n-Heptane adsorption in periodic mesoporous silica by in situ positron annihilation lifetime spectroscopy

2013 ◽  
Vol 179 ◽  
pp. 104-110 ◽  
Author(s):  
Agnieszka Kierys ◽  
Radosław Zaleski ◽  
Marek Gorgol ◽  
Jacek Goworek
Keyword(s):  
Mesoporous Silica ◽  
Positron Annihilation ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Annihilation Lifetime

Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

2010 ◽  
Vol 666 ◽  
pp. 99-102 ◽  
Author(s):  
Maria Fatima Ferreira Marques ◽  
A.M.G. Moreira Da Silva ◽  
P.M. Gordo ◽  
Z. Kajcsos
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Source ◽  
Lifetime Component ◽  
Positron Annihilation Lifetime ◽  
Long Lifetime

Positron annihilation lifetime spectroscopy was used to study the free-volume parameters in various pure -, - and -cyclodextrins samples and, in the case of β-cyclodextrin, with inclusion of S-carvone and thymoquinone. The results clearly indicate the presence of long lifetime components related to Ps-formation. The data show that the addition of S-carvone to β-cyclodextrin results in a decrease of o-Ps lifetime that we ascribe to a reduction of free volume holes from 81.8 to 63.7 Å3. The long lifetime component disappears when thymoquinone is added to -cyclodextrin, indicating this substance acts as an o-Ps quencher. For all samples studied, a decrease in the long lifetime component values was observed with increasing source in situ time, a result that might be attributed to the irradiation of the sample by the 22Na positron source.

In Situ Monitoring of Adsorption and Desorption of n-Heptane on Porous Silica by Positron Annihilation Lifetime Spectroscopy

2012 ◽  
Vol 733 ◽  
pp. 207-211 ◽  
Author(s):  
Radosław Zaleski ◽  
Waldemar Dolecki ◽  
Jacek Goworek
Keyword(s):  
Positron Annihilation ◽  
Porous Silica ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Intensity Change ◽  
Adsorption And Desorption ◽  
Positron Annihilation Lifetime ◽  
Adsorption Desorption ◽  
Kinetics Of ◽  
Insight Into

Positron annihilation lifetime spectroscopy study of n-heptane adsorption and desorption on silica gel Si-60 gives insight into a free volume evolution during those processes. Analysis of the lifetime distribution allows to ascribe particular ortho-positronium components to silica walls, mesopores and n-heptane. Hysteresis loop of the intensities of the mesopore and n-heptane related components similar to classic adsorption/desorption isotherms is observed. Transition from an adsorbate multilayer structure to liquid when pores become completely filled, manifests itself as an intensity change. Kinetics of desorption and adsorption studies allows to determine the time of reaching the equilibrium by the Si 60–n-heptane system at various pressures.

scholarly journals In situinvestigation of the kinetics and microstructure during photopolymerization by positron annihilation technique and NIR-photorheology

RSC Advances ◽  
2018 ◽  
Vol 8 (65) ◽  
pp. 37085-37091 ◽  
Author(s):  
Helena Švajdlenková ◽  
Ondrej Šauša ◽  
Gernot Peer ◽  
Christian Gorsche
Keyword(s):  
Positron Annihilation ◽  
Microstructural Evolution ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Annihilation Lifetime ◽  
Sensitive Tool

Positron annihilation lifetime spectroscopy is a sensitive tool for thein situstudy of the microstructural evolution during photopolymerization.

Positron Annihilation Lifetime Spectroscopy Application to In Situ Monitoring of n-Heptane Sorption in Mesopores

2017 ◽  
Vol 373 ◽  
pp. 288-294
Author(s):  
Radosław Zaleski ◽  
Marek Gorgol ◽  
Agnieszka Kierys
Keyword(s):  
Positron Annihilation ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Exponential Functions ◽  
Spectra Analysis ◽  
Time Constants ◽  
Positron Annihilation Lifetime ◽  
Cylindrical Pores ◽  
Simplified Method ◽  
Time Required

The dynamics of n-heptane adsorption and desorption on two silicas (Si-A and SBA-15) with different porosity was studied using positron annihilation lifetime spectroscopy (PALS). Simplified method of spectra analysis consisting in the summation of counts in the long-lived part of PALS spectra was used. It allowed to observe changes occurring in the minute time scale. The dependence of the number of counts on time could be fairly well approximated by exponential functions. It was found that the time required for reaching equilibrium in long cylindrical pores is up to ten times longer than in bell-mouthed interconnected ones. The longest time constants (ca. 5 min in Si-A and ca. 60 min in SBA-15) were observed for desorption in both samples.

scholarly journals Open Porosity and Pore Size Distribution of Mesoporous Silica Films Investigated by Positron Annihilation Lifetime Spectroscopy and Ellipsometric Porosimetry

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3371
Author(s):  
Bangyun Xiong ◽  
Jingjing Li ◽  
Chunqing He ◽  
Jiale Lai ◽  
Xiangjia Liu ◽  
...  
Keyword(s):  
Mesoporous Silica ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Positron Annihilation ◽  
Open Porosity ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Silica Films ◽  
Ellipsometric Porosimetry ◽  
Positron Annihilation Lifetime

Tunable mesoporous silica films were prepared though a sol-gel process directed by the self-assembly of various triblock copolymers. Positron annihilation γ-ray energy spectroscopy and positron annihilation lifetime spectroscopy (PALS) based on intense pulsed slow positron beams as well as ellipsometric porosimetry (EP) combined with heptane adsorption were utilized to characterize the open porosity/interconnectivity and pore size distribution for the prepared films. The consistency between the open porosities was examined by the variations of orthopositronium (o-Ps) 3γ annihilation fractions and the total adsorbed volumes of heptane. The average pore sizes deduced by PALS from the longest-lived o-Ps lifetimes are in good agreement with those by EP on the basis of the Barrett–Joyner–Halenda model, as indicated by a well fitted line of slope k = 1. The results indicate that the EP combined with heptane adsorption is a useful method with high sensitivity for calibrating the mesopore size in highly interconnected mesoporous films, whereas PALS is a novel, complementary tool for characterizing both closed and open pores in them.

Porous Structure of Mesoporous Silica Studied by Positron Annihilation Lifetime Spectroscopy

2008 ◽  
Vol 607 ◽  
pp. 207-209
Author(s):  
Yang Xi ◽  
Wei Chang Hao ◽  
Dan Ni Wang ◽  
Tian Min Wang ◽  
Run Sheng Yu ◽  
...  
Keyword(s):  
Mesoporous Silica ◽  
Porous Structure ◽  
Positron Annihilation ◽  
Silica Particles ◽  
Tetraethyl Orthosilicate ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Ammonium Bromide ◽  
Structure Directing Agent ◽  
Structure Information ◽  
Positron Annihilation Lifetime

In this paper, a series of mesoporous silica particles with different pore diameters were fabricated using tetraethyl orthosilicate (TEOS) as the network precursor, hexadecyl trimethyl ammonium bromide (CTAB) as a structure directing agent and 1,3,5-Trimethylbenzene (TMB) as a pore enlarge reagent. Compared with SAXRD and BET, the PALS may not only show the mesoporous information but also provide the structure information of microporous.

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