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1.
A series of tungsten‐doped Titania photocatalysts were synthesized using a low‐temperature method. The effects of dopant concentration and annealing temperature on the phase transitions, crystallinity, electronic, optical, and photocatalytic properties of the resulting material were studied. The X‐ray patterns revealed that the doping delays the transition of anatase to rutile to a high temperature. A new phase WyTi1‐yO2 appeared for 5.00 wt% W‐TiO2 annealed at 900 °C. Raman and diffuse reflectance UV–Vis spectroscopy showed that band gap values decreased slightly up to 700 °C. X‐ray photoelectron spectroscopy showed that surface species viz. Ti3+, Ti4+, O2?, oxygen‐vacancies, and adsorbed OH groups vary depending on the preparation conditions. The photocatalytic activity was evaluated via the degradation of methylene blue using LED white light. The degradation rate was affected by the percentage of dopants. The best photocatalytic activity was achieved with the sample labeled 5.00 wt% W‐TiO2 annealed at 700 °C. 相似文献
2.
The phase stability of the two TiO2 modifications (anatase and rutile) in fumed SiO2/TiO2 nano-composites (0–24.8 wt-% silica) under thermal and hydrothermal conditions was investigated by X-ray powder diffraction, transmission electron microscopy (TEM) and gas adsorption methods (BET). The results show that the phase transformation from anatase to rutile type of structure and the growth of anatase crystallites are significantly retarded by mixing small amounts of SiO2 into TiO2, while the specific surface area is maintained. The SiO2/TiO2-composites reveal a remarkable shift in the anatase to rutile transformation temperature from approx. 500 °C (pure TiO2) to approx. 1000 °C (samples with SiO2 contents of more than 10%). The rate of phase transformation from anatase to rutile is enhanced under hydrothermal conditions compared to conventional thermal treatment, e.g. pure titania (AEROXIDE® TiO2 P25) annealed under hydrothermal conditions (100 g/m3 absolute humidity, 4 h at 600 °C) had a rutile content of 85%, while the same specimens annealed in absence of humidity contained only 46% rutile. However, the difference in rate of phase transformation became less pronounced when the silica content in SiO2/TiO2-composites was further increased.TEM results showed that the surface of the anatase crystallites was covered with silica. This averts coalescence of anatase crystallites and keeps them under a critical size during the annealing process. When the crystal domains grew larger, a rapid conversion to rutile took place. The critical size of anatase crystallites for the phase transformation was estimated to be 15–20 nm. 相似文献
3.
Nitrogen-doped TiO2 nanoparticle photocatalysts were obtained by an annealing method with gaseous ammonia and nitrogen. The influence of dopant N on the crystal structure was characterized by XRD, XPS, BET, TEM and UV-Vis spectra. The results of XRD indicate that, the crystal phase transforms from anatase to rutile structure gradually with increase of annealing temperature from 300 to 700 ℃. XPS studies indicate that the nitrogen atom enters the TiO2 lattice and occupies the position of oxygen atom. Agglomeration of particles is found in TEM images after annealing. BET results show that the specific surface areas of N-doped samples from 44.61 to 38.27 m2/g are smaller than that of Degussa TiO2. UV-Vis spectra indicate that the absorption threshold shifts gradually with increase of annealing temperature, which shows absorption in the visible region. The influence of annealing condition on the photocatalytic property has been researched over water decomposition to hydrogen, indicating that nitrogen raises the photocatalytic activity for hydrogen evolution, and the modified TiO2 annealed for 2 h at 400 ℃ under gas of NH3/N2 (V/V=1/2) mixture shows better efficiency of hydrogen evolution. Furthermore, the N-doped TiO2 nanoparticle catalysts have obvious visible light activity, evidenced by hydrogen evolution under visible light (λ>400 nm) irradiation. However, the catalytic activity under visible light irradiation is absent for Degussa as reference and the N-doped TiO2 annealed at 700 ℃. 相似文献
4.
C.K. Lee D.K. Kim J.H. Lee J.H. Sung I. Kim K.H. Lee J.W. Park Y.K. Lee 《Journal of Sol-Gel Science and Technology》2004,31(1-3):67-72
The peroxo titanic acid solution was successfully prepared using titanium trichloride as a precursor. The basic properties of the TiO2 film prepared by the solution were investigated in view of phase change, bandgap energy, crystalline size etc. The film displayed amorphous TiO2 at room temperature, anatase above 281°C and a mixture of anatase and rutile at 990°C. The crystalline size increases with annealing temperatures, while the bandgap energies decrease due to the quantum size effect and the formation of rutile phase which has low bandgap energy. As a result of TG-DTA, it was found that annealing treatment at 990°C for 2 h formed a mixture of anatase and rutile through three steps: (1) the removal of physically adsorbed water (2) the decomposition of peroxo group (3) amorphous-anatase or anatase-rutile phase transformation. 相似文献
5.
