One-Step Phosphoric Acid Activated Pomegranate Peel Powder for Adsorptive Removal of Tetracycline in Aqueous Solution: Synthesis, Adsorption and Mechanism

In this study, a high surface area biochar was synthesized from pomegranate peel powder via one-step phosphoric acid activation and pyrolysis (at 600oC for 1 h), and evaluated for the adsorption of tetracycline (TCL) from aqueous solution. Characterization using BET, FESEM and FTIR confirmed the development of mesoporous architecture and the presence of functional groups favorable for TCL interaction. The activated biochar exhibited high specific surface area of 1882 m²/g, total pore volume of 1.67 cm³/g, and average pore radius of 3.5 nm. Batch adsorption experiments were performed to assess the effects of adsorption parameters. The biochar achieved a maximum TCL adsorption capacity of 435.4 mg/g. Equilibrium data were fitted to Langmuir, Freundlich, Redlich–Peterson, and Sips isotherm models, with the Langmuir model providing the best fit, indicating monolayer adsorption. Kinetic data fitted the pseudo second-order model, suggesting chemisorption as the dominant mechanism. Mechanistic analysis revealed that TCL removal was driven by electrostatic interactions, π–π electron donor–acceptor interactions, and hydrogen bonding. These results demonstrate the efficacy of phosphoric acid-activated pomegranate peel biochar as a low-cost, sustainable adsorbent for removing pharmaceutical contaminants from water.