Catalytic and photocatalytic properties of zinc-nickel ferrites

A synthetic procedure combining high energy ball-milling and calcination at 900 °C was applied to obtain mixed metal oxides of the type Zn 1−x Ni x Fe 2 O 4 (x = 0.25; 0.5; 0.75). The formation of spinel-like structures and the phase composition were confirmed by XRD in combination with Mössbauer, IR and Raman spectroscopy. The crystallite size was analysed from X-ray diffraction data revealing nanometric crystallites with an average size in the interval 20–60 nm. The IR spectra showed two fundamental absorption bands in the range 650–400 cm −1 , which are characteristics of the metal-oxygen vibrations in tetrahedral and octahedral configurations. The mixed metal oxides were tested as catalysts for the decomposition of methanol to syngas and the degradation of the water pollutant malachite green in model solutions under UV light irradiation. Both the catalytic and photocatalytic activities were found to increase with increasing content of Ni(II) in the mixed metal oxides. The reduction behaviour of the samples was characterized by temperature-programmed reduction—thermogravimetric analysis and related to the catalytic conversion of methanol in the presence of the oxides. The most active samples for malachite degradation had the lowest band gap energy of 1.43 and 1.45 eV. The measurements of the reaction liquor by atomic absorption spectroscopy verified the stability of the samples tested as photocatalysts during the photocatalytic test. Graphic Abstract Zn/Ni ferrites of the type Zn 1−x Ni x Fe 2 O 4 (x = 0.25; 0.5; 0.75) active both as catalysts for methanol conversion (a) and malachite green decomposition in model solutions under UV light irradiation (b)