Preparation Of Novel Heterogeneous Fenton Catalysts And Their Catalytic Degradation Properties Over Organic Contaminants

The rapid development of industrialization has not only brought affluent material culture life to human being, but also caused the ever increasingly serious damage to water environment and human health. As one of the most intensively studied advanced oxidation processes, Fenton process has its own unique advantages including high degradation efficiency, benign process, inexpensive materials and general applicability. However, traditional Fenton system requires highly acidic conditions(pH 2-4) to avoid ferrous and ferric ion hydrolysis. Additionally, the removal of the sludge containing iron ions complicates the overall process and makes the method uneconomical. To overcome these disadvantages of the homogeneous Fenton process, increasing attention has been paid to develop heterogeneous catalysts. In the present work, we synthesized a series of heterogeneous catalysts and used them for the degradation of organic contaminants. The possible photocatalytic mechanism was also proposed. The main research work is as follows:(1) A series of graphene oxide(GO)-FePO4 composites with different GO weight ratios(2.5, 5, 10%, w/w) were prepared using a simple precipitation process and were firstly used as heterogeneous photo-Fenton catalysts. XRD analysis confirmed the amorphous state of the composite. FESEM images prove the loose structure of the 5GO-FePO4 composite. UV-vis analysis demonstrates that the introduction of GO could enhance solar energy utilization of the composites. Under visible light irradiation, the discoloration rate of rhodamine B(RhB) by the 5GO-FePO4 composite was 2.87 times more than that of by the pure FePO4 in the presence of hydrogen peroxide. Moreover, the composite was highly effective for the discoloration of RhB in a wide pH range of 2.18-10.40 with negligible iron leaching and the composite still showed high catalytic activity after six cycles, which make it a promising heterogeneous catalyst for wastewater treatment. The introduction of GO promotes the photo-Fenton reaction of GO-FePO4 via three roles: offering more active sites, increasing adsorption capacity and accelerating the Fe3+/Fe2+ cycle by improving the utilization of solar energy. Our work may provide new insights for the development of new effective heterogeneous photo-Fenton catalyst.(2) Fe-MMT-RhB composite was prepared using a Fenton oxidation method during the degradation of RhB(1000 mg/L). The composite was used as both adsorbent and catalyst. Kinetic study exhibited that the adsorption of RhB onto Fe-MMT-RhB followed a pseudo-second-order model. The equilibrium data could be well fitted with the Langmuir isotherm, indicating a monolayer adsorption process. The adsorption capacity of RhB by Fe-MMT-RhB was much higher than that of Fe-MMT and MMT due to the introduction of RhB which increased the layer spacing of MMT. The maximum adsorption capacity of Fe-MMT-RhB toward RhB is 207.5 mg g-1, which is higher than most of the adsorbents reported in the literatures. Heterogeneous Fenton degradation method was used to regenerate the Fe-MMT-RhB, and the adsorbent still showed high adsorption capacity toward RhB even after 5 runs, indicating the heterogeneous Fenton degradation method is a promising regeneration method for adsorbents. Using Acid Red G as simulated pollutants, the as-prepared Fe-MMT-ARG also possessed high adsorption capacity toward RhB, indicating the generalizability of the preparation method.Moreover, as a heterogeneous Fenton catalyst, the Fe-MMT-RhB exhibited high degradation efficiency toward RhB over a wide pH range(2.01-11.67), which could overcome the drawback of narrow pH range of homogeneous Fenton reaction. FT-IR analysis and XPS analysis confirmed the structure stability of the catalyst. PL and controlled experiments indicated that the hydroxyl(?OH) radicals which generated from the surface of the catalyst were the main active species.(3) A simple calcination was used to treat the iron sludge which generated from Fenton process. XRD analysis showed that the iron sludge was mainly FeOOH and the treated iron sludge was mainly α-Fe2O3 and γ-Fe2O3. The result of XPS and TG/DSC analyses were in good agreements with XRD analysis. The iron sludge calcined at 600 °C showed much higher degradation efficiency of RhB in heterogeneous Fenton process as compared to that of the untreated iron sludge. Simulated iron sludge was also prepared using RhB and ARG as simulated pollutants and they also showed good degradation efficiency toward RhB. ESR and capture experiments indicated that ?OH radicals were the main active species for the heterogeneous degradation process.(4) Graphene-iron sludge composites were synthesized using little amount of graphene doped with the iron sludge which generated from Fenton process. XRD, XPS and Raman analyses clearly showed the existence of graphene in the composite, the iron sludge in the composite was mainly FeOOH. FESEM showed the smooth and uniform structure of the Fe-G-0 sample and the particle size was 1-2 μm. Under optimum conditions(0.03 g of graphene doping, 1 g/L of catalyst dosage and 10 mmol/L of H2O2 dosage), the Fe-G-3 showed much higher catalytic degradation efficiency of RhB as compared to the Fe-G-0, which could be ascribed to the increased pore size and enhanced adsorption property toward RhB. The degradation of ARG confirmed the catalytic property of the Fe-G-3. PL and capture experiments indicated that ?OH radicals were the main active species for the heterogeneous degradation process.