An efficient way to introduce hierarchical structure into biomass-based hydrothermal carbonaceous materials

Hydrothermal carbonization of biomass is regarded as the most sustainable technique to fabricate functional carbonaceous materials. The absence of nanoporous structures in the as-obtained materials remains a stumbling block to their wide applications. A hard-templating method and KOH activation are mostly frequently applied to introduce porous structures into HTC materials, but they always suffer from either tedious synthetic processes or massive use of a strong base. Here, the hierarchically porous structure was developed by heat treatment in the static air atmosphere. The textual properties were investigated by TEM and N₂ sorption analyses. The structural order and surface chemistry were characterized by XRD, Raman, and XPS. The results show that the activated HTC carbons are rich in micropores and mesopores with high surface areas up to 1704 m²/g. The mesopore volume would reach over 50% of the total pore volume. In addition, these carbons show high performance in CO₂ and dye adsorption.