Developing hierarchically ultra-micro/mesoporous biocarbons for highly selective carbon dioxide adsorption

Activated carbons represent one of the important categories of the adsorbent materials for CO 2 capture currently under development. However, the low adsorption capacity and selectivity at low CO 2 partial pressure and/or relatively high flue gas temperatures is the main barrier for carbons to be applied in post-combustion CO 2 capture under practical conditions. Here, we report the successful preparation of hierarchical ultra-micro/mesoporous bio-carbons from using a facile one-step method with a low-grade biomass waste as the feedstock. The bio-carbons exhibit high adsorption capacities (1.90 mmol/g) and record-high Henry’s law CO 2 /N 2 selectivities up to 212 at ambient temperature and low CO 2 partial pressure. Unlike conventional chemical activation process for manufacturing carbon materials, the integrated compaction-carbonization-activation method proposed endows the biowaste-derived carbons with unique hierarchical bio-modal pore structures, which are highly characterised by their high mesoporosity and high ultra-microporosity with narrow pore size distributions. The results demonstrated that the unique surface textural properties along with the enhanced surface chemistry due to the simultaneously achieved potassium intercalation created favourable conditions for CO 2 adsorption with high CO 2 /N 2 selectivity at low CO 2 partial pressures, whilst the presence of mesoporosity greatly increased the CO 2 adsorption kinetics. Measurements of CO 2 adsorption heat confirmed the strong surface affinity of the prepared bio-carbons to CO 2 molecules.