Rutile Anatase Research Articles

Titanium dioxide catalytic activity contributes to the process of free radical scavenging

TiO2 crystallochemical properties have been explored and correlated with the activity of this material in the scavenging of reactive oxygen and nitrogen species (ROS/RNS). It is well known that those highly reactive species are produced by inflammatory cells and neutralized by some oxides, such a titanium dioxide under light. Nevertheless, the mechanism of action of this ceramic material is yet to be fully understood. A set of reactions have been proposed that imply the presence of different valence states of titanium as the basis for the ROS/RNS scavenging, but in this work, we have demonstrated that those species are not always detected in TiO2-based materials, which are, in addition, active in depleting ROS/RNS. TiO2 powders with undetected Ti3+ have been obtained with a range of different properties—surface area, particle size, rutile–anatase ratio, and band gap values—by varying the powder processing conditions after synthesis through the sol precipitation route. The properties of the powders have been correlated with the scavenging activity of the materials toward two reactive species, DPPH· and peroxynitrite, always conducted under dark conditions. It was observed that despite the lack of Ti3+ states, TiO2 powders can still neutralize ROS/RNS. For the first time, this study explain how the catalytic activity of different TiO2 contribute to the free radical scavenging mechanism and the differences in scavenger activity shown by different TiO2 phases and mixtures.

2D/1D graphitic carbon nitride/titanate nanotubes heterostructure for efficient photocatalysis of sulfamethazine under solar light: Catalytic “hot spots” at the rutile–anatase–titanate interfaces

2D/1D graphitic carbon nitride hybridized with titanate nanotubes (g-C3N4/TNTs) was prepared through a hydrothermal reaction–calcination method. The photocatalyst exhibited high degradation efficiency for sulfamethazine (SMT) through photocatalysis under simulated solar light. The optimized material was composed of anatase, rutile, titanate and g-C3N4 crystalline phases. In situ transformation of titanate to anatase and rutile with specific content proportion (∼80:20, P25-type composition) leaded to formation of nanoscale “hot spots” at rutile–anatase–titanate interfaces, and then subsequent charge transfer occurred. Large specific surface area of TNTs as skeleton resulted in high-efficient interface reaction, while heterojunction with g-C3N4 further extended the adsorption to visible light region and retarded electron-hole pairs recombination. Density functional theory (DFT) calculation indicated the SMT sites with high Fukui nucleophilic (f-) index prefered to be attacked by radacils. Reduced toxicity of SMT degradation intermediates, good reusability and stability of g-C3N4/TNTs all suggested the great application potential in practical water treatment area.

Synthesis of Fe, Mn and Cu modified TiO2 photocatalysts for photodegradation of Orange II

The residual dyes from different sources are considered a wide variety of organic pollutants introduced into the natural water resources. One of the main sources with severe pollution problems worldwide is the textile industry and its dye-containing wastewaters. The aim of this study was the photocatalytic degradation of the azoic dye “Orange II” using Mn, Cu and Fe modified titania. The catalysts were prepared by two different methods, sol–gel and an impregnation method in a commercial titania (Degussa P25), after drying the samples were calcined at 400°C. The samples were characterized by BET method for surface area measurement (SBET), XRD, Raman spectroscopy, XPS, UV–vis spectroscopy by diffuse reflectance technique and its photocatalytic activity was evaluated in the degradation of the azo dye Orange II in aqueous solutions using the Langmuir–Hinshelwood model. The catalysts prepared by sol–gel method exhibit a larger surface area than the prepared by impregnation and the introduction of the oxides leads to a slight reduction of SBET. The sol–gel samples show lower photoactivity than the impregnated samples due to the presence of both anatase and rutile phases in these powders, the phase junction anatase–rutile facilitate transfer of the photogenerated electron from the conduction band of the rutile phase to the trapping sites on the anatase surface and prevents the electron–hole recombination and allows the holes generated to move to the surface of the catalyst. XRD, Raman, XPS and UV–Vis data show that the metallic cations are incorporated in the titania lattice in greater extend in SG samples while remain dispersed on the surface in impregnated samples. Although the entrance of metallic cations in solid solution enhance the photocatalytic activity due to the enhanced formation of electrons–hole pairs, at a high doping content, a large number of structural defects are induced serving as a recombination center of electron–hole pairs and sol–gel samples show higher photoactivity than impregnated samples, except in the case of Fe modified samples that shows the higher red shift with Eg=1.8eV and compensate the induced recombination center of electron–hole pairs.

