Enhanced photocatalytic degradation of methyl red and thymol blue using titania–alumina–zinc ferrite nanocomposite

Nanocomposite of magnetically separable, TiO2–ZnFe2O4 with an intermediate layer of alumina has been synthesized by a multistep wet chemical process. UV–vis absorption spectra show a red shift of the absorption edges for the composite systems compared to single phase TiO2. Magnetic measurements indicate that the ZnFe2O4 is ferromagnetic at room temperature with low coercivity when the applied field is low, typical of soft magnetic materials. After TiO2 and alumina coatings, the samples show similar magnetic behaviour. Photocatalytic activity studies for methyl red and thymol blue degradation indicate an enhanced activity for the composites when the alumina interlayer is present between TiO2 and ZnFe2O4. When Pd is used as a co-catalyst in TiO2–ZnFe2O4, an enhanced activity is observed, which is comparable to that of TiO2–Al2O3–ZnFe2O4. The present study leads to a new result that an insulating interlayer like alumina can enhance the photocatalytic activity of TiO2 coated ferrites as much as that of a noble metal co-catalyst like Pd. The enhanced photocatalytic activity of TiO2–Al2O3–ZnFe2O4 is attributed to the decrease in the migration of photogenerated charge carriers to zinc ferrite layer and due to the increased adsorption of the reactants on the surface of TiO2–Al2O3–ZnFe2O4.

Photocatalytic degradation of (left) methyl red (right) thymol blue.Figure optionsDownload as PowerPoint slideHighlights
► An interlayer of alumina enhances the photocatalytic activity of TiO2–ZnFe2O4.
► Enhanced adsorption of dyes is observed in the TiO2–Al2O3–ZnFe2O4 composites.
► Enhanced activity is attributed to the decreased charge transfer to zinc ferrite.
► Photocatalytic activity of TiO2–Al2O3–ZnFe2O4 is comparable to Pd/TiO2–ZnFe2O4.
► TiO2–Al2O3–ZnFe2O4 is ferromagnetic at low applied fields.