Adsorption of Levofloxacin on Microplastics in Aqueous Solution

Abstract

Objectives : Recently, microplastics (MPs) is observed at surface water in worldwide because of massive use of plastics. Since MPs have a large specific surface area, they could provide adsorption sites to water contaminants such as Levofloxacin (LVF). LVF is one of widely used antibiotics and is detected in surface water. Therefore, the aim of this study is to evaluate adsorption trend of LVF on polypropylene (PP) and polyethylene(PE) microplastics in aqueous solution.Methods : For kinetic adsorption experiment, 0.02 g of PP and PE MPs were placed in glass vials and mixed with LVF solution (10 mg/L) for 1-48 hours. And the experimental data was fitted to pseudo-first order and pseudo-second order. For isotherm adsorption experiment, initial LVF concentrations were varied from 1 to 25 mg/L for 24 hours and the results were applied to Langmuir and Freundlich models. The Thermodynamic adsorption experiment was conducted in the temperature range of 298-318 K. Each cations (Na+, Ca2+, Cu2+, Cr3+, Pb3+) and LVF solution were both reacted with the MPs to determine effect of LVF adsorption when cations were coexistence.Results and Discussion : Based on the FT-IR analysis, it was confirmed that the prepared PP and PE MPs were consisted of the respective single polymer. The kinetic experiment results showed that LVF adsorption on PP and PE MPs reached equilibrium at 24 hours with adsorption capacities of PP (0.748 mg/g) and PE (0.801 mg/g) MPs, respectively. Kinetic data of PP MPs was well fitted to the pseudo-first order (R2=0.986) model, while the data of PE MPs was described well by the pseudo-second order (R2=0.992) model. The results of the isotherm experiments were explained well by the Freundlich model (R2>0.97), indicating that multilayer adsorption occurred in both MPs. The thermodynamic experiments showed that LVF adsorptions on each MPs were exothermic reaction and physical adsorption process. Cations can inhibit the adsorption of LVF to the MPs.Conclusion : This study shows that LVF could be adsorbed to PP and PE MPs in aqueous solution and its adsorption capacity can be changed according to the various factors: characteristics of polymer, reaction time, initial concentration of LVF, temperature, and coexistence of cations.