TiO2 Polymorphs Research Articles

Nanomineralogy of hydrothermal magnetite from Acropolis, South Australia: Genetic implications for iron-oxide copper gold mineralization

Abstract Magnetite is the dominant Fe-oxide at the Acropolis IOCG prospect, Olympic Dam district, South Australia. Complementary microbeam techniques, including scanning transmission electron microscopy (STEM), are used to characterize titanomagnetite from veins in volcanic rocks and Ti-poor magnetite from a granite body with uplifted position in the volcanic sequence. A temperature of 670 ± 50 °C is estimated for Ti-poor magnetite using XMg-in-magnetite thermometry. Titanomagnetite, typified by Ti-rich trellis lamellae of ilmenite in magnetite, also displays sub-micrometer inclusions forming densely mottled and orbicular subtypes of titanomagnetite with increasing degree of overprinting. STEM analysis shows nanoparticles (NPs) of spinels and TiO2 polymorphs, anatase, and rutile. These vary as dense, finest-scale, monophase-NPs of spinel sensu stricto in Ti-poor magnetite; two-phase, ulvöspinelhercynite NPs in primary titanomagnetite; and coarser clusters of NPs (hercynite±gahnite+TiO2-polymorphs), in mottled and orbicular subtypes. Nano-thermobarometry using ilmenite-magnetite pairs gives temperatures in the range ~510–570 (±50) °C, with mineral-pair re-equilibration from primary to orbicular titanomagnetite constrained by changes in fO2 from ilmenite-stable to magnetite+hematite-stable conditions. Epitaxial relationships between spinel and Fe-Ti-oxides along trellis lamellae and among phases forming the NPs support exsolution from magnetitess, followed by replacement via mineral-buffered reactions. Lattice-scale intergrowths between ulvöspinel and ilmenite within NPs are interpreted as exsolution recording cooling under O2-conserving conditions, whereas the presence of both TiO2-polymorphs displaying variable order-disorder phenomena is evidence for subtly fO2-buffered reactions from anatase (reducing) to rutile (more oxidizing) stabilities. Transient formation of O-deficient phases is retained during replacement of ilmenite by anatase displaying crystallographic-shear planes. Development of dense inclusion mottling and orbicular textures are associated with NP coarsening and clustering during vein re-opening. Fluid-assisted replacement locally recycles trace elements, forming gahnite NPs or discrete Sc-Ti-phases. Hydrothermal titanomagnetite from Acropolis is comparable with magmatic magnetite in granites across the district and typifies early, alkali-calcic alteration. Open-fracture circulation, inhibiting additional supply of Si, Ca, K, and so on during magnetite precipitation, prohibits formation of silician magnetite hosting calc-silicate NPs, as known from IOCG systems characterized by rock-buffered alteration of host lithologies. Obliteration of trellis textures during subsequent overprinting could explain the scarcity of this type of hydrothermal magnetite in other IOCG systems.

First X-ray Spectroscopic Observations of Atmospheric Titanium Species: Size Dependence and the Emission Source.

Titanium dioxide (TiO2) in mineral dust is considered as one of the driving forces of photocatalytic reaction at the aerosol surface in the atmosphere. As a precursor of mineral dust, soil contains ilmenite (FeTiO3) and titanite (CaSiTiO5), which have lower photochemical reactivities than TiO2. However, Ti species other than TiO2 in aerosol particles are not well recognized due to the lack of observation in ambient samples. In this study, Ti species in size-fractionated aerosol samples collected in the Noto Peninsula, Japan, were determined by macroscopic and semi-microscopic X-ray absorption fine structure spectroscopy. Regardless of aerosol particle size, Ti species were primarily composed of rutile, anatase, ilmenite, and titanite. Semi-microscopic Ti speciation showed that Ti-poor spots associated with mineral dust were composed of a mixture of rutile, anatase, ilmenite, and titanite, and Ti-rich spots were primarily composed of TiO2 (rutile or anatase) derived from authigenic minerals or anthropogenic materials. Thus, the Ti species in aerosol particles, especially mineral dust, were not composed solely of TiO2 polymorphs. Therefore, the photochemical reactivities of Ti in aerosol particles may be overestimated when laboratory experiments or model studies employ TiO2 as the representative Ti species.

