Controlled synthesis of organic ligand passivated ZnO nanostructures and their photocatalytic activity under visible light irradiation

Zinc oxide (ZnO) nanostructures were synthesized and their photocatalytic activity was evaluated using methylene blue (MB) as a model pollutant. Ethylenediamine (EDA) was used as a passivating agent to control the morphology and size of the ZnO nanostructures. In the absence of EDA, agglomerated ZnO nanoparticles were obtained. The addition of EDA at varying concentrations considerably influenced the morphological size. The as-prepared samples were extensively characterized using various techniques. The morphology-and size-dependent photocatalytic degradation of MB was studied under visible light irradiation. The maximum degradation efficiency was observed for ZnO nanoflakes; the MB-related absorbance peak completely disappeared after 15 min of irradiation. Furthermore, the effect of various photocatalytic reaction parameters, such as pH (3-12) of the solution, the concentration of the dye (5, 10, 15, and 20 ppm), and the dosage of the photocatalyst (25, 50, 75, and 100 mg L-1), on the photodegradation of MB was investigated to determine the maximum degradation efficiency. The optimum values of solution pH, dye concentration, and photocatalyst dosage were 11, 10 ppm, and 75 mg L-1, respectively.