some hydrothermal systems Coarse-grained …

New carbon xerogel-TiO2 composites with high performance as visible-light photocatalysts for dye mineralization

Abstract: A series of carbon xerogels-TiO2 samples was prepared by sol-gel synthesis, modifying the synthesis procedure to have carbon-TiO2 composite or TiO2-coated materials. Textural, morphological and chemical properties were extensively characterized and correlated with the photocatalytic activity. In the case of composites, a homogeneous and highly mesoporous structure is formed, where the intimate contact between both phases allows a high and homogeneous dispersion of TiO2 nanoparticles. During carbonization, the formation of oxygen vacancies is favoured, but the transition anatase to rutile is avoided by the carbon matrix. In the case of coated samples, microporous materials structured as microspheres were obtained, TiO2 present a greater crystal size and some transformation to rutile. The synergetic role of carbon phase and the formation of oxygen vacancies in the TiO2-phase contribute to narrow the composite band gap in such a manner that all samples are active under visible radiation reaching the total mineralization of the pollutant and the elimination of the toxicity.

Solar-driven Z-scheme water splitting using tantalum/nitrogen co-doped rutile titania nanorod as an oxygen evolution photocatalyst

Abstract: A visible-light-driven water-splitting system that involves two-step photoexcitation (Z-scheme) was constructed using rutile TiO2 nanorod doped with Ta and N (TiO2:Ta/N) as an O2 evolution photocatalyst. The Ta-doped TiO2 nanorods, prepared by a solvothermal synthesis, underwent nitridation to possess visible-light absorption under mild conditions, even at 623 K under an ammonia flow. The TiO2:Ta/N powders modified with a RuO2 cocatalyst were active under visible light up to 540 nm for water oxidation for producing O2 in the presence of reversible electron acceptors (IO3− or Fe3+), while TiO2:N exhibited negligible activity. The results of time-resolved infrared absorption spectroscopy indicated that co-doping Ta with N into TiO2 prolonged the lifetime of photogenerated free electrons, leading to high photocatalytic activity. Simultaneous H2 and O2 evolution via water splitting was achieved using a combination of RuO2-modified TiO2:Ta/N, Ru-loaded SrTiO3:Rh and an Fe3+/Fe2+ redox couple under visible-light irradiation (λ > 420 nm) and under AM 1.5G simulated sunlight.

Photocatalytic Performance of Highly Active Brookite in the Degradation of Hazardous Organic Compounds Compared to Anatase and Rutile

Abstract: The photocatalytic activity of brookite was studied and compared with anatase, rutile, and commercial titania P25 (Degussa). Brookite exhibited relatively high activity in the degradation of different hazardous compounds under sunlight equivalent conditions. Brookite and other titania polymorphs anatase and rutile were hydrothermally synthesized under the similar reaction conditions starting with the same amorphous titania precursor. The highly crystalline titania polymorphs were characterized by XRD, SEM, TG-DSC, Raman- and diffuse reflectance UV–vis spectroscopy. Brookite (B) and anatase (A) crystallized in form of agglomerated spherical-shaped nanoparticles of ca. 10 nm in size. Rutile (R) formed up to 500 nm large rod-like nanocrystals. The band gaps of the titania polymorphs were about 3.25–3.34 eV. The aromatic ring opening in different hazardous compounds was monitored by UV–vis absorption spectroscopy and the mineralization was determined by total organic carbon (TOC) measurements. Additionally, the formation of intermediates was studied by electrospray ionization time-of-flight mass spectra (ESI-TOF-MS). The recalcitrance of organic compounds against the photocatalytic degradation increases in the following order: cinnamic acid R.

Interfacial Manipulation by Rutile TiO2 Nanoparticles to Boost CO2 Reduction into CO on a Metal-Complex/Semiconductor Hybrid Photocatalyst.

