The crucial role of different NaOH activation pathways on the algae-derived biochar toward carbamazepine adsorption

Abstract

In this study, algae present in wastewater were utilized as precursors for synthesizing a range of biochar (BC) samples to serve as efficient adsorbents for the removal of carbamazepine (CBZ). The impact of modification on BC, activated through the NaOH impregnation method (IBC), and the NaOH dry mixing-pyrolysis (DBC) method, was systematically explored. It was observed that only the surface of IBC became rough due to NaOH impregnation activation, while the DBC structure exhibited additional fine pores within its interior. Furthermore, after NaOH activation, a significant number of oxygen-containing functional groups were introduced onto the surface of the prepared BC samples, with the proportion of O species differing between the two NaOH activation methods. Based on the results from adsorption experiments and kinetic model simulation, CBZ adsorption by BC samples followed a monolayer homogeneous adsorption reaction with excellent pH tolerance, where H-bond (Cdouble bondO⋯H–N) was identified as the primary driving force. From an adsorption thermodynamics perspective, it is hypothesized that the high proportion of Cdouble bondO causes the ΔG value to shift from positive to negative, indicating that CBZ adsorption by DBC is a spontaneous reaction. Under optimal conditions, the DBC samples demonstrated an exceptional adsorption capacity, reaching 118.4 mg/g, with the removal rate of CBZ exceeding 99 %. This study offers theoretical insights into the preparation, modification, and adsorption mechanisms of BC-based adsorbents.