Showing papers on "Rutile published in 2011"

Review of the anatase to rutile phase transformation

Abstract: Titanium dioxide, TiO2, is an important photocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis.

A two-dimensional phase of TiO 2 with a reduced bandgap

Abstract: Titanium dioxide is the prototypical transition metal oxide photocatalyst However, the larger than 3 eV bandgap of common bulk phases of TiO₂ limits its light absorption to UV light, making it inefficient for solar energy conversion Attempts at increasing visible light activity by narrowing the bandgap of TiO₂ through doping have proven difficult, because of defect-induced charge trapping and recombination sites of photo-excited charge carriers Here, we report the existence of a dopant-free, pure TiO₂ phase with a narrow bandgap This new pure TiO₂ phase forms on the surface of rutile TiO₂(011) by oxidation of bulk titanium interstitials We measure a bandgap of only ~21 eV for this new phase, matching it closely with the energy of visible light

Oxygen Rich Titania: A Dopant Free, High Temperature Stable, and Visible-Light Active Anatase Photocatalyst

Abstract: The simultaneous existence of visible light photocatalytic activity and high temperature anatase phase stability up to 900 °C in undoped TiO2 is reported for the first time. These properties are achieved by the in-situ generation of oxygen through the thermal decomposition of peroxo-titania complex (formed by the precursor modification with H2O2). Titania containing the highest amount of oxygen (16 H2O2-TiO2) retains 100% anatase phase even at 900 °C, where as the control sample exists as 100% rutile at this temperature. The same composition exhibits a six-fold and two-fold increase in visible light photocatalytic activities in comparison to the control sample and the standard photocatalyst Degussa P-25 respectively. Among the various para­meters affecting the photocatalytic action, such as band gap narrowing, textural properties, crystallite size, and anatase phase stability, band gap narrowing was identified as the major factor responsible for the visible light photocatalytic activity. Increased Ti–O–Ti bond strength and upward shifting of the valence band (VB) maximum, which is responsible for the high temperature stability and visible light activity respectively, are identified from FT–IR, XPS, and photoluminescence (PL) spectroscopic studies. It is therefore proposed that the oxygen excess defects present in these titania samples are responsible for the high temperature stability and enhanced visible light photocatalytic activities.

How the Anatase-to-Rutile Ratio Influences the Photoreactivity of TiO2

Abstract: In 1991, Bickley et al. proposed a synergetic effect between anatase and rutile in Degussa P25. Since then, there has been an intensive debate about the correctness of this proposal, the origin of the synergism, and the right polymorph composition. However, a comparison of pure titanium dioxide samples with various anatase-to-rutile ratios, but otherwise identical properties, is missing. In this paper, we report about a series of utterly pure, highly porous titanium dioxide films with identical grain sizes, surface areas, and crystallinity, but varying polymorph compositions. Photocatalytic oxidation of methylene blue was utilized to investigate the influence of the anatase-to-rutile ratio on the photoreactivity. We clearly observe the synergetic effect within a well-defined range of anatase-to-rutile ratios. A film with ∼60% anatase and ∼40% rutile exhibits optimal performance at a 50% improved activity compared with pure anatase.

Visible light responsive iodine-doped TiO2 for photocatalytic reduction of CO2 to fuels

Abstract: Iodine-doped titanium oxide (I-TiO2) nanoparticles that are photocatalitically responsive to visible light illumination have been synthesized by hydrothermal method. The structure and properties of I-TiO2 nanocrystals prepared with different iodine doping levels and/or calcination temperatures were characterized by X-ray diffraction, transmission electron microscopy and diffraction, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. The three nominal iodine dopant levels (5, 10, 15 wt.%) and the two lower calcination temperatures (375, 450 °C) produced mixture of anatase and brookite nanocrystals, with small fraction of rutile found at 550 °C. The anatase phase of TiO2 increased in volume fraction with increased calcination temperature and iodine levels. The photocatalytic activities of the I-TiO2 powders were investigated by photocatalytic reduction of CO2 with H2O under visible light (λ > 400 nm) and also under UV–vis illumination. CO was found to be the major photoreduction product using both undoped and doped TiO2. A high CO2 reduction activity was observed for I-TiO2 catalysts (highest CO yield equivalent to 2.4 μmol g−1 h−1) under visible light, and they also had much higher CO2 photoreduction efficiency than undoped TiO2 under UV–vis irradiation. I-TiO2 calcined at 375 °C has superior activity to those calcined at higher temperatures. Optimal doping levels of iodine were identified under visible and UV–vis irradiations, respectively. This is the first study that investigates nonmetal doped TiO2 without other co-catalysts for CO2 photoreduction to fuels under visible light.

