Anatase Fraction Research Articles

"Core/Shell" Nanocomposites as Photocatalysts for the Degradation of the Water Pollutants Malachite Green and Rhodamine B.

"Core/shell" composites are based on a ferrite core coated by two layers with different properties, one of them is an isolator, SiO2, and the other is a semiconductor, TiO2. These composites are attracting interest because of their structure, photocatalytic activity, and magnetic properties. Nanocomposites of the "core/shell" МFe2O4/SiO2/TiO2 (М = Zn(II), Co(II)) type are synthesized with a core of MFe2O4 produced by two different methods, namely the sol-gel method (SG) using propylene oxide as a gelling agent and the hydrothermal method (HT). SiO2 and TiO2 layer coating is performed by means of tetraethylorthosilicate, TEOS, Ti(IV) tetrabutoxide, and Ti(OBu)4, respectively. A combination of different experimental techniques is required to prove the structure and phase composition, such as XRD, UV-Vis, TEM with EDS, photoluminescence, and XPS. By Rietveld analysis of the XRD data unit cell parameters, the crystallite size and weight fraction of the polymorphs anatase and rutile of the shell TiO2 and of the ferrite core are determined. The magnetic properties of the samples, and their activity for the photodegradation of the synthetic industrial dyes Malachite Green and Rhodamine B are measured in model water solutions under UV light irradiation and simulated solar irradiation. The influence of the water matrix on the photocatalytic activity is determined using artificial seawater in addition to ultrapure water. The rate constants of the photocatalytic process are obtained along with the reaction mechanism, established using radical scavengers where the role of the radicals is elucidated.

Total Specific Energy as a New Figure of Merit for the Design of Porous TiO2 Surfaces Synthesized via Plasma Electrolytic Oxidation

The plasma electrolytic oxidation (PEO) is a variation of the anodic oxidation technique, one of the simplest and most economical methods to obtain crystalline and porous TiO2 coatings. Beyond the conventional approach of establishing a relationship between the variables of synthesis and the characteristics of the TiO2 coatings, a new figure of merit was defined in the present work for the synthesis of TiO2 coatings by PEO: the total energy per unit of surface (TSE). A strong relationship was found between TSE and the TiO2 anatase fraction. The application of TSE, together with the known influence of the variables of synthesis on the coating characteristics, allows a prediction, previously to the anodization and with reasonable precision, of the anatase fraction and the pore diameter of the coating. Applying the TSE new concept, three coatings were successfully designed. This is the first step toward a surface design using the PEO technique.

Light-assisted synthesis of Au/TiO2 nanoparticles for H2 production by photocatalytic water splitting

A series of Au/TiO2 photocatalysts was synthesized via the light assistance through the photo-deposition for H2 production by photocatalytic water splitting using ethanol as the hole scavenger. Effect of solution pH in the range of 3.2–10.0 on the morphology and photocatalytic activity for H2 production of the obtained Au/TiO2 photocatalysts was explored. It was found that all Au/TiO2 photocatalysts prepared in different solution pH exhibited comparable anatase fraction (∼0.84–0.85) and crystallite size of TiO2 (21–22 nm), but showed different quantity of deposited Au nanoparticles (NPs) and other properties, particularly the particle size of the Au NPs. Among all prepared Au/TiO2 photocatalysts, the Au/TiO2 (10.0) photocatalyst exhibited the highest photocatalytic activity for H2 production, owning to its high metallic state and small size of Au NPs. Via this photocatalyst, the maximum H2 production of 296 μmol (∼360 μmol/g⋅h) was gained at 240 min using the 30 vol% ethanol as the hole scavenger at the photocatalyst loading of 1.33 g/L under the UV light intensity of 0.24 mW/cm2 with the quantum efficiency of 61.2% at 254 nm. The loss of the photocatalytic activity of around 20% was observed after the 5th use.

