Design Of Novel Heterogeneous Fenton Systems And Their Enhanced Performance On Organic Pollutants Degradation

In recent years, the rapid developments of industry and technology have greatly promoted the convenience of people’s life. But it also caused serious environmental pollution. For example, the industrial wastewater, sewage and agricultural wastewater led to a major threat in our water environment. Therefore, how to effectively control the water pollution became a focus of global concern. Among the treatments of environmental pollution, Fenton oxidation as an advanced oxidation technology, has attracted much attention due to its capability to produce non-selective oxidants (such as hydroxyl radical). However, the classical Fenton system always restricted by the low solution pH and the generation of iron sludge, which led to the high cost or complicated operations during the actual wastewater treatment. Therefore, we need to develop more efficient Fenton systems for the increasingly serious water pollution control.Heterogeneous Fenton reaction means the use of iron-containing material as the Fenton’s reagent. Due to the reactions mainly occur on the solid-liquid interface, the heterogeneous Fenton systems always demand lower concentration of ferrous ions, and which could avoid the formation of iron sludge. In addition, the hydrogen peroxide utilization efficiency in the heterogeneous Fenton system is much higher than that in the homogeneous Fenton system. More importantly, the heterogeneous Fenton’s reagent could realize high pollutants degradation efficiency at the neutral pH. Currently, the widely used heterogeneous Fenton’s reagents include iron oxides, oxyhydroxides, iron loaded materials and so on. The use of the abundant iron-containing materials on the earth as the Fenton reagent for degradation of organic pollutants has become a hot topic in Fenton research.Therefore, our work mainly aimed to use the widespread iron-based material (such as zero valent iron, pyrite, greigite, etc.) as heterogeneous Fenton’s reagents and studied the mechanism of organic pollutants degradation in the environment. We also investigated the mechanism of the molecular oxygen activation and hydrogen peroxide generation at room temperature and pressure in the developed Fenton process. After that, we attempted to clarify the routes and the contributions of the molecular oxygen activation process and the enhanced pollutants degradation mechanism in the different heterogeneous Fenton systems.The detailed works were shown as the following:1. We investigated the effect of extra ferrous ions on the aerobic simazine degradation with Fe@Fe2O3 core-shell nanowires at circumneutral pH and interestingly found that ferrous ions could promote the aerobic simazine degradation efficiency of nanowires by about 5 times. The aerobic simazine degradation improvement was realized by maintaining enough dissolved ferrous ions and enhancing single-electron reduction molecular oxygen activation via providing more surface bound ferrous ions on the iron oxide shell. These increased surface bound ferrous ions could produce more surface hydroxyl radicals to enhance the simazine degradation. The 2,2’-bipytridine inhibition and reactive oxygen species detection results revealed that the contribution of sequential single-electron molecular oxygen activation by surface bound ferrous ions to reactive oxygen species production was more than 60%, higher than that of two-electron molecular oxygen activation pathway. We determined the degradation intermediates of simazine with high performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry to tentatively propose a possible simazine degradation pathway. These interesting findings could provide new insight on nanoscale zero valent iron induced molecular oxygen activation and its aerobic removal of organic pollutants at circumneutral pH.2. We demonstrated that hydrothermal synthesized FeS2 (syn-FeS2) is highly efficient to catalyze the H2O2 decomposition for the alachlor degradation in a wide range of initial pH (3.2-9.2). The alachlor degradation rate of syn-FeS2 heterogeneous Fenton system was almost 55 times that of commercial pyrite (com-FeS2) counterpart at an initial pH of 6.2. Experimental results revealed that the alachlor oxidation enhancement in the syn-FeS2 Fenton system was attributed to the molecular oxygen activation induced by more surface bound ferrous ions on syn-FeS2. The molecular oxygen activation process could generate superoxide anions to accelerate the Fe(II)/Fe(III) cycle on the syn-FeS2 surface, which favored the H2O2 decomposition to generate more hydroxyl radicals for the alachlor oxidation. It was found that the hydroxyl radical generation rate constant of syn-FeS2 Fenton system was 71 times that of cow-FeS2 counterpart, and even 1-3 orders of magnitudes larger than those of commonly used Fe-bearing heterogeneous catalysts, respectively. We detected the alachlor degradation intermediates with gas chromatography-mass spectrometry to tentatively propose a possible alachlor degradation pathway. These interesting findings could provide some new insights on the molecular oxygen activation induced by FeS2 minerals and the subsequent heterogeneous Fenton degradation of organic pollutants in the environment.3. We demonstrated that solvethermal synthesized Fe3S4 is highly efficient to catalyze the H2O2 decomposition for the roxarsone degradation. Although the single Fe3S4 could reduce the nitro group of roxarsone to amino group, it hardly achieved the ultimate organoarsenic removal. However, the additional hydrogen peroxide could promote the nitro group reduction, roxarsone mineralization and subsequently inorganic arsenic immobilization on the Fe3S4 surface. Meanwhile, due to its good magnetism, the Fe3S4 could easily be recycled after the Fenton reaction, which could also promote the cycling stability for the roxarsone degradation. These interesting findings could provide some new insights on the convension of organic moleculars at the interface of magntic iron sulfides.4. We demonstrated a novel three-dimensional Electro-Fenton system (3D-E-Fenton) for wastewater treatment with foam nickel, activated carbon fiber and Ti/RuO2-IrO2 as the particle electrodes, the cathode, and the anode respectively. This 3D-E-Fenton system could exhibit much higher rhodamine B removal efficiency (99%) than the counterpart three-dimensional electrochemical system (33%) and E-Fenton system (19%) at neutral pH in 30 minutes. The degradation efficiency enhancement was attributed to much more hydroxyl radicals generated in the 3D-E-Fenton system because foam nickel particle electrodes could activate molecular oxygen to produce ·O2 via a single-electron transfer pathway to subsequently generate more H2O2 and hydroxyl radicals. This is the first observation of molecular oxygen activation over the particle electrodes in the three-dimensional electrochemical system. These interesting findings could provide some new insight on the development of high efficient E-Fenton system for wastewater treatment at neutral pH.