Effect of ion (Al, Fe and Zn) co-doped TiO2 nanotubes on photocatalytic degradation of humic acids under UV/ozonation for drinking water purification

Abstract

O3/UV/TiO2 was used to effectively decompose humic acids (HAs) in drinking water. A series of Al-doped, Fe-doped, Zn-doped and co-doped TiO2 nanotubes were successfully synthesized by a hydrothermal method. According to the characterization of ion-doped TiO2 nanotubes, Al3+ and Fe3+ ions occupied substitutional positions in the crystal lattice, and Zn2+ ions were partially dispersed in the bulk of the TiO2 nanotubes, with ZnO formed on the surface of the TiO2. The calcination temperature and doping concentration could affect the anatase phase weight fractions, average crystallite sizes, Brunauer–Emmett–Teller (BET) surface area, bandgap energy, and photocatalytic activity of the catalysts. For single ion-doped TiO2 nanotubes, the best photocatalytic activities were achieved when the ion-doping amount was 1.0%, and the optimal calcination temperatures for Al-, Fe- or Zn-doped TiO2 were 600°C, 550°C and 550°C, respectively. The highest HA removal efficiency of 80.1% was achieved in the presence of 550°C calcined, 1.0% co-doped TiO2 nanotubes with an Fe:Zn ratio of 1:1 (atomic percent), with second-order rate constant of 0.0394 L/(min·mg). The addition of a third ion had little effect on the photocatalytic activity. The pollutants in filter influent from No. 9 waterworks in Beijing could be efficiently removed, with UV254 and total organic carbon (TOC) removal efficiencies of 57.2% and 44.7%, respectively.