Tailoring a novel hierarchical cheese-like porous biochar from algae residue to boost sulfathiazole removal

Aquatic pollution caused by antibiotics poses a significant threat to human health and the ecosystem. Inspired from "Emmental Cheese" that owns lots of natural pores, we here fabricated a hierarchical cheese-like porous Spirulina residue biochar (KSBC) activated by KHCO₃ for efficiently boosting the removal of sulfathiazole (STZ). Through learning form nature that the CO₂ produced by bacteria can serve as the natural pore maker (like cheese-making), KHCO₃ was thus selected as the gas generating agent in this study. The effect of adding KHCO₃ on the surface properties of KSBC was comprehensively investigated. Benefiting from the activation, the KSBC with the mass ratio of 2:1 (2K-SBC) possessed the largest specific surface areas (1100 m² g^-1), which was approximately 81 times that of the original (not activated) Spirulina residue biochar (SBC) (13.56 m² g^-1). Moreover, 2K-SBC exhibited the maximum adsorption capacity for STZ (218.4 mg g^-1), dramatically higher than the SBC (25.78 mg g^-1). The adsorption kinetics and adsorption isotherms exhibited that the adsorption behavior of 2K-SBC for STZ was consistent with the pseudo-second-order and Langmuir models. Additionally, the adsorption thermodynamics revealed that the adsorption of STZ on 2K-SBC was spontaneous and exothermic. The pore-filling and electrostatic interaction were considered the main mechanism for the adsorption of STZ on 2K-SBC, whereas the π-π electron donor-acceptor (EDA) interaction and hydrogen bond would also partially contribute to the adsorption process.