文献名：  Efficient and Ultrafast Adsorption of Rhenium by Functionalized Hierarchically Mesoporous Silica: A Combined Strategy of Topological Construction and Chemical Modification

作者：  Hanqin Weng*, Peng Zhang, Zifang Guo, Geng Chen, Wanglai Shen, Jialiang Chen, Xing Zhao, and Mingzhang Lin*

School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026, China

摘要： Radioactive Tc-99 released by nuclear accidents threatens the environment and human health due to its long half-life and strong transportability. A combined strategy synergizing topological construction and chemical modification was proposed for the synthesis of high-performance adsorbents for Re as an analogue to Tc. On the one hand, hierarchically mesoporous SiO ₂  with a fibrous structure (F-SiO ₂ ), a peculiar topology integrating wrinkled open mesopores around 12 nm and on-wall mesopores around 3 nm, was adopted as the substrate of adsorbents. The larger mesopores can act as the superhighway for mass transfer, while the abundant smaller mesopores provide numerous adsorption sites. On the other hand, a series of dicationic pyridine (DCP) derivative groups (−Py ⁺ C _n H _{2 n} N ⁺ Me ₃ ) were designed to functionalize F-SiO ₂  for improving the adsorption performance toward ReO ₄ ^–  anions, the dominating form of Re in aqueous solution. Density functional theory (DFT) calculation combined with batch adsorption experiments revealed that the ReO ₄ ^–  adsorption on −Py ⁺ C ₅ H ₁₀ N ⁺ Me ₃  was the most favorable when the length of the spacer between the two positively charged N atoms ranged from 2 to 7 carbons ( n  = 2–7). However, −Py ⁺ C ₅ H ₁₀ N ⁺ Me ₃  exhibited a much slower adsorption rate than −Py ⁺ C ₂ H ₄ N ⁺ Me ₃ . The stronger interaction between ReO ₄ ^–  and −Py ⁺ C ₅ H ₁₀ N ⁺ Me ₃  suppresses the adsorbate diffusion. The two positive charges of −Py ⁺ C ₅ H ₁₀ N ⁺ Me ₃  may be perpendicularly distributed, sterically hindering ReO ₄ ^–  transport in smaller mesopores. The longer and flexible carbon chains may be aggregated to form the hydrophobic region, repulsing the hydrated ReO ₄ ^–  anions. Therefore, the efficient and ultrafast Re adsorption was achieved by synergizing the unique topology of F-SiO ₂  and functionalization by −Py ⁺ C ₂ H ₄ N ⁺ Me ₃  with a shorter spacer and weaker affinity ReO ₄ ^– . The detailed investigation demonstrated that −Py ⁺ C ₂ H ₄ N ⁺ Me ₃  possessed exothermic adsorption nature, adequate radiation-resistance, and excellent reusability. Meanwhile, −Py ⁺ C ₅ H ₁₀ N ⁺ Me ₃  exhibited stronger salinity tolerance and higher selectivity. The DCP groups are promising in decontamination of radioactive Tc, as they can meet specific requirements by manipulating the length of spacers.

关键词： quaternary pyridinium ，  anion exchange ，  pertechnetate ，  DFT calculation ，  hierarchically mesoporous SiO2