Lele Zhao Shouxin Wang Yuanyang Wang Zhihong Li 《Surface and interface analysis : SIA》2017,49(3):173-176
Titanium dioxide (TiO2) aerogels were prepared with sol–gel ambient pressure drying method by using titanium tetrachloride (TiCl4) as precursor and tetraethoxysilane as modifier, calcinated at different temperature and characterized by X‐ray diffraction, transmission electron microscopy and small angle X‐ray scattering. The results showed that the TiO2 aerogels remained amorphous under 500 °C, changed to anatase from 600 °C and further changed to rutile from 900 °C. Between 60 °C and 500 °C, the primary particles within the samples concentrated mainly upon small sizes, enlarged and diverged remarkably above 600 °C. The crystalline grains grew and agglomerated with the rise of the calcination temperature. The TiO2 aerogels at a temperature higher than 800 °C have better stability than anatase because of the formation of partial Ti―O―Si bonds. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
6.
Yahia Djaoued Subramanian Balaji Normand Beaudoin 《Journal of Sol-Gel Science and Technology》2013,65(3):374-383
Mesoporous WO3–TiO2 composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600 °C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N2 adsorption–desorption measurements, μ-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500 °C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO3, respectively. The degree of crystallization of TiO2 present in these composite films was not evident. The composite films annealed at 600 °C, however, consist of orthorhombic (o) WO3 and anatase TiO2. It was found that the o-WO3 phase was stabilized by nanocrystalline anatase TiO2. The thus obtained mesoporous WO3–TiO2 composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO3–TiO2 composite layer heat treated at 600 °C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500 °C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO2 embedded in the orthorhombic WO3 matrix of the WO3–TiO2 composite layer annealed at 600 °C. 相似文献
7.
Yahia Djaoued Subramanian Balaji Normand Beaudoin 《Journal of Sol-Gel Science and Technology》2013,68(3):516-525
Mesoporous WO3–TiO2 composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600 °C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N2 adsorption–desorption measurements, μ-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500 °C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO3, respectively. The degree of crystallization of TiO2 present in these composite films was not evident. The composite films annealed at 600 °C, however, consist of orthorhombic (o) WO3 and anatase TiO2. It was found that the o-WO3 phase was stabilized by nanocrystalline anatase TiO2. The thus obtained mesoporous WO3–TiO2 composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO3–TiO2 composite layer heat treated at 600 °C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500 °C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO2 embedded in the orthorhombic WO3 matrix of the WO3–TiO2 composite layer annealed at 600 °C. 相似文献
8.
Influence of thermal annealing on the microstructure,hardness and corrosion behavior of TiAlSiCuN nanocomposite films
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J. Shi M. Q. Wan H. L. Wang X. Wang T. ‐G. Wang 《Surface and interface analysis : SIA》2016,48(12):1310-1315
Nanocomposite TiAlSiCuN films were deposited on high speed steels by filtered magnetic arc ion plating. Detailed properties of the films annealed at various temperatures are studied. After thermal annealing at different temperatures ranging from 400 to 800 °C, changes in the film micro‐structure, chemical and phase composition, surface morphology, hardness and polarization curve properties were systematically characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, nano‐indenter and electrochemical workstation, respectively. It was found that the TiAlSiCuN films could be fully oxidized at 800 °C, Al and Ti atoms all diffused outwards and formed dense protective Al2O3 and TiO2 layer. Simultaneously, the TiAlN phase gradually disappeared. The films annealed at 400 °C obtained the highest hardness because of the certain grain growth and little generated oxides. Besides, the certain formation of dense protective Al2O3 layer made the TiAlSiCuN film annealed at 600 °C present the least corrosion current density and the corrosion voltage. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
9.
