Stability and degradation mechanisms of metal–organic frameworks containing the Zr6O4(OH)4 secondary building unit

Abstract

Metal-organic frameworks (MOFs) with the Zr 6 O 4 (OH) 4 secondary building unit (SBU) have been of particular interest for potential commercial and industrial uses because they can be easily tailored and are reported to be chemically and thermally stable. However, we show that there are significant changes in chemical and thermal stability of Zr 6 O 4 (OH) 4 MOFs with the incorporation of different organic linkers. As the number of aromatic rings is increased from one to two in 1,4-benzene dicarboxylate (UiO-66, ZrMOF-BDC) and 4,4 0 -biphenyl dicarboxylate (UiO-67, ZrMOF-BPDC), the Zr 6 O 4 (OH) 4 SBU becomes more susceptible to chemical degradation by water and hydrochloric acid. Furthermore, as the linker is replaced with 2,2 0 -bipyridine-5,5 0 -dicarboxylate (ZrMOF-BIPY) the chemical stability decreases further as the MOF is susceptible to chemical breakdown by protic chemicals such as methanol and isopropanol. The results reported here bring into question the superior structural stability of the UiO-67 analogs as reported by others. Furthermore, the degradation mechanisms proposed here may be applied to other classes of MOFs containing aromatic dicarboxylate organic linkers, in order to predict their structural stability upon exposure to solvents.

Origin of highly active metal–organic framework catalysts: defects? Defects!

“…9). 76 From direct first-principles simulations at various water loadings, the ligand displacement was also defined as the main route for the framework decomposition of hydrophobic IRMOFs. 77 It has been found that in addition to the water molecule involved in the ligand displacement, additional water stabilized both the hydrated metal species and the displaced ligand.…”

Emerging adsorptive removal of azo dye by metal–organic frameworks

“…Scheme 1. Schematic of ligand displacement mechanism in the presence of water for a typical MOF material (ZrMOFs)(DeCoste et al, 2013).…”

Synthesis of flower-shaped ZrO2–C composites for adsorptive removal of trichlorophenol from aqueous solution

“…5B), as has been observed for other carbonaceous materials. 37,40,41 In the current study, the capacity of ZrO 2 -C to adsorb TCP was observed to be greatest at pH 4.0, and then decline as the solution pH was increased. Since the pK a of TCP is pH 5.99, 42 the majority of TCP exists in the neutral and un-ionized forms in acid solution, and ionizes gradually and becomes negatively charged at solution pH values greater than 5.99.…”