Investigation on the mechanism of structural reconstruction of biochars derived from lignin and cellulose during graphitization under high temperature

The structural reconstruction mechanism of lignin and cellulose-derived biochars during direct graphitization under ultra-high temperatures was intensively investigated. It was demonstrated that cellulose-derived char was almost composed of carbon microcrystallites, whereas lignin-derived char reserved some of its skeleton structures, and such structural difference played a vital role in the morphology of formed graphitic layers. The results illustrated that the graphitized lignin-derived sample under 2800 ℃ had graphitic degree of 89.53%, interlayer spacing of 0.3363 nm and electronic conductivity of 104.6 S cm −1 , while cellulose-derived sample had graphitic degree of 76.74%, layer distance of 0.3374 nm, and electronic conductivity of only 48.8 S cm −1 . Combined with the results of structural analysis of the chars derived from lignin and cellulose, it was inferred that the stable and aromatic ring containing skeleton structure in lignin was beneficial to the ring-enlarging reconstruction and the formation of large areas of continuous graphitic layers during graphitizing process, leading to high electronic conductivity. Meanwhile, the interwoven microcrystallites in cellulose-derived char strongly restricted the expanding of continuous lamellar graphitic areas even at such ultra-high temperature, causing the formation of turbostratic structure with numerous structural defects as well, and finally resulting in relatively lower electronic conductivity. This work is expected to provide theoretical guidance for preparing high-performance functional carbon materials from lignocellulosic biomass. Graphical Abstract Highlights The different characteristics of lignin and cellulose resulted in the significant structural differences of the pyrolytic chars. Large area of lamellar graphitic layers formed in lignin-derived graphitic carbon, of which the graphitization degree was as high as nearly 90%, leading to excellent electronic conductivity. The structural differences of pyrolytic chars had a significant impact on the structural reconstruction under high temperature.