Simple, additive-free, extra pressure-free process to direct convert lignin into carbon foams

To achieve lignin valorization, we reported a simple method to direct covert lignin into carbon foam materials in this work. Unlike multiple steps required to fabricate traditional carbon foams from most of other precursors (often non-renewable), the approach herein required solely heating for carbon production. We found that the intrinsic features of lignin render the formation of lignin block meanwhile generate the porous structure under the invented heating course. Three key factors including glass transition temperature, crosslinking ability, and thermal stability of lignin were identified to determine the successful fabrication of lignin foam (i.e., precursor of carbon foam). Upon tuning the heating profile or fractionating the lignin, lignin foam with different morphologies and properties were obtained. After carbonization, the selected lignin-derived carbon foams possessed well porous structures with bulk densities of 0.52 or 0.62 g cm−3, superior integrity with strength properties of around 10 MPa, BET surface areas of 143.29 or 325.86 m2 g−1, and many other attractive properties. This work is expected to stimulate further seek of lignin valorization in carbon foam production. •Lignin was converted into carbon foams via a facial process.•Formation mechanism of carbon foam during thermal conversions are proposed.•Lignin carbon foams with different properties are successfully tailored.•The produced carbon foam has comparable properties to pitch/coal-based carbon foams.