Single Anatase Phase Research Articles

Synthesis and characterization of anatase TiO2:Cu2+ powders prepared via a sol-gel technique

Anatase TiO2 powders doped with different amounts of Cu2+ ions (0, 0.5, 1.0 and 4 mol%) were successfully synthesized by sol-gel method from precursors of TiCl4, (CH3COO)2Cu. Effect of Cu2+ concentrations on the structural and optical properties of TiO2 host was investigated by X-ray diffraction, Raman spectroscopy and diffuse reflection spectroscopy. The XRD analysis showed that the doped samples exhibit anatase single phase at annealing temperature 600 oC. The Cu2+ contents did not affect on the lattice of TiO2 hot, but affected on positions of these Raman modes. The band gap of the TiO2:Cu2+ was decreased with the increase of doping concentration.

Microstructural analysis of undoped and moderately Sc-doped TiO2 anatase nanoparticles using Scherrer equation and Debye function analysis

UV light sensitive undoped and moderate (4 at.%) Sc-doped anatase nanocrystallites were prepared by an efficient and environmentally benign method based on homogeneous hydrolysis of TiOSO4 and Sc2(C2O4)3.5H2O aqueous solutions using urea as a precipitation agent, without post-synthesis calcination or annealing.X-ray diffraction study of the obtained powders revealed single phase anatase in both samples. Two different methods were applied to estimate the anatase crystallite size and shape from the X-ray diffraction data. The first one is based on the more conventional Scherrer equation (as implanted in GSAS-II program) while the second one is based on Debye function analysis (as implanted in DUBUSSY suite version 2.2), which is considered to be more adequate for nanocrystallites. Although each program has its own shape models, both methods indicated similar results of elongated nanocrystallite geometry for Sc-doped TiO2: (i) GSAS-II confirmed ellipsoid shape with equatorial size of 5.1(0) nm and axial size of 6.8(0), (ii) DEBUSSY suite 2.2 showed cylinder shape with diameter of equivalent circle in the ab-plane, Dab = 4.9(1.0) nm and crystallite length along the c-axis, Lc = 5.4(3.2) nm. For the undoped TiO2 sample, equatorial size of 5.5(0) nm and axial size of 7.3(0) nm for the ellipsoid shape was determined according to GSAS-II, while Dab = 5.5(1.3) nm and Lc = 6.0(2.2) nm for the cylinder shape was determined by DEBUSSY suite 2.2. These outcomes were found to corroborate with HRTEM analysis.Doping with 4 at.% Sc caused ~0.3% growth of lattice parameters from a = 3.7979 [4] Å, c = 9.4995 [9] Å for the undoped sample to a = 3.8110 [7] Å, c = 9.5274 [16] Å for the moderately Sc doped sample, while reduction in the Ti vacancies by half was confirmed by both methods.The introducing of Sc as electronically active secondary species into the crystal lattice of TiO2 can greatly alter its optical absorption. The incorporation of Sc into the crystal lattice of TiO2 favors the substitution of Ti, as both have approximately the same ionic size, and generates surface oxygen vacancies which can act as trapping center for the photogenerated electrons and reduce the recombination of electron–hole pairs. We can expect Sc doped TiO2 nanomaterials to have applications as effective photocatalysts for selective photocatalytic oxidation of various environmental organic pollutants.

A facile and green synthetic approach toward fabrication of Alcea- and Thyme-stabilized TiO2 nanoparticles for photocatalytic applications

A facile and green synthetic approach was considered for the synthesis of stabilized titanium dioxide (TiO2) nanoparticles. Extracts of Alcea and Thyme plants were used to synthesis TiO2 nanoparticles for photocatalytic applications. Evaluation of the structural and phase formation via X-ray diffraction (XRD) indicated the formation of the anatase phase of TiO2 along with the rutile phase. A desired single phase of anatase was obtained upon heating the as-synthesized samples at 500 °C for 3 h. Using the information provided by the XRD analyzer and the Debye Scherer relationship, the average crystallite size was found to be around 6 and 10 nm for the samples synthesized using Alcea and Thyme plants, respectively. To determine the elemental analysis and chemical structure, the energy dispersive X-ray (EDX) analyzer and Fourier Transform Infrared (FTIR) spectroscopy were employed. Field emission scanning electron microscopy (FESEM) indicated batches of ultrafine agglomerated particles for both samples, which their sizes grew by the heating process. The UV–visible analysis of photocatalytic properties confirmed the priority of TiO2 nanoparticles prepared with Thyme extracts.

