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 degrees C and 2.01 mmol/g at 25 degrees C were achieved for the carbon prepared at 600 degrees 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/N-2 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.

Automated summary

This study successfully prepared a series of advanced bio-carbon materials using the underutilized industrial by-product Kraft lignin as a precursor through a facile chemical activation process. The properties of these bio-carbons were highly tailorable by adjusting the activation conditions, and they exhibited outstanding CO2 adsorption performance and high CO2/N2 selectivity at low CO2 partial pressures. The results indicate that the unique three-dimensional aromatic structures of lignin contributed to the development of high-level ultra-microporosity.