Highly efficient visible photocatalytic degradation of MB organic dye by heteromorphic ZnO/AZO/ZnO nanocatalysts: effect of AZO thickness

Heteromorphic ZnO/AZO/ZnO (zinc oxide/aluminum-doped zinc oxide/zinc oxide) nanocatalysts have been successfully prepared by the sol–gel method by using Zn(CH3COO)2•2H2O and Al(NO3)3•9H2O as precursors. We have studied the effect of modifications in the thickness of ZnO:Al (AZO) on the structural, optical, and photocatalytic properties of the stacked heteromorphs. Fourier transform-infrared spectroscopy and X-ray diffraction (XRD) measurements show that the formed heteromorphic ZnO/AZO/ZnO has a wurtzite hexagonal structure. The crystallite size of the heteromorphic photocatalysts decreases with an increase in the thickness of ZnO:Al. Photoluminescence (PL) spectra suggest that the nature of the observed green emission is mainly due to the oxygen vacancy, which has a major role in the photocatalytic activity. The photocatalytic activity of heteromorphic ZnO/AZO/ZnO is much higher (up to 95% only in 180 min) than that of ZnO and ZnO/AZO for the degradation of methylene blue dye in water under visible light irradiation. The increase in the photocatalytic performance of the ZnO/AZO/ZnO is mainly due to their smaller crystallite size, high amount of OH− groups on the surface, surface defect levels, and efficient separation of photogenerated electron–hole pairs. This work provides a heteromorphic ZnO/AZO/ZnO nanocatalyst for the highly efficient photocatalytic performance in the application of low-cost water treatment. The elimination of the filtration step after the dye removal process is the advantage of using our suggested heteromorphic nanocatalyst. The results of our study indicate that a thin film can be used for coating the systems that are not directly filterable.