Progress in linking accessory mineral growth and breakdown to major mineral evolution in metamorphic rocks: a thermodynamic approach in the Na2O‐CaO‐K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O‐TiO2‐ZrO2 system

Abstract: Activity-composition (a–x) models have been generated for zirconium-bearing haplogranitic silicate melt and garnet from experimental data on zircon dissolution and natural rock data, respectively. Additionally including the recently proposed a–x model for Zr-bearing rutile [Tomkins et al., Journal of Metamorphic Geology25 (2007) 401], calculated phase diagrams that explicitly include ZrO2 in the bulk composition predict the growth and dissolution of zircon at sub- and supra-solidus conditions. This occurs within the context of the evolution of major metamorphic minerals and mineral assemblages in pressure-temperature-composition space for a metapelitic rock composition. The stability of zircon is a function of the bulk ZrO2 content. Garnet contains insufficient Zr to affect the stability of zircon whereas rutile does contain sufficient Zr that zircon stability can be curtailed in rocks with significant rutile. Silicate melt contains appreciable Zr and zircon abundance varies inversely with melt abundance. Thermometers based on the Zr-content of rutile (and potentially garnet) can be graphically portrayed as compositional contours in mineral assemblage fields on the phase diagrams, thereby potentially adding to the utilization of such thermometers. The ability to calculate phase diagrams explicitly including Zr is a major step towards more systematically linking zircon growth – and zircon geochronology – and accessory phase thermometry in a readily adaptable way to the metamorphic evolution of major silicate minerals in a wide range of rocks.

In situ U–Pb rutile dating by LA-ICP-MS: 208Pb correction and prospects for geological applications

Abstract: Rutile is a common accessory mineral that occurs in a wide spectrum of metamorphic rocks, such as in blueschists, eclogites, and granulites and as one of the most stable detrital heavy minerals in sedimentary rocks. The advent of rutile trace element thermometry has generated increased interest in a better understanding of rutile formation. This study documents important analytical advances in in situ LA-ICP-MS U/Pb geochronology of rutile: (1) Matrix matching, necessary for robust in situ dating is fulfilled by calibrating and testing several rutile standards (R10, R19, WH-1), including the presentation of new TIMS ages for the rutile standard R19 (489.5 ± 0.9 Ma; errors always stated as 2 s). (2) Initial common lead correction is routinely applied via 208Pb, which is possible due to extremely low Th/U ratios (usually <0.003) in most rutiles. Employing a 213 nm Nd:YAG laser coupled to a quadrupole ICP-MS and using R10 as a primary standard, rutile U/Pb concordia ages for the two other rutile standards (493 ± 10 Ma for R19; 2640 ± 50 Ma for WH-1) and four rutile-bearing metamorphic rocks (181 ± 4 Ma for Ivrea metapelitic granulite; 339 ± 7 Ma for Saidenbach coesite eclogite; 386 ± 8 Ma for Fjortoft UHP metapelite; 606 ± 12 Ma for Andrelandia metepelitic granulite) always agree within 2% with the reported TIMS ages and other dating studies from the same localities. The power of in situ U/Pb rutile dating is illustrated by comparing ages of detrital rutile and zircon from a recent sediment from the Christie Domain of the Gawler Craton, Australia. While the U/Pb age spectrum from zircons show several pronounced peaks that are correlated with magmatic episodes, rutile U/Pb ages are marked by only one pronounced peak (at ca 1,675 Ma) interpreted to represent cooling ages of this part of the craton. Rutile thermometry of the same detrital grains indicates former granulite-facies conditions. The methods outlined in this paper should find wide application in studies that require age information of single spots, e.g., provenance studies, single-crystal zoning and texturally controlled dating.

