Influence of pyrolysis atmosphere and temperature co-regulation on the sorption of tetracycline onto biochar: structure-performance relationship variation

Presently, as the prevalent pyrolysis atmospheres, N₂ is widely used, while air-limitation and CO₂ are rarely considered, to produce biochar to adsorb tetracycline. This study thus used N₂, CO₂, and air-limitation to produce various biochars at 300 ∼ 750 °C, and explored their structure-performance relationship for tetracycline sorption. The maximum sorption capacities of biochars produced in CO₂ and air-limitation were 55.36 mg/g and 71.11 mg/g (at 750 °C), respectively, being 2.34 and 3.01 times that of biochars produced in N₂ (23.60 mg/g at 750 °C). Interestingly, except for high pore volume and specific surface area supported pore filling and sites providing effect, ash (containing metal cations, P-O, and S=O) induced complexing effect was the primary mechanism for tetracycline sorption, rather than hydrophobic effect, π-π interaction, and hydrogen bond caused by C composition. This study provides important information about adjusting the pyrolysis atmosphere to improve the sorption performance of biochar toward tetracycline.