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1.
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   

2.
《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   

3.
The photocatalytic characteristics of the TiO2/ZnO nanofibers synthesized by electrospinning followed by calcinating at different temperatures to alter the anatase-to-rutile ratio are investigated. The results demonstrate that the photocatalytic activity of TiO2/ZnO nanofibers is enhanced by optimizing the anatase/rutile ratio among the trade-off effects of the band-gap energy, the electron/hole recombination rate, and the surface area. When calcined at 650 °C, the TiO2/ZnO nanofibers with optimal anatase/rutile ratio (48:52) balancing these trade-off effects have the highest photocatalytic efficiency both in the degradation of RhB in liquid and conversion of NO gas.  相似文献   

4.
《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   

5.
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   

6.
Heterogeneous photocatalysis can be exploited for the decomposition of micro-organisms which have developed on the surfaces of building materials. In this work, the efficiency of titanium dioxide coatings on fired clay products is examined. The sol–gel method is used to synthesize a fine TiO2 powder with a specific surface area of 180 m2 g?1. Thermal treatment of the chemical gel at 340 °C leads to crystallisation in the anatase phase and with further temperature increase, crystallite growth. For thermal treatments in the range 580–800 °C, there is a progressive transition from anatase to rutile. However, despite a decrease in specific surface area of the powder attributed to aggregation/agglomeration, the coherent domain size deduced from X-ray diffraction measurements remains almost constant at 23 nm. Once the transition is completed, increase of thermal treatment temperature above 800 °C leads to further crystallite growth in the rutile phase. The thermally treated titania powders were then sprayed onto fired clay substrates and the photocatalytic activity was assessed by the aptitude of the coating to degrade methylene blue when exposed to ultraviolet light. These tests revealed that the crystallite size is the important controlling factor for photocatalytic activity rather than the powder specific surface area or the anatase/rutile polymorph ratio.  相似文献   

7.
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   

8.
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   

9.
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   

10.
《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   

11.
TiO2 nanopowders have been synthesized via Ar/O2 thermal plasma oxidation of titanium butoxide (TBO) solutions stabilized with diethanolamine (DEA). Experiments were conducted by varying the O2 input in the plasma sheath (10–90 L/min) and the DEA/TBO molar ratio (R), while keeping the plasma generation power at 25 kW and the reactor pressure at 500 Torr. The resultant powders are mixtures of the anatase and rutile polymorphs in the studied range, whose anatase content and crystallite size exhibit weak dependence on the O2 input at a fixed R. Increasing R decreases the anatase content, signifying the role of CO gas, generated via oxidation of the organic precursor, on the phase structure. FE-SEM and TEM analysis show that the resultant powders contain majority of nanoparticles (<50 nm) and some large spheres (>100 nm), whose size and/or number tends to decrease at a higher O2 input, leading to gradually increased specific surface area. Raman spectroscopy reveals no significant differences in the crystallite size and oxygen-vacancy concentration of the nanocrystals by varying the O2 input.  相似文献   

12.
One-step route based on the thermal decomposition of the double salt (NH4)2TiO(SO4)2 (ammonium titanyl sulfate, ATS) is presented to prepare size-defined aggregates of Ti-based nanoparticles with structural hierarchy. The component of Ti-based networks is tunable from anatase/rutile TiO2, nitrogen-doped TiO2, TiNxO1−x, to TiN depending on the atmospheres and reaction temperatures. The as-prepared Ti-based powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS), and BET surface area techniques. It is found that TiO2 in the predominant rutile phase could be achieved by the thermal decomposition of ATS in flowing Ar gas. Furthermore, the nitrogen-doped TiO2, TiNxO1−x solid solution and TiN were prepared by the thermal decomposition of ATS in flowing NH3 gas by varying the temperatures. The network of anatase TiO2 with a specific surface area up to 64 m2 g−1 contains large mesopores with a mean diameter of ca. 15 nm, and the large pore size allows more accessible surface and interface available for the photocatalytic degradation of large-molecule dyes. The photocatalytic activity of the prepared TiO2 and nitrogen-doped TiO2 under UV–vis light irradiation is compared to Degussa P-25 using the photocatalytic degradation of methylene blue (MB) as a model reaction. The anatase TiO2 nanoparticles derived from one-step route show the highly efficient photocatalytic activity for the degradation of MB in comparison with Degussa P-25. The presence of large-sized rutile in the TiO2 powder decreases the specific surface area and thus the powder exhibits a lower photocatalytic activity.  相似文献   