Elaboración de un fotocatalizador flotante basado en un composito de TiO2/aglomerado para tratamiento de contaminantes orgánicos usando luz solar

Floating photocatalysts have caused interest due to the benefits they provide. For example, the floating support has characteristic lightness and flexibility; while the photocatalyst has the advantage of being able to interact with sunlight without the need of stirring or oxygenation. In this paper, a floating photocatalyst based on a TiO2/ agglomerate composite is evaluated. The agglomerate is made from post-consumer packaging of multilayer containers. The catalyst was prepared by synthesizing of titanium dioxide powders with phase mixture anatase/rutile. The photocatalyst powder was attached to substrate surface using a varnish obtained by dissolving post-consumer polystyrene containers in toluene. The photocatalyst has different phase A-R (Anatase-Rutile) ratios. The approximate size of the nanostructure is 13.29 ± 3.28 nm, calculated using UV-Vis spectroscopy, the bandgap has values ranging from 2.56 eV to 2.90 Ev. The agglomerates have a rupture modulus of 14.95 N/mm2; they are hydrophobic materials and possess dimensional stability against changes in humidity (length) less than 10%, chemical resistance, are flame retardant. The TiO2/agglomerate composite is used for the photocatalytic degradation of a model pollutant (methylene blue) using sunlight.

Metal–organic framework-derived porous TiO2 nanotablets with sensitive and selective ethanol sensing

Porous TiO2 nanotablets were fabricated by calcining the MIL-125 metal–organic framework (MOF) precursors formed by a solvothermal method. Sensing results indicated that this kind of MOF-derived TiO2 nanotablets exhibited excellent ethanol sensing properties, including high response (46.12–500 ppm), relatively low operating temperature (250 °C), and low detection limit (0.417 ppm). The response of TiO2 nanotablets to 500 ppm ethanol at 250 °C was about 4.18 times higher than that of commercial TiO2 powder at the optimum operating temperature of 275 °C. Moreover, TiO2 nanotablets also displayed high stability and ethanol selectivity. The special porous structure, high valence state of absorbed oxygen species, and formation of rutile–anatase n–n junctions can enhance the resistance modulation of MOF-based TiO2 nanotablets, contributing to their excellent ethanol sensing properties.

Photodegradation of Herbicide Imazapyr and Phenol over Mesoporous Bicrystalline Phases TiO2: A Kinetic Study

Mesoporous TiO2 nanoparticles were synthesized at different temperatures (400–800 °C). The resulting mesoporous anatase–rutile TiO2 mixtures between 27 and 82% were found to have different structural properties (morphology, mesoporosity, crystallite phases, and sizes) affected through the calcination process. They were tested for the photocatalytic degradation of the herbicides imazapyr and phenol, compared with the nonporous TiO2 P-25. The present work is an extension of a previously published study discussing the influence of the rutile content on the photocatalytic performance of the nanocrystals, based on the modified first order kinetic model, where the degradation rate is a function of the specific surface area of the material. The apparent degradation rate using T-800 is 10-fold higher than in the case using TiO2 P-25. The material with the lowest anatase content (T-800) exhibits the highest photocatalytic activity in terms of initial reaction rate per unit surface area. It is considered that mixed-phase photocatalysts with rutile–anatase exhibit enhanced photoactivity with the increase of the rutile proportion.

Synthesis of V-modified TiO2 nanorod-aggregates by a facile microwave-assisted hydrothermal process and photocatalytic degradation towards PCP-Na under solar light.