Photocatalytic Activity of TiO2 Nanofibers with Doped La Prepared by Electrospinning Method
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La‐TiO2 nanofibers are prepared by a sol‐gel assisted electrospinning method. The structure and morphology of La‐TiO2 nanofibers are characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis shows that the weight percentage of anatase and rutile in the 1.5 mol% La‐TiO2 nanofibers calcined at 600 °C is about 8:2, which is similar to P‐25. The XRD data of La‐TiO2 nanofibers with different La content shows that La3+ dopant has a great inhibition on TiO2 phase transformation. The photocatalytic activity of the as‐prepared La‐TiO2 nanofibers is evaluated by photocatalytic decolorization of Methylene Blue (MB) aqueous solution. The results show that the 1.5 mol% La‐TiO2 nanofibers calcined at 600 °C exhibit high photocatalytic activity, indicating that 600 °C and 1.5 mol% are the appropriate calcination temperature and optimal molar ratio of La to Ti, respectively. 相似文献
10.
Graham Dawson Wei Chen Tiekai Zhang Zheng Chen Xiaorong Cheng 《Solid State Sciences》2010,12(12):2170-2176
Mixed phase TiO2 powders of different composition and particle size were subjected to the hydrothermal reaction with 10 M NaOH. It was found that the anatase phase component of the starting material is easily converted to trititanate nanotubes at 140 °C. At this temperature the rutile phase remains unreacted, however at 170 °C it reacts to form trititanate plates and belts. When the reaction time is increased to 7 days, all the TiO2 is converted to trititanate and the morphology is exclusively nanoplates and belts, with the tube phase destroyed. Many researchers have observed some heterogeneity in their reaction products, but have mainly focussed on the nanotubes. We observed that the tubes are only prepared from the anatase phase component of a TiO2 precursor, whereas the rutile component produces trititanate plates and sheets, irrespective of the reaction length. The particle size affects the rate of reaction, resulting in the phase transition being more easily visible in the reactions starting with the larger TiO2 particle size. 相似文献
11.
Tereza Václavů Alexandra Rudajevová Michal Václavů Stanislav Daniš Daniela Popelková Radomír Kužel 《Journal of Thermal Analysis and Calorimetry》2017,128(2):779-785
Thermal stability of titanate nanotubes (Ti-NT) was studied in temperature range from room temperature up to 1000 °C in three different atmospheres—in air, vacuum and helium—and differences were observed. In air, vacuum and helium, the release of adsorbed and crystal water was detected in temperatures up to 200 °C. Transformation of the initial structure to anatase form of TiO2 was found independently of the atmosphere used. But in air the transformation to anatase occurred at lower temperature. The difference between these atmospheres was approximately 100 °C. However, only in air, the transformation to sodium hexatitanate and rutile form of TiO2 occurred at higher temperatures. In vacuum, only the anatase phase was detected up to 800 °C. In helium, the transformation to rutile was observed but not to sodium hexatitanate. The changes of the initial structure of Ti-NT during the elevation of temperature were studied by combination of in situ powder X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis and mass spectroscopy. 相似文献
12.
A comparative study of TiO2 powders prepared by sol–gel methods is presented. Titanium tetraisopropoxide was used as the precursor for the sol–gel processes.
The effects of the annealing treatment on phase, crystallite size, porosity and photodegradation of dyes (methyl orange and
methylene blue) were studied. The phase structure, microstructure and surface properties of the films were characterized by
using X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). The X-ray diffraction was used for crystal phase identification,
for the accurate estimation of the anatase–rutile ratio and for the crystallite size evaluation of each polymorph in the samples.
It was found that the only TiO2 anatase phase of the synthesized TiO2 develops below 500 °C, between 600 and 800 °C the anatase coexist with rutile and above 800 °C only the rutile phase was
found in the samples. Attention has been paid not only to crystal structures, but also to the porosity, the particle size
and the photocatalytic properties. However, the annealing temperature was found to have significant influence on the photocatalytic
properties. Different TiO2 doctor blade thin films were obtained mixing the sol gel powder (100% anatase) and TiO2 Aldrich with TiO2 Degussa P25. The surfactant (Triton X100 or sodium dodecyl sulfate) affects the packing density of the particles during deposition
and the photocatalytic degradation efficiency of the dyes. The photocatalytic degradation kinetics of methyl orange and methylene
blue using TiO2 thin film were investigated. 相似文献
13.
D. Regonini A. Jaroenworaluck R. Stevens C.R. Bowen 《Surface and interface analysis : SIA》2010,42(3):139-144
Titanium oxide (TiO2) nanotubes prepared by electrolytic anodisation of a titanium electrode have been systematically heat treated to control the conversion of the as‐prepared amorphous structure to nanocrystalline anatase and rutile. Raman spectroscopy revealed that the temperature of calcination is critical in determining the structure and crystallinity of the titania. X‐ray Photoelectron Spectroscopy analysis shows the as‐prepared film to consist mainly of oxide, although a small amount of fluoride contamination remains from the electrolyte. Organic components from post‐anodising cleaning treatments were also present. Fluorine ions are gradually ejected from the anodic layer during annealing and the fluorine concentration is negligible in samples that are heat treated above 400 °C. Choosing the appropriate annealing temperature allows the structure to be made up of defined proportions of anatase and rutile with a reduced contamination of species from the electrolyte or organic solvents. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
14.