Thermal Stability of the Structure and Optical Properties of Nanostructured TIO2 Films

The structure and optical properties of titanium dioxide films have been studied during annealing from 100 to 400°C. The films were obtained by ion-plasma high-frequency magnetron sputtering of polycrystalline rutile target in an argon atmosphere. It was shown that as-prepared TiO2 films are nanostructured with ~8 nm rutile crystallites and ~3.3 A interplanar distances and contain a small fraction of anatase. The optical band gap of the films is 3.01 eV, and the refractive index under normal conditions is 2.25. The film annealing at tamperatures from 100 to 400°C does not practically change their structure, optical band gap, and refractive index under normal conditions, i.e., the obtained nanostructured TiO2 films are thermally stable.

Formation of carbon-added anatase-rich TiO2 layers on titanium and their antibacterial properties in visible light

ObjectiveTo avoid risk of infections associated with dental implants, thermal oxidation processes for practical dental Ti alloys were studied for both high bonding strength and antibacterial properties in visible light. MethodsTwo-step thermal oxidation, comprising carburization (first step of treatment: in Ar-1%CO gas) and subsequent oxidation (second step of treatment: in air), was conducted on commercially pure (CP) Ti, Ti-6Al-4V (Ti64), and Ti-6Al-7Nb (Ti67) alloys to form TiO2 layers. Their bonding strengths and antibacterial properties against Escherichia coli (E. coli) in visible light (λ ≥ 400 nm) were evaluated. ResultsTiO2 layers formed on each metal were composed of anatase and/or rutile. Anatase fraction and carbon concentration in the layers decreased with increasing temperature in the second step of treatment. Antibacterial properties of the TiO2 layers were dependent on the temperature in the second step of treatment. An approximate antibacterial activity value of 2 (killing ∼99% bacteria) was obtained when the temperatures in the second step of treatment were 673 and 773 K for CP Ti, 773 K for Ti64, and 773 and 873 K for Ti67. It was found that the TiO2 layer must contain carbon and be anatase-rich to exhibit excellent antibacterial properties. Bonding strength between the substrate and TiO2 layers formed at 773 K in the second step of treatment exceeded 80 MPa and was independent of substrate type. SignificanceTiO2 layers, possessing both high bonding strength and excellent antibacterial properties, were successfully formed on practical dental Ti alloys via two-step thermal oxidation.

Performance of TiO2/Graphene (cocoPAS) Composite as Photocatalyst for Removal of Phenols in Aqueous Solution

As one of the hazardous industrial wastes, an excessive amount of phenol in the environment can cause damage to the biological ecosystem and nutrient cycle. Phenol removal can be done by photocatalysis process using photocatalyst materials such as titanium dioxide (TiO2). The photocatalysis activity of TiO2 can be improved by making TiO2-graphene (cocoPAS) composite. The obtained TiO2-graphene (cocoPAS) composite was characterized by Scanning Electron Miscroscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared absorption spectroscopy (FTIR), and Breneur Emmet Teller (BET). The performance of the TiO2-graphene (cocoPAS) composite in phenol degradation was tested in a photocatalysis process with variation are the concentration of phenol (10, 20, and 30 ppm, respectively) and photocatalysis temperature (30, 40, and 50 °C, respectively). TiO2 particle loaded on the graphene sheet and Ti-O-C bond was formed at 719 cm−1. The size of anatase and rutile crystals are 26.39 nm and 27.39 nm with the fraction of anatase and rutile are 57% and 43%. The surface area of the TiO2-graphene (cocoPAS) composite is 40.9 m2/g. The highest efficiency of phenol degradation was achieved when the concentration of phenol is 10 ppm and photocatalysis temperature is 50°C which efficiency of phenol degradation is 96.9%. The higher concentration of phenol will decrease the efficiency of degradation but the degradation efficiency of phenol increases with an increase in photocatalysis temperature.

