Effect of precursor concentration in the starting solution on the photocatalytic activity of ZnO thin films

Undoped zinc oxide, ZnO, thin films were deposited on sodacalcic glass substrates by the ultrasonic spray pyrolysis technique, starting from zinc acetylacetonate as Zn precursor. Molar concentrations, varying in the 0.05-0.2M interval, were used. The ZnO thin films were deposited at different substrate temperatures, 375, 400, and 450°C. The photocatalytic characterization of ZnO thin films was performed by testing the degradation of an aqueous solution containing methylene blue (MB), at a concentration of 2.5×10^-5 M, under UV irradiation, (15W Germicidal-UV lamp) for periods from 1 to 5 h. Absorbance of the solutions was measured by an UV-visible spectrophotometer at a wavelength of 664 nm. The variation of concentration of MB as a function of the irradiation time was calculated from the absorbance versus concentration calibrated curve. All films were characterized by XRD (X-ray diffraction), and ultraviolet-visible spectrophotometry. The XRD patterns confirmed the hexagonal wurtzite structure of the deposited ZnO films.