Photocatalytic Degradation of Eriochrome Black-T Azo Dye Using Eu-Doped ZnO Prepared by Supercritical Antisolvent Precipitation Route: A Preliminary Investigation

The aim of this work is to preliminary investigate the photocatalytic performances toward the removal of eriochrome black-T dye under UV and visible irradiation using Eu-doped ZnO obtained through a supercritical antisolvent (SAS) process in comparison with Eu-doped ZnO prepared by drying-precipitation method and Eu-doped TiO2 prepared by sol–gel route. XRD patterns show that the presence of Eu+3 does not change the crystalline structure of both TiO2 and ZnO, evidencing that Eu+3 is successfully incorporated into the semiconductors lattice. The morphology of samples obtained after SAS micronization consists of nanoparticles with a regular shape and characterized by average size in the range 65.0–84.7 nm. UV–Vis DRS spectra evidence that the doping of TiO2 and ZnO with Eu+3 leads to an increase of band gap value with respect to undoped samples because of the presence of dopant ions into the host structure. Eu-doped ZnO sample synthetized by the SAS process shows better photocatalytic efficiency in terms of both discoloration and mineralization, reaching the almost total dye removal after 240 min of UV light irradiation. The enhancement of the photocatalytic activity of Eu-doped ZnO sample synthetized by SAS process is ascribed to the presence of Eu+3 in the lattice, but also to the higher specific surface area, smaller crystallite size and its morphology features, if compared with Eu-doped ZnO prepared by drying-precipitation method and Eu-doped TiO2 prepared by sol–gel route.