Structural engineering on keratin to tailor porous structure of biochar for high-efficiency tetracycline removal

The inherent complexity of biomass poses challenges in designing or controlling the porous structure of biochar after intense activation reactions. Here, structural engineering on keratin was developed to modulate the porous structure of bovine-horn-derived biochar via the controllable coupled oxidation and pyrolysis reactions. The possible chemical reaction pathways of the coupled oxidation and pyrolysis reactions were proposed. The structural transition involving β-sheets and random coils and the chemical changes in sulfur-containing functional groups regulate the rigidity of keratin molecules, impacting the pore formation of gas expansion. After the coupled oxidation and pyrolysis reactions at 180 °C, the resulting material contains approximately 35 % β-sheet content and 0.915 wt% oxidative sulfur. These characteristics contribute to production of micro-/meso-porous biochar, which has a mesopore content of 61 %, a specific surface area exceeding 2800 m² g^-1, and an average pore size of 2.68 nm. The obtained porous biochar shows a high adsorption capacity (1362.5 mg g^-1) for tetracycline owing to the tailored micro-/meso-porous structures, as analyzed through model fitting and density functional theory calculations. This work provides a facile structural engineering strategy towards biomass for the sustainable and controllable production of high-performance porous carbon materials.