Vanadia–silica xerogels: optical and structural properties

Devi, P. Sujatha; Ganguli, Dibyendu

doi:10.1016/j.jnoncrysol.2004.02.003

Cited by 17 publications

(17 citation statements)

References 25 publications

(30 reference statements)

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“…The line shape and spectral parameters of the abovementioned multicomponent 77 K VO(II) EPR spectra are very similar to those previously reported [57][58][59][60][61][62][63][64][65]75] for VO(II) spin-probes, as present in silica gels and xerogels. Figure 2B shows that no substantial changes occur in the ''frozen-solution'' VO(II) EPR spectra of the low-viscous and high-viscous solutions in stages (a) and (b), although the peak-to-peak line width (DB pp ) was found to increase slightly.…”

Section: Resultssupporting

confidence: 88%

“…In this case, the dry-gel hydration, sample (h), gives very similar VO(II) EPR spectra (and likewise their spectral parameters) to those seen in both the stage (c) and the closed capillary (z). The spin Hamiltonian parameter values all agree well with those reported in the literature for similar systems [57][58][59][60][61][62][63][64][65].…”

Section: Resultssupporting

confidence: 86%

“…Even when air-dried, the gels still contained some liquid fraction, albeit that its effective viscosity was higher than that of a free aqueous solution. When the samples were frozen at 77 K, the molecular motion of the hydrated cation complexes became immobilised on the EPR spectroscopic timescale [55][56][57][58][59][60][61][62][63][64][65].…”

Section: B [ 10 -4 T ]mentioning

confidence: 99%

“…At low VO(II) concentrations (ca 1 mmol or less), the X-band EPR spectra recorded from borate, phosphate and silicate glasses [3,4,7] and also those from the sol-gel process products [57][58][59][60][61][62][63][64][65] are rich in hyperfine structure from the 51 V isotope (I = 7/2, natural abundance 99.76 %). VO(II) cations are especially useful as spin-probes, since they consistently give relative sharp EPR spectra from solutions recorded both at RT and when frozen to 77 K [71].…”

Section: Interpretation and Simulation Of Vo(ii) Epr Spectramentioning

confidence: 99%

“…It is well documented that Cu(II) and Mn(II) ions are very sensitive as spin-probes to monitor the structural changes that occur in silica xerogels during the process of calcination, or in general, the properties of the sol-gel process products, and numerous EPR experiments, have been devised for this purpose [5,. However, there have been far fewer systematic EPR studies made of Cu(II) and Mn(II) cations with which to explore the earlier stages of the silica sol-gel process [55][56][57][58][59], while VO(II) ions have been employed relatively rarely to investigate the silica sol-gel process at all [57][58][59][60][61][62][63][64][65].…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Tetraethyl orthosilicate (TEOS)-based sol–gel process monitored by EPR spectroscopy with VO(II) cations as a spin-probe

Mazúr

Husáriková

Rhodes

et al. 2015

J Sol-Gel Sci Technol

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The various stages of the TEOS-based sol-gel process were studied by EPR spectroscopy using a VO(II) spin-probe. A detailed analysis of the multicomponent VO(II) EPR spectra recorded at 77 K showed that three main types of individual signals appeared superimposed at the various stages of the sol-gel process, which corresponds to different environments of the paramagnetic VO(II) cations. The spin Hamiltonian parameters of each individual subspectrum remain unchanged throughout the various stages of the sol-gel process. However, the relative contribution of individual signals changed significantly as the sol-gel process proceeded. The results show that the VO(II) cations are not directly incorporated into the siloxane network, but are trapped relatively freely as [VO(H 2 O) 5 ] 2? complexes in a solution-like environment during the evolution of the sol-gel process. It was amply demonstrated that the sol-to-gel transformation from the viscous, colloid suspension to the viscoelastic gel can be successfully monitored by EPR spectroscopy with VO(II) as a spin-probe.Dedicated to the 70th anniversary of the discovery of Electron Paramagnetic Resonance

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Section: Resultssupporting

confidence: 88%

Section: Resultssupporting

confidence: 86%

Section: B [ 10 -4 T ]mentioning

confidence: 99%

Section: Interpretation and Simulation Of Vo(ii) Epr Spectramentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Tetraethyl orthosilicate (TEOS)-based sol–gel process monitored by EPR spectroscopy with VO(II) cations as a spin-probe

Mazúr

Husáriková

Rhodes

et al. 2015

J Sol-Gel Sci Technol

View full text Add to dashboard Cite

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Small‐angle X‐ray scattering and nitrogen adsorption study of the nanoporosity elimination in TEOS sonohydrolysis‐derived xerogels

Vollet

Castro

Donatti

et al. 2005

Physica Status Solidi (a)

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Small‐angle X‐ray scattering (SAXS) and nitrogen adsorption techniques were used to study the temperature and time structural evolution of the nanoporosity in silica xerogels prepared from acid‐ and ultrasound‐catalyzed hydrolysis of tetraethoxysilane (TEOS). Silica xerogels present a structure of nanopores of fully random shape, size, and distribution, which can be described by an exponential correlation function γ(r) = exp (–r/a), where a is the correlation distance, as predicted by the Debye, Anderson, and Brumberger (DAB) model. The mean pore size was evaluated as about 1.25 nm from SAXS and about 1.9 nm from nitrogen adsorption. The nanopore elimination in TEOS sonohydrolysis‐derived silica xerogels is readily accelerated at temperatures around 900 °C probably by the action of a viscous flow mechanism. The nanopore elimination process takes place in such a way that the pore volume fraction and the specific surface are reduced while the mean pore size remains constant. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Structural characteristics of gels prepared from sonohydrolysis and conventional hydrolysis of TEOS: an emphasis on the mass fractal as determined from the pore size distribution

Vollet

Torres

Donatti

et al. 2005

Physica Status Solidi (a)

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Silica gels were preparated from fixed proportion mixtures of tetraethoxysilane, water and hydrocloric acid, using either ultrasound stimulation (US) or conventional method (CO) in the hydrolysis step of the process. Wet gels were obtained with the same silica volume concentration and density. According to small‐angle X‐ray scattering, the structure of the wet gels can be described as mass fractal structures with mass fractal dimension D = 2.20 in a length scale ξ = 7.9 nm, in the case of wet gels US, and D = 2.26 in a length scale ξ = 6.9 nm, in the case of wet gels CO. The mass fractal characteristics of the wet gels US and CO account for the different structures evolved in the drying of the gels US and CO in the obtaining of xerogels and aerogels. The pore structure of the dried gels was studied by nitrogen adsorption as a function of the temperature. Aerogels (US and CO) present high porosity with pore size distribution (PSD) curves in the mesopore region while xerogels (US and CO) present minor porosity with PSD curves mainly in the micropore region. The dried gels US (aerogels and xerogels) generally present pore volume and specific surface area greater than the dried gels CO. The mass fractal structure of the aerogels has been studied from an approach based on the PSD curves exclusively. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Vanadia–silica xerogels: optical and structural properties

Cited by 17 publications

References 25 publications

Tetraethyl orthosilicate (TEOS)-based sol–gel process monitored by EPR spectroscopy with VO(II) cations as a spin-probe

Tetraethyl orthosilicate (TEOS)-based sol–gel process monitored by EPR spectroscopy with VO(II) cations as a spin-probe

Small‐angle X‐ray scattering and nitrogen adsorption study of the nanoporosity elimination in TEOS sonohydrolysis‐derived xerogels

Structural characteristics of gels prepared from sonohydrolysis and conventional hydrolysis of TEOS: an emphasis on the mass fractal as determined from the pore size distribution

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