Time-resolved photoluminescence of anatase/rutile TiO_2 phase junction revealing charge separation dynamics

Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an anatase/rutile TiO2 phase junction using time-resolved photoluminescence spectroscopy. Visible （-S00 nm） and near-infrared （NIR, -830 nm） emissions were monitored to give insight into the photoinduced charges of anatase and rutile in the junction, respectively, New fast photoluminescence decay components appeared in the visible emission of futile-phase dominated TiO2 and in the NIR emission of many mixed phase TiO2samples. The fast decays confirmed that the charge separation occurred at the phase junction. The visible emission intensity from the mixed phase TiO2 increased, revealing that charge transfer from rutile to anatase was the main pathway. The charge separation slowed the microsecond time scale photolumines- cence decay rate for charge carriers in both anatase and rutile. However, the millisecond decay of the charge carriers in anatase TiO2 was accelerated, while there was almost no change in the charge carrier dynamics of rutile TiO2. Thus, charge separation at the anatase/rutile phase junction caused an increase in the charge carrier concentration on a microsecond time scale, because of slower electron-hole recombination. The enhanced photocatalytic activity previously observed at ana- tase/rutile phase junctions is likely caused by the improved charge carrier dynamics we report here. These findings may contribute to the development of improved photocatalytic materials.

Mixed Phase Anatase/rutile Titanium Dioxide Nanotubes for Enhanced Photocatalytic Degradation of Methylene-blue

Titanium dioxide Nanotubes(TNTs) prepared by electroless deposition have been annealed at air ambient and low temperature. As a result, the anatase/rutile phase composition of the TNTs can be tailored to the needs of later applications. Nanotubes with anatase/rutile mixed phase ratio of 4:1 have been produced in this report and further examined for their photocatalytical behavior. The photocatalytical properties of the TNTs have been observed by degradation of methylene-blue in aqueous solution under low power UV-light irradiation. The results shown in this report are based on the synergetic effect between rutile and anatase,which results in the mixed phase TiO 2 nanotubes having enhanced photocatalytical properties.

Influence of cerium ions on the anatase-rutile phase transition of TiO_2 prepared by sol-gel auto-igniting synthesis

The anatase-rutile phase transformation of TiO_2 doped cerium up to 5 molpercent was studied by X-ray diffraction and X-ray photoelectron spectroscopy. The samples wereprepared by sol-gel auto-igniting synthesis process from a TiO(NO_3)_2-Ce(NO_3)_2-NH_4NO_3-citricacid complex compound system. The combusted amorphous powders were calcined at differenttemperatures. Significant structural changes were observed during the various stages of the phasetransformation. It was concluded that at low dopant contents, cerium ions were incorporated into theTiO_2 structure, and the anatase phase was stabilized; but at larger amounts, part of the dopantwas segregated on the surface of TiO_2 and the rutile formation was accelerated at elevatedcalcination temperature.

Unique Pulsed-Laser Deposition Production of Anatase and Rutile TiO₂on Al₂O₃

Two pure hexagonal phases of titanium dioxide, anatase and rutile, were grown on c-cut Al2O3 substrates via pulsed-laser deposition by changing only the growth and annealing conditions, but without changing the substrate, target, or working gas. Purity of each phase was confirmed by x-ray diffraction, the quality of each film was studied using atomic force microscopy and scanning electron microscopy, and the interface between each substrate and film was studied using x-ray photoelectron spectroscopy. A binding layer of Ti2O3 was found to explain anatase growth under the very large lattice mismatch conditions.