STUDY OF THE STRUCTURAL-PHASE STATE OF NITROGEN – CONTAINING COATINGS OF TITANIUM DIOXIDE SYNTHESIZED BY THE REACTIVE MAGNETRON SPUTTERING

The paper presents the results of the study of the effect of ratios of reactive gases N2 and O2 on the structural phase state and the mechanical properties of nitrogen-containing titanium dioxide coatings obtained by reactive magnetron sputtering on the surface of AISI 304 stainless steel. According to the results of the X-ray phase analysis, the coatings contain titanium dioxide in the form of anatase, rutile and a small amount of brookite. It was found that with an increase in the nitrogen content in the working atmosphere, the volume fraction of anatase and rutile increases. An increase in the nitrogen content in the gas atmosphere leads to the formation of a quasihomogeneous surface texture with a less pronounced block structure. Based on the results of nanoindentation, it can be assumed that the formation of a quasihomogeneous texture can cause a decrease in the physicomechanical parameters of the coatings. It was established that the structure, phase composition, and mechanical properties of the coatings depend on the gas ratio N2/O2 in theт negative bias mode (Ubias = −150 V).

NITROGEN-DOPED TITANIUM DIOXIDE NANOFILMS FOR MEDICAL APPLICATION

The results of study of nitrogen-containing titanium dioxide nanofilms (N-TiO2) are presented in this work. These nanofilms are used in biomedicine as a biocoating of the implants that is why the problem of increasing resistance is very essential. Biocoatings were deposited by reactive magnetron sputtering at different bias voltages Ub = 0-100 V. Doping of the oxide film with nitrogen, with technological replacement of oxygen by nitrogen atoms, changes the material properties: antithrombogenic qualities appear and hemocompatibility rates increase. The corrosion resistance rates of the film are also increased. The biocoatings are partially dissolved, when interacting with biological fluids, with a further release/formation of compounds with an N-O bond, which are essential for human activity. X-ray diffraction (XRD) was used to study the phase transition and crystallinity of nanofilms. The rutile phase dominates (68%) when a negative bias in these films was used. The volume of the fraction increases permanently with increasing of nitrogen content in the composition of the reactive gas, while the volume fraction of anatase decreases to 10%. The surface morphology was studied using scanning electron microscopy. It was established that the films have a more fine-grained structure than at the displacement equals zero. Chemical stability and the presence of elements were observed using X-ray fluorescence spectrometry (XFS) and atomic emission spectrometry (AES). The results of measurement of the contact angle and the surface energy are presented. The results of the study showed the influense of bias voltage on the phase composition, surface morphology and chemical properties of N-TiO2 nanofilms. The analysis of the results suggests that N-TiO2 films under consideration may play the role of nitric oxide depot directly in the field of pathology if they serve as implants coating.

Enhanced photodegradation activity of electrospun porous TiO2 fibers

Mesoporous titanium dioxide (TiO2) hollow nanofibers (HNFs) were successfully prepared by a facile electrospinning and calcination method. Techniques such as X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize TiO2 fibers. It was revealed that TiO2 crystals with an appropriate anatase fraction (71.58%) were grown and a tubular mesoporous structure was formed with a high specific surface area. Photodecomposition of methyl orange (MO) solution showed that TiO2 HNFs exhibited much higher photocatalytic activity than corresponding TiO2 nanofibers (NFs) and loose-structured nanofibers (LNFs). The significant enhancement of photocatalytic activity was attributed to both the sufficient growth of active anatase phase primarily and a tubular mesoporous nature of TiO2 HNFs.

Enhanced protective coatings on Ti-10V-2Fe-3Al alloy through anodizing and post-sealing with layered double hydroxides

Anodic oxidation is a prevalent technique to introduce superior corrosion and wear resistance upon the surface of titanium (Ti) alloys, in which the selection of appropriate electrolytes and defect-sealing strategies is a key. This study aims to address such issues through anodizing Ti-10V-2Fe-3Al alloy in malic acid, followed by a post-sealing treatment with Mg-Al layered double hydroxides (LDHs). The characteristics of the samples were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), glow discharge optical emission spectroscopy (GDOES), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). SEM micrographs reveals that the anodic coating had a surface full of bulges and cracks, and was almost sealed by the following LDHs treatment. XRD pattern indicate that the anodic coating was mainly consisted of amorphous TiO2 with a small fraction of anatase, but its crystallization degree was increased through the post-sealing. Moreover, electrochemical and tribological measurements demonstrate that corrosion current density was 2.8 × 10−6, 2.0 × 10−7, 5.9 × 10−9 A cm−2, and wear rate was 1.45 × 10−3, 1.30 × 10−4 and 6.90 × 10−5 mm3 N-1 m-1 for respective bare Ti-10V-2Fe-3Al alloy substrate, anodized specimens without and with the LDHs post treatment. Finally, a plausible wear mechanism was proposed.

