Anatase Particles Research Articles

Mineralogical and geochemical research on Pengyang deposit: A peculiar eolian sandstone-hosted uranium deposit in the southwest of Ordos Basin

The newly discovered Pengyang uranium prospect area in the southwest of the Ordos Basin is the world's first uranium deposit hosted in eolian sandstone, which overturned the conventional view of uranium mineralization in fluvial-delta sedimentary strata. Uranium ore body occurring as tabular or lens-shaped is hosted in the gray-green reductive eolian sandstone of Lower Cretaceous Luohe Formation at depths ranging from 700 m to 3000 m. The host eolian sandstone is characterized by the typical high angle cross-bedding, wind sand ripple and grainflow strata. In this study, we conducted borehole log, petrographic observation, whole rock geochemistry analysis, geochemical and mineralogical study of uranium occurrence (SEM), element mapping of uranium minerals and in-situ sulfur isotope determination of pyrite by LA-MC-ICP-MS to reveal the uranium enrichment mechanism. The observations by SEM show that the predominant uranium mineral is pitchblende, primarily occurring as aggregates of nano to micro crystals absorbed on amorphous TiO2 or as colloform replacing the detritus Fe-Ti oxide minerals, both demonstrating the excellent absorption property of small particles of anatase. The contents of altered minerals such as chlorite and pyrite in gray-green sandstone increased significantly under scanning electron microscope (SEM). Whole rock geochemistry analysis data of sandstone samples collected in the target layers display the strong positive correlation between U and S. Whereas, in the elements mapping images, uranium enrichments display complete dissociation with pyrite as the uranium contents adjacent to or around the pyrite grains are under detection limit, demonstrating that uranium precipitation likely occurred earlier than the sulfuration of red eolian sandstone. Sulfur isotope of the two morphological types of pyrite are both characterized by a relatively light signature, ranging from − 19.23 to − 27.22 ‰ and from − 21.60 to − 29.64‰ respectively, implying that they are generated from bacterial sulfate reduction in the open systems with an adequate supply of sulfate. Anaerobic sulfate-reducing bacteria use the hydrocarbon transferred along faults to the sandstone as energy to reduce sulfate (SO42−) to H2S. In addition to the typical vertical red - yellow - gray color zonation, we also observed distinct reverse color zonation of sandstone, which can hardly be interpreted by traditional interlayer-oxidation-zone theory. We attribute the uranium reduction to the encounter of downward penetrating oxygenated groundwater with the upward migrating oil and gas conducted by thrust faults, which are widespread distributed in the west margin of the Ordos Basin. This study gives a new insight into uranium metallogenic mechanism in eolian sandstone and underpins an effective vector for the exploration of sandstone-type uranium deposits in the western of the Ordos Basin.

Hydrogarnet-derived Rh/TiO2 catalysts with a low rhodium content for a photocatalytic hydrogen production

A novel protocol for the preparation of Rh-decorated TiO2 photocatalysts with the rhodium content of 0.01–1.0 wt% has been developed based on the deposition of the low-soluble hydrogarnet type salt Ca3[Rh(OH)6]2. Under 380-nm irradiation in water–ethanol mixtures the photoinduced reduction of Ca3[Rh(OH)6]2/TiO2 results in the formation of highly active Rh/TiO2 photocatalysts with nanoparticulated rhodium co-catalyst preferably attached to the surface of anatase particles. The catalysts generate up to 21 mol of H2 per gram of rhodium per hour via a photocatalytic hydrogen evolution reaction (HER) outperforming the activity of the analogous materials reported to date.

Does Symmetry Control Photocatalytic Activity of Titania-Based Photocatalysts?

Decahedral anatase particles (DAPs) have been prepared by the gas-phase method, characterized, and analyzed for property-governed photocatalytic activity. It has been found that depending on the reaction systems, different properties control the photocatalytic activity, that is, the particle aspect ratio, the density of electron traps and the morphology seem to be responsible for the efficiency of water oxidation, methanol dehydrogenation and oxidative decomposition of acetic acid, respectively. For the discussion on the dependence of the photocatalytic activity on the morphology and/or the symmetry other titania-based photocatalysts have also been analyzed, that is, octahedral anatase particles (OAP), commercial titania P25, inverse opal titania with and without incorporated gold NPs in void spaces and plasmonic photocatalysts (titania with deposits of gold). It has been concluded that though the morphology governs photocatalytic activity, the symmetry (despite its importance in many cases) rather does not control the photocatalytic performance.

