Visualizing sub-layer structural transformation in carbonized wood tracheid by Raman mapping

Characterizing the pore structure evolution of biomass-derived carbon during processing and exploring the relationship between the porous carbon structure and the intrinsic micro-structure of biomass precursor are of great importance to advance the knowledge of pore creation/evolution mechanism and manufacture demanded pore structures by controlled processing. So far, the manipulation of pore structure still heavily relies on trial-and-error approach due to the lack understanding of the relationship between precursor structure/composition and the pore evolution during processing. In this work, the micro-structural evolution across the multi-layered wood tracheid in carbonization and oxidation processes was revealed by Raman mapping which can provide a unique insight into the pore structure evolution of carbon materials. The different degrees of graphitization enable the differentiation of carbonized forms of lignin and cellulose by Raman mapping and thus quantify the changes of both species during carbonization and oxidation. It is revealed that micropore formation is more related to the degradation of lignin and mesopore formation is closely associated with cellulose. The diffusion of reactive gas through the multi-layered wood tracheid and the corresponding reactions occurred along the diffusion path create the comprehensive porous channels. This work provides a new and convenient method to get a comprehensive understanding of biomass structure/composition in related to the pore structure evolution and allows a more specific regulation of pore structure in biomass-derived porous carbon materials.