Photocatalytic Activities of Different Well-defined Single Crystal TiO2 Surfaces: Anatase versus Rutile

Abstract: The photocatalytic activities of well-defined TiO2 single-crystal anatase (101) surfaces have been assessed by methanol oxidation and by terephthalic acid hydroxylation evincing the formation of OH• radicals and have been compared with that of rutile single-crystal (001), (100), and (110) surfaces. The results showed that the anatase (101) surface exhibits a higher photocatalytic activity than all investigated rutile surfaces toward the oxidation of methanol and exhibits a comparable activity to that of the rutile (001) surface with respect of terephthalic acid hydroxylation. The rutile (001) surface shows a higher photocatalytic activity than both the rutile (110) and (100) surfaces for both photocatalytic test reactions. Because anatase (101) and rutile (110) are the thermodynamically most stable surfaces, anatase and rutile nanomaterials possess, thus, a large percentage of (101) and (110) surfaces, respectively. This offers a reasonable explanation why anatase nanoparticles usually exhibit higher phot...

Band Lineup and Charge Carrier Separation in Mixed Rutile-Anatase Systems

Abstract: Calculations by the HSE06 functional for rutile and anatase crystals reproduce the observed width of the valence and conduction bands, as well as of the gap. From the band structures the branching point energies are obtained as reference for both phases, allowing us to deduce a generic band alignment scheme without a specific interface model. The results show that both bands of rutile lie higher than those of anatase, so in mixed systems the holes are accumulated in the former while the electrons in the latter. Consequences for photocatalytic and photoelectrochemical applications are discussed.

Stoichiometry Engineering of Monoclinic to Rutile Phase Transition in Suspended Single Crystalline Vanadium Dioxide Nanobeams

Abstract: Coexisting monoclinic M1 (insulating) and rutile (metallic) domains were observed in free-standing vanadium dioxide nanobeams at room temperature. Similar domain structures have been attributed to interfacial strain, which was not present here. Annealing under reducing conditions indicated that a deficiency of oxygen stabilizes the rutile phase to temperatures as low as 103 K, which represents an unprecedented suppression of the phase transition by 238 K. In a complementary manner, oxygen-rich growth conditions stabilize the metastable monoclinic M2 and triclinic T (or M3) phases. A pseudophase diagram with dimensions of temperature and stoichiometry is established that highlights the accessibility of new phases in the nanobeam geometry.

Hydrogen Adsorption and Diffusion on the Anatase TiO2(101) Surface: A First-Principles Investigation

Abstract: The mechanisms of adsorption of hydrogen on the anatase TiO2(101) surface and of its diffusion in the bulk are investigated with DFT calculations and compared with similar results obtained for the diffusion of hydrogen on the rutile (110) surface. Because of the different oxygen environments in anatase and rutile surfaces, the H binding energy on the anatase surface is 0.2−0.3 eV smaller than in rutile. Various processes for H diffusion are investigated using the climbing nudged-elastic-band (cNEB) approach. We have identified three main diffusion mechanisms, leading to migration of H on the surface, diffusion into the bulk, and desorption of H2 molecule. Our calculated activation barrier (Eact) shows that migration of H into the bulk is the kinetically most favorable process.

Photoluminescence of dense nanocrystalline titanium dioxide thin films: effect of doping and thickness and relation to gas sensing.

Abstract: The photoluminescence (PL) of dense nanocrystalline (anatase) TiO2 thin films is reported as a function of calcination temperature, thickness, and tungsten and nickel doping. The dependence of the optical absorption, Raman spectra, and PL spectra on heat treatment and dopants reveals the role of oxygen vacancies, crystallinity, and phase transformation in the performance of TiO2 films used as gas sensors. The broad visible PL from defect states of compact and undoped TiO2 films is found to be much brighter and less sensitive to the presence of oxygen than that of mesoporous films. The dense nanocrystalline grains and the nanoparticles comprising the mesoporous film are comparable in size, demonstrating the importance of film morphology and carrier transport in determining the intensity of defect photoluminescence. At higher calcination temperatures, the transformation to rutile results in the appearance of a dominant near-infrared peak. This characteristic change in the shape of the PL spectra demonstrate...

Water photolysis with a cross-linked titanium dioxidenanowire anode

Abstract: We report efficient water photolysis using a cross-linked TiO2 nanowire anode containing mixed anatase and rutile phases. Under simulated AM 1.5 G illumination, the peak solar energy conversion efficiency is measured to be 1.05%, a new record for TiO2 photoanodes. A photocurrent density as high as 2.6 mA cm−2 is observed when the film thickness is 22 μm. These observations indicate that the high surface area architecture afforded by the cross-linked TiO2 nanowires enables both long optical path lengths and high photon-to-electron conversion efficiency. We also report photocurrent in the visible range due to sub-band gap absorptions, which is enhanced by up to a factor of 10 when the TiO2 nanowires are coated with gold or silver nanoparticles. This enhancement is observed only in thinner (up to 1 μm) TiO2 nanowire films, however, indicating that the effect stems from enhanced light retention by nanoparticle scattering.

