冠醚离子液体萃取分离水溶液中Rb^+和Cs^+

Extraction of Rubidium and Cesium from Aqueous Solution with Crown Ether Ionic Liquids

合成了1-丁基-3-乙酰基苯并21冠7双三氟甲磺酰亚胺盐、1-己基-3-乙酰基苯并21冠7双三氟甲磺酰亚胺盐和1-辛基-3-乙酰基苯并21冠7双三氟甲磺酰亚胺盐3种不同烷基链长的冠醚离子液体([C_n(benzo21C7)AIm]NTf_2,n=4,6,8,简称为C_n-CrownIL)。将合成的冠醚离子液体与1-丁基-3-甲基咪唑双三氟甲磺酰亚胺离子液体([C_4MIm]NTf_2)混合,构建了C_n-CrownIL/[C_4MIm]NTf_2复配系统。结果表明,C_n-CrownIL/[C_4MIm]NTf_2对水溶液中的Rb^+和Cs^+具有非常高的萃取能力,即使溶液中Rb^+和Cs^+质量浓度低至10 mg/L,萃取剂对Rb^+和Cs^+仍保持高达97%以上的萃取率。吸附Rb^+和Cs^+的萃取剂可利用稀硝酸洗脱而实现重复利用,5次循环后,萃取剂对Rb^+和Cs^+的萃取率依然可达90%。理论计算表明,C_4-CrownIL/[C_4MIm]NTf_2萃取Rb^+和Cs^+依赖的是冠醚单元中的O原子与Rb^+和Cs^+之间较强的络合作用,冠醚空腔大小与Rb^+和Cs^+的离子半径高度匹配是C_4-CrownIL/[C_4MIm]NTf_2优先萃取Rb^+和Cs^+的重要原因。

The hydrophobic 1-alkyl-3-acetyl-benzo21 crown 7 bis(trifluoromethylsulfonyl)imide ionic liquid[Cn(benzo21C7)AIm]NTf2(n=4,6,8)abbreviated by Cn-CrownIL were synthesized.The synthesized crown ether ionic liquids were characterized by IR and NMR.The crown ether ionic liquid was mixed with 1-butyl-3-methyl-imidazole bis(trifluoromethylsulfonyl)imide ionic liquid([C4MIm]NTf2)to construct Cn-CrownIL/[C4MIm]NTf2 complexes.It was found that the hydrophobicity of Cn-CrownIL/[C4MIm]NTf2 ensured the formation of a phase separation system of aqueous solution.The results showed that Cn-CrownIL/[C4MIm]NTf2 had a high extraction for Rb^+and Cs^+,the extraction efficiency was almost 100% which was higher than other metal ions,and the order of metal ions extraction efficiency was Cs^+ >Rb^+ >K^+ >Ca^2+ >Na^+ >Mg^2+ >Li^+.Even though the concentrations of Rb^+and Cs^+were as low as 10 mg/L,the extraction efficiency remained above 97%.The addition of [C4MIm]NTf2 in the extractant greatly improved the extraction efficiency.The extraction rate of Cn-CrownIL/[C4MIm]NTf2 was very high and the extraction equilibrium could be achieved after 10 min.By increasing of alkyl chain length,the extraction efficiency of NTf-2 crown ether for Rb^+and Cs^+decreased slightly,but still was maintained above 85%.The extraction efficiency of Rb^+and Cs^+increased with the increase of solution pH.The recycle of Cn-CrownIL/[C4MIm]NTf2 can be realized by adding diluted nitric acid to reextract Rb^+and Cs^+.Results from recycling tests showed that the extraction efficiency of Rb^+and Cs^+was still above 90% after five recycling tests.Theoretical calculations showed that the extraction of C4-CrownIL/[C4MIm]NTf2 for Rb^+and Cs^+depended on the strong complexation of the oxygen atom in the crown ether with Rb^+and Cs^+,but the primary reason was that the cavity size of crown ether highly matched the ion-radius of Rb^+and Cs^+.