Zn- vs Bi-based oxides for o-toluidine photocatalytic treatment under solar light

The photodegradation of the highly toxic o-toluidine pollutant was deeply investigated both under UV and solar irradiations by using three different semiconductors: pure ZnO, Bi-impregnated ZnO, and Bi₂O₃ nanopowders (synthesized by precipitating method). All the samples were deeply characterized on structural, morphological, surface, and optical points of view. The disappearance and the relative mineralization of o-toluidine molecules were followed by linear sweep voltammetry (LSV) and total organic carbon (TOC) determinations, respectively. Hence, correlations between their physico-chemical properties and the photocatalytic performances, passing from UV to solar light, were drawn and a hypothesis on the photodegradation mechanism has been proposed, on the basis of the HPLC/MS results. Bare Bi₂O₃ samples, due to the exploitation of both their visible light absorption and the negligible intermediates formation, resulted to be higher performing under solar irradiation than either pure or Bi-doped ZnO nanopowders. Graphical abstract.