Phosphonium salt and ZnX2–PPh3 integrated hierarchical POPs: tailorable synthesis and highly efficient cooperative catalysis in CO2 utilization

Abstract

A series of quaternary phosphonium salt and ZnX₂–PPh₃ integrated hierarchical porous organic polymers (POPs) with tailorable stoichiometric copolymerization proportions were obtained through the method of solvothermal synthesis. The resultant POP materials feature hierarchical porous structures, high BET surface areas (up to 1115 m² g⁻¹), excellent CO₂ uptake abilities (87 mg g⁻¹ at 273 K under 1 atm CO₂) and multifunctional sites. Owing to the cooperative effect of quaternary phosphonium salt and homogeneously distributed ZnX₂–PPh₃ species, which is probably strengthened by the confined hierarchical structure and flexible frameworks, these POP catalysts provided the highest activity (initial turnover frequencies up to 6022 h⁻¹) among heterogeneous catalysts reported to date within the context of cyclic carbonate formation. The effect of reaction parameters (reaction time, temperature, and CO₂ pressure) on the catalytic performance as well as other epoxide substrates was also investigated in detail. Furthermore, these catalysts can be easily recovered and reused five times without a significant loss of activity.