The Preparation Of Photo-Fenton Photocatalysts And Their Application In The Catalytic Degradation Of Organic Dyes

Recently, advanced oxidation technologies (AOTs) which are used to remove organic dyes in wastewater have become a research hotspot in the field of wastewater treatment because of their advantages such as safety, simplicity, and cleanliness. However, the single oxidation process may have some disadvantages, such as high cost and incomplete degradation. In order to avoid these imperfections, researchers have payed attention to the combination of several AOPs. It has been proved that the Fenton oxidation technology combined with a photocatalytic process can greatly improve the efficiency of mineralization of organic pollutants, which occupies an important position in the field of wastewater treatment as a new kind of advanced oxidation process.In the thesis, photocatalytic technology and heterogeneous Fenton oxidation technology have been combined together to degrade the organic dyes in wastewater. The coupling of heterogeneous Fenton-like catalysts with semiconductor photocatalysts will not only increase catalytic efficiency but also recycle the composite catalyst, which will reduce the cost and avoid the secondary pollution. Based on the research works in the field of wastewater treatment and in our lab, we have done the following research works in this thesis.Graphene oxide (GO) with high specific surface area and high electron transfer ability and heterogeneous Fenton-like reagent of MnFe2O4/H2O2 were combined together to remove organic dyes in the second chapter of this paper. The GO/MnFe2O4 composite catalysts with different mass fraction of GO were prepared by ultrasonic method. Under visible light and in the presence of H2O2,4% GO/MnFe2O4 shows the best catalytic efficiency over the catalytic degradation of methylene blue (MB). The rate constant value reaches 0.053 min-1, which is about 8.7 times higher than that of uising pure MnFe2O4 as the Fenton catalyst. A possible photo-Fenton photocatalytic reaction mechanism for the GO/MnFe2O4 composite was proposed based on the comparison of photocatalytic effect, Fenton oxidation effect, and photo-Fenton photocatalytic effect.In the third chapter, the photocatalyst g-C3N4 and heterogeneous Fenton-like reagent α-Fe2O3/H2O2 was combined together to form a composite catalyst. The α-Fe2O3/g-C3N4 composites with different mass fraction of α-Fe2O3 were prepared by calcining urea in the presence of α-Fe2O3. Under visible light and in the presence of H2O2,0.38% α-Fe2O3/g-C3N4 shows the best catalytic efficiency through the photo-Fenton photocatalytic degradation of rhodamine B (RhB). The rate constant value is 0.11 min-1, which is about 1.7 and 17 times higher than that of using pure g-C3N4 as the photocatalyst and α-Fe2O3 as the Fenton catalyst, respectively. A possible photo-Fenton photocatalytic reaction mechanism for the α-Fe2O3/g-C3N4 composite was proposed based on the comparison of photocatalytic effect, Fenton oxidation effect, and photo-Fenton photocatalytic effect. The α-Fe2O3/g-C3N4 is proved to be stable and reusable, through the cycle experiments and the comparation of XRD patterns of 0.38% α-Fe2O3/g-C3N4 before and after the catalytic reactions.In the forth chapter, the photocatalyst of g-C3N4 and the Fenton reagent of Cu2(OH)PO4/H2O2 was combined together. The Cu2(OH)PO4/g-C3N4 composites with different weight ratio of Cu2(OH)PO4 were prepared by the hydrothermal method. The 30% Cu2(OH)PO4/g-C3N4 shows the best catalytic activity through the photo-Fenton photocatalytic degradation of RhB. The rate constant value reaches 0.093 min-1, which is about 12 and 2.4 times higher than that of using pure Cu2(OH)PO4 as the Fenton catalyst and g-C3N4 as the photocatalyst. A possible photo-Fenton photocatalytic reaction mechanism for the Cu2(OH)PO4/g-C3N4 composite was proposed based on our experiments and the previous works. The Cu2(OH)PO4/g-C3N4 is proved to be stable and reusable through the cycle experiments and the comparation of XRD patterns of 30% Cu2(OH)PO4/g-C3N4 before and after the catalytic reactions.By combination of photocatalytic and Fenton oxidation technologies, photo-Fenton photocatalytic technology become a kind of new advanced oxidation technology. We found that the catalytic reaction rate under visible light and in the presence of H2O2 is much greater than the sum of those of the Fenton and photocatalytic reactions. By comparing photocatalytic reaction rate, Fenton reaction rate, and photo-Fenton photocatalytic degradation reaction rate, the catalytic reaction mechanism has been proposed. It was suggested that the synergetic interaction between the Fenton regent and the photocatalyst boosts the overall catalytic efficiency. Thus, the combination of the photocatalytic and heterogenous Fenton technologies can take advantage of the complementarity and synergetic interaction to make up the deficiency of the single method. The combination of several oxidation technologies, therefore, is the development trend of wastewater treatment technology, and has great potential and application prospect in wastewater treatment.