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1.
《Ceramics International》2015,41(6):7461-7465
Titanium dioxide is widely used in a lot of applications. The properties of TiO2 strongly depend on its phase composition. The transformation temperature between phases is influenced by a lot of factors. One of them is a type of substrate under the TiO2 film. In presented work, thin films of TiO2 were deposited by the sol–gel method on silicon, stainless steel (304 L) and Co–Cr–Mo alloy (Vitallium). The process of anatase–rutile phase transformation was investigated by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) studies of deposited coatings. The results were compared with anatase–rutile transformations temperature of TiO2 powders obtained by analogous sol–gel process. The temperature of anatase–rutile phase transformation changed in the range of 700–1000 °C and strongly depends on a kind of substrate. It was found that anatase–rutile transformation of TiO2 coating proceeded at a higher temperature than rutilization of titania powders. 相似文献
2.
《Journal of the European Ceramic Society》2006,26(13):2735-2742
Nitrogen-doped anatase, rutile and brookite titania photocatalyst TiO2−xNy which can be excited by visible light were prepared by mixing aqueous TiCl3 solutions with urea ((NH2)2CO) and various type of alcohols followed by solvothermal treatment at 190 °C. The phase composition, crystallinity, microstructure and specific surface area of titania powders greatly changed depending on the pH and type of solvents. Violet, yellowish and grayish TiO2−xNy with excellent visible light absorption and photocatalytic activity were prepared. The TiO2−xNy powders prepared in urea–methanol solution showed excellent photocatalytic ability for the oxidative destruction of nitrogen monoxide under irradiation of visible light λ > 510 nm. 相似文献
3.
《Ceramics International》2016,42(11):13136-13143
Kinetics of anatase transition to rutile TiO2 from titanium dioxide precursor powders synthesized by a sol-gel process have been studied using differential thermal analysis (DTA), X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED) and high resolution TEM (HRTEM). The DTA result shows residual organic matter decomposed at 436 K. The transition temperature for amorphous precursor powders converted to anatase TiO2 occurred at 739 K. Moreover, the full anatase transition to rutile TiO2 occurred at 1001 K. The activation energy of anatase TiO2 formation was 128.9 kJ/mol. On the other hand, the activation energy of anatase transition to rutile TiO2 was 328.4 kJ/mol. Mesoporous structures can be observed in the TEM image. 相似文献
4.
Xunhua Mo Yu-Tung Tsai Jia Gao Dongsen Mao James G. Goodwin 《Journal of Catalysis》2012,285(1):208-215
Co/CuZnO is known as a base metal catalyst active for C2+ oxygenate synthesis. This study probed the interactions of the different components of Co/CuZnO catalysts on CO hydrogenation using Fischer–Tropsch synthesis (250 °C, H2/CO = 2) and SSITKA. Only combination of all three metal components produced a catalyst with relatively high C2+ oxygenate selectivity, but with much lower activity compared to that for Co/Al2O3. In situ reaction characterizations, albeit at somewhat different conditions than alcohol synthesis, helped explain interaction of the components. SSITKA, under methanation conditions, indicated that the most striking feature for the combination of Co with ZnO and/or Cu was a much decreased amount of reaction intermediates. Ethane hydrogenolysis results suggested that the different components for these catalysts were in close contact and few or no large ensembles (n ? 12) of Co atoms existed, confirming that ZnO and/or Cu covered/blocked a substantial number of active sites on Co for CO hydrogenation. 相似文献
5.
