journal experiment on radioactive substance
Answers
Long-lived radioactive elements such as uranium, thorium and potassium and any of their decay products, such as radium and radon are examples of NORM. These elements have always been present in the Earth's crust and atmosphere, and are concentrated in some places, such as uranium orebodies which may be mined.
Design principles of metal-organic frameworks for sequestering radionuclides
The radioactive substances in the nuclear fuel cycle can be divided into three groups: (1) cationic radionuclides, such as ; (2) anionic radionuclides, such as ; and (3) gaseous radionuclides, such as 133Xe, 85Kr, and 129I2. To achieve a decent uptake of certain radionuclides, strong and specific interactions between the host framework and radionuclide are highly desirable. These interactions include electrostatic interaction, coordination, hydrogen bond interaction, hydrophobic interaction, etc. For a specific host/guest interaction, multiple driving forces are often present. Based on the unique coordinating behaviors of different types of radionuclides, the design strategies for uptaking MOFs are variable. As shown in Fig. 11.2A, for efficiently removing cationic radionuclides, a robust framework with a negative net charge is desirable to achieve strong electrostatic interactions. In addition, functional chelating groups (–COOH, –PO3H2, amidoxime, etc.) can be deliberately grafted onto the framework to improve the coordinating ability toward high-valent cationic radionuclides. Likewise, anionic radionuclides can be effectively captured by those MOFs with positive net charge on the extended framework (Fig. 11.2B). In addition, the hydrogen atoms in the organic ligands play an important role in forming a dense hydrogen bonding, contributing to the host framework/anion interaction. MOFs containing Ti or Zr clusters with exchangeable –OH groups are also applicable for trapping anions that exhibit strong affinities with those hard metal nodes. For the cases of gaseous radionuclides uptake, the pore size of the MOFs largely determines the separation properties, especially for the inert noble gases, 133Xe and 85Kr. Proper functionalization with reactive or polarizable groups, nanoparticles, and open metal sizes can further improve the sequestration ability and/or separation factors.