Upgrading Lignocellulose to Porous Graphene Enabled by Deep Eutectic Solvent Pretreatment: Insights into the Role of Lignin and Pseudo-lignin

Converting lignocellulosic biomass into graphene-based materials in a cost-effective approach remains a grand challenge. This study tackled this challenge by implementing direct laser writing (DLW) to lignocellulosic biomass for synthesis of porous graphene (i.e., laser-induced graphene (LIG)). Deep eutectic solvents (DESs), including choline chloride:oxalic acid (ChCl:OA), choline chloride:formic acid (ChCl:FA), and choline chloride:ethylene glycol (ChCl:EG), were used to enable the fabrication of biomass-based films for DLW. It was found that the cellulose pulp resulting from the ChCl:OA pretreatment was a suitable substrate for LIG formation, requiring no surface treatment of the fabricated film prior to exposure to laser scribing. The obtained LIG had a 3D porous structure and high crystallinity. Pseudo-lignin present in the ChCl:OA pulp was proposed to contribute to the formation of LIG. Lignin in situ regenerated from the pretreatment slurry and redeposited onto the cellulose pulps can further promote the LIG formation on the cellulose pulp film (CPF). The LIG-embedded films were fabricated into on-chip supercapacitors (SCs) and dopamine sensors and further evaluated for electrochemical properties. All the devices showed good energy storage and electrochemical sensing performance, suggesting versatile applications of disposable and low-cost lignocellulose-derived electronics. Overall, the present work demonstrated a feasible and scalable photothermal route based on direct laser writing toward mass production of lignocellulose-derived porous graphene materials.