How phase composition influences optoelectronic and photocatalytic properties of TiO2

Abstract: In the present study the ratio of rutile and anatase phases in sol−gel-synthe-sized TiO2 was varied by calcination at temperatures ranging from 500 to 900 °C. Changes in opto-electronic properties were analyzed by time-resolved microwave conductance measurements (TRMC) and evaluated by comparison of the photocatalytic activity. The presence of rutile improves the charge separation efficiency by trapping of positive charges at the rutile surface, as derived from the increased levels of conductivity and electron lifetimes. These phenomena result in a decrease in the effective hole concentration at the anatase surface, the TiO2 surface with the highest intrinsic reactivity, when in contact with rutile. Indeed, the presence of rutile results in inferior performance in the degradation of methylene blue and cyclohexane-selective photocatalytic oxidation. The negative effect of the presence of rutile can be compensated by improved morphological properties of the anatase phase, such as those present in P25. A novel structure−activity relationship is proposed and discussed

Synthesis of Nanostructured Reduced Titanium Oxide: Crystal Structure Transformation Maintaining Nanomorphology†

Abstract: There is an increasing need for the synthesis of nanostructured reduced oxides because of their attractive properties; for example, compared with titanium dioxide (TiO2), reduced titanium oxides are attractive for photovoltaics, photocatalysts, and fuel cells owing to their narrow band gap enabling absorption of visible light, chemical stability, and relatively high electrical conductivity, comparable to that of graphite. Generally, reduced titanium oxides have been synthesized by 1) thermal reduction of TiO2 at about 1000 8C with H2 gas or Ti powder, 2) photochemical reduction of TiO2 with UV laser irradiation, or 3) direct synthesis from unique precursors or using laser ablation techniques. These reductive techniques in turn cause particle growth or compositional inhomogeneity, making it difficult to obtain high-quality nanostructures. Ti4O7 and Ti8O15 nanowires were synthesized by annealing H2Ti3O7 nanowires in a hydrogen atmosphere. [2] These nanostructures seem the most sophisticated reported so far; however, particle growth is inevitable and the method seems to be inapplicable to other nanostructures. Since nanostructures are of significant importance for exploiting reduced titanium oxides, development of novel techniques for synthesizing them on the nanoscale is needed. Herein we report a novel method for synthesizing nanostructured reduced titanium oxides by reducing nanostructured TiO2 with a strong reducing agent at much lower temperatures than in conventional techniques. Interestingly, nanostructured reduced titanium oxide with the same morphology as its precursor was obtained, though its crystal structure was transformed from the tetragonal to the hexagonal system. The synthesis is applicable to other nanostructured titanium dioxides, and thus opens up fascinating possibilities for designing nanostructures of reduced titanium oxides for a wide range of applications. We chose TiO2 nanoparticles with rutile structure (tetragonal, P42/mnm), which is a high-temperature phase obtained above about 800 8C and irreversibly stable at room temperature, as precursor. The as-received TiO2 nanoparticles were thoroughly mixed with a fourfold molar excess of CaH2 powder, and then heated at 350 8C for 15 d. Low-temperature reduction with binary metal hydrides was first demonstrated by Hayward et al., who used solid NaH as a reducing agent to topotactically synthesize infinite-layer LaNiO2 from perovskite LaNiO3. [11] Since then, alkali and alkaline earth metal hydrides such as CaH2 and LiH have been employed by Hayward et al. and others to obtain unprecedented reduced phases inaccessible by conventional reduction techniques. The powerful reducing activity even at low temperatures of such binary metal hydrides was expected to enable us to synthesize nanostructured reduced titanium oxides from nanostructured TiO2. The final product was a black powder (see Figure 3), which is typical for reduced titanium oxides. Figure 1 compares the synchrotron powder X-ray diffraction (SXRD) patterns of the rutile TiO2 precursor and the reduced product. After reduction, SXRD patterns significantly changed; all major peaks of the product were readily