Enhanced photocatalytic and antibacterial activities of Ag-doped TiO2 nanoparticles under visible light

In this paper, we report the photocatalytic and antibacterial activities of nanosized Ti1-xAgxO2 (0.00 < x < 0.08) photocatalyst synthesized by sol-gel method. The X-ray diffraction (XRD) and Raman spectra reveal single phase anatase structure for all substituted samples, ruling out the presence of any secondary phase. This is well supported by TEM micrographs which show that shapes of the nanoparticles are non-spherical. UV- visible spectrum illustrates that an absorption edge shifts toward the visible region. The 4.0 mol % of Ag-doped TiO2 shows 96% degradation of methylene blue (MB) within 60 min under visible light irradiation and exhibit highest photocatalytic performance. The active catalyst has superb stability and durability, maintaining its high degradation efficiency as more as 89% after the five successive runs. An enhancement in bactericidal activity is also observed against bacterial strain (Escherichia Coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Enterobacter Cloacae) with increased Ag substitution.

Effect of deposition potential on efficiency of TiO2/Cu2O photoelectrochemical cells

TiO2/Cu2O heterojunction solar cells have been successfully deposited on Ti foils using the electrochemical route. The effect of deposition potential on the efficiency of TiO2/Cu2O heterojunction solar cells has been studied. The SEM images show yarn ball like morphology of Cu2O layer. The XPS spectra indicate the formation of TiO2/Cu2O heterojunction from their corresponding oxidation states. Raman spectroscopy displays single anatase phase of TiO2 in presence of Cu2O. From J–V characteristics of TiO2/Cu2O heterojunction, the solar cell parameters such as Jsc, Voc, Pmax, fill factor and efficiency have been measured. The heterojunction solar cell shows 41% maximum fill factor and power conversion efficiency 0.21%.

Low Temperature Synthesis of Several Titanium Dioxide Solid Solutions through the Sol-Gel Method

Titanium dioxide powders constituted by anatase single phase are very useful to understand several properties of that semiconductor applied as photocatalyst material. In addition, the reconstructive transformation involved in the anatase-to-rutile phase transition is also dependent of compositional and structural characteristics, which is consequence of the xerogel precursors. In this work, it was provided some structural investigation and the thermal event associated to different compositions of titanium dioxide xerogel samples obtained by Sol-Gel method. It was prepared two different doped-sample sets, one with bared titanium dioxide matrix and other with 10 mol% of zirconium-silicon one, and both sample sets were submitted to doping with 2 mol% of cation pairs, taking in account the ionic radii and oxidation states. The small and pentavalent vanadium cation was combined with trivalent and bigger lanthanum and bismuth ones, in order to provide non strained unit cell making an average values for ionic radii and oxidation states, taking in account the tetravalent titanium cation. By thermal analysis, X-ray diffractometry, FTIR and Raman spectroscopies it was possible to demonstrate the insertion of bigger dopants as lanthanum and bismuth, as well as the smaller one as vanadium, which are usually dopants not supported in isolated forms were successfully incorporated to anatase phase when combined as expected in previous composition design stage. DOI: http://dx.doi.org/10.17807/orbital.v10i1.1038

Synergistic effect of La and Co co-doping on room-temperature ferromagnetism enhancement of TiO2 nanoparticles