Plasma-modified TiO2/polyetherimide nanocomposite fibers for photocatalytic degradation of organic compounds

For the first time, submicrometric polyetherimide (PEI) fibers were electrospun with incorporated TiO2 nanoparticles. Moreover, the fibers were submitted to cold plasma in air and nitrogen atmospheres to enhance adhesion and photocatalytic performance. The nanocomposites were characterized by scanning and transmission electron microscopy, X-ray diffractometry, UV–vis diffuse reflectance spectroscopy, contact angle, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. PEI-TiO2 nanocomposite fiber diameter was 691 ± 416 nm (d50) with TiO2 nanoparticles of ˜30 nm particle diameter. Nanocomposite fibers exhibited a band gap of 3.55 eV and high hydrophilic behavior. The results suggest that the plasma treatment modified the interface between TiO2 nanoparticles and the PEI substrate but did not change expressively the anatase fraction of incorporated nanoparticles. After exposure to plasma-modified TiO2/PEI nanocomposite fibers, concerning photocatalysis, a total discoloration of methylene blue was achieved after 40 min; as well as 75% of methyl orange and tetracycline (TC) after 120 min. Moreover, the immobilized photocatalyst presented high stability after 5 successive cycles. Plasma-treated nanocomposite fibers reached kinetic constants up to 0.10 min−1, 3 times higher than the values found in the literature.

One-pot synthesis visible-light-active TiO2 photocatalysts at low temperature by peroxotitanium complex

A series of TiO2 nanoparticles with different anatase/rutile ratio were prepared by peroxotitanium complex at low temperature (≤200 °C). Our approach provides the notable advantage of a one-step reaction without any addition of solvents or pH-adjusting agents, which is green and energy-efficient. The structural, morphological, as well as spectroscopic properties of prepared samples were characterized by XRD, Raman, BET, TEM, UV–vis, XPS, FTIR and TG-MS techniques. The results showed that anatase fraction of TiO2 increased with the increase of aging temperature. Moreover, carbonate-like species, probably formed by the in-situ oxidation of the substituent group of titanium precursor by H2O2, was incorporated into the TiO2 matrix at certain temperatures (150 and 175 °C) and enhanced visible light absorption, such samples represented as T150 and T175. It was found that T150 and T175 exhibited the superior photocatalytic activity for the degradation of Rhodamine B (RhB) aqueous solution under visible light irradiation (λ ≥ 400 nm), which is about 10-fold more active than commercial Evonik-Degussa P25. The excellent activity of as-prepared samples can be attributed to the enhanced visible light absorption and the enhanced dye adsorption capacity, and the plausible photocatalytic mechanism was studied.

Room‐Temperature Hydrolysis of Potassium Titanyl Oxalate and Water‐Assisted Crystallization for TiO2 with High Photocatalytic Activity

AbstractThe commonly adopted approach to synthesize nanostructured TiO2 starting from titanates demands a hydrothermal environment to achieve the titanate precursor, and a subsequent high temperature calcination to fulfill the decomposition of titanates and crystallization of TiO2. In this report, hydrogen titanate aggregates were achieved by a room‐temperature hydrolysis of a potassium titanyl oxalate in an aqueous H2O2 solution. The subsequent immersion in water at 80 °C induced the crystallization of TiO2 with a mixture of anatase nanoparticles and rutile nanorods. The anatase fraction increased with increasing immersing duration in hot water for up to 72 h. The low‐temperature crystallized TiO2 powders possessed abundant surface hydroxyl groups (∼38 %), high specific surface area (∼126 m2/g) and pore volume (∼0.50 cm3/g). When utilized to assist photodegradation of rhodamine B in water under UV light illumination, the reaction rate constant was twice that of the commercial P25 TiO2 nanoparticles. The high photocatalytic activity is contributed to the abundant surface hydroxyl groups, high specific surface area, and the appropriate mixture of anatase nanoparticles and rutile nanorods (∼84:16 in weight).

