Morphological investigations on mesostructured metal oxides (original) (raw)
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Microporous and Mesoporous Materials, 2021
The effect of the introduction of heteroelement (Si, P, Al, Ge, Ga and Zr) by direct synthesis on the thermal stability of mesostructured titania prepared by the soft templating pathway has been investigated. All materials have been surfactant-extracted with EtOH and calcined at different temperatures up to 900°C. Ti 4+ can be partially substituted by most of the investigated heteroelements but they mainly form an oxide amorphous phase surrounding the titania anatase particles. Results obtained by SAXS, X-Ray diffraction, Raman spectroscopy and manometry nitrogen adsorption-desorption show that the crystallization of the amorphous titania into nanosized anatase particles and the transition from anatase to rutile occur at higher temperature with the addition of the heteroelement. Even if the lattice distortion introduced by the partial Ti 4+ substitution can participate to this phenomenon, it is mainly due the «glass» effect induced by the presence of the heteroelement in the TiO2 amorphous phase, which limits the growth of the nanosized anatase crystallites. However, when the crystallites reach a limit size, the collapse of the mesostructure occurs. With increasing the calcination temperature, the anatase titania particles become bigger and bigger, the transition from anatase to rutile takes place and the heteroelement can crystallize or be integrated in a crystalline phase. Among the considered heteroelements and by comparison with the bare mesostructured TiO2, the most beneficial effect is obtained in the presence of Si 4+ and PO4 3for which the mesostructure collapse at higher temperature by about two hundred Celsius degrees. Al 3+ and Ge 4+ enhance the thermal stability by about a hundred Celsius degrees and Ga 3+ or Zr 4+ have no significant effect on the temperature at which the mesostructure collapses.
The Journal of Physical Chemistry C, 2019
A strategy is presented to deposit defined layers of TiO 2 onto the pore surface within ordered mesoporous, crystalline CeO-ZrO 2 thin films using atomic layer deposition (ALD). As structure-directing agent a special diblock copolymer was used, poly(isobutylene)-block-poly(ethylene oxide) (PIB 50-b-PEO 45), resulting in a 3D arrangement of spherical pores with sizes around 13 nm in diameter. Transmission electron microscopic investigations evidence the presence of anatase TiO 2 coatings within the mesopores, as evidenced by high-resolution transmission electron microscopy, while ellipsometric porosimetry studies together with ToF-SIMS depth profiles indicate the deposition inside the mesopores up to 50 ALD cycles. Afterwards, the interconnecting channels between the mesopores are filled completely prohibiting further transport of the gaseous TiO 2 precursor into the ordered structure of mesopores and hence, limit the layer growth on the pores surfaces. Therefore, the size of the mesopores and their connections are decisive when growing transition metal oxide layers on the surface of porous substrates and need to be considered for future depositions using ALD. The hybrid TiO 2 / CeO 2-ZrO 2 materials are studied by several complementary analytical techniques, in order to validate the deposition process and also the applicability of these techniques for such materials in general.
Mesostructured Silica−Titania Mixed Oxide Thin Films
Chemistry of Materials, 2002
The synthesis of porous silica-titania mixed metal oxides is still a challenging task, despite the many industrial applications of the material, for example, in the oxidation of various organic molecules. 1 Not only good accessibility, high dispersion, and homogeneous distribution combined with a high loading of titanium species is required, but also for many applications a deliberate design of porosity is necessary. Moreover, the processing in a controlled morphology is a prerequisite because not only powders but also porous silica-titania thin films are of special interest, for example, for sensor applications. Synthetic procedures that have been applied in the synthesis of mesoporous silica-titania mixed metal oxide powders, such as hydrothermal Si/ Ti coprecipitation or postsynthetic grafting, are not viable for the preparation of thin films. [2][3][4][5][6][7][8] There are several publications on porous but non ordered silica-titania mixed metal oxide films, 9-13 several on mesostructured porous silica