| A radionuclide, Pd-107 with a half-life of 6.5×106 yrs, is one of the long-lived fission products. It has potential and long-term adverse impact on the ecological environment and human health. It was reported that the removal of Pd-107 likely makes the vitrification of highly active liquid waste (HLW) easier which is of great significance to the final disposal of HLW. However, the effective separation of Pd(II) from HLW has always been one of the most challenging works for several decades. Application of new materials, new technologies and new methods are effective to overcome the international scientific and technological frontier issues. Pillar[n]arenes are novel class of macrocyclic host molecules. Owing to their unique characteristics, such as rigid, highly symmetric and rich electronic structure, pillar[n]arenes show excellent host-guest properties fluorescence sensor, molecular switch and others. However, the study on the host-guest recognition of metal ions espcially Pd-107 and has not been reported. In the present work, the host-guest recognition behavior between pillar[5]arene derivatives and Pd(Ⅱ) was investigated, the results were as follows:(1) Four derivatives of pillar[5]arenes, Ethoxycarbonylmethoxy-substituted pillar[5]arene (C2-EP5A), Carboxylic Acid Groups-Substituted Pillar[5]arene (C2-CP5A), Ethoxycarbonylpropoxy-substituted pillar[5]arene C4-Epillar[5]arene (C4-EP5A) and per-1-bromopropylated pillar[5]arene (C3-BP5A), were synthesized. The structure and composition of these materials were characterized by NMR, ESI-MS, FT-IR, TG-DSC and others.(2) The extraction properties and mechanism of Pd(Ⅱ) and more than 20 co-existent metal ions in HNO3 solution with pillar[5]arene/chloroform were investigated in the range of 0.4M to 8.0M. The results showed that in HNO3 solution, Pd(Ⅱ) was extracted with C4-EP5A and C3-BP5A, respectively. The optimum HNO3 concentration in the extraction of Pd(Ⅱ) was 4.0M. The composition of the extracted species of pillar[5]arene with Pd(Ⅱ) was determined to be 1:2 type. It was confirmed by the analysis of ESI-MS in organic phase. Based on the results of the extraction experiment, a possible flow sheet for Pd(Ⅱ) separation from a simulated HLW by solvent extraction was proposed.(3) Four novel polymer-based supramolecular recognition materials, C2-EP5A/XAD-7, C2-CP5A/XAD-7, C4-EP5A/XAD-7 and C3-BP5A/XAD-7 were prepared by impregnation and immobilization. It was characterized by SEM, N2 adsorption desorption isotherm, XRD, FT-IR and TG-DSC and others. The composite mechanism between pillar[5]arene and XAD-7 through intermolecular interaction was discussed.(4) The adsorption of Pd(Ⅱ) and more than 20 co-existent elements onto pillar[5]arene/XAD-7 were investigated. The effect of contact time, the HNO3 concentration in the range of 0.4M to 8.0M and temperature on the adsorption of Pd(Ⅱ) and others onto pillar[5]arene/XAD-7 was examined. It was showed that in 3.0M HNO3 solution, C2-CP5A/XAD-7 had excellent adsorption ability and high selectivity for Pd(Ⅱ) over all of the tested metal ions except Ru(Ⅲ). It was hopeful to separate Pd(Ⅱ) from geniune HLW with C2-CP5A/XAD-7. In order to investigate the adsorption mechanism, the pillar[5]arene/XAD-7 materials were characterized by SEM, N2 adsorption desorption isotherm, EDS, TG-DSC and FT-IR before and after the adsorption of Pd(Ⅱ). Based on the results of the static-state adsorption experiments, a possible flow sheet for Pd(Ⅱ) separation from a simulated HLW by extraction chromatography was proposed. |
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