Heat-resistant TiO2 nanocomposites with anatase phase as carriers for highly efficient CO oxidation catalysts

Thermally stable nanocomposites TiO2 with anatase structure doped with ceria or yttria have been synthesized by impregnation method with using a special precursor of titania. All dopants used in this research increase the temperature of anatase to rutile transition and stabilize anatase phase up to 900 °C. In obtained composites calcined at 300-600 °C, microstructural analysis revealed the formation of nanocristalline TiO2 structure consisting of intergrown incoherently 3–8 nm fine anatase particles with the formation of inrerblock boundaries between them. In the region of interblock boundaries the anatase structure is disordered and dopants are localized there in near atomic state. Under the heating at high temperatures, all composites have the rather high surface area and uniform pore diameter. The ceria doped composite was used as support for preparation of 2% Pt/Ce-TiO2 catalyst for CO oxidation. The obtained catalyst demonstrates a high catalytic activity at rather low temperature.

Enhanced photocatalytic activity of accordion-like layered Ti3C2 (MXene) coupled with Fe-modified decahedral anatase particles exposing {1 0 1} and {0 0 1} facets

New composites consisting of decahedral anatase particles exposing {001} and {101} facets coupled with accordion-like layered Ti3C2 with boosted photocatalytic activity towards phenol and carbamazepine degradation were investigated. The photocatalysts were characterized with X-ray diffraction (XRD), diffuse reflectance spectroscopy (DR/UV–Vis), Brunauer-Emmett-Teller (BET) specific surface area, Raman spectroscopy, scanning electron microscopy (SEM), electron paramagnetic resonance (EPR) spectroscopy, emission spectroscopy, luminescence decay analysis, electrochemical impedance spectroscopy (EIS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and electrophoretic mobility measurements. The effect of hydrothermal reaction parameters on physicochemical, structural, and photocatalytic properties was studied. In all photodegradation processes, ortho-hydroxyphenol and para-hydroxyphenol were detected as the first intermediates of phenol decomposition. For the TiO2/Ti3C2(140,12) sample containing VTi, a higher concentration of para-hydroxyphenol than ortho-hydroxyphenol was observed, whereas for sample TiO2/Ti3C2(220,24) higher concentration of ortho-hydroxyphenol was noticed. The formation of surface heterojunction between {101} and {001} facets of decahedral anatase particles grown on Ti3C2 surface led to improved photoelectron transfer and enhanced photocatalytic activity towards degradation of carbamazepine - non-biodegradable and susceptible to bioaccumulation in living organisms commonly used pharmaceutical agent. Moreover, modification of TiO2/Ti3C2 surface with iron by magnetron sputtering deposition markedly improved photocatalytic activity in carbamazepine decomposition, with nearly 100% degradation in 60 min of irradiation under simulated solar light.

Solvothermal growth of {0 0 1} exposed anatase nanosheets and their ability to mineralize organic pollutants. The effect of alcohol type and content on the nucleation and growth of TiO2 nanostructures