《Applied catalysis. B, Environmental》2005,55(3):195-200
A visible-light-active N-containing TiO2 photocatalysts were prepared from crude amorphous titanium dioxide by heating amorphous TiO2 in gaseous NH3 atmosphere. The calcination temperatures ranged from 200 to 1000 °C, respectively. UV–vis/DR spectra indicated that the N-doped catalysts prepared at temperatures <400 °C absorbed only UV light (Eg = 3.3 eV), whereas samples prepared at temperatures ≥400 °C absorbed both, UV (Eg = 3.10–3.31 eV) and vis (Eg = 2.54–2.66 eV) light. The chemical structure of the modified photocatalysts was investigated using FT-IR/DRS spectroscopy. All the spectra exhibited bands indicating nitrogen presence in the catalysts structure. The photocatalytic activity of the investigated catalysts was determined on a basis of a decomposition rate of nonionic surfactant (polyoxyethylenenonylphenol ether, Rokafenol N9). The most photoactive catalysts were those calcinated at 300, 500 and 600 °C. For the catalysts heated at temperatures of 500 and 600 °C Rokafenol N9 removal was equal to 61 and 60%, whereas TOC removal amounted to 40 and 35%, respectively. In case of the catalyst calcinated at 300 °C surfactant was degraded by 54% and TOC was removed by 35%. The phase composition of the most active photocatalysts was as follows: (a) catalyst calcinated at 300 °C—49.1% of amorphous TiO2, 47.4% of anatase and 3.5% of rutile; (b) catalyst calcinated at 500 °C—7.1% of amorphous TiO2, 89.4% of anatase and 3.5% of rutile; (c) catalyst calcinated at 600 °C—94.2% of anatase and 5.8% of rutile. 相似文献
6.
Different types of TiO2 (anatase, P25 and rutile) supported ruthenium catalysts were synthesized by wet impregnation and directly reduced in H2. The distribution characteristics of ruthenium species were thoroughly studied before and after trichloroethylene oxidation. The results show that ruthenium oxide species are very unstable in the anatase phase, but quite stable in the rutile phase of TiO2. This phenomenon results in different catalytic behaviors for the Ru/TiO2 catalysts. The Ru/TiO2 (P25) catalyst has the best catalytic performance among these catalysts. The complete conversion temperature of trichloroethylene is in the temperature range of 260–270 °C. 相似文献
7.
《Applied Catalysis A: General》2002,223(1-2):195-203
The effect of the addition of small amounts of boron, ruthenium and rhenium on the Fischer–Tropsch (F–T) catalyst activity and selectivity of a 10 wt.% Co/TiO2 catalyst has been investigated in a continuously stirred tank reactor (CSTR). A wide range of synthesis gas conversions has been obtained by varying space velocities over the catalysts. The addition of a small amount of boron (0.05 wt.%) onto Co/TiO2 does not change the activity of the catalyst at lower space times and slightly increases synthesis gas conversion at higher space times. The product selectivity is not significantly influenced by boron addition for all space velocities investigated. Ruthenium addition (0.20 wt.%) onto Co/TiO2 and CoB/TiO2 catalysts improves the catalyst activity and selectivity. At a space time of 0.5 h-g cat./NL, synthesis gas conversion increases from 50–54 to 68–71% range and methane selectivity decreases from 9.5 to 5.5% (molar carbon basis) for the promoted catalyst. Among the five promoted and non-promoted catalysts, the rhenium promoted Co/TiO2 catalyst (0.34 wt.% Re) exhibited the highest synthesis gas conversion, and at a space time of 0.5 h-g cat./NL, synthesis gas conversion was 73.4%. In comparison with the results obtained in a fixed bed reactor, the catalysts displayed a higher F–T catalytic activity in the CSTR. 相似文献
8.
《Ceramics International》2016,42(4):5113-5122
TiO2 nanoparticles are currently used as coating for self-cleaning building products. In order to achieve high self-cleaning efficiency for outdoor applications, it is important that titania is present as anatase phase. Moreover, it is desirable that the particle sizes are in nano-range, so that a large enough surface area is available for enhanced catalytic performance. In this work, TiO2 nanoparticles doped with 0–5 mol% Nb2O5 were synthesized by co-precipitation. Nb2O5 postponed the anatase to rutile transformation of TiO2 by about 200 °C, such that after calcination at 700 °C, no rutile was detected for 5 mol% Nb2O5-doped TiO2, while undoped TiO2 presented 90 wt% of the rutile phase. A systematic decreasing on crystallite size and increasing on specific surface area of TiO2 were observed with higher concentration of Nb2O5 dopant. Photocatalytic activity of anatase polymorph was measured by the decomposition rate of methylene blue under ultraviolet and daylight illumination and compared to commercial standard catalyst (P25). The results showed enhanced catalysis under UV and visible light for Nb2O5-doped TiO2 as compared to pure TiO2. In addition, 5 mol% Nb2O5-doped TiO2 presented higher photocatalytic activity than P25 under visible light. The enhanced performance was attributed to surface chemistry change associated with a slight shift in the band gap. 相似文献
9.
