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1.
Ba 0.5Sr 0.5TiO 3–MgO–Mg 2TiO 4 composite ceramics were prepared by a solid-state reaction method, and the dielectric tunable properties were investigated. It is observed that the addition of MgO–Mg 2TiO 4 into the Ba 0.5Sr 0.5TiO 3 forms ferroelectric (Ba 0.5Sr 0.5TiO 3)–dielectric (Mg 2TiO 4–MgO) composites. Increasing Mg 2TiO 4 content causes an increase of Curie temperature T c towards room temperature and a decrease of dielectric constant peak ε max. The dielectric constant and loss tangent of Ba 0.5Sr 0.5TiO 3–MgO–Mg 2TiO 4 composites have been reduced and the overall tunability is maintained at a sufficiently high level. With the increase of Mg 2TiO 4 content and the decrease of MgO content, the dielectric constant and tunability of Ba 0.5Sr 0.5TiO 3–MgO–Mg 2TiO 4 composite ceramics increase and the Q × f values decrease. Ba 0.5Sr 0.5TiO 3–Mg 2TiO 4–MgO composites have dielectric constant of 123.0–156.5 and tunability of 14.4–28.5 % at 10 kHz under 3.9 kV/mm, indicating that they are promising candidate materials for tunable microwave applications requiring a low dielectric constant. 相似文献
2.
Brookite TiO 2 nanoparticles were prepared by ambient condition sol process of hydrolyzing TiCl 4 in an acidic alcohol under refluxing. The spherical morphology of the particles was found from the SEM and TEM micrographs. The crystalline nature and the brookite phase were confirmed from the X-ray diffractometry. The mean particle size was found to be in the range of 30 nm. Agglomerate formation was observed and could be predicted from the heat released during the hydrolysis of TiCl 4. This work presents a simple/direct method for the preparation of high purity brookite TiO 2 nanoparticles. 相似文献
3.
Pure TiO2 and Cu–doped TiO2 containing different amounts of copper ions with anatase/rutile/brookite triphasic structure were successfully synthesized through a simple hydrothermal method. The obtained samples were characterized by X–ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), X–ray photoelectron spectroscopy (XPS), UV?vis diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL) and Brunauer–Emmett–Teller surface area analyze (BET). Both pure and Cu–doped TiO2 show relatively high photocatalytic activity owing to their considerable surface areas. Moreover, the three–phase coexisting structure and the conversion between Cu2+ and Cu+ ions facilitate the separation of photogenerated electrons and holes, which is favorable for photocatalytic performance. 1%Cu–TiO2 exhibits the highest photocatalytic activity and the degradation degree of rhodamine B (RhB) reaches 93.5% after 30 min, which is higher than that of monophasic/biphasic 1%Cu–TiO2. ·O2? radical is the main active species, and h+ and ·OH species are subsidiary in the degradation process. 相似文献
4.
A low-temperature hydrothermal method was used to synthesize ultrafine TiO 2 nanowires with the diameter of 4–6 nm. The ultrafine nanowires tend to gather together, forming nanowire bundles. The length of the nanowires is about 1–4 μm, depending on the growth time. Multilayered TiO 2 nanowires with the height more than 10 μm have been synthesized by a multi-step growth process. Furthermore, the dye-sensitized solar cells (DSSCs) are assembled using single-layered, double-layered and triple-layered TiO 2 nanowires as photoanode respectively. The DSSC based on triple-layered TiO 2 nanowires shows the highest power conversion efficiency of 3.96 % among the prepared samples. The relatively high energy conversion efficiency is attributed to the large surface area, which enhances the absorption of dye molecules. 相似文献
5.
An oriented titania (brookite) film containing neither anatase nor rutile was synthesized by a new modified sol–gel method. The precursor was TiCl 4 with cellulose and oxalic acid as complexing agent. The XRD results show oriented pure brookite titania thin film. The SEM micrograph shows square particles on the crack free continuous film. A diffusion of sodium from the substrate was detected by XPS. It was found that the nature of complexation, the concentration of the precursors, the polymer additive, solution media (low pH, solvent-EG) and the substrate were significant of the oriented brookite TiO 2 films obtained. 相似文献
6.
