Characterization of Nanostructured Titanates Obtained by Alkali Treatment of TiO 2 -Anatases with Distinct Crystal Sizes (original) (raw)
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Crystal Research and Technology, 2012
Controllable preparation of different nanoscale-shaped titania materials was realized by hydrothermal treatment of anatase TiO 2 in an alkaline solution. The gradually changing morphologies and microstructures of titanium dioxide were investigated by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. And a top-down path is illuminated to have an insight to the morphological evolution from nanoparticle to nanosheet by adjusting the concentrations of Na ion in the aqueous solution. The results of photocatalytic experiments indicated that the TiO 2 nanobelts exhibited enhanced photocatalytic performance, due to their lower electron-hole recombination rate confirmed from the photoluminescence spectra. This study suggests that the photocatalysis efficiency of nanocrystals can be significantly improved by the shape-dependent morphological transformation.
Journal of Porous Materials, 2011
The influence of the neutralization process after hydrothermal synthesis on the structure and morphology of titanate nanotubes was investigated by X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy. Well formed nanotubes were obtained during the hydrothermal treatment of anatase in highly alkaline conditions. Synthesis at 150°C led to the formation of layered titanate structure with the general formula Na 2-x H x Ti 2 O 5 Á1.8 H 2 O, where x depends on pH. The tubular morphology is not dependent on the Na ? /H ? ion exchange reaction.
A study on the structure and thermal stability of titanate nanotubes as a function of sodium content
Solid state sciences, 2006
TiTanate NanoTubes (TTNT) were synthesized by hydrothermal treatment of TiO 2 anatase in 10 M NaOH at 120 • C followed by repeated water washing, with and without ion exchanging by HCl 0.1 M. Samples with different contents of remnant sodium in nanotubes were characterized, as synthesized and after heat-treatment, by X-ray diffraction, transmission electron microscopy, thermal analysis and N 2 adsorption. It was demonstrated that TTNT consisted of a trititanate structure with general formula Na x H 2−x Ti 3 O 7 ·nH 2 O, where 0 < x < 2 and n < 1.2, depending on the degree of proton exchange after washing. As-synthesized nanotubes retained interlayer water in its multi-walled structure. The removal of sodium reduced the amount of this intercalated water and increased the specific surface area, while thermal stability was reduced. The mechanism through which TTNT dehydrated and converted into their condensed titanates and/or TiO 2 polymorphs after thermal treatment as a function of the sodium content was discussed and a schematic picture of the thermal transformations was proposed.
CrystEngComm, 2010
Crystal transformation of a titanate nanotube (TNT) into titanium(IV) oxide (TiO 2 ) particles proceeded under various hydrothermal conditions with an inorganic acid. The contents of the crystal structure of TiO 2 , i.e., anatase, rutile and brookite, and the particle shape were greatly influenced by the type and concentration of inorganic acid, hydrothermal duration and temperature. TiO 2 particles with larger contents of brookite structure (more than 0.9 of the relative fraction of the crystal structures) were obtained by 50 h of hydrothermal treatment with 2 mol dm À3 of perchloric acid at a hydrothermal temperature of 200 C.
Tracking the Effect of Sodium Insertion/Extraction in Amorphous and Anatase TiO2 Nanotubes
The Journal of Physical Chemistry C, 2017
We report a mechanistic investigation of the electrochemical behavior of TiO 2 nanotubes (NTs) in amorphous and anatase phases during sodiation/desodiation. The local structure variations of these two host structures upon Na + uptake/release are comparatively examined by X-ray absorption near edge structure (XANES) at the Ti K and L, O K, and Na K edges. Upon Na + insertion/extraction, the surface/near surface XANES analysis at the Ti K edge suggests that the surface/near surface of TiO 2 NTs in both phases is partially reduced to metallic Ti from the unstable sodium titanate formed at the electrolyte/electrode interface, and the sodiation of amorphous NTs is more effective than anatase ones. More importantly, it further reveals that irreversible phase transformations from pure amorphous and anatase TiO 2 to amorphous sodium titanate take place on the NT surface/near surface after the first cycle of discharge/charge. The bulk XANES analysis at the Ti L edge demonstrates that irreversible phase transformation also proceeds in the bulk of these two phase structures, where, however, the formation stable amorphous sodium titanate is observed. All the findings are corroborated by energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and XANES analysis at the O K and Na K edges.
Influence of synthetic conditions in the hydrothermal preparation of TiO2 nanotubes
Proceedings of MOL2NET, International Conference on Multidisciplinary Sciences, 2015
TiO2 nanotubes have been synthesized using a 2-step strategy that involves the hydrothermal preparation of intermediate titanates followed by a subsequent thermal/hydrothermal treatment of these species to produce the oxide. In the first step the influence of parameters such as temperature, pH or reaction time on the composition, structure and morphology of the intermediate species has been studied. Then we have examined how temperature and the presence of surfactants may affect the composition, structure, morphology and particle size of the titanium dioxide obtained in the second thermal/hydrothermal treatment. In particular, we have studied the effects that the presence of CTAB has upon the morphology of the final product. Both intermediate and final species have been studied by means of X-ray diffraction, transmission electron microscopy, IR spectroscopy and thermogravimetric analysis. This way we have been able to identify NaTi3O6(OH).2H2O and (TiO2)x(H2O)y as the intermediate titanate species and rutile and anatase as the final TiO2 polymorphs. Finally, it is worth mentioning the preparation of spindle-or oval-shaped anatase, obtained via hydrothermal synthesis in the presence of CTAB.