The synergistic influence of lanthanum and cobalt co-doping on room temperature ferromagnetism (RTFM) of TiO2 system is investigated. A series of Ti0.97−xCo0.03LaxO2 nanoparticles were prepared and their structures and properties were systematically studied with X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, UV–vis spectrophotometer, Raman spectra and magnetic measurement techniques, respectively. Detailed experimental characterizations indicate that the as-prepared La and Co co-doped samples exhibit single anatase phase, and all the samples exhibit strong visible photoluminescence associated with oxygen vacancies and a clear ferromagnetic hysteresis loop, both of which were dramatically enhanced with La and Co co-doping, and the maximum saturation magnetization (Ms) reaches 1.38emu/g at the La content of 6mol%. It is speculated that oxygen vacancies modulated by ionic La play an important role in the enhanced RTFM, which can be attributed to the bound magnetic polarons (BMPs) formed via ferromagnetic coupling between two neighboring Co2+ ions mediated by oxygen vacancy (F+ center). Our results present an alternative method to obtain high performance RTFM.

Structural and magnetic study of undoped and cobalt doped TiO2 nanoparticles.

The present study investigates the influence of cobalt doping on the structural and magnetic properties of TiO2 nanoparticles prepared by a simple wet chemical method. The single phase anatase structure of Co-doped TiO2 nanoparticles was confirmed by X-ray powder diffraction. A morphological study using scanning electron microscopy and transmission electron microscopy indicates the formation of TiO2 nanoparticles of sizes 6–10 nm. The high resolution TEM image shows clear lattice fringes indicating the highly crystalline nature of the nanoparticles which was further analysed by selected area electron diffraction pattern which indicates a polycrystalline nature of anatase TiO2. The shifting and broadening of the most intense Eg (1) mode in micro-Raman study of Co-doped TiO2 nanoparticles and XPS spectra indicate the incorporation of Co in TiO2. Magnetic measurement shows ferromagnetic behavior at room temperature in undoped TiO2 which has originated due to the presence of oxygen vacancies which are intrinsic in nature. But the M–H curve of Co-doped TiO2 shows the coexistence of ferromagnetic and paramagnetic phases with enhanced magnetization. The enhancement in magnetization has arisen due to Co doping and the paramagnetism may be due to the presence of some undetected clusters of oxides of cobalt.

Preparation and photocatalytic activity analysis of nanometer TiO2 modified by surfactant

Combining the advantages of the sol–gel method and solvothermal method, the single anatase phase of nano-titanium dioxide (TiO2) with high crystallinity had been prepared by means of the sol–solvent thermal improved process, in which butyl titanate was used as titanium source; anhydrous ethanol as solvent; concentrated nitric acid as inhibitor; and cationic surfactant cetyl trimethyl ammonium bromide (CTAB), anionic surfactant sodium dodecyl benzene sulfonate (SDBS), and nonionic surfactant polyethylene glycol (PEG) as dispersants. The analysis results of Brunauer–Emmett–Teller, scanning electron microscopy, and transmission electron microscopy characterizations indicated that CTAB-modified TiO2 with the optimum ratio had the most apparent dispersibility and the highest specific surface area compared with unmodified TiO2, SDBS-modified TiO2, and PEG-modified TiO2. At the same time, the photocatalytic degradation rate of methyl orange could be improved to 99.16%. It indicated that the modification effect of CTAB was significantly better than those of SDBS and PEG, which made the nanoparticles uniformly dispersed, resulting in higher photocatalytic activity.

Role of Temperature on the Phase Modification of TiO2 Nanoparticles Synthesized by the Precipitation Method

Nanostructured TiO2 samples have been synthesized successfully by a simple precipitation method. The prepared samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), photoluminescence (PL) spectroscopy, ultra violet (UV) spectroscopy and Raman spectroscopy respectively. The as-prepared TiO2 nanoparticls appear to be a single anatase phase with average crystalline size 37.68 nm at 150 ∘C and found to be transformed from anatase to rutile phase during the annealing of samples in the temperature range from 150 ∘C to 600 ∘C. The TEM images indicate the particle sizes are in the range between 12 and 25 nm for anatase phase TiO2 at 400 ∘C and 30–45 nm for rutile phase TiO2 at 600 ∘C. The luminescence property of the TiO2 nanoparticles studied by the emission properties confirms the presence of defect levels caused by the oxygen vacancies. Raman spectroscopy was used to identify and quantity the amorphous and crystalline TiO2 phases. FTIR studies reveal weak complex vibrations between the titanium and oxygen species and also additional unsaturated sites (Ti3+) through incorporation of (OH) groups, not otherwise seen in bulk TiO2.