In situ U-Pb dating and trace elements of magmatic rutile from Mujicun Cu-Mo deposit,North China Craton:Insights into porphyry mineralization

Porphyry Cu(Mo-Au)deposit is one of the most important types of copper deposit and usually formed under magmatic arc-related settings,whilst the Mujicun porphyry Cu-Mo deposit in North China Craton uncommonly generated within intra-continental settings.Although previous studies have focused on the age,origin and ore genesis of the Mujicun deposit,the ore-forming age,magma source and tectonic evolution remain controversial.Here,this study targeted rutile(TiO_(2))in the ore-hosting diorite porphyry from the Mujicun Cu-Mo deposit to conduct in situ U-Pb dating and trace element composition studies,with major views to determine the timing and magma evolution and to provide new insights into porphyry Cu-Mo metallogeny.Rutile trace element data show flat-like REE patterns characterized by relatively enrichment LREEs and depleted HREEs,which could be identified as magmatic rutile.Rutile U-Pb dating yields lower intercept ages of 139.3–138.4 Ma,interpreted as post magmatic cooling timing below about 500℃,which are consistent or slightly postdate with the published zircon U-Pb ages of diorite porphyry(144.1–141.7 Ma)and skarn(146.2 Ma;139.9 Ma)as well as the molybdenite Re-Os ages of molybdenum ores(144.8–140.0 Ma).Given that the overlap between the closure temperature of rutile U-Pb system and ore-forming temperature of the Mujicun deposit,this study suggests that the ore-forming ages of the Mujicun deposit can be constrained at 139.3–138.4 Ma,with temporal links to the late large-scale granitic magmatism at 138–126 Ma in the Taihang Orogen.Based on the Mg and Al contents in rutile,the magma of ore-hosting diorite porphyry was suggested to be derived from crust-mantle mixing components.In conjunction with previous studies in Taihang Orogen,this study proposes that the far-field effect and the rollback of the subducting Paleo-Pacific slab triggered lithospheric extension,asthenosphere upwelling,crust-mantle interaction and thermo-mechanical erosion,which jointly facilitated the formation of dioritic magmas during the Early Cretaceous.Subsequently,the dioritic magmas carrying crust-mantle mixing metallic materials were emplaced and precipitated at shallow positions along NNE-trending ore-controlling faults,eventually resulting in the formation of the Mujicun Cu-Mo deposit within an intracontinental extensional setting.

Identifying the effect of photo-generated carriers on the phonons in rutile TiO_(2) through Raman spectroscopy

Investigating lattice vibrations through Raman spectroscopy is a crucial method for studying crystalline materials.Carriers can interact with lattices and influence lattice vibrations;thus,it is feasible to study the effect of photo-generated carriers on phonons by analyzing changes in the Raman spectra of semiconductors.Rutile is one of the predominant crystalline phases of TiO_(2),which is a widely utilized metal oxide semiconductor.In this work,rutile TiO_(2) is coated on a thinned optical fiber to concentrate ultraviolet light energy within the material,thereby enhancing the generation of carriers and amplifying the changes in the Raman spectra.A Raman detection laser with a wavelength of 532 nm is utilized to collect the Raman spectra of rutile TiO_(2) during irradiation.Using this setup,the impact of photo-generated carriers on the phonons corresponding to Raman vibrational modes is researched.The localization and non-radiative recombination of photo-generated carriers contribute to a reduction in both the frequencies and lifetimes of phonons.This work provides a novel approach to researching the effect of carriers on phonons.

Activity and Adsorption Behavior of Oxygen on Rutile TiO_(2)(110)

