The Preparation And Application Of WO₃/Cu₂O Composite Films

WO₃/n-Cu₂O and WO₃/p-Cu₂O composite films have been fabricated on titanium (Ti) substrates with a consecutive cathodic electrodeposition route. Those resulting films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Their photocatalytic activity under simulated natural light illumination was evaluated using orangeâ…¡(mainly) and Cr (â…¥) as model pollutants.The results indicates that WO₃ film exhibits very low photocatalytic activity. The photocatalytic activity of WO₃/n-Cu₂O is higher than WO₃, but lower than n-Cu₂O. WO₃/p-Cu₂O composite film exhibits highest activity among WO₃, n-Cu₂O, p-Cu₂O, and WO₃/n-Cu₂O films. Even in the absence of other reducing agents (hole scavengers), WO₃/p-Cu₂O also showed certain photocatalytic activity towards reduction of Cr (â…¥). The photocatalytic activity of WO₃/p-Cu₂O is closely related to the deposition amount of p-Cu₂O. Additionally, WO₃/p-Cu₂O composite film also possesses a relatively high stability during the reactions. The difference in photocatalytic activity between the two types of composite films is interpreted in terms of different mechanisms for transfer of charge carriers photogenerated within the heterostructures.The photocatalytic conditions for photocatalytic oxidation of orangeâ…¡and photocatalytic reduction of Cr(â…¥) over WO₃/p-Cu₂O composite films were experimentally investigated. The results indicate that the pH, initial concentration and the presence of inorganic anions have influence on the degradation efficiency of orangeâ…¡. The highest degradation rate was reached at the natural pH(5.7) of orangeâ…¡solution. The lower the initial concentration of orangeâ…¡, the higher the degradation rate. However, the absolute amount of degradation incrased with the increase in initial concentration of orangeâ…¡. In the present of NO₃^-, SO₄^2- and Cl^-, only NO₃^- ions promote the the degradation efficiency of orangeâ…¡. The photodegration rate for orangeâ…¡ increased from 30% in the absence of NO₃^- ions to 42% in the present of 0.05 mmol/L NO₃^-. Arganic acids as hole scavengers present in the Cr(â…¥) solution play an important role in the photocatalytic reduction of Cr(â…¥). In the presence of 1.6 mmol/L citric acid, the conversion efficiency for Cr(â…¥) increased from 18% to 58%. Among the four organic acids in our study, the order of the influence on the photocatalytic reduction of Cr(â…¥) was: tartaric acid>citric acid>oxalate>acetic. The conversion efficiency of Cr(â…¥) incrases with the decrease in pH value of Cr(â…¥) solutions. Although at the low initial concentration the high conversion efficiency was obtained, the absolute amount of conversion incrased with the increase in initial concentrations.