13.
《Catalysis communications》2005,6(11):705-710
This present study revealed a dependence of rutile:anatase ratios in titania on the characteristics and catalytic properties of Co/TiO2 catalysts during CO hydrogenation. In this study, Co/TiO2 catalysts were prepared using various titania supports consisting of various rutile:anatase ratios of titania. In order to identify the characteristics, all catalyst materials were characterized using XRD, SEM/EDX, TPR, and hydrogen chemisorption. CO hydrogenation (H2/CO = 10/1) was also performed to determine the overall activity and selectivity. It was found that both activity and selectivity were altered by changing the rutile:anatase ratios in the titania support.  相似文献   

14.
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   

15.
《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   

16.
The preparation of rubber sheet impregnated with titanium dioxide particles is presented. This method is simple and low cost based on the use of commercial TiO2 powder directly mixing with rubber latex (60% HA) and distilled water. The morphology and roughness of the sheet surface increased with increasing amount of distilled water. Sheet impregnated with anatase (Imp-An) showed uniform, small grains with dense structure and well surface coverage more than one with P25 (Imp-P25). Their photocatalytic activities were evaluated using methylene blue (MB) as a model organic dye compound. These impregnated sheets could degrade MB solution under UV-light irradiation. Comparing with the commercial TiO2 samples in powder form (anatase from Carlo Erba and Degussa P25) the efficiencies of photocatalytic degradation of MB fall in the decreasing order as: P25 (powder) > anatase (Carlo Erba) (powder) > Imp-An sheet > Imp-P25 sheet. However, the impregnated sheet has an advantage over the loose powder that the catalyst sheet can be recovered after used and can be reused.  相似文献   

17.
Single-walled carbon nanotubes (SWCNTs)/TiO2 hybrid gas sensors operated at a room temperature were fabricated. SWCNTs were stabilized on a Si substrate with interdigitated Pt-electrodes to prepare a gas sensor. Sensing properties of the gas sensor were measured in various concentrations of NO gas. Resistance of the prepared SWCNT based gas sensor decreased with increase of NO gas concentration due to electron transfer from p-type SWCNTs to NO molecules. The SWCNT gas sensor showed high sensitivity and rapid response to the test gas. The hybrid gas sensor using SWCNTs doped with anatase TiO2 nano-particles was developed, which could work at room temperature under UV-LED (λ = 377 nm) irradiation. It showed rapid recovery to the initial state and higher sensitivity than the SWCNT gas sensor due to TiO2 photocatalytic effect.  相似文献   

18.
Carbon coated titanium dioxide (TiO2) nano powder has been synthesized by combustion of TiCl4 precursor in a laminar diffusion flame using inexpensive liquid petroleum gas (LPG) as a fuel, air as an oxidant, nitrogen gas as a carrier, and characterized with regard to phase(s), surface area, carbon content, morphology and optical absorption. The product is shown to contain both the anatase and rutile phases and exhibits (i) decrease in rutile content, (ii) increase in BET specific surface area, and (iii) increase in the amount of carbon (soot) present with increase in fuel flow rate. Further, the maximum attainable temperature depends on carbon content and determines the phase content and morphology of nano powder, e.g. spherical particles result and display reduced agglomeration when carbon content is more. The rutile phase essentially emerges by transformation of the anatase phase, formed initially with lattice parameters somewhat smaller than the bulk due to oxygen deficiency. On the other hand, use of oxygen (instead of air) leads to formation of spherical particles (average diameter ~104 nm) of a pure anatase phase (as transformation to rutile phase is totally suppressed) with lattice parameters, a=3.776(5) Å, c=9.507(5) Å, close to bulk.  相似文献   

19.
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   

20.
The aim of this work is to study the dielectric of two porcelains containing TiO2 in the form of anatase and rutile. TiO2 was added in compositions by means of raw kaolin with a relative high quantity of anatase, or the addition of anatase powder (10 wt%) in the initial mixture. An alternative porcelain containing kaolin–anatase mixture was obtained by a preliminary firing at 1300 °C. Beside kaolin, compositions also contain quartz and alkaline feldspar.The microstructural observations show various crystalline phases and micropores, which also have an effective role in affecting the properties. The dielectric characterization of fired porcelain, in the frequency range of 105–109 Hz, shows that permittivity value can be increased from 7.19 to 8.41, depending in TiO2 crystal type, morphology and content. Permittivity depends also on mullite, quartz and cristobalite, quantities, but the role of TiO2 phase is predominant. The macroscopic permittivity of porcelains can be calculated using a mixing rule, which fit accurately experimental results.  相似文献   

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