Herein, the series of {001} exposed anatase nanosheets from HF-assisted solvothermal growth synthesis were obtained. The two-dimensional TiO2 were characterized, including both bulk (XRD, DR-UV–Vis, Mott-Schottky) and surface characteristics (N2 sorption, XPS, SEM) with experimental results compiled with Density Functional Theory (DFT) calculations. The effect of alcohol amount and type was studied, demonstrating the crucial role of nucleation rate on the final material properties, which was connected with the possible ligand exchange between F− and ROH in the [TiF6]2− octahedra, leading to further TiO2 condensation through an ether elimination reaction. Highly active 2D nanoparticles were easily obtained for different reaction times when a moderate amount of n-butanol or n-hexanol was introduced to the synthesis. The photoactivity of 2D TiO2 with exposed {001} facet strongly depended on the photocatalytic available surface area with an increased amount of ortho–hydroxyphenol (catechol) formed as aby-product. Meanwhile, the rise of n-butanol or n-hexanol content during solvothermal reaction or changing it to ethanol allowed to form smaller and more crystalline anatase particles, but their activity was hindered. For these samples, the slow phenol disappearance and no catechol formation occurred due to (i) alower amount of adsorbed fluorine, (ii) band position shifting towards lower values, and (iii) the surface presence of Ti3+, which prevented the generation of OH radicals. It was also found that changing the nucleation rate by modifying the reaction environment influences the fluorine ions distribution, determining the final properties of 2D structure photocatalyst.

(Invited) A Pure Titania Photocatalyst: Preparation, Characterization and Photocatalytic Activity of Octahedral-Shaped Anatase Particles

Different from organic molecules and metal complexes, which can be identified by chemical composition and structural characteristics such as NMR spectra, inorganic solid materials especially metal oxides cannot be identified, i.e., their purity cannot be evaluated in a strict scientific sense, because at least three structural parameters, bulk structure, surface structure and bulk/surface size, must be determined. However, in the other words, solid metal-oxide samples can be assigned to be "pure", if their three parameters are determined, by macroscopic measurements, to be uniform. Here, attempts to prepare octahedral-shaped anatase titanium(IV) oxide (titania) particles (OAPs) of uniform bulk structure (anatase with negligible non-crystalline components), surface structure (only exposing {101} facets) and particle size are reported as the first and sole example of a "pure" metal-oxide powder. In this study, OAP samples were prepared by sonication-hydrothermal (HT) reaction of potassium-titanate nanowires. Characterization of the samples by Rietveld analysis of XRD patterns, reversed double-beam photoacoustic spectroscopy and SEM observations revealed the homogeneousness of crystalline bulk, surface and particle size, respectively, to indicate the samples "pure".

The Influence of In Situ Anatase Particle Addition on the Formation and Properties of Multifunctional Plasma Electrolytic Oxidation Coatings on AA2024 Aluminum Alloy

Plasma electrolytic oxidation (PEO) with in situ anatase particle addition is applied to functionalize the surface of AA2024 alloy. A base potassium titanium oxide oxalate dihydrate aqueous electrolyte is used with up to 30 g L−1 anatase particle addition. The coatings’ morphology and phase composition as a function of the anatase concentration in the electrolyte are characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and glow discharge optical emission spectroscopy (GDOES). Photocatalytic activity, stability in chloride solution, and tribological properties are also determined. The main coating forming phases are anatase and rutile on top of a mixed interface region consisting of TiAl2O5 as reaction product between the TiO2 and an Al2O3 barrier layer on top of the Al substrate. The mixed layer is extending with increasing amount of particles added, due to intensified discharges. In addition, anatase‐to‐rutile phase ratio increases due to the additional anatase particles in the electrolyte. Thus, the photocatalytic activity is improving with the particle addition. The coatings’ mechanical resistance is dropping first before increasing again with more particles added. Chemical and restored mechanical stability seems to be related to the extended mixed interface formation, which strengthens the bond to the substrate when more particles are added.

Suppressing the Photocatalytic Activity of Titania by Precisely Controlled Silica Coating.

A homogeneous thin silica layer with the thickness of a few nanometers was successfully deposited on an anatase particle by the hydrolysis and condensation of tetraethyl orthosilicate. The heat treatment of the titania/silica hybrid at 1000 °C led to the densification of the silica layer on the anatase particles. The anatase particle after the silica coating did not transform to rutile, and no change in the crystallite size was seen by the heat treatment at 1000 °C. The coating and subsequent heating were repeated to vary the thickness of the silica layer to obtain each coating with similar thickness by each coating procedure (ca. 3 and 2 nm, before and after the heat treatment). The samples were evaluated for the photocatalytic decomposition of methylene blue by the UV irradiation to find that the decomposition became slower after the coating and subsequent heat treatment, and the repeated procedures led to further suppression of the photocatalytic decomposition of methylene blue. The quite small decomposition rate constant (0.01 h-1) was successfully achieved by the coating and subsequent heating for three times (the thickness of the dense silica layer was ca. 7 nm).

