Di-ionic multifunctional porous organic frameworks for efficient CO2 fixation under mild and co-catalyst free conditions†
Abstract
Conversion of CO2 into value-added chemicals is currently considered to be a significant field in the energy industry mainly due to its environmental and economic benefits. Porous organic frameworks (POFs), as a new class of advanced porous materials, have demonstrated great potential in catalysis, because the functionality and spatial arrangement of their active sites can be precisely managed. We report herein a new strategy for the construction of di-ionic multifunctional POF materials using multiple building blocks with different ion exchange functional sites to construct di-ionic POFs. Based on this strategy, a new di-ionic POF material, POF-DI, was prepared for the first time, which could serve as a substrate material for the preparation of a series of di-ionic multifunctional POF heterogeneous catalysts, POF-Zn2+-Cl−, POF-Zn2+-Br− and POF-Zn2+-I− by a feasible post-synthesis ion exchange method. Because of the synergetic role of dual functional ionic sites including Zn2+ cations as the Lewis acid site and halogen anions (Cl−, Br− or I−) as the nucleophile, POF-Zn2+-Cl−, POF-Zn2+-Br− and POF-Zn2+-I− demonstrate excellent catalytic performance in the cycloaddition of CO2 and epoxides under mild and co-catalyst free conditions. Moreover, such di-ionic multifunctional POF heterogeneous catalysts can be easily recovered and recycled several times without leaching or loss of activity. Overall, our work could not only open a new route for the development of novel POF catalysts for CO2 conversion, but also advance di-ionic POFs as a new kind of platform for multifunctional material design.