Structure-performance correlation of high surface area and hierarchical porous biochars as chloramphenicol adsorbents

Biochars have attracted widespread attention as a low-cost adsorbent for antibiotic removal. High surface area and hierarchical porous biochars, originating from five types of feedstocks, were prepared via simple carbonization and alkaline activation route and tested for chloramphenicol removal from the water environment. All biochars showed a maximum adsorption capacity of over 300 mg g⁻¹ at room temperature, with a large specific surface area of 1687–2003 m² g⁻¹. Adsorption isotherms and kinetics adhered well to Langmuir and pseudo-first-order models. The structure-performance correlation was analyzed to explore the effects of adsorbents' physical properties, morphology, and functional groups on adsorption performance. The pseudo-first-order kinetic constant, representing the adsorption rate, was strongly correlated with the external surface area and mesoporous pore volume. The maximum monolayer adsorption capacity, calculated by the Langmuir model, was strongly correlated with the microporous surface area and pore volume. A higher proportion of graphite and stronger hydrophilicity decreased the adsorption capacity. The primary adsorption mechanism appears to be physical adsorption through micropore filling, along with π-π electron donor–acceptor, electrostatic and hydrophobic interactions. Thus, a key factor influencing adsorption performance is the ratio of the microporous and mesoporous pore volume of adsorbents. To simultaneously enhance the adsorption rate and capacity, it is crucial to regulate the ratio of microporous and mesoporous pores of biochars. Establishing this relationship could have important implications for regulating the adsorbent structure and improving adsorption behavior.