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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. [ABSTRACT FROM AUTHOR]

The photocatalytic process is used to remove organic contaminants, dyes, industrial sewage from wastewater before reusing it for human consumption again. Here a simple cost-effective ultrasonic spray pyrolysis (USP) technique is used to deposit ZnO microflower on glass and stainless steel (SS) mesh in a single step. X-Ray Diffraction (XRD) and Raman spectroscopy indicate the polycrystalline wurtzite nature of ZnO. Field emission scanning electron microscope (FESEM) shows the ZnO microflower structure. PL and XPS studies show the oxygen defect in the films. Photocatalytic degradation results show that methylene blue (MB) dye with 1 × 10−5 M concentration can be degraded around 97.94% and 85% in 120min and 210 min with a degradation rate of 0.03035 min−1 and 0.00917 min−1 respectively using ZnO deposited on SS mesh and glass substrate in both UV–Vis and sunlight condition. ZnO deposited on SS mesh shows high repeatability performance to degrade the MB and it can degrade 96% of MB at 10th cycle. Degradation rate at base medium is higher than acidic medium. A plausible photocatalysis mechanism is also explained. Image 1 • A simple single step deposition of ZnO microflower on stainless steel (SS) mesh. • Degradation rate of MB for ZnO on SS mesh is more than thin film. • Highly repeatable performance over 10th cycle with 96% degradation for SS mesh ZnO. • Degradation rate at base medium is higher than acidic medium. [ABSTRACT FROM AUTHOR]