Herein, novel V-modified titania nanorod-aggregates (VTNA), consisting of fine individual nanorods in radial direction, were fabricated via an efficient microwave-assisted hydrothermal (MWH) route. VTNA with high crystallinity and homogeneous mesopores were obtained by 30 min MWH processing at 190 °C; moreover, a mixed rutile–anatase phase appeared after vanadium doping. XPS analysis revealed that vanadium existed in the forms of V4+ and V5+ on the surface of MWV05 with V5+ being the dominant component, the content of which was approximately 3.5 times that of V4+. Vanadium implanting was achieved efficiently by doping 0.5 and 1 at% V using a rapid MWH process and contributed towards the dramatic improvement of the visible-light response, with Eg decreasing from 2.91 to 2.71 and 2.57 eV with the increasing V doping content. MWV05 exhibited optimal photocatalytic degradation activity of water-soluble PCP-Na under solar light irradiation. The enhanced photodecomposition was attributed to the red-shift in the TiO2 band-gap caused by vanadium impregnation, efficient charge separation due to the V4+/V5+ synergistic effects and the free migration of charge carriers along the radial direction of the nanorods arranged in a self-assembled VTNA microstructure.

Fabrication of Fiber Optic Based Temperature Sensor

The metal oxide semiconductors (ZnO, SnO2, Al2O3 and TiO2) were synthesized by co-precipitation method. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and UV-Visible spectrometer in diffused reflectance (DR) mode. The XRD results stipulated that the ZnO nanoparticle is crystallized in hexagonal wurtzite structure, SnO2 nanoparticles in rutile tetragonal structure, Al2O3 nanoparticle in rombohedral structure and TiO2 nanoparticle in rutile anatase structure. The SEM investigation affirms that all the synthesized nanopowders are composed of uniformly distributed grains. The UV-Vis spectrum proclaimed that the synthesized nanoparticles having the band gap of 3.2 eV (ZnO), 3.3 eV (SnO2) and 3.5 eV (TiO2) respectively. The synthesized nanoparticles were replaced with small cladding region of the optical fiber and act as a temperature sensing materials. The temperature sensing characteristics of the synthesized nanoparticles were investigated for broad wavelength range (200-1000 nm). It reveals that the synthesized Al2O3 nanoparticles were given linear and high sensitivity (∼27) at 697 nm compared with other sensing materials. Further, we have studied the wavelength dependent temperature sensing characteristics of Al2O3nanopowders and it show better sensitivity (∼34) in blue wavelength region (450 nm-495 nm).

Theoretical analysis of band alignment and charge carriers migration in mixed-phase TiO2 systems

Photocatalysts based on mixtures of rutile and anatase forms of titania usually show a better catalytic performance than each individual component. In order to understand this behavior, several experimental and theoretical approaches have been proposed in the past, looking for an adequate reference frame for aligning energy bands, and arriving sometimes to opposite results. In this work, the theoretical results obtained for the band alignment applying a modified common anion rule for different possibilities of mixed-phase (anatase–rutile) interaction are presented. According to our results, mixed-phase systems involve the transfer of electrons from rutile to anatase and holes from anatase to rutile. This analysis would be applicable to real samples of mixed phase of titania with large particle size. However, for heterogeneous size particulate systems, it is not only necessary to consider the alignment of bands of the bulk system, but also those of the corresponding surfaces. In keeping with the analysis performed, the best mixed systems are those composed by large particles of both polymorphs or by small particles of anatase dissolved in rutile. Our results could explain the disagreement found in the literature regarding the experimental works.