BiVO 4/TiO 2 nanocomposites were fabricated by a facile wet-chemical process, followed by the synthesis of TiO 2 hierarchical spheres via hydrothermal method. The BiVO 4/TiO 2 nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The results showed that prepared TiO 2 presented hierarchical spherical morphology self-assembled by nanoparticles and an anatase–brookite mixed crystal phase. The introduction of monoclinic BiVO 4 components retained the hierarchical structures and expanded the light response to around 510 nm. Type II BiVO 4/TiO 2 heterostructured nanocomposites exhibited improved photocatalytic degradation towards methylene blue under visible-light irradiation, especially for the composite photocatalysts with atomic Ti/Bi?=?10, which showed double degradation rate than that of pure BiVO 4. The enhanced photocatalytic mechanism of the heterostructured BiVO 4/TiO 2 nanocomposites was discussed as well. 相似文献
7.
Hydrophobic titanium dioxide (TiO 2) was successfully grown on a wood surface using a hydrothermal method. Energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and water contact angle (WCA) were employed to characterize the features of grown TiO 2 and its hydrophobicity. EDS, XRD, and FTIR proved that anatase TiO 2 chemically bonded to the wood surface through the combination of hydrogen groups during the hydrothermal process. The values of WCAs manifested that the hydrophobicity of the treated wood was mainly dependent on specific reaction conditions, especially on reaction pH value and hydrothermal temperature. The highest WCA reached 154° when the hydrothermal temperature was 130 °C. The treated wood thus possessed a superhydrophobic surface. 相似文献
8.
TiO 2 nanoparticles have been prepared by hydrothermal method at different temperatures. The X-ray diffraction results showed that anatase TiO 2 nanoparticles with grain size in the range of 7–27 nm has been obtained. HRTEM images show the formation of TiO 2 nanoparticles with grain size ranging from 7 to 26 nm. The Raman spectra exhibited peaks corresponding to the anatase phase of TiO 2. Optical absorption studies reveal that the absorption edge shifts towards longer wavelength (red shift) with increasing hydrothermal temperature. 相似文献
9.
Nanocrystalline titanium dioxide (TiO 2) powders with different crystal phase composition were obtained by controlled hydrolysis and post-thermal treatments. The physicochemical properties of the powders were investigated by XRD, TEM/EDS, N 2 physic adsorption and DRS. The results obtained show that the particle size and crystalline structure are parameters strongly dependent on the calcination conditions, mainly temperature and heating rate. The influence of the TiO 2 phase composition on its photocatalytic activity, concerning the methylene blue photodegradation was studied. It was found that higher TiO 2 photocatalytic activity is related with the co-existence of the three TiO 2 polymorphs: anatase, brookite and rutile. 相似文献
10.
Titanium dioxide (TiO 2)-multiwalled carbon nanotube (MWCNT) nanocomposites with a novel morphology of rice-grains are prepared by electrospinning method. Anatase-MWCNT composites (with a negligibly small percentage of rutile and brookite) are obtained by high temperature sintering of the as-spun (polymer-TiO 2-MWCNT) composite fibers. The nanocomposites are characterized using spectroscopy and microscopy. The results show that the functionalized MWCNTs are integrated into the TiO 2 rice grain structures. The enhanced photocatalysis of the nanocomposites in comparison to TiO 2 rice grains and commercially available P-25 is demonstrated in photodegradation of Alizarin Red dye. 相似文献
11.
The nanocrystalline S doped titanium dioxide films were successfully prepared by the improved sol-gel process. Here TiO(C 4H 9O) 4 and CS(NH 2) 2 were used as precursors of titania and sulfur, respectively. The as-prepared specimens were characterized using x-ray diffraction (XRD), x-ray energy dispersive spectroscopy (EDS), high-resolution field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) surface area, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of organic dyes in aqueous solution. The results of XRD, FE-SEM, and BET analyses indicated that the TiO 2 films were composed of nanoparticles. S doping could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO 2 film, S doped TiO 2 film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the modified films is responsible for improving the photocatalytic activity. 相似文献
12.
