Abstract:
This study investigates the adsorption behavior of Ciprofloxacin (CPX) antibiotic on
polyethylene (PE) microplastics through batch adsorption experiments under various
environmental conditions, i.e., ionic strengths, pH and in the presence of dissolved
organic matter (DOM). The adsorption of CPX showed a gradual increase with increasing
pH reaching the maximum adsorption at pH 6.5–7.5 and then decreased, which is
likely due to the redistribution of CPX species with pH. The overall CPX adsorption
capacity of PE microplastics decreased with an increase in the ionic strength revealing
the hydrophobic and electrostatic interactions. Fourier-transform infrared spectra (FTIR)
bands ascribable to −CH2 and −CH3 functional groups exhibited non-polar hydrophobic
properties of PE microplastics. CPX adsorption kinetics data were compatible with
the parabolic diffusion model and the Elovich model in the presence of humic acid,
suggesting that the adsorption was assisted through diffusion-controlled processes.
The isotherm equilibrium data fitted well for Hill and Dubinin–Radushkevich models
implying multilayer adsorption through physical adsorption processes on the heterogeneous
PE microplastics surface. Hence, PE microplastics could be a potential vector
to transport CPX in a natural aquatic environment where the adsorption mechanism is
being influenced primarily by the pH, ionic strength, DOM of the water system, and the
properties of the plastic.
