Synergetic metronidazole removal from aqueous solutions using combination of electro-persulfate process with magnetic Fe3O4@AC nanocomposites: nonlinear fitting of isotherms and kinetic models

Abstract

The removal of metronidazole (MNZ) from aqueous solutions by the electro-persulfate (EC-PS) process was performed in combination with magnetic Fe3O4@activated carbon (AC) nanocomposite. In the first step, the Fe3O4@AC nanocomposites were synthesized and characterized using energy-dispersive X-ray spectroscopy (XRD), vibrating-sample magnetometer (VSM) and field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), mapping, and Fourier-transform infrared spectroscopy (FTIR) analysis. The effect of Fe3O4@AC, PS and EC processes were studied separately and in combination and finally, the appropriate process for MNZ removal was selected. The effect of key parameters on the EC-Fe3O4@AC-PS process including pH, Fe3O4@AC dosage, initial MNZ concentration, and PS concentration were investigated. Based on the results obtained, the Fe3O4@AC had a good structure. The MNZ removal in EC, PS, Fe3O4@AC, EC-Fe3O4@AC, EC-PS, EC-Fe3O4@AC-NaCl, EC-Fe3O4@AC-PS, and EC-Fe3O4@AC-PS-NaCl processes were 0, 0, 59.68, 62, 68.94, 67.71, 87.23 and 88, respectively. Due to the low effect of NaCl insertion on the EC-Fe3O4@AC-PS process, it was not added into the reactor and optimum conditions for the EC-Fe3O4@AC-PS process were determined. Under ideal conditions, including MNZ = 40 mg/L, Fe3O4@AC dose = 1 g/L, pH = 3, PS concentration = 1.68 mM, current density (CD) = 0.6 mA/cm(2) and time = 80 mM, the MNZ removal was 92. Kinetic study showed that the pseudo-second-order model was compatible with the obtained results. In the isotherm studies, the Langmuir model was the most consistent for the data of the present study, and the Q(max) for Fe3O4@AC dose from 0.25 to 1 g/L was 332 to 125 mg/g, respectively.