Thermodynamic analysis of phase stability of nanocrystalline titania

Zhang, Hengzhong; Banfield, Jillian F.

doi:10.1039/a802619j

Cited by 1,212 publications

(1,053 citation statements)

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“…This enhanced stability was reasoned to be due to the non-negligible effect of surface energy on Gibbs free energy at the nanoscale, a well-known phenomenon in nanocrystals. [10][11][12] The suspected lower surface energy of bixbyite is thought to alter the relative energetics of the two phases, potentially favoring bixbyite over corundum below some critical size. lines mark the border of the unit cell in each structure.…”

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confidence: 99%

Oxygen Incorporation and Release in Metastable Bixbyite V₂O₃ Nanocrystals

2016

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A new, metastable polymorph of V 2 O 3 with a bixbyite structure was recently stabilized in colloidal nanocrystal form. Here, we report the reversible incorporation of oxygen in this material, which can be controlled by varying temperature and oxygen partial pressure. Based on X-ray diffraction (XRD) and thermogravimetric analysis, we find that oxygen occupies interstitials sites in the bixbyite lattice. Two oxygen atoms per unit cell can be incorporated rapidly and with minimal changes to the structure, while the addition of three or more oxygen atoms destabilizes the structure, resulting in a phase change that can be reversed upon oxygen removal. Density functional theory (DFT) supports the reversible occupation of interstitial sites in bixbyite by oxygen and the 1.1 eV barrier to oxygen diffusion predicted by DFT matches the activation energy of the oxidation process derived from observations by in situ XRD. Thus, the observed rapid oxidation kinetics are facilitated by short diffusion paths through the bixbyite nanocrystals. Due to the exceptionally low temperatures of oxidation and reduction, this earthabundant material is proposed for use in oxygen storage applications.The oxides of vanadium are known for both their structural complexity and fascinating properties, as manifested in the many stable and metastable phases and phase transitions that exist in these materials. Vanadium sesquioxide (V 2 O 3 ) is one such oxide, transforming from the antiferromagnetic, insulating monoclinic phase to the paramagnetic, metallic corundum phase at 170 K. [1][2][3] This phase transformation is of great fundamental importance due to its model Mott-Hubbard transition behavior. 4 Recently, a metastable phase of V 2 O 3 with a cubic, bixbyite structure was discovered. 5 This new polymorph has since been the subject of several studies, both fundamental and applied, including its proposed use as a p-type conductor and battery electrode. 6,7 Synthesizing V 2 O 3 nanocrystals stabilizes the metastable phase and allowed us, in 2013, to prepare phase pure bixbyite. 8 Using our colloidal synthetic method, we now demonstrate low temperature, reversible oxidation and reduction of bixbyite V 2 O 3 nanocrystals, a phenomenon which could be harnessed for oxygen storage.The bixbyite structure has a body-centered cubic lattice with space group Ia-3. Often described as anion deficient fluorite, bixbyite is comparable to a 2 x 2 x 2 fluorite supercell with a quarter of the anions removed, as demonstrated in Figure 1. These vacated sites are the 16c Wyckoff positions in the Ia-3 space group, which are inherently unfilled in bixbyite. 9 Cations in the bixbyite structure populate two symmetry inequivalent positions-the 8b and 24d Wyckoff positions, otherwise known as b-and d-sites,

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Oxygen Incorporation and Release in Metastable Bixbyite V₂O₃ Nanocrystals

2016

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“…The result illustrates that CTAB template not only induces the formation of small and uniform anatase crystallites but also generates crystalline brookite. In general, the anatase-to-rutile phase transformation depends on several factors including the size of anatase crystallites, the existence of brookite phase, and the packing of titania nanocrystals [23][24][25][26] . It is expected that the loose packing here has a predominant influence, and therefore inhibits the transformation from anatase to rutile phases.…”

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confidence: 99%

Sol-gel template synthesis and photocatalytic behaviour of anatase titania nanoparticles

Loryuenyong¹,

Angamnuaysiri²,

Sukcharoenpong³

et al. 2012

ScienceAsia

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In this study, titania nanoparticles were successfully prepared by a sol-gel template method, employing cetyltrimethylammonium bromide (CTAB) and CaCO3 nanoparticles as templates. Titanium(IV) tetraisopropoxide and ethanol were used as a titanium precursor and alcoholic solvent, respectively. The obtained nanosized-titania was characterized by X-ray diffraction, transmission-electron microscopy, and N2 adsorption and desorption methods. The photocatalytic activity of titania was investigated from the photodegradation of methylene blue solution under UVC irradiation. The results indicated that the amount of anatase crystallites and pore characteristics were important factors influencing the degree of photocatalysis of titania nanoparticles. Highly crystalline anatase titania could be obtained through the controlled hydrolysis reaction rate and the formation of loose-packed titania nanoparticles, while high specific surface area could be achieved with a template method.

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“…102 This can be attributed to the lower surface energy of anatase driving its preferential formation due to the large surface area to bulk volume ratio of the small particles typically formed during sol-gel processing. 103,104,105,106 Additional factors, such as the precursors employed and reaction conditions can also influence TiO 2 crystal growth. 107,108 The predominance of anatase TiO 2 in the sol-gel coatings employed in the present study (only a small amount of rutile polymorph found in P25(5)) is consistent with previous sol-gel TiO 2 calcination studies carried out at below 700 °C, 45 and TiO 2 -P25 nanocomposite coatings deposited onto glass and flat steel substrates.…”

Section: Discussionmentioning

confidence: 99%

Magnetic recyclable microcomposite silica-steel core with TiO2 nanocomposite shell photocatalysts for sustainable water purification

Wilson

Cheng

Oswald

et al. 2017

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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(2017) 'Magnetic recyclable microcomposite silica-steel core with TiO 2 nanocomposite shell photocatalysts for sustainable water puri cation.', Colloids and surfaces A : physicochemical and engineering aspects., 523 . pp. 27-37.Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTMicron-sized steel particles encapsulated within a silica host matrix and then coated with a photocatalytic TiO 2 nanocomposite shell have been prepared using sol-gel chemistry and shown to readily degrade waterborne organic pollutants during UV illumination. These silica-steel microcomposite core with TiO 2 nanocomposite shell photocatalysts can be recycled multiple times from solution by magnetic separation.

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Thermodynamic analysis of phase stability of nanocrystalline titania

Cited by 1,212 publications

References 8 publications

Oxygen Incorporation and Release in Metastable Bixbyite V₂O₃ Nanocrystals

Oxygen Incorporation and Release in Metastable Bixbyite V₂O₃ Nanocrystals

Sol-gel template synthesis and photocatalytic behaviour of anatase titania nanoparticles

Magnetic recyclable microcomposite silica-steel core with TiO2 nanocomposite shell photocatalysts for sustainable water purification

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Thermodynamic analysis of phase stability of nanocrystalline titania

Cited by 1,212 publications

References 8 publications

Oxygen Incorporation and Release in Metastable Bixbyite V2O3 Nanocrystals

Oxygen Incorporation and Release in Metastable Bixbyite V2O3 Nanocrystals

Sol-gel template synthesis and photocatalytic behaviour of anatase titania nanoparticles

Magnetic recyclable microcomposite silica-steel core with TiO2 nanocomposite shell photocatalysts for sustainable water purification

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Oxygen Incorporation and Release in Metastable Bixbyite V₂O₃ Nanocrystals

Oxygen Incorporation and Release in Metastable Bixbyite V₂O₃ Nanocrystals