Nickel oxide films by chemical spray: Effect of deposition temperature and solvent type on structural, optical, and surface properties

Nickel(II) oxide (NiO) films were grown via spray pyrolysis method. The effects of deposition temperature (Ts) and solvent type (aqueous, alcoholic) on the properties of the NiO films were studied. It was found that Ts significantly influenced the surface chemical composition, wettability, and photocatalytic activity (PA) toward degradation of methyl orange (MO) pollutant. The solvent type significantly affected the optical and structural properties of the NiO films. In accordance with the XRD and Raman studies, all deposited NiO films were nanocrystalline defective NiO. According to the XPS study, the OH-/Ni-O ratio decreased from 3.31 to 0.59 for the films grown from aqueous solutions at Ts = 300 and 420 degrees C, respectively, indicating that the surfaces of films grown at lower temperatures were richer in hydroxyl groups. Photocatalytic degradation efficiency was primarily affected by the hydroxyl group content on the surface. The NiO films grown at lower Ts (Ts = 300 degrees C) demonstrated 4-fold higher degradation efficiency toward MO degradation, at 45% over 3 h, relative to that of the films grown at Ts = 420 degrees C (11% over 3 h).