In this study, the zinc oxide (ZnO) films have been prepared via the green-synthesis method with rind extract of red watermelon (Citrullus lanatus) as bio-stabilizer, at various acidity (pH) conditions. The ZnO films were prepared as thin films by spin-coating colloidal ZnO onto a glass substrate. The physical properties of ZnO films were characterized using UV-Vis spectrophotometer, XRD, SEM/EDX, and FTIR. The photocatalytic activity of ZnO films was evaluated systematically in the degradation process of methylene blue (MB). The sample prepared at pH 12 possesses the highest purities and exhibits the maximum degradation percentage of 94.61%, with a reaction rate constant of 0.019 min-1 . The efficiency of the ZnO photocatalyst has a strong correlation with the pH value in the synthesis process. Based on the results of this study, ZnO films prepared via green synthesis using Citrullus lanatus show an effective photocatalytic activity in degradation of MB, so that it could be developed in the photocatalytic process of water purification.
Keywords: Citrullus lanatus; green synthesis; photocatalytic; red watermelon rind; ZnO