Tailoring highly surface and microporous activated carbons (ACs) from biomass via KOH, K₂C₂O₄ and KOH/K2C2O4 activation for efficient CO₂ capture and CO2/N2 selectivity: characterization, experimental and molecular simulation insights

The environmental impact of wood waste disposal and limitations of conventional chemical activation underscore the need for sustainable strategies to convert lignocellulosic biomass into efficient CO₂ sorbents. In this study, pine wood was activated at 800 °C using KOH, K₂C₂O₄, and their mixtures (mass ratios 1:1 to 1:4) to tailor porosity and surface chemistry for selective CO₂ capture. Co-activation at a 1:2:2 ratio (biomass:KOH:K₂C₂O₄) delivered optimal textural features, including a BET surface area of 2029 m 2 /g, total pore volume of 1.028 cm 3 /g, and micropore volumes of 0.923 cm 3 /g (N₂) and 0.156 cm 3 /g (CO₂). The KOH-activated carbon (1:1) achieved the highest CO₂ uptake 9.65 mmol/g at 0 °C and 5.95 mmol/g at 25 °C due to extensive ultramicropore development. In contrast, the K₂C₂O₄-derived sample (1:4) exhibited lower uptake (8.79 mmol/g at 0 °C) but superior CO₂/N₂ selectivity (>21 at 5 % CO₂, 1 bar), linked to narrower pores and higher surface polarity. Structural and surface analyses (XRD, FTIR, XPS, XRF, SEM, TGA) confirmed turbostratic carbon, abundant oxygenated groups (C O, C O), and sponge-like morphology with residual inorganic species. Isosteric heats of CO₂ adsorption (26–36 kJ/mol) indicated strong physisorption, and isotherm modeling identified Radke–Prausnitz as the best-fit model. Grand canonical Monte Carlo simulations supported the experimental results, revealing that sub-nanometer pores and carbonyl-rich surfaces enhance CO₂ affinity. This work presents a comprehensive comparison of K-based activation strategies and demonstrates that co-activation offers a scalable, less harsh route to high performance porous carbons for CO₂ capture. • Pine wood was activated with KOH, K₂C₂O₄, and their mixtures at 800 °C. • Co-activation (1:2:2) produced balanced porosity and high CO₂ uptake. • CO₂ adsorption reached 9.65 mmol/g at 0 °C and 5.95 mmol/g at 25 °C. • K₂C₂O₄ activation gave the highest CO₂/N₂ selectivity (21–54 via IAST). • GCMC analysis revealed carbonyl-rich ultramicropores enhance CO₂ affinity.