Creating Pores in Chitosan-Derived Humins via in Situ CO₂ Formation

Converting chitosan-derived humins into nitrogen-doped porous carbon (NPC) is a promising approach to the valorization of humins owing to their inherent nitrogen-containing advantage. Herein, we report the first example of NPC made from chitosan-derived humins, whereby a novel method to fabricate porous humins from chitosan by in situ CO2 strategy was demonstrated. By means of GPC, FT-IR, XPS, and TEM, the formation mechanism of chitosan-derived humins by catalysis of weak acids was proposed via oligomer mechanism. By catalysis of oxalic acid (OA), oxalic ester oligomers were generated to form soluble nanoparticles as precursors for humins formation. Then through intramolecular and intermolecular deamination/dehydration, the ester oligomers precipitate as humins solid due to reduced solubility, which further decompose to release CO2 from the interior of humins and transform into porous material. Otherwise, without the in situ release of CO2, humins remain almost nonporous by catalysis of HOAc.