Phase quantification by X-ray photoemission valence band analysis applied to mixed phase TiO2 powders

A method of quantitative phase analysis using valence band X-ray photoelectron spectra is presented and applied to the analysis of TiO2 anatase-rutile mixtures. The valence band spectra of pure TiO2 polymorphs were measured, and these spectral shapes used to fit valence band spectra from mixed phase samples. Given the surface sensitive nature of the technique, this yields a surface phase fraction. Mixed phase samples were prepared from high and low surface area anatase and rutile powders. In the samples studied here, the surface phase fraction of anatase was found to be linearly correlated with photocatalytic activity of the mixed phase samples, even for samples with very different anatase and rutile surface areas. We apply this method to determine the surface phase fraction of P25 powder. This method may be applied to other systems where a surface phase fraction is an important characteristic.

Mesoporous thin film structures as metal nanoparticle reactors for electronic circuits: Effects of matrix crystallinity and nanoparticle functionalization

There is an increasing interest in versatile nanoelectronic structures based on stable, accessible and spatially located arrays of metal nanoparticles. In this study, the influences of mesoporous titania thin film crystallinity and pore features over electrical conductivity of embedded Ag-nanoparticles were analyzed. Although matrices treated at lower temperatures have shown less pore connectivity, less extensive anatase fraction and lower silver content, they revealed higher electrical conductivity than matrices treated at higher temperatures. This was interpreted as better connectivity among particles from plasmon behavior. The stability of this system was significantly enhanced through upon chemisorption of 1-octanethiol self-assemble monolayers over Ag-nanoparticles. The maximum plasmon absorbance remained practically unaltered after storage for at least 15 days and the current remains stable up to 20 voltage cycles. This demonstrates that a stable and accessible conductive nanocomposite circuit consisting of alkanethiol-functionalized metal nanoparticles embedded in a mesoporous oxide thin film matrix can be produced.

Advances on the synthesis of porous TiO2 coatings by anodic spark oxidation. Photocatalytic reduction of Cr(VI)

Porous TiO2 coatings were obtained by anodic oxidation in spark discharge conditions, varying the range of current density (200–3000 A m−2) and the electrolyte concentration (H2SO4; 1 and 4 M). The samples were characterized by SEM, XRD and DRS. The photocatalytic activity was evaluated using the Cr(VI)/EDTA reductive system to find the optimal conditions for a high photocatalytic activity. A higher electrolyte concentration increased the pore diameter, the porous fraction and the coating thickness and, consequently, the photocatalytic activity; a higher current density improved the performance of coatings. A relationship between the anatase fraction and the photocatalytic activity of the samples was demonstrated, with a maximum activity close to 0.65 anatase fraction. The thermal treatment of the anodic coatings improved also the photocatalytic activity, without changes on neither the morphology nor the anatase fraction. The maximum Cr(VI) transformation achieved by the most active coating was 89.1% while a coating prepared with Evonik P25 achieved only 69.9%. The obtained TiO2 anodic coatings present great potential for application in heterogeneous photocatalysis processes in water and wastewater treatment as supported photocatalysts.

Influence of the Dopant Concentration on the Photocatalytic Activity: Al-Doped TiO2

A set of Al-doped titania x-Al-TiO2 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.1 wt % Al) has been synthesized by a sol–gel method and tested in the reaction of the photocatalytic degradation of phenol in aqueous suspension. XRD and Raman studies show that the TiO2 samples have a mixed-phase rutile-anatase crystalline structure with linear increase of the anatase fraction from 0.0 wt % for 0.0-Al-TiO2 up to 18 wt % for 1.1-Al-TiO2. A decrease of the particle size from ∼800 to 50 nm and an increase of the specific surface area from 1.7 m2/g up to 28 m2/g with increased content of Al have been observed. The data of XRD, XPS, Raman spectroscopy, and EDS techniques show rather homogeneous aluminum distribution with only the Al(3+) oxidation state of aluminum incorporated in the TiO2 lattice. The bandgap energy Eg = (2.93 ± 0.1) eV corresponding to indirect allowed transitions does not depend on the aluminum content within the 0.0–1.1 wt % Al concentration range. The photocatalytic testing of Al-doped TiO2 samples i...

