Transformation mechanism from cork into honeycomb–like biochar with rich hierarchical pore structure during slow pyrolysis

Abstract

Cork–based carbon materials are promising in adsorption, energy, catalysis, and electromagnetic shielding, but the transformation mechanism of cork during pyrolysis remains unclear. Herein, cork was heat–treated at 150–550 °C with an interval of 50 °C and the samples were characterized using TG, FTIR, TG–FTIR, SEM, BET, and XRD, etc. to describe thermal degradation characteristics and establish transformation mechanism of cork during pyrolysis. Results showed that the most of the cork’s main components (suberin, lignin, and polysaccharides) were degraded at 200–430 °C and had a significant effect on the cell wall microstructure. Especially, suberin (49.54%) was the most abundant component in cork, and its degradation at 300–400 °C led to a significant reduction in the cell wall thickness by 70–80%, i.e., from 500–600 nm to 100–200 nm. Within the treatment temperature range of 450–550 °C, the residual lignin, unstable carbon, and tar underwent secondary degradation and volatilization, forming a hierarchical pore structure and primary specific surface area. Finally, the obtained biochar exhibited a honeycomb–like structure composed of micro–mesopores carbon nanosheets. This research will promote the controllable preparation and efficient application of cork–based carbon materials.