Post-synthetic modification of UiO-66-OH toward porous liquids for CO2 capture

Abstract

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.