Electronic, Structural, and Optical Properties of Mono-Doped and Co-Doped (210) TiO2 Brookite Surfaces for Application in Dye-Sensitized Solar Cells-A First Principles Study.

Titanium dioxide (TiO2) polymorphs have recently gained a lot of attention in dye-sensitized solar cells (DSSCs). The brookite polymorph, among other TiO2 polymorphs, is now becoming the focus of research in DSSC applications, despite the difficulties in obtaining it as a pure phase experimentally. The current theoretical study used different nonmetals (C, S and N) and (C-S, C-N and S-N) as dopants and co-dopants, respectively, to investigate the effects of mono-doping and co-doping on the electronic, structural, and optical structure properties of (210) TiO2 brookite surfaces, which is the most exposed surface of brookite. The results show that due to the narrowing of the band gap and the presence of impurity levels in the band gap, all mono-doped and co-doped TiO2 brookite (210) surfaces exhibit some redshift. In particular, the C-doped, and C-N co-doped TiO2 brookite (210) surfaces exhibit better absorption in the visible region of the electromagnetic spectrum in comparison to the pure, S-doped, N-doped, C-S co-doped and N-S co-doped TiO2 brookite (210) surfaces.

Chemical Modification of Polaronic States in Anatase TiO2(101).

Two polymorphs of TiO2, anatase and rutile, are employed in photocatalytic applications. It is broadly accepted that anatase is the more catalytically active and subsequently finds wider commercial use. In this work, we focus on the Ti3+ polaronic states of anatase TiO2(101), which lie at ∼1.0 eV binding energy and are known to increase catalytic performance. Using UV-photoemission and two-photon photoemission spectroscopies, we demonstrate the capability to tune the excited state resonance of polarons by controlling the chemical environment. Anatase TiO2(101) contains subsurface polarons which undergo sub-band-gap photoexcitation to states ∼2.0 eV above the Fermi level. Formic acid adsorption dramatically influences the polaronic states, increasing the binding energy by ∼0.3 eV. Moreover, the photoexcitation oscillator strength changes significantly, resonating with states ∼3.0 eV above the Fermi level. We show that this behavior is likely due to the surface migration of subsurface oxygen vacancies.

The role of TiO2 polymorphs as support for the Keggin-type tungstophosphoric heteropolyacid as catalysts for n-butanol dehydration

An effect of using different TiO2 polymorphs as support for H3PW12O40 heteropolyacid on the (photo)catalytic performance of the H3PW12O40/TiO2 catalyst was investigated. Two kinds of synthesis methods of the catalysts have been applied. In the first, the H3PW12O40/TiO2 catalyst was prepared by impregnation of either the pure anatase (A), or rutile (R), or a mixture of the two (P25) in a solution of H3PW12O40. In the second method, an additional pre-treatment is being applied to all three types of support, A, R and P25, consisting of hydrothermal sonication with KOH solution. The catalysts and supports were characterized by XRD, SEM, BET analysis and FTIR spectroscopy. Catalytic tests show that H3PW12O40/P25 catalyst exhibits a higher (photo)activity to n-butanol dehydration in gas phase compared to the catalysts supported on either of pure polymorphs and that the sonication pre-treatment did not improve the activity of the catalysts so prepared. The application of the not treated P25 - the mixture of anatase and rutile as the support of heteropolyacid allowed to find the efficient heterogeneous catalyst.

