*2.5. 1H NMR*

The 1H NMR spectra of [C4mim]Cl were also measured (see Figure 4). The yield of [C4mim]Cl was 98.2%. The structure and impurities of [C4mim]Cl are shown in Figure 4a. The 1H NMR analysis of [C4mim]Cl revealed values of δ 9.66 (s, 1 H), 8.00 (t, *J* = 1.6 Hz, 1 H), 7.87 (t, *J* = 1.6 Hz, 1 H), 4.23 (t, *J* = 7.2 Hz, 2 H), 3.09 (s, 3 H), 1.75 (m, 2 H), 1.22 (m, 2 H) and 0.84 (t, *J* = 7.6 Hz). In Figure 4b, interactions occurred between [C4mim]<sup>+</sup> and the different extracts. Therefore, a downshift of the protons in the imidazole ring (δ 9.66→9.69) was observed. The chemical structure of the imidazole ring in [C4mim]+ was slightly disturbed in the presence of vermiculite (see Figure 4c). However, HA and Cr(VI) were the main species that were observed to interact with the imidazole ring in [C4mim]<sup>+</sup> because the same field shifts (δ 9.66→9.68 and 9.66→9.72) were also obtained in Figure 4d,e. Note that less 1% of the Cr(III) compounds was able to be extracted into [C4mim]Cl [32]. Moreover, the intensities at δ 3.69 were diminished due to interactions between the methyl protons in [C4mim]+ and the extracts (vermiculite, humic acid, and Cr(VI)), as seen in Figure 4. The 1-methylimidazole in [C4mim]Cl played an important role in extracting the Cr(VI), which bonded with HA on the vermiculite, transforming it into the [C4mim]Cl phase. Weaker

interaction between [C4mim]Cl and the vermiculite was shown to affect the extraction efficiency of Cr(VI).

**Figure 4.** The 1H NMR spectra of (**a**) [C4mim]Cl, (**b**) Cr-contaminated simulated sorbent in soil remediation–extracted [C4mim]Cl, (**c**) vermiculite-extracted [C4mim]Cl, (**d**) humic acid–extracted [C4mim]Cl, and **(e)** Cr(VI)–extracted [C4mim]Cl.
