Adsorptive Removal of Benzophenone‐4 (BP‐4) Using Magnetically Recoverable Fe 3 O 4 / Alhagi maurorum Activated Biochar: Optimization, Kinetics, Reusability, and Mechanistic Insights

ABSTRACT Benzophenone‐4 (BP‐4) is an emerging pollutant with extensive applications in daily life. BP‐4 is extensively documented as a persistent, bioaccumulative, hydrophilic compound that spreads rapidly in water and is toxic to aquatic organisms. This study aims to develop a novel adsorbent that efficiently adsorbs BP‐4 from aqueous solutions. Thus, biochar was prepared from Alhagi maurorum biomass (AM‐ BC ). To enhance the adsorption capacity of this adsorbent by increasing surface area, promoting the formation of micro/mesopores, improving structural stability, and introducing oxygen‐containing functional groups, a chemical activation with KOH followed by thermal activation was employed. Then, magnetic biochar (Fe 3 O 4 /AM‐ BC ) was prepared by co‐precipitation using FeCl 3 and FeCl 2 . Fe 3 O 4 nanoparticles were incorporated to provide magnetic recoverability and facilitate the rapid separation and reuse of the adsorbent after BP‐4 adsorption. Fe 3 O 4 /AM‐ BC was characterized by scanning electron spectroscopy (SEM/EDS), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) analysis, and vibrating sample magnetometer (VSM). Results confirmed that Fe 3 O 4 /AM‐ BC exhibited significant characteristics, including saturation magnetization (Ms) of 23.4 emu/g, a hierarchical porous structure with a specific surface area of 741.383 m 2 /g, and abundant functional groups. Adsorption experiments of BP‐4 revealed a maximum removal efficiency of 94.05% at optimized conditions of pH 5, 0.5 g/L Fe 3 O 4 /AM‐ BC dose, 15 mg/L BP‐4 concentration, and 180 min contact time. Langmuir isotherm model fitted the data with R 2 of 0.955 and a maximum adsorption capacity of 62.87 mg/g. PSO kinetic model described the adsorption of BP‐4 with R 2 of 0.996, confirming the chemisorption process. The study indicated that the adsorption of BP‐4 on Fe 3 O 4 /AM‐ BC occurred through various mechanisms, including electrostatic attraction, pore filling, π–π interactions, hydrogen bonding, and surface complexation. The regeneration study confirmed the significant reusability and structural stability of Fe 3 O 4 /AM‐ BC , with a slight reduction in efficiency after 5 cycles. In conclusion, Fe 3 O 4 /AM‐ BC proved to be an efficient adsorbent for the remediation of emerging contaminants and a potentially effective means of reusing and managing agricultural waste. To the best of our knowledge, no comprehensive study has evaluated magnetically modified biochar as a recyclable adsorbent for the removal of BP‐4 from aqueous solutions.