Enhanced photocatalytic degradation of caffeine as a model pharmaceutical pollutant by Ag-ZnO-Al_2O_3 nanocomposite

摘要

In this paper, an Ag-ZnO-Al2O3 nanocomposite with enhanced photocatalytic activity has been obtained by calcination of an Ag-loaded zinc/aluminum layered double hydroxide (LDH). First, LDH materials intercalated by carbonates ions (Zn-Al-CO3) were synthesized by the co-precipitation method at a Zn/Al molar ratio of 3 and were calcined at different temperatures (300, 400, 500, 600, 800, and 1000 degrees C). Thereafter, in order to increase photocatalytic activity, catalysts obtained at optimal temperature were doped by Ag noble metal with various amounts (1, 3, and 5 wt %) using a ceramic process. Samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM/EDX). The photocatalytic activity was evaluated for the degradation of caffeine as a model of pharmaceutical pollutant in aqueous solutions under UV irradiation. The effect of irradiation time, initial concentration of caffeine, catalyst dosage, solution pH, and reuse were investigated. The Ag-doped calcined LDH materials showed significantly higher photocatalytic activity compared with undoped and standard Degussa P-25 titanium dioxide. The photocatalytic degradation of caffeine was increased with an increase in the Ag-loaded amounts. The photocatalyst showed high stability after three regeneration cycles.