JOURNAL ARTICLE

Hygroscopic Properties of CH<sub>3</sub>SO<sub>3</sub>Na, CH<sub>3</sub>SO<sub>3</sub>NH<sub>4</sub>, (CH<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>Mg, and (CH<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>Ca Particles Studied by micro-FTIR Spectroscopy

Yong Liu (6908)Alexander Laskin (1354857)

Year: 2016 Journal:   OPAL (Open@LaTrobe) (La Trobe University)   Publisher: La Trobe University

Abstract

The hygroscopic behavior of CH<sub>3</sub>SO<sub>3</sub>Na, CH<sub>3</sub>SO<sub>3</sub>NH<sub>4</sub>, (CH<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>Mg, and (CH<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>Ca particles as a function of relative humidity (RH) has been studied using microscopic Fourier transform infrared (micro-FTIR) spectroscopy. The approach used exposure of substrate-deposited, ∼1 μm dry-size particles to humidified nitrogen followed by micro-FTIR spectroscopy over a selected sample area. The results show that CH<sub>3</sub>SO<sub>3</sub>Na particles undergo characteristic phase transitions at deliquescence relative humidity (DRH) of 71% and efflorescence relative humidity (ERH) of ∼40%. In contrast, CH<sub>3</sub>SO<sub>3</sub>NH<sub>4</sub>, (CH<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>Mg, and (CH<sub>3</sub>SO<sub>3</sub>)<sub>2</sub>Ca particles do not undergo phase transitions and exhibit continuous, reversible uptake and evaporation of water under the influence of changing RH. The extent of water uptake is quantified and presented as water-to-solute ratios (WSR) in particles as a function of RH. The WSR values are determined from the integrated absorbance of the water and the solute-specific bands in IR spectra recorded at different RH.

Keywords:
Relative humidity Efflorescence Analytical Chemistry (journal) Absorbance Evaporation Infrared spectroscopy Spectroscopy Fourier transform infrared spectroscopy

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Solid-state spectroscopy and crystallography
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