Simultaneous photocatalytic removal of ammonium and nitrite in water using Ce3+–Ag+ modified TiO2

Simultaneous photocatalytic removal of both ammonium and nitrite from water via coupled oxidation and reduction for N2 formation was studied, using TiO2 loaded with different ratios of Ce3+ and Ag+. The catalysts were prepared using a sol–gel method with PEG or P123 as soft template. The catalysts with the highest activity (cerium and silver loading both at 0.1%) in N removal were characterized by TEM, XRD and UV–vis spectra. The crystalline TiO2 was mainly anatase type, its size averaged at 8.8–9.6 nm. Contents of Ce and Ag and ratios of ammonium to nitrite (NH4–N/NO2−–N) in the reaction solution affected either the catalyst activity or the nitrogen removal efficiency. The best removal rates were 69.9% NH4+–N, simultaneously 59.9% NO2−–N, and 64.9% TN (total nitrogen) in annular reactor, after 2 h UV (254 nm, 20 W) irradiation when ratio of NH4–N/NO2−–N was 1. Using solar light, the same solution after 2 h reaction using the same Ce and Ag co-modified TiO2, removal of NH4–N, NO2–N and TN was 44.8%, 45.3% and 45.1% respectively using a tubular reactor.