Anatase Crystalline Structure Research Articles

Bacterial cellulose derived monolithic titania aerogel consisting of 3D reticulate titania nanofibers

Monolithic titania (TiO2) aerogel was fabricated by using bacterial cellulose (BC) as the bio-template and preceramic polymer as titanium resource, via freeze-drying and two-step calcination process. As-prepared TiO2 aerogel BCTi-air-2 h possessed low bulk density (0.04 g/cm3) and moderate mechanical strength. SEM images showed that TiO2 aerogel was composed of 3D reticulate TiO2 nanofibers. The anatase crystalline structure of TiO2 with crystal size around several nanometers was revealed by XRD measurements. N2 adsorption/desorption analysis indicated that TiO2 aerogel possessed high specific area (115 m2/g) and macroporous structure, which contributed to the high photocatalytic activity. Most importantly, the monolithic state will ease the usage, recycling, and regeneration of TiO2 aerogel as photocatalyst.

An electron microscopy three-dimensional characterization of titania nanotubes.

To characterize complex, three-dimensional nanostructures, modern microscopy techniques are needed, such as electron tomography and focused ion beam (FIB) sectioning. The aim of this study was to apply these two techniques to characterize TiO2 nanotubes in terms of their size, shape, volume, porosity, geometric surface area, and specific surface area (SSA). For these experiments, titania nanotubes were fabricated by means of the electrochemical oxidation of titanium at a voltage of 20 V for 2 hr followed by heat treatment at 450°C for 3 hr to change the amorphous structure into a crystalline anatase structure. The quantitative data obtained from the FIB and electron tomography reconstructions show a high similarity in porosity and some differences in SSA. These might be the result of differences in resolution between the two reconstruction techniques.

Laser Selective Photoactivation of Amorphous TiO2 Films to Anatase and/or Rutile Crystalline Phases

Titanium dioxide (TiO2) is a remarkable metal-oxide semiconductor with unique optoelectronic properties ideal for photovoltaics and photocatalytic conversion. The principal crystalline phases for TiO2 are anatase, rutile, and brookite. The combination of both anatase and rutile crystalline structures can positively impact the optoelectronic properties of TiO2 films. With standard sol–gel processing, high-temperature conversion generally yields one dominant phase and limits the combined use of anatase and rutile TiO2 for optoelectronic devices. We report on a singular route to controllably engineer hybrid nanocrystalline films of TiO2 at room temperature to synergistically exploit both anatase and rutile TiO2 phases. Relying on sol–gel chemistry, this approach starts from an amorphous film and uses photoinduced activation using a low-power laser to achieve specific spatially controlled pattern consisting of different TiO2 crystalline phases within the same film. While achieving remarkable precision, reprod...

Morphological and Raman Study of an Anodized Tio2 Nanotubular Matrix without Presence of Nanograss, Using Graphite as Cathode

One set of TiO2 nanotubes is anodized to identify and study the time lapse of a matrix of them without presence of nanograss as a residual layer. The anodization process consists of an organic media of ethylene glycol and NH4 F salts, constant voltage for a time period from 10 to 60 minutes. All anodized samples are rinsed and annealed to 400 °C by 2 hours to obtain an anatase crystalline structure. The morphological characterization was carried out by Field Emission Scanning Electron Microscopy to verify the presence of the nanotubes and calculate the surface roughness factor and film porosity. It was observed that roughness factor and porosity doesn’t have important variations, as time function, except for 60 minutes where nanograss has a strong presence and the gaps between nanotubes are minimal. Raman Spectroscopy was used for optical characterization in order to identify the changes in signal intensity and Eg mode Shift associated with anodization time. It was observed that intensity suffers an increment and Eg mode Shift suffers a decrement as thickness function (anodization time).

