Interplay and selectivity of selected pharmaceuticals and organic contaminants adsorption onto magnetic biochar: Mechanistic insights

Biochar (BC) is widely recognized as an effective adsorbent owing to its porous structure, while magnetic biochar (MBC) offers the added advantage of easy separation and enhanced performance. However, few studies have systematically investigated competitive adsorption among multiple contaminants under environmentally relevant conditions. The adsorption characteristics of nine selected organic contaminants onto raw biochar and magnetic biochar were compared under varying conditions (pH, ionic strength, and organic substances). MBC exhibited superior adsorption capacity because of its increased surface area from 6.5 (BC) to 1,101 m² · g⁻¹. Ketoprofen (KP), antipyrine (AP), and propranolol hydrochloride (PH) were selected as representative anionic, neutral, and cationic contaminants, respectively, to investigate the competitive adsorption behavior of MBC. MBC showed higher adsorption for KP and PH compared to AP, mainly through electrostatic interactions, π–π stacking, and hydrogen bonding. The adsorption mechanisms for KP and PH predominantly followed monolayer chemisorption, which was best described by pseudo-second-order kinetic and Langmuir isotherm models, indicating spontaneous (ΔG = −4.4 to −12.1 kJ·mol-1) and exothermic (ΔH = −33.7 to −35.0 kJ·mol-1) processes. X-ray photoelectron spectroscopy analyses further supported electron donor–acceptor and electrostatic interactions, which occurred between the functional groups of MBC and the adsorbed contaminants, as evidenced by binding energy shifts in C1s, O1s, and Fe2p spectra. The competitive effects of background ions and organic substances emphasize the multifunctional adsorption capacity of MBC. Importantly, MBC maintained high reusability over multiple adsorption-desorption cycles, highlighting its practical application potential for contaminant removal.