Study On The Degradation Of Methylene Blue Catalyzed By Metal Oxide/Graphene Composites

Due to the various activities of human beings, water in natural system has been polluted by lots of toxic and hazardous organic contaminants. This dissertation mainly deals with the model organic pollutant Methylene Blue with Advanced Oxidation Processes based on the generation of hydroxyl and sulfate radicals.Graphene oxide (GO) was prepared from natural flask graphite according to the method reported by Hummers. Magnetic Fe3O4/rGO was prepared through co-precipitation of ferric and ferrous iron salts using GO as the presoma. Fe0/Fe3O4/rGO was finally prepared by insitu reduction of ferrous iron salt. The physicochemical properties of the synthesized nanocomposites were characterized by several techniques, such as XRD, FTIR, TEM, XPS, BET, and VSM. The results revealed that small size Fe3O4 nanoparticles were distributed on GO sheets evenly, the relatively bigger size nanoscale zero valent iron synthesized by insitu reduction of iron salts was wrapped by Fe3O4 nanoparticles on the rGO nanosheets. BET measurements indicate that the synthesized nanocomposites has high surface area, which is beneficial for the improvement of catalytic activity. VSM measurement shows that the hybrids were superparamagnetic. The saturation magnetization Ms of Fe3O4/rGO and Fe0/Fe3O4/rGO was 48.86 emu/g and 65.77 emu/g. The catalytic activity was evaluated by activate H2O2 to degrade model pollutant Methylene Blue. The comparison of Fe0/Fe3O4/rGO with nanoscale zero valent iron, magnetic Fe3O4, and Fe3O4/rGO indicate that Fe0/Fe3O4/rGO was the most efficient in the degradation of MB. The effect of pH value, initial concentration of MB, catalyst dosage, and hydrogen peroxide (H2O2) concentration on the degradation of MB were investigated. The results showed that increase of pH value and initial MB concentration was not favorable for the increase of efficiency of MB degradation; However increase the catalyst dosage and H2O2 concentration in a proper range was conducive to the improvement of catalytic activity. Typically,98.0% removal of 100 mL 50 mg/L MB was achieved under the condition:initial pH 3.0, catalyst dosage 0.10 g/L, H2O2 concentration 0.8 mmol/L. Kinetics analysis indicate that the degradation process followed the pseudo second order kinetics. The apparent kinetic constants increased with the increase of temperature. The apparent activity energy was calculated using Arrhenius equation. Finally, the reusability of the catalyst was measured and the results suggest that the material has the potential to be used as a heterogeneous Fenton catalyst to degrade organic pollutants.Fe3O4/Mn3O4/rGO nanocomposite was synthesized as a heterogenous catalyst for the degradation of organic dyes in aqueous solution using sulfate radical-based advanced oxidation process. The synthesis of Fe3O4/Mn3O4/rGO was divided into two separate steps:first, the coprecipitation method was used to synthesize according to the method described by our previous study. Second, hybrids were synthesized using manganese acetate tetrahydrate as a source of manganese at room temperature. The surface structure and physicochemical properties of the composite were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) method. The characterization indicate that few layers GO sheets was fully wrapped by thick Mn3O4 nanoflakes, while Fe3O4 nanoparticles were embedded into the gaps between GO nanosheets and Mn3O4 nanoflakes. The preliminary test of catalytic activity of the catalyst was conducted by comparison of different catalyst, the results show that Fe3O4/Mn3O4/rGO (Fe/Mn= 0.5) was more effective in the degradation of MB than Mn3O4/rGO and Fe3O4/rGO. The catalytic activity of Fe3O4/Mn3O4/rGO in MB decomposition was evaluated in view of the effects of various processes, pH, PMS concentration, MB concentration, and temperature. The results show that initial pH has little impact on the degradation of MB, increase of catalyst dosage and Oxone was favor for the decomposition of MB, while increase the concentration of MB will decrease the degradation rate. Typically, 98.8% removal of 50 mg/L MB and 68.3% TOC removal was achieved in 30 min at temperature 25 ℃,100 mg/L of catalyst, and PMS dosage of 0.3 g/L. The analysis of reaction kinetic indicates that the process followed the pseudo-second-order kinetic model. The activity energy of reaction was calculated by valuate the kinetic constants at different temperature based on Arrhenius equation to be 25.4 kJ/mol. Based on the radical quenching experiment, it is believed that the dominant species in the reaction system was sulfate radicals. Based on the XPS analysis of catalyst before and after reaction, we proposed the possible mechanism of the route of PMS activation:the active sites of catalyst surface, Fe cooperate with Mn sites to activate PMS to degrade MB. Finally, the catalyst exhibited high stability and good reusability according to the three successive repeated reactions.