Engineering banana-peel-derived biochar for the rapid adsorption of tetracycline based on double chemical activation

Recycling biomass resources for conversion to biochar absorbents toward pollutant capturing is an important strategy for realizing “two birds with one stone”. The lack of efficient and straightforward conversion processes prompts us to explore double chemical (MnCl2/KOH) activation to convert banana peels to highly porous biochar, BC-MK, straightforwardly. BC-MK possesses a specific surface area of 1276.63 m2/g, much higher than those produced through single chemical activation using MnCl2 or KOH alone. The initial MnCl2 solution impregnation of biomass is essential to loosen the internal structure of the biomass, which makes the subsequent KOH activation homogeneous. Besides, MnO2 formed during high-temperature pyrolysis can serve as a template for more porous structure formation. Experimental evidence indicates that π-π stacking interactions play a more critical role than hydrogen bonding interactions in enabling the BC-MK-based fast adsorption of tetracycline (TC). The maximum monolayer adsorption capacity of the BC-MK adsorbent toward TC exceeds 295 mg/g.