TiO 2 hollow spheres with controllable size were successfully synthesized through a hydrothermal silica etching method; SiO 2 cores were easily removed without the use of a toxic reagent. The parameters for the synthesis of SiO 2 cores and TiO 2 hollow spheres, including stirring time, ammonia concentration, tetrabutyl titanate content, hydrothermal time, and reflux time, were systematically investigated. SiO 2 cores and TiO 2 hollow structure were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectra (EDX), X-ray photoelectron spectroscopy (XPS), and N 2 adsorption-desorption isotherms. The results revealed that the mean diameter of SiO 2 was ∼280 nm when the concentration of ammonia was 4.8 M and the stirring time was 0.5 h. For hollow TiO 2, when the operation process was optimized (ammonia volume 0.35 mL, TBOT addition 1.5 mL, hydrothermal time 3 h, and reflux time 3 h), the average size and the shell thickness were 270 and 100 nm, respectively. The process exhibited a high drug loading capacity (33.12 ± 0.01%) and encapsulation rate (99.03 ± 0.24%) due to its high specific surface area of 121.62 m 2·g −1. In addition, TiO 2 hollow spheres displayed pH-responsive sustained-controlled drug release behavior in vitro which released 80% of doxorubicin at 5.0 pH within 120 h, its release kinetic showed that it fits well with Zero-order kinetic equation, demonstrating that DOX·HCl/hollow TiO 2 maintains constant release rate, and the investigation of blood compatibility showed that the hemolysis rate of hollow TiO 2 did not exceed 3% in the concentration range of 100 and 4000 μg/mL, further confirming that prepared hollow TiO 2 is a relatively safe medical inorganic material. 相似文献
13.
Anatase TiO 2 nanocrystal colloids with high dispersion and photocatalytic activity were rapidly synthesized from peroxo-titanium-acid precursor by microwave-assisted hydrothermal method within 30?min at low temperature (120–180?°C). The transmission electron microscopy results indicate that the as-prepared TiO 2 have a narrow particle size distribution (25–29?nm) and high dispersion. The crystal structure of all these products are pure anatase phase (XRD, Raman), and they show good crystallinity and large surface area (N 2 adsorption–desorption measurements BET). The results of the UV–Visible absorbance and Fourier transform infrared spectra indicate that the surface peroxo group Ti(O 2) still remains in TiO 2 nanoparticles prepared by microwave-assisted hydrothermal method at 120?°C, and this surface peroxo group can be decomposed effectively by drying at 140?°C. The photocatalytic activity of the as-prepared TiO 2 were evaluated by the degradation of reactive brilliant red X-3B, it is found that the as-prepared TiO 2 exhibited good photocatalytic performance. Moreover, the existence of surface peroxo group greatly suppressed the photocatalytic activity of the TiO 2 nanoparticles. 相似文献
14.
Anatase TiO 2 nanospheres having a high degradation efficiency are prepared through hydrothermal method employing titanium (IV) isopropoxide as precursor. The effects of hydrothermal temperature on structural, morphological and optical properties of TiO 2 nanospheres are investigated. X-ray diffraction (XRD) results show that, the TiO 2 nanospheres crystallise in the anatase phase, the tetragonal crystal system. The crystallite size increases with the increase in hydrothermal temperature and the values are in the range of 10–19 nm. On the other hand, the spherical particles evenly distributed on the surface are observed in the scanning electron microscope (SEM) images. The band gap of the nanospheres is determined from the reflectance spectra using Kubelka–Munk function. The band gap energy decreases from 3.189 (2) to 3.023 (5) eV with the increase in hydrothermal temperature. The decrease in band gap values well agree with the XRD results of higher crystallite size and enhanced crystallinity. The removal of Congo red dye under dark condition varies with the hydrothermal temperature and it is maximum for the higher crystallinity anatase TiO 2 synthesised at 160 °C having a lower band gap of 3.023 (5) eV. Maximum efficiency of 96.9% and rate constant value of 0.01413 g mg ?1 min ?1 are observed for the sample hydrothermally synthesised at 160 °C. 相似文献
15.
TiO 2 nanotube arrays were synthesized by anodization of Ti metal sheets followed by thermal annealing at elevated temperatures
from 400 to 600 °C. Scanning electron microscopic measurements showed that dense arrays of nanotubes were produced with the
inner diameter about 100 nm, wall thickness 35 nm, and length about 10 μm. X-ray diffraction measurements showed that the
as-prepared nanotubes were largely amorphous, whereas thermal annealing led to the formation of well-defined anatase crystalline
phase. More interestingly, at 470 °C, the brookite crystalline phase also started to emerge, which became better defined at
500 °C and disappeared eventually at higher temperatures, a phenomenon that has not been observed previously in TiO 2 nanotube arrays prepared by anodization. The impacts of the TiO 2 nanocrystalline structure on the photocatalytic activity were then examined by using the reduction of methylene blue in water
as an illustrating example. Upon exposure to UV lights, the visible absorption profiles of methylene blue exhibited apparent
diminishment. Based on these spectrophotometric measurements, the corresponding pseudo-first-order rate constant was estimated,
and the sample thermally annealed at 500 °C was found to exhibit the highest activity. The strong correlation between the
TiO 2 crystalline characteristics and photocatalytic performance suggests that the synergistic coupling of the anatase and brookite
crystalline domains led to effective charge separation upon photoirradiation and hence improved photocatalytic activity, most
probably as a consequence of the vectorial displacement at the nanoscale junctions between these crystalline grains that impeded
the dynamics of electron–hole recombination. These results demonstrate the significance of nanoscale engineering in the manipulation
of oxide photocatalytic performance. 相似文献
16.
