Preparation of K2CO3-activated biochar from peanut shell and Chlorella for enhanced carbamazepine adsorption: Performance, mechanism, and reusability.

Leveraging the fibrous architecture of peanut shell and the intrinsic nitrogen-rich composition of Chlorella, a porous biochar (KBC) was synthesized via one-step K2CO3-activated pyrolysis using peanut shell and Chlorella as precursors to address the persistence of carbamazepine (CBZ) in conventional water treatment. K2CO3 activation substantially enhanced the physicochemical properties of KBC, which possessed a high specific surface area of 362.67 m2/g, a total pore volume of 0.34 cm3/g, and enhanced graphitization, suggesting reduced surface polarity. Adsorption kinetics and isotherms were well fitted by the pseudo-second-order and Langmuir models, with a maximum capacity of 121.56 mg/g at 318 K. Thermodynamic analysis confirmed spontaneous and endothermic adsorption with increased entropy. KBC exhibited consistent adsorption performance across a wide pH range of 3-12 and retained approximately 66.26% of its initial capacity after four consecutive cycles, indicating favorable reusability. Combined experimental characterization and density functional theory (DFT) calculations collectively revealed that CBZ uptake is governed by synergistic physisorption mechanisms, including pore filling, π-π electron donor-acceptor (EDA) interactions, hydrogen bonding, and hydrophobic interaction, with adsorption energies ranging from -0.361 to -0.753 eV. This work provides an efficient, sustainable biochar adsorbent for emerging contaminant removal while supporting agricultural waste valorization.