Effects of Aromatic Linker Structures on Carbon Dioxide Adsorption and Conversion Performance in Melamine-Based Porous Organic Polymers

The climate change is accelerating with the increase in the concentration of carbon dioxide (CO₂) in the atmosphere. CO₂ capture and conversion are effective strategies for stabilizing such environmental conditions. In this study, a series of melamine-based porous organic polymers (POPs), each incorporating different aromatic aldehydes as linkers, were synthesized. The POPs (MPOP-6C, MPOP-6N, MPOP-5N, and MPOP-5O) were characterized by Fourier-transform infrared spectroscopy, solid-state ¹³C nuclear magnetic resonance, X-ray diffraction, thermogravimetric analysis, and high-resolution field-emission scanning electron microscopy. The gas adsorption characteristics, including adsorption–desorption isotherms, pore size distribution, and adsorption at 298 and 323 K, were assessed through a Brunauer–Emmett–Teller analysis. The cycloaddition of CO₂ with styrene oxide was performed using POPs as catalysts for conversion to styrene carbonate. Melamine-based POPs bearing heterocycles with high π-electron densities exhibited enhanced CO₂ selectivity performances. MPOP-6N, which incorporated a pyridine motif, exhibited a notable enhancement in the conversion rate among the synthesized catalysts.