The activity and adsorption behavior of oxygen on rutile TiO_(2)(110)(RTiO_(2)(110))were investigated using the temperature programmed desorption(TPD)method with methanol(CH_(3)OH)as the probe molecule.By controlling the coverage of molecular O_(2)on the surface via increasing or decreasing O_(2)exposure,two chemisorbed O_(2)species on the surface are confirmed,one at the bridging oxygen vacancy(Ov)site(O_(2)^(2-)/Ov)and the other at the five-fold coordinated titanium(Ti_(5c))site(O^(2-)/Ti_(5c)).At low O_(2)exposure,O^(2-)/Ov is the main species on the surface,which only leads to the O-H bond cleavage of CH_(3)OH,producing methoxy groups(CHgO).However,after the Ov sites are nearly filled by O_(2)at about 0.1 L O_(2)exposure,O_(2)/Tisc species begins to appear on R-TiO_(2)(110)surface,resulting in the formation of formaldehyde(CH_(2)O)via the reaction of O_(2)/Tisc species with CH_(3)OH or CH3O to break the C-H bond at low surface temperature.Moreover,the yield of CH_(2)O increases linearly with that of H_(2)O.In addition,when the 1 L O_(2)covered surface is irradiated with 355 nm UV irradiation to desorb and dissociate O_(2)/Ti_(5c)species,the yield of CH_(2)O decreases linearly with that of H_(2)O.Further analysis suggests that the charge state of O_(2)/Ti_(5c)may not change as the exposure of O_(2)changes on the R-TiO_(2)(110)surface,and O_(2)is most likely to adsorb on the Ti_(5c)sites in the form of O_(2)^(2-),not O_(2)^(-),The result not only advances our understanding on the adsorption state of O_(2)on TiO_(2),but also provides clues for low temperature C-H bond activation with O_(2)on TiO_(2).

Assembly of functional carboxymethyl cellulose/polyethylene oxide/anatase TiO_(2) nanocomposites and tuning the dielectric relaxation, optical, and photoluminescence performances

Nanocomposite films consisting of carboxymethyl cellulose,polyethylene oxide(CMC/PEO),and anatase titanium diox-ide(TO)were produced by the use of sol-gel and solution casting techniques.TiO2 nanocrystals were effectively incorporated into CMC/PEO polymers,as shown by X-ray diffraction(XRD)and attenuated total reflectance fourier transform infrared(ATR-FTIR)analysis.The roughness growth is at high levels of TO nanocrystals(TO NCs),which means increasing active sites and defects in CMC/PEO.In differential scanning calorimetry(DSC)thermograms,the change in glass transition temperature(Tg)val-ues verifies that the polymer blend interacts with TO NCs.The increment proportions of TO NCs have a notable impact on the dielectric performances of the nanocomposites,as observed.The electrical properties of the CMC/PEO/TO nanocomposite undergo significant changes.The nanocomposite films exhibit a red alteration in the absorption edge as the concentration of TO NCs increases in the polymer blend.The decline in the energy gap is readily apparent as the weight percentage of TO NCs increases.The photoluminescence(PL)emission spectra indicate that the sites of the luminescence peak maximums show slight variation;peaks get wider,while their intensities decrease dramatically as the concentration of TO increases.These nanocomposite materials show potential for multifunctional applications including optoelectronics,antireflection coatings,pho-tocatalysis,light emitting diodes,and solid polymer electrolytes.

Surface Chemistry and Photochemistry of Cyclohexane on Rutile TiO_(2)(110)

Cyclohexane is a high-valued chemical receivingsignificant interest in liquid hydrogen storage technology.TiO_(2)-based catalysts show high performance in the photocatalytic dehydrogenation of cyclohexane under mild conditions,but the detailed reaction mechanism is not well understood.With the surface science approaches,we have studied the adsorption and surface chemistry of cyclohexane on rutile TiO_(2)(110).The thermal desorption spectroscopy and X-ray photoelectron spectroscopy results both demonstrate the molecular adsorption of cyclohexane on rutile TiO_(2)(110).Upon the UV Hg light irradiation,photodesorption of cyclohexane occurs from both the chemisorbed monolayer and the multilayer.No decomposition nor dehydrogenation of cyclohexane occurs on rutile TiO_(2)(110).These results deepen the fundamental understanding of the surface chemistry of cyclohexane on the TiO_(2)surface.

Synthesis of rutile from high titania slag by pyrometallurgical route

A new technique was developed for the conversion of high titania slag,containing 70%-75% TiO2 and with MgO,FeO,CaO,Al2O3 and SiO2 as main impurities,into a synthetic rutile,90%-95% TiO2,which satisfies the requirements for fluidizing chlorination process with respect to impurity contents.After a pre-oxidation at around 1 042 ℃ and a heat-treatment above 1 510 ℃,the Ti components in high titania slag can be enriched into the rutile phase which can precipitate and grow,and can be separated with dilute hydrochloric and sulfuric acid,respectively.The results show that the average crystal size of rutile phase is over 25 μm,and the synthetic rutile containing more than 95% TiO2 can be produced by selective leaching.

