Effect Of Doping La, Ce On The Phase Transition And Surface Adsorption Behavior Of Iron Oxide Nanoparticles

Today, with the development of the economy, the environmental pollution has become a direct threat to the survival of mankind and a focal problem to solve immediately. It has great significance to develop the new energy-efficient nano-materials for environmental treatment. Iron is an important and ubiquitous rich element in the earth, and its (hydro-)oxide, with good environmental compatibility, is the most common mineral in the soil and the water. Nano-iron oxide has stability, gas sensitivity, magnetism, catalysis properties, etc., however, it has tendency of agglomeration, and magnetic component alone can't satisfy the wider use. Therefore, in this study, we have selected the appropriate doped metal ion and controlled the micro-structure of material to improve the material performance effectively. As the rare earth element has the special atomic structure, a lot of inner 4f orbital unpaired electron, higher atomic magnetic moment, been extremely rich in electronic energy level, and almost all elements can be reacted with the rare earth elements to form a multi-valence state, multi-coordination number (3¹2) compounds, with many excellent optical, electrical, magnetic, nuclear and other features. Therefore, we chose the rare earth elements lanthanum and cerium to dop nano-iron oxide in order to improve material properties.In this thesis, the ferric nitrate with 9 crystal water is used as the iron source to prepare nano-iron oxide and rare earth elements (La, Ce)-doped nano-iron oxide by the sol-gel method. The synthesized products were characterized and analyzed by the X-ray powder diffraction (XRD), Infrared absorption spectra (IR), thermogravimetric and differential thermal analysis (TG/DTA), N2 adsorption-desorption measurement (BET) and fluorescence spectroscopy (FS) techniques. The results showed: doping rare earth elements (La, Ce) inhibited the grain growth significantly, promoted grain refinement, lowered crystallinity, increasesed specific surface area, thus rare earth elements (La, Ce)-doped nano-iron oxides can be as a good adsorbent, a catalyst, and an important source of carrier beause of its advantageous special surface. In addition, controlling the reaction atmosphere and the reaction temperature could control the crystalline type and the particle size of the prepared nano-iron oxide; doped rare earth elements (La, Ce) played an inhibition for nano-iron oxide phase transition behavior from theγ-Fe₂O₃ phase toα-Fe₂O₃ phase, increased considerably the phase transition temperature, respectively.Studying the acid-base properties and adsorption behavior of mineral surface can provide more theoretical basis for environmental treatment. The surface acid-base titration of the sample was studied by automatic potentiometric titration techniques. FITEQL software was used to simulate the acid-base equilibrium constants. The sample surface adsorption behavior had been studied using atomic absorption spectrophotometer to measure the sidual concentration of metal ions. The WinSGW software was used to simulate the complexation equilibrium constant of the sample surface adsorbing the metal ions (Cu²⁺, Pb²⁺, Zn²⁺). The results showed that in acid solution, the buffer capacity of the rare-earth-doped nano-iron oxide is significantly greater than that of the non-doped. Moreover, the buffer capacity of the La-doped is greater than that of the Ce-doped. In alkaline condition, the the Ce-doped nano-iron oxide has the maximum buffer capacity. After hydration for 12h, the La-doped iron oxides after heat treatment at 500℃are stabilized in the water solution and the amount of sample is proportional to its buffer capacity. In a certain range of pH values, the adsorption of heavy metal ions (Cu²⁺, Pb²⁺, Zn²⁺) on the sample surface is proportional to the changes of the pH value. The maximum adsorption of Cu²⁺, Pb²⁺, Zn²⁺ occurs at pH 5.30, 5.35, 5.65 respectively, and at the pH near to the maximum adsorption capacity, the adsorption capacity of Ce-doped nano-iron oxide is higher than that of La-doped and undoped nano-iron oxide. Within a certain range, increasing the dosage of the Ce-doped iron oxides after heat treatment at 500℃, the adsorption amount was increased significantly, in the order of Pb²⁺> Zn²⁺> Cu²⁺.