Thermal stability and phase transformation of semi-crystalline mesostructured TiO2 in the presence of heteroelements

The effect of the introduction of heteroelement (Si, P, Al, Ge, Ga and Zr) by direct synthesis on the thermal stability of mesostructured titania prepared by the soft templating pathway has been investigated. All materials have been surfactant-extracted with EtOH and calcined at different temperatures up to 900 °C. Ti4+ can be partially substituted by most of the investigated heteroelements but they mainly form an oxide amorphous phase surrounding the titania anatase particles. Results obtained by SAXS, X-Ray diffraction, Raman spectroscopy and manometry nitrogen adsorption-desorption show that the crystallization of the amorphous titania into nanosized anatase particles and the transition from anatase to rutile occur at higher temperature with the addition of the heteroelement. Even if the lattice distortion introduced by the partial Ti4+ substitution can participate to this phenomenon, it is mainly due the «glass » effect induced by the presence of the heteroelement in the TiO2 amorphous phase, which limits the growth of the nanosized anatase crystallites. However, when the crystallites reach a limit size, the collapse of the mesostructure occurs. With increasing the calcination temperature, the anatase titania particles become bigger and bigger, the transition from anatase to rutile takes place and the heteroelement can crystallize or be integrated in a crystalline phase. Among the considered heteroelements and by comparison with the bare mesostructured TiO2, the most beneficial effect is obtained in the presence of Si4+ and PO43− for which the mesostructure collapse at higher temperature by about two hundred Celsius degrees. Al3+ and Ge4+ enhance the thermal stability by about a hundred Celsius degrees and Ga3+ or Zr4+ have no significant effect on the temperature at which the mesostructure collapses.

Speckle patterning of a pumping laser light as a limiting factor for stimulated fluorescence emission in dense random media.

The features of fluorescence emission in a dye-doped dense multiple scattered medium under pulsed laser pumping are considered in terms of confined excitation in small zones associated with laser speckles occurring in a pumped medium. The results of numerical modeling of the fluorescence emission kinetics are compared to the experimental data obtained using the rhodamine 6G-doped layers of the densely packed TiO2 (anatase) particles pumped at 532 nm by 10 ns laser pulses. The intensity of pump radiation during the action of laser pulses was varied from 1·105 W/cm2 to 5·107 W/cm2. In the recovery of the ratios of stimulated to a spontaneous emission, the spectra of the stimulated component were fitted using the spectral function derived by R. Dicke. In the framework of the considered concept, saturation of the ratio of the stimulated to a spontaneous emission and linear growth of an integrated fluorescence output with a practically unchangeable half-width of the emission spectra at high pump intensities are interpreted.

Formation of multi-functional TiO2 surfaces on AA2024 alloy using plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was applied to functionalise the surface of AA2024 alloy. A potassium titanium-oxide oxalate dihydrate based aqueous electrolyte was used, which allowed the direct formation of a TiO2 surface layer on the aluminium alloy substrate. The effect of PEO treatment time and the additional presence of anatase particles in the electrolyte solution on the surface layer and its properties (corrosion, wear and photocatalytic activity) were investigated.It was found that the coating thickness and surface morphology are strongly dependent on the PEO processing time. However, the phase composition is not much affected by the treatment time and the main coating phase is rutile with a smaller amount of anatase. Adding additional anatase in the form of particles increases the amount of anatase in the coatings. The additional particle addition has only minor effect on the corrosion resistance, but reduces the wear resistance remarkably. Interestingly, the addition of anatase particles and the PEO treatment time are not effective in increasing the photocatalytic activities of the samples.