TiO 2 nanofibres were synthesized by the hydrothermal method. The result shows that the growth of TiO 2 nanofibres is sensitive to the concentration of NaOH and the heating temperature. 相似文献
17.
Titanium dioxide with different ratios of anatase to brookite has been prepared by a facile hydrothermal method in the presence of tartaric acid. The resulting samples were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectra, and Brunauer–Emmett–Teller analysis. The contents of anatase and brookite in the TiO 2 particles have been successfully controlled by simply adjusting molar ratio of tartaric acid to Ti in reaction system. The degradation of Rhodamine B in aqueous solutions reveals that the catalyst containing 78.7?% anatase and 21.3?% brookite has the highest photocatalytic activity. A proposed mechanism is discussed to interpret the evolution of the phases based on the effect of different C 4H 6O 6/Ti molar ratios. 相似文献
18.
Titania (TiO 2) nanoparticles (NPs) with different morphologies (spherical, rod-shaped, and mixed) were prepared by hydrothermal treatment of different nitric acid (HNO 3)/titanium (IV) isopropoxide (TTIP) molar ratios (0.25, 0.5, 1.0, and 1.7) at different hydrothermal temperatures (90, 150, 200, and 250 °C), hydrothermal times (6, 12, and 24 h), and calcination temperatures (500, 625, and 750 °C). The crystalline structure, morphology, and surface texture of the obtained TiO 2 NPs were characterized by X-ray diffraction, nitrogen adsorption–desorption isotherm, field emission-scanning electron microscopy, and high resolution -transmission electron microscopy analyses. Under a larger HNO 3: TTIP molar ratio, higher hydrothermal temperature, and higher hydrothermal time, the spherical mixed anatase–rutile phase TiO 2 NPs were converted to a nanorod (NR)-shaped rutile phase (TiO 2-R). The TiO 2-R NRs gave the highest methanol conversion level (65%) and hydrogen yield (45%) in the oxidative steam reforming of methanol at 400 °C. 相似文献
19.
AbstractThe effect of the use of the triblock copolymer Pluronic P123[(PEO) 20(PPO) 70(PEO) 20, Aldrich] and the non-ionic polyoxyethylene-lauryl ether Brij 35 as surfactants on the textural, structural and electrical properties of nanosized TiO 2 is analyzed in this work. The as-obtained samples were thermally treated at 400 °C to eliminate the surfactant, promote dehydroxylation and crystallize the sample. The TiO 2 samples were characterized by thermal analysis, N 2 physisorption, x-ray diffraction analysis, micro-Raman spectroscopy and scanning electron microscopy. To evaluate the TiO 2 electrical features, I–V data were obtained. The x-ray diffraction results show that in the chemical synthesis using surfactants, the crystallite size is smaller than that of the commercial sample. The Raman spectroscopy results clearly indicate that, when P123 is used, the anatase phase of TiO 2 is obtained, whereas when Brij 35 is used a mixture of the anatase and brookite phases is obtained. The specific surface area and crystallite size of the TiO 2 prepared as indicated above are higher and smaller, respectively, than the corresponding properties found in commercial TiO 2. The I–V plot showed a nonlinear behavior of the nanosized TiO 2. The samples obtained with P123 showed the best electrical conductivity. 相似文献
20.
A TiO 2 film was prepared on Pt/Ti/SiO 2/Si substrate by a laser chemical vapor deposition method. The rutile TiO 2 film with pyramidal grains and columnar cross-section was obtained at a high deposition rate ( R dep = 11.4 μm h ?1). At 300 K and 1 MHz, the dielectric constant ( ε r) and loss (tan δ) of the TiO 2 film were about 73.0 and 0.0069, respectively. The electrical properties of TiO 2 film were investigated by ac impedance spectroscopy over ranges of temperature (300–873 K) and frequency (10 2–10 7 Hz). The Cole–Cole plots between real and imaginary parts of the impedance ( Z′ and Z′′) in the above frequency and temperature range suggested the presence of two relaxation regimes that were attributed to grain and grain boundary responses. The ionic conduction in the rutile TiO 2 film was dominated by the oxygen vacancies. 相似文献
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