Activation of persulfate by heat, FeNPs, and Fe/MnO2 for the advanced oxidation processes

In this work, we used only persulfate (S2O82), Fe0/S2O82), Fe/MnO2/S2O82) systems as an activator to generate reactive radical species for the chemical oxidation of Congo red azo dye. The formation of a new colored species at 363 nm and its decomposition was observed at a specific reaction condition for the first time. Congo red-S2O82) redox reaction was very slow at 22 C. After the addition of small amount of Fe/MnO2, the red color was decolorized completely within 6 min. The maximum degradation of Congo red was achieved at optimum parametric values of [S2O82)] = 0.2 mM, [Congo red] = 0.6 mM, amount of Fe/MnO2 = 10 mg, pH = 6.5, and temperature = 22 C. The presence of MnO2 accelerates the generation of sulfate radicals (SO4? & BULL;) during the Fenton-like reaction between Fe/MnO2 andS(2)O(8)(2)) due to the synergistic effect. The activation energy was found to be 40.1, 48.0, and 92.2 kJ/mol for Fe/MnO2/S2O82, Fe/S2O82, and only S2O82, respectively. The oxidation of Congo red follows complex order kinetics with respect to pH as well as concentrations ofS(2)O(8)(2). Chemical probes experiments with various radical scavengers such as ethanol, tertiary butyl alcohol (TBA), and potassium iodide showed that the SO4? & BULL; radicals participate effectively in situ chemical oxidation of Congo red. Cationic cetyl-trimethylammonium bromide (CTAB) retarded the persulfate activation by Fe/MnO2 significantly. The morphology of Fe/MnO2 was determined by XRD, EDX, FTIR, SEM, and TEM.