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.