Magnetic core-shell ZnFe2O4/ZnS nanocomposites for photocatalytic application under visible light.

Magnetic core-shell ZnFe2O4/ZnS composites were synthesized through a two-step chemical process including the hydrothermal and the co-precipitation methods. The structural characterization revealed that the composites consisted of a layer of ZnS clusters on the surface of ZnFe2O4 nanoparticles. The band gap energy of the composite was estimated to be 2.2eV through the Kubelka-Munk plot, implying the possible application as a photocatalyst under the visible light radiation. The improved photocatalytic efficiency of the ZnFe2O4/ZnS composites was confirmed through the photocatalytic degradation of Methyl Orange. The increased absorption of the visible light and the enhanced separation of the electron-hole pairs due to the relative energy band positions in ZnFe2O4 and ZnS are considered as the main advantages. Additionally, the moderate magnetization of the ZnFe2O4 core insured the easy magnetic collection of the composite materials without affecting the photocatalytic performance. Our results showed that ZnFe2O4-based nanocomposites could be used as an effective and magnetic retrievable photocatalyst.

Magnetic and electric properties of stoichiometric BiMnO3 thin films.

It has been suggested that BiMnO3 is a material exhibiting both ferromagnetism and ferroelectricity. Stoichiometry is rather easily achieved in a polycrystalline sample, and ferromagnetic properties have been well documented for bulk samples. Stoichiometry in thin films has been difficult to obtain, and many physical properties have exhibit wide distributions mainly due to the stoichiometry problem. Thin film studies on BiMnO3 have not shown clear evidence of ferroelectricity, while other physical properties measured for the BiMnO3 films showed wide spectra, which has been attributed to cation and/or oxygen vacancies. We fabricated BiMnO3 thin films with good stoichiometry and with ferromagnetic properties comparable to those reported for stoichiometric BiMnO3: Tc ~ 105 K and M sat ~ 3.6 µB/Mn. The charge-electric field (Q-E) curve measured at 5 K was fairly linear and free from hysteresis and showed no ferroelectric order. This finding is consistent with the centrosymmetric crystal structure recently suggested by theoretical calculations and structural studies on ceramic samples of stoichiometric BiMnO3.