Critical Nuclei Size, Initial Particle Size and Packing Effect on the Phase Stability of Sol-Peptization-Gel-Derived Nanostructured Titania

Winardi, Suminto; Mukti, Rino R.; Kumar, Krishnankutty-Nair P.; Wang, Junzheng; Wunderlich, Wilfried; Okubo, Tatsuya

doi:10.1021/la904619x

Cited by 22 publications

(14 citation statements)

References 42 publications

(57 reference statements)

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“…After calcination at 500°C for 4 h, around 5 % of the anatase had transformed to rutile, whilst after heating at 600°C almost complete transformation of anatase to rutile had occurred. The onset of the anatase-rutile phase transition is known to be dependent on the initial particle size of the anatase crystals and also their packing density [33][34][35]. A critical anatase crystallite size of *30 nm is considered necessary for the nucleation of rutile, in good agreement with our findings (Table 3).…”

Section: Effect Of Test Conditions On the Rate Of Methylenesupporting

confidence: 90%

Effect of the TiO2 Crystallite Size, TiO2 Polymorph and Test Conditions on the Photo-Oxidation Rate of Aqueous Methylene Blue

et al. 2014

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This study systematically re-examines the titania-catalysed photo-oxidation of methylene blue (MB) in aqueous solution at 20°C, placing particular emphasis on the effects of TiO 2 crystallite size, TiO 2 polymorph (anatase, brookite, rutile and combinations thereof) and experimental test conditions on the rate of MB photo-oxidation. For all TiO 2 samples tested, the highest rate of MB photo-oxidation was observed at pH 6, slightly above the isoelectric point of TiO 2 (*5.8 for P25 TiO 2 ). Increasing the ionic strength at pH 6 induced MB dimer formation in solution, and lowered the rate of MB photo-oxidation by TiO 2 . For all TiO 2 polymorphs, the surface area normalised rate increased with crystallite size reflecting the corresponding reduction in surface and bulk defects (electronhole pair recombination sites). The optimum crystallite sizes were *20-25 nm for anatase and *50 nm for brookite. The photocatalytic activity of the different TiO 2 powders followed the general order P25 [ anatase [ brookite ) rutile, with the high activity of P25 TiO 2 providing strong evidence that anatase-rutile heterojunctions act as ''hotspots'' for MB photo-oxidation. Mixed phase anatase-rutile or brookite-rutile powders, each containing *5 wt% rutile, demonstrated superior area normalized photocatalytic activities for MB photo-oxidation compared to pure phase anatase or brookite powders of comparable crystallite size. Finally, deposition of Pd, Pt or Au nanoparticles decreased the activity of P25 TiO 2 for MB photo-oxidation. This paper clarifies long-standing confusion in the scientific literature about the photo-oxidation of aqueous MB over TiO 2 and M/TiO 2 (M = Pd, Pt and Au) photocatalysts.

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Section: Effect Of Test Conditions On the Rate Of Methylenesupporting

confidence: 90%

Effect of the TiO2 Crystallite Size, TiO2 Polymorph and Test Conditions on the Photo-Oxidation Rate of Aqueous Methylene Blue

et al. 2014

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“…Reported research has shown that the anatase to rutile transformation occurs at temperatures between 450 and 850 • C, depending on fabrication method and precursors [4][5][6][7][8]. Various methods such as metal dopant and morphology control have been investigated to resist the anatase-rutile transformation [9,10]. However, until now, there was little report on successfully fabricating pure anatase TiO 2 film stabilized at high temperature of over 900 • C. In order to apply anatase phase TiO 2 for various environmental applications such as gas sensors, anti-microbial sanitary wares, and self-cleaning ceramic tiles, high temperature stable anatase TiO 2 without phase transformation is essential [11,12].…”

Section: Introductionmentioning

confidence: 99%

High Temperature Stable Anatase Phase Titanium Dioxide Films Synthesized by Mist Chemical Vapor Deposition

Zhang

2020

Nanomaterials

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Pure anatase-phase titanium dioxide films stable up to high temperatures were successfully fabricated by the mist chemical vapor deposition method. A post-annealing treatment of the synthesized films was carried out in oxygen atmosphere in the temperature range from 600 to 1100 °C and no anatase to rutile transformation was observed up to 1000 °C. Based on the grazing incidence X-ray diffraction data, the average crystallite size of the titanium dioxide films increased gradually with increasing annealing temperature. The structural analysis revealed that the high thermal stability of the anatase phase can be attributed to the small crystallite size and a sheet-like grain structure. An incomplete anatase to rutile transformation was observed after annealing at 1100 °C.

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“…Here, D is the average nanocrystalline size, K is a constant (here, a value of 1.38 was assumed (Winardi et al, 2010)), λ is the wavelength of the CuKα line (=1.5406 Å), B is the full width at half maximum which was obtained by subtracting the system value from the measured value, and θ is the peak angle. Raman spectroscopies were performed using a Horiba JY T64000 micro-Raman spectrometer (Horiba Ltd.) (excitation line was 514.5 nm).…”

Section: Methodsmentioning

confidence: 99%

Effects of Annealing on the Morphology and Porosity of Porous TiO<sub>2</sub> Films Fabricated by Deposition of Aerosol Nanoparticles

Kubo

Mantani

2015

J. Chem. Eng. Japan / JCEJ

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The present study investigates the impact of post annealing of TiO 2 nanoparticulate lms on their crystallinity, mechanical strength, and morphology. Non-agglomerated and amorphous TiO 2 nanoparticles of 46 nm diameter were synthesized in a plasma eld, and were subsequently deposited on substrates to form nanoparticulate lms. The lms were annealed at various temperatures in the range of 100-1,200°C. Phase transformations from amorphous-to-anatase and from anatase-to-rutile were observed at 400°C and at 1,000°C, respectively. The high rutile transformation temperature was considered to be due to a tensile eld induced by shrinkage of the lm. The as-deposited lm and the lms annealed at below 400°C had poor mechanical strength. Conversely, the lms annealed at over 500°C were strengthened by necking of the nanoparticles. The size of nanoparticles changed with increasing temperature. Annealing at 100-300°C caused the nanoparticles to shrink to approximately 30 nm. The nanoparticle diameters changed only slightly when annealed at 400-600°C because the annealing time was insu cient for changes to manifest. Annealing at 700-900°C caused the nanoparticle diameter to increase to approximately 50 nm because of sintering and coalescence of the nanoparticles. The diameter of the nanoparticles annealed at over 1,000°C became approximately 200 nm because of densi cation during the anatase-to-rutile transformation. The porosities of the lms annealed at below 900°C were over 80%. However, the porosities of the lms annealed at over 1,000°C decreased signi cantly due to densi cation.

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Critical Nuclei Size, Initial Particle Size and Packing Effect on the Phase Stability of Sol-Peptization-Gel-Derived Nanostructured Titania

Cited by 22 publications

References 42 publications

Effect of the TiO2 Crystallite Size, TiO2 Polymorph and Test Conditions on the Photo-Oxidation Rate of Aqueous Methylene Blue

Effect of the TiO2 Crystallite Size, TiO2 Polymorph and Test Conditions on the Photo-Oxidation Rate of Aqueous Methylene Blue

High Temperature Stable Anatase Phase Titanium Dioxide Films Synthesized by Mist Chemical Vapor Deposition

Effects of Annealing on the Morphology and Porosity of Porous TiO<sub>2</sub> Films Fabricated by Deposition of Aerosol Nanoparticles

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