Post-synthetic modification of UiO-66-OH toward porous liquids for CO₂capture

Porous liquids (PLs), a new class of materials with permanent pores and macroscopic flowing behaviors, have attracted much attention for CO2 capture. However, the preparation of PLs is always complicated, which is not suitable for the scale-up. Herein, we propose a rather simple and feasible strategy based on post-synthetic modification of pore generators and the like-dissolves-like principle to synthesize UiO-66-PLs with low-viscosity. To be specific, the metal-organic framework (MOF) UiO-66 with hydroxyl groups (denoted UiO-66-OH) was modified by an organosilane (denoted KH550 or SID) via a post-synthetic modification method, obtaining the pore generator UiO-66-OS (denoted UiO-66-KH550 or UiO-66-SID). Then, the UiO-66-OS was dispersed into two different sterically hindered polydimethylsiloxane solvents (PDMS400 or PDMS6000). Thereby, a series of type 3 PLs (UiO-66-PLs) with superior fluidity at room temperature and accessible porosity were obtained. For instance, the viscosities of UiO-66-KH550-PDMS400 and UiO-66-SID-PDMS400 were 1.1 and 1.5 Pa S at 25 °C, respectively, which were far lower than those of values reported thus far. In addition, gas sorption-desorption measurements indicated that the UiO-66-PLs exhibit superior CO2 sorption performance and great potential for CO2/N2 separation. Moreover, molecular simulation was carried out to verify the retained accessible porosity. Notably, the strategy of constructing type 3 PLs based on the post-synthetic modification of MOFs with organosilane and the like-dissolves-like principle not only provides a new solution for the development of low-viscosity PLs, but also opens a new path for the construction of other types of advanced porous material (APM)-based (e.g., covalent organic frameworks (COFs), porous organic cages (POCs)) PLs, which have potential applications in the fields of gas trapping storage, and catalysis.