Abstract: Metal-complex/semiconductor hybrids have attracted attention as photocatalysts for visible-light CO2 reduction, and electron transfer from the metal complex to the semiconductor is critically important to improve the performance. Here rutile TiO2 nanoparticles having 5–10 nm in size were employed as modifiers to improve interfacial charge transfer between semiconducting carbon nitride nanosheets (NS-C3N4) and a supramolecular Ru(II)–Re(I) binuclear complex (RuRe). The RuRe/TiO2/NS-C3N4 hybrid was capable of photocatalyzing CO2 reduction into CO with high selectivity under visible light (λ > 400 nm), outperforming an analogue without TiO2 by a factor of 4, in terms of both CO formation rate and turnover number (TON). The enhanced photocatalytic activity was attributed primarily to prolonged lifetime of free and/or shallowly trapped electrons generated in TiO2/NS-C3N4 under visible-light irradiation, as revealed by transient absorption spectroscopy. Experimental results also indicated that the TiO2 modifier...

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

Abstract: 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.

Ilmenite breakdown and rutile-titanite stability in metagranitoids: Natural observations and experimental results

Abstract: Rutile and titanite commonly form by replacement of ilmenite in metamorphic rocks. Exhumed orthogneiss from the Western Alps show that titanite is mostly stable below 1 GPa while rutile seems to dominate within rocks recrystallized under higher pressures. We herein investigate phase relationships for four granitic compositions with variable CaO content at medium to high-pressure conditions (0.7–1.6 GPa, 450–650 °C) with a focus on ilmenite breakdown and Ti-bearing species formation. Our piston-cylinder experiments show that, in the investigated P-T range, ilmenite reacts during metamorphism above 1.2–1.4 GPa to form rutile. Below this pressure, titanite is the dominant Ti-bearing species for most granitoid compositions. We also show that the position of this reaction curve is strongly influenced by the whole-rock Ca activity. For low-Ca activities, rutile may be stable down to 0.7 GPa (and below) within ilmenite pseudomorphs while the titanite stability field may extend to pressures >1.3 GPa for Ca-richer compositions. Both species may be stable in one single sample depending on the local Ca activity gradients. The finding of metamorphic rutile within metagranitoids with CaO contents >2 wt% can be considered, under certain conditions, as a reliable indicator of high-pressure metamorphism. This study also highlights the importance of improving our knowledge of the phase relationships between rutile and titanite as a function of P-T-X to better interpret the textural and tectonic history in natural samples as well as the meaning of age values yielded by rutile and titanite geochronometers.

Photocatalytic TiO2 Nanorod Spheres and Arrays Compatible with Flexible Applications

Abstract: In the present study, titanium dioxide nanostructures were synthesized through microwave irradiation. In a typical microwave synthesis, nanorod spheres in the powder form were simultaneously produced with nanorod arrays grown on polyethylene terephthalate (PET) substrates. The syntheses were performed in water or ethanol with limited temperature at 80 °C and 200 °C. A simple and low-cost approach was used for the arrays growth, which involved a PET substrate with a zinc oxide seed layer deposited by spin-coating. X-ray diffraction (XRD) and Raman spectroscopy revealed that synthesis in water result in a mixture of brookite and rutile phases, while using ethanol as solvent it was only observed the rutile phase. Scanning electron microscopy (SEM) showed that the synthesized spheres were in the micrometer range appearing as aggregates of fine nanorods. The arrays maintained the sphere nanorod aggregate structures and the synthesis totally covered the flexible substrates. Transmission electron microscopy (TEM) was used to identify the brookite structure. The optical band gaps of all materials have been determined from diffuse reflectance spectroscopy. Photocatalytic activity was assessed from rhodamine B degradation with remarkable degradability performance under ultraviolet (UV) radiation. Reusability experiments were carried out for the best photocatalyst, which also revealed notable photocatalytic activity under solar radiation. The present study is an interesting and competitive alternative for the photocatalysts existing nowadays, as it simultaneously results in highly photoactive powders and flexible materials produced with low-cost synthesis routes such as microwave irradiation.

