Photocatalytic Degradation of Mixed Dyes in Aqueous Phase by MgAlTi and ZnAlTi Mixed Oxides

This study reported the synthesis and evaluation of mixed metal oxides MgO/Al₂O₃–TiO₂ and ZnO/Al₂O₃–TiO₂ as heterogeneous photocatalysts for the potential degradation of a mixture of organic dyes such as methylene blue and methyl orange. First, hydrotalcites were synthesized by two different methods (conventional and microwave); then they were treated at 500 °C to obtain the corresponding Mg/Al–Ti and Zn/Al–Ti mixed metal oxides. The Layered Double Hydroxide (LDH) and the Mixed Metal Oxides were characterized by N₂ adsorption–desorption, X-ray Diffraction, Fourier transform infrared, X-Ray photoelectron Spectrometry and Scanning Electron Microscopy. The degradation processes of the dyes were carried out under ultraviolet light irradiation and absorbance readings were compared using a UV–vis spectrometer. The ensuing degradation of products was corroborated through a mass spectrometry analysis. According to the photodegradation efficiency of dyes under UV irradiation, the activity of the samples showed the following order: ZnAlTiM > ZnAlTiC > MgAlTiC > MgAlTiM. The improvement in the activity of ZnAlTiM may be attributed to its lowest reflectance and highest degree of UV light absorbance, its smallest valence band and its ZnO-support interaction. Degradations of 25% and 68% were achieved for methyl orange and methylene blue, respectively, after 120 min of reaction. The degradation process conforms to the Langmuir–Hinshelwood type kinetic model. Graphic Abstract: [Figure not available: see fulltext.]