Removal of Metronidazole residues from aqueous solutions based on magnetic multiwalled carbon nanotubes by response surface methodology and isotherm study

Antibiotics and pharmaceutical products cannot remove by conventional sewage treatment. In this work, an effective adsorbent magnetic multiwalled carbon nanotube (Fe3O4@MWCNTs; MMWCNTs) was synthesized by co-precipitation of MWCNTs with Fe3O4 and used for removal of Metronidazole from aqueous solutions. Response surface methodology on central composition design (CCD) was applied for designing of experiments and building of models for Metronidazole removal before determination by HPLC. Four factors including pH, the adsorbent dose, time, and temperature were studied and used for the quadratic equation model to the prediction of optimal points. By solvent the equation and considering the regression coefficient (R2 =0.9997), the optimal points obtained as follows: pH =2.98; adsorbent dosage =2.16 g; time =22 min and temperature = 37.9 oC. The isotherm study of adsorption showed that the metronidazole adsorption on Fe3O4@MWCNTs follows the Langmuir model. The maximum adsorption capacity (AC) is 215 mg g-1 obtained from Langmuir isotherm. The results showed that three factors including pH, amount of adsorbent, and temperature are significant on removal efficiency and an experimental point was found to agree satisfactorily with the predicted values. The proposed methods coupled to HPLC were used to analysis of metronidazole in six real samples. The results showed the best removal efficiency was obtained at optimal points. Moreover, the reusability of adsorbent showed that the Fe3O4@MWCNTs can be efficiently removed the Metronidazole from aqueous solutions as compared to other