The removal of radioactive 137Cs from nuclear waste is of great importance for both the environment and energy saving. Herein, we report a study on the removal of Cs+ using a calix crown ether bis(2-propyloxy)calix[4]crown-6 (BPC6) in ionic liquids [Cnmim][NTf2], where [Cnmim]+ is 1-alkyl-3-methylimidazolium and [NTf2]− is bis(trifluoromethylsulfonyl)imide. The BPC6/[Cnmim][NTf2] system is highly efficient in removing Cs+ from aqueous solution, even at a low concentration of BPC6. HNO3 and metal ions such as Na+, Al3+ in the aqueous phase interfered with the extraction of Cs+ by competitive interaction with BPC6 and/or salting-out effect. UV analysis confirmed that the extraction of Cs+ by the BPC6/[Cnmim][NTf2] system involves a dual extraction mechanism, i.e., via exchange of BPC6·Cs+ complex or Cs+ by [Cnmim]+. Irradiation of [C4mim][NTf2] dramatically decreases Cs+ partitioning in the ionic liquid phase by the competitive interaction of radiation-generated H+ with BPC6, while irradiation of BPC6/[C4mim][NTf2] decreases Cs+ partitioning more markedly due to the radiolysis of BPC6.
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