Improvement of the photocatalytic activity after reusing one-dimensional dark-ZnO films

One-dimensional ZnO nanostructures with intrinsic defects were obtained by thermal oxidation of commercial zinc foils. Zn foils were oxidized using a tube furnace at 420 °C for 20, 30 and 44 h in air atmosphere to analyze the impact of the oxidation time in the surface morphology and photocatalytic response. The as-grown ZnO samples had a dark aspect and were characterized by Scanning Electron Microscopy, Raman Spectroscopy, X-Ray Diffraction, UV–Vis Diffuse Reflectance Spectroscopy and Photoluminescence. These samples were evaluated in photocatalytic experiments using a 10 mg/L aqueous solution of indigo carmine dye under solar simulated irradiation. The photocatalytic dye removal increased after each reuse. Physical changes were observed, such as the “dark” aspect of the surface that appeared whiter after each cycle. The characterization of the samples was performed after 5 photocatalytic cycles to confirm the evolution of the as-grown materials. The repeated photocatalytic process of the films in contact with the aquaeous solution and under irradiation contributed to a better oxidation of the zinc foils, as the presence of the metallic zinc peak in XRD disappeared. PL measurements revealed a diminution of the band-to-band transition respect to the visible band emission after the cycles, indicating a drastic change in the recombination process. The synthesis of ZnO using commercial zinc foils is a simple, reproducible and scalable option to produce materials with excellent and long-lasting photocatalytic activity. • 1-D ZnO nanostructured dark films were obtained by thermal oxidation of Zn foils. • The adsorption capacity of as-grown films was high, removing 80 % of IC dye at 5, 10 and 15 mg/L. • After reusing the films, the photocatalytic activity increased up to 100 % dye removal. • The photocatalytic efficiency prevailed after several reuse cycles. • The surface changed from dark to white ZnO indicating a better oxidation.