Short Time Synthesis of Titania Nanotubes: Effect of Pre-Mixing Prior Hydrothermal
Indonesian Journal of Chemistry
The effect of pre-mixing by mechanical stirring before hydrothermal and hydrothermal time on the crystalline phases and morphology of titania has been studied. It was shown that nanotubes titania can be obtained after 5 h hydrothermal at 150 °C. The XRD patterns and Raman spectra of the produced powders showed the existence of anatase and titanate crystalline phases. At the longest stirring, TiO2 (B) was observed. High textural coefficient for [200] plane of anatase (TC200) confirmed oriented growth of one-dimensional anatase along [200]. All powders resulted at various stirring time were nanotubes, as confirmed by Transmission Electron Microscope (TEM). It was found that the longer the stirring, the higher the surface area of the nanotubes. All powders showed type-IV isotherm for nitrogen gas adsorption/desorption, indicating the existence of mesoporous materials. However, long hydrothermal induced the nanospheres formation, hence reducing the surface area. The band-gap of the resu...
Ceramics International, 2014
Anatase TiO 2 nanotubes were synthesized from a natural leucoxene mineral by the hydrothermal method at 105 1C over a period of 24 h. The prepared samples were calcined at various temperatures from 100 to 1000 1C in air for 2 h. The samples were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), thermogravimetry-differential thermal analysis (TG-DTA), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis to determine the specific surface area. The XRD patterns revealed that the as-synthesized samples were titanate (H 2 Ti 3 O 7) nanotubes. The as-synthesized samples calcined at 400 1C showed anatase TiO 2 with inner and outer diameters of $ 6 nm and 16 nm, respectively, and lengths in the range of 20-100 nm. The BET surface area of the anatase TiO 2 nanotubes was $82.98 m 2 /g. The photocatalytic activity of the anatase TiO 2 nanotubes was observed to be higher than that of commercial anatase TiO 2 nanoparticles (JRC-01).
Characterization of nanocrystalline anatase titania: an in situ HTXRD study
Thermochimica Acta, 2005
Nanocrystalline titania was synthesized by the hydrolysis of titanium iso-propoxide using ultrasonication. The powder XRD patterns of the sample were recorded in static air and vacuum using a Philips X-pert Pro diffractometer equipped with a high-temperature attachment (HTK16) from room temperature (298 K) to 1173 K and were analyzed by the Rietveld refinement technique. The anatase to rutile phase transformation was observed at 1173 K for the data collected in static air. Only 3% of anatase titania transformed to rutile when the experiments were carried out at 1173 K in vacuum. The phase transformation from anatase to rutile is accompanied by a continuous increase in the crystallite size of the anatase phase from 9 nm at room temperature to 28 nm at 873 K and then to 50 nm at 1173 K in air while the process of crystallite growth was suppressed in vacuum. A linear increase in the unit cell parameters 'a' and 'c', and thus, an overall linear increase in the unit cell volume was observed as a function of temperature in static air as well as vacuum. The lattice and volume thermal expansion coefficients (TEC), α a , α c and α V at 873 K are 8.57 × 10 −6 , 8.71 × 10 −6 and 25.91 × 10 −6 K −1 in air and 18.01 × 10 −6 , 14.95 × 10 −6 and 51.13 × 10 −6 K −1 in vacuum, respectively.
Anatase-type TiO 2 nanotube arrays (TiO 2-NTAs) were grown on Ti foil by anodic oxidation in CH 3 COOH/NH 4 F solutions followed by thermal treatment. The surface of TiO 2-NTAs was further decorated by palladium and silver metal clusters through a chemical-reduction method and its photocatalytic activity was tested by investigating the degradation of p-nitrophenol (PNP) in aqueous solution under visible-light irradiation and electrical polarization. The effects of preparation variables both on microstructural properties of samples and photocatalytic activity were examined by using the 3D response surface and the 2D contour plots. The experimental investigations carried out by using XRD, SEM, HRTEM, EDS, XRF, ICP-AES, XPS, DRS, and PL, demonstrated a strong relation between the phase structure and the photocatalytic activity of TiO 2-NTAs. Titania nanotubes grown in acetic acid solution and thermally post-treated have stable anatase crystal structure, to a point that by performing annealing at 800 • C for 3 h, only the 35% of anatase transforms into rutile. Finally, it was shown that the TiO 2-NTAs decorated with Pd(0.72 wt%) and Ag(1.26 wt%) particles show higher photocatalytic activity compared with nanotubes modified with single metal particles. It is believed that the high photoactivity of TiO 2 nanotubes decorated with Pd–Ag heterostructures is due to the prolonged lifetimes of photogenerated electron–hole pairs. The possible mechanism for the enhanced photocatalytic activity is discussed in detail.