Study On The Preparation And Application Of Iron Oxiden Nanoparticles

Iron oxides, including oxyhydroxides, are a kind of natural minerals and geocatalysts, naturally existing in the earth’s crust with great content. Since these iron oxides are very reactive, a number of secondary iron oxides such as maghemite(γ-α-Fe_2-x Al_x O₃), hematite(α-α-Fe_2-x Al_x O₃), lepidocrocite（α-FeOOH）, goethite（γ-FeOOH）, ferrihydrite（Fe5HO8·4H₂O）, and magnetite（Fe₃O₄） were found in aqueous streams as suspended materials with significant amount. Hence, the iron oxides in aquatic ecosystems play a vital role in a variety of chemical and biological processes relevant to the transformation of organic compounds. Different kinds of iron oxides have different structure, coupled with in natural environments, Fe（III）（hydr）oxides rarely exist as pure iron oxide phases, and often contain several metal impurities, such as Al, Si, and Mn, resulting in its nature especially interfacial properties, there is a big difference.Therefore, the research on interfacial properties of the iron oxides formed under the different environment and the adsorption, desorption and degradation rules on pollutants has important theoretical significance and practical application value. The results not only can provide theoretical and experimental data for the objective evaluation of iron oxide in environmental self-purification, but also can provide a useful reference for development of iron oxide in wastewater treatment application.Our research group is mainly engaged in the liquid phase synthesis of iron oxides and its application in sewage treatment. Based on the long-term basic research and the analysis, the basic properties and application in wastewater treatment of hematite and maghemite were studied. In this paper the main research contents and research achievements include:（1） A series of Al-substituted hematite was prepared. The as-prepared products were characterized by XRD, SEM, HRTEM, XPS, and BET. The magnetic properties of the products were determined. The results indicate that the crystal structure and crystalline, magnetization and the surface area of as-prepared samples depend strongly on Al content. The BET surface area and micropore surface area increased with increasing Al content. Al substitution in α-α-Fe_2-x Al_x O₃ induces strain in the structure of hematite and decrease in the size of samples. The remanent magnetization is almost the same for hematite with and without Al-substitution and the coercivity of the samples increases with Al substitution up to nAl/nFe 0.03, and then decreases as Al content further increases. Compared with pure α-α-Fe_2-x Al_x O₃ andα-Al₂O₃, the introduction of Al ions increases both the adsorption capacity and the affinity of the samples.（2） A series of Al-substituted hematite nanoparticles were prepared by co-precipitation（CP） and successive precipitation（SP） methods, respectively. The as-prepared products were characterized by XRD, SEM, HRTEM, XPS, and BET. The magnetic properties of the products were determined. The results indicate that Al ions incorporate into the structure of hematite, with the isomorphous substitution of Fe³⁺ in the process of forming both in the two prepared methods. The products prepared by co-precipitation obtained a smaller size and greater surface area than the products prepared by successive precipitation. The adsorption capacity and the affinity of the samples prepared by co-precipitation are better than the products prepared by successive precipitation.（3） Fusiform-like maghemite particles were prepared through a distinct two-step transformation from Fe（II） to γ-FeOOH and then to γ-α-Fe_2-x Al_x O₃ by precipitation and calcination respectively. The structure and property of as-prepared sample were characterized by XRD, SEM, XPS, UV–vis and FTIR. The degradation of Acid Blue 74 by γ-α-Fe_2-x Al_x O₃ was investigated under visible light irradiation. 1H NMR, TOC, UV–VIS, direct infusion-ESI-（-）MS and FTIR spectroscopic techniques provide an insight into the nature of the degradation products. A more complete degradation mechanism of Acid Blue 74 on γ-α-Fe_2-x Al_x O₃ was presented. The results indicate the total degradation rate is close to 100% for a 100 mg/L Acid Blue 74 solution. Among them, about 60% was completely mineralized and the other 40% was degraded to aliphatic acids. The magnetic γ-α-Fe_2-x Al_x O₃ could be conveniently recovered by applying a magnet and recycled. The γ-α-Fe_2-x Al_x O₃ retained 100% degradation capacity for Acid Blue 74 after 6 cycles.（4） The γ-α-Fe_2-x Al_x O₃ were prepared by the method of（3）. The degradation of phenol by γ-α-Fe_2-x Al_x O₃ was investigated under visible light irradiation. The results indicate that phenol in the experimental system are directly degraded into carbon dioxide and does not appear in the middle of the product.