Design guidelines for titania-silica-alumina ceramics with tuned anatase to rutile transformation

Feltrin, Jucilene; Noni, Agenor De; Hotza, Dachamir; Frade, J.R.

doi:10.1016/j.ceramint.2018.12.026

Cited by 6 publications

(5 citation statements)

References 53 publications

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“…Ex situ measurements performed after heat treatment at 1200 °C have shown, however, that these and other films transform indeed into rutile ( Figure S2 ), the most stable phase thermodynamically [ 31 , 57 ] being in agreement with earlier studies [ 32 , 35 ]. This temperature is, nonetheless, a very high temperature for phase transformation when compared to other studies, which often show transformation temperatures in the range of 465–775 °C [ 31 , 35 , 57 ].…”

Section: Resultssupporting

confidence: 90%

“…This transition can lead, however, to instability and cracks in films and nanostructures [ 22 ]. Furthermore, whilst the rutile phase is desired due to its high refractive index, the anatase phase is often desired for its higher activity in photocatalytic applications [ 32 ]. As a consequence, there is a strong need to exactly control the phase transformation of titanium oxide to either assure the presence of a phase, needed for a specific target application, or to avoid undesirable phase transformation upon service.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Alumina Addition on the Optical Properties and the Thermal Stability of Titania Thin Films and Inverse Opals Produced by Atomic Layer Deposition

et al. 2021

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TiO2 thin films deposited by atomic layer deposition (ALD) at low temperatures (<100 °C) are, in general, amorphous and exhibit a smaller refractive index in comparison to their crystalline counterparts. Nonetheless, low-temperature ALD is needed when the substrates or templates are based on polymeric materials, as the deposition has to be performed below their glass transition or melting temperatures. This is the case for photonic crystals generated via ALD infiltration of self-assembled polystyrene templates. When heated up, crystal phase transformations take place in the thin films or photonic structures, and the accompanying volume reduction as well as the burn-out of residual impurities can lead to mechanical instability. The introduction of cation doping (e.g., Al or Nb) in bulk TiO2 parts is known to alter phase transitions and to stabilize crystalline phases. In this work, we have developed low-temperature ALD super-cycles to introduce Al2O3 into TiO2 thin films and photonic crystals. The aluminum oxide content was adjusted by varying the TiO2:Al2O3 internal loop ratio within the ALD super-cycle. Both thin films and inverse opal photonic crystal structures were subjected to thermal treatments ranging from 200 to 1200 °C and were characterized by in- and ex-situ X-ray diffraction, spectroscopic ellipsometry, and spectroscopic reflectance measurements. The results show that the introduction of alumina affects the crystallization and phase transition temperatures of titania as well as the optical properties of the inverse opal photonic crystals (iPhC). The thermal stability of the titania iPhCs was increased by the alumina introduction, maintaining their photonic bandgap even after heat treatment at 900 °C and outperforming the pure titania, with the best results being achieved with the super-cycles corresponding to an estimated alumina content of 26 wt.%.

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Section: Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Influence of Alumina Addition on the Optical Properties and the Thermal Stability of Titania Thin Films and Inverse Opals Produced by Atomic Layer Deposition

et al. 2021

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“…Doping with metal ions is a one of the profitable ways to retard the ART [14,21,[23][24][25][26][27][28][29][30][31]. Metal ions could improve the thermal stability of TiO 2 through the reduction in contact points, and nucleation sites [32].Generally, doping of an element with higher oxidation state compared to Ti 4+ would improve charge carrier separation on the photocatalyst surface [33]. Molybdenum (Mo; with a highest oxidation state of Mo 6+ ) as a dopant is inexpensive, non-toxic and has high solubility in the TiO 2 anatase lattice [33].…”