Electrochemical hydrogenation of mixed-phase TiO2 nanotube arrays enables remarkably enhanced photoelectrochemical water splitting performance

We first report that photoelectrochemical (PEC) performance of electrochemically hydrogenated TiO2 nanotube arrays (TNTAs) as high-efficiency photoanodes for solar water splitting could be well tuned by designing and adjusting the phase structure and composition of TNTAs. Among various TNTAs annealed at different temperature ranging from 300 to 700 °C, well-crystallized single anatase (A) phase TNTAs-400 photoanode shows the best photoresponse properties and PEC performance due to the favorable crystallinity, grain size and tubular structures. After electrochemical hydrogenation (EH), anatase-rutile (A-R) mixed phase EH-TNTAs-600 photoanode exhibits the highest photoactivity and PEC performance for solar water splitting. Under simulated solar illumination, EH-TNTAs-600 achieves the best photoconversion efficiency of up to 1.52% and maximum H2 generation rate of 40.4 µmol h−1 cm−2, outstripping other EH-TNTAs photoanodes. Systematic studies reveal that the signigicantly enhanced PEC performance for A-R mixed phaes EH-TNTAs-600 photoanode could be attributed to the synergy of A-R mixed phases and intentionally introduced Ti3+ (oxygen vacancies) which enhances the photoactivity over both UV and visible-light regions, and boosts both charge separation and transfer efficiencies. These findings provide new insight and guidelines for the construction of highly efficient TiO2-based devices for the application of solar water splitting.

A novel route to synthesize C/Pt/TiO2 phase tunable anatase–Rutile TiO2 for efficient sunlight-driven photocatalytic applications

Herein, we report a novel air-assisted carbon sphere combustion process to produce phase-tunable anatase-rutile (A/R) C/Pt-TiO2 photocatalysts for hydrogen generation and organic pollutant degradation under solar light irradiation. In the formed carbon/amorphous TiO2 core/shell structure, the carbon-core was acted as a fuel to prepare the mixed phase A/R TiO2 nanostructures. The A/R ratio of the TiO2 nanoparticles was tuned by varying the purged air flow during the combustion process. The obtained materials exhibited several unique properties not achievable using conventional methods, including anatase/rutile homojunction, co-existence of C and Pt/PtO and very high surface area, significantly improved charge separation and transfer characteristics towards excellent photocatalytic properties. Eventually, the photocatalytic activities of the obtained materials were found to be more than 23 and 17 folds higher than commercial TiO2-P25 for hydrogen generation and organic pollutant degradation, respectively.

Marginally Hydrogenated Triphasic Titania Nanotubes for Effective Visible‐Light Photocatalytic Hydrogen Generation

AbstractWe report the first demonstration of hydrogen‐annealed triphase TiO2 nanotubes (anatase–rutile–brookite) (T‐ARB) as a visible‐light‐active photocatalyst for water splitting with high quantum efficiency. As‐synthesized T‐ARB was annealed under hydrogen atmosphere at 250 and 450 °C for 2 h. We found that the tubular structures were retained in the hydrogenated TiO2 samples. It was observed that the concentrations of Ti3+ and the oxygen vacancies and their distribution significantly increased with respect to the hydrogen annealing temperature. Such changes in defects were found to be critical in enhancing the photocatalytic activity of the hydrogen‐annealed triphase TiO2 nanotubes. The triphase TiO2 nanotubes hydrogen annealed at 450 °C were 16 times more efficient than pristine TiO2. Such an increase in the photocatalytic activity was explained by a triphase band diagram with defect states below the conduction band of each phase, which facilitated visible‐light activity and easy transfer of charge carriers from one phase to another. Our study showed that the well‐designed multiphase construction with oxygen vacancies enhanced the photocatalytic activity tremendously owing to the presence of a higher number of phase junctions.

Structural and Ferromagnetic Properties SnO2/TiO2 Nanotubes Obtained by Electrospinning

SnO2/TiO2 (Sn/Ti [Formula: see text]/1) nanotubes were prepared by the electrospinning method. The morphology was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the inner diameter of prepared materials was about 100[Formula: see text]nm and the wall thickness was about 10[Formula: see text]nm. The results of X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) showed that SnO2/TiO2 nanotubes had a mixed phase of SnO2 rutile and TiO2 anatase structures and no impurity phases. The magnetic properties of the SnO2/TiO2 nanotubes were characterized by a superconducting quantum interferometer (SQUID). The results indicated that the samples exhibited room temperature ferromagnetism which may be attributed to the interface between TiO2 and SnO2 phases.

