Issue 4, 2021

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

Abstract

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.

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

Article information

Article type
Paper
Submitted
20 Oct 2020
Accepted
26 Dec 2020
First published
07 Jan 2021
This article is Open Access
Creative Commons BY license

RSC Adv., 2021,11, 2103-2111

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

A. R. Abid, M. Reinhardt, N. Boudjemia, E. Pelimanni, A. R. Milosavljević, C. Saak, M. Huttula, O. Björneholm and M. Patanen, RSC Adv., 2021, 11, 2103 DOI: 10.1039/D0RA08943E

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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