Photocatalytic performance and magnetic separation of TiO2-functionalized γ-Fe2O3, Fe, and Fe/Fe2O3 magnetic particles

Abstract

Fe2O3@TiO2, Fe/TiO2 and Fe@Fe2O3@TiO2 catalysts are synthesized by the hydrothermal method combined with the sol-gel method. γ-Fe2O3 nanoparticles are initially synthesized, and some are coated with MgO to obtain Fe2O3@MgO particles. MgO is used to prevent the magnetic particles from aggregating in the subsequent high temperature reduction and oxidation processes. To improve the magnetic separability, strongly magnetic Fe@MgO particles are prepared by reducing Fe2O3@MgO in a mixed H2/N2 atmosphere. To investigate the effects of the Fe2O3 intermediate layer on the photocatalytic performance, Fe@MgO is oxidized in air at 500 and 900 °C to prepare Fe@Fe2O3@MgO. MgO is then dissolved in aqueous hydrochloric acid, yielding Fe and Fe@Fe2O3 magnetic particles. The magnetic Fe2O3, Fe, and Fe@Fe2O3 particles are then functionalized with TiO2 to obtain the final photocatalysts. The Fe2O3@TiO2 catalyst exhibits strong adsorption of methylene blue, and the adsorption efficiency reaches 99% within 10 min. The Fe/TiO2 catalyst has the highest degradation efficiency (94%) and apparent reaction rate constant kapp (1.19 × 10−2 min−1) among the tested photocatalysts. Fe/TiO2 also has the highest saturation magnetization (61.5 emu/g), which is beneficial for magnetic separation. The adsorption efficiencies, degradation efficiencies, apparent reaction rate constants, and saturation magnetizations of the Fe@Fe2O3@TiO2 catalysts are sensitive to the properties of the Fe2O3 intermediate layer. The Fe2O3 particles contain both α-Fe2O3 and γ-Fe2O3. Coating TiO2 on Fe@Fe2O3 suppresses the formation of α-Fe2O3.