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.