Micro-Raman observation on the HPO 4 2- association structures in an individual dipotassium hydrogen phosphate (K 2HPO 4) droplet

Kamran Ajmal Syed, Shu Feng Pang*, Yun Zhang, Guang Zeng, Yun Hong Zhang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)

Abstract

A single K 2HPO 4 droplet with size of ∼50 μm on a Teflon substrate was forced to enter into the supersaturated state by decreasing the relative humidity (RH), allowing accurate control over the concentration of the solute within a droplet of a nanogram. The K 2HPO 4 solutions from dilute (0.1-1.0 mol•L -1 bulk) to concentrated state (a droplet from RH 98.2% to 25.1%) were studied through micro-Raman spectroscopy in the spectral region of about 200-4000 cm -1. The area ratio between the water stretching band to the sum of the ν 1-PO 3, ν 2-POH, and ν 4-PO 3 bands of the HPO 4 2- at various RHs was used to describe the dehydration behavior of a microsized single K 2HPO 4 droplet in dehumidifying process. The peak position of the v 1-PO 3 band for the 1 mol•L -1 bulk solution appeared at 991 cm -1 and moved to 986 cm -1 at 98.2% RH, to 978 cm -1 at 70.2% RH, and then to 964 cm -1 at 30.0% RH for a droplet, accompanying an increase of the full width at half-height (fwhh) of this peak from 16.3 to 17.2, 22.2, and then to 24.2 cm -1, indicating transition of the HPO 4 2- anions from monomers to dimers/trimers/oligomers and then to polyanions with chain structures in the K 2HPO 4 solutions. After 25.1% RH, the solid was proved to be K 2HPO 4•3H 2O according to the Raman spectral features. Furthermore, the O-H stretching envelope of a K 2HPO 4 droplet showed that the intensity ratios of the strong hydrogen bonding component (3255 cm -1) to the weak one (3417 cm -1) and the cage-like water (2925 cm -1) to the weak one (3417 cm -1) were sensitive to the HPO 4 2- association structures, which can be used to understand the effects of dimers/trimers/oligomers and chain structures of the HPO 4 2- associations on the hydrogen bonding of water molecules.

Original languageEnglish
Pages (from-to)1558-1564
Number of pages7
JournalJournal of Physical Chemistry A
Volume116
Issue number6
DOIs
Publication statusPublished - 16 Feb 2012

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