Complexation of heavy metal cations with imidazolium ionic liquids lowers their reduction energy: implications for electrochemical separations

Ionic liquids (ILs) are emerging as potential materials for the separation of heavy metals from complex feed streams through selective complexation. A predictive understanding of the coordination chemistry between ILs...


Operando Raman Spectroscopy
An aqueous solution of 1 M EMIMCl + 10 mM PbCl2 was filled into a glass NMR tube (5 mm diameter, Wilmad® NMR tubes, Sigma Aldrich), sealed, and mounted on an aluminum sample holder with a built-in temperature control system.Raman spectroscopy measurements were performed using an in-house spectrometer equipped with a 633 nm excitation laser and a chargecoupled device (CCD) detection system (Andor, Shamrock 303i and iDus 416).The objective lens of the Raman microscope was placed at the curved edge of the NMR tube and a laser beam with an intensity of 2  3 mW was focused on the sample.The presented Raman data is spatially (10 spectra in an area of 1 x 1 mm 2 ) and temporally (integration time of 360 sec/spectra) averaged to ensure sample integrity throughout the measurements.Raman spectra were collected as a function of temperature after the set temperature was reached for 1 hour.The spectra resolution of Raman spectra is 2 cm -1          Table S3.Diffusion coefficients of H2O and EMIM + and their ratios measured using pulsed field gradient (PFG)-NMR.

Figure S3 .
Figure S3.(A) Raman spectra in the range of 140  4000 cm -1 and (B) 140  400 cm -1 with deconvoluted fitting for the 1 M EMIMCl + 10 mM PbCl2 aqueous solution.The inset of (B) is the spectrum between 140  200 cm -1 .(C) Change in the percent intensity of the Pb-Cl peak in PbCl2 and Pb-Clb in the EMIMCl-PbCl2 complex as a function of temperature.

Figure S4 .
Figure S4.Visualization of the calculated HOMO and LUMO for gas phase PbCl3 -clusters with EMIMCl.

Figure S5 .
Figure S5.Visualization of the calculated HOMO and LUMO for gas phase Pb2Cl5 -clusters with EMIMCl.

Figure S6 .
Figure S6.Visualization of the calculated HOMO and LUMO for aqueous phase Pb-Cl clusters with EMIM + cations identified by experimental NMR shifts.

Figure S9 .
Figure S9.Visualization of the calculated ESP for aqueous phase PbCl4-5 clusters with EMIM cations identified by experimental NMR shifts.
aThe experimental ADE represents an estimate of its upper limit.

Table S2 .
NMR 1 H T 1 and T 2 values of the two solutions containing EMIMCl and the difference in T 1 and T 2 values.

Table S4 .
Calculated HOMO and LUMO energies and HOMO-LUMO gaps of gas-phase PbCl3 - and Pb2Cl5 -clusters and their complexes with EMIMCl as a function of EMIMCl molecules.

Table S5 .
Calculated HOMO and LUMO energies and HOMO-LUMO gaps of solution-phase PbCl2, PbCl3 -, PbCl4 2-and PbCl5 3-clusters and their complexes with EMIMCl as a function of EMIMCl molecules.