films, 14-16 and a few on mesostructured porous titania films. [17][18][19] However, only very recently the preparation of a mesostructured porous silica-titania mixed metal oxide film with a Si:Ti ratio of 50:1 has been reported by Ogawa et al. 20 This study extends the publication by Ogawa et Fröba, M.; Wang, J.; Tanev, P. T.; Wong, J.; Pinnavaia, T. J. J. Am. Chem. Soc. 1996, 118, 9164. (3) Golubko, N. V.; Yanovskaya, Y. I.; Romm, I. P.; Ozerin, A. N.; Maschmeyer, T.; Rey, F.; Sankar, S.; Thomas, J. M. Nature 1995, 378, 159. (4) Walker, J. V.; Morey, M.; Carlsson, H.; Davidson, A.; Stucky, G. D.; Butler, A. Brusatin, G.; Guglielmi, M.; Martucci, A.; Battaglin, G.; Pelli S.; Righini, G. J. Non-Cryst. Solids 1997, 220, 202. (13) Seco, A. M.; Goncalves, M. C.; Almeida, R. M. Mater. Sci. Eng. B 2000, B76, 193. (14) Lu, Y.; Ganguli, R.; Drewien, C. A.; Anderson, M. T.; Brinker, C. J.; Gong, W.; Guo, Y.; Soyez, H.; Dunn, B.; Huang, M. H.; Zink, J. I. Nature 1997, 389, 364. (15) Zhao, D.; Yang, P.; Melosh, N.; Feng, J.; Chmelka, B. F.; Stucky, G. D. Adv. Mater. 1998, 10, 1380. (16) Grosso, D.; Balkenende, A. R.; Albouy, P. A.; Lavergne, M.; Babonneau, F. J. Mater. Chem. 2000, 10, 2085. (17) Kavan, L.; Rathuosky, J.; Grä tzel, M.; Shklover, V.; Zukal, A.
Effect of synthesis methods for mesoporous zirconia on its structural and textural properties
Journal of Materials Science, 2013
Zirconia was synthesized by sol-gel and posthydrothermal treatment under autogenous pressure in order to study the effect of synthesis methods on its structural and textural properties. On the basis of thermal analysis, in situ X-ray diffraction and Raman spectroscopy techniques, the synthesis processes exhibit similar thermal behavior and zirconia phase transformation. The effect of in situ calcination temperature on the crystallization behavior, crystal phase transition, and crystallite size analysis was studied. The results obtained revealed that amorphous zirconia transformed into tetragonal phase above 400°C and thermally stabilized up to 700°C. A biphasic mixture of tetragonal and monoclinic zirconia was formed at 750°C. Activation energy of sintering due to grain growth mechanism predicted that the zirconia phase transformation is due to the increase in the crystallite size of tetragonal phase above its critical size. The posthydrothermal treatment resulted in the formation of high surface area mesoporous zirconia (213 m 2 g -1 ). Upon increasing the calcination temperature, a pronounced decrease in the specific surface area of zirconia samples due to sintering process and phase transformation.
Amorphous mesostructured zirconia with high (hydro)thermal stability
RSC Advances, 2020
Here, combining the evaporation-induced self-assembly (EISA) method and the liquid crystal templating pathway, mesostructured amorphous zirconium oxides have been prepared by a soft templating method without addition of any heteroelement to stabilize the mesopore framework. The recovered materials have been characterized by SAXS measurements, nitrogen adsorption-desorption analysis and X-ray diffraction (XRD). The obtained mesostructured zirconia exhibits a high thermal stability. An in situ XRD study performed as a function of temperature shows that the amorphous ZrO 2 , obtained after removal of the pore templating agent (pluronic P123), begins to crystallize in air from 420 C. Amorphous mesostructured ZrO 2 also presents a high hydrothermal stability; these materials are not degraded after 72 hours in boiling water.
Phase formation in mixed TiO2-ZrO2 oxides prepared by sol-gel method
Journal of Structural Chemistry, 2011
Pure titania, zirconia, and mixed oxides (3-37 mol.% of ZrO 2 ) are prepared using the sol-gel method and calcined at different temperatures. The calcined samples are characterized by Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption porosimetry. Measurements reveal a thermal stability of the titania anatase phase that slightly increases in the presence of 3-13 mol.% of zirconia. Practically, the titania anatase-rutile phase transformation is hindered during the temperature increase above 700°C. The mixed oxide with 37 mol.% of ZrO 2 treated at 550°C shows a new single amorphous phase with a surface area of the nanoparticles double with respect to the other crystalline samples and the formed srilankite structure (at 700°C). The anatase phase is not observed in the sample containing 37 mol.% of ZrO 2 . The treatment at 700°C causes the formation of the srilankite (Ti 0.63 Zr 0.37 O x ) phase.
