Phosphine oxides functionalized pillar[5]arenes for uranyl extraction: Solvent effect and thermodynamics

• Published in: Separation and purification technology 2020-01, Vol.230, p.115843, Article 115843
• Main Authors: Yuan, Xiangyang, Cai, Yinmin, Chen, Lixi, Lu, Shihang, Xiao, Xin, Yuan, Lihua, Feng, Wen
• Format: Article
• Language: English
• Subjects: Diluent effect; Extraction thermodynamics; Phosphine oxide; Pillararene; Uranyl
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2019.115843

[Display omitted] •Thermodynamics of uranyl extraction by P5POs was studied for the first time.•Uranyl extraction by P5POs in all diluents tested was exothermic.•The ligand with a longer spacer exhibited better uranyl extraction performance.•Uranyl extraction was significantly affected by polarity of diluent.•Extraction was enthalpy & entropy driven in DCM, but enthalpy driven in DCE, NTFB and NP. As pre-organized multidentate extractants, phosphine oxides functionalized pillar[5]arenes (POP5As) have showed superior efficiency for uranyl extraction. In this work, the effect of type of organic diluents including dichloromethane (DCM), 1,2-dichloroethane (DCE), 1-nitro-3-(trifluoromethyl)benzene (NTFB) and nitropropane (NP) with different polarity and the fundamental thermodynamic behaviour were investigated in the solvent extraction of uranyl by POP5As from nitric acid (1 M) solution. The extraction ability pertaining to spacer length (CnH2n, n = 2, 4, 6), diluent polarity and temperature has been evaluated by comparing the distribution coefficients. The extractant with longer spacer exhibited a better performance in all diluents examined. Particularly, influencing factors including structural variation of ligands and property of organic diluents for the extraction efficiency were discussed from the thermodynamic point of view (ΔH, ΔS and ΔG). Generally, the extraction processes of uranyl by POP5As were exothermic and spontaneous in nature. In the case of DCE, NTFB and NP, ΔH