Low pressure cold spraying of TiO2 on acrylonitrile butadiene styrene (ABS)

The deposition mechanism of low-pressure cold spraying of ceramics on polymeric substrates is still unclear. In the presented study titanium dioxide powders were self-synthesized on the sol-gel route and deposited on ABS polymer by low pressure cold spraying. Three variants of powders that differ in the structure were prepared: amorphous powder, anatase, and the mixture of them. The hard crystalline anatase particles, formed by the sintering of amorphous powder, penetrate the polymer mainly via aggregates fragmentation. As a result of delivering excessive energy, the polymer and coating are subjected to erosion. Increasing the working gas temperature or substrate pretreatment via grit-blasting only reduces deposition efficiency. The use of soft amorphous titanium dioxide agglomerates, an example of soft ceramics containing several pores, are characterized by relatively lower energy, allows to reduce the erosion of the substrate, and leads to the satisfactory coating of the untreated substrate material. After all, the performed analysis of topography and cross-sections shows that the highest deposition efficiency was obtained by using a lower working gas temperature (200 °C) and this applies to all types of used powers.

A Pure Titania Photocatalyst: Preparation, Characterization and Photocatalytic Activity of Octahedral-Shaped Anatase Particles

Different from organic molecules and metal complexes, which can be identified by chemical composition and structural characteristics such as NMR spectra, inorganic solid materials especially metal oxides cannot be identified, i.e., their purity cannot be evaluated in a strict scientific sense, because at least three structural parameters, bulk structure, surface structure and bulk/surface size, must be determined. However, in the other words, solid metal-oxide samples can be assigned to be "pure", if their three parameters are determined, by macroscopic measurements, to be uniform. Here, attempts to prepare octahedral-shaped anatase titanium(IV) oxide (titania) particles (OAPs) of uniform bulk structure (anatase with negligible non-crystalline components), surface structure (only exposing {101} facets) and particle size are reported as the first and sole example of a "pure" metal-oxide powder. In this study, OAP samples were prepared by sonication-hydrothermal (HT) reaction of potassium-titanate nanowires. Characterization of the samples by Rietveld analysis of XRD patterns, reversed double-beam photoacoustic spectroscopy and SEM observations revealed the homogeneousness of crystalline bulk, surface and particle size, respectively, to indicate the samples "pure".

Do Particles Interact Electronically? —Proof of Interparticle Charge-transfer Excitation between Adjoined Anatase and Rutile Particles

Abstract Here, we report experimental evidence of interparticle spatial overlapping of orbitals to result in interparticle charge-transfer excitation (ICTE) at an anatase-rutile interface which is expected to be applicable to clarify the relative band position of metal-oxides and mixture homogeneity of mixture samples measured by reversed double-beam photoacoustic spectroscopy.

Effects of physiochemical characteristic of nano-sized TiO2 on the adhesion of monocytes to endothelial cells

Nano-sized titanium dioxide (TiO2) particles are produced on a large scale and are widely used. However, the effects of exposure to nano-sized TiO2 particles on the cardiovascular system remain elusive. The present study investigated how the crystal structure and surface characteristics of nano-sized TiO2 particles affect the adhesion of monocytes to endothelial cells, which is an essential process in atherosclerogenesis. Human umbilical vein endothelial cells (HUVECs) and human monocytic leukemia cells (THP-1) were exposed to anatase (NM102), rutile hydrophobic (NM103), and rutile hydrophilic (NM104) TiO2 nanoparticles. Incubation of HUVECs with NM102, NM103, or NM104 at 100 μg/ml significantly reduced cell viability, and cell viability was also significantly reduced after exposure to 75 μg/ml of the anatase particles (NM102). Brief exposure to NM102 and NM103 increased the level of intercellular adhesion molecule-1 (ICAM-1) in HUVECs. Exposure to NM102 also upregulated the expression of lymphocyte function-associated antigen-1 (LFA-1) in THP-1 cells, resulting in enhanced adhesion of these cells to HUVECs. The amount of titanium uptake of NM102 in cells was higher than that of NM103 or NM104, as evidenced by inductively coupled plasma optical emission spectroscopy (ICP-OES). To examine the effects of long-term exposure to nano-sized TiO2 on the process of atherosclerosis, apolipoprotein E deficient (ApoE−/−) mice were exposed to TiO2 NPs (NM102, NM103, or NM104 at 10 or 40 μg/mouse) by pharyngeal aspiration once every other week for 10 weeks. As the results, NM102 (40 μg/mouse) increased plaque formation in the aorta, and this increase correlated with a significant upregulation of ICAM-1 and F4/80 expression in the aorta. Anatase, but not rutile, TiO2 nanoparticles promoted the adhesion of monocytes to endothelial cells, and enhanced atherosclerogenesis in a susceptible animal model.

