Structural Modulation in Viologen-Based Ionic Porous Organic Polymers for Catalytic Non-Redox CO2 Fixation

Abstract

The rational design of metal-free, porous, and heterogeneous catalysts with large specific surface areas for efficient CO₂ capture and utilization has remained a significant challenge. In this study, two structurally distinct viologen-based novel ionic porous organic polymers (iPOPs) featuring a triazine core are developed, employing different polymerization methods to modulate their porosity and catalytic properties. The alkyne-linked SC-iPOP, synthesized through Sonogashira polycondensation, exhibits high porosity (specific BET surface area: 616 ± 9 m² g⁻¹) over BHC-iPOP with secondary amine linkages fabricated by Buchwald-Hartwig polymerization. SC-iPOP demonstrates superior catalytic efficiency in the metal-free cycloaddition of CO₂ with epoxides to form cyclic organic carbonates under atmospheric pressure and solvent-free conditions, with excellent recyclability. This enhanced catalytic performance, compared to BHC-iPOP, is attributed to the high porosity of SC-iPOP and the presence of abundant CO₂-philic ionic active sites. The current study emphasizes the role of structural modifications in designing efficient porous catalysts for metal-free CO₂ fixation.