Synthesis and characterization of advanced bio-carbon materials from Kraft lignin with enhanced CO2 capture properties

Biomass-derived porous carbons have received enormous attention for CO2 capture in post-combustion scenarios owing to their wide availability, excellent physicochemical stability, and cost-effective preparation. Here, a series of advanced bio-carbon materials were successfully prepared by using the underutilized industrial by-product Kraft lignin as precursor via a facile chemical activation process. Both the textural and surface properties of the bio-carbons were found to be highly tailorable by tuning the activation temperature, KOH/lignin ratio and pre-oxidation treatment. It was found that the Kraft lignin-derived carbons were exceedingly ultra-microporous with ultra-microporosity accounting for up to 92% of total micropores, while the carbons prepared with pre-oxidation treatment were uniquely characterised by distinctive hierarchical micro-mesoporous structures. Applying the Kraft lignin-derived carbons for CO2 adsorption demonstrates that at a CO2 partial pressure of 15 kPa, rarely obtainable CO2 adsorption capacities of 3.29 mmol/g at 0 °C and 2.01 mmol/g at 25 °C were achieved for the carbon prepared at 600 °C. Advanced characterizations confirm that the unique desirable combination of textural properties and surface chemistry, which favours the intercalation of potassium in the form of surface extra-framework K+ ions, underpinned the extraordinary CO2 adsorption performance and high CO2/N2 selectivity (up to 38) of the prepared carbons especially at low CO2 partial pressures. The results indicate that the unique three-dimensional aromatic structures of the lignin provide the matrix for the liable development of the well-defined ultra-microporosity at high levels. Our work provided a promising strategy for valorization of Kraft lignin as a precursor for producing advanced carbon materials.