Controlled formation of Ag-AgxO nanoparticles on the surface of commercial TiO2 based composites for enhanced photocatalytic degradation of oxalic acid and phenol

Abstract

It is widely accepted that the photocatalytic efficiency of TiO2 can be enhanced by modifying its surface with noble metal nanoparticles, such as Ag. On the surface of TiO2, Ag nanoparticles are exposed to rapid oxidation, resulting AgxO. Therefore, in the present work, the photocatalytic activities of TiO2 composites Ag nanoparticles were investigated. They consisted of commercial titanium dioxide mixtures (Aldrich anatase and rutile) in well-defined ratios and Ag nanoparticles, which were deposited on the surface of titania, with or without using a reducing agent. The transformation of Ag nanoparticles into AgO was monitored considering the anatase/rutile ratio of the reference catalyst(s). The effect of transformation on the photocatalytic activity of commercial TiO2 was also studied via the degradation of phenol and oxalic acid under UV light irradiation. It was concluded that the Ag nanoparticles deposited on the surface of rutile could increase the efficiency of charge separation. In the case of anatase, similar results were obtained for the as-formed amorphous AgO nanoparticles. The tertiary and quaternary composites generally exhibited higher photocatalytic efficiencies towards oxalic acid degradation than the corresponding commercial TiO2 mixtures. Ag nanoparticles were found to be unstable during the experiments as they transformed into Ag2O, which could transform back to Ag during the photocatalytic processes, under appropriate conditions. On the other hand, the stability of AgO was not affected during the aging period. Therefore, it was deduced that AgO is more stable on the surface of anatase compared to Ag and Ag2O nanoparticles deposited on the surface of rutile.