Comparative study of the effect of the Hubbard coefficient U on the properties of TiO2 and ZnO

First-principles calculations combined with Hubbard U correction based on Density Functional Theory has been used to investigate the effect of its inclusion on electronic, structural, and optical properties and to reproduce correct band gap for TiO2 (anatase and rutile) and ZnO (wurtzite) structures. The effect of the implementation of U for only metal (Ti or Zn) d state (Ud) or for both 3d (Ud) and Op (Up) states was investigated to exploring changes in valence and conduction bands and their origin. Bader’s charge analysis has been used to revealing the nature of chemical bonding. We can conclude that for both TiO2 polymorphs as the Ud factor increases, both the BG and the lattice parameter increase. On the contrary, for ZnO, as Ud increases the value of BG increases but the cell parameter decreases. The optimal values correspond to Ud =8 eV (TiO2) and Ud =13 eV (ZnO). The corresponding optical properties using Ud, such as real and imaginary parts of dielectric function, reflectivity R(ω), refractive index n(ω), extinction coefficient k(ω), absorption coefficient α(ω) and electron energy loss function L(ω) has been calculated. It is important to highlight that the curves obtained considering the inclusion of the Ud show an excellent agreement with those reported experimentally.

Different antibacterial effect of Ag3PO4/TiO2 heterojunctions and the TiO2 polymorphs

Herein, we analyzed the antibacterial effect of the TiO2 polymorphs and Ag3PO4/TiO2 heterojunctions. The sol-gel-derived TiO2 was calcined at 400 °C, 550 °C and 700 °C to get different polymorphs. Subsequently, Ag3PO4/TiO2 composites were synthesized by the in-situ precipitation method. These photocatalysts were characterized by XRD, TEM, UV–VIS–NIR, XPS, FP, AAS, and SEM. Photocatalytic sterilization was employed by the transferring and spreading tests with Gram-positive S. aureus (ATCC 25933) and Gram-negative E. coli (ATCC 25922) bacteria. It was noted that the anatase TiO2 has better antibacterial effect than rutile. And there was an existing synergetic effect between these two polymorphs. Besides partially preventing the photo corrosion, the Ag3PO4/TiO2 heterojunctions exhibit a remarkable bactericidal activity and almost completely collapse the high concentration bacterial cells. Moreover, The Ag3PO4/TiO2 heterojunctions show more pronounced in E. coli than S. aureus for their different cellular structure. The sterilization of the tolerant Gram-positive bacteria often needs the assistance of Ag-ion, while Gram-negative E. coli is more sensitive to •O2− radicals, and h+ during the photocatalytic sterilization.

Synchrotron Radiation Spectroscopy and Transmission Electron Microscopy Techniques to Evaluate TiO2 NPs Incorporation, Speciation, and Impact on Root Cells Ultrastructure of Pisum sativum L. Plants.

Biosolids (Bs) for use in agriculture are an important way for introducing and transferring TiO2 nanoparticles (NPs) to plants and food chain. Roots of Pisum sativum L. plants grown in Bs-amended soils spiked with TiO2 800 mg/kg as rutile NPs, anatase NPs, mixture of both NPs and submicron particles (SMPs) were investigated by Transmission Electron Microscopy (TEM), synchrotron radiation based micro X-ray Fluorescence and micro X-ray Absorption Near-Edge Structure (µXRF/µXANES) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). TEM analysis showed damages in cells ultrastructure of all treated samples, although a more evident effect was observed with single anatase or rutile NPs treatments. Micro-XRF and TEM evidenced the presence of nano and SMPs mainly in the cortex cells near the rhizodermis. Micro-XRF/micro-XANES analysis revealed anatase, rutile, and ilmenite as the main TiO2 polymorphs in the original soil and Bs, and the preferential anatase uptake by the roots. For all treatments Ti concentration in the roots increased by 38–56%, however plants translocation factor (TF) increased mostly with NPs treatment (261–315%) and less with SMPs (about 85%), with respect to control. In addition, all samples showed a limited transfer of TiO2 to the shoots (very low TF value). These findings evidenced a potential toxicity of TiO2 NPs present in Bs and accumulating in soil, suggesting the necessity of appropriate regulations for the occurrence of NPs in Bs used in agriculture.

