Facile and sustainable preparation of hierarchical porous carbon material from lignin/DES mixture after pretreatment

Deep eutectic solvent (DES) pretreatment of lignocellulose is an appealing and green approach for efficient lignin extraction. However, the process of lignin regeneration and DES recovery was time-consuming and labor-intensive. Herein, without any separation and purification after the DES pretreatment of Eucalyptus, the lignin/DES mixture was firstly used to fabricate hierarchical porous carbon materials through DES-thermal carbonization (DTC) and activation. Results revealed that the DTC processing involved degradation, condensation, aromatization, and aggregation, which significantly improved the carbonization degree and thermostability of carbon materials. X-ray photoelectron spectroscopic results confirmed the introduction of nitrogen atom from the choline chloride/lactic acid DES into the fabricated carbon materials during the DTC processing. This phenomenon can generate extra pseudocapacitance and thus increase the specific capacitance of supercapacitors. The capacitance retention of the resultant porous carbon materials (AC-200–12) reached above 95% after 10,000 charge-discharge cycles, which was much superior to commercial activated carbon. This facile and sustainable methodology overcomes traditional complex and expensive methods for preparing carbon materials from hardwood, which show promising potential to be used as electrode materials in a supercapacitor.