Phase-Dependent Adsorption of Ciprofloxacin on Copper-Doped Alumina Spheres: Insights into the Role of Surface Properties and Water Matrix Effects

The presence of ciprofloxacin (CPX)—a commonly used antibacterial drug belonging to the quinolones—has been identified as one of the major emerging pollutants within our environment, it can persist in the ecosystems and contribute to the growing problem of antibiotic resistance. Therefore, this study evaluates spherical Al2O3 having either alpha or gamma phase and containing no dopant or copper nanometer-sized particles (CuNPs). This study aims to assess their ability to remove CPX from aqueous systems. Kinetic investigations demonstrated that CPX uptake is very sensible to initial adsorbate concentration, pH value and temperature of the system. Adsorption by γ-Al2O3-based materials was generally higher than by α-Al2O3 ones. Kinetic data were evaluated using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models. Fitted equations depend on the experimental conditions investigated. The effects of adsorption onto the alumina particles were also examined under distilled water and ionic water conditions. Furthermore, the adsorbed amounts at equilibrium were modeled using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. It was determined that the phase of alumina was significant in determining the adsorption capacity. γ-Al2O3 had the largest adsorption capacity towards CPX. Its adsorption capacity in kinetic tests was found to be 5.6 mg/g in distilled water, while its capacity was greater (12.9 mg/g) when tested in ionic water (CPX = 25 mg/L). However, the addition of CuNPs into the alumina spheres reduced their overall capacity to adsorb CPX, as evidenced by decreased values for their respective adsorption isotherms. Furthermore, equilibrium data were fitted using four isotherm models and the best fitting model depended on both the nature of the adsorbent and the characteristics of the liquid phase. Overall, this study suggests that γ-Al2O3-based sorbent systems are highly capable and potentially useful for removing antibiotics from contaminated waters.