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.

Influence of TiO2 Support on Activity of Co3O4/TiO2 Photocatalysts for Visible-Light Water Oxidation

Abstract Co3O4-loaded TiO2 is a photocatalyst capable of oxidizing water into O2 by absorbing an entire range of visible light (400 &amp;lt; λ &amp;lt; 850 nm). In this work, the photocatalytic activity for water oxidation was investigated with respect to crystal phase, specific surface area, and surface morphology of TiO2 support. Results of photocatalytic reactions using six different TiO2 samples that possessed single-phase anatase or rutile structure indicated that the activity could be improved by applying a TiO2 support that had larger specific surface area, because it could accommodate larger amount of Co3O4 with minimal impact of undesirable aggregation. It was also suggested that when the specific surface area is similar, the activity is largely insensitive to crystal phase of TiO2, but is influenced by the surface morphology of TiO2, which can affect the dispersion of Co3O4.

Surface, structural, energy band-gap, and photocatalytic features of an emulsion-derived B-doped TiO2 nano-powder

Different amounts of boron-doped TiO2 (BDT) (B=0–10wt.%) nano-powders were prepared by following an emulsion-based sol-gel (EBSG) route and were calcined at 550°C for 6h. These calcined nano-powders were then thoroughly characterized by means of various techniques including XRD, XPS, SEM, FT-IR, FT-Raman, DRS, BET surface area, zeta-potential, and photocatalytic degradation of methylene blue (MB) in order to establish the effects of B-doping on structural, surface, band-gap energy, and photocatalytic characteristics of TiO2 nano-powder formed in the EBSG route. These characterization results revealed that after calcination, the pure TiO2 nano-powder formed in the EBSG route was in the form of a mixture of anatase and rutile phases in 70:30 ratio, whereas, the 0.2wt.% B-doped TiO2 nano-powder formed in the same route was in the form of a single anatase phase. These BDT nano-powders were also found to possess negative zeta-potentials (ζ) (<−55mV), high specific surface areas (up to >65m2/g), and low band-gap energies (<3.161eV). The photocatalytic results revealed that BDT nano-powders adsorbed considerable amounts MB (up to 50%) from aqueous solutions of 0.01mM, 0.02mM and 0.03mM MB during 30min stirring in the dark, whereas, the commercial Degussa P-25 TiO2 nano-powder did not adsorb any MB. Owing to adsorption of MB on the surface of photocatalyst, the quantum efficiency values determined did not match with those of total photocatalytic MB concentration reduction. Among various photocatalysts investigated in this study, the highest activity was noted over pure TiO2 nano-powder formed in the EBSG route.

Measuring and interpreting quantum efficiency of acid blue 9 photodegradation using TiO2-based catalysts

A series of highly-active catalysts were obtained from the same precursor and calcined at different temperatures to generate single-phase anatase and anatase-rutile composite powders. Performance of the catalysts was compared with the P25 reference and assessed through the measurement of the optical properties of the materials and calculation of the efficiency of the photodegradation of a multifunctional dye, acid blue 9. X-ray diffraction, porosimetry, UV–vis and photoluminescence spectroscopies were used to analyze the physico-chemical properties of the catalysts and to test their stability under reaction conditions. Through the calculation of the reaction rate and total organic carbon (TOC) observables as well as the apparent and true quantum efficiency parameters we analyzed quantitatively the performance of the materials. We observe that a high surface area anatase sample showed optimum activity and adequate selectivity towards full mineralization. The catalysts were subjected to sedimentation and recycling experiments and the catalytic performance compared on the basis of the true quantum efficiency. The use of this last parameter leads to different conclusions than those supported by an analysis based in the kinetic constant, reaction rate or apparent quantum efficiency. The high quantum efficiency and easy recovery after repeated experiments shown by the catalysts were interpreted on the basis of the characterization results.

