Photocatalytic degradation of caffeine as a model pharmaceutical pollutant on Mg doped ZnO-Al2O3 heterostructure

In this work, a promising photocatalyst was prepared and investigated for the photocatalytic degradation of caffeine as a model pharmaceutical pollutant. Mg-doped ZnO-Al2O3 heterostructure with different content of Mg (1, 3 and 5 wt%) was prepared from Zn-Al-CO3 layered double hydroxides precursors using ceramic process. The synthesized catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) coupled with energy dispersive X-ray analysis (EDX) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The photocatalytic activity of the catalysts was evaluated for the degradation of caffeine in aqueous solutions under UV irradiation. Detailed experiments based on the effect of doping amount, irradiation time, photocatalyst dose, initial solution pH, caffeine concentration and reuse were performed and discussed in this study. The 1%Mg-ZnO-Al2O3 sample showed the highest photocatalytic activity with a degradation efficiency of 98.9% after 70 min of irradiation. This catalyst showed significantly higher degradation efficiency compared to undoped, pure ZnO and standard Degussa P-25 titanium dioxide. The photocatalyst showed good stability after three regeneration cycles.