Adsorption properties of flouroquinolone type antibiotic ciprofloxacin into 2:1 dioctahedral clay structure: Box-Behnken experimental design

Abstract In this study, the removal of ciprofloxacin (CPx) from aqueous solutions by usingmontmorillonite (MMT) clay was studied. The effect of adsorbent amount, contact time, solution pH and temperature were experimentally performed in batch adsorption experiments to examine the adsorption capacity, isotherm, kinetic and thermodynamic parameters of the adsorption process. Under the experimental conditions the system reached equilibrium in 60 min and adsorption capacity was obtained 113.64 mg g−1. The maximum adsorption of CPx on the MMT clay was around 98% and the maximum adsorption capacity was found as 128 mg g−1 at pH 7. Adsorption mechanism was clarified with Langmuir, Freundlich, DubininRadushkevich and Temkin isotherm models. Adsorption experiments were performed at different temperatures to explain kinetic studies with pseudo first order, pseudo second order, intraparticle diffusion and Elovich model. The pseudo second-order kinetic model and Temkin isotherm model could better define the experimental data. Thermodynamic parameters showed that the CPx adsorption was endothermic and spontaneous. Also, the effect of such parameters as solid/liquid ratio (S/L), temperature (T) and pH on the adsorption of CPx was examined using response surface methodology based on Box–Behnken surface statistical design. According to Box-Benhken design, higher values of the correlation coefficients and p-values greater than 0.05 were in good adaptation with the optimum combination of process parameters, which demonstrated the fitness of the chosen model for evaluating the experimental data. In order to explain the interaction mechanism between MMT and CPx, FTIR, XRD, zeta potential and BET surface area analysis were performed before and after adsorption.