Abstract
The liquid phase selective hydrogenation of cinnamaldehyde has been investigated on cobalt (15 wt%) impregnated on alumina, silica and various phases of titania supports. The multiple reduction stages observed in the TPR studies suggest the presence of cobalt aluminate/silicate/titanate species, and DRIFT spectra results seem to corroborate this observation. An optimum level of conversion and selectivity to cinnamyl alcohol was observed at 120 °C and 10 kg/cm2 hydrogen pressure. Co/TiO2 exhibited a greater conversion (47.4%) and selectivity to cinnamyl alcohol (58%) than Co/Al2O3 and Co/SiO2, which may be attributed to the presence of TiO x (x < 2) species on the catalyst surface and to the preferential adsorption of C=O on the catalyst surface. The stability of Co/TiO2 was found to be better than Co/Al2O3 and Co/SiO2. Between the various phases of titania (high surface area, anatase and rutile), the crystalline phases exhibited a better conversion and selectivity to cinnamyl alcohol, while the stability was found to be better for high surface area titania. 相似文献10.
《Journal of the European Ceramic Society》2014,34(3):809-816
In this study, hierarchically porous bicrystalline nitrogen-doped titania (N-doped TiO2) monolithic material was fabricated by a simple two-step approach: (i) preparation of TiO2 porous monolith by a sol–gel process of titanium alkoxide in a mild condition utilizing a chelating agent and mineral salt and (ii) annealing of TiO2 porous monolith obtained under a modest flow of ammonia gas at 700 °C for 2 h. The phase composition, crystal structure, morphology, pore structure, and porous properties of the final product were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury porosimetry, and nitrogen physisorption measurement, respectively. The resultant N-doped TiO2 porous monolith possesses a bicrystalline (anatase and rutile) framework with a well-defined macroporosity. The results from X-ray photoelectron spectroscopy (XPS) confirm the formation of OTiN bonds in the N-doped TiO2 porous monolith. The photocatalytic activity of N-doped TiO2 porous monolith was evaluated by the photodegradation of Rhodamine B over the samples under visible light. Nearly 50% of Rhodamine B in aqueous solution was efficiently degraded by N-doped TiO2 porous monolith with the mixed-phase of anatase and rutile under visible light within 120 min. 相似文献
11.
M. Shamshi Hassan Touseef Amna O-Bong Yang Hyun-Chel Kim Myung-Seob Khil 《Ceramics International》2012,38(7):5925-5930
In the present study rare earth doped (Ln3+–TiO2, Ln = La, Ce and Nd) TiO2 nanofibers were prepared by the sol–gel electrospinning method and characterized by XRD, SEM, EDX, TEM, and UV-DRS. The photocatalytic activity of the samples was evaluated by Rhodamine 6G (R6G) dye degradation under UV light irradiation. XRD analysis showed that all the synthesized pure and doped titania nanofibers contain pure anatase phase at 500 °C but at 700 °C it shows both anatase and rutile phase. XRD result also shows that Ln3+-doped titania probably inhibits the phase transformation. The diameter of nanofibers for all samples ranges from 200 to 700 nm. It was also observed that the presence of rare-earth oxides in the host TiO2 could decrease the band gap and accelerate the separation of photogenerated electron–hole pairs, which eventually led to higher photocatalytic activity. To sum up, our study demonstrates that Ln3+-doped TiO2 samples exhibit higher photocatalytic activity than pure TiO2 whereas Nd3+-doped TiO2 catalyst showed the highest photocatalytic activity among the rare earth doped samples. 相似文献
12.
Rutile/anatase TiO2 heterojunction nanoflowers were prepared via a facile one-step hydrothermal approach using titanium tetrachloride and urea as the raw materials, cetyl trimethyl ammonium bromide (CTAB) as the template. The prepared TiO2 nanoflowers were characterized by XRD, SEM, TEM and BET analyses. The photocatalytic performance of the as-prepared TiO2 samples for methyl blue degradation under simulated solar light was investigated. TiO2 heterojunction nanoflowers with mixed rutile/anatase phase (prepared with 3 mmol CTAB) give the highest photocatalytic activity. In addition, TiO2 nanoflowers show excellent stability after 9 cycles under the same conditions. These results suggested that the mixed phase anatase/rutile TiO2 heterojunction nanoflowers have great potential for the future photodegradation of real dye waste water. 相似文献
13.