The role of titania layers in decomposition of endocrine disruptors under UV Light

Degradation of three different endocrine disruptors (EDs) was thoroughly studied on prepared durable thin layers of titanium dioxide with an anatase crystalline structure. Specially constructed laboratory reactors bringing information on all individual processes (photolysis, photocatalysis, sorption) involved in decomposition of the studied EDs (17α-ethynylestradiol, bisphenol A and 4-nonylphenol) were applied. It was found that photolytic removal of EDs is the fastest degradation process; nevertheless, this method may be less effective regarding all indicators including toxicity. It was verified that individual degradation processes (photolysis and photocatalysis) showed a significantly different influence on toxicity of resulting solutions. During the photolytic process, EDs degradation caused increasing toxicity contrary to the photocatalytic process. Obtained results were corroborated by a mathematical model, which showed that a limitation step for photocatalysis is a sorption and for photolysis a toxicity of resulting products.

PHOTOCATALYTIC DEGRADATION OF FORMIC ACID INAQUEOUS WITH Ni DOPED TiO2 COATED ON SILICAGEL

Formic acid (FA) photocatalytic degradation using nickel doped TiO2 (Ni-TiO2) coated on silica grain (Ni-TiO2/SiO2) by sol-gel method has been studied. Nickel with a different molar ratio as 0.2, 0.4, and 0.8 % mole was used in this study. Samples were characterized by XRD, SEM, and UV-vis spectroscopy. Conditions such as dark, ultraviolet-visible and visible light were performed to assess the photocatalytic ability of Ni-TiO2/SiO2. The results showed that, catalyst samples had uniform nanosize, anatase crystalline structure and the band-gap energy of Ni-TiO2/SiO2 was lower than that of TiO2/SiO2 sample. The highest photocatalyst activities were obtained at 0.2 % mol of Ni for both irradiations. The FA concentration was not changed in the dark condition. Under ultraviolet-visible irradiation, FA concentration decreased from 10-4 mM to 2.10-5, 7.10-5 and 9.10-5 mM with 0.2, 0.4 and 0.8 % mole of Ni, respectively. With visible light condition, FA concentration decreased from 10-4 mM to 7.10-5 mM when Ni dopant amount was 0.2 % mole. Change in FA concentration was negligible with 0.4 and 0.8 % mole of Ni dopant amount. It proved that the photocatalytic activity of Ni-TiO2/SiO2 under visible light irradiation was generated by doping a small amount of nickel into TiO2. However, under visible light irradiation with 420 nm filter, FA photodegradation of Ni/TiO2/SiO2 increases when Ni dopant content increases from 0 % mole to 0.8 % mole.

Ordered mesoporous Au/TiO2 nanospheres for solvent-free visible-light-driven plasmonic oxidative coupling reactions of amines

Imines are important intermediates for the synthesis of fine chemicals and pharmaceuticals. Design of a “green” oxidation catalyst to promote the direct oxidation of amines to imines by dioxygen have attracted great attention. Herein, we designed a catalyst of ordered mesoporous Au/M-TiO2 nanoparticles using a template-based approach. The as-prepared Au/M-TiO2 nanoarrays of anatase crystalline structure, with high specific surface area (222 m2/g), small pore size (∼2.1 nm) and ordered arrangements, gave dense array of ultrasmall pore-confined gold nanoparticles. The mesoporous Au/M-TiO2 exhibits particularly high visible light activity for photocatalytic selective aerobic oxidation of benzylamine to N-benzylidene benzylamine in a green approach by utilizing dioxygen as an oxidant in solvent-free conditions. The yield of N-benzylidene benzylamine can reach 1.73 mmol (TOF = 178.6 h−1, based on Au) in Au/M-TiO2 system, which is 1.5 and 1.6 times higher than that of the Au/P25 and Au/Acros anatase photocatalysts, respectively. Furthermore, we can also achieve high yield of N-benzylidene benzylamine (1.30 mmol, TOF = 134.2 h−1, based on Au) in air atmosphere. The confinement effect of the mesopores in Au/M-TiO2 facilitate the formation of O2− radicals and make the bi-molecular reaction highly preferred for promoting the high selectivity and conversion in plasmonic photocatalysis. Meanwhile, the Au/M-TiO2 with mesoporous structure can facilitate the efficient contact between the solvent and the nanomaterial, while possessing sufficient interfacial area for active oxidation reactions. This work paves a promising way to develop visible light-responsive TiO2-based photocatalysts with high specific surface area for highly efficient green oxidative organic synthesis.