Doping and transformation mechanisms of Fe3+ions in Fe-doped TiO2

A series of Fe-doped TiO2 samples with different concentrations of Fe3+ ions annealed at different temperatures were prepared using a sol–gel method. For Fe-doped TiO2, the existing states of Fe3+, the transformation of these existing states and the phase transition are investigated. It is revealed that the existing states of Fe3+ and the transformation of these existing states (substitutional Fe3+, α-Fe2O3 and Fe2TiO5) are closely related to the annealing temperature and the concentration of Fe3+. The anatase–rutile (A–R) transition is promoted by the substitutionally doped Fe in the TiO2 lattice. In addition, the Fe-doped TiO2 with a high calcination temperature (800 °C) and high doping concentration (x > 20) shows obvious ultrasonic piezoelectric catalytic activity for the reduction of CO2 to CH4. This work may be useful in understanding the doping mechanisms of Fe-doped TiO2, and the fabrication of new catalytic materials.

Study of synthesis parameters and photocatalytic activity of TiO2 nanostructures

ABSTRACTIn this present study, various types of TiO2 nanostructures were synthesised via hydrothermal method from a commercial titanium dioxide. The effects of the initial concentration of titanium dioxide and the reaction time on the morphology of synthesised nanostructures were investigated. The TiO2 nanostructures were calcined at 500 °C and examined for the photocatalytic performance by decomposing formic acid as an organic pollutant. Scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller and X-ray diffraction were employed to characterise the synthesised TiO2 nanostructures. The outcomes showed more influence of reaction time rather than initial TiO2 concentration on the properties of TiO2 nanostructures. Various TiO2 nanostructures such as, nanorods and nanotubes were fabricated at different initial TiO2 concentrations and reaction times. In addition, the synthesised nanorod structures showed higher photocatalytic activity than the nanotubes. This is owing to the presence of rutile–anatase combined crystalline phases in the nanorod structures.

Characterization of ZnO–TiO2 and zinc titanate nanoparticles synthesized by hydrothermal process

Solutions containing zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and potassium titanium oxalate dihydrate (C4K2O9Ti·2H2O) with different molar ratios of Zn:Ti at a pH of 10 were hydrothermally processed at 120, 160, and 200 °C to form ZnO–anatase, ZnO–anatase–rutile and ZnO–rutile nanocomposites. Upon subsequent calcination the precursors at high temperatures, ZnTiO3, Zn2TiO4 , and Zn2Ti3O8 nanoparticles were synthesized. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, Raman spectrophotometry, and photoluminescence (PL) spectroscopy revealed the existence of nanocomposites and nanoparticles with strong emission at 386 nm for Zn2TiO4 and Zn2Ti3O8 and at 370 nm for ZnTiO3.

Probing the charge recombination in rGO decorated mixed phase (anatase-rutile) TiO2 multi-leg nanotubes

Recombination of photo-generated charges is one of the most significant challenges in designing efficient photo-anode for photo electrochemical water oxidation. In the case of TiO2, mixed phase (anatase-rutile) junctions often shown to be more effective in suppressing electron-hole recombination compared to a single (anatase or rutile) phase. Here, we report the study of bulk and surface recombination process in TiO2 multi-leg nanotube (MLNTs) anatase-rutile (A-R) junctions decorated with reduced graphene oxide (rGO) layers, through an analysis of the photo-current and impedance characteristics. To quantify the charge transport/transfer process involved in these junctions, holes arriving at the interface of semiconductor/electrolyte were collected by adding H2O2 to the electrolyte. This enabled us to interpret the bulk and surface recombination process involved in anatase/rutile/rGO junctions for photo-electrochemical water oxidation. We correlated this quantification to the electrochemical impedance spectroscopy (EIS) measurements, and showed that in anatase/rutile junction the increase in PEC performance was due to suppression in electron-hole recombination rate at the surface states that effectively enhances the hole transfer rate to the electrolyte. On the other hand, in rGO wrapped A-R MLNTs junction it was due to both phenomenon i.e decrease in bulk recombination rate as well as increase in hole transfer rate to the electrolyte at the semiconductor/electrolyte interface.

