University of Oulu

RSC Adv., 2021,11, 2103-2111,

The effect of relative humidity on CaCl₂ nanoparticles studied by soft X-ray absorption spectroscopy

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Author: Abid, Abdul Rahman1,2; Reinhardt, Maximilian1; Boudjemia, Nacer1;
Organizations: 1Nano and Molecular Systems Research Unit, Faculty of Science, University of Oulu, P.O. Box 3000, 90570 Oulu, Finland
2Molecular and Condensed Matter Physics, Uppsala University, Ångströmlaboratoriet, Uppsala, Sweden
3SOLEIL Synchrotron Facility, L'Orme des Merisiers, BP 48, 91190 Saint-Aubin, France
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Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.1 MB)
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Language: English
Published: Royal Society of Chemistry, 2021
Publish Date: 2021-01-18


Ca- and Cl-containing nanoparticles are common in atmosphere, originating for example from desert dust and sea water. The properties and effects on atmospheric processes of these aerosol particles depend on the relative humidity (RH) as they are often both hygroscopic and deliquescent. We present here a study of surface structure of free-flying CaCl₂ nanoparticles (CaCl₂-NPs) in the 100 nm size regime prepared at different humidity levels (RH: 11–85%). We also created mixed nanoparticles by aerosolizing a solution of CaCl₂ and phenylalanine (Phe), which is a hydrophobic amino acid present in atmosphere. Information of hydration state of CaCl₂-NPs and production of mixed CaCl₂ + Phe nanoparticles was obtained using soft X-ray absorption spectroscopy (XAS) at Ca 2p, Cl 2p, C 1s, and O 1s edges. We also report Ca 2p and Cl 2p X-ray absorption spectra of an aqueous CaCl₂ solution. The O 1s X-ray absorption spectra measured from hydrated CaCl2-NPs resemble liquid-like water spectrum, which is heavily influenced by the presence of ions. Core level spectra of Ca²⁺ and Cl⁻ ions do not show a clear dependence of % RH, indicating that the first coordination shell remains similar in all measured hydrated CaCl₂-NPs, but they differ from aqueous solution and solid CaCl₂.

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Series: RSC advances
ISSN: 2046-2069
ISSN-E: 2046-2069
ISSN-L: 2046-2069
Volume: 4
Issue: 11
Pages: 2103 - 2111
DOI: 10.1039/D0RA08943E
Type of Publication: A1 Journal article – refereed
Field of Science: 116 Chemical sciences
Funding: The research leading to this result has been supported by the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie I4Future (Grant agreement no. 713606). This project was also granted travel funding from CALIPSOPlus from the EU Framework Programme for Research and Innovation Horizon 2020 (Grant agreement no. 730872) and the Magnus Ehrnrooth Foundation, Finland. MR, MP, EP, and MH acknowledge the Academy of Finland funding. EP further acknowledges the financial support from the Finnish Cultural Foundation. OB acknowledges funding from the Swedish Research Council (VR) for the project VR 2017-04162.
EU Grant Number: (713606) I4FUTURE - Novel Imaging and Characterisation Methods in Bio, Medical, and Environmental Research and Technology Innovations
Copyright information: © 2021 The Author(s). Published by the Royal Society of Chemisty. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.