Fluidized-bed chlorination thermodynamics and kinetics of Kenya natural rutile ore

Natural rutile and gaseous chlorine with carbon as reductant were used to prepare titanium tetrachloride. Thermodynamics and kinetics of chlorination of Kenya natural rutile particles in a batch-type fluidized bed were studied at 1173-1273 K. Thermodynamic analysis of this system revealed that the equation of producing CO was dominant at high temperatures. Based on the gas-solid multi-phase reaction theory and a two-phase model for the fluidized bed, the mathematical description for the chlorination reaction of rutile was proposed. The reaction parameters and the average concentration of gaseous chlorine in the emulsion phase were estimated. The average concentration of emulsion phase in the range of fluidized bed was calculated as 0.3 mol/m^3. The results showed that the chlorination of natural rutile proceeded principally in the emulsion phase, and the reaction rate was mainly controlled by the surface reaction.

Preparation of three-dimensional interconnected mesoporous anatase TiO_2-SiO_2 nanocomposites with high photocatalytic activities

In this article, we report the preparation of a three-dimensional（3D） interconnected mesoporous anatase TiO2-SiO2 nanocomposite. The nanocomposite was obtained by using an ordered two-dimensional（2D） hexagonal mesoporous anatase 70 TiO2-30 SiO2-950 nanocomposite（crystallized at 950 °C for 2 h） as a precursor, NaO H as an etchant of SiO2 via a ＂creating mesopores in the pore walls＂ approach. Our strategy adopts mild conditions of creating pores such as diluted NaO H solution, appropriate temperature and solid/liquid ratio, etc. aiming at ensuring the integrities of mesopores architecture and anatase nanocrystals. XRD, TEM and N2 sorption techniques have been used to systematically investigate the physico-chemical properties of the nanocomposites. The results show that the intrawall mesopores are highly dense and uniform（average pore size 3.6 nm）, and highly link the initial mesochannels in a 3D manner while retaining mesostructural integrity. There is no significant change to either crystallinity or size of the anatase nanocrystals before and after creating the intrawall mesopores. The photocatalytic degradation rates of rhodamine B（RhB, 0.303 min^–1） and methylene blue（MB, 0.757 min^–1） dyes on the resultant nanocomposite are very high, which are 5.1 and 5.3 times that of the precursor; even up to 16.5 and 24.1 times that of Degussa P25 photocatalyst, respectively. These results clearly demonstrate that the 3D interconnected mesopores structure plays an overwhelming role to the increments of activities. The 3D mesoporous anatase TiO2-SiO2 nanocomposite exhibits unexpected-high degradation activities to RhB and MB in the mesoporous metal oxide-based materials reported so far. Additionally, the nanocomposite is considerably stable and reusable. We believe that this method would pave the way for the preparation of other 3D highly interconnected mesoporous metal oxide-based materials with ultra-high performance.

Bio-desilication of rutile concentrate and analysis of community structure in bio-desilication reactor

The original strain HY-7 was isolated from the bauxite mine drainage（BMD） taken from a reservoir in Sanmenxia Mine,Henan Province,China.The optimum temperature and pH for the growth of strain HY-7 were 30 ℃ and 7.0,respectively.The optimum UV radiating time was 20 s and the positive mutation rate was 23.0%.The growth curves show that strain HY-7 needs144 h to reach the stationary phase after its mutagenesis,which is 24 h earlier than that of the original strain.Sequence homology analysis indicated that this community consisted of mainly two branches：one sharing high homology with Paenibacillus stellifer and the other sharing high homology with Sporolactobacillus laevolacticus.The experimental results showed that the TiO2 grade of mtile concentrate increased from 78.21%to 91.80%and the recovery of TiO2 reached 95.24%after 7 d of bioleaching.The bio-desilication process can not only effectively improve the TiO2 grade of rutile concentrate but also meet the requirements of environmental protection.

