Complexation between uranyl(VI) and CMPO in a hydroxyl-functionalized ionic liquid: An extraction, spectrophotography, and calorimetry study

The extraction complexes of uranyl(VI) in HNO3 to a hydroxyl-functionalized ionic liquid (IL) phase, HOEtmimNTf(2) bearing CMPO, were investigated. Three possibly successive extraction complexes, UO2L2+ (L =CMPO), UO2L22+ and UO2L32+, were detected based on variable U/L ratios. Uranyl(VI) prefers to be extracted as complex UO2L32+, combining with the ions from HOEtmimNTf(2) to construct a solid material through self-assembly. The thermodynamics of complexes, UO(2)L(j)2(+) (j=1-3), were studied by spectrophotometry and microcalorimetry. All the formation reactions are principally driven by entropy, although a small part of the driving force of complexes UO2L2+ and UO2L32+ comes from enthalpy. Based on the thermodynamic properties for complex UO2L32+, we provide a possible coordination mode in HOEtmimNTf(2): the first CMPO molecule coordinates with UO22+ in a bidentate fashion while the others do in a monodentate fashion. The results offer a thermodynamic insight into the formation behaviors of the uranyl(VI)/CMPO complexes involving the special IL HOEtmimNTf(2), which is of significance to advance the novel IL extraction strategy. (C) 2022 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.