Photocatalytic removal of atrazine using N-doped TiO2 supported on phosphors

Visible light-active N-doped TiO2 (N-TiO2) was successfully immobilized on ZnS-based phosphors microparticles (ZSP) by a modified sal-gel method. Core-shell catalysts were prepared to serve as photoactive support, able to harvest the external irradiation and to emit a luminescence with wavelength suitable for activation of N-doped TiO2. The nominal loading of N-TiO2 on ZSP was in the range of 15-50 wt% and the effect of the progressive increase in N-TiO2 loading on the coverage of phosphors particles was evaluated. The preparation method did not induce alterations of the initial ZSP crystallographic structure and allowed to obtain N-TiO2 dispersion on ZSP surface. By varying the N-TiO2 loadings on the surface of ZSP, its morphology gradually evolved from pseudo-spherical shape, until 30 wt%N-TiO2 loading, to elongated shape for an N-TiO2 content of 50 wt%. The photocatalytic activity of N-TiO2/ZSP was evaluated for the removal of atrazine under UVA light irradiation. Enhanced performance compared to either pure N-TiO2 nanoparticles or bare ZSP was observed. The photocatalyst N-TiO2/ZSP at 30 wt% of N-TiO2 loading (30N-TiO2/ZSP) demonstrated the highest photocatalytic activity. Photocatalytic performances were strongly dependent on the concentration of catalyst and the initial pH of solution. The optimal catalyst concentration was 0.5 g L-1 and the optimal initial pH was 5.8. A study of the reaction intermediates during the photocatalytic removal of atrazine was carried out, evidencing that the sequence of intermediates for 30N-TiO2/ZSP and for the phosphors ZSP alone included dealkylation reactions and alkyl chain oxidation. (C) 2014 Elsevier B.V. All rights reserved.