Melamine-based nitrogen-heterocyclic polymer networks as efficient platforms for CO2 adsorption and conversion

Constructing green and efficient porous material platforms for carbon dioxide (CO 2 ) adsorption and chemical conversion can effectively solve a series of environmental problems caused by the greenhouse effect. Herein, four melamine-based polymer networks PANs (PAN-P, PAN-PY, PAN-PZ, and PAN-IM) with abundant N sites and hydrogen bond donor (HBD) groups were synthesized by simple polymerization. The chemical structure of PANs was determined by various characterizations, and then the CO 2 uptake of PANs and their catalytic activity for the cycloaddition of CO 2 with epoxides were investigated. Among them, PAN-P has the largest CO 2 adsorption capacity, reaching values of 73.5 cm 3 /g at 273 K. Meanwhile, PAN-IM exhibits the best catalytic activity with 93 % yield and 99 % selectivity under metal-, halogen-, solvent-, and cocatalyst-free conditions (120 ◦C, 1.0 MPa CO 2 , 8 h), which mainly attribute to the multi-site synergistic activation of the imidazole heterocycle. In addition, PAN-IM also has satisfactory activity to various epoxides and exhibited good recyclability. Density functional theory (DFT) and FT-IR analysis were used to further reveal the interaction of PANs towards CO 2 and epoxides. Finally, a possible mechanism was suggested, including activation of CO 2 and epoxide, ring-opening of epoxide, insertion of CO 2 and ring-closing to form cyclic carbonate. The research in this paper will provide a reference for the development of a green and efficient CO 2 adsorption conversion platform.