Formation of TiO2 layers on commercially pure Ti and Ti–Mo and Ti–Nb alloys by two-step thermal oxidation and their photocatalytic activity

Anatase-containing TiO2 layers were formed on commercially pure (CP) Ti and Ti–25mass%Mo (Ti–25Mo) and Ti–25mass%Nb (Ti–25Nb) alloys by two-step thermal oxidation. The first-step treatment was conducted in an Ar–1%CO atmosphere at 1073K for 3.6ks, and the second-step treatment was conducted in air at 673–1073K for 10.8ks. The second-step temperature range for anatase formation was wider in the Ti alloys than in CP Ti. Photo-induced superhydrophilicity under UV irradiation was observed for the TiO2 layers with anatase fractions ≥0.6 on CP Ti and the Ti–25Mo alloy, and with anatase fractions ≥0.18 on the Ti–25Nb alloy. The TiO2 layers on the Ti–25Nb alloy exhibited excellent photocatalytic activity in the low anatase fraction region, which is considered to be caused by the incorporation of 1–3at% Nb into the TiO2 layers. The rate constant of methylene blue degradation showed maxima at anatase fractions of 0.6–0.9.

Structure–activity relationship of nanosized porous PEG-modified TiO2 powders in degradation of organic pollutants

This study aims to gain insights in structure–activity relationship of TiO2 photocatalysts. For this purpose photocatalysts were synthesized via classical sol–gel method using titanium isopropoxide as a precursor and polyethylene glycols (PEGs) of different molecular mass (Mn=200, 600, 2000, 10,000) as a template agents. Incorporating PEG into TiO2 network enhanced not only catalyst porous structure, but also increased the fraction of anatase phase. The use of low-molecular-weight PEGs resulted in catalysts with increased anatase content and enlarged specific surface area. The catalyst photoactivity was estimated through degradation of organic pollutants: Reactive Black 5, arylazo pyridone dye and phenol. The results revealed that the photoactivity was following the same order independently of target pollutant: TiO2/P600>TiO2/P200>TiO2/P2000>TiO2/P10000>TiO2. BET surface area and anatase fraction, rather than pore diameter or pore volume, were found to be predominant catalyst property determining the activity for particular reaction system. The existence of synergistic effect between anatase and rutile phases was confirmed for the most active catalysts TiO2/P200 and TiO2/P600. These catalysts showed similar activity in dye degradation, while TiO2/P200 displayed significantly lower activity in phenol degradation, which was attributed to its lower sorption capacity and lower UV light utilization. The difference in the reactivity between investigated pollutants was discussed in relationship with their size, structure and sorption ability.

Macroporous Titanate Nanotube/TiO2 Monolith for Fast and Large-Capacity Cation Exchange

Centimeter-scale monolithic composites constituted of titanate nanotubes (TNTs) and titania nanoparticles were hydrothermally prepared from a concentrated aqueous emulsion of anatase TiO2 powder. The monolith was composed of a nanotube-interconnected framework containing micrometer-scale pores. Enhanced growth of TNTs in cavities surrounded by TNT/TiO2 aggregated particles resulted in the formation of entangled/interconnected TNT bridges between TNT/TiO2 aggregates. The macroporosity depends on a volume fraction of anatase to the aqueous solution. The resulting monolithic TNT/TiO2 composite had sufficient mechanical strength for various applications. The monolith exhibited a faster rate and a higher capacity of Li+ exchange than simple compacted TNTs. The TNT monolith has potential in cation exchange and adsorption applications, because of its macroporous flow channels.