Synthesis and optimization of biobased carbon adsorbent monoliths from chitosan-polybenzoxazine for efficient CO₂...

The present study introduces a novel method for the preparation of a CO₂ carbon adsorbent derived from biobased precursors. Porous carbon adsorbents were synthesized through the carbonization and thermal activation of biobased chitosan-polybenzoxazine. First, the study explored the influence of varying amounts of the key polymer precursors, lysine (0.05-0.1 g) and chitosan (0.6-0.12 g), on the surface and adsorption characteristics of the obtained carbons. This aimed to identify the most favourable amounts of these precursors that resulted in the highest CO₂ adsorption performance. In the subsequent stage, the study investigated the impact of different activation times (1-7 h) to enhance the surface characteristics and CO₂ adsorption capacity of the activated carbon. Both carbonization and activation processes were conducted in a tubular furnace at 900 °C under N₂ and CO₂ atmospheres, respectively. After carbonization, the resulting carbon monoliths exhibited a char yield of approximately 49 wt%, with a BET surface area of up to 541 m² g^-1 and a CO₂ uptake of 4.0 mmol g^-1 at 0 °C and 1 bar. After activation, the obtained samples displayed a surface area in the range of 650-1000 m² g^-1, with CO₂ adsorption capacities at 1 bar ranging from 4.5 to 5.6 mmol g^-1 at 0 °C and 3.2 to 4 mmol g^-1 at 25 °C. The activated carbons also demonstrated excellent selectivities for CO₂/N₂ and CO₂/CH₄ mixtures, along with a stable CO₂ adsorption-desorption performance after 10 cycles.