Synthesis And Properties Of Iron Oxide And Its Hybrid Nanostructures

The iron oxides of maghemite (y-Fe2O3) and magnetite (Fe3O4) are promising candidates in environmental issues. Magnetic iron oxides are widely reported with low cost, strong adsorption capacity, easy separation in wastewater treatment. Here, we report the assembly of y-Fe2O3nanoparticles into particulate nanosheets in solvothermal system, the magnetic adsorbents display extraordinary performance in removing Cr6+and methyl orange. Also, the synthesis and properties of α-Fe2O3/TiO2hybrid nanostructure are studied. The details are as follows:1. The possible polymorphous transformations of α-Fe2O3,β-Fe2O3, y-Fe2O3and ε-Fe2O3are reviewed. The structural, magnetic properties, methods of synthesis, and applications of y-Fe2O3are summarized. In addition, the toxicity of heavy metals and organic pollutants are discussed in detail.2. The maghemite particulate nanosheets are prepared in solvothermal system by connecting the nanoparticles in two-dimension. The reaction temperature, reaction time and the ratios of the solvents have direct influences on the product. When the reaction time is6h, the product is mainly composed of agglomerated nanoparticles. When the reaction time is prolonged to12h, more nanosheets are observed. A great number of nanosheets are obtained when the reaction time extended to24h. A two-stage growth process is proposed for the formation of the maghemite particulate nanosheets. N2adsorption-desorption isotherm curve are conducted to investigate the specific surface area. Our results suggest that the maghemite particulate nanosheets have more accessible surface area comparing with that of the nanoparticles. We also measured the magnetic properties of the maghemite particulate nanosheets and nanoparticles, both of them exhibit ferromagnetic characteristics at4K and superparamagnetic characteristics at300K. The γ-Fe2O3nanoparticles shows that the blocking temperatures is ca.75K, which is common for superparamagnetic nanoparticles. For the maghemite particulate nanosheets, the peak temperature shifts to a higher value of ca.170K comparing with that of γ-Fe2O3nanoparticles,3. The adsorption experiments of Cr6+and methyl orange onto the γ-Fe2O3nanoparticles and maghemite particulate nanosheets are performed at room temperature. The pH of the solution influences the surface properties of the adsorbent. Therefore, the adsorption process is critically associated with pH value. When the y-Fe2O3nanoparticles and maghemite particulate nanosheets are used in removal of Cr6+, the optimized pH value is3.0. The Cr6+removal process fit with Langmuir adsorption model with an adsorption capacity of20.41mg/g. The purified solution could reach a residual concentration of0.002mg/L for maghemite particulate nanosheets, which is much less than the concentration in the solution of0.249mg/L when the nanoparticles are used. The used MPNs are regenerated by immersing in NaOH and the removal efficiency could reach98.79%after ten cycles. In addition, the maghemite particulate nanosheets also exhibit excellent adsorption efficiency to methyl orange. The removal process fit with Langmuir adsorption model with an adsorption capacity of22.79mg/g.4. TiO2and α-Fe2O3/TiO2hybrid nanostructures are synthesized using hydrothermal method. For the preparation of TiO2, anatase and rutile TiO2could be obtained with different amount of HCl. For the synthesis of α-Fe2O3/TiO2hybrid nanostructures, by adjusting the amount of Fe(NO3)3·9H2O, we can get the hybrid nanostructures with different morphologies. The photocatalytic experiments are conducted using TiO2and a-Fe2O3/TiO2hybrid nanostructures, the Fe2O3/TiO2hybrid nanostructures exhibit higher photocatalytic properties compared with that of TiO2.