The influence of calcination on the size of nanocrystals, porous structure and acid–base properties of mesoporous anatase used as catalytic support

Zacharaki, Irene; Kontoyannis, Christos G.; Lycourghiotis, Alexis; Kordulis, Christos

doi:10.1016/j.colsurfa.2008.04.019

Cited by 12 publications

(9 citation statements)

References 42 publications

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“…Inspection of Figures and , as well as of Table , shows that calcination causes important decrease of the pore volume and pore area in the range of the pores with small width and a considerable increase in the range of the pores with large width. Assuming that titania exhibits mainly interparticle porosity, one may easily relate this effect to the increase in the particle size of titania with the calcination temperature reported recently by us . Upon calcination small titania particles sinter to larger ones which allows the development of greater and greater interparticle pores.…”

Section: Resultsmentioning

confidence: 73%

Temperature-Dependent Evolution of the Molecular Configuration of Oxo-Tungsten(VI) Species Deposited on the Surface of Titania

Tribalis

Panagiotou²,

Tsilomelekis

et al. 2014

J. Phys. Chem. C

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The pH and temperature evolution of the molecular configuration of oxo-tungsten(VI) species deposited on TiO2 by equilibrium deposition filtration and the temperature evolution of the samples texture are studied using in situ Raman spectroscopy, DR spectroscopy, N2 adsorption–desorption measurements, and TGA. Prior to drying, WO4 2– monomers retained above a bridging surface hydroxyl of TiO2 through H bonding (with a Ti2OH···O–WO3 umbrella configuration) prevail at pH = 9. A pH decrease results in a gradual transformation to an inner sphere monosubstituted species located above terminal surface oxygen (Ti–O–WO3). At pH = 7 both species coexist, whereas at pH = 5 the latter prevails with electrostatically retained polyoxotungstes also present. Heating to 100 °C causes the same effect resulted by the pH decrease at room temperature, that is, transformation of Ti2OH···O–WO3 into Ti–O–WO3, attributed to the removal of H2O molecules upon heating, thereby liberating surface Ti atoms. Progressive heating to higher temperatures causes further removal of surface hydroxyls (confirmed also by TGA) liberating more neighbor surface Ti atoms and favoring further anchoring. This leads to formation of bisubstituted dioxo (Ti–O)2–W(O)2 sites in the range 120–250 °C and to the prevalence of trisubstituted mono-oxo (Ti–O)3-WO sites at 430 °C. Polyoxotungstates are also detected in the sample with the highest W loading. The DRS spectra indicate a charge transfer effect between the surface O and Ti atoms proceeding via Ti–O–W surface bridges. Calcination of the support causes a decrease of the pore volume and pore area in the range of pores with small width and an increase in the range of pores with large width. This effect is not affected by the presence of the well dispersed “bi-dimensional” W species inferred by the Raman study.

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Section: Resultsmentioning

confidence: 73%

Temperature-Dependent Evolution of the Molecular Configuration of Oxo-Tungsten(VI) Species Deposited on the Surface of Titania

Tribalis

Panagiotou²,

Tsilomelekis

et al. 2014

J. Phys. Chem. C

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“…The value of d BET is estimated for the particle in a powder form, and it would be different from the real size for the particles dispersed in aqueous solution. By applying a laser scattering technique, Kordulis and co-workers have measured the particle size for different anatase samples ( d XRD = 8.1, 8.6, 10.6, and 17.5 nm) dispersed in water . They found that those samples not only displayed similar size distribution but also had mean diameter all in a micrometer scale ( D = 12.8, 9.1, 10.6, and 17.5 μm).…”

Section: Resultsmentioning

confidence: 99%

Larger Effect of Sintering Temperature Than Particle Size on the Photocatalytic Activity of Anatase TiO₂