Heterogeneous oxidation of elemental mercury vapor over RuO2/rutile TiO2 catalyst for mercury emissions control

Abstract: The catalytic oxidation of elemental mercury (Hg(0)) vapor is an effective way to enhance mercury removal from coal-fired power plants. RuO2 catalyst was found to be an excellent Hg(0) oxidation catalyst. When rutile TiO2 was used as the catalyst support, RuO2 formed well dispersed nano-layers due to the very similar crystal structures of RuO2 and rutile TiO2, giving higher Hg(0) oxidation activity over anatase TiO2 support. The RuO2/rutile TiO2 catalyst can be used at the tail end section of the selective catalytic reduction (SCR) unit for Hg(0) oxidation. It showed good Hg(0) oxidation performance under sub-bituminous and lignite coal simulated flue gas conditions with low concentration of HCl or HBr gas. The RuO2/rutile TiO2 catalyst also showed excellent resistance to SO2 under bituminous coal simulated flue gas, maintaining higher than 90% Hg(0) oxidation with up to 2,000 ppmv SO2 present. The oxidized mercury in a form of HgCl2 has a high solubility in water and can be easily captured by other air pollution control systems such as wet scrubbers in coal-fired power plants.

Analysis of Photocatalytic Nitrogen Fixation on Rutile TiO$_2$(110)

Abstract: Photocatalytic nitrogen fixation provides a promising route to produce reactive nitrogen compounds at benign conditions. Titania has been reported as an active photocatalyst for reduction of dinitrogen to ammonia; however there is little fundamental understanding of how this process occurs. In this work the rutile (110) model surface is hypothesized to be the active site, and a computational model based on the Bayesian error estimation functional (BEEF-vdW) and computational hydrogen electrode is applied in order to analyze the expected dinitrogen coverage at the surface as well as the overpotentials for electrochemical reduction and oxidation. This is the first application of computational techniques to photocatalytic nitrogen fixation, and the results indicate that the thermodynamic limiting potential for nitrogen reduction on rutile (110) is considerably higher than the conduction band edge of rutile TiO$_2$, even at oxygen vacancies and iron substitutions. This work provides strong evidence against the most commonly reported experimental hypotheses, and indicates that rutile (110) is unlikely to be the relevant surface for nitrogen reduction. However, the limiting potential for nitrogen oxidation on rutile (110) is significantly lower, indicating that oxidative pathways may be relevant on rutile (110). These findings suggest that photocatalytic dinitrogen fixation may occur via a complex balance of oxidative and reductive processes.

Quantum Monte Carlo study of the energetics of the rutile, anatase, brookite, and columbite TiO 2 polymorphs

Abstract: The relative energies of the low-pressure rutile, anatase, and brookite polymorphs and the high-pressure columbite polymorph of ${\mathrm{TiO}}_{2}$ have been calculated as a function of temperature using the diffusion quantum Monte Carlo (DMC) method and density functional theory (DFT) The vibrational energies are found to be important on the scale of interest and significant quartic anharmonicity is found in the rutile phase Static-lattice DFT calculations predict that anatase is lower in energy than rutile, in disagreement with experiment The accurate description of electronic correlations afforded by DMC calculations and the inclusion of anharmonic vibrational effects contribute to stabilizing rutile with respect to anatase Our calculations predict a phase transition from anatase to rutile ${\mathrm{TiO}}_{2}$ at $630\ifmmode\pm\else\textpm\fi{}210$ K

Sol-Gel Synthesis of Titanium Dioxide

Abstract: The basic principles of sol-gel synthesis, its advantages and disadvantages along with various applications are discussed. This technique is widely used for making semiconducting metal oxide nanoparticles such as titanium dioxide (TiO2). Depending on the titanium metal precursor type, two different approaches of sol-gel synthesis of TiO2 nanomaterials can be identified and are discussed here: (i) an alcohol-based process where the starting precursor is metal alkoxide and (ii) an aqueous-based process where the starting precursor is inorganic metal salts. The three different phases of TiO2, anatase, rutile and brookite are also discussed. Among the three, anatase is found to be more photocatalytically active than the other two phases. However, anatase was converted into rutile at low temperature; hence, the high-temperature stability of anatase TiO2 and its application as a photocatalyst which has also discussed.

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

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