Post-synthetic ligand exchange in the prototypical zirconium-based metal-organic framework (MOF) UiO-66 was investigated by in situ solution H NMR spectroscopy. Samples of UiO-66 having different degrees of defectivity were exchanged using solutions of several terephthalic acid analogues in a range of conditions. Linker exchange only occurred in defect-free UiO-66, whereas monocarboxylates grafted at defect sites were found to be preferentially exchanged with respect to terephthalic acid over the whole range of conditions investigated. A 1:1 exchange ratio between the terephthalic acid analogue and modulator was observed, providing evidence that the defects had missing-cluster nature. Ex situ characterisation of the MOF powders after exchange corroborated these findings and showed that the physical-chemical properties of the MOF depend on whether the functionalisation occurs at defective sites or on the framework.

The effect of post-synthetic incorporation of functional monocarboxylates at defective sites of UiO-66 is systematically investigated, observing enhanced CO2 capture performance.

Decoupling amine loading from diffusion resistance is one of the main challenges in the development of immobilized amine CO 2 sorbents. Water has been reported to serve this goal, alleviating CO 2 diffusional hindrance in highly loaded amine sorbents. Acting as a mass transport facilitator, water is not the only partner molecule able to enhance bulk CO 2 diffusion. Herein, we show that the enhancing effect of methanol is comparable to that of water in polyethyleniminebased sorbents. Other molecules, such as ethanol, isopropanol, and chloroform, were also examined but did not appear to facilitate CO 2 transport and uptake. Based on a comparison of the Hansen solubility parameters of these molecules, it appears that polarity plays a crucial role in enhancing CO 2 diffusion together with molecular hindrance and hydrogen bonding to a lesser extent.