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Optical absorption properties of mineral dust particles generated by storm events in a desert environment
Martin Rigler, Asta Gregorič, Matic Ivančič, Mohamed M. Mahfouz, Bálint Alföldy, 2021, objavljeni povzetek znanstvenega prispevka na konferenci

Najdeno v: ključnih besedah
Ključne besede: mineral dust, optical absorption
Objavljeno: 17.11.2021; Ogledov: 623; Prenosov: 27
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The role of substrate on thermal evolution of Ag/TiO[sub]2 nanogranular thin films
Vincenzo Balzano, Emanuele Cavaliere, Mattia Fanetti, Sandra Gardonio, Luca Gavioli, 2021, izvirni znanstveni članek

Najdeno v: ključnih besedah
Povzetek najdenega: ...thin film, substrate driven properties, morphology, optical absorption, Ag/TiO2...
Ključne besede: nanogranular composite thin film, substrate driven properties, morphology, optical absorption, Ag/TiO2
Objavljeno: 03.12.2021; Ogledov: 517; Prenosov: 35
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Monitoring of chemical processes at the atomic level by X-ray absorption spectrometry using extremely bright synchrotron radiation sources
Iztok Arčon, vabljeno predavanje na konferenci brez natisa

Opis: X-ray absorption spectroscopy (XAS) is a powerful tool for characterisation of local structure and chemical state of selected elements in different new functional materials and biological or environmental samples. The XAS spectroscopy is based on extremely bright synchrotron radiation X-rays sources, which allow precise characterisation of bulk, nanostructured or highly diluted samples. The rapid development of extremely bright synchrotron sources of X-ray and ultraviolet light in recent years has opened new possibilities for research of matter at the atomic or molecular level, indispensable in the development of new functional nanostructured materials with desired properties. The lecture will present the possibilities offered by X-ray absorption spectroscopy with synchrotron light for ex-situ and in-situ or operando characterization of various functional porous and other nanomaterials before, after and during their operation. With the operando micro-XANES and EXAFS methods it is possible to track changes in the valence states and local structures of selected elements in different energy storage materials or in various (photo)catalysts, during chemical reactions under controlled reaction conditions, thus gaining insight into the dynamic functional properties and reaction mechanisms of these materials. New synchrotron light sources also opened the possibility of combining X-ray absorption or emission spectroscopy and microscopy with a resolution of up to a few tens of nanometres, crucial for analysis of environmental and biological samples on sub-cellular level, to understand the mechanisms of uptake, transport, accumulation, and complexation of metal cations on subcellular level in various plant tissues or accumulation in environment, to develop effective remediation approaches.
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Ključne besede: X-ray absorption spectroscopy, EXAFS, XANES, synchrotron radiation sources, operando
Objavljeno: 15.12.2021; Ogledov: 611; Prenosov: 0
.pdf Polno besedilo (287,07 KB)

Photoexcitation processes in atoms
Jana Padežnik Gomilšek, Iztok Arčon, Alojz Kodre, 2021, samostojni znanstveni sestavek ali poglavje v monografski publikaciji

Opis: Photoelectric absorption is characterized by a smooth power-law decrease of the cross section with photon energy. Absorption edges reveal rich structure, which continues into the high-energy side. The quasiperiodic signal, superposed onto the smooth basis, due to scattering of the photoelectron on the neighbours of the target atom provides the basis for the structural (XAFS) analysis of the material. Irregular tiny resonances and edges that appear over the same general range as XAFS are recognized as intra-atomic effects: multielectron excitations (MEE) owing to correlated motion in the electronic cloud. The systematic study of MEE began on noble gases and metallic vapours, both of which are gases of free atoms. With some extremely strong MEE, mostly coexcitations of the subvalence d and f electrons, the structural XAFS analysis may be compromised; hence, there is a need to independently determine the MEE signal, the atomic absorption background (AAB) for the analyzed element, and remove it prior to analysis. In view of the scarcity of elements which can practically be prepared in a free-atom gas state, several approaches to approximate the AAB have been developed: analysis of disordered compounds, where the weak and simple XAFS signal can be modelled and removed, and correlation analysis of the absorption spectra of several independent samples, where the AAB is extracted in an iterative procedure.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Photoelectric absorption is characterized by a smooth power-law decrease...
Ključne besede: photoexcitation, XAFS, multielectron excitations, atomic absorption background
Objavljeno: 15.12.2021; Ogledov: 613; Prenosov: 0
.pdf Polno besedilo (3,26 MB)

Contribution of coal combustion to black carbon
A. I. Calvo, A. Castro, E. Coz, F. Oduber, A. S. H. Prevot, Griša Močnik, C. Blanco-Alegre, Paulo Fialho, C. Alves, F. Giardi, G. Pazzi, R. Fraile, 2022, izvirni znanstveni članek

Najdeno v: ključnih besedah
Povzetek najdenega: ... absorption coefficient, coal-mining, equivalent black carbon, meteorological variables,...
Ključne besede: absorption coefficient, coal-mining, equivalent black carbon, meteorological variables, seasonal pattern
Objavljeno: 03.01.2022; Ogledov: 458; Prenosov: 0
.pdf Polno besedilo (9,47 MB)

Structure and population of complex ionic species in FeCl[sub]2 aqueous solution by X-ray absorption spectroscopy
Matjaž Valant, Iztok Arčon, Uroš Luin, 2022, izvirni znanstveni članek