Facile Synthesis of [101]-Oriented Rutile TiO2 Nanorod Array on FTO Substrate with a Tunable Anatase–Rutile Heterojunction for Efficient Solar Water Splitting

Generating a sustainable energy source through photoelectrochemical (PEC) water splitting requires a suitable photocatalyst. A [101]-oriented rutile TiO2 nanorod (NR) array in heterojunction with anatase on a fluorine-doped tin oxide (FTO) substrate is successfully prepared using a facile single-step hydrothermal process. The presence of anatase phase over the predominant rutile NRs’ surface is confirmed by transmission electron microscopy and tip-enhanced Raman spectroscopy. Solar water-splitting performances of anatase–rutile heterojunction with low energy (101) and high energy (001) rutile facets are compared. The low energy (101) facet rutile–anatase heterojunction shows higher photoconversion efficiency of 1.39% at 0.49 VRHE than the high energy (001) facet rutile–anatase heterojunction (0.37% at 0.73 VRHE). The mechanism for enhanced photocatalytic activity of the low energy (101) facet rutile–anatase heterojunction has been proposed. The role of NaCl in tuning the anatase portion, morphology, and P...

Synthesis of Mixed-Phase TiO2 Powders in Salt Matrix and Their Photocatalytic Activity

Three mixed-phase TiO2 powders, containing ∼80 volume % anatase and ∼20 volume % rutile, were prepared from amorphous titanium hydroxide and three different salt matrices—pure sodium chloride, pure Na2CO3, and pure disodium hydrogen phosphate (DSP). Amorphous titanium hydroxide and salt mixtures were heat treated at 875°C in a rapid thermal annealing system for different times, according to the time–temperature phase transformation graphs. Time-dependent UV degradation of aqueous solutions of methylene blue dye (15 ppm) in the presence of mixed-phase powders was used to monitor the activity of the catalysts. Microstructural study of the powders by scanning electron microscope and transmission electron microscope combined with phase analysis by XRD and optical absorbance by UV-absorption spectroscopy indicated that the higher photocatalytic activity of the powder obtained from pure DSP salt could be explained by its smaller rutile particle size and anatase–rutile interparticle bonding.

Effect of Molar Concentration of NH4OH on Photocatalytic Activity in Preparation of Nanosized TiO2 Powder from Spent Titanium Chip by Sol-Gel Method.

The TiO2 powder was prepared from the spent titanium chips by applying the sol-gel method. The spent titanium chip was dissolved in HCl solution, and then NH4OH solution was added. The molar concentration of NH4OH solution was 2 M, 4 M, 8 M, and 10 M. Obtained TiO2 powders were calcined at 200 degrees C, 400 degrees C, and 600 degrees C. The prepared TiO2 powder was characterized using a particle size analysis, BET surface area, and XRD analysis. The crystal structure of the TiO2 powder was rutile type and anatase. The highest BET surface area of TiO2 powder was 432.8 m2/g. The photocatalytic property of the TiO2 powder was evaluated as decomposition rate of methylene blue(MB) by using a liquid phase stirred reactor. UV source was a UV-A, and concentration of MB in most experiments was 8 ppm. The concentration of MB was measured by absorbance at 664 nm using UV spectroscopy. Photocatalytic efficiency of prepared TiO2 powder depended highly on concentration of NH4OH solution. The TiO2 powder prepared with 8 M-NH4OH solution showed the highest efficiency, the decomposition efficiency at decomposition time of 2 hr and MB concentration of pH 8 was 98%.