Defects in metal–organic frameworks: a compromise between adsorption and stability?

Abstract

Defect engineering has arisen as a promising approach to tune and optimise the adsorptive performance of metal-organic frameworks. However, the balance between enhanced adsorption and structural stability remains an open question. Here both CO2 adsorption capacity and mechanical stability are calculated for the zirconium-based UiO-66, which is subject to systematic variations of defect scenarios. Modulator-dependence, defect concentration and heterogeneity are explored in isolation. Mechanical stability is shown to be compromised at high pressures where uptake is enhanced with an increase in defect concentration. Nonetheless this reduction in stability is minimised for reo type defects and defects with trifluoroacetate substitution. Finally, heterogeneity and auxeticity may also play a role in overcoming the compromise between adsorption and stability.

Thermodynamic Insight in the High-Pressure Behavior of UiO-66: Effect of Linker Defects and Linker Expansion

“…After removing a first linker, the bulk modulus drops from 22.2 to 19.9 GPa, whereas the removal of a second linker leads to a bulk modulus in the range of 15.5–18.9 GPa, confirming the trends observed in recent DFT results. 54 Likewise, a first linker defect decreases the loss-of-crystallinity pressure from 1.83 to 1.55 GPa, as indicated by the black arrow in Figure 8, while removal of a second linker yields a loss-of-crystallinity pressure between 1.17 and 1.51 GPa. Note that the ranges of both bulk moduli (15.5–18.9 GPa) and loss-of-crystallinity pressures (1.17–1.51 GPa) agree very well with the experimental values of 17(1.5) GPa and 1.4 GPa, respectively.…”

Gel-based morphological design of zirconium metal–organic frameworks

“…While difficult to compare with literature data due to the limited number of reports and the defect-dependence of UiO-66's mechanical properties, at least one computational study indicates this to correspond to about 20–33% of the value determined for UiO-66 with a similar number of missing linkers. 68 …”

Missing Linkers: An Alternative Pathway to UiO-66 Electronic Structure Engineering

“…46 The incorporation of multiple types of defects in a highly controllable manner 45−47 was found to lead to different mechanical properties, 48 catalytic behavior, 49−53 and absorption properties. 54,55 …”