《Ceramics International》2017,43(17):15288-15295
Nano-structured TiO2 coatings were produced by suspension high velocity oxy fuel (SHVOF) thermal spraying using water-based suspensions containing 30 wt% of submicron rutile powders (~180 nm). By changing the flame heat powers from 40 kW to 101 kW, TiO2 coatings were obtained with distinctive microstructures, phases and photocatalytic behaviour. Spraying with low power (40 kW) resulted in a more porous microstructure with the presence of un-melted nano-particles and a lower content of the anatase phase; meanwhile, high powers (72/101 kW) resulted in denser coatings and rougher surfaces with distinctive humps but not necessarily with a higher content of anatase. Linear sweep voltammetry (LSV) was used to evaluate the photocatalytic performance. Surprisingly, coatings with the lowest anatase content (~20%) using 40 kW showed the best photocatalytic behaviour with the highest photo-conversion efficiency. It was suggested that this was partially owing to the increased specific surface area of the un-melted nano-particles. More importantly, the structural arrangement of the similarly sized TiO2 nano-crystallites between rutile and antase phases also created catalytic “hot spots” at the rutile−anatase interface and greatly improved the photo-activity. 相似文献
14.
《Ceramics International》2016,42(10):12010-12026
Pd-doped anatase TiO2 nanoparticles were synthesized by a modified sol–gel deposition technique. The synthetic strategy is applicable to other transition and post-transition metals to obtain phase-pure anatase titania nanoparticles. This is important in the sense that anatase titania forms the most hydroxyl radicals (compared to other polymorphs like rutile, brookite, etc.) for better photocatalytic performance. XRD and Raman data confirm the phase-pure anatase formation. Doping of Pd2+ into Ti4+ sites (for substitutional doping) or interstitial sites (for interstitial doping) creates strain within the nanoparticles and is reflected in the XRD peak broadening and Raman peak shifts. This is because of the ionic radii difference between Ti4+(∼68 pm) and Pd2+(∼86 pm). XPS data confirm the formation of high surface titanol groups at the nanoparticle surface and a large number of loosely bound Ti3+–O bonds, both of which considerably enhance the photocatalytic activity of the doped nanoparticles. A comparative study with other metal doping (Ga) shows that TiO2: Pd nanoparticles have more Ti3+–O bonds, which enhance the charge transfer rate and hence improve the photocatalytic activity compared to other transition and post-transition metal-doped titania nanostructures. 相似文献
15.
Jae-Kyung Oh Jin-Kyu Lee Sung Justin Kim Kyung-Won Park 《Journal of Industrial and Engineering Chemistry》2009,15(2):270-274
The TiO2 nanoparticles with anatase (5.7–12.7 nm), rutile (5.4–8.8 nm), mixed (4.4–8.6 nm) phase were individually prepared using the hydrothermal method. The structure and shape of the particles could be controlled by careful alterations of the hydrothermal conditions. Herein, the TiO2 nanoparticles were successfully synthesized by employing Ti-isopropoxide as the titanium source into hydrochloric acid solution at mild conditions. The crystal structures such as anatase, rutile and mixed phase of TiO2 nanoparticles were determined by means of concentration of hydrochloride. Especially, we observed that the rutile TiO2 crystallites were grown into one-dimensional nanostructures, especially, nanowires, with increasing reaction time. The mechanism of the crystallization of the nanoparticles and the growth habit of TiO2-rutile structure were discussed. 相似文献
16.
The nanocrystalline TiO2 materials with average crystallite sizes of 9 and 15 nm were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO2 catalysts. The average size of Au–Pd alloy particles increased slightly from sub-nano (< 1 nm) to 2–3 nm with increasing TiO2 crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H2 1 bar, 30 °C). The exertion of electronic modification of Pd by Au–Pd alloy formation depended on the TiO2 crystallite size in which it was more pronounced for Au/Pd on the larger TiO2 (15 nm) than on the smaller one (9 nm), resulting in higher hydrogenation activity and lower selectivity to 1-heptene on the former catalyst. 相似文献
17.
