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. Keywords: Persulfate, Methylene blue, Graphite, Graphene oxide, Kinetic

Activation of Persulfate Using an Industrial Iron-Rich Sludge as an Efficient Nanocatalyst for Landfill Leachate Treatment

In this research, the performance of nanomaterials obtained from the converter sludge (CS) of Esfahan Steel Company, Iran was investigated for the activation of persulfate (PS). The experiments were conducted on real and synthetic leachates. CS showed high catalytic activity for removal of chemical oxygen demand COD and NH3 because of its high iron oxide content. The effects of pH, CS dosage, and PS/COD ratio, temperature, and reaction time on the removal of COD and NH3 were evaluated to optimize operational conditions (pH 2, CS dosage: 1.2 g L−1, PS/COD: 4, and reaction time: 60 min). Maximum COD and NH3 removal efficiencies were 73.56 and 63.87%, respectively. Finally, the optimized process was applied for treatment of a real leachate sample. Although the treated leachate was not suitable to discharge into the environment, an increase in the 5-day biochemical oxygen demand (BOD5) and biodegradability (BOD5/COD) of leachate after treatment indicated that the effluent can be biologically treated. As a consequence, it can be combined with sewage or can be returned to the landfill