M. Chandra Sekhar N. Nanda Kumar Reddy B. Venkata Rao G. Mohan Rao S. Uthanna 《Surface and interface analysis : SIA》2014,46(7):465-471
Titanium dioxide (TiO2) thin films were deposited onto p‐Si substrates held at room temperature by reactive Direct Current (DC) magnetron sputtering at various sputter powers in the range 80–200 W. The as‐deposited TiO2 films were annealed at a temperature of 1023 K. The post‐annealed films were characterized for crystallographic structure, chemical binding configuration, surface morphology and optical absorption. The electrical and dielectric properties of Al/TiO2/p‐Si structure were determined from the capacitance–voltage and current–voltage characteristics. X‐ray diffraction studies confirmed that the as‐deposited films were amorphous in nature. After post‐annealing at 1023 K, the films formed at lower powers exhibited anatase phase, where as those deposited at sputter powers > 160 W showed the mixed anatase and rutile phases of TiO2. The surface morphology of the films varied significantly with the increase of sputter power. The electrical and dielectric properties on the air‐annealed Al/TiO2/p‐Si structures were studied. The effect of sputter power on the electrical and dielectric characteristics of the structure of Al/TiO2/p‐Si (metal‐insulator‐semiconductor) was systematically investigated. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
15.
Leonardo Soriano Petri P. Ahonen Esko I. Kauppinen Jorge Gómez-García Carmen Morant Francisco J. Palomares Marta Sánchez-Agudo Patrick R. Bressler José M. Sanz 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):849-857
Summary. A complete characterization of nanostructures has to deal both with electronic structure and dimensions. Here we present
the characterization of TiO2 nanoparticles of controlled size prepared by aerosol methods. The electronic structure of these nanoparticles was probed
by X-ray absorption spectroscopy (XAS), the particle size by atomic force microscopy (AFM). XAS spectra show that the particles
crystallize in the anatase phase upon heating at 500°C, whereas further annealing at 700°C give crystallites of 70% anatase
and 30% rutile phases. Raising the temperature to 900°C results in a complete transformation of the particles to rutile. AFM
images reveal that the mean size of the anatase particles formed upon heating at 500°C is 30 nm, whereas for the rutile particles
formed upon annealing at 900°C 90 nm were found. The results obtained by these techniques agree with XRD data.
Received October 5, 2001. Accepted (revised) December 6, 2001 相似文献
16.
《Arabian Journal of Chemistry》2020,13(2):3946-3956
The influence of TiO2 nanopowder doping with 4 wt% indium and 2 wt% each of indium and chromium on phase transformation was studied. Samples were heated from ambient temperature to 950 °C in sealed quartz capillaries, and in-situ synchrotron radiation diffraction measurements were obtained. Capillary sealing yielded an increase in capillary gas pressure to 0.42 MPa at 950 °C in proportion to absolute temperature by Gay-Lussac’s Law. The initial synthesized samples were amorphous, and crystalline anatase appeared at 200 °C. Crystalline rutile appeared at 850 °C for the nanomaterials that were doped with In and In and Cr. A change in sealed-capillary oxygen partial pressure yielded a decrease and an increase in crystallization temperature, respectively, for the amorphous-to-anatase and anatase-to-rutile transformations. Crystalline titania (anatase and rutile) formed from the amorphous titania by 800 °C and 900 °C, for materials doped with In and In-Cr, respectively. The anatase concentration that was dominant in the In-doped materials up to 950 °C and the higher rutile concentration for the In-Cr doped materials from 900 to 950 °C results from the defect structure that was induced by doping. Cr-ions in the Ti sub-lattice retarded the transformation of anatase to rutile when compared with the retarding effect of mixed In/Cr ions. The transformation results because of the relatively smaller radius of Cr-ions when compared with the In-ions. The differences in phase-transformation kinetics for In, In-Cr and for undoped nanopowders in the literature agree with the calculated transformation activation energies. 相似文献
17.
