Repurposing waste plastic through catalytic conversion for use in the removal of tetracycline antibiotics from wastewater

Tetracycline (TC) is a widely used antibiotic that is frequently detected in various aquatic environments, posing a serious ecological threat. In this study, carbon nanotubes (CNTs) synthesized from recycled polymer using a trimetallic catalyst were acid-functionalized to improve their adsorption performance toward TC. The properties of the resulting adsorbent were characterized using multiple analytical techniques, including N₂ adsorption/desorption isotherms, high-resolution transmission electron microscopy (HR-TEM), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. The F-CNTs exhibited a BET-specific surface area of 100.20 m²/g, with the presence of OH functional groups and reduced structural defects confirmed through characterization. TC adsorption on the functionalized CNTs was strongly influenced by pH and temperature, with optimal performance observed at 30°C and pH 4. Kinetic analysis showed that the intraparticle diffusion model provided the best fit (R² = 0.9776), outperforming the pseudo-first-order (R² = 0.7982) and pseudo-second-order (R² = 0.9045) models. Thermodynamic parameters (ΔG⁰, ΔH⁰, and ΔS⁰) indicated that the adsorption process was spontaneous and exothermic. An adsorption efficiency of approximately 94% demonstrates the effectiveness of the developed F-CNTs in removing TC from wastewater. The findings show that the adsorption of TC on F-CNTs is primarily governed by the surface characteristics and the chemistry of the aqueous environment.