Structural phase-dependent resistivity of intrinsic-extrinsic co-doped transparent titanium dioxide films

The authors report a method of enhancing the conductivity of TiO2 films by controlling their structural phases. Thin films of Nb:TiO2 (TNO) were prepared on glass and silicon substrates by RF sputtering with varying Nb content at 200°C. It is shown that fine control over the structural phases of TiO2 is critical for achieving low resistivity. The resistivity values of the films doped with oxygen vacancies and Nb+5 decreased from 3.8 × 10−1 to 4.1 × 10−3Ωcm when the weight percent of rutile in anatase-rutile phase mixture decreases from 52.8% to 32%. Furthermore, the lowest resistivity value of 2.37 × 10−3Ωcm was obtained for the doped TiO2 films having single phase anatase structure. The physical processes responsible for the diverse electrical properties are discussed and are associated with the growth conditions. Our result indicates that highly conductive doped-TiO2 film can be obtained by controlling the anatase phase formation via the growth temperature. The obtained results can significantly contribute to the development of transparent electrodes by RF sputtering, a suitable technique for coating large area substrates.

Epitaxial growth and properties of Nb-doped anatase TiO2 films on LSAT by MOCVD

High quality single crystalline Nb-doped anatase phase TiO2 films with different Nb concentrations were deposited on LSAT (100) substrates by metal organic chemical vapor deposition (MOCVD) at 600 °C. The influences of Nb concentration on the structural, electrical and optical properties of the films have been investigated. The obtained films were single crystalline anatase TiO2 and the epitaxial relationship between the films and the substrates was confirmed as TiO2 (001) || LSAT (100) with TiO2 [010] || LSAT [010]. The resistivity of the films was reduced by almost 8 orders of magnitude after Nb doping and a minimum resistivity of 4.0 × 10−2Ω⋅cm was obtained in 0.6% Nb-doped samples. The films achieved a maximum mobility as high as 13.5 cm2⋅V−1⋅s−1. The carrier concentration was in a range of 9.4 × 1017–1.7 × 1019 cm−3. The optical transmittance of the films in the visible range exceeded 93% and the optical band gap was varied from 3.48 to 3.53 eV.

Comparative study on the performance of Au/F-TiO2 photocatalyst synthesized from Zamzam water and distilled water under blue light irradiation

Abstract Recurring problems of titanium dioxide (TiO 2 ) for needing UV light to be activated and high electron-hole recombination rate limit the application of TiO 2 as a prolific photocatalyst. By modifying the morphology and introducing electron trapping species into TiO 2 , the photocatalytic activity of TiO 2 could be improved. Solvents of two different kinds; distilled water and Zamzam water were used in peroxotitanic acid synthesis of TiO 2 and the photocatalyst was utilized to degrade Reactive Blue 19 (RB19) dye under blue light irradiation (475 nm) to assess the visible light activity of synthesized TiO 2. Fluorine was incorporated to control the morphology while gold nanoparticles (GNP) stabilized by arabic gum were deposited to trap electrons. The morphology of F-TiO 2 which appeared to be in ovoid shape was confirmed by Field Emission-Scanning Electron Microscope (FE-SEM) and Transmission Electron Microscope (TEM). Brunauer-Emmett-Teller (BET) surface area and crystallite size estimated from X-ray Diffraction (XRD) data revealed that F-TiO 2 modified using HF was smaller in size and exhibited single anatase phase. The band gap of Au-TiO 2 synthesized by distilled and Zamzam water was 2.78 eV and 2.89 eV respectively; shifted from 3.08 eV in blank TiO 2 . Peroxo Au/F-TiO 2 synthesized with the incorporation of arabic gum as GNP stabilizer and HF as fluorine modifier degraded up to 49.23% of RB19 within two hours of reaction. The addition of fluorine and gold demonstrated high ability to enhance visible light activity of TiO 2 with distilled water used as solvent displayed higher photocatalytic performance compared to Zamzam water.

