Parameters controlling the photocatalytic performance of ZnO/Hombikat TiO2 composites

Commercial TiO2 (Hombikat, UV-100) was impregnated with different loadings of zinc nitrate solution and subsequently calcined at different temperatures in order to obtain a stable homogeneous solid composite of ZnO/TiO2. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), UV–vis and Raman spectroscopy, inductively coupled plasma mass spectroscopy (ICP), X-ray photoelectron spectroscopy (XPS) as well as N2 adsorption and desorption measurements. Results show that ZnO was incorporated within the TiO2 crystals and did not form a separate bulky phase or metallic zinc. Moreover, the calcination temperature dramatically modifies the texture properties of the prepared samples compared with original Hombikat TiO2. The photocatalytic performance of the prepared samples was evaluated by monitoring the degradation of methyl orange dye under black light illumination. Three main parameters were studied; ZnO loading, surface area and initial pH of the methyl orange solution. The variation in ZnO loading appears to have less influence on the catalytic activity than either the surface area or the pH.

► Hombikat TiO2 was impregnated with different ZnO loadings and calcined at various temperatures to obtain ZnO/TiO2 composites.
► Increasing the calcination temperature lead to a reduction of the surface area, and lowered the nanocomposites photocatalytic activity.
► At low calcination temperatures zinc salt residues (used during loading) lead to lower pH in the test solution.
► This pH reduction increased the photocatalytic activity of the nanocomposites.
► The ZnO loading appears to have less influence on the catalytic activity than the surface area or the pH.