Hydroxyl-Incorporated Microporous Polymer Comprising 3D Triptycene for Selective Capture of CO₂ over N₂ and CH₄

The rising CO₂ concentration in the atmosphere contributes significantly to global warming, necessitating effective carbon capture techniques. Amine-based solvents are widely employed for the chemisorption of CO₂, although they have drawbacks, such as degradation, corrosion, and high regeneration energy requirements. Physical adsorption of CO₂ utilizing microporous adsorbents is a viable alternative that offers excellent efficiency and selectivity for CO₂ capture. This work presents the facile one-pot synthesis of a 3D-triptycene-containing hyper-cross-linked microporous polymer (TBPP-OH) possessing hydroxyl groups. The presence of triptycene units in the TBPP-OH polymeric structure gives several desirable features, such as inherent microporosity, larger surface area, and improved thermal stability. TBPP-OH showed considerable microporosity (%V_mic = 70%), a larger BET-specific surface area (SA_BET) of 838 m² g^-1, and good thermal stability (T_d = 372 °C and char yield > 60%) which makes it a promising adsorbent for CO₂ capture. A strong affinity for CO₂ was shown by TBPP-OH with Q_st of 32.9 kJ/mol demonstrating a superior CO₂ adsorption capacity of 2.77 mmol/g at 273 K and 1 bar pressure where the volume of the micropore plays a significant role. The selectivity values of CO₂ over N₂ and CH₄ for the polymer TBPP-OH were also estimated to be reasonably high indicating good potential for CO₂ separation in different applications. The mechanism of CO₂ adsorption was investigated by using Langmuir and dual-site Langmuir models.