Light intensity-dependence studies on the role of surface deposits for titania-photocatalyzed oxygen evolution: Are they really cocatalysts?

The effects of surface loading of iridium(II) oxide (IrO2), manganese(IV) oxide (MnO2), and cobalt(II) phosphate (CoPi) on the rate of photocatalytic oxygen evolution by anatase or rutile titania particles suspended in aqueous solutions of an electron acceptor, iodate ions, were studied by light intensity-dependence (LID) kinetic analyses. Although the role of these deposits has been reported to be a cocatalyst without showing results of any kinetic analysis, the present LID kinetic study suggested that the deposits may act as a "positive-hole capturer" for oxygen evolution, not as a cocatalyst for both metal oxides and CoPi. Further studies on the effects of loading amount, deposit types, titania crystalline type, and titania-particle size on the reaction order were also performed by LID analysis based on the proposed kinetic model. The observed LID behaviors could be interpreted consistently using a virtual parameter of "effective volume" as the target volume of photoabsorption by one positive-hole-bearing titania particle to govern the probability of two positive-hole accumulations in a titania particle.

Characterization of the in Vitro Osteogenic Response to Submicron TiO2 Particles of Varying Structure and Crystallinity.

Titanium oxide (TiO2) nano-/microparticles have been widely used in orthopedic and dental sciences because of their excellent mechanical properties, chemical stability, and ability to promote the osseointegration of implants. However, how the structure and crystallinity of TiO2 particles may affect their osteogenic activity remains elusive. Herein, we evaluated the osteogenic response to submicron amorphous, anatase, and rutile TiO2 particles with controlled size and morphology. First, the ability of TiO2 particles to precipitate apatite was assessed in an acellular medium by using a simulated body fluid (SBF). Three days after the addition to SBF, anatase and rutile TiO2 particles induced the precipitation of aggregates of nanoparticles with a platelike morphology, typical for biomimetic apatite. Conversely, amorphous TiO2 particles induced the precipitation of particles with poor Ca/P atomic ratio only after 14 days of exposure to SBF. Next, the osteogenic response to TiO2 particles was assessed in vitro by incubating MC3T3-E1 preosteoblasts with the particles. The viability and mineralization efficiency of osteoblastic cells were maintained in the presence of all the tested TiO2 particles despite the differences in the induction of apatite precipitation in SBF by TiO2 particles with different structures. Analysis of the particles’ surface charge and of the proteins adsorbed onto the particles from the culture media suggested that all the tested TiO2 particles acquired a similar biological identity in the culture media. We posited that this phenomenon attenuated potential differences in osteoblast response to amorphous, anatase, and rutile particles. Our study provides an important insight into the complex relationship between the physicochemical properties and function of TiO2 particles and sheds light on their safe use in medicine.

Physicochemical approaches for optimization of perovskite solar cell performance

Perovskite solar cells (PSCs) with photovoltaic parameters improved using a number of physicochemical approaches for optimization of structure and properties of their components were fabricated and studied under both standard illumination conditions AM1.5G and reduced illumination intensity. Photoelectrodes based on mesoscopic TiO2 layers with different content of anatase and rutile particles were constructed, as well as the perovskite material and the TiO2—perovskite interface were modified. As a result, the optimized PSCs had increased stability in a humid atmosphere and showed high efficiencies (10–14%) in a wide range of illumination intensities of 10–1000 W m−2.

In Vivo Interactions of Nanosized Titania Anatase and Rutile Particles Following Oral Administration

In Vivo Interactions of Nanosized Titania Anatase and Rutile Particles Following Oral Administration