Radiation synthesis of binary poly(ionic liquid) functionalized silica-based materials for selective adsorption of ReO4- as analogue of TcO4- from simulated radioactive wastewater

Pertechnetate (TcO4-) poses long-term potential radioactive hazards to the ecological environment, so it is an urgent challenge to selectively separate TcO4- from radioactive wastewater. In this work, we firstly developed a series of binary ionic liquid functionalized silica (SiO2-g-PC2-C(n)vimBr) by simultaneous radiation grafting of the hydrophilic ionic liquid 1-vinyl-3-ethylimidazole bromide ([C(2)VIm]Br) and hydrophobic ionic liquid 1-vinyl-3-alkylimidazolium ([C(n)VIm]Br, n = 4, 6, 8, and 12) onto silica for the removal of ReO4- as an analogue of TcO4-; single ionic liquid functionalized silica (SiO2-g-PC(2)vimBr) was also synthesized for comparison. The effects of absorbed dose and RAFT agent content on grafting yield were investigated. The grafting yield (GY) increased with increasing absorbed dose and decreasing RAFT agent content. SiO2-g-PC2-C(n)vimBr showed excellent acid and irradiation resistance; the adsorption efficiency was still more than 90% after soaking in acid solution for 3 months or after being irradiated at 1000 kGy. SiO2-g-PC2-C(n)vimBr presented superior selectivity for ReO4- over SiO2-g-PC(2)vimBr. Furthermore, the continuous uptake of ReO4- using SiO2-g-PC2-C(n)vimBr with varying alkyl chain lengths of hydrophobic imidazolium was investigated and compared in the simulated radioactive wastewater. It was found that the relative column adsorption capacity and selectivity increased with increasing alkyl chain length of hydrophobic imidazolium. In addition, SiO2-g-PC2-C(8)vimBr displayed excellent reusability; the adsorption capacity did not change and the desorption efficiency could reach 97% in the flow-through column cycle experiment. On the basis of experimental results, SiO2-g-PC2-C(n)vimBr was deemed to be promising for continuous separation of TcO4-/ReO4- in the practical treatment of radioactive wastewater and TcO4- contaminated groundwater.