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.