Study of the surface layer of aerosil–8CB composites by TG/DTA/DSC measurements

Frunzǎ, S.; Kosslick, H.; Schönhals, Andreas; Frunză, Ligia; Enache, I.; Beica, T.

doi:10.1016/s0022-3093(03)00319-3

Cited by 18 publications

(4 citation statements)

References 46 publications

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“…For a limited temperature range at the beginning of the experiments, the heating rate was 2 K/min. The data were processed as described elsewhere …”

Section: Methodsmentioning

confidence: 99%

“…The data were processed as described elsewhere. 33 The equipment to measure the complex dielectric function, ε*( f ) ) ε′( f ) -iε′′( f ) (f, frequency; ε′, real part; ε′′, loss part), is already discussed in detail. 34 From 10 -2 to 10 7 Hz, a high resolution ALPHA analyzer (Novocontrol, Germany) with an active sample head was used.…”

Section: Methodsmentioning

confidence: 99%

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Molecular Relaxation Processes in a MOF-5 Structure Revealed by Broadband Dielectric Spectroscopy: Signature of Phenylene Ring Fluctuations

et al. 2010

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The molecular mobility of a MOF-5 metal-organic framework was investigated by broadband dielectric spectroscopy. Three relaxation processes were revealed. The temperature dependence of their relaxation rates follows an Arrhenius law. The process observed at lower temperatures is attributed to bending fluctuations of the edges of the cages involving the Zn-O clusters. The processes ("region II") at higher temperatures were assigned to fluctuations of phenyl rings in agreement with the NMR data found by Gould et al. (J. Am. Chem. Soc. 2008, 130, 3246). The carboxylate groups might also be involved. The rotational fluctuations of the phenyl rings leading to the low frequency part of relaxation region II might be hindered either by some solvent molecules entrapped in the cages or by an interpenetrated structure and have a broad distribution of activation energies. The high frequency part of region II corresponds nearly to a Debye-like process: This is explained by a well-defined structure of empty pores.

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“…For a limited temperature range at the beginning of the experiments, the heating rate was 2 K/min. The data were processed as described elsewhere …”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Molecular Relaxation Processes in a MOF-5 Structure Revealed by Broadband Dielectric Spectroscopy: Signature of Phenylene Ring Fluctuations

et al. 2010

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“…Alternatively to the complex dielectric function, the complex electric conductivity σ * is used to describe the dielectric behavior. Its relationship to the complex dielectric function is given by with the real part 17b The water loading degree c w was estimated by thermogravimetric measurements as already described for different other composites . These measurements were performed by a Setaram TG-DTA 92 apparatus, under a dry, oil-free air atmosphere, using a part of the sample prepared for dielectric measurements.…”

Section: Methodsmentioning

confidence: 99%

Rotational Fluctuations of Water Confined to Layered Oxide Materials: Nonmonotonous Temperature Dependence of Relaxation Times

et al. 2007

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The rotational molecular dynamics of water confined to layered oxide materials with brucite structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(7) Hz and in a broad temperature interval. The layered double hydroxide samples show one relaxation process, which was assigned to fluctuations of water molecules forming a layer, strongly adsorbed to the oxide surface. The temperature dependence of the relaxation rates has an unusual saddlelike shape characterized by a maximum. The model of Ryabov et al. (J. Phys. Chem. B 2001, 105, 1845) recently applied to describe the dynamics of water molecules in porous glasses is employed also for the layered materials. This model assumes two competing effects: rotational fluctuations of water molecules that take place simultaneously with defect formation, allowing the creation of free volume necessary for reorientation. The activation energy of rotational fluctuations, the energy of defect formation, a pre-exponential factor, and the defect concentration are obtained as main parameters from a fit of this model to the data. The values of these parameters were compared with those found for water confined to nanoporous molecular sieves, porous glasses, or bulk ice. Several correlations were discussed in detail, such as the lower the value of the energy of defect formation, the higher the number of defects. The pre-exponential factor increases with increasing activation energy, as an expression of the compensation law, and indicates the cooperative nature of the motional process. The involvement of the surface OH groups and of the oxygen atoms of the interlayer anions in the formation of hydrogen bonds was further discussed. For the birnessite sample, the relaxation processes are probably overlaid by a dominating conductivity contribution, which is analyzed in its frequency and temperature dependence. It is found that the conductivity of birnessite obeys the characteristics of semiconducting disordered materials. Especially the Barton/Nakajima/Namikawa relationship is fulfilled. Analyzing the temperature dependence of the direct current (dc) conductivity sigma0 in detail gives some hint that sigma0(T) has also an unusual saddlelike form.

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“…FTIR, UV-Vis spectroscopy and thermal analysis methods [22] were applied to characterize the HRP immobilization.…”

Section: Hrp Immobilizationmentioning

confidence: 99%

Oxidation activity of horseradish peroxidase hosted in molecular sieves: spectroscopic investigations show hindering of the enzyme activity

Frunză

Gheorghe

Ganea

et al. 2011

Reac Kinet Mech Cat

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Horseradish peroxidase immobilization inside molecular sieves with pores hexagonally structured as such or functionalized with copper ions is presented in comparison with the bidimensional immobilization onto aerosil A380 particles. Immobilization was performed under mild conditions that do not lead to enzyme denaturation. Guest-host interactions were pursued spectrophotometrically and by thermal analysis measurements. FTIR spectroscopy showed no major secondary structural change for the entrapped enzyme despite some influence of the support functionalization that can be supposed. The activity of the immobilized enzyme was tested in the oxidation of Alizarin Red S (ARS) with hydrogen peroxide. It was found that the dye oxidation is catalyzed by the enzyme in homogeneous reaction but the rate becomes much slower in heterogeneous catalytic processes with prepared catalysts. It seems that horseradish peroxidase immobilization in simple porous silica or alumino-silica post synthesis blocks the enzyme activity. In addition, copper ions make a stable complex with ARS hindering its oxidation as well.

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Study of the surface layer of aerosil–8CB composites by TG/DTA/DSC measurements

Cited by 18 publications

References 46 publications

Molecular Relaxation Processes in a MOF-5 Structure Revealed by Broadband Dielectric Spectroscopy: Signature of Phenylene Ring Fluctuations

Molecular Relaxation Processes in a MOF-5 Structure Revealed by Broadband Dielectric Spectroscopy: Signature of Phenylene Ring Fluctuations

Rotational Fluctuations of Water Confined to Layered Oxide Materials: Nonmonotonous Temperature Dependence of Relaxation Times

Oxidation activity of horseradish peroxidase hosted in molecular sieves: spectroscopic investigations show hindering of the enzyme activity

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