This study investigates the use of recycled carbon fibers as precursors for activated adsorbents and applies nitric acid modification to enhance their selectivity toward two antibiotics: ciprofloxacin and oxytetracycline. A design of experiments was employed to optimize key modification parameters: acid concentration (1 – 6 M), hold time (16 – 24 h), and temperature (20 – 60°C), and their influence on adsorption. The modified adsorbents were characterized using N2 adsorption isotherms, Boehm titrations, and potentiometric titrations to determine porosity, acidity/basicity, and point of zero charge. Optimal conditions were identified as 1 M HNO3, 16 h, and 28°C. Under these conditions, modified adsorbents achieved adsorption capacities of 9.63 mg/g for ciprofloxacin and 7.72 mg/g for oxytetracycline. While ciprofloxacin removal decreased by 7% compared with unmodified counterparts, this reduction was not statistically significant. By contrast, oxytetracycline removal improved by 21%, a statistically significant increase. The superior uptake of oxytetracycline was attributed to its greater hydrophilicity and enhanced affinity for the oxidized, hydrophilic surface. Overall, acidic surface modification represents a promising strategy to improve the performance of recycled carbon fiber-derived adsorbents, particularly for tetracycline antibiotics. Further investigation is required to assess whether oxidative treatment methods can improve the removal of fluoroquinolones.
Taylor et al. (Sun,) studied this question.