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confidence: 99%

Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

et al. 2020

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This work outlines an experimental and theoretical investigation of the effect of molybdenum (Mo) doping on the oxygen vacancy formation and photocatalytic activity of TiO 2 . Analytical techniques such as x-ray diffraction (XRD), Raman, x-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to probe the anatase to rutile transition (ART), surface features and optical characteristics of Mo doped TiO 2 (Mo-TiO 2 ). XRD results showed that the ART was effectively impeded by 2 mol% Mo doping up to 750°C, producing 67% anatase and 33% rutile. Moreover, the crystal growth of TiO 2 was affected by Mo doping via its interaction with oxygen vacancies and the Ti-O bond. The formation of Ti-O-Mo and Mo-Ti-O bonds were confirmed by XPS results. Phonon confinement, lattice strain and non-stoichiometric defects were validated through the Raman analysis. DFT results showed that, after substitutional doping of Mo at a Ti site in anatase, the Mo oxidation state is Mo 6+ and empty Mo-s states emerge at the titania conduction band minimum. The empty Mo-d states overlap the anatase conduction band in the DOS plot. A large energy cost, comparable to that computed for pristine anatase, is required to reduce Mo-TiO 2 through oxygen vacancy formation. Mo 5+ and Ti 3+ are present after the oxygen vacancy formation and occupied states due to these reduced cations emerge in the energy gap of the titania host. PL studies revealed that the electron-hole recombination process in Mo-TiO 2 was exceptionally lower than that of TiO 2 anatase and rutile. This was ascribed to introduction of 5s gap states below the CB of TiO 2 by the Mo dopant. Moreover, the photo-generated charge carriers could easily be trapped and localised on the TiO 2 surface by Mo 6+ and Mo 5+ ions to improve the photocatalytic activity. coatings [8,9]. The most commonly existing crystalline polymorphs of TiO 2 are anatase, rutile and brookite [10][11][12]. Anatase is accepted to be the more active phase of TiO 2 and is preferred by the ceramic industries to fabricate light active antimicrobial indoor building materials such as ceramics, glass, tiles and sanitary surfaces [13,14]. This requires thermal stability of the anatase phase under typical ceramic processing conditions. TiO 2 anatase is mainly fabricated at low calcination temperatures (∼500°C) to prevent the anatase to rutile phase transition (ART) [15][16][17], which produces the less photo-active rutile phase. The photo-activity of anatase arises from its appropriate band edge positions, electron affinity, ionisation potential, and the long lifetime of charge carriers [10,12,18]. Moreover, transient photo-conductance analysis has revealed that the electron-hole recombination phenomena in anatase (101) phase is much slower compared to rutile (110), which is credited in part to the indirect band gap of anatase [11,19].The unit cells of anatase and rutile phases are composed of TiO 6 octahedra with titanium atoms at the centre and oxygen atoms at the vertices [20]. Both anatase and rutile have a t...

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“…Firstly, both Ticontaining phases formed at pre-reduction (TiCO and Ti2O3) are capable of forming TiO2 on oxidation, either in the form of rutile or anatase, or as a co-existence of these polymorphs by postoxidation at intermediate temperatures. Secondly, the presence of silica is expected to stabilize the fraction of anatase, in accordance with the results [22,23]. Thus, relatively mild post-oxidation conditions were selected, including the temperatures in the range 400-500 °C and different times.…”

Section: Processing Effects On the Phase Compositionmentioning

confidence: 58%

“…This work demonstrates a new microscale material design approach to process redox-transformed TiO 2 + SiC mixtures as suitable photocatalysts. The choice of silica as a secondary phase is determined by its inhibitory effect on the anatase transformation [22,23] and also because it is one of the main components of conventional ceramics. The presence of silicon carbide (SiC) may allow the self-heating of the catalyst by microwave radiation, combining the photocatalytic activity with a thermal co-activation functionality [24].…”

Section: Introductionmentioning

confidence: 99%

Design of Multifunctional Titania-Based Photocatalysts by Controlled Redox Reactions

et al. 2020

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This work aims at the preparation of multifunctional titania-based photocatalysts with inherent capabilities for thermal co-activation and stabilisation of anatase polymorph, by designing the phase composition and microstructure of rutile-silicon carbide mixture. The processing involved a conventional solid state route, including partial pre-reduction of rutile by SiC in inert Ar atmosphere, followed by post-oxidation in air. The impacts of processing conditions on the phase composition and photocatalytic activity were evaluated using Taguchi planning. The XRD studies confirmed the presence of rutile/anatase mixtures in the post-oxidised samples. The results emphasise that pre-reduction and post-oxidation temperatures are critical in defining the phase composition, while post-oxidation time is relevant for the photocatalytic performance. Microstructural studies revealed the formation of core-shell particles, which can suppress the photocatalytic activity. The highest apparent reaction rate of the photodegradation of methylene blue was observed for the sample pre-reduced in Ar at 1300 °C for 5 h and then calcined in air at 400 °C for 25 h. Though its performance was ~1.6-times lower than that for the same amount of nanostructured industrial P25 photocatalyst, it was achieved in the material possessing 2–3 times lower surface area and containing ~50 mol% of SiO2 and SiC, thus demonstrating excellent prospects for further improvements.

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Design guidelines for titania-silica-alumina ceramics with tuned anatase to rutile transformation

Cited by 6 publications

References 53 publications

Influence of Alumina Addition on the Optical Properties and the Thermal Stability of Titania Thin Films and Inverse Opals Produced by Atomic Layer Deposition

Influence of Alumina Addition on the Optical Properties and the Thermal Stability of Titania Thin Films and Inverse Opals Produced by Atomic Layer Deposition

Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

Design of Multifunctional Titania-Based Photocatalysts by Controlled Redox Reactions

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Design guidelines for titania-silica-alumina ceramics with tuned anatase to rutile transformation

Cited by 6 publications

References 53 publications

Influence of Alumina Addition on the Optical Properties and the Thermal Stability of Titania Thin Films and Inverse Opals Produced by Atomic Layer Deposition

Influence of Alumina Addition on the Optical Properties and the Thermal Stability of Titania Thin Films and Inverse Opals Produced by Atomic Layer Deposition

Mo doped TiO2: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

Design of Multifunctional Titania-Based Photocatalysts by Controlled Redox Reactions

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Product

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Mo doped TiO₂: impact on oxygen vacancies, anatase phase stability and photocatalytic activity