Heterostructure TiO2 polymorphs design and structure adjustment for photocatalysis

Atomic composite-structure materials play an important role in energy generation and storage application fields for their advanced performance. Constructing heterostructured semiconductors is a promising strategy to devise photocatalytic systems with high activity. However, most studied hererostructures are those semiconductors with different materials formed by multi-steps, researches on in-situ formed hererostructure originated from the same precursor are few reported, and the effects of different structure ratios on photocatalytic performance are ambiguous. Here, according to in-situ temperature X-ray diffraction and transmission electron microscope techniques, a nano-sized in-situ formed heterostructure of TiO2 semiconductors with anatase and TiO2-B crystalline structures were designed, their structure ratios were adjusted, the heterostructure interface and photocatalytic reaction mechanism were also detected. Results show that high-quality heterojunction and optimum structure ratios have vital influence on photocatalytic performance, there is an obvious synergetic effect between anatase and TiO2-B structure, degradation reactions on methyl orange (MO) under ultraviolet light irradiation prove that the highest activity toward MO removal can be obtained for material with 82.5% anatase structure.

A mechanistic study of stable dispersion of titanium oxide nanoparticles by humic acid

Stable dispersion of nanoparticles with environmentally-friendly materials is important for their various applications including environmental remediation. In this study, we systematically examined the mechanisms of stable dispersion of two types of TiO2 nanoparticles (TNPs) with anatase and rutile crystalline structures by naturally occurring dissolved organic matter (humic acid) at different pHs, including at, below and above the Point of Zero Charge (PZC). The results showed that stable dispersion of TNPs by humic acid (HA) at all pHs tested can only be achieved with the assistance of ultra-sonication. The dispersion of TNPs by HA differed at the three pHs tested. Generally, HA greatly decreased the hydrodynamic diameters of TNPs at a very low concentration. The dispersion of TNPs became relatively stable when the HA concentration exceeded 5 mg/L, indicating that this HA concentration is required for stable dispersion of TNPs. The mechanisms involved in dispersion of TNPs by HA included electrostatic repulsion, steric hindrance and hydrophobic interaction. Electrostatic repulsion was identified to be the dominant mechanism. The dispersion of TNPs was enhanced when HA was added before ultra-sonication to avoid the partly irreversible re-aggregation of TNPs after sonication. The crystalline phases and concentrations of TNPs were also found to influence their stable dispersion. The findings from this work enhance understanding of the combined effects of HA, pH, ultra-sonication and crystalline structures of TNPs on their stable dispersion. The mechanisms identified can improve applications of TNPs in environmental water pollution control.

Sol-gel template synthesis of mesoporous carbon-doped TiO2 with photocatalytic activity under visible light

Mesoporous TiO2 powders with an anatase framework were synthesized through surfactant-assisted template method. The concentrated titania sol (7-8 wt.%) prepared from TiCl4 as a precursor was used in this synthesis. The soluble triblock copolymer Pluronic F127 was employed as a structure-directing agent and a carbon precursor to fabricate the carbon-doped mesoporous titania. The synthesized powders were characterized by XRD, HRTEM, Raman spectroscopy, UV-Vis reflectance spectroscopy, N2 adsorption/desorption and TG/DSC methods. The mesoporous titania annealed at 350°C was shown to have a high specific surface area up to 192 m2/g and a narrow pore size distribution. After annealing, carbon species in graphitic form were detected in the template-prepared TiO2 samples using Raman spectroscopy measurements. The photocatalytic performance of the samples was characterized in the process of Rhodamine B decomposition under visible light irradiation. The enhanced visible light photocatalytic efficiency of the template-prepared TiO2 powders as compared with that of Degussa P25 can be attributed to the associated effects of high specific surface area, pure anatase crystalline structure and carbon doping.