Vapor-phase selective hydrogenation of maleic anhydride to succinic anhydride over Ni/TiO2 catalysts
《Journal of Industrial and Engineering Chemistry》2014,20(6):4140-4145
A series of supported Ni/TiO2 catalysts were prepared by incipient wetness impregnation method under different calcination temperatures, and the as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic properties of these Ni/TiO2 catalysts were investigated in the vapor phase hydrogenation of maleic anhydride (MA) to succinic anhydride (SA). The results showed that the catalytic activity and the selectivity of the Ni/TiO2 catalysts were strongly affected by the calcination temperature. The catalyst calcined at 1023 K showed a relatively higher SA selectivity of 96% at high MA conversion (96%) under the tested conditions (493 K and 0.2 MPa). The improvement of SA selectivity could be mainly assigned to the presence of suitable metal–support interaction, which can play a role in catalytic property of active nickel species as electron promoter. Besides, the change of surface properties of TiO2 support with the increasing calcination temperatures, e.g., the decrease of Lewis acid sites, might also have some positive role in reducing the side-products like γ-butyrolacetone (GBL). 相似文献
18.
The synergic effect of cation doping and phase composition for the further improvement of the photocatalytic activity of TiO2 under visible light is reported for the first time. Fe3 + and Sn4 + co-doped TiO2 with optimized phase composition were synthesized through a simple soft-chemical solution method. The visible-light-driven photocatalytic activity of Fe3 + and Sn4 + co-doped TiO2 was 5 times of that of Evonik P25 TiO2 using degradation of methylene blue as model reaction. The synthesized photocatalysts were characterized by powder X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, 119Sn Mössbauer spectroscopy, and X-ray absorption fine structure spectroscopy. It is indicated that Sn4 + doping can facilitate the phase transition from anatase to rutile. The different ratios of anatase and rutile can be achieved by tuning the amount of Sn4 + doped into the lattice. Furthermore, the doping of Sn4 + into TiO2 lattice can stabilize the phase composition when Fe3 + is co-doped. In the Fe3 + and Sn4 + co-doped TiO2, Sn4 + is mainly used to tune and stabilize the phase composition of TiO2 and Fe3 + acts as a doping cation to narrow the band gap of TiO2. Both band gap and phase composition of TiO2 can be tuned effectively by the simultaneous introduction of Fe3 + and Sn4 +. The synergic effect of optimized phase composition (anatase/rutile = 25/75) and narrowed band gap should be the two main reasons for the promoted photocatalytic activity of TiO2 under visible light. 相似文献
19.
《Journal of the European Ceramic Society》2017,37(1):43-51
Oxidation of commercial Ti2AlC MAX phase powders at 200–1000 °C has been investigated by XRD, XPS, SEM, STA and TGA coupled with FTIR. These powders are a mixture of Ti2AlC, Ti3AlC2, TiC and Ti1.2Al0.8. Oxidation at 400 °C led to disappearance of carbide phases from Ti 2p, Al 2p and C 1s XPS spectra. At 600 °C, powders changed from dark grey to light grey with a significant volume increase due to crack formation. Powders were severely oxidized by detecting rutile with minor anatase TiO2. At 800 °C, α-Al2O3 was detected while anatase transformed into rutile TiO2. The cracks were healed and disappeared. At 1000 °C, the Ti2AlC powders were fully oxidized into rutile TiO2 and α-Al2O3 with a change of powder color from light grey to yellow. FTIR detected the release of C as CO2 from 200 °C onwards but with additional CO above 800 °C. 相似文献
20.
The effect of two TiO2 polymorphs with different optical activity (rutile and anatase) on UV-stability of four polymeric binders used in water-borne paints is described. The latexes employed in this study are based on acrylic, styrene–acrylic, vinyl acetate and vinyl acetate–butyl acrylate (co)polymers. Thin films obtained from the respective latexes doped with 1% TiO2 were exposed to accelerated weathering by irradiation with UV light (λ ≥ 275 nm) and analysed using electrokinetic potential (ζ-potential), FTIR ATR spectroscopy, SEM microscopy and contact angle. The study shows that while rutile particles dispersed evenly in all the polymer matrices, the anatase remained partly aggregated. Despite markedly different optical properties, both titania polymorphs showed similar and minor effects on accelerated weathering of all the polymeric binders. The trends in surface charge and wettability remained the same as for the undoped films. More pronounced changes were observed in spectroscopic measurements, which probe the films deeper into the bulk. For the styrene-based films a photochemical interaction between TiO2 and the styrene chromophore resulted in quenching the absorption band of the titania's photogenerated surface-trapped holes. 相似文献