Advanced fitting algorithms for analysing positron annihilation lifetime spectra

Pascual-Izarra, C.; Dong, Aurelia W.; Izgorodina, Ekaterina I.; Hill, Anita J.; Boyd, Ben J.; Drummond, Calum J.

doi:10.1016/j.nima.2009.01.205

Cited by 57 publications

(62 citation statements)

References 26 publications

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“…The PALS spectra were best fitted by six exponential lifetime components. Their relative fractions were extracted using a fitting method based on Markov chain MonteCarlo Bayesian inference calculations in the PAScual data suite 53 after subtraction of the background due to accidentals, that is, uncorrelated start-stop signals. The fitting procedure is fully detailed in Supplementary Methods and Supplementary Figs 10 and 11.…”

Section: Discussionmentioning

confidence: 99%

Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

et al. 2014

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Deactivation due to coking limits the lifetime of zeolite catalysts in the production of chemicals and fuels. Superior performance can be achieved through hierarchically structuring the zeolite porosity, yet no relation has been established between the mesopore architecture and the catalyst lifetime. Here we introduce a top-down demetallation strategy to locate mesopores in different regions of MFI-type crystals with identical bulk porous and acidic properties. In contrast, well-established bottom-up strategies as carbon templating and seed silanization fail to yield materials with matching characteristics. Advanced characterization tools capable of accurately discriminating the mesopore size, distribution and connectivity are applied to corroborate the concept of mesopore quality. Positron annihilation lifetime spectroscopy proves powerful to quantify the global connectivity of the intracrystalline pore network, which, as demonstrated in the conversions of methanol or of propanal to hydrocarbons, is closely linked to the lifetime of zeolite catalysts. The findings emphasize the need to aptly tailor hierarchical materials for maximal catalytic advantage.

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Section: Discussionmentioning

confidence: 99%

Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

et al. 2014

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“…Figure 2a shows an example of a timing histogram of the original MFI30 sample fitted with three ortho-positronium (o-Ps) lifetime components (τ 3, τ 4 and τ 5 ), which are used to calculate the mean pore sizes of the samples. Figure 2b (inset) shows the pore size distribution determined using the PAScual fitting program for PALS analysis [31]. PALS is therefore a useful means to observe the hierarchical structure of MFI-type zeolites, with pores of around 0.27 nm, 1.1 nm, and 7.8 nm corresponding to its intracrystalline/intrinsic zeolite channels, intercrystalline micropores and interparticle mesopores respectively.…”

Section: Palsmentioning

confidence: 99%

Designing hierarchical porous features of ZSM-5 zeolites via Si/Al ratio and their dynamic behavior in seawater ion complexes

Zhu

Doherty

et al. 2013

Microporous and Mesoporous Materials

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MFI-type zeolites were characterized using powder x-ray diffraction (XRD), and positron annihilation lifetime spectroscopy (PALS) to uncover the hierarchical porous * Corresponding author. Tel: +61 3 9919 7682; fax: +61 3 9919 7696. Email: mikel.duke@vu.edu.au (M. Duke). overall release of ions, principally Na + and K + , which were liberated mainly from the zeolite channels, yet these materials adsorbed Ca 2+ in the microporous grain boundaries and Mg 2+ in the mesoporous grain boundaries. Si/Al = 100 appeared to be a unique ratio, allowing the material to possess the same Na + adsorption features (and hydrophilicity) of high alumina materials, but ion interactions resembling high silica materials. MFI-type zeolite is therefore shown to be highly configurable using Si/Al ratio for a wide variety of applications in the presence of ions.

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“…26,27,42 The samples were contained in a specially designed insulated copper holder sealed using o-rings to prevent evaporation and temperature controlled using a peltier that is accurate to AE1 1C. 26,27,42 The samples were contained in a specially designed insulated copper holder sealed using o-rings to prevent evaporation and temperature controlled using a peltier that is accurate to AE1 1C.…”

Section: Characterization Of Amphiphile Self-assembly Materialsmentioning

confidence: 99%

“…3). 27,42 Fig . 26,27,42 The two parameters of interest in the following discussion are oPs lifetime (t) and the oPs intensity (I) which are related to molecular packing, with the lifetime representing the relative size of oPs annihilation sites and the intensity representing the relative concentration of sites.…”

Section: Bulk Non-dispersed Lamellar Mesophase Systemsmentioning

confidence: 99%

Packing and mobility of hydrocarbon chains in phospholipid lyotropic liquid crystalline lamellar phases and liposomes: characterisation by positron annihilation lifetime spectroscopy (PALS)

Dong

Fong

Waddington

et al. 2015

Phys. Chem. Chem. Phys.

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Lipid lamellar mesophases and their colloidal dispersions (liposomes) are increasingly being deployed in vivo as drug delivery vehicles, and also as models of biological membranes in fundamental biophysics studies. The permeability and diffusion of small molecules such as drugs is accommodated by a change in local curvature and molecular packing (mesophase behaviour) of the bilayer membrane molecules. Positron annihilation lifetime spectroscopy (PALS) is capable of providing in situ molecular level information on changes in free volume and void space arising from such changes in a non-perturbative manner. In this work PALS was used to systematically characterise the temperature-induced melting transitions (Tm) of saturated and unsaturated phospholipid-water systems while systematically varying lipid chain length, as both bulk lamellar mesophase and as aqueous colloidal dispersions (liposomes). A four-component fit of the data was used that provides separate PALS lifetimes for the aqueous (τ3) and organic domains (τ4). The oPs lifetime (τ4), for the lamellar phases of DSPC (C18:0), DPPC (C16:0), DMPC (C14:0) and DLPC (C12:0) was found to be independent of chain length, with characteristic lifetime value τ4 ∼ 3.4 ns. τ4 is consistently larger in the dispersed liposomes compared to the bulk mesophases, suggesting that the hydrocarbon chains are more mobile. The use of contemporary and consistent analytical approaches as described in this study is the key to future deployment of PALS to interrogate the in situ influence of drugs on membrane and cellular microenvironments.

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Advanced fitting algorithms for analysing positron annihilation lifetime spectra

Cited by 57 publications

References 26 publications

Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

Mesopore quality determines the lifetime of hierarchically structured zeolite catalysts

Designing hierarchical porous features of ZSM-5 zeolites via Si/Al ratio and their dynamic behavior in seawater ion complexes

Packing and mobility of hydrocarbon chains in phospholipid lyotropic liquid crystalline lamellar phases and liposomes: characterisation by positron annihilation lifetime spectroscopy (PALS)

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