Optimizing the removal of methylene blue from aqueous solutions using persulfate activated with nanoscale zero valent iron (nZVI) supported by reduced expanded graphene oxide (rEGO)

Background: To remove methylene blue (MB) from aqueous solutions, nanoscale zero-valent iron (nZVI) predicated on reduced expanded graphene oxide (rEGO) was used as the activator of persulfate. Methods: Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analyses were used to investigate the surface morphology and to examine the surface elemental composition. X-ray diffraction (XRD) was used to determine the chemical compositions of the synthesized compound. In this study, the effects of pH (3-9), activator dose (0.4-1.6 g L-1), persulfate concentration (0.192-0.768 g L-1), and reaction time (0-60 minutes) on the removal of 10 mg L-1 MB were studied by nZVI -reduced expanded graphene oxide/persulfate (nZVI@rEGO/PS) process. Results: The maximum removal efficiencies of MB at optimum operational conditions (pH 3, activator dose = 1.2 g L-1, persulfate concentration = 0.576 g L-1, and reaction time = 20 minutes) by nZVI@rEGO/PS process was 96%. The chemical method was used to prepare expanded graphene. The volume of natural flake graphite increased about 25 times after the process. SEM image of the nZVI@rEGO showed the presence of nZVI placed on the EGO surface in chain structure with a diameter about 100 nm. The EDS analysis of the activator indicated the existence of Fe element to an amount greater than 50%. Conclusion: According to the results, nZVI@rEGO is considered as a promising activator of persulfate.