Triazine-Based Microporous Polymers for Selective Adsorption of CO₂

Propeller-shaped triazine was used to synthesize microporous polycarbazole materials through an inexpensive FeCl₃-catalyzed reaction using direct oxidative coupling (PCBZ) and extensive cross-linking (PCBZL) polymerization routes. PCBZL has a Brunauer–Emmett–Teller specific surface area of 424 m² g^–1 and shows larger CO₂ uptake (64.1 mg g^–1 at 273 K, 1 atm). Selective adsorption of CO₂ over N₂ calculated using the ideal adsorbed solution theory shows that both PCBZ (125) and PCBZL (148) exhibit selectivity at 298 K, which is significantly higher than PCBZ (110) and PCBZL (82) at 273 K. These values of selectivity are among the highest reported for any triazine-based microporous material. By introducing the electron-rich carbazole structure into the nitrogen fertile triazine-based system, the adsorption enthalpy is increased drastically, which in turn contributes to high selective adsorption values. The larger existing binding energy between CO₂ and propeller specifies more stable and favorable interactions between adsorbent and adsorbate, which transforms into reasonable adsorption capacity at low pressure and eventually high selectivity. These polymeric networks also show moderate working capacity with high regenerability factors. The combination of a simple inexpensive synthesis approach, high thermal/chemical stability, and reasonable selective adsorption make these materials potential candidates for CO₂ storage and separation applications

Highly Selective and Stable Carbon Dioxide Uptake in Polyindole-Derived Microporous Carbon Materials

Adsorption with solid sorbents is considered to be one of the most promising methods for the capture of carbon dioxide (CO₂) from power plant flue gases. In this study, microporous carbon materials used for CO₂ capture were synthesized by the chemical activation of polyindole nanofibers (PIF) at temperatures from 500 to 800 °C using KOH, which resulted in nitrogen (N)-doped carbon materials. The N-doped carbon materials were found to be microporous with an optimal adsorption pore size for CO₂ of 0.6 nm and a maximum (Brunauer–Emmett–Teller) BET surface area of 1185 m² g^–1. The PIF activated at 600 °C (PIF6) has a surface area of 527 m² g^–1 and a maximum CO₂ storage capacity of 3.2 mmol g^–1 at 25 °C and 1 bar. This high CO₂ uptake is attributed to its highly microporous character and optimum N content. Additionally, PIF6 material displays a high CO₂ uptake at low pressure (1.81 mmol g^–1 at 0.2 bar and 25 °C), which is the best low pressure CO₂ uptake reported for carbon-based materials. The adsorption capacity of this material remained remarkably stable even after 10 cycles. The isosteric heat of adsorption was calculated to be in the range of 42.7–24.1 kJ mol^–1. Besides the excellent CO₂ uptake and stability, PIF6 also exhibits high selectivity values for CO₂ over N₂, CH₄, and H₂ of 58.9, 12.3, and 101.1 at 25 °C, respectively, and these values are significantly higher than reported values