Novel Ag-ZnO-La2O2CO3 photocatalysts derived from the Layered Double Hydroxide structure with excellent photocatalytic performance for the degradation of pharmaceutical compounds

Abstract

Abstract In this work, we have prepared the Ag-ZnO-La2O2CO3 nanomaterials as promising photocatalysts for the photocatalytic degradation of pharmaceutical pollutants. Firstly, a series of ZnAl1-xLax(CO3) (0 ≤ x ≤ 0.5) layered double hydroxides (LDHs) were synthesized by the co-precipitation method at the component molar ratio of Zn/(Al + La = 3, where La/Al = 0, 0.25 and 0.5). Photocatalysts were prepared by the calcination of the LDH precursors at different temperatures of 300, 400, 500, 600, 800 and 1000 °C. The effects of the La/Al molar ratio and the calcination temperature on the photocatalytic activity of the catalysts were evaluated by the degradation of caffeine as a model pharmaceutical pollutant in aqueous solutions under the UV irradiation. Thereafter, in order to increase the photocatalytic activity, the catalysts obtained at the optimal La/Al molar ratio and calcination temperature were doped with the Ag noble metal at various concentrations (i.e. 1, 3 and 5 wt%) using the ceramic preparation process to obtain the desired Ag-ZnO-La2O2CO3 catalysts. The synthesized photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) and UV-visible diffuse reflectance spectroscopy (UV-Vis DRS). Detailed photocatalytic experiments based on the effects of the irradiation time, the dopant amount, the catalyst dose, the initial solution pH and reuseability were performed and discussed in this study. The Ag doped material showed significantly a higher photocatalytic activity compared to the undoped, pure ZnO and P-25 catalysts. The experimental results show that the highest photocatalytic activity was obtained from the Ag (5%) doped Zn-0.75Al-0.25La-CO3 photocatalysts calcined at 500 °C with a degradation efficiency of 99,4% after 40 min of irradiation only. This study could provide a new route for the fabrication of high performance photocatalysts and facilitate their application in the environmental remediation issues.