Phase evolution and optical properties of nanometric Mn-doped TiO2 pigments

This paper aims to evaluate the effects of calcination temperature and manganese doping on optical properties and phase evolution of Mn-doped TiO2 pigments. The powders were prepared by the polymeric precursor method at Mn contents of 0, 1, 2 and 3 % and calcined at 600, 700 and 800 °C. The results demonstrated that crystalline powders were produced in all conditions evaluated. It was further noted that the samples calcined at 600 °C were composed of rutile and anatase TiO2 polymorphs. However, the anatase phase was completely converted into rutile at temperatures above 700 °C. The particle size increased with increasing temperature. The same behavior was observed for the measured crystallite sizes. The Mn3+ ion charge was determined as the main valence for manganese ions in the TiO2 host. Oxygen vacancies are the probable crystal defects formed for charge balancing in the Mn-doped rutile structure. The results obtained for the powder with 3 % Mn and calcined at 800 °C demonstrated dopant cation segregation to form Mn2O3. It is important to emphasize that the absorbance values of the powders increase in the visible range when adding manganese compared to the absorbance values of pure TiO2. The band gap of the powders was reduced in accordance with the content of doping: from 3.04 eV (0 % Mn) to 2.05–2.20 eV (3 % Mn), with small differences depending on the calcination temperature. The increase in visible light absorbance led to a brown color in Mn-doped materials. Thus, the color intensity varied with the Mn content, ranging from light brown to dark brown powders. In conclusion, the temperature of 700 °C was established in this paper as the best condition to produce Mn-doped TiO2 pigments, based on the absence of anatase polymorph, small contents of residual carbon, and undetectable amounts of Mn2O3 due to segregation.

Low-pressure flame synthesis of carbon-stabilized TiO2-II (srilankite) nanoparticles

Nanoparticulate (3–10 nm) TiO2 polymorphs, i.e., rutile, anatase, and srilankite (also known as TiO2-II or α-PbO2-type TiO2) phases are produced via low-pressure (e.g., 20 torr) flame synthesis at temperatures ranging from 1560K to 2650K, with burner flow velocities varying from 150 to 300 cm/s, using titanium tetra-isopropoxide (TTIP) as precursor. Interestingly, added carbon (i.e., ethylene) in the feed stream produces nanoparticles of the generally characteristic low-temperature high-pressure metastable srilankite phase. The as-synthesized nanopowder is composed of either rutile or srilankite phase, with composition dependent on particle residence time in the flow field. Under the same conditions, feed gas without carbon, e.g., hydrogen, yields anatase phase TiO2. Post heat treatment up to 773K in thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) highlights the thermal stability of the samples, while x-ray photoelectron spectroscopy (XPS) indicates the presence of carbon, with absences of Ti3+, Ti–C, and nitrogen. Microscopy reveals morphology on both the micrometer scale (scanning electron microscopy, SEM) and nanometer scale (transmission electron microscopy, TEM), while x-ray diffraction (XRD) and selected area electron diffraction (SAED) confirm polymorph variation under different synthesis conditions. CHN analysis determines that the synthesized srilankite contains a greater weight percentage of carbon than does anatase. Excess carbon doped into the lattice during low-pressure flame synthesis seems to be the key in stabilizing the high-pressure srilankite phase for such nanoparticles.

Correct Structural Phase Stability of FeS2, TiO2, and MnO2 from a Semilocal Density Functional

The structural phase stabilities of iron disulfide (FeS2), titanium dioxide (TiO2), and polymorphs of manganese oxides (MnO2) are known to be challenging problems for the semilocal exchange-correlation (xc) approximations of the Density Functional Theory. Popular and nonempirical semilocal xc functionals fail badly for at least one of these solids. For example, the strongly constrained and appropriately normed (SCAN) meta-GGA xc functional fails to predict the correct ground state for FeS2 (pyrite and marcasite polymorphs) and TiO2 (rutile and anatase polymorphs) structures but yields accurate formation energies and the correct ground state of all MnO2 polymorphs. In this work, we find that the recently proposed meta-GGA constructed from the cuspless hydrogen exchange hole density (MGGAC) [Phys. Rev. B 2019, 100, 155140] can predict the correct ground state of polymorphs of FeS2, TiO2, and MnO2. Moreover, when compared to the experimental results, we also obtain the quantitatively good agreement from the MGGAC functional for the structural properties and bandgaps of those solids, and this agreement indicates the feasibility of this method.

