Photocatalytic activity of Ag/Al₂O₃–Gd₂O₃photocatalysts prepared by the sol–gel method in the degradation of 4-chlorophenol

The photocatalytic activity in the degradation of 4-chlorophenol (4-ClPh) in aqueous medium (80 ppm) using 2.0 wt% Ag/Al₂O₃-Gd₂O₃ (Ag/Al-Gd-<i>x</i>; where <i>x</i> = 2.0, 5.0, 15.0, 25.0 and 50.0 wt% of Gd₂O₃) photocatalysts prepared by the sol-gel method was studied under UV light irradiation. The photocatalysts were characterized by N₂ physisorption, X-ray diffraction, SEM, HRTEM, UV-Vis, XPS, FTIR and fluorescence spectroscopy. About 67.0% of 4-ClPh was photoconverted after 4 h of UV light irradiation using Ag/γ--Al₂O₃. When Ag/Al-Gd-<i>x</i> photocatalysts were tested, the 4-ClPh photoconversion was improved and more than 90.0% of 4-ClPh was photoconverted after 3 h of UV light irradiation in the materials containing 15.0 and 25.0 wt% of Gd₂O₃. Ag/Al-Gd-25 was the material with the highest efficacy to mineralize dissolved organic carbon, mineralizing more than 85.0% after 4 h of UV light irradiation. Silver nanoparticles and micro-particles of irregular pentagonal shape intersected by plane nanobelts of Al₂O₃-Gd₂O₃ composite oxide were detected in the Ag/Al-Gd-25 photocatalyst. This material is characterized by a lowest recombination rate of electron-hole pairs. The low recombination rate of photo-induced electron-hole pairs in the Ag/Al-Gd-<i>x</i> photocatalysts with high Gd₂O₃ contents (≥15.0 wt%) confirmes that the presence of silver nanoparticles and microparticles interacting with Al₂O₃-Gd₂O₃ composite oxide entities favors the separation of photo-induced charges (e^- and h⁺). These materials could be appropriate to be used as highly efficient photocatalysts to eliminate high concentrations of 4-ClPh in aqueous medium.