Preparation,characterization Of Co^Ⅱ/Co^Ⅲ And Cu^Ⅱ/Cu^Ⅰ Based Heterogeneous Fenton Catalysts For The Degradation Of Congo Red

Owing to the growth of global population and escalation of environment pollution, which recent years have witnessed an ever-increasing demand for supplies of clean and safe water sources. Thus, it is of great importance to explore technologies for water treatment. Synthetic dyes constitute a large group of water pollutants. Congo Red(CR), a type of azo dyes, is widely utilized in the textile industries. Due to the stability, CR is resistant to biological degradation, resulting in low efficiency of conventional biological treatment. Other methods, such as adsorption, membrane separation, electrochemical oxidation and flocculation have been studied to remove CR from aqueous solutions. However, these methods suffer some drawbacks such as low efficiency and/or high cost. Currently, the Heterogeneous Fenton reactions show great application potentials for pollutant degradation and remediation because of the high efficiency, simple operation and low cost. In this thesis, two types of heterogeneous Fenton catalysts were reported in this thesis. The content of this thesis can be categorized as follows:(1) Cobalt-copper oxalate nanofibers were synthesized by a facile precipitation method and further examined as catalysts for reactions. The morphology of samples was observed by field emission scanning electron microscopy and transmission electron microscopy, Brunauer–Emmett–Teller method.The crystallographic structures of the samples were examined by X-ray diffraction. Using CR as a pollutant, the catalytic performance of cobalt-copper oxalate was studied. Experimental parameters including initial pHs of pollutant solutions, concentrations of CR and H2O2, and reaction temperature significantly affected the degradation of CR. To explore the catalytic mechanism of the cobalt-copper oxalate, the pH and concentrations of H2O2 and metal ions were monitored. It was found that the hydroxyl radicals derived from the activation of H2O2 molecules by metal centers were mainly responsible for the degradation of CR molecules, and that cooper ions played a critical role on the superior catalytic performance of cobalt-copper oxalate. Further experiments indicated that the solid-liquid interface was the main place where the degradation reaction took place. The degradation products were analyzed by a liquid chromatography-mass spectrometer and the degradation pathway was revealed.(2) A series of oxides were synthesized via the calcination of corresponding oxalates and further examined as catalysts for the heterogeneous Fenton reaction. The structures of as-prepared oxides were characterized by field emission electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The catalytic activity of the oxides was evaluated by the degradation of Congo red. It was found that Co0.5Cu0.5O showed the best catalytic performance. Subsequently, the effects of operating parameters including the substrate concentration, pH, H2O2 concentration and reaction temperature in the catalytic performance of the Co0.5Cu0.5O were systematically studied. Under optimized conditions of catalyst loading = 200 mg L-1, pollutant concentration = 100 mg L-1, H2O2 concentration = 3 wt. %, temperature = 30 oC and pH = 9, the Co0.5Cu0.5O catalyst could completely degrade the Congo red within 60 min. To investigate the catalytic mechanism, the pH and concentrations of H2O2 and metal ions were monitored during the Fenton process. Mechanistic studies revealed that hydroxyl radicals and superoxide radicals derived from the activation of H2O2 molecules by metal centers were mainly responsible for the degradation of Cong red, and that cooper ions played a critical role on the superior catalytic performance of the Co0.5Cu0.5O catalyst. The Co0.5Cu0.5O catalyst showed negligible metal leaching and outstanding recyclability, which are highly favorable for the practical application in the Fenton process. The degradation products were analyzed by a liquid chromatography-mass spectrometer and the degradation pathway was revealed.It was demonstrated from this thesis that the redox pairs of CoⅡ/CoⅢ and CuⅡ/CuⅠ can be utilized to activate H2O2 molecules to produce highly oxidative radicals for heterogeneous Fenton process and that a significant synergistic effect was present in the Fenton-like degradation of CR when these two redox pairs were involved. Heterogeneous cobalt-copper oxalate and cobalt-copper oxalate oxide catalysts not only showed excellent catalytic performance for the degradation of CR, but also offer the advantage of facile separation from the effluents. The heterogeneous Fenton reaction mainly occurred at the solid-liquid interface where the metal species remains substantially in the solid phase. Pollutants can be degraded by heterogeneous Fenton reaction in a wider pH range with less metal losses in comparison with the homogeneous Fenton reaction. Thus, the Fenton-degradation of organic dyes mediated by the redox pairs of CoⅡ/CoⅢ and CuⅡ/CuⅠ could provide a new route to water treatment.