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

Artikel i vetenskaplig tidskrift, 2025

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 m²/g, total pore volume of 1.028 cm³/g, and micropore volumes of 0.923 cm³/g (N₂) and 0.156 cm³/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[sbnd]O, C[dbnd]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.