Positron Annihilation Studies in Silica Supported Nickel Carbonate Systems

and, G. P. Babu; Manohar, V.; Sudarshan, K.; Pujari, P. K.; Manohar, and S. B.; Goswami, A.

doi:10.1021/jp014099n

Cited by 10 publications

(7 citation statements)

References 27 publications

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“…Positron annihilation lifetime spectroscopy (PALS) has attracted interest due to its ability to dynamically probe open volumes, − providing complementary insights into more widespread equilibrium techniques, such as gas sorption. This has been demonstrated for silica powders − and films, ,, aluminosilicate gels, metal–organic frameworks, , zeolites, − and layered materials. , The high sensitivity of PALS stems from the possibility of positrons binding with electrons in solids to form metastable ortho -positronium ( o -Ps) atoms, which are sufficiently long-lived to diffuse through open pore networks and be annihilated with a lifetime characteristic of the pore size . This property has recently been exploited in the characterization of zeolitic materials in discriminating the effectiveness of hierarchical pore networks in enhancing transport properties, − in studying coking and detemplation mechanisms, , in assessing the micropore topology, , and in monitoring pore evolution during structural transformations …”

Section: Introductionmentioning

confidence: 99%

Acidity Effects in Positron Annihilation Lifetime Spectroscopy of Zeolites

et al. 2018

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Positron annihilation lifetime spectroscopy (PALS) is a tool used to study pore networks in zeolites, as the diffusion of metastable ortho-positronium (o-Ps, an electron–positron bound pair) provides insights into connectivity that cannot be obtained by other techniques. The accurate assessment of porosity requires knowledge of the interaction of o-Ps with acid centers commonly present in these materials. Although previous studies have highlighted a potential effect, the specific impact of the nature and concentration of the acid sites remains unclear. By preparing a series of well-crystallized aluminum- and tin-containing MFI-type zeolites and with the study of commercial samples, we map the effects of Brønsted and Lewis acidity on the PALS response. The results reveal that both types of acid sites decrease the amount of o-Ps detected but through different mechanisms. Brønsted acid sites strongly affect the amount of o-Ps being annihilated in the micropore network but only nominally influence the amount out-diffusing from the crystal, which is attributed to an energy threshold for the interaction. Lewis acid sites originating from the incorporation of framework tin have a more substantial but uniform impact ascribed to the suppressed formation of o-Ps. A similar effect is observed due to the Lewis acid sites in sodium-exchanged aluminum-containing MFI, but the introduction of larger extraframework cations also hinders the diffusion of o-Ps. A preliminary model is put forward to describe the changes in the PALS response in the presence of acid centers.

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Section: Introductionmentioning

confidence: 99%

Acidity Effects in Positron Annihilation Lifetime Spectroscopy of Zeolites

et al. 2018

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“…The growing interest in the recent years in the positron annihilation studies on amorphous silica or silica gel material (not only bulk but also thin films) [1][2][3][4][5][6][7] revealed that positronium (Ps) formation occurs with high efficiency in intrinsic microvoids of molecular network which was confirmed with several experimental techniques like positron annihilation lifetime spectroscopy (PALS), 2 angular correlation of annihilation radiation (ACAR), 8 and age-momentum correlation spectroscopy (AMOC). 9 Now that to these events the stimulating and contemplated effect of coherent emission of γ-rays via Bose-Einstein condensation 10 has been added with a further motivation, which in fact beckons more intense investigations in the field.…”

Section: Introductionmentioning

confidence: 99%

Effect of Temperature on Positronium Annihilation in Silica Gel

Dutta¹,

Ganguly²,

Chatterjee³

et al. 2005

J. Phys. Chem. B

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A systematic temperature-dependent study of positronium annihilation rate within the void spaces (micro- and mesopores) of silica gel material has been performed through positronium annihilation spectroscopy. The results find their plausible interpretation through a novel theoretical explanation based on vibrational interaction of thermally energized atoms on the surface layer of the pores with positronium, which in fact justifies the observed increase in the annihilation rate of the latter, with the increase in temperature.

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“…[49][50][51] When the sample was slowly heated up to 420°C, the s 3 value suddenly fell by 0.175 ns and remained almost unchanged thereafter. However, the o-Ps intensity showed a small increase at 420°C and remained constant on the subsequent isothermal pyrolysis at 420°C for up to 45 min.…”

Section: Full Papermentioning

confidence: 99%

Hierarchical Porosity in Self‐Assembled Polymers: Post‐Modification of Block Copolymer–Phenolic Resin Complexes by Pyrolysis Allows the Control of Micro‐ and Mesoporosity

Valkama¹,

Nykänen²,

Kosonen³

et al. 2006

Adv Funct Materials

105

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It is shown that self‐assembled hierarchical porosity in organic polymers can be obtained in a facile manner based on pyrolyzed block‐copolymer–phenolic resin nanocomposites and that a given starting composition can be post‐modified in a wide range from monomodal mesoporous materials to hierarchical micro‐mesoporous materials with a high density of pores and large surface area per volume unit (up to 500–600 m2 g–1). For that purpose, self‐assembled cured composites are used where phenolic resin is templated by a diblock copolymer poly(4‐vinylpyridine)‐block‐polystyrene (P4VP‐b‐PS). Mild pyrolysis conditions lead only to monomodal mesoscale porosity, as essentially only the PS block is removed (length scale of tens of nanometers), whereas during more severe conditions under prolonged isothermal pyrolysis at 420 °C the P4VP chains within the phenolic matrix are also removed, leading to additional microporosity (sub‐nanometer length scale). The porosity is analyzed using transmission electron microscopy (TEM), small‐angle X‐ray scattering, electron microscopy tomography (3D‐TEM), positron annihilation lifetime spectroscopy (PALS), and surface‐area Brunauer–Emmett–Teller (BET) measurements. Furthermore, the relative amount of micro‐ and mesopores can be tuned in situ by post modification. As controlled pyrolysis leaves phenolic hydroxyl groups at the pore walls and the thermoset resin‐based materials can be easily molded into a desired shape, it is expected that such materials could be useful for sensors, separation materials, filters, and templates for catalysis.

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Positron Annihilation Studies in Silica Supported Nickel Carbonate Systems

Cited by 10 publications

References 27 publications

Acidity Effects in Positron Annihilation Lifetime Spectroscopy of Zeolites

Acidity Effects in Positron Annihilation Lifetime Spectroscopy of Zeolites

Effect of Temperature on Positronium Annihilation in Silica Gel

Hierarchical Porosity in Self‐Assembled Polymers: Post‐Modification of Block Copolymer–Phenolic Resin Complexes by Pyrolysis Allows the Control of Micro‐ and Mesoporosity

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