Porous Carbon Nanofibers with Sulfur and Oxygen Composite Surfaces Derived from Ultrafine Polypropylene Fibers in Waste Masks for CO₂ Adsorption

Heteroatom-doped porous carbon nanofibers exhibit strong potential for CO₂ adsorption, owing to their unique morphology and physicochemical properties. However, their large-scale application has been restricted by complex synthesis procedures and the high cost of conventional precursors. In this study, porous carbon nanofibers (ACFs) with S-O composite surfaces were synthesized using ultrafine polypropylene fibers (PP) from waste masks as precursors. PP was stabilized through temperature-time-controlled sulfonation, followed by one-step carbonization and activation with KOH and ZnCl₂ at 800 and 600 °C, respectively. The resulting materials showed a high total pore volume (1.33-1.65 cm³·g^-1) and substantial S-O content (7.85-13.19 atom %). They achieved excellent CO₂ adsorption capacities of 3.69-4.73 mmol·g^-1 (0 °C, 1 bar) and CO₂/N₂ selectivities of 13-19, surpassing those of porous carbon fibers derived from commercial polyacrylonitrile. The enhanced CO₂ uptake was attributed to the synergistic effect of the S-O surface active sites located in slit pores with a pore size of 1.1 nm. This work demonstrates a cost-effective approach for producing porous carbon nanofibers and offers a sustainable route for converting waste into materials for environmental and energy applications.