2013

J. Phys. Chem. C

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Photocatalytic activity of anatase TiO2 that increases with the increase of its synthesis temperature has been widely reported, but the reason for that remains incompletely understood. In this work, the positive effect of synthesis temperature, presumably due to the growth of particle size, has been examined. Three series of anatase samples with various particle sizes were prepared from the hydrolysis of TiOSO4 in water at 150 °C, followed by calcinations in air. The particle size of TiO2, estimated by X-ray diffraction and N2 adsorption, increased with the increase of the hydrothermal time, calcination time, and calcination temperature. For phenol photodegradation in aerated aqueous suspension, three series of the catalysts showed different correlation between the activity and particle size of TiO2. However, with the same amount of Ag+ adsorbed on the oxide surface for phenol photodegradation in a N2-purged aqueous suspension, those catalysts showed activities all increasing with the particle size of TiO2, whereas at given particle size, the thermally treated TiO2 was much more active than the hydrothermally treated one. These observations are discussed in terms of the solid crystallinity, surface area, exposed facets, surface hydroxyl groups, and light absorption. But, there only appears a positive correlation between the particle size, calcination temperature, and the number of surface defects, as revealed by photoluminescence spectroscopy. The increase of surface defects may facilitate separation of the photogenerated charges, consequently improving the efficiency for phenol degradation at the solid–liquid interface.

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“…The DR spectrum of titania exhibits a broad band in the range 200-400 nm. [38] According to the literature [39] this is due to the charge transfer process O 2À !Ti 4 + taking place in the Ti IV oxide. This broad band should have not been detected in the spectra of Figure 4, because these spectra were recorded with the support as reference.…”

Section: Investigation Of the Mode Of Interfacial Deposition By Meansmentioning

confidence: 99%

Interfacial Impregnation Chemistry in the Synthesis of Cobalt Catalysts Supported on Titania

Petsi

Panagiotou

Garoufalis

et al. 2009

Chemistry A European J

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The interfacial chemistry of the impregnation step involved in the synthesis of cobalt catalysts supported on titania was investigated with regard to the mode of interfacial deposition of the aqua complex [Co(H(2)O)(6)](2+) on the "titania/electrolyte solution" interface, the structure of the inner-sphere complexes formed, and their relative interfacial concentrations. Several methodologies based on the application of deposition experiments and electrochemical techniques were used in conjunction with diffuse-reflectance spectroscopy and EPR spectroscopy. These suggested the formation of mononuclear/oligonuclear inner-sphere complexes on deposition of the [Co(H(2)O)(6)](2+) ions at the "titania/electrolyte solution" interface. The joint application of semiempirical quantum-mechanical calculations, stereochemical considerations, and modeling of the deposition data revealed the exact structure of these complexes and allowed their relative concentrations at various Co(II) surface concentrations to be determined. It was found that the interface speciation depends on the Co(II) surface concentration. Mononuclear complexes are formed at the compact layer of the "titania/electrolyte solution" interface for low and medium Co(II) surface concentrations. Formation of mono-hydrolyzed Ti(2)O-TiO and the dihydrolyzed TiO-TiO disubstituted configurations is very probable. In the first configuration one water ligand of the [Co(H(2)O)(6)](2+) ion is substituted by a bridging surface oxygen atom and another by a terminal surface oxygen atom. In the second configuration two water ligands of the [Co(H(2)O)(6)](2+) ion are substituted by two terminal surface oxygen atoms. Binuclear and trinuclear inner-sphere complexes are formed, in addition to the mononuclear ones, at relatively high Co(II) surface concentrations.

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The influence of calcination on the size of nanocrystals, porous structure and acid–base properties of mesoporous anatase used as catalytic support

Cited by 12 publications

References 42 publications

Temperature-Dependent Evolution of the Molecular Configuration of Oxo-Tungsten(VI) Species Deposited on the Surface of Titania

Temperature-Dependent Evolution of the Molecular Configuration of Oxo-Tungsten(VI) Species Deposited on the Surface of Titania

Larger Effect of Sintering Temperature Than Particle Size on the Photocatalytic Activity of Anatase TiO₂

Interfacial Impregnation Chemistry in the Synthesis of Cobalt Catalysts Supported on Titania

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The influence of calcination on the size of nanocrystals, porous structure and acid–base properties of mesoporous anatase used as catalytic support

Cited by 12 publications

References 42 publications

Temperature-Dependent Evolution of the Molecular Configuration of Oxo-Tungsten(VI) Species Deposited on the Surface of Titania

Temperature-Dependent Evolution of the Molecular Configuration of Oxo-Tungsten(VI) Species Deposited on the Surface of Titania

Larger Effect of Sintering Temperature Than Particle Size on the Photocatalytic Activity of Anatase TiO2

Interfacial Impregnation Chemistry in the Synthesis of Cobalt Catalysts Supported on Titania

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Larger Effect of Sintering Temperature Than Particle Size on the Photocatalytic Activity of Anatase TiO₂