Self-Cleaning Properties of Silk Fabrics Functionalized with Tio2/Sio2 Composites

ABSTRACTSilk fabrics were treated with TiO2/SiO2 composites using the pad-dry-cure method. TiO2/SiO2 composites were prepared through a low-temperature sol-gel method with five different TiO2:SiO2 weight ratio of 100:0, 70:30, 50:50, 30:70, and 0:100. The photocatalytic self-cleaning properties of the TiO2/SiO2 composite of samples were assessed by analyzing the degradation of coffee stain under UV irradiation. The presence of anatase crystalline structure in synthesized composites was confirmed using the X-ray diffraction patterns. Fourier transform infrared study confirmed the existence of Si-O-Si and Ti–O–Si bonds in the composites. Surface modifications were confirmed by scanning electron microscopy images. The EDS spectrum of samples showed a well-defined peak for the carbon, oxygen, titanium, and silicon elements, also indicating the existence of TiO2/SiO2 on the treated silk fabrics. The samples treated with TiO2/SiO2 (70:30) composite showed the highest efficiency in coffee stain removal, followed by samples treated with TiO2/SiO2 (50:50). The laundering durability of treated sample showed the strongly interaction between the silk fabrics and the TiO2/SiO2 nanoparticles. The physical properties of treated silk fabrics were investigated.

Electrospun nanoporous TiO2 nanofibers wrapped with reduced graphene oxide for enhanced and rapid lithium-ion storage

A high reversible Li-ion storage capacity (200mAh/g) with C/10 rate and good rate capability is achieved in reduced graphene oxide (rGO) wrapped anatase mesoporous TiO2 nanofiber anodes fabricated by electrospinning. X-ray analysis of rGO wrapped TiO2 nanofibers confirmed the crystalline anatase structure of TiO2, while Raman spectroscopy established high frequency shift caused by the interaction of TiO2 with 2–4 layers of rGO. FT-IR analysis of rGO wrapped TiO2 nanofibers revealed disappearance of CC, CO, and COH stretching frequencies suggesting the successful reduction of GO to graphene, further confirmed by X-ray Photoelectron spectroscopy. The BET surface area of TiO2 nanofibers (54m2g−1) increased to 105m2g−1 after wrapping rGO leading to mesoporous structure with pore diameters 5–20nm, complementary observations with scanning and transmission electron microscopies. The oxidation/reduction peaks revealed lithium insertion and lithium extraction mechanism, from 1D TiO2 fibers with superior electrode/electrolyte contacts, with shorter Li-ion diffusion length and improved ionic conductivity. Successful anchoring of rGO on TiO2 nanofiber with Ti3+-C bonds energetically favors the electrochemical reaction yielding high rate and specific TiO2 capacity as a promising anode of lithium ion battery.

TiO2 coatings obtained by reactive sputtering at room temperature: Physical properties as a function of the sputtering pressure and film thickness

TiO2 layers with crystalline anatase structure have been attained on unheated glass substrates, by reactive sputtering from a metallic target, using the sputtering pressure to change the energy of the particles arriving to the film surface. Such energy and the time of plasma exposure also influence the morphology and other physical properties of the sputtered films. The deposition time has been ranged to obtain TiO2 coatings with different thicknesses from 0.24 to 1.08μm and at various total pressures from 0.2 to 1.0Pa. Overall characterization of the samples has been performed by X-ray diffraction, atomic force microscopy and spectrophotometry. The effects of the sputtering pressure and the film thickness on the crystalline structure (interplanar distance and mean crystallite size), the morphology (roughness and surface area) as well as the optical properties (refractive index, extinction coefficient) have been established. A direct relation between optical and morphological characteristics, and the calculated film porosity has been proven. Such porosity is well controlled by the deposition parameters; these allow tuning the optical and morphological properties of the sputtered TiO2 coatings as required for different applications.

Sol–gel synthesis of highly TiO2 aerogel photocatalyst via high temperature supercritical drying

Nanocrystalline powders of TiO2 xerogel and aerogel were prepared by using acid-modified sol–gel approach. For TiO2 aerogel material (TA), the solvent was high temperature supercritically extracted at 300°C and 100bars. However, the TiO2 xerogel material (TX) was dried at 200°C and ambient pressure. The effects of the drying processes on the crystalline structure, phase transformation and grain growth were determined by Raman spectroscopy, SAED and X-ray diffraction (XRD) analyses using Rietveld refinement method. The TiO2 aerogel was composed of anatase crystalline structure. The TiO2 xerogel material was composed of anatase, brookite and small amount of amorphous phase with anatase as dominant phase. The TX sample still contains a relatively high concentration of carbon than that of TA, indicating the amorphous character of TiO2 xerogel. These materials were applied as catalyst for the degradation of indigo carmine in aqueous medium. Photo-degradation ability of TA and TX was compared to the TiO2 commercial Degussa P25. The photo-catalytic results showed that the degradation efficiency was in the order TA>P25>TX. The photo-degradation of indigo carmine followed pseudo first order reaction kinetics.