Upper temperature limits of orogenic gold deposit formation: Constraints from TiO2 polymorphs in the Dongyuan Au deposit, Jiangnan Orogen, China

Abstract Gold (Au) deposits have formed in orogenic belts throughout Earth’s history. However, the upper temperature limits of orogenic Au vein formation are difficult to constrain because measurements made on fluid inclusions focus on intermediate to late-stage minerals (e.g., quartz and calcite) or are based on P-T estimates for the metamorphic mineral assemblages of the host rocks. We conducted a study of TiO2 polymorphs that are among the earliest minerals that grew in Au-bearing veins of the Dongyuan deposit, Jiangnan orogenic Au belt, South China. Based on Raman analyzes, we identified TiO2 polymorphs of anatase (with Raman peaks at 396, 515, and 638 cm−1), rutile (with Raman peaks at 235, 447, and 613 cm−1), and anatase–rutile intergrowths. Transmission electron microscope (TEM) confirmed the polymorphs identifying the [111] zone axis of anatase, [110] zone axis of rutile, and [111] and [111] zone axes of rutile–anatase intergrowths. The TiO2 polymorphs in the Dongyuan Au veins constrain a temperature range for early mineral precipitation in the veins of 450–550 °C. The results show that ore-forming fluids for this orogenic Au deposit emplaced in the shallow crust originated from deeper and hotter crustal levels (e.g., high-grade metamorphic rocks in the middle to lower crust).

Characteristics of the hierarchical porous TiO2 layer synthesized on Ti via plasma electrolytic oxidation: Role of the applied voltage

A tailored porous ceramic layer of TiO2 was in-situ synthesized through Plasma Electrolytic Oxidation (PEO) process, using phosphate-based electrolyte at different applied voltages. The set-up was regulated to carry the process in low (430 V), medium (470 V), and high (510 V) voltages. The effects of applied voltage on the phase arrangement, microstructural, and morphological characteristics of the ceramic layer were then studied using X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The results showed that utilizing a relatively medium applied voltage of 470 V (ΔV of 130 V) can lead to a hierarchical TiO2 layer, which not only includes a mixture of both anatase and rutile TiO2 polymorphs but also presents a combined micro/nano-pores morphology. It was also found that while the lowest applied voltage leads to a relatively homogenous layer from morphological and roughness approaches, higher applied voltages may promote heterogeneities of the morphological characteristic. The formation mechanisms and morphological outcomes were finally discussed and graphically illustrated.

Significant influences of crystal structures on photocatalytic removal of NOx by TiO2

NOx are ubiquitous pollutants and TiO2 has been widely used for photocatalytic removal of NOx. However, effects of TiO2 crystal structures on the NOx removal still remain unclear. Different TiO2 polymorphs, including anatase, rutile and mixed phase TiO2, were prepared by controlling the acidity or alkalinity in hydrothermal synthesis process. The composition, structure and property of photocatalysts were well characterized using X-ray diffractometer, scanning electron microscopy, Fourier transform infrared spectra, Raman spectra, X-ray photoelectron spectroscopy and UV–vis spectra. It was confirmed that the photocatalytic activity of TiO2 strongly depended on the percentage of anatase in photocatalysts. The NOx removal efficiency of TiO2 presented an increase with increasing the anatase content, while the selectivity of NO2 exhibited an opposite trend. This may be ascribed to higher inherent photoactivity, more surface hydroxyl groups and larger specific surface area of anatase TiO2 compared to rutile TiO2.

Templated epitaxy of TiO2(B) on a perovskite

The bronze-phase TiO2(B) has an open atomic framework that makes it a good candidate for applications in photochemical and electrochemical conversion of energy. However, the synthesis of bronze-phase TiO2(B) thin films on perovskite substrates, such as SrTiO3 (STO), which is one of the most conventional versatile substrates for oxide epitaxy, has been extremely challenging owing to the preferential formation of the anatase TiO2 over TiO2(B). The main reason is that the anatase TiO2 has not only a smaller lattice mismatch than TiO2(B), but also a better structural symmetry match when grown on STO. Here, we demonstrate a way to circumventing this problem by using a VO2(B) buffer layer, yielding the growth of a high-quality single crystalline TiO2(B) film on a (001)-oriented STO substrate. From the resulting TiO2(B) film, we found that this film has a large optical bandgap of ∼3.6 eV, which is close to the known theoretical value, the largest among TiO2 polymorphs, and useful for developing high-power energy devices.

