Photocatalytic treatment of aqueous solutions at high dye concentration using praseodymium-doped ZnO catalysts

In this work the photocatalytic activity of Pr-doped ZnO (Pr-ZnO) photocatalysts has been addressed for the first time in the treatment of aqueous solutions at high concentration of organic dyes under UV or visible light irradiation. Pr-ZnO photocatalysts were prepared by a precipitation method. The catalysts have been characterized by different techniques such as X-ray diffraction (XRD), UV–Vis diffuse reflectance (UV–Vis DRS) and Raman spectroscopy. XRD results showed that Pr3+ ions were successfully incorporated into the ZnO lattice. UV–Vis DRS spectra evidenced that Pr-ZnO samples present band-gap values of about 3.0 eV, lower than undoped ZnO (3.3 eV). The efficiency of photocatalysts has been tested in the photocatalytic removal of the azo dye Eriochrome Black T (EBT) under UV or visible light irradiation. The experimental results showed that the values of discoloration and mineralization rate are correlated to the Pr doping level, evidencing that the optimal loading of Pr in the ZnO structure is 0.46 mol%. The influence of process parameters (catalyst dosage, initial dye concentration and presence of carbonate ions) on the extent of photocatalytic performances has been investigated. The efficiency of the optimized photocatalyst was also evaluated in the photocatalytic treatment of aqueous solutions containing the triphenylmethane Patent Blue V (PB) dye and in the treatment of a solution containing simultaneously the two selected dyes (EBT and PB). Photocatalytic activity tests in presence of ion scavengers (carbonate ions) showed that the formulated Pr-ZnO photocatalyst is not subjected to deactivation phenomena. At last, a very interesting result was observed for the treatment of a real wastewater containing Basic Red 51 dye, showing that the complete discoloration and mineralization was achieved.