Single-step fabrication of ZnO microflower thin films for highly efficient and reusable photocatalytic activity

Zinc oxide microflower thin films were deposited in a single-step process using cost-effective ultrasonic spray pyrolysis technique. Different molarity of precursor solution was used to grow the films. X-ray diffraction and Raman spectroscopy reveal the wurtzite structure of ZnO. Scanning electron microscope images showed the microflower morphology which has a better surface to volume ratio. Defects such as O interstitial and Zn vacancy were identified in these thin films with the help of photoluminescence (PL) spectroscopy. The contact angle of the films was found to decrease with increase in molarity of the precursor. Photocatalytic activity of three different molar samples (0.05, 0.1 and 0.15 M) of ZnO were studied for methylene blue (MB) degradation and 0.15 M film demonstrated better degradation efficiency under UV-Vis light. Further degradation studies were performed on this film under exposure to natural sunlight. 90% degradation of the dye was observed in both the conditions upon exposure of 3.5 h. Effect of defects, molarity, bandgap and contact angle of ZnO on the photocatalytic performance is discussed. Repeatability studies performed under both UV-Vis and natural sunlight exposures showed only a minor deviation of 1% from the initial degradation efficiency.