Enhanced electron transfer and silver-releasing suppression in Ag–AgBr/titanium-doped Al2O3 suspensions with visible-light irradiation

Highlights: ► Ag–AgBr was deposited onto mesoporous alumina (MA) and titanium-doped MA. ► The Ag+ release from the photocatalyst was inhibited by titanium-doped MA. ► The dissolution of Ag+ was related to the charge transfer and photocatalytic activity. ► Some donors in tap water inhibited the Ag+ release by trapping the h+ on Ag NPs. ► Ag–AgBr/MA-Ti1 was considered as a better catalyst for practical application. - Abstract: Ag–AgBr was deposited onto mesoporous alumina (MA) and titanium-doped MA by a deposition–precipitation method. The photocatalytic activity and the dissolution of Ag+ from different catalysts were investigated during the photodegradation of 2-chlorophenol (2-CP) and phenol in ultrapure water and tap water with visible-light irradiation. With the increase in doped titanium, the Ag+ dissolution decreased with a decrease in the photocatalytic activity. Ag–AgBr/MA-Ti1 was considered the better catalyst for practical applications because its Ag+ dissolution was minimal (0.4 mg L−1 in ultrapure water and 5 μg L−1 in tap water), although its photoactivity was slightly less than that of Ag–AgBr/MA. The dissolution of Ag+ was related to a charge–transfer process based on the study of cyclic voltammetry analyses under a variety of experimental conditions. The results suggested that several types of anions in the water, including CO32−, SO42−, and Cl−, could act as electron donors that trap the photogenerated holes on Ag nanoparticles to facilitate electron circulation; this would decrease the release of Ag+. Our studies indicated that the catalyst had a higher activity and stability in water purification.