Removal of drug and dye from aqueous solutions by graphene oxide: Adsorption studies and chemometrics methods

Pharmaceutical products and dyes are the main environmental pollutants in the effluent of textile, cosmetic, and pharmaceutical industries. Therefore, in this study, the central composite design (CCD) based on the response surface methodology (RSM) was used to investigate the operating parameters and determine the optimal conditions for the removal of enrofloxacin (ENF) and Rhodamine B (RhB) by graphene oxide (GO). The structure and morphology of GO were studied using scanning electron microscopes (SEM) and X-ray diffraction (XRD) techniques. Quadratic model was confirmed to describe each of the removal efficiency responses (%R) a with high correlation coefficient (R2 = 0.9987 for ENF and R2 = 0.9999 for RhB) (R2-Adj = 0.9963 for ENF and R2-Adj = 0.9991 for RhB). In optimal conditions, RhB concentration of 10 mg L−1, adsorbent amount of 0.24 g, sonication time of 23 min, ENF concentration of 10 mg L−1, and pH 7, removal rates of more than 92.5% were obtained for both analytes. Adsorption equilibrium was studied with Langmuir, Freundlich, Langmuir-Freundlich, Redlich-Peterson, Toth and Khan isotherm models. Equilibrium data were best fitted with the Langmuir-Freundlich isotherm model. Maximum adsorption capacity of ENF and RhB on GO were 45.035 mg g−1 and 107.230 mg g−1, respectively. The recyclability of GO was evaluated during the ENF and RhB adsorption process. The results showed that up to 4 cycles of adsorbent, the adsorption efficiency is reduced by a tiny amount. The present study showed that GO is highly effective in removing ENF and RhB from environmental water samples.