Activated biochars derived from green coconut pericarp and polyurethane waste for CO₂ capture

Porous carbon materials derived from waste resources have been widely investigated for gas separation applications due to their tunable surface chemistry and pore structure. In this work, biochars (BC) obtained from coconut pericarp and from co-pyrolysis with waste polyurethane were chemically activated using H₃PO₄ and KOH and evaluated as adsorbents for post-combustion CO₂ capture. The materials were prepared by pyrolysis and characterized in terms of textural properties and surface functionality. CO₂ adsorption performance was assessed through low-pressure isotherms at different temperatures and dynamic experiments under a binary CO₂/N₂ mixture. KOH-activated biochars exhibited highly developed microporosity, with BET surface areas of 2675 and 2291 m² g^-1 for BC-OH and NBC-OH, respectively. BC-OH showed the highest CO₂ uptake, whereas NBC-OH exhibited the highest apparent CO₂/N₂ selectivity, reaching a value of 6.10. Adsorption was diffusion-controlled and driven mainly by physical interactions, as indicated by fractional-order kinetic model and isosteric heat values in the range of approximately 20-30 kJ mol^-1. Moreover, BC-OH maintained stable adsorption capacity and selectivity over multiple adsorption-desorption cycles, confirming the relevance of precursor composition and activation route for cyclic CO₂ capture. Overall, these results show that coconut pericarp and waste polyurethane can be effectively converted into waste-derived and regenerable carbon adsorbents, offering a sustainable route for post-combustion CO₂ capture and the valorization of biomass and polymer wastes.