Nitrogen-doped microporous carbon materials with uniform pore diameters: Design and applications in CO₂ and H₂ adsorption

Nitrogen-doped microporous carbon materials (N-MCs) with uniform pore diameters have promising applications in gas absorption, however their fabrication is challenging. Herein, we report a new approach to prepare N-MCs with uniform pore size using azo-linked organic polymers (AOPs) as the N-containing precursors. The AOPs were synthesized via the reactions of 1,3,5-tris(4-nitrophenyl)benzene (TNPB) and melamine (MA), and their N contents were tuned by changing the molar ratios of MA to TNPB. Followed by calcination of the resultant precursors at 800 °C, porous N-MCs were produced, which were characterized by means of different techniques including FT-IR analysis, N₂ sorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental analysis. It was demonstrated that the pore diameters of N-MCs could be tuned by changing the MA: TNPB ratio for preparing azo-polymer precursors, and N-MCs with pore size centered at 0.72 and 1.06 nm were obtained. The resultant N-MCs showed excellent CO₂ uptake capacity up to 191 mg g⁻¹ at 1 bar and 273 K, with a CO₂/N₂ selectivity of 58 at 298 K and good H₂ adsorption capacity of 14.7 mg g⁻¹ at 77 K.