A comprehensive adsorption study and modeling of antibiotics as a pharmaceutical waste by graphene oxide nanosheets

The adsorption behavior of tetracycline (TCN), doxycycline (DCN) as the most common antibiotics in veterinary and ciprofloxacin (CPN) onto graphene oxide nanosheets (GOS) in aqueous solution was evaluated. The four factors influencing the adsorption of antibiotics (initial concentration, pH, temperature and contact time) were studied. The results showed that initial pH similar to 6 to 7 and contact time similar to 100 - 200 min are optimum for each drug. The monolayer adsorption capacity was reduced with the increasing temperature from 25 degrees C to 45 degrees C. Nonlinear regressions were carried out in order to define the best fit model for every system. To do this, eight error functions were applied to predict the optimum model. Among various models, Hill and Toth isotherm models represented the equilibrium adsorption data of antibiotics while the kinetic data were well fitted by pseudo second-order (PSO) kinetic model (DCN and TCN) and Elovich (CPN) models. The maximum adsorption capacity (q(max)) is found to be in the following order: CPN > > DCN > TCN, obtained from sips equation at the same temperature. The GOS shows highest adsorption capacity towards CPN up to 173.4 mg g(-1). The study showed that GOS can be removed more efficiently from water solution.