Photocatalytic activities of TiO2 layers immobilized on glass substrates by dip-coating technique toward the decolorization of methyl orange as a model organic pollutant

The aim of this article is to evaluate the photocatalytic activities of the immobilized catalyst layers of titanium dioxide for the decolorization of methyl orange aqueous solution (MO) as a model organic contaminant under UV irradiation. Three stable layers of TiO2 powder were coated on glass substrate by facile dip-coating technique. XRD analysis showed anatase crystalline structure of catalyst films. The films crystallinity increased with the layers number. SEM analysis showed porous TiO2 films. The multi-coating increased the coverage surface of glass support. The catalyst films showed well reproducibility and good adhesion to the support after tests. The effects of operating parameters and the number of catalyst layers on the MO decolorization were investigated. The kinetic study of the MO photodecolorization showed a pseudo-first-order reaction. The MO color removal by the use of three coated layers of catalyst in the optimum reactor was more effective and 5 times faster than that with the use of one coated layer of catalyst at normal conditions. The immobilized layers of TiO2 powder was found photocatalytic active for complete MO decolorization in the optimum reactor. The immobilized system may replace suspension mode and eliminate the costly separation process.

Solvothermal Synthesis of Anatase TiO2 Nanosheets with Exposed {001} Facets

Enhancing the catalytic activity of titania (TiO2) nanomaterials by controlling the size, surface area and percentage of highly reactive exposed {001} facets has become attractive in the recent years because of its wider applications in the different fields of scientific research. In the present study, anatase TiO2 nano-sized sheets (TNS) were synthesized using a simple ethanol assisted solvothermal chemical route. The TNS structures were characterized using Field Emission Scanning Electron Microscopy (FE-SEM), Transmission electron microscopic (TEM), Raman analysis, X-ray diffraction (XRD) and Accelerated surface area and porosimetry (ASAP) analysis. The results from TEM, Raman and XRD analysis confirmed the presence of anatase crystalline structure of TNS with the size range of 20-40 nm. The synthesized TNS structures possess 60% of highly reactive exposed {001} facets with a total surface area of 73 m²/g. These tremendous crystalline properties of solvothermally synthesized TNS structure makes it as an attractive catalyst for environmental and bio-fuel applications.

Photocatalytic degradation of diazinon under visible light using TiO 2 /Fe 2 O 3 nanocomposite synthesized by ultrasonic-assisted impregnation method

Abstract Diazinon is one of the organophosphorus pesticides. It can threaten human and animal health, if stays in water and soil resources. Herein, the photocatalytic degradation of Diazinon under visible light was accomplished using TiO 2 /Fe 2 O 3 nanocomposite, which has been never employed for diazinon degradation. Firstly, TiO 2 /Fe 2 O 3 nanopowder was synthesized via ultrasonic-assisted impregnation method. To achieve this goal, TiO 2 nanoparticles were effectively dispersed in the solution. Then, Fe 3+ was impregnated on TiO 2 nanopowder under sonication process and calcined at 300 °C. The prepared photocatalyst was authenticated by XRD, EDX, FESEM, TEM, PL, and DRS analysis methods yielding following results: Anatase and maghemite crystalline structure of TiO 2 /Fe 2 O 3 nanoparticles, successful impregnation of Fe 2 O 3 on the surface of TiO 2 nanopowder, mean diameter size of 17 nm, extended absorption spectra of Fe 2 O 3 /TiO 2 nanocomposite in the visible region, and the better inhibition of electron and electron-hole recombination. Secondly, Kinetics of degradation was systematically optimized by multi variable central composite design based on response surface method. Degradation efficiency was highly affected by Diazinon dosage. The maximum experimental degradation efficiency was 95.07%. Optimum condition which was determined by software, included 0.1 g/L catalyst, 10 ppm Diazinon dosage, 45 min reaction time and 14 W/cm 2 light intensity and predicted 88.93% degradation efficiency with desirability of 0.873.

