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

Abstract

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_nvimBr) by simultaneous radiation grafting of the hydrophilic ionic liquid 1-vinyl-3-ethylimidazole bromide ([C₂VIm]Br) and hydrophobic ionic liquid 1-vinyl-3-alkylimidazolium ([C_nVIm]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-PC₂vimBr) 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_nvimBr 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_nvimBr presented superior selectivity for ReO₄⁻ over SiO₂-g-PC₂vimBr. Furthermore, the continuous uptake of ReO₄⁻ using SiO₂-g-PC₂-C_nvimBr 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-C₈vimBr 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_nvimBr was deemed to be promising for continuous separation of TcO₄⁻/ReO₄⁻ in the practical treatment of radioactive wastewater and TcO₄⁻ contaminated groundwater.