Synthesis and characterization of amorphous TiO2 with wormhole-like framework mesostructure
Journal of Non-Crystalline Solids, 2003
Using neutral amine surfactant (dodecylamine) as an organic template and neutral inorganic material (tetrabutyl titanate) as a precursor, amorphous TiO 2 with wormhole-like framework mesostructure was synthesized with the variation of surfactant-to-Ti alkoxide ratios. Powder X-ray diffraction (XRD), thermogravimetric analysis, Fourier transformed infrared spectra, transmission electron microscopy (TEM), nitrogen adsorption-desorption, and X-ray photoelectron spectroscopy (XPS) have been used to characterize the TiO 2 mesostructure. The interaction between surfactant and titanium dioxide was displayed by XPS. The samples exhibit a wormhole-like framework from XRD patterns and TEM images, and high surface area (221 m 2 /g) for the sample calcined at 450°C for 2 h. The formation of the titanium oxide mesostructure is proposed to be due to the presence of the interactions between surfactant head group and inorganic precursors prior to hydrolysis, and the condensation under condition favorable for liquid crystal formation.
EPR study of nitrogen-doped mesoporous TiO2 powders
Journal of Physics and Chemistry of Solids, 2010
Mesoporous titanium dioxide powders were synthesized by the sol-gel route either directly or using the P123 templating agent and nitrogen doping from thiourea. X-ray diffraction studies show that doping and structuring give rise to rutile growth at a relatively low temperature of 400 1C compared to the transition point of pure TiO 2 , which is close to 900 1C. Systematic EPR experiments were performed in order to monitor the involved paramagnetic centres with respect to calcination treatments and also to probe the nitrogen doping efficiency in the host media. Several paramagnetic species were found in these mesostructured samples mainly with oxygen radicals for calcinations at 400 1C, while nitrogen centres appear for calcination temperature as high as 500 1C. The effect of material microstructure on the effective incorporation of nitrogen in the TiO 2 lattice is also examined and compared in representative samples.
Science of Sintering, 2016
In the current paper we present a study of the sinterability of two zirconia (ZrO2) nanopowders with different content of yttrium oxide (Y2O3) 3 and 8 % tetragonal and cubic zirconia, respectively. After sintering between 900-1500?C, the samples were characterized in terms of their density and porosity using Archimedes technique. Their grain size was evaluated using scanning electron microscope (SEM). Vickers hardness and fracture toughness (KIC) were measured by the indentation method. The results showed that pores are almost eliminated at sintering temperatures higher than 1400?C and grain size is larger due to the agglomerates formed as a result of grain growth. Vickers hardness evaluated at 1400?C sintering temperature is greater than that obtained at 1500?C due to the grain growth produced at this temperature. In addition, we show a correlation between Vickers hardness and the porosity, obtained by evaluating empirical and theoretical models.
CrystEngComm, 2010
In this paper, the detailed study of the microstructural evolution under annealing of zirconium-based inorganic-organic hybrid materials to give silica-zirconia mixed oxides was addressed by X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The silica materials embedding different amounts of ZrO 2 nanoparticles were prepared by copolymerisation of the organically modified oxozirconium cluster (Zr 4 O 2 (OMc) 12 (OMc ¼ methacrylate)) with methacryloxypropyltrimethoxysilane (MAPTMS). By the free radical copolymerisation of the oxoclusters bearing 12 methacrylate groups with the methacrylatefunctionalised siloxanes, a stable anchoring of the clusters to the silica network was achieved. The thermal treatment of these hybrids at high ($500 C) temperatures yielded the SiO 2-ZrO 2 mixed oxides. The microstructural evolution upon heating was studied at increasing temperatures, namely 500, 600, 700, 900, 1000 and 1300 C. Furthermore, different samples characterised by different Zr : Si atomic ratios and annealed at 1000 C were comparatively analysed to study the effect of the composition on the evolution of the hybrids to give the mixed oxides. In a third experiment, samples characterised by the same composition were annealed at the same temperature by using either a conventional muffle or a microwave oven in order to evidence whether the different processing could also affect the microstructural features of the final oxide materials. Through XRD and XAFS it was demonstrated that at temperatures above 800 C, crystallisation of tetragonal zirconia occurs in the samples of high zirconium concentration treated in muffle, whereas amorphous oxide materials form upon annealing in microwave oven. The presence of zirconia nanoclusters having an average size of 5-10 nm was evidenced by TEM.