Microwave-assisted synthesis of TiO2-ZnO oxide systems with enhanced photocatalytic and photovoltaic activity

A microwave method was used for the synthesis of TiO₂-ZnO oxide systems. A detailed investigation was made of the effect of the molar ratio of components (TiO₂:ZnO=9:1, 7:3, 5:5, 3:7, 1:9) on the crystalline structure and morphology. Based on the TEM pictures, confirmed the presence of octahedral and rod-shaped titania particles and sheet zinc oxide particles. Moreover, the synthesized materials were analyzed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), and two crystalline forms - anatase and wurtzite were detected. Based on the adsorption-desorption N₂ isotherms confirmed mesoporous characters of the analyzed binary materials, also the parameters of the porous structure have been defined. The key element of the work was to determine the photocatalytic activity of the obtained TiO₂-ZnO oxide systems in the degradation of phenol. Photo-oxidation tests proved that the binary oxide materials (especially the (9)TiO₂-(1)ZnO and (7)TiO₂-(3)ZnO samples) demonstrate high photocatalytic activity in the decomposition of phenol (95% after 80 min irradiation) compared with the reference titania sample. Furthermore, it was also pointed out that the dye-sensitized solar cells can be a second application for the synthesized TiO₂-ZnO materials. The best photovoltaic parameters have been found in the case of the (9)TiO₂-(1)ZnO material, which was characterized by an efficiency of 8.84%. The improvement effect is caused by introducing a material (ZnO) with a higher conductivity band into the TiO₂-ZnO oxide system, additionally improving the transport of electrons inside the semiconductor layer.