Adsorptive removal of diclofenac by graphene oxide: Optimization, equilibrium, kinetic and thermodynamic studies

Diclofenac is a pharmaceutical compound which is listed as a priority substance to be removed from wastewater. The current research investigated the adsorption of diclofenac using graphene oxide (GO) which was characterized by Fourier transform infrared, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. Response surface methodology was employed to optimize the adsorption of diclofenac onto GO based on central-composite design. According to the developed model, the dominant parameters affecting the process were dosage and initial concentration. The optimum adsorption conditions were dosage of 0.16 g/L, time of 14.75 min, initial concentration of 400 mg/L and temperature of 40 degrees C. Under these conditions, GO exhibited a maximum adsorption capacity of 653.91 mg/g for diclofenac. The diclofenac uptake by GO was consistent with the Langmuir adsorption and pseudo-second-order kinetic models. The active binding sites for diclofenac in GO might be hydroxyl, carboxyl and alkoxy as determined by FTIR analysis. The results provided sufficient evidence to support GO as a promising adsorbent for removal of diclofenac in aqueous solution. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.