Surface functionalized N-C-TiO2/C nanocomposites derived from metal-organic framework in water vapour for enhanced photocatalytic H2 generation

Surface-functionalized nitrogen/carbon co-doped polymorphic TiO2 phase junction nanoparticles uniformly distributed in porous carbon matrix were synthesized by a simple one-step pyrolysis of titanium based metal–organic framework (MOF), NH2-MIL-125(Ti) at 700 °C under water vapour atmosphere. Introducing water vapour during the pyrolysis of NH2-MIL-125(Ti) not only functionalizes the derived porous carbon matrix with carboxyl groups but also forms additional oxygen-rich N like interstitial/intraband states lying above the valence band of TiO2 along with the self-doped carbon, which further narrows the energy band gaps of polymorphic TiO2 nanoparticles that enhance photocatalytic charge transfer efficiency. Without co-catalyst, sample N-C-TiO2/CArW demonstrates H2 evolution activity of 426 µmol gcat-1 h−1, which remarkably outperforms commercial TiO2 (P-25) and N-C-TiO2/CAr with a 5-fold and 3-fold H2 generation, respectively. This study clearly shows that water vapour atmosphere during the pyrolysis increases the hydrophilicity of the Ti-MOF derived composites by functionalizing porous carbon matrix with carboxylic groups, as well as enhancing the electrical conductivity and charge transfer efficiency due to the formation of additional localized oxygen-rich N like interstitial/intraband states. This work also demonstrates that by optimizing the anatase–rutile phase composition of the TiO2 polymorphs, tuning the energy band gaps by N/C co-doping and functionalizing the porous carbon matrix in the N-C-TiO2/C nanocomposites, the photocatalytic H2 generation activity can be further enhanced.

A new methodological approach (QEMSCAN®) in the mineralogical study of Polish loess: Guidelines for further research

Abstract This article presents in detail the methodology dedicated strictly to loess mineralogical investigation by automated mineralogy system QEMSCAN® (quantitative evaluation of minerals by scanning electron microscopy (SEM)), which couples SEM and energy dispersive X-ray spectrometry to automatically deliver mineral and phase mapping. The present study provides guidelines for further loess investigation in Poland, in order to maintain the complete comparability of results which will be obtained. The methodology is then used to obtain the data on complex mineralogical composition (heavy, light, transparent and opaque phases). In total 1,159,107 particles have been measured for five bulk loess samples and 4–6% of them were heavy minerals (c.a. 10,000 per sample). The bulk samples are dominated by quartz (57.3–62.9%) and contain plagioclase (7.8–9.2%), K-feldspar (7.9–8.7%), carbonates (5.0–7.8%), muscovite (3.2–6.2%), biotite (4.2–7.5%), heavy minerals (4.3–5.8%) and clay minerals (0.9–1.6%). The heavy minerals (as a group recalculated to 100%) are mainly represented by phases such as clinopyroxene (38–51%), garnets (14–21%), TiO2 polymorphs (8–12%), Al2SiO5 polymorphs (3–7%), ilmenite (3–6%), iron oxides, e.g., hematite and magnetite (2–5%) and zircon (∼2%). Nearly 50% of the heavy minerals is classified in the 16–31 µm fraction, which determine the changes in the current research procedure traditionally used for Polish loess.

