Competitive positron and positronium trapping in porous media

Kajcsos, Zs.; Liszkay, L.; Duplâtre, G.; Lázár, K.; Lohonyai, L.; Varga, L.K.; Gordo, P.M.; Lima, A.P. de; Gil, C. Lopes; Marques, M.F. Ferreira; Bosnar, D.; Bosnar, Sanja; Kosanović, Cleo; Subotić, Boris

doi:10.1016/j.radphyschem.2006.03.041

Cited by 16 publications

(3 citation statements)

References 19 publications

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“…When increasing further the Co/Mo ratio up to 1.12, a similar trend was observed, namely, the positron lifetime components τ 1 (∼0.193–0.195 ns) and τ 2 (∼0.399 ns) remained almost the same. The associated I 1 value kept increasing slightly, while the I 2 decreased slightly to fulfill a total intensity of 100% . A slight decrease in I 2 implied a decrease in the concentration of Mo,S-vacancy clusters.…”

Section: Resultsmentioning

confidence: 94%

“…The associated I 1 value kept increasing slightly, while the I 2 decreased slightly to fulfill a total intensity of 100%. 34 A slight decrease in I 2 implied a decrease in the concentration of Mo,S-vacancy clusters. Looking in the size of vacancy clusters, it slightly increased from V 8 in the Co 0.18 MoS sample to V 11 in the Co 0.72 MoS and Co 1.12 MoS ones (Figure 3e).…”

Section: Introductionmentioning

confidence: 99%

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Exploring the Sub-nanoscale Structure of Cobalt Molybdenum Sulfide and the Role of a Cobalt Promoter in Catalytic Hydrogen Evolution

Nguyen¹,

Luu

Nguyen³

et al. 2023

ACS Appl. Mater. Interfaces

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Cobalt-promoted molybdenum sulfide (CoMoS) is known as a promising catalyst for H2 evolution reaction and hydrogen desulfurization reaction. This material exhibits superior catalytic activity as compared to its pristine molybdenum sulfide counterpart. However, revealing the actual structure of cobalt-promoted molybdenum sulfide as well as the plausible contribution of a cobalt promoter is still challenging, especially when the material has an amorphous nature. Herein, we report, for the first time, on the use of positron annihilation spectroscopy (PAS), being a nondestructive nuclear radiation-based method, to visualize the position of a Co promoter within the structure of MoS at the atomic scale, which is inaccessible by conventional characterization tools. It is found that at low concentrations, a Co atom occupies preferably the Mo-vacancies, thus generating the ternary phase CoMoS whose structure is composed of a Co-S-Mo building block. Increasing the Co concentration, e.g., a Co/Mo molar ratio of higher than 1.12/1, leads to the occupation of both Mo-vacancies and S-vacancies by Co. In this case, secondary phases such as MoS and CoS are also produced together with the CoMoS one. Combining the PAS and electrochemical analyses, we highlight the important contribution of a Co promoter to enhancing the catalytic H2 evolution activity. Having more Co promoter in the Mo-vacancies promotes the H2 evolution rate, whereas having Co in the S-vacancies causes a drop in H2 evolution ability. Furthermore, the occupation of Co to the S-vacancies leads also to the destabilization of the CoMoS catalyst, resulting in a rapid degradation of catalytic activity.

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Section: Resultsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Exploring the Sub-nanoscale Structure of Cobalt Molybdenum Sulfide and the Role of a Cobalt Promoter in Catalytic Hydrogen Evolution

Nguyen¹,

Luu

Nguyen³

et al. 2023

ACS Appl. Mater. Interfaces

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“…The other components carry the relavant information on the inside status of pores. The longer life-time (1 -5 ns) can be attributed to the positronuim trapped in microvoids (small zeolite cages), and the longest one (10 -50 ns) may correspond to the annihilation events originated from elongated channels of the structure [15]. Evaluating the data obtained for the A type samples it can be concluded first that the sum of the intensities of the two longest lifetime components does not exceed 2.5 %.…”

Section: Figure 1mössbauer Spectra Of Fe-fer and (Alfe)-fer Samplesmentioning

confidence: 87%

o-Ps Lifetimes in Iron Containing Micro- and Mesoporous Media

Dũng

Lázár

Havancsák

et al. 2012

MSF

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Positron annihilation lifetime (LT) measurements were used to study the influence of addition of iron on ortho-positronium (o-Ps) in micro and mesoporous media. Three types of porous samples containing iron were chosen for the investigation. LT spectra were decomposed to four components in the 0.1 - 50 ns lifetime range. An attempt is made to correlate the data with sites occupied by iron in the framework as derived from Mössbauer studies. No significant correlation could be detected in this respect. Instead, dominating role of presence or absence of iron can be deduced. Certain influence can also be attributed to the presence of adsorbed water.

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Positron Annihilation Lifetimes in Cucurbiturils: Evidence of Internal Inclusion of Gold in CB[7]

2009

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Positron annihilation lifetime (PAL) measurements are carried out to determine the cavity dimensions of hydrated and dehydrated cucurbiturils (CB[n]; n=5,6,7,8). In the case of hydrated samples, the dimensions of the cavity are unrelated to the number of glycoluril units of the CB, whereas for dehydrated samples the cavity dimensions measured by PAL follow the expected order, although the experimental values obtained by PAL are significantly smaller than the dimensions of each CB determined by crystallography. For a host-guest complex in which colloidal gold nanoparticles are assumed to be included inside CB[7], a significant reduction of the cavity size is measured. This represents an experimental evidence of the inclusion of gold inside CB[7], which complements previous high-resolution transmission electron microscopy (TEM) images.

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Competitive positron and positronium trapping in porous media

Cited by 16 publications

References 19 publications

Exploring the Sub-nanoscale Structure of Cobalt Molybdenum Sulfide and the Role of a Cobalt Promoter in Catalytic Hydrogen Evolution

Exploring the Sub-nanoscale Structure of Cobalt Molybdenum Sulfide and the Role of a Cobalt Promoter in Catalytic Hydrogen Evolution

o-Ps Lifetimes in Iron Containing Micro- and Mesoporous Media

Positron Annihilation Lifetimes in Cucurbiturils: Evidence of Internal Inclusion of Gold in CB[7]

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