Photoelectroactivity and Raman spectroscopy of anodized titania (TiO2) photoactive water-splitting catalysts as a function of oxygen-annealing temperature

Abstract: The photoelectrochemical (PEC) activity of untreated (not anodized) and anodized nanotubular TiO2 films (synthesized by the electrochemical anodization of Ti foil) was correlated with the phase composition of the film as a function of O2-annealing temperature at 400, 500 and 600 °C. TiO2 nanotubes have been shown to be more efficient than polycrystalline TiO2 for the photocatalytic splitting of water. Raman spectroscopy was used to identify the amorphous and crystalline TiO2 phases as well as the carbon species. The amorphous TiO2 nanotubular array (unheated) exhibits a Raman spectrum consistent with TiO68− octahedra having the same average structure as those present in the anatase and rutile phases of TiO2. Ratios of integrated Raman peaks were used as a semi-quantitative measure of the degree of crystallinity for rutile and the rutile/anatase weight ratio in the films. Results show that the anatase-to-rutile transformation on Ti metal initiates at much lower temperatures compared to polycrystalline TiO2 and this is attributed to oxygen vacancies located at the metal/oxide interface. For untreated films, the amorphous TiO2 crystallizes directly to rutile, and the photocurrent density increases almost linearly with rutile crystallinity as the O2-annealing temperature is increased; anatase does not form on untreated O2-annealed Ti foil. By comparison, amorphous TiO2 nanotubular arrays are converted to about three times as much anatase as rutile at 400 °C, where the photocurrent density is only slightly greater than the corresponding untreated film. At 500 °C, however, the photocurrent density increases to 2.3× that of the untreated-oxidized film, where ∼83% of the TiO2 nanotubular film is rutile and ∼17% is anatase; this enhancement is attributed to the increase in surface area and photoactive sites of the rutile provided by the TiO2 nanotubular array architecture acting as a support. At 600 °C the rutile transformation continues (∼92% rutile), but this is countered by the significant loss of surface area and surface photoactive sites due to degradation and collapse of the nanotubular structure as seen by SEM.

Morphology and photocatalytic activity of highly oriented mixed phase titanium dioxide thin films

Abstract: Thin TiO2 films on quartz substrates were prepared by spin coating of undoped and metal-ion-doped Sol–Gel precursors. These films were characterised by Scanning Electron Microscopy, Laser Raman Microspectroscopy, X-ray Diffraction and UV–Vis Transmission. The photocatalytic performances of the films were assessed by the photo-degradation of methylene-blue in aqueous solution under UV irradiation. Films exhibited a high degree of orientation and a thermal stabilization of the anatase phase as a result of substrate effects. In the absence of dopants, the rutile phase formed as parallel bands in the anatase which broadened as the transformation progressed. TiO2 films doped or co-doped with transition metals exhibited the formation of rutile in segregated clusters at temperatures under ~ 800 °C as a result of increased levels of oxygen vacancies. Photocatalytic activity of the films synthesised in this work was low as likely a result of poor TiO2 surface contact with dye molecules in the solution. The presence of transition metal dopants appears detrimental to photocatalytic activity while the performance of mixed phase films was not observed to differ significantly from single phase material.

Growth of Rutile Titanium Dioxide Nanowires by Pulsed Chemical Vapor Deposition

Abstract: Recently, we developed a surface reaction-limited pulsed chemical vapor deposition (CVD) technique that can grow highly uniform anatase TiO2 nanorods (NRs) over a large area, even inside highly confined submicrometer-sized spaces. Here, we report the growth of rutile TiO2 NWs using this technique by introducing a Au seeding layer at higher deposition temperature, where a small amount of anatase phase was also found. A bifurcated growth of rutile TiO2 NWs was observed. The resulting TiO2 NWs exhibited high-quality crystallinity and large surface areas with exposure of high-index surfaces. Control experiments illustrated the influence of deposition conditions on the TiO2 growth behavior. Higher deposition temperature could convert the TiO2 phase from anatase to rutile. A thin film of Au was able to induce rapid crystal growth resulting in particle formation, while the anisotropic NW growth preferred no Au coating. Shorter purging time could significantly enhance the deposition rate because of the incomplete...

CO2 adsorption on TiO2(110) rutile: insight from dispersion-corrected density functional theory calculations and scanning tunneling microscopy experiments.

