Preparation, characterization and photocatalytic activity of ZnO, Fe₂O₃ and ZnFe₂O₄

ZnO, Fe₂O₃ and ZnFe₂O₄ were synthesized by precipitation or coprecipitation at constant pH. After aging, washing and drying, the solids were calcined at 800°C. The samples were characterized by XRD, TGA, N₂ physisorption, UV-Vis and TPR. The photocatalytic degradation of phenol was studied in a batch reactor and TiO₂ (Degussa, P-25) was used as a reference catalyst. Pure ZnO and Fe₂O₃ were obtained at 800°C, whereas ZnFe₂O₄ and α-Fe₂O₃ (segregated) were detected in the zinc ferrite sample. TPR experiments showed the reduction peaks in the range of 350-800°C only with Fe₂O₃ and ZnFe₂O₄, attributed to Fe³⁺ to Fe²⁺ reduction and complete dehydroxylation. The photodegradation of phenol (samples calcined at 800°C) showed small but significant variations that decreased in the order: TiO₂ > ZnFe₂O₄ > ZnO > Fe₂O₃. Subproducts such as hydroquinone, catechol and benzoquinone were mainly detected. In particular, attention was focused on our prepared materials because after 24 h they did not dissolve as happened with TiO₂.