Impacts of oxygen vacancies on the electrocatalytic activity of AuTiO2 nanocomposites towards oxygen reduction

Nanocomposites based on metal nanoparticles supported on oxide surfaces have been used extensively as effective catalysts for fuel cell electrochemistry. In this study, functional nanocomposites based on gold nanoparticles deposited onto TiO2 colloids were prepared by a simple wet chemistry method, and subject to hydrothermal treatment at a controlled temperature in the presence of ascorbic acid. Transmission electron microscopic measurements showed that the gold nanoparticles (10–30 nm in diameter) were embedded within the TiO2 matrix consisting of colloids of 5–10 nm in diameter and anatase crystalline structures, as evidenced in x-ray diffraction studies. Interestingly, electron paramagnetic resonance measurements showed the formation of oxygen vacancies after hydrothermal treatment and the concentrations of oxygen vacancies increased with the amount of ascorbic acid added. Consistent results were obtained in x-ray photoelectron spectroscopic measurements, which suggested partial charge transfer from gold to oxygen-deficient TiO2. The Au:Ti atomic ratio in the nanocomposites was estimated to be ca. 11% and consistent among the series of samples. Electrochemically, the nanocomposites exhibited apparent electrocatalytic activity towards oxygen reduction reactions in alkaline media, which showed a peak-shaped variation with the concentration of the oxygen vacancies. This was accounted for by the deliberate manipulation of the binding energy of oxygen species onto the nanocomposite surfaces. In addition, the AuTiO2 nanocomposites exhibited markedly enhanced tolerance against methanol crossover, as compared to commercial Pt/C catalysts.

Preparation of Co doped TiO2 nano thin films by Sol Gel technique and photocatalytic studies of prepared films in tannery effluent

Simple dip and drive deposition unit for the preparation of thin films was designed and fabricated indigenously. TiO2 nano thin films were prepared using the fabricated unit with different amount of dopants (5%, 10% and 15% of Co). The films were annealed at 550°C using muffle furnace for one hour and allowed to cool till room temperature. The structural and composition of the thin films were analyzed using XRD and EDAX measurements. The X-ray diffraction peaks revealed that the films exhibit anatase crystalline structure. The composition of the film is confirmed as TiO2 with trace of Co from the percentage of constituents in EADX results. The optical properties of the films were studied by using spectrophotometer with wavelength range of 190nm to 2500nm. The nature of the band gap is direct and it is nearly 3.4eV. The surface morphology of the films was studied using AFM, SEM and TEM analysis. The films are identified that they are made out of nano particles of size below 25nm. The films are found to be defect free and they are excellent films for photocatalytic studies. The films (without and with Co doped) were dipped in tannery effluent with different time intervals (1–3h). The concentration of carbonate, chloride and sulphate present in the remaining effluent were analyzed by conventional methods. It is found that as percentage of dopant increases, the catalytic activity increases.

Ga<sub>2</sub>O<sub>3</sub>-Doped ZnO-Nb<sub>2</sub>O<sub>5</sub>-TiO<sub>2</sub> Dielectric Resonators for Terrestrial and Space Telecommunications Applications

Dielectric ceramics find application as dielectric resonators (DRs) in communications systems operating at microwave frequencies. RDs for this application require a unique set of properties: high value of the dielectric constant, low dielectric loss and high frequency stability. This paper presents an investigation of the correlation between the dielectric properties, the characteristics of microstructure and the crystalline phases of Ga2O3-doped ZnO-Nb2O5-TiO2 ceramic system. The ceramics sintered at 1200 °C were characterized as for density, crystalline phases, microstructure and microwave dielectric properties. The results showed that these dielectric ceramics, obtained from the TiO2 anatase crystalline structure, present dielectric constant and quality factor (Q) values appropriate for their use as dielectric resonators in microwave circuits. According to the experiments, as the gallium doping has raised, the dielectric constant increased, the Q factor decreased and the temperature coefficient had a tendency to decrease to a certain extent.