Opis: Technologies for mass production require cheap and abundant materials such as ferrous chloride (FeCl2). The literature survey shows the lack of experimental studies to validate theoretical conclusions related to the population of ionic Fe-species in the aqueous FeCl2 solution. Here, we present an in situ X-ray absorption study of the structure of the ionic species in the FeCl2 aqueous solution at different concentrations (1–4 molL−1) and temperatures (25–80 ◦C). We found that at low temperature and low FeCl2 concentration, the octahedral first coordination sphere around Fe is occupied by one Cl ion at a distance of 2.33 (±0.02) Å and five water molecules at a distance of 2.095 (±0.005) Å. The structure of the ionic complex gradually changes with an increase in temperature and/or concentration. The apical water molecule is substituted by a chlorine ion to yield a neutral Fe[Cl2(H2O)4]0. The observed substitutional mechanism is facilitated by the presence of the intramolecular hydrogen bonds as well as entropic reasons. The transition from the single charged Fe[Cl(H2O)5]+ to the neutral Fe[Cl2(H2O)4]0 causes a significant drop in the solution conductivity, which well correlates with the existing conductivity models.
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Ključne besede: structure, population, ionic species, aqueous ferrous chloride, in situ X-ray absorption spectroscopy
Objavljeno: 24.01.2022; Ogledov: 577; Prenosov: 13
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Comparing black-carbon- and aerosol-absorption-measuring instruments – a new system using lab-generated soot coated with controlled amounts of secondary organic matter
Antti-Pekka Hyvärinen, Konstantina Vasilatou, Matthias Oscity, Ernest Weingartner, Bradley Visser, Jannis Röhrbein, Luka Drinovec, Daniel M. Kalbermatter, Griša Močnik, 2022, izvirni znanstveni članek

Opis: We report on an inter-comparison of black-carbon- and aerosol-absorption-measuring instruments with laboratory-generated soot particles coated with controlled amounts of secondary organic matter (SOM). The aerosol generation setup consisted of a miniCAST 5201 Type BC burner for the generation of soot particles and a new automated oxidation flow reactor based on the micro smog chamber (MSC) for the generation of SOM from the ozonolysis of α-pinene. A series of test aerosols was generated with elemental to total carbon (EC  TC) mass fraction ranging from about 90 % down to 10 % and single-scattering albedo (SSA at 637 nm) from almost 0 to about 0.7. A dual-spot Aethalometer AE33, a photoacoustic extinctiometer (PAX, 870 nm), a multi-angle absorption photometer (MAAP), a prototype photoacoustic instrument, and two prototype photo-thermal interferometers (PTAAM-2λ and MSPTI) were exposed to the test aerosols in parallel. Significant deviations in the response of the instruments were observed depending on the amount of secondary organic coating. We believe that the setup and methodology described in this study can easily be standardised and provide a straightforward and reproducible procedure for the inter-comparison and characterisation of both filter-based and in situ black-carbon-measuring (BC-measuring) instruments based on realistic test aerosols.
Najdeno v: ključnih besedah
Ključne besede: black carbon, aerosol absorption, secondary organic aerosol, coating
Objavljeno: 01.02.2022; Ogledov: 465; Prenosov: 13
.pdf Polno besedilo (752,94 KB)

A dual-wavelength photothermal aerosol absorption monitor
Konstantina Vasilatou, Griša Močnik, Ernest Weingartner, Daniel M. Kalbermatter, Bradley Visser, Jannis Röhrbein, Luca Ferrero, Kristijan Vidović, Mario Kurtjak, Miha Škarabot, Luka Pirker, Luka Drinovec, Uroš Jagodič, 2022, izvirni znanstveni članek

Opis: There exists a lack of aerosol absorption measurement techniques with low uncertainties and without artefacts. We have developed the two-wavelength Photothermal Aerosol Absorption Monitor (PTAAM-2λ), which measures the aerosol absorption coefficient at 532 and 1064 nm. Here we describe its design, calibration and mode of operation and evaluate its applicability, limits and uncertainties. The 532 nm channel was calibrated with ∼ 1 µmol mol−1 NO2, whereas the 1064 nm channel was calibrated using measured size distribution spectra of nigrosin particles and a Mie calculation. Since the aerosolized nigrosin used for calibration was dry, we determined the imaginary part of the refractive index of nigrosin from the absorbance measurements on solid thin film samples. The obtained refractive index differed considerably from the one determined using aqueous nigrosin solution. PTAAM-2λ has no scattering artefact and features very low uncertainties: 4 % and 6 % for the absorption coefficient at 532 and 1064 nm, respectively, and 9 % for the absorption Ångström exponent. The artefact-free nature of the measurement method allowed us to investigate the artefacts of filter photometers. Both the Aethalometer AE33 and CLAP suffer from cross-sensitivity to scattering – this scattering artefact is most pronounced for particles smaller than 70 nm. We observed a strong dependence of the filter multiple scattering parameter on the particle size in the 100–500 nm range. The results from the winter ambient campaign in Ljubljana showed similar multiple scattering parameter values for ambient aerosols and laboratory experiments. The spectral dependence of this parameter resulted in AE33 reporting the absorption Ångström exponent for different soot samples with values biased 0.23–0.35 higher than the PTAAM-2λ measurement. Photothermal interferometry is a promising method for reference aerosol absorption measurements.
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Ključne besede: aerosol absorption, calibration, black carbon
Objavljeno: 28.06.2022; Ogledov: 120; Prenosov: 3
.pdf Polno besedilo (2,90 MB)
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