Organic Linker Effect on Iodine Adsorption in Thorium-Based UiO-66-Type Metal Organic Frameworks

Abstract

Thorium-based UiO-66/67 metal-organic frameworks (MOFs) are studied among the most promising radioactive iodine traps to achieve sustainable clean nuclear energy. Here, seven MOFs, namely, Th-BDC, Th-1,4-NDC, Th-ADC, Th-ABDC, Th-2,6-NDC, Th-BiPhDC, and Th-BiPyDC (where BDC= benzene-1,4-dicarboxylic acid; 1,4-NDC = naphthalene-1,4-dicarboxylic acid; ADC = anthracene-9,10-dicarboxylic acid; ABDC = 2-aminobenzene-1,4-dicarboxylic acid; BiPhDC = 1,1′-biphenyl-4,4′-dicarboxylic acid; BiPyDC = 2,2′-bipyridyl-5,5′-dicarboxylic acid), are synthesized and characterized employing powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, surface area measurement, Fourier-transform infrared, and Raman spectroscopy. MOFs having large linker lengths, namely, Th-2,6-NDC, Th-BiPhDC, and Th-BiPyDC, are collapsed during solvent drying. I₂ vapor adsorption studies are carried out, and the I₂@MOFs are characterized. MOFs with similar linker lengths but different numbers of aromatic rings (Th-BDC, Th-1,4-NDC, Th-ADC) have similar SSA (specific surface area) normalized I₂ adsorption capacities (≈0.9 g/g). Among the UiO-66-type MOFs, ThBDC stands out to have highest I₂ adsorption capacity of ≈1.7 g/g due to the presence of an electron-donating group on the aromatic ring. This study provides the rationale to design better MOFs for I₂ adsorption and gives insight that the electron density modulated by the electron-donating group on the linker is more significant than increasing the number of aromatic rings in UiO-66 family.