Metal Oxides Synthesis And Their Performance On The Catalytic Oxidation Of Tetracycline And Phenol

Hydroyxl radical based advanced oxidation processes (AOPs) are extensively applied to degrade non-biodegrable organic compounds. In these processes, active radical species are produced with the activation of oxidants in an aqueous solution, leading to destroy organic pollutants efficiently. Up to now, the most commonly used oxidants are hydrogen peroxide, ozone, and persulfate. They can be active by the homogeneous catalysts or the heterogenous catalysts. However, the homogenous catalytic processes have some drawbacks, such as iron sludge was produced during the reactions, causing secondary pollution, and the oxidation conditions were limited in narrow pH range. To address these problems, the heterogeneous catalytic processes were of great concern. Iron oxides, minerals, and transition metal oxides were used instead of homogeneous catalysts, simplying the separation processes, and avoiding the secondary pollutions. In this case, the solid catalysts can be recycled after the oxidation processes, and can be further reused. The activiation of the oxidants can initiate on the catalyst surface, and then generated·OH or other active species, leading to obtain high removal and mineralization of non-biodegradable organic compounds.Iron oxide and transistion metal oxides are rich in natural environment. Especially, the iron oxides were the most used in the catalytic processes. In our studies, three kinds of metal oxides, such as iron oxide, lanthanum cobalt oxides and lanthanum manganese mixed oxides, were chosen as the heterogenous catalysts, which have different components, structures, special surface areas, crystal sizes, and active site densities. Two kinds of model organic compounds, hydrochloride tetracycline and phenol, were selected. They are widely used, non-biodegradable, and toxic to the environment. In this work, we focused on the mechanism of the heterogeneous catalytic processes based on degraded two kinds of model pollutants. Batch of experiment showed the heterogeneous catalytic processes are considered as a surface reaction over the metal oxides. In addition, combined with other advanced processes (such as ultrasound, UV) can enhance the catalyst stability and its catalytic activity. The main work of this thesis can separate into followed parts.(1) hydrogen peroxide was selected as an oxidant, and it can be active by the magnetite (Fe3O4). Hydrochloride tetracycline was selected as the model organic compound, and its degradation efficiency over this catalyst was investigated using a coupled ultrasound/heterogeneous Fenton process. The effects of the reaction parameters, the evolution of the toxicity of the system, and the reaction mechanism were addressed. The results demonstrated that the stability of the catalyst was significantly improved when ultrasound was employed during the reaction. More intrestingly, a novel membrane separation system was used to explore the surface oxidation mechanism. It should be noted that the surface hydroxyl radicals were determined to be the major reactive species during this oxidation process.(2) sodium peroxydisulfate (Na2S2O8) can be acted as another oxidant, and it also be activated by magnetite (Fe3O4) and ultrasound to produce sulfate radicals and hydroxyl radicals on the degradation of tetracycline effectively. The effects of Na2S2O8concentration, Fe3O4addition, ultrasonic power, initial concentration and initial pH on the degradation of tetracycline were investigated in the process of Na2S208/Fe3O4/ultrasound. The results showed that the removal efficiency of tetracycline increased with the increase of Fe3O4dosage, but decreased with the increase of initial pH and initial tetracycline concentration. The quenching effect was examined by using ethanol, tert-butyl alcohol and1,4-benzoquinone under ultrasound irradiation to evaluate the roles of sulfate radicals, hydroxyl radicals and superoxide radicals. The results indicated that sulfate radicals and the hydroxyl radicals played the major roles for the degradation.(3) ozone was employed as the oxidant, and it also can be activated by magnetite catalyst. The degradation of tetracycline was investigated using the ultrasound-enhanced magnetite catalytic ozonation process (US/Fe3O4/O3). Thorough assessments of the operational parameters, biodegradability and acute toxicity were performed. The results indicated that the TC degradation rate was strongly influenced by the initial pH and the ultrasonic power density over the range investigated, but it was almost independent of the dosage of Fe3O4at the range of0.3-1.0g L-1. The TC degradation rate was diminished in the presence of tert-butanol, isopropanol and NaF. Under the optimized conditions, TC was almost completely removed after20min of treatment, and the COD removal reached41.8%. The COD removal further increased to89.1%when the reaction time was extended to120minutes, and the corresponding biochemical degradability (BOD5/COD) rose to0.694. The acute toxicity reached its maximum value after60min treatment and then decreased with further reaction time. The catalyst stability was evaluated by measuring the TC removal rate and iron leaching for three successive cycles.(4) to enhance the catalytic performance, we try to optimize the catalyst surface properites. Nanostructured Fe3O4particles with different shapes were obtained via an ionic liquid assisted hydrothermal process. The morphology and microstructure of the nano-sized Fe3O4particles were characterized using X-ray diffraction, N2physisorption, transmission electron microscopy, and temperature-programmed reduction. As-prepared magnetite samples show microcube, nanosphere, and porous nanorod morphologies. Activity of the nanostructures was evaluated for the Fenton reaction, using phenol as model molecule. While commercial Fe3O4presents very limited activity, rod-type nanostructure exhibited exceptional activity toward phenol removal under mild conditions;98%phenol was removed, and the TOC removal efficiency was74%. The reusability of porous nanorods of Fe3O4was also investigated after three successive runs, which demonstrated the promising application of the catalyst in the oxidative degradation of organic pollutants. Interestingly, the material activity is strongly affected by the reduction degree, highlighting the beneficial effect of Fe0/Fe3O4mixed phase formation to achieve higher activity.(5) the successful synthesis of highly crystalline nanocomposites, based on LaAxO3(A=Co, Mn) perovskites, are reported via a novel non-aqueous thermal route. The final materials were characterised by X-ray diffraction, transmission electron microscopy and N2physisorption. The solid obtained by this non-aqueous route presents a large difference in specific surface area, redox properties (as measured by reduction by H2), and lower crystallite size, when compared to conventional methods. The reactivity was evaluated using oxygen isotopic exchange (OIE). The results obtained from the exchange reaction showed that the activity was strongly influenced by the crystal size and surface area. These observations correlated well with catalytic activity for phenol conversion under the heterogenous Fenton processes.