Accumulation mechanism of tetracycline hydrochloride from aqueous solutions by nylon microplastics

Nylon microplastics and tetracycline hydrochloride (TH) coexist ubiquitously in the coastal aquaculture areas. In this study, the nylon microplastics were characterized by the scanning electron microscope (SEM) and Fourier transform-infrared spectroscopy (FTIR). Kinetic experiments were performed at various microplastics size and reaction temperature, respectively. The effects of adsorbate concentration, initial solution pH, ionic strength and Pb2+ ions concentration were investigated. Desorption experiments were quantified in aqueous solutions and under simulated gut conditions, respectively. The results show that the sorption kinetics of TH onto nylon microplastics closely conform to both the pseudo-second-order model and the intraparticle diffusion model. The fitting sorption isotherm models (Linear, Freundlich and Langmuir) of TH onto nylon microplastics were highly linear. In addition, the activation energy (E-a), activation enthalpy (Delta H-#), activation entropy (Delta S-#) and free energy (Delta G(#)) of the sorption process were obtained by the Arrhenius and Eyring equations, indicating the TH sorption process was spontaneous and exothermic in nature. TH uptake by nylon microplastics was essentially independent on ionic strength, the presence of Pb2+ ions was found to inhibit TH sorption and TH uptake is highly dependent upon solution pH. These results suggest that the sorption of TH by nylon microplastics is predominated by Van der Waals forces and the migration of nylon microplastics after TH sorption in the presence of metal ions requires further research attention. (C) 2020 Elsevier B.V. All rights reserved.