Abstract: Adsorption of CO2 on the rutile(110) surface was investigated using dispersion-corrected density functional theory and scanning tunneling microscopy (STM). On the oxidized surface the CO2 molecules are found to bind most strongly at the five-fold coordinated Ti sites adopting tilted or flat configurations. The presence of bridging oxygen defects introduces two new adsorption structures, the most stable of which involves CO2 molecules bound in tilted configurations at the defect sites. Inclusion of dispersion corrections in the density functional theory calculations leads to large increases in the calculated adsorption energies bringing these quantities into good agreement with experimental data. The STM measurements confirm two of the calculated adsorption configurations.

Effects of material properties on sedimentation and aggregation of titanium dioxide nanoparticles of anatase and rutile in the aqueous phase.

Abstract: This study investigated the sedimentation and aggregation kinetics of titanium dioxide (TiO2) nanoparticles with varying material properties (i.e., crystallinity, morphology, and chemical composition). Used in the study were various types of commercially available TiO2 nanoparticles: three spherical anatase (nominal diameters of 5, 10, and 50 nm) and two rutile nanoparticles (10 × 40 and 30 × 40 nm). The 50 nm anatase and 10 × 40 nm rutile showed higher stability in deionized water and 5 mM NaCl solutions at pH 7 than the 5, and 10 nm anatase nanoparticles in sedimentation experiments. In aggregation experiments, critical coagulation concentration values for the 50 nm anatase were the highest, followed by the 10 × 40 nm rutile and the 5 nm anatase nanoparticles in NaCl and CaCl2 solutions. The aggregation kinetics was fitted reasonably well with the Derjaguin–Landau–Verwey–Overbeek (DLVO) equations for the TiO2 nanoparticles tested. Results showed that crystallinity and morphology are not influential factors in determining the stability of TiO2 nanoparticle suspensions; however, the differences in their chemical compositions, notably, the varying concentrations of impurities (i.e., silicon and phosphorus) in the pristine materials, determined the surface charge and therefore the sedimentation and aggregation of TiO2 nanoparticles in the aqueous phase.

Effects of material properties on sedimentation and aggregation of titanium dioxide nanoparticles of anatase and rutile in the aqueous phase. J Colloid Interface Sci

Abstract: This study investigated the sedimentation and aggregation kinetics of titanium dioxide (TiO(2)) nanoparticles with varying material properties (i.e., crystallinity, morphology, and chemical composition). Used in the study were various types of commercially available TiO(2) nanoparticles: three spherical anatase (nominal diameters of 5, 10, and 50 nm) and two rutile nanoparticles (10×40 and 30×40 nm). The 50 nm anatase and 10×40 nm rutile showed higher stability in deionized water and 5 mM NaCl solutions at pH 7 than the 5, and 10 nm anatase nanoparticles in sedimentation experiments. In aggregation experiments, critical coagulation concentration values for the 50 nm anatase were the highest, followed by the 10×40 nm rutile and the 5 nm anatase nanoparticles in NaCl and CaCl(2) solutions. The aggregation kinetics was fitted reasonably well with the Derjaguin-Landau-Verwey-Overbeek (DLVO) equations for the TiO(2) nanoparticles tested. Results showed that crystallinity and morphology are not influential factors in determining the stability of TiO(2) nanoparticle suspensions; however, the differences in their chemical compositions, notably, the varying concentrations of impurities (i.e., silicon and phosphorus) in the pristine materials, determined the surface charge and therefore the sedimentation and aggregation of TiO(2) nanoparticles in the aqueous phase.

Effect of Crystal Imperfections on Reactivity and Photoreactivity of TiO2 (Rutile) with Oxygen, Water, and Bacteria

Abstract: The present work considers the effect of crystal imperfections (point defects) on several properties of TiO2 (rutile), such as semiconducting properties and segregation-induced surface properties as well as crystalline structure-related quantities, such as lattice parameter and electronic structure. This work considers the defect disorder of rutile and its solid solutions in terms of both intrinsic and extrinsic defects. The collected empirical data and the related theoretical models indicate that the development of oxide semiconductors with enhanced performance as photocatalysts and photoelectrodes requires recognition of the profound influence of crystal imperfections (point defects) on reactivity and photoreactivity. The effect of defect disorder on the performance of rutile is discussed in terms of its photocatalytic properties in solar water disinfection. The chemistry of the photocatalytic system, consisting of the semiconducting photocatalyst immersed in water involving bacteria, is considered in t...