Design of halogen-free hyper-crosslinked porous ionic polymers for efficient CO2 capture and conversion

Abstract

Hyper-crosslinked porous ionic polymers (HCPIPs) are important materials for CO₂ capture and catalytic conversion. In this work, we used ion exchange to combine the cross-linking-active tetraphenylborate anion (BPh₄⁻) with a guanidine-based (Gua) ionic liquid (IL), forming a halogen-free IL ([Gua][BPh₄]). Using different proportions of formaldehyde dimethyl acetal (FDA), we successfully constructed a series of halogen-free guanidine-functionalized HCPIPs (Gua-HCPIP-x) and achieved efficient CO₂ capture and conversion. Specifically, Gua-HCPIP-4, which had rich porosity and a high specific surface area, achieved a CO₂ adsorption capacity of up to 3.2 mmol g⁻¹. Gua-HCPIP-x, with guanidine and BPh₄⁻ groups, exhibited higher efficiency and selectivity in the catalytic N-formylation reaction of CO₂. Under mild conditions (3 bar, 80 °C), Gua-HCPIP-4 achieved a 94% yield in the CO₂N-formylation reaction and maintained catalytic activity after 5 cycles. This study provides new insights into enhancing the catalytic activity of the CO₂N-formylation reaction and offers practical guidance for synthesizing halogen-free HCPIPs.