Photon Factory Activity Report 2022 #40 (2023)

BL-7A/2021P012

XAS measurements for ionic liquids: imidazolium salts

Haoran XU, and Takehiko SASAKI*Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa,Chiba, 277-8561, Japan

Absorption (arb. units)

Ionic liquids have received much attention because of
their versatile properties such as electrolytes inelectrochemistry, environmentally friendly solvents inorganic synthesis, and immobilizing phases for biphasic
catalysis. They are also regarded as precursor materials forcatalysts. Dialkylimidazolium and N-alkyl pyridinium orquaternary ammonium based salts are typical ionic liquids
most widely studied due to the ease of synthesis. The
completely ionic nature of ionic liquids makes them useful
as solvents for highly charged complexes and the low
vapor pressure of ionic liquids allows us to use them invacuum and as “green” solvents in industrial processes.
Moreover, when metal ion containing ionic liquids areprepared, a potential catalytic performance was observed.
In this context, application of a new analysis technique onionic liquids is awaited to clarify physical properties ofionic liquids.
XAS measurements for liquid samples have beenenabled by Nagasaka, Kosugi and coworkers, giving new
insights for physicochemical properties of materials [1]. In
this project we have studied N-K edge XAS measurements
for imidazolium salts to examine a possibility to find anovel aspect of ionic liquids by XAS measurements andanalyses.

nitrogen atom. For the simulation of the XAS spectra
quantum chemical calculations and MD calculations
including solvent molecules are underway. It is expectedthat measurements of N-K XAS would give theinformation on the charge of nitrogen atom.

396

398

400

402

404406408

410

Photon energy / eV

Absorption (arb. units)

1 Introduction

2 Experiment
XAS measurements for liquid samples wereconducted at BL7A using facilities developed by Nagasaka
et al. [1]. The liquid sample cell with SiC membranes wasadopted, where the thickness of the liquid layer wascontrolled by the He gas pressure around the cell. The
XAS spectra of the ProLINE polymer film were measured
in parallel to calibrate the photon energies.
3 Results and Discussion
Fig. 1 shows N-K XAS spectra for 1-ethyl-3-methyl
imidazolium chloride (EmimCl) 0.20 M and 0.10 M
aqueous solution samples and 1-butyl-2,3-dimethylimidazolium chloride aqueous solution (0.10M). In allcases a sharp peak at 401.0 eV was found, indicating that
this position is intrinsic to imidazolium N atom without
dependence on concentration and substitute groups.
We also measured N-K XAS spectra for other related
nitrogen-containing molecules (not shown). It was foundthat the peak position is dependent on the charge on396398400402404406408410

Photon energy / eVFig. 1:N-K XAS spectra : Upper panel: EmimCl aqueous
solution (Upper 0.20 M, Lower 0.10 M), Lower panel: 1butyl-2,3-dimethyl-imidazolium chloride aqueous
solution (0.10M)
Acknowledgement
We thank Dr. Masanari Nagasaka (IMS) and Dr.
Fumitoshi Kumaki (PF) for their assistance on thisproject. .
References[1] M. Nagasaka et al., J. Electrosc. Relat. Phenom. 200(2015) 293.
* takehiko@k.u-tokyo.ac.jp