Comment on “Sonophotocatalytic degradation of textile dyes over Cu impregnated ZnO catalyst in aqueous solution” by J. Shah et al., Process Saf. Environ. Prot. 2018. 116 (2018) 149–158

Abstract

In a recent study, Shah et al. reported on the impregnation ofZnO particles with copper in order to get ZnO as a photocatalyst that performs in the visible light regime (Shah et al., 2018). To demonstrate the successful impregnation of Cu onto the ZnO surface, Shah et al. compared the XPS data of pure ZnO with the XPS data of ZnO after Cu impregnation in Fig. 5 in Shah et al. (2018). Indeed, the XPS survey spectrum of Cu impregnated ZnO displays a distinct Cu-2p peak whereas this peak is missing in the spectrum of pure ZnO. However, this result is far from being reliable because in the XPS data of Cu-impregnated ZnO, the appearance of the Cu-2p peak is not the result of the ¨successful impregnation of copper onto ZnO surface" (Shah et al., 2018) – it is the result of the successful use of a graphic tool.