Effect of TiO2 phase on the photocatalytic degradation of methylene blue dye

Several industrial processes make use of dyes in order to impart colour into their products. These processes release large amounts of dye-containing wastewater which can be hazardous to human health and the environment. This has necessitated the development of cheap, reliable and sustainable technologies that can remediate the effluent, heterogeneous TiO2 photocatalysis is one such technology that has proven successful. Different polymorphs of TiO2 exist and literature suggests that the photocatalytic efficiency of various phases depends on the target pollutant. This study investigated the photocatalytic degradation of methylene blue (MB) dye using of three commercial TiO2 powders with different crystal phases as catalysts. The materials properties for each catalyst were first determined using x-ray diffraction and microscopy. Degradation studies were then conducted on 10 ppm MB solutions using the three powders. Degussa P25 TiO2, a mixture of anatase and rutile was the most efficient compared to the neat anatase and rutile powders, degrading 81.4% of the MB. This catalyst was chosen for optimisation studies, where 95% degradation was achieved at a 0.5 g/L catalyst loading and pH of 10. The degree of mineralisation decreased with increasing MB concentration. The effect of metal doping on the photocatalytic performance of the catalyst was also investigated. Copper doping increased degradation by 2% whilst zinc reduced it to 90%. The complete decolourisation of the MB coupled with the significant decrease in TOC upon completion of the degradation process, indicate that Degussa P25 catalysed photocatalysis is a viable pre-treatment technology in dye contaminated wastewater treatment.

Role of surrounding crystallization media in TiO2 polymorphs coexistence and the effect on AOPs performance

Two TiO2 catalysts were prepared by sol-gel method, with the only singularity of the critical solvent removal step prior to heat-induced crystallization. Their different physico-chemical properties caused very distinct activity in the phenol degradation by several AOPs: heterogeneous photocatalysis and ozonation based processes (catalytic and photocatalytic). The remarkable differences found in structural, morphological and chemical surface properties, for both TiO2 catalysts, were ascribed to the differences in the crystallization environment, driving to diverse titania polymorphs. Titanium dioxide (TiEt-B) prepared with an exhaustive step for organics removal by dialysis, has given place to open-structured metastable brookite/anatase mixtures. This crystal structure has generated a texture governed by meso- and macroporosity with a large surface area, acidity and hydroxyl density. The lower hydrodynamic particle size in the aqueous media increased photo-exposed surface, which has led to higher mineralization degrees in phenol catalytic degradation performance, especially in all light-driven catalytic AOPs studied here.

Convenient Route to Heterometallic Group 4-Zinc Precursors for Binary Oxide Nanomaterials.

In this study, simple and efficient synthetic routes to a family of uncommon group 4-zinc heterometallic alkoxides were developed. Single-source molecular precursors with the structures [Cp2TiZn(μ,η-OR)(THF)Cl2] (1), [Zr3Zn7(μ3-O)(μ3,η2-OR)3(μ-OH)3(μ,η2-OR)6(μ,η-OR)6Cl6] (2), and [Hf3Zn7(μ3-O)(μ3,η2-OR)3(μ-OH)3(μ,η2-OR)6(μ,η-OR)6Cl6] (3) were prepared via reduction of Cp2TiCl2 with metallic zinc or protonolysis of the metal-cyclopentadienyl bond in Cp2M'Cl2 (M' = Zr or Hf) in the presence of 2-methoxyethanol (ROH) and Zn(OR)2. This synthetic route enables the creation of compounds with well-defined molecular structures and therefore provides precursors suitable for obtaining group 4-zinc oxides. Precursors 1-3 were characterized by elemental analysis, nuclear magnetic resonance and infrared spectroscopies, and single-crystal X-ray diffraction. Compound 1 decomposed at 800-900 °C to give a mixture of binary metal oxides (i.e., Zn2Ti3O8, ZnTiO3, or Zn2TiO4) and common polymorphs of TiO2 and ZnO. After calcination at 1000 °C, only TiO2 and the high-temperature-stable phase Zn2TiO4 were observed. Thermolysis of compounds 2 and 3 gave mixtures of ZnO and ZrO2 or HfO2, respectively. The obtained ZnO-ZrO2 and ZnO-HfO2 mixed oxide materials have constant phase compositions across a broad temperature range and therefore are attractive host lattices for Eu3+ for applications as yellow/red double-light-emitting phosphors. It was established that Eu3+ ions were successfully introduced into the ZnO and ZrO2/HfO2 lattices. It was revealed that Eu3+ ions prefer to occupy low-symmetry sites in ZrO2/HfO2 rather than in ZnO.