Coupled Al-Ga-xAg composites prepared by the sol–gel method and their efficient photocatalytic performance in the degradation of diclofenac

The photocatalytic performance of coupled Al-Ga-xAg composites prepared by the sol-gel method (where Al: γ-Al2O3; Ga: 1.0 wt.% Ga2O3; and xAg: x = 0.5, 1.0, 2.0 and 5.0 wt.% of Ag2O) was studied in the degradation of diclofenac in aqueous medium (50 ppm) using UV light irradiation. The structural and optical properties of Al-Ga-xAg reveals the presence of highly dispersed Ag0 nanoparticles and Ag+ ions in the materials. The Eg and the recombination rate of photo-induced electron-hole pairs of γ-Al2O3 decreased by coupling 1.0 wt.% of Ga2O3 and 0.5 - 5.0 wt.% of silver oxide in the coupled Al-Ga-xAg composites. Bare γ-Al2O3 photo-converts 66.0% of diclofenac after 20 min of reaction, however at this reaction time coupled Al-Ga-xAg composites with silver oxide contents between 1.0 and 5.0 wt.%. photoconverts more than 90.0% of diclofenac and mineralizes more than 80% of dissolved total organic carbon. The diclofenac photodegradation reaction kinetics were adjusted well to a first-order Langmuir-Hinshelwood reaction kinetics. The improvement in the photocatalytic activity of coupled Al-Ga-xAg composites could be due to that highly dispersed Ag0 nanoparticles and Ag+ ions act as electron (e−) traps, whereas Al-Ga mixed oxide acts as hole (h+) traps, promoting the decrease in the recombination rate of photo-induced electron-hole pairs. Transient photocurrent response experiments confirm that the silver species effectively increase efficiently the separation of photo-generated (e−, h+) charges. Experiments of diclofenac photodegradation with addition of scavengers indicates that h+ and ·O2− radicals are the main active species during the photocatalytic reaction using Al-Ga-xAg composite photocatalysts. A possible diclofenac photodegradation reaction mechanism under UV light irradiation and using Al-Ga-xAg composite photocatalysts was proposed.