Adsorptive removal of oxytetracycline using MnO₂-engineered pine-cone biochar: thermodynamic and kinetic...

Indiscriminate use of oxytetracycline is linked to the development of antibiotic-resistant genes, posing a serious threat to human health and ecosystem balance. This article reports the adsorptive elimination of oxytetracycline (OTC) from aqueous solution using a newly developed MnO₂-modified pine-cone biochar (MnO₂/PCBC). The MnO₂/PCBC was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, CHNS analyzer, inductively coupled plasma-optical emission spectroscopy, and Brunauer-Emmett-Teller N₂ adsorption analyzer. Batch adsorption experiments, designed using the central composite design framework of response surface methodology, were conducted to investigate the influence of process variables on the adsorption of OTC onto MnO₂/PCBC. The optimized conditions for achieving maximum removal (88.1%) were found to be at pH 8, MnO₂/PCBC dose 0.44 g/L, initial OTC concentration 200 mg/L, and temperature 303 K. The adsorption process follows Langmuir (R²=0.95) and Freundlich (R²=0.95) isotherms and pseudo-second-order (R²=0.99) adsorption kinetics. The adsorption process was found to be endothermic (ΔH⁰ = 33.04 kJ/mol) and spontaneous in nature (ΔG⁰ from -1.33 kJ/mol at 283 K to -5.65 kJ/mol at 313 K). The synthesized MnO₂/PCBC could be recycled and reused for OTC removal with a percentage removal of around 80% after fifth cycle. The results indicate an effective removal of oxytetracycline with only 0.44 g/L MnO₂/PCBC with maximum adsorption capacity of 357.14 mg/g which demonstrates improved performance in comparison to many adsorbents reported in literature. This implies that MnO₂/PCBC offers potential to be developed into a cost-effective technique for antibiotic removal from water.