Photocatalytic performance of ZnAl vs ZnAlTi in the degradation of 2,4-dichlorophenoxyacetic acid herbicide

This study focused on the synthesis and evaluation of mixed metal oxides ZnO/Al₂O₃ and ZnO/Al₂O₃/TiO₂ as heterogeneous photocatalysts for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). Hydrotalcites were synthesized using three different methods (conventional, microwave, and ultrasonic) and then treated at 700 ºC to obtain the corresponding Zn/Al and Zn/Al/Ti mixed metal oxides. The layered double hydroxide (LDH) and the mixed metal oxides were characterized by various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectrometry (XPS), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FTIR), pH_PZC analysis and UV–Vis techniques. A 95.6% photodegradation of 2,4-D was achieved after 240 min of UV exposure radiation (λ = 254 nm). The degradation of the products was confirmed by mass spectrometry analysis. The activity of the samples under UV irradiation followed this order: OZnTU > OZnTC > OZnTM, with ZnO/Al₂O₃/TiO₂ showing the highest activity due to its chemical composition and the interaction between ZnO and TiO₂. The degradation process was described by a Langmuir–Hinshelwood type kinetic model. Mass spectrometry was used to analyze the photodegradation results, suggesting the potential of these photocatalysts for the oxidation of 2,4-D in industrial wastewater under UV irradiation, particularly for the degradation and mineralization of 2,4-D herbicides from an aqueous solution.