Morphological effect of ZnO nanoflakes and nanobars on the photocatalytic dye degradation

ZnO films with nanoflake and nanobar morphologies were obtained by spray pyrolysis by changing the precursor salt and without any structure-directing agents. Nanoflakes were obtained from zinc acetate while nanobars with zinc chloride. Both films presented ZnO hexagonal wurtzite structure, a transmittance above 80% and band gap of 3.2 eV. The photocatalytic activity of the films was evaluated by the degradation of methyl orange and indigo carmine dyes in different concentrations. The film with nanoflake morphology showed the best performance in discoloration (96%) and it achieved a 51% in mineralization. The film with nanobars attained only a 67% in discoloration whereas it failed to mineralize the dye solution. The principal factors involved in the best performance of the nanoflake films were the less defective surface in the ZnO structure that diminished the electron-hole recombination, allowing the generation of hydroxyl radicals in a sufficient amount. The nanoflake film showed also a high stability after 10 degradation cycles, indicating a promising material for photocatalytic water treatment. (C) 2016 Elsevier B.V. All rights reserved.