Adsorption behavior and mechanism of Bi(Ⅲ) ions on rutile-water interface in the presence of nonyl hydroxamic acid

The adsorption behavior and mechanism of Bi（Ⅲ） ions on the rutile-water interface were investigated through micro-flotation, Zeta potential measurement, adsorption amount measurement and X-ray photoelectron spectroscopy（XPS）. According to the results of micro-flotation, Bi（Ⅲ） ions could largely improve the rutile flotation recovery（from 62% to 91%）, and they could increase the activating sites and reduce the competitive adsorption between nonyl hydroxamic acid negative ions and OH-ions, which determined that Bi（Ⅲ） ions were capable of activating rutile flotation. The adsorption of Bi（Ⅲ） ions onto the rutile surface led to the shift of Zeta potential into the positive direction, which was good for the adsorption of nonyl hydroxamic acid anions. In addition, the results of XPS indicated that the chemical environment around Ti atom had not changed before and after the adsorption of Bi（Ⅲ） ions. Based on the adsorption mechanism of Bi（Ⅲ） ions, it was deduced that firstly Bi（Ⅲ） ions occupied the vacancies of the original Ca^2＋, Mg^2＋ and Fe^2＋ ions on the rutile surface; secondly Bi（Ⅲ） ions covered on the rutile surface in the form of hydroxides.

Sonocatalytic degradation of methyl orange in the presence of (nanometer and ordinary) anatase TiO_2 powders

The nanometer and ordinary anatase titanium dioxide(TiO_2) powders were adopted as the sonocatalysts for the degradation of methyl orange used as a model compound for the first time. It was found that the sonocatalytic degradation effect of methyl orange in the presence of TiO_2 powder were much better than that without TiO_2, but the sonocatalytic activity of the nanometer anatase TiO_2 particle was obviously higher than that of ordinary anatase TiO_2 particle. Although there are many factors influencing sonocatalytic degradation of methyl orange, the experimental results showed that the best degradation ratio of methyl orange could be obtained when the experimental conditions were: initial concentration 15 mg/L, nanometer anatase TiO_2 adding amount 750 mg/L, ultrasonic frequency 40 kHz, output power 50 W, pH = 3.0 and temperature 40℃ within 150 min. In addition, the catalytic activity of reused nanometer anatase TiO_2 catalyst was also studied and found to decline gradually comparing with initial nanometer anatase TiO_2 catalyst. All experiments indicated that the method of the sonocatalytic degradation of organic pollutants in the presence of TiO_2 powder was an advisable choice for non- or low-transparent organic wastewaters.

Geology and Geochemistry of the Yangtizishan-Moshishan Metamorphosed Sedimentary Anatase Deposit in Zhenglan Qi,Inner Mongolia:Discovery of a New Genetic Type of Titanium Deposit