Silvester Tursiloadi Yu Yamanaka Hiroshi Hirashima 《Journal of Sol-Gel Science and Technology》2006,38(1):5-12
Porous anatase is attractive because of its notable photo-electronic properties. Titania wet gel prepared by hydrolysis of
Ti-alkoxide was immersed in the flow of supercritical CO2 at 60°C and the solvent was extracted (aerogel). Mesoporous TiO2 consisting of anatase nano-particles, about 5 nm in diameter, have been obtained. Thermal evolution of the microstructure
of the aerogel was evaluated by TGA-DTA, N2 adsorption, TEM and XRD, and discussed in comparison with that of the corresponding xerogel. The diffraction peaks of anatase
were found for the as-extracted gel while the xerogel dried at 90°C was amorphous. After calcination at 600°C, the average
pore size of the aerogel, about 20 nm in diameter, was 4 times larger than that of the xerogel, and the pore volume, about
0.35 cm3 g−1, and the specific surface area, about 60 m2 g−1, were 2 times larger than those of the xerogel. XRD peaks of rutile have been found after calcination at 600°C. The particle
sizes of anatase and rutile are about 13 and 25 nm in diameter, respectively. The surface morphology of TiO2 nano-particles has been discussed in terms of their surface fractal dimensions estimated from the N2 gas adsorption isotherms. 相似文献
18.
The photocatalytic activity of TiO2 nanofibers immobilized on quartz substrates was investigated by evaluating the decomposition of organic pollutants. TiO2 nanofibers were synthesized by electrospinning the Ti-precursor/polymer mixture solution, followed by hot-pressing for enhancing
the adhesion of TiO2-nanofiber films to the substrates. TiO2 started to crystalize in the anatase form at 500 °C and reached the optimal photocatalytic anatase/rutile phase ratio of
70:30 at a calcination temperature of 600 °C. The TiO2-nanofiber film was demonstrated to be an efficient photocatalyst by ranitidine decomposition under UV illumination and was
proven to have a comparable photocatalytic activity with the well-known Degussa P25 nanoparticulate photocatalyst and excellent
recyclability during 10 cycles of photocatalytic operation, indicating no loss of TiO2 nanofibers during photocatalytic operations. 相似文献
19.
Nicoleta Doriana Banu Ionut Banu Banu Marios S. Katsiotis Anjana Tharalekshmy Samuel Stephen Jamie Whelan Gisha Elizabeth Luckachan Radu Vladea Saeed M. Alhassan 《Chemical Papers》2016,70(11):1503-1511
Open cell 3D titanium carbide/silicon carbide (TiC/SiC) composite was oxidised to titanium oxide/silicon carbide (TiO2/SiC) following different temperature profiles in a thermal gravimetric analysis (TGA) instrument in continuous air-flow and static air (oven) environments. The TiC oxidation to anatase, starting at temperatures over 450°C, was confirmed by Raman spectroscopy and X-Ray diffraction (XRD). By increasing the temperature, the mass fraction of anatase diminished, while the mass fraction of rutile increased. SiC oxidation started at 650°C when a mixture of TiO2/SiO2/SiC could be observed by Raman, XRD and HRTEM. 相似文献
20.
二氧化钛多相催化是一种极具前途的环境污染深度净化技术。 本文以钛酸四丁酯和四氯化锡为原料,无水乙醇为溶剂,采用溶胶-凝胶法制备了掺杂二氧化锡的二氧化钛薄膜和复合氧化物粉体。通过测量薄膜的吸收光谱推算光学能隙,结果发现掺杂样品的光学能隙比纯二氧化钛样品有所变小。随着热处理温度的提高,掺杂和纯二氧化钛样品的光学能隙都略微降低。X-射线衍射分析表明,复合氧化物粉体的热处理温度对样品的晶体结构和光催化性能有重要影响。以掺杂二氧化锡5 % 摩尔比的样品与纯二氧化钛对照,500 ℃以下热处理样品以锐钛矿结构为主,600 ℃热处理样品为锐钛矿与金红石相共存,并显示了较好的光催化性能。透射电子显微镜观察显示,同样600 ℃热处理,掺杂样品要比纯二氧化钛具有更小的颗粒尺寸。在700 ℃热处理的样品中,掺杂样品只存在金红石相而纯二氧化钛样品中仍存有锐钛矿相。用阿伦尼乌斯经验关系式推测的晶粒生长的活化能,纯二氧化钛47.486 kJ.mol, 掺杂5 % 摩尔比的复合氧化物样品33.103 kJ.mol。以亚甲基蓝为降解物质,考察了掺杂量和热处理温度对样品的光催化性能。 相似文献