The Synthesis, Characterization, And Properties Of Iron Oxides And Iron Oxide Hydroxides Nanomaterials

Iron oxides(Fe_xO_y) and Iron oxide hydroxides(FeOOH) nanomaterials have been prepared by hydrothermal/solvothermal methods that employed Fe(NO₃)₃·9H₂O and KOH(mineralizer) as starting materials. The effects of solvent, surfactant, reaction temperature, mineralizer concentration and holding time on the phase formation, performance, and reaction mechanism of Fe_xO_y and FeOOH nanostructures were studied. The preparation processes have been investigated by means of XRD, TEM, HRTEM, SEM, FI-IR, PPMS and TG-DTA. The main work in this thesis is as follows:1. Based on the effect of eth on the growth of α-Fe₂O₃ nanoparticles, mass α-Fe₂O₃ nanoparticles surface-modified by polyvinyl alcohol (PVA) have been synthesized via solvothermal treatment of Fe(NO₃)₃·9H₂O and KOH. The as-prepared α-Fe₂O₃ nanoparticles showed well crystalline and disperser with the diameter of 20～100nm. It was found PVA is one kind of excellent surfactant to control the size of particles and improve the disperser and stability of nanoparticles in the solution. A lot of free hydroxyls with highly polar in the structure of PVA make it have easy to form chelating-bonds with metal ion by using its hydroxyls as ligands so that metal ion can be surround by it to form limited space for the ligands of PVA restricting, which prevented the growth of nanoparticles and their congregation.2. Large-scale Fe₃O₄ nanoparticles with uniform diameter of 16nm were synthesized using a simple solvothermal route that employed Fe(NO₃)₃·9H₂O and KOH as starting materials, ethylene glycol (eg) as the solvent. The effects of temperature and mineralizer concentration on the morphology of products were studied. The results showed that size of cubic phase Fe₃O₄ nanoparticles could be controlled by the temperature and mineralizer concentration. The present method is simple, large-production and nanocrystals prepared using this method exhibited significantly small size effect.3. When the Fe₃O₄ powers were synthesized by solvothermal treatment ofFe(NO₃)₃·9H₂O and KOH, using PEG as a capping agent, ethylene glycol (eg) as thesolvent, it can be found that some Fe₃O₄ nanopins with the diameter of 5nm and the length of 30～50nm were formed in solutions. The concentration of PEG was supposed to play an important role in the formation of Fe₃O₄ nanopins. The mechanism of PEG accelerating Fe₃O₄ nanopins' formation was preliminarily discussed.4. Large-scale α-FeOOH nanowires were synthesized by hydrothermal treatment of Fe(NO₃)₃·9H₂O and KOH. X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) images show that the products are orthorhombic structure α-FeOOH nanowires with diameter of 80nm and length up to 1.5²um. Selected area electron diffraction (SAED) and high resolution TEM (HRTEM) studies indicated the single-crystalline nature of α-FeOOH nanowires with an oriented growth along the [001] axis direction. The effects of temperature, mineralizer concentration and time on the morphology of products were studied. It was found that: No effect on the crystallinity of α-FeOOH when different mineralizer concentration were used at low temperature(40oC), amorphous phase will be obtained; With the increase of the mineralizer concentration, the crystallinity of α-FeOOH decrease and a few hexagonal α-Fe₂O₃ were gained at 100°C; At high temperature(200oC), α-FeOOH nanowires obtained by hydrothermal synthesis processing convert to hexagonal α-FejOs rapidly.5. Heat treatment of the as-prepared α-FeOOH nanowires in this dissertation at different temperature for 0.5h. The results showed that phase transformation of α-FeOOH occured between 240°C and 295.1°C, which obeyed the same process described as 2α-FeOOH→α-Fe₂O₃+H₂O at different heat treatment temperature. XRD and TEM showed that the products of heat treatment also remained nanowire morphology with many holes on the surface. The experiment on catalytic performance for ammonium perchlorate (AP) indicated that all the products obtained by heat treatment of α-FeOOH nanowires at different temperature made the temperature of high-temperature exothermic peak of AP decrease. The sample obtained upon heating α-FeOOH nanowires at 350°C made it largest decrease by 71.4°C.