Synthesis Rare-earth Iron-based Oxide Nanoparticles For Visible Light Degradation Of Rhodamine B

Oxide semiconductor-mediated photocatalytic purification of polluted air and waste water is now a promising environmental remediation technology, especially for low levels of organic contaminants. To date, most researches on photocatalysts are focused on TiO2, due to its biological and chemical inertness, strong oxidizing power, nontoxicity nature, and long-term stability. However, on one hand, the wide band gap (3.2 eV) of TiO2 limits its applications in utilizing the visible light (λ> 400 nm). On the other hand, a photocatalytic reaction is usally conducted in a suspension of submicrometer TiO2, and therefore the catalysts would inevitably encounter an obstacle when applied in practice, that is, the difficulties in separation and manipulation due to their small size. Thus, development of easy recovery and efficient visible-light-induced photocatalysts is the hot spot of photocatalytic studies. Recently, rare-earth orthoferrites ReFeO₃ (Re= rare earth) have received increasing attention, because of its extensive applications in solid oxide fuel cells, sensors, magnetooptic materials, electrode materials, and so on. Besides the above mentioned applications, ReFeO₃ has been regarded as potential visible light photocatalyst due to its narrow band gap (often less than 3.0 eV).In this thesis, EuFeO₃ nanoparticles were prepared by sol-gel method with an aid of tartaric acid at different calcination temperatures. The prepared EuFeO₃ samples were characterized by Differential thermal analysis-thermogravimetry, X-ray diffraction, Fourier transform infrared spectra, Raman spectra, Transmission electron microscopy, UV-visible diffuse reflectance spectrum, N2 adsorption/desorption measurements, and Photoluminescence spectra. The photocatalytic activity of the samples was evaluated by the photocatalytic decolorization of rhodamine B aqueous solution under visible-light irradiation. The calcination temperature for the highest photocatalytic activity of the EuFeO₃ nanoparticles was found to be 750 oC. Much enhanced photocatalytic activity was observed when adding a small amount of H₂O₂ during the photocatalysis, indicating EuFeO₃ nanoparticles have photo-Fenton-like catalytic activity. Moreover, EuFeO₃ nanoparticles were also demonstrated to have an excellent photocatalytic stability, which is useful for the efficient recovery of photocatalyst. This work was published in Journal of the American Ceramic Society.Since the prepared EuFeO₃ nanoparticles exhibited the characteristic of weak ferromagnetism, we expected such magnetic properties may used for the efficient separation of the catalyst from the treated water. However, it must be noted the magnetic moment of the present EuFeO₃ nanoparticles is not high enough to enable the separation of nanoparticles from the treated solution. In order to enhance ferromagnetism in photocatalyst, EuFeO₃/Eu₃Fe₅O₁₂ multiphase nanoparticles were prepared by sol-gel method with adjusting the gel-drying temperature. Our results showed that at the same calcination temperature, the higher gel-drying temperature leaded to the higher room temperature magnetic moment of multiphase nanoparticles, while the photocatalytic activity were decreased. Such behavior might be ascribed to the agglomeration of nanoparticles, which decreased adsorption of RhB on the photocatalyst surface.