Isotherm and kinetic studies of amoxicillin adsorption from aqueous solutions with activated carbons obtained from biowastes

In recent years, antibiotics have been increasingly used not only in medicine but also in agriculture and animal production. Specifically, amoxicillin (AMX), a broad-spectrum β-lactam antibiotic, is effective against many Gram-positive organisms and a limited number of Gram-negative organisms. Since AMX is stable and does not easily decompose in water, it is commonly found in wastewater, soil, and sediments. Water containing antibiotics needs to be treated with an effective process to protect human and environmental health. In this thesis, the morphological, structural, chemical, and adsorption properties of activated carbons synthesized from abundant lignocellulosic agricultural wastes such as tomato, pepper, and eggplant have been investigated. A two-step chemical activation method was applied under a N2 atmosphere. First, the biomasses were carbonized at 500°C for 1 hour, followed by activation at 800°C for 1 hour with different KOH impregnation ratios (1:1, 1:2, 1:3). The characterization of the porous activated carbon materials was performed using elemental analysis (C, H, N, S), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area analysis, and Scanning Electron Microscopy (SEM) techniques. The adsorption properties of the activated carbons were investigated by batch adsorption method for the removal of amoxicillin from aqueous solutions at different concentrations. Since the activated carbons with a 1:3 biomass/KOH weight ratio exhibited the highest surface areas (2070-2254 m²/g), these samples were used in the adsorption experiments. The adsorption mechanism was elucidated using Langmuir and Freundlich isotherms, while the kinetic analysis was conducted using the Intra-Particle Diffusion, Pseudo-First-Order, and Pseudo-Second-Order models. The most suitable model for the adsorption mechanism was the Langmuir isotherm, while the Pseudo-Second-Order model was found to be the most appropriate for adsorption kinetics. The removal of amoxicillin from aqueous solutions was successfully achieved with an efficiency of 96.4%, and the maximum Langmuir adsorption capacity was calculated to be 330.60 mg/g at an initial concentration of 50 ppm and a contact time of 75 minutes. In conclusion, it has been determined that activated carbon derived from agricultural waste is strategically important for environmental sustainability and the protection of water quality.