Thermal behaviour of the TiO2-based gels obtained by microwave-assisted sol–gel method

In order to establish the influence of the preparation method on thermal behaviour of gels obtained by the sol–gel and microwave-assisted sol–gel methods, a comparative thermal analysis study was conducted by the thermogravimetric and differential thermal analysis (TG/DTG/DTA) and evolved gas analysis (EGA) on TiO2 and V2O5-doped TiO2 gels, where TiO2:V2O5 molar ratio was set to 99.95:0.05 and 98.0:2.0. In contrast to TiO2 gels, for which the thermal behaviour was not significantly influenced by the preparation method, the microwave-irradiated binary samples showed a more complex and prolonged decomposition compared to their non-irradiated counterparts. This observation was correlated with influence of microwaves in enhancing the reaction rate between the Ti and V reagents leading to formation of more complex compositions of gels. Based on TG/DTG/DTA results, the temperatures of 300 and 450 °C were chosen for the processing of powders in air. All samples thermally treated at 300 and 450 °C crystallized in a single anatase phase except the TiO2:V2O5 with a molar ratio 99.95:0.05, obtained by microwave-assisted sol–gel method that contains also small amount of rutile phase. At 550 °C all samples contain mixture of anatase and rutile phases.

ZnO/TiO2 composites for photocatalytic inactivation of Escherichia coli

ZnO/TiO2 composite was synthesized from zinc nitrate and anatase TiO2 by using the incipient wet impregnation method followed by calcination at 350°C for 3h. These samples were characterized through several characterization techniques. XRD peaks confirms the presence of single anatase phase of titania in the 3 and 6wt% ZnO/TiO2 composite, whereas in all other composites both anatase titania and zinc oxide phases were found. UV–visible (diffuse) reflectance spectra show titania and ZnO absorbs in the ultraviolet (UV) region whereas ZnO/TiO2 absorbs both UV and visible light. The shift in absorbance facilitates ZnO/TiO2 composites to exhibit photocatalytic activity under UV–visible light irradiation. FE-SEM and TEM analysis reveals that the particle size of ZnO is around 0.2μm and its size significantly reduced to 25nm when it is deposited on TiO2 support. The E. coli inactivation study shows that ZnO/TiO2 composites exhibit high inactivation compared to ZnO and titania under UV alone and the combination of both UV–visible. With the increasing loading concentration of ZnO, the photocatalytic inactivation potential of ZnO/TiO2 composites also increases. The E. coli inactivation of ZnO/TiO2 is explained based on the photocatalytically generated ROS, ZnO dissolution and charge carrier separation due to hybrid structures.

Flower-structured titanium oxide with two phase coexistence supported Pt electrocatalyst for effective enhancement of electrocatalytic activity

TiO2 microflowers assembled by nanosheets are prepared by a one-step solvothermal process. The anatase-TiO2(B) dual-phase coexistence or anatase single phase is obtained under different annealing temperatures. Pt nanoparticles supported on the anatase-TiO2(B) microflowers are first applied to alcohol electrooxidation. The electrocatalytic performances of Pt/anatase-TiO2(B), Pt/anatase and Pt/carbon-black (Pt/C) on graphite substrates are systematically investigated. The Pt/anatase-TiO2(B) catalyst exhibits superior electrocatalytic activity and stability compared with that of Pt/anatase and Pt/C catalysts for methanol and ethanol in acidic and alkaline media, which is attributed to the large specific surface area, the porous channels to reduce the liquid sealing effect, the enhanced electronic conductivity by dual-phase coexistence and quick electron transfer from anatase phase to TiO2(B).