Anatase and its allomorphic mineral rutile have the most prominent economic significance among titanium mineral resources and constitute one of the badly needed mineral resources currently in China. The Yantizishan-Moshishan anatase deposit was formerly referred to as an iron deposit. Based on recent investigation and exploration the authors believe that it is actually a large metamorphosed sedimentary anatase-dominated deposit belonging to a new genetic type. Ore bodies occur in stratoid and lenticular forms in Mesoproterozoic （1751 Ma） schist, metasandstone （metasiltstone）, and amphibolite. Rich ores have perthitic structure comprising chiefly interbedded quartz perthite （with disseminated anatase and rutile） and anatase perthite. Ore minerals are mainly anatase and subordinately rutile and ilmenite （±hematite）, while nonmetallic minerals are chiefly quartz with a certain amount of anthophyllite and biotite （±garnet）. The grain sizes of anatase, ruffle and ilmenite are 0.01-0.1 mm. Rich ores contain 3.14% to 15.46% TiO2. averaging 6.91%, while the low-grade ores have TiO2 content about 1.2%to 2.97%, averaging 1.76%. The ores have relatively high TFe and V contents. Trace elements in anatase and rutile such as Nb and Cr were analyzed by the electron microprobe. According to their relatively low Nb and Cr contents, source anatase and rutile must have come from meta-mafic rocks. Trace elements of the associated ilmenite show relatively high MnO and low MgO contents, just in contrast to those of ilmenite in V-Ti-magnetite ores of magmatic origin. The protoliths of amphibolite wall rocks should be basalt and picrite-basalt. Pertochemical data suggest that the tectonic setting of these rocks belongs to an island arc or a transitional belt between the island arc and oceanic ridge. Silicon isotope study shows that δ30Si values of different anatase ores, quartzite, and schist in this deposit are 0.1‰ to -0.9‰, similar to those of marine hydrothermal exhalative sedimentary deposits. All of these geological and geochemical characteristics of the ore deposit suggest that the anatase ores and amphibolite are products of submarine basic volcanism. The ores had chemical precipitation features, but were later subjected to regional intermediate （or somewhat lower） grade metamorphism （1158 Ma）. Rutile was formed mainly in the process of this metamorphism. The ore belt locally underwent hydrothermal modification during the emplacement of Late Yanshanian granite （118 Ma）.

Depressing effect of sodium hexametaphosphate on apatite in flotation of rutile

The separation of rutile from apatite by flotation and the mechanism of depressing the apatite of sodium hexametaphosphate were studied. The results showed that rutile and apatite could be separated by using alkyl-imino-bismethylene phosphoric acid and sodium hexametaphosphate as a collector and a regulator, respectively. Sodium hexametaphosphate could selectively dissolve calcium ions on the apatite surface, and make calcium ions break away from lattice binding through combining.

Preparation and Photocatalytic Behaviors of Nanoporous Polyoxotungstate-Anatase TiO_2 Composites

Nanoporous anatase TiO2 crystalline particles coupled with Keggin or Wells-Dawson unit, H3PW12O40/TiO2 or H6P2W18O62/TiO2, were prepared at a low temperature （200℃ ） using sol-gel method combined with hydrothermal treatment at programmed temperature. The as-prepared composites have uniform anatase phase, and they exhibit both micrand mesoporosities with pore sizes of 0.6 and 4.0 nm, respectively, and their average size is lower than 10 nm. Photocatalytic tests show the composites exhibit relatively higher photocatalytic activities to decompose the organocholorine pesticide hexachlorobenzene（HCB） than anatase TiO2, the starting polyoxotungstates, and EuEOa/TiO2 prepared by using sol-gel method, and this was attributed to （ 1 ） the synergistic effect of photoactive anatase TiO2 with the polyoxotungstate, and （2） the fascinating physical and chemical properties of the porous materials.

Photo-depositing Ru and RuO2 on Anatase TiO2 Nanosheets as Co-catalysts for Photocatalytic O2 Evolution from Water Oxidation

TiO2 nanosheets mainly exposed （001） facet were prepared through a hydrothermal process with HF as the morphology-directing agent. Ru and RuO2 species were loaded by photo-deposition methods to prepare the photocatalysts. The structural features of the catalysts were characterized by X-ray di raction, transmission electron microscopy, inductively cou-pled plasma atomic emission spectrum, and H2 Temperature-programmed reduction. The photocatalytic property was studied by the O2 evolution from water oxidation, which was examined with respect to the in uences of Ru contents as well as the oxidation and reduction treatments, suggesting the charge separation effect of the Ru species co-catalysts on di erent facets of TiO2 nanosheets. In contrast to Ru/TiO2 and RuO2/TiO2 with the single deposited co-catalyst, the optimized catalyst 0.5%Ru-1.0%RuO2/TiO2 with dual co-catalysts achieved a much